Dr Rajiv Desai
An Educational Blog
HEARING AID
HEARING AID:
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Prologue:
I was working in Saudi Arabia as a doctor from 2001 to 2006. I was designated female medical specialist. All female medical patients used to come to me for treatment. I noticed that I cannot hear properly what they say. The language barrier and lack of lip reading (Muslim women wear burka covering their face) compounded hearing disability. I got myself checked and found that I was suffering from otosclerosis. I started wearing hearing aid which improved my hearing significantly. Although one should remove hearing aids while sleeping at night, I used to wear hearing aid in one ear and sleep on side with ear having hearing aid on the top to attend night calls for emergency. In 2007/2008, I got operated in both ears, and after surgery my hearing improved so much that I did not need hearing aid. Hearing is one of the major senses and like vision is important for distant warning and communication. The function of the ear is to convert sound into an encoded nervous impulse. It can be thought of as a biological microphone. We the humans are obsessed with vision and generally ignore hearing loss. How many people know that World Hearing Day is held each year on March 3rd to promote hearing! Hearing loss is one of the most common sensory disorders in humans and can present at any age. Nearly 10% of the adult population has some hearing loss and one-third of people with age >65 years have a hearing loss of sufficient magnitude to require a hearing aid. However, statistics from developed nations show only one out of five individuals who could benefit from the use of hearing aids actually pursue treatment. Factors suggested as reasons for lack of hearing aid use include cost, ignorance, perceived lack of benefit, denial of hearing loss and stigma associated with hearing loss & use of hearing aids. Imagine dining in a busy restaurant. In the background there are dishes clattering, chairs scraping, people talking and laughing, and waiters rushing about. You are straining to follow what is happening at your table – and the effort of doing this is starting to make you feel more and more tired. Eventually, you start pretending you can hear. You nod, look interested and laugh with the crowd even though you didn’t get the jokes. You begin to feel left out. When you leave the restaurant you have a throbbing headache, disappointment and no plans to repeat the experience anytime soon. All these could be avoided if you accept that you have hearing loss and wear hearing aid. Humans can only perceive light but can generate and perceive sound. Blindness separates people from things. Deafness separates people from people.
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Abbreviations and synonyms:
SPL = sound pressure level
HL = hearing level
dB = decibel
FM = frequency modulated
SSD = single sided deafness (unilateral profound sensorineural hearing loss)
ITE = in the ear hearing aid
BTE = behind the ear hearing aid
CIC = completely in canal hearing aid
ITC = in the canal hearing aid
IIC = invisible in canal hearing aid
RIC = receiver in canal = RITE = receiver in the ear hearing aid
BAHA = bone anchored hearing aid
CI = cochlear implant
T-coil = telecoil = telephone coil
HATS = hearing assistive technology systems
ALD = assistive listening devices
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Introduction to hearing:
Hearing is one of the five senses, along with vision, taste, smell, and touch. Often considered the most important sense for humans, hearing allows us to communicate with each other by receiving sounds and interpreting speech. The ears receive sound and transmit it to the brain, where it is interpreted, so that speech, music, and other signals can be heard. Therefore, the auditory system requires a source of sound, a mechanism for receiving this sound, mechanisms for relaying sounds to the central nervous system, and pathways in the central nervous systems to deliver this sensory information to the brain where it can be interpreted, integrated, and stored.
We rely on our hearing for:
•understanding speech – the symbolic level. Informs, educates and entertains.
•appreciating sounds that please us – the aesthetic level. Gives pleasure.
•recognising sounds that alert us – the warning level. Alerts and prepares.
•recognising the changing background sounds of the world around us – the primitive level. Auditory background for daily living.
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Hearing is one of the human body’s most remarkable senses. It integrates seamlessly with our brains to help us connect with the world around us. Made up of a complex system of delicate and synchronous parts, it’s easy to take this vital sense for granted. If any of these components aren’t working properly, your ability to hear can decline.
The most common causes of hearing loss are:
1. Earwax (cerumen) accumulation
2. Noise
3. Aging
4. Ear infections (particularly among children and young adults)
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Difference between Hearing and Listening:
What is Hearing?
Hearing is an action in which a sound is perceived by the ear. Very little or no effort is required as your mind may be occupied with other thoughts or perhaps you are engaged in a different task while the other person is sharing his or her thoughts with you. This is a passive process. We hear something around us all the time. While you are at home, you might hear the sound of other people talking, the sound of cooking in the kitchen, the sound of the television, and the sound of anything that is happening around. While you are at work, depending on where you work, you hear the sound of various things around you. While on the road you hear the sound of traffic and any events in the public, the people laughing, talking, shouting etc. At the end of the day, after you go to bed and fall asleep, you hear sounds even while you sleep. All these happen around you, and you do not necessarily notice it. It is just sound waves reaching your ears. Hearing is an alarm system which operates even outside your immediate awareness.
What is Listening?
Listening is a broad term used to refer to complex affective, cognitive, and behavioral processes. Affective processes include the motivation to attend to others; cognitive processes include attending to, understanding, receiving, and interpreting content and relational messages; and behavioral processes include responding with verbal and nonverbal feedback. Listening is an action in which you choose to actively concentrate on what you hear. You need to put in a lot more effort in terms of attention, processing, thinking, and analysing. You do not think about anything else, or get engaged in any other tasks, but instead sit down and listen to what the speaker is saying. You notice the feeling and meaning of what is being said. This is an active process. When you listen, you need to pay attention in order to interpret and respond. Listening is a skill that can be improved with a little bit of hard work, dedication and determination. Listening differs from obeying. Parents may commonly conflate the two, by telling a disobedient child that he “didn’t listen to me”. A person who receives and understands information or an instruction, and then chooses not to comply with it or to agree to it, has listened to the speaker, even though the result is not what the speaker wanted. Along with speaking, reading, and writing, listening is one of the “four skills” of language learning.
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Selective auditory attention:
Selective auditory attention or selective hearing is a type of selective attention and involves the auditory system of the nervous system. Selective hearing is characterized as the action in which people focus their attention on a specific source of a sound or spoken words. The sounds and noise in the surrounding environment is heard by the auditory system but only certain parts of the auditory information are processed in the brain. Most often, auditory attention is directed at things people are most interested in hearing. In an article by Krans, Isbell, Giuliano, and Neville (2013), selective auditory attention is defined as the ability to acknowledge some stimuli while ignoring other stimuli that is occurring at the same time. An example of this is a student focusing on a teacher giving a lesson and ignoring the sounds of classmates in a rowdy classroom. This is an example of bottlenecking which means that information cannot be processed simultaneously so only some sensory information gets through the “bottleneck” and is processed. A brain simply cannot process all sensory information that is occurring in an environment so only that which is most important is thoroughly processed. Selective hearing is not a physiological disorder but rather it is the capability of humans to block out sounds and noise. It is the notion of ignoring certain things in the surrounding environment. Over the years, there has been increased research in the selectivity of auditory attention, namely selective hearing. Selective hearing is not known to be a disorder of the physiological or psychological aspect. Selective hearing is not “deafness” to a certain sound message. Rather, it is the selectivity of an individual to attend audibly to a sound message. The whole sound message is physically heard by the ear but the idea is the capacity of the mind to systematically filter out unwanted information. Therefore, selective hearing should not be confused as a physiological hearing disorder.
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Importance of hearing:
The ability to relate to others, share ideas, participate in activities, and experience one’s surroundings depends greatly on the capacity to hear. Hearing provides essential information about the environment, including the presence of danger. Sirens, smoke alarms, and warning shouts require hearing. Hearing loss significantly influences this ability to communicate and participate in activities and data document the multiple negative effects it has on the person with hearing loss as well as his or her partner. In general and irrespective of the age at which it develops, disabling hearing impairment has devastating consequences for interpersonal communication, psychosocial well-being, quality of life and economic independence. If it develops in the young, such impairment impedes speech and language development and sets the affected children on a trajectory of limited educational and vocational attainment. Children with hearing impairment may also be at increased risk of physical, social, emotional and sexual abuse and even murder. In adulthood, disabling hearing impairment can lead to embarrassment, loneliness, social isolation and stigmatization, prejudice, abuse, psychiatric disturbance, depression, difficulties in relationships with partners and children, restricted career choices, occupational stress and relatively low earnings.
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Hearing is living: A study:
On the occasion of the fifth anniversary of the founding of the Hear the World initiative, authors commissioned a large study to shed light on the lesser known aspects of hearing. In all, they surveyed over 4,000 people in five countries, on diverse topics related to hearing in all areas of life. In addition, they asked experts from relevant specialist areas for their assessment of the study results, and once again reached the conclusion: Hearing is Living! For example, did you know that our hearing is partly responsible for how well we sleep at night, how often we exercise, where we go on vacation or how attractive we think we are? Or would you have thought that the quality of our hearing also affects our personal relationships? Or how happy we are in partnerships? With its large number of participants and its comprehensive study design “Hearing is Living” provides many fascinating insights. Not only the overall results, but also the international comparison between responses is interesting, as there are distinct differences between the different countries.
Three important findings:
1. Firstly, hearing influences so many areas of our everyday life that improved hearing has one benefit above all others: enhanced quality of life. Better hearing means better communication – in our relationships with our partners, as well as toward friends and family. Good hearing is not merely of benefit to yourself: its positive effects are also directly measurable among family, relatives and partners – this is the first significant insight gained from this study.
2. The second important insight of the study is that better hearing enables us to experience life in a more active, healthier way, and with fewer restrictions. Stress is reduced, or may be avoided in the first place, concentration is improved, and relaxation is easier. In this way, good hearing also contributes to enhanced personal wellbeing and general health.
3. And thirdly, looking at the way people perceive the hearing capability of others, the study shows very clearly that wearing a hearing aid does not have any negative effect on attractiveness. On the contrary: not only relatives and partners, but also the unaffected people in the control group have a very open and positive attitude to the subject of “hearing loss and hearing aids”. That is the final, and very welcome, insight to come out of the “Hearing is Living” research study.
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Consequences and impacts of hearing loss:
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The figure below summarises harms of hearing loss:
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Effects of untreated Hearing Loss:
Reduced hearing acuity is frustrating for people with hearing loss as well as for those around them. In fact, a 2009 study showed that relationships are failing because of unmanaged hearing loss. The survey of 1,500 hearing-impaired people over 55 revealed that almost half (44 percent of people) said that relationships with their partner, friends or family have suffered because they can’t hear properly. Hearing loss isn’t just an ear issue; it’s a quality of life and health issue. Untreated hearing loss can have serious consequences. A decrease in hearing sensitivity is associated with diminished cognitive function, poorer mental health, and social withdrawal. A nationwide survey of 4,000 adults with hearing loss compiled by the National Council on Aging (Kochkin & Rogin, 2000) found significantly higher rates of psychosocial disorders including depression and anxiety in individuals with untreated hearing loss — those who were not wearing hearing aids. A separate study at Johns Hopkins found that cognitive diminishment was 41 percent greater in seniors with hearing loss. The study identified a link between the degree of hearing loss and the risk of developing dementia. Individuals with mild hearing loss were twice as likely to develop dementia, those with moderate hearing loss were three times as likely, and those with severe hearing loss were five times as likely to develop dementia when compared to individuals with normal hearing. Researchers and hearing care professionals have long understood the link between cognition and hearing acuity. When you are listening to someone speak your brain is processing the sound so that you can understand it. A listener with untreated hearing loss is trying to understand degraded speech signals therefore their brain has to work harder to process those sounds. While your brain is busy working to understand incoming speech signals other tasks like memory and comprehension can suffer. When we lose our ability to hear, the ear stops sending needed information to the brain, which affects our ability to understand what is being said. This is called Auditory Deprivation. Auditory Deprivation may impair the way the brain processes sound. Johns Hopkins Medical study revealed that a mild 25dB hearing loss can increase falling by three times. Fortunately, hearing loss is treatable. According to the Better Hearing Institute, 95 percent of Americans with hearing loss can be treated with hearing aids and individuals who treat their hearing loss early have shown significant benefit. Hearing aids help process incoming sound making it easier for your brain to understand them. Other benefits of hearing aids include reduced mental fatigue, decreased feelings of social isolation and depression, improved ability to do several things at once, improved memory, attention and focus, as well as improved communication skills.
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Many people are aware that their hearing has deteriorated but are reluctant to seek help. Perhaps they don’t want to acknowledge the problem, are embarrassed by what they see as a weakness, or believe that they can “get by” without using a hearing aid. And, unfortunately, too many wait years, even decades, to address the effects of hearing loss before getting treatment. But time and again, research demonstrates the considerable effects of hearing loss on development as well as negative social, psychological, cognitive and health effects of untreated hearing loss . Each can have far-reaching implications that go well beyond hearing alone. In fact, those who have difficulty hearing can experience such distorted and incomplete communication that it seriously impacts their professional and personal lives, at times leading to isolation and withdrawal.
Studies have linked untreated hearing loss effects to:
•irritability, negativism and anger
•fatigue, tension, stress and depression
•avoidance or withdrawal from social situations
•social rejection and loneliness
•reduced alertness and increased risk to personal safety
•impaired memory and ability to learn new tasks
•reduced job performance and earning power
•diminished psychological and overall health
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Hearing loss in babies and children:
Hearing loss is not just an ailment of old age. It can strike at any time and any age, even childhood. For the young, even a mild or moderate case of hearing loss could bring difficulty learning, developing speech and building the important interpersonal skills necessary to foster self-esteem and succeed in school and life. A child’s development and quality of life depend fundamentally on his ability to hear. Children learn how to speak by listening to others and communicating among themselves. Hearing helps your child learn to read, appreciate music and pick up warnings about dangerous situations. Without a good sense of hearing, your child will have difficulty tackling life’s challenges and opportunities – whether at home or at school.
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Economic impact of hearing loss:
In developing countries, children with hearing loss and deafness rarely receive any schooling. Adults with hearing loss also have a much higher unemployment rate. Among those who are employed, a higher percentage of people with hearing loss are in the lower grades of employment compared with the general workforce. Improving access to education and vocational rehabilitation services, and raising awareness especially among employers about the needs of people with hearing loss, would decrease unemployment rates among this group. In addition to the economic impact of hearing loss at an individual level, hearing loss substantially affects social and economic development in communities and countries. Analysis of the Labour Force Survey, a government survey of the employment circumstances of the UK population, found that people with hearing loss were less likely to be employed than people with no long-term health issue or disability.
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Hearing loss and job performance:
Hearing is critical to effective communication in the workforce. Most jobs require proficiency in spoken communication in order to engage effectively in commerce and in dealing with the public. Effective hearing may also be critical to assure safety on the job. Without aided hearing, the individual with a hearing impairment can be expected to suffer losses in compensation due to underemployment, may make mistakes on the job, is likely to experience higher rates of unemployment, and may experience an overall reduction in quality of life (e.g., anxiety, depression, social isolation, and reduced physical and mental health and cognitive function), which may damage job performance. Most hearing health professionals have encountered patients who delayed hearing loss treatment due to fear of stigmatization on the job. We know people who suffered needlessly during their school years with “hidden” hearing loss. Unfortunately, untreated hearing loss is not hidden, for it results in underachievement for nearly all who delay treatment while they are in the prime of their life. The tragedy is that untreated hearing loss negatively affects individuals and their families for the rest of their lives in the form of lost wages, lost promotions, lost opportunities, lost retirement income, and, perhaps worst of all, in unrealized dreams.
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The Impact of Hearing Loss on Seniors: 2016 study:
For seniors between the ages of 60 to 69, researchers found that for every 10-decibel drop in hearing sensitivity, the odds of social isolation increased by 52%. This increased risk is significant, especially given that social relationships have been found to seriously impact health. For example, researchers mentioned a meta-analytic review of 148 studies that found a 50% increased likelihood for survival in individuals with stronger social relationships. This impact is comparable to the effect of smoking and alcohol consumption on mortality; and it surpasses the influence of physical inactivity and obesity. A 10-decibel reduction of hearing sensitivity was also linked to cognitive declines comparable to nearly four years of chronological aging, researchers found. Cognitive decline-especially if it leads to dementia-can significantly reduce quality of life and health. The physical, psychological and financial toll that dementia imparts on family caregivers is considerable. Consequently, it is important to identify predisposing factors that might be addressed to lower that risk.
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So why might hearing loss lead to social isolation? It may be because hearing loss often interferes with communication, leading to possible frustration and embarrassment in social situations. Favourite social activities may no longer be enjoyable if they require adequate hearing to participate. As a consequence, people with hearing loss may experience reduced social support and increased loneliness or may isolate themselves to cope. According to authors, the connections between hearing loss and cognitive decline are less clear, and a causal connection has not been established definitively. Social interaction may stimulate the brain, thus protecting it against cognitive decline. Consequently, if the brain is not being stimulated due to a lack of social interaction, it may be more susceptible to cognitive decline. Mental strain could be another cause. People with hearing loss must devote much of their mental resources to understand speech because it often sounds muffled, distorted, or inaudible. This constant mental strain could reduce the amount of cognitive reserves available for other tasks, like memory and executive functions, and as a result symptoms of dementia may arise earlier. Another theory is that hearing loss might affect brain structure and function, as demonstrated by longitudinal studies that have shown hearing loss to be associated with diminished brain volume over time. Finally, another possibility is that a yet unknown common neuropathological cause might underlie both accelerated auditory aging and cognitive decline.
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This study was unique because it focused specifically on people who were either unaware that they had hearing loss, or knew they did but had not yet sought a hearing test or treatment. Although many people in the general population meet such criteria, a diagnosis is often delayed because hearing loss usually starts and progresses gradually. According to authors, treatments for hearing loss such as hearing aids and auditory rehabilitation programs are underused, due to barriers such as cost, stigma, low availability, or simply because people don’t know where or how to access these services. Individuals with hearing loss may also forego treatment simply because they don’t believe that their hearing loss is significantly impacting their lives.
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Stigma of hearing loss and wearing hearing aid:
Historically, hearing loss has been seen as an ailment, and some even thought it was a disability because children who had hearing loss had trouble learning. According to the Journal of Medical Professionals with Hearing Losses, people viewed the deaf and hard of hearing “with a mixture of fear, scorn, distaste, misunderstanding and pity.” Many were under the misconception that those with hearing loss didn’t have the capacity to be educated, and it wasn’t until the mid-1700s that people began considering that youth with hearing loss could in fact learn. What many people don’t know is that hearing loss can affect anyone, and the issue can be very detrimental to a person’s self-esteem. Someone with hearing loss can become distant from family and friends because they have trouble comprehending conversations, and they may even be looked down upon by others. Nearly 40 million Americans suffer from hearing loss and, shockingly so, only 25 percent of those people have hearing aids. People avoid getting hearing aids, not only for reasons of cost or accessibility, but due to fear of being perceived as older, uncool or socially awkward.
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Hearing impaired people are subject to prejudice and misconceptions.
The hearing impaired person may be considered to be:
•Old.
•Less intelligent.
•Mentally ill.
•Only hearing what he/she wants to hear.
Many people also think that hearing aids are unsightly, uncomfortable, expensive and do not function optimally. They may put off obtaining an aid or avoid using it. Stigmas such as the belief that hearing aids are for senior citizens are known to limit hearing aid use. Hearing impaired people may say they would rather live with some hearing loss than wear a hearing aid.
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Overcoming the stigma:
As people are getting educated on the condition, more people are becoming accepting and conscious of hearing loss. There has always been resistance of hearing aids, especially for someone who is getting a hearing aid for the first time. According to audiologist Dr. Douglas Chen, “the size of the social stigma is out of proportion compared to that of eyeglasses, canes, walkers and wheelchairs.” Thanks to modern technology, people who need hearing devices have more options available to them, which eliminates the stigma for users. Customizable hearing aids and digital settings make it a seamless transition, and instruments just continue to get more intelligent. Making the leap to go to a healthy hearing professional can be scary, but it is a decision that will improve your quality of life. Do you have trouble talking with family members? Do you feel left out because you can’t understand what others can? Don’t wait any longer. Visiting an audiologist is the first step toward getting your hearing back.
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The good news is that 95 percent of hearing losses can be treated with hearing aids. Yet fewer than 20 percent of people with hearing loss choose to correct it. So why don’t more people seek hearing help? People usually suffer needlessly for several years before they look for hearing help. A study published in 2010 by Margaret I. Wallhagen, Ph.D., found that the perceived stigma associated with hearing loss negatively impacts an individual’s initial acceptance of it and whether or not they choose to wear hearing aids. The study found that hearing loss stigma is directly related to three main factors: alteration in self-perception, ageism, and vanity. Unfortunately, just the idea of wearing hearing aids was found to negatively change self-perception for participants in the study. Participants perceived themselves differently and worried about how they would be viewed by others if they wore hearing aids before they actually tried them. The study also found that the negative associations were markedly diminished if the hearing aids were discreet and unnoticeable. The stigma associated with hearing loss and hearing aids often prevents a person from seeking hearing help. Typically the same people that worry needlessly are pleased to find that there are many discreet customizable options that greatly improve quality of life.
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Why delay in seeking treatment for hearing loss?
Unlike eyesight, which people address by getting glasses as soon as it fades, hearing loss tends to be ignored or put off for as long as possible. The reasons for delay in seeking treatment are as varied as the people who experience hearing loss:
1. The onset of hearing loss is usually gradual — making it easier to ignore or go unnoticed.
2. It is not always recognized for what it is — instead, it’s other people talking too softly or mumbling.
3. It is viewed as inconsequential — “So what if I can’t hear as well? It’s not hurting anyone but me.”
4. It is relatively easy to work around — you can just turn the TV up louder or avoid places where it’s more of a problem.
5. There’s a concern about how hearing aids look and what others will think — “My hearing isn’t bad enough for hearing aids.”
On average, people wait 4.8 years between first noticing their hearing loss and finally taking action.
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Sound:
Sound is a common form of communication throughout a vast variety of species because sound is very useful in both day and night; sound can travel over long distances and can bend around corners, and bounce off walls; sound can travel through air, water and solid objects; sound is very versatile as it can be heard as the actual sound; and an individual can produce a variety of sounds.
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Most sounds are produced by vibration of air molecules from an oscillating source. In the case of speech, the lungs produce adequate airflow and air pressure to vibrate vocal folds in the larynx (voice-box) and vocal folds (vocal cords) are a vibrating valve that chops up the airflow from the lungs into audible speech. Like the visual system, our hearing system picks up several qualities in the signals it detects (for example, a sound’s location, its loudness, and its pitch). Our hearing system does not blend the frequencies of different sounds, as the visual system does when different wavelengths of light are mixed to produce color. Instead, it separates complex sounds into their component tones or frequencies so that we can follow different voices or instruments as we listen to conversations or to music.
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Hearing begins with the propagation of a sound wave. Therefore, to understand hearing and hearing loss, it is necessary to understand how sound is generated and how it travels from its source to the ear. Sound is produced by a vibrating or oscillating body. It then travels as longitudinal waves through a medium, usually air, to the ear. It can also travel through other mediums, such as liquids and solids. The vibrating body transmits the vibration to the molecules of air in contact with it, making them vibrate. This motion is resisted by the frictional resistance of air, which converts some of the kinetic energy of motion into heat and reduces the amplitude of the oscillation until the air molecules stop moving. However, the vibration is communicated to other molecules and will travel through the air until it encounters an object that acts as an opposing force. Objects that are elastic, such as the eardrum (tympanic membrane), will start oscillating due to the force of the air molecules striking them. When something vibrates in the atmosphere, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air. To see how this works, let’s look at a simple vibrating object: a bell. When you hit a bell, the metal vibrates — flexes in and out. When it flexes out on one side, it pushes on the surrounding air particles on that side. These air particles then collide with the particles in front of them, which collide with the particles in front of them, and so on. This is called compression. When the bell flexes away, it pulls in on the surrounding air particles. This creates a drop in pressure, which pulls in more surrounding air particles, creating another drop in pressure, which pulls in particles even farther out. This pressure decrease is called rarefaction. In this way, a vibrating object sends a wave of pressure fluctuation through the atmosphere. We hear different sounds from different vibrating objects because of variations in the sound wave frequency. A higher wave frequency simply means that the air pressure fluctuation switches back and forth more quickly. We hear this as a higher pitch. When there are fewer fluctuations in a period of time, the pitch is lower. The level of air pressure in each fluctuation, the wave’s amplitude, determines how loud the sound is. The effect of frictional resistance is to reduce the amplitude as time progresses.
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Sound waves are what physicists call longitudinal waves, which consist of propagating regions of high pressure (compression) and corresponding regions of low pressure (rarefaction).
Spherical longitudinal waves
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Sound can propagate through a medium such as air, water and solids as longitudinal waves and also as a transverse wave in solids. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation. Sound waves may be “viewed” using parabolic mirrors and objects that produce sound. The energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter, and the kinetic energy of the displacement velocity of particles of the medium. The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, and displacement of the medium vary in time. At an instant in time, the pressure, velocity, and displacement vary in space. Note that the particles of the medium do not travel with the sound wave. This is intuitively obvious for a solid, and the same is true for liquids and gases (that is, the vibrations of particles in the gas or liquid transport the vibrations, while the average position of the particles over time does not change). During propagation, waves can be reflected, refracted, or attenuated by the medium.
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Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. In 20 °C (68 °F) air at sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph). In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).
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Important features of a sound wave include amplitude (intensity), frequency (pitch), phase and complexity.
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Amplitude:
The amplitude of a sound wave is the maximum displacement of an air molecule from its rest position. Since it is produced by a vibrating body making contact with air molecules and applying a force to them, sound amplitude is measured as the sound pressure level (SPL), as pressure is equal to force divided by area, in this case the force from the vibrating body over the area into which it comes in contact with or the area of the eardrum when this vibration is transmitted to the eardrum. The smallest SPL at which sound can be perceived is taken as 20 microPa (micropascals). This gives the first point (zero decibel) of the amplitude scale. The amplitude of sound measured is generally measured relative to the peak amplitude, i.e. the SPL measured in micropascals at the peak. Sound pressure can also be measured at other points than peaks on a sound wave.
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Sound Pressure is the difference between the pressure produced by a sound wave and the barometric (ambient) pressure at the same point in space. The root-mean-square pressure (abbreviated as RMS pressure) is the square root of the average of the square of the pressure of the sound signal over a given duration. The root-mean-square pressure is most often used to characterize a sound wave because it is directly related to the energy carried by the sound wave. Sound Pressure Level (SPL) is the RMS value of the instantaneous sound pressures measured over a specified period of time.
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Sound Intensity and the Decibel Scale:
The amplitude or SPL of a sound is also related to the intensity of a sound. Intensity is the measure of energy used per unit of time per unit of area. Since the area of molecular movement for sound waves is fairly small, it is usually measured in centimetres squared (cm2) and time is measured in units of seconds. Thus, intensity is measured as joules/second/cm2 or equivalently as watts/cm2. Sound intensity is used in acoustics, for example, when measuring sound from a loudspeaker. However, in hearing it is the pressure of sound striking the eardrum rather than the sound intensity that is significant. Studies of sound perception have shown that sound intensity is related to the ratio of the measured pressure Pm for the sound under investigation to the pressure Pr for the softest sound that can be heard (called the reference pressure). This reference pressure is Pr = 20 microPa. Thus, sound intensity is perceived as the ratio (Pm/Pr) squared. The ratio is squared due to inverse-square law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity. It has also been shown experimentally that multiplying the sound pressure in micropascals by a factor of ten is required to give a perceived doubling of loudness. The perception of loudness relates roughly to the sound power to an exponent of 1/3. For example, if you increase the sound power by a factor of ten, listeners will report that the loudness has increased by a factor of about two (101/3 ≈ 2). This is a major problem for eliminating undesirable environmental sounds, for instance, the beefed-up stereo in the next door apartment. Suppose you diligently cover 99% of your wall with a perfect soundproof material, missing only 1% of the surface area due to doors, corners, vents, etc. Even though the sound power has been reduced to only 1% of its former value, the perceived loudness has only dropped to about 0.011/3 ≈ 0.2, or 20%. A sound of 200microPa is twice as loud as one of 20microPa, and a sound of 2000 micro Pa is four times as loud as one of 20microPa. This finding suggests the use of a scale based on logarithms to the base ten would be convenient. Such a scale, called the bel (B) scale, is used in sound and acoustics and is named after the pioneering engineer in this field, Alexander Graham Bell. However, when measurements of sound are made, using bels gives a rather small range and also gives many sound pressures with values of one decimal place, such as 3.5 or 6.4 B. This is not so convenient, so the decibel (dB) is generally used. A bel is equal to 10 dB, and 6.4 B would become 64 dB.
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Ear is capable of detecting pressure variations of less than one billionth of atmospheric pressure. The sensitivity of the ear is amazing; when listening to very weak sounds, the ear drum vibrates less than the diameter of a single molecule! The difference between the loudest and faintest sounds that humans can hear is about 120 dB, a range of one-million in amplitude. Listeners can detect a change in loudness when the signal is altered by about 1 dB (a 12% change in amplitude). In other words, there are only about 120 levels of loudness that can be perceived from the faintest whisper to the loudest thunder.
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The intensity of a sound wave depends not only on the pressure of the wave, but also on the density of the medium and speed of sound in the medium. Higher density and higher sound speed both give a lower intensity. Water is about 800 times more dense than air and has a speed of sound 4.5 times faster. Thus, sounds with the same pressure amplitude are about 3600 times more intense in air than in water. This is one of the reasons humans hear so poorly underwater. The other reason is that our ears are really designed to work with air as the driving fluid, not water.
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Intensity of sound is measured in decibels (dB). The scale runs from the faintest sound the human ear can detect, which is labelled 0 dB, to over 180 dB, the noise at a rocket pad during launch. Decibels are measured logarithmically, being 10 times the log of the ratio of a particular sound pressure to a reference sound pressure. On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. Sound intensity may be given in two different units. Persons interested in the actual physical quantification of sound use units of sound pressure level (SPL). SPL is calibrated to a constant sound pressure level that does not vary with frequency. On audiograms, however, sound intensity is calibrated in hearing level (HL), meaning that the reference sound is one that that just barely heard by a normal population. Thus HL units are relative ones and do not generally correspond to SPL units. On the decibel scale, the range of human hearing extends from 0 dB, which represents a level that is all but inaudible, to about 130 dB, the level at which sound becomes painful. Higher intensity (db) of sound causes more damage. Many experts agree that continual exposure to more than 85 decibels may become dangerous.
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The following table illustrates some common sounds and their intensity.
| Approximate Decibel Level | Examples |
| 0 dB | the quietest sound you can hear. |
| 30 dB | whisper, quiet library. |
| 60 dB | normal conversation, sewing machine, typewriter. |
| 90 dB | lawnmower, shop tools, truck traffic; 8 hours per day is the maximum exposure (protects 90% of people). |
| 100 dB | chainsaw, pneumatic drill, snowmobile; 2 hours per day is the maximum exposure without protection. |
| 115 dB | sandblasting, loud rock concert, auto horn; 15 minutes per day is the maximum exposure without protection. |
| 140 dB | gun muzzle blast, jet engine; noise causes pain and even brief exposure injures unprotected ears; maximum allowed noise with hearing protector. |
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Phase:
As already seen above, sound waves can be represented by sine waves. The phase of a sine or sound wave indicates at what point in the cycle the sound wave starts. For instance, a sound wave with phase of 90° starts with its maximum amplitude rather than at rest. Phase angle varies from 0 to 360°. It is also useful to compare the phase angles of different sine waves to obtain the relative phase. This factor becomes important when considering that sound in the environment is made from various sine waves that may have differing phases. The interaction of phase becomes important when, for example, two sounds of the same frequency and intensity are 180° out of phase. In such a case, the sounds cancel each other out, leading to no sound being perceived. This is one method for eliminating unwanted sound.
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Frequency and Period:
Frequency is the number of cycles or complete oscillations per second. A cycle is an oscillation of an air molecule from rest through the points of maximum displacement and back to the initial point of rest. Frequency is generally measured in hertz or cycles per second. In terms of circular motion, a cycle is equivalent to moving round the circle once or going through 360° or 2Pi radians. Therefore, frequency is also sometimes measured as angular frequency in radians per second. Period is the length of time taken to complete one cycle. Therefore, it is the inverse of the frequency. Thus, a sound with a frequency of 1000 Hz has a period of 1/1000 s or 1 ms. The higher the pitch of the sound, the higher the frequency. A low pitch such as a deep voice or a tuba makes fewer vibrations per second than a high voice or violin. Generally noise induce hearing loss occurs at a pitch of about 2000-4000 Hz. Young children, who generally have the best hearing, can often distinguish sounds from about 20 Hz, such as the lowest note on a large pipe organ, to 20,000 Hz, such as the high shrill of a dog whistle that many people are unable to hear. Human speech, which ranges from 300 to 5,000 Hz, sounds louder to most people than noises at very high or very low frequencies. When hearing impairment begins, the high frequencies are often lost first, which is why people with hearing loss often have difficulty hearing the high-pitched voices of women and children. Loss of high frequency hearing also can distort sound, so that speech is difficult to understand even though it can be heard. Hearing impaired people often have difficulty detecting differences between certain words that sound alike, especially words that contain S, F, SH, CH, H, or soft C, sounds, because the sound of these consonant is in a much higher frequency range than vowels and other consonants.
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Simple and Complex Sounds:
A simple sound has a single frequency regardless of amplitude or SPL. Thus, 1000 Hz, 250 Hz, and 12,500 Hz are all simple sounds. The term pure tone is sometimes used to denote a sound at a single frequency. Pure tones are used in measuring hearing and hearing loss. A simple sound is produced by a single vibrating mass (sound source) producing an audible sound (of 0 dB SPL or greater); the sound is of a single frequency. However, most vibrating sources are more than just a single mass. For example, the vocal folds that produce voice are housed in a structure (the throat or pharynx) that is itself able to vibrate. The initial sound from the vocal folds then causes oscillation in the vocal tract of the pharynx. The oscillation of other masses or structures due to an original sound is called resonance and the structure is said to resonate. Therefore, most complex sounds, such as speech, are due to an initial sound mixed with resonated sounds. A complex sound consists of a base or fundamental frequency plus harmonics, i.e. multiples of the fundamental frequency. For example, a complex sound with fundamental frequency of 100 Hz could also have harmonics at 200, 300, 400, and 500 Hz. The harmonics are often denoted f0, f1, f2 and so on, with f0 the first harmonic or fundamental frequency, f1 the first overtone or second harmonic, and so on. However, a complex sound does not always have its entire harmonics. For instance, a complex sound with five harmonics could consist of the first five harmonics or the fundamental plus odd harmonics, e.g. 100, 300, 500, and 700 Hz. Speech is produced by this fundamental plus odd harmonics resonance pattern and, therefore, the ability to hear complex sounds rather than only pure tones is important for understanding speech. In the case of speech, the vocal tract is a tube that can be thought of as a resonant tube. The initial sound produced by the vocal folds is called the fundamental frequency of voice (for the given person).The resonance characteristics of the vocal tract determine the fundamental plus odd harmonics characteristics of speech. Resonance is an important factor in speech and hearing. In addition to speech resulting from sound resonating within the vocal tract, the ear itself is a resonator. This resonance affects the ability to hear. Damage to the ear or using a hearing aid can change the resonant characteristics of the auditory system.
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Sound wave and heat:
On a very tiny scale (as tiny as 1/100,000,000thof a centimeter) everything is made of tiny vibrating particles called molecules. An object’s temperature is the measurement of how fast these molecules are moving around. The faster they’re moving the higher the temperature. Sound is just another form of energy, and one that isn’t too different from heat. Sound and heat are both macroscopic descriptions of the movement of atoms and molecules. Sound is the ordered movement of atoms and molecules in rapid waving patterns. Heat is the disordered, random, movement of atoms and molecules. Therefore, all you have to do in order to turn sound into heat is transform some of the ordered movement of the atoms and molecules into disordered movement. This effect always happens to some extent. This effect happens a lot whenever the sound wave encounters irregularities as it travels. Sound waves always generate a little heat as they travel and they ultimately almost always end up completely as heat when they are absorbed by materials. However, the amount of energy carried by sound waves is very small, so that the amount of heat they generate is typically insignificant. The average human yells at about 80 decibels, which carries along with it about 0.001 watts of energy, about a 100,000 times less than the energy needed to light a standard 100 watt bulb. If you were to focus this energy at the average 250 ml cup of coffee, the average yell lasting a single second would warm the cup of coffee by 0.00000095 degrees Celsius!!! Ultrasound is distinguished by vibrations with a frequency greater than 20,000 Hz, compared to audible sounds that humans typically hear with frequencies between 20 and 20,000 Hz. One characteristic of ultrasound is attenuation of an ultrasound signal partly due to the conversion of mechanical wave energy to thermal energy. Researchers and doctors have made medical applications to harness this heat conversion and use it in successful medical procedures. Ultrasound energy is a form of therapy being studied as an anticancer treatment. Intensified ultrasound energy can be directed at cancer cells to heat them and kill them.
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Anatomy and physiology of hearing:
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The main function of the ear is to receive auditory and vestibular input. It locates the directional source of sound, collects sound waves and conducts them to the special organ of sense in the inner ear, where sound is converted to electrical impulses and transmitted to the brain. The external ear receives sounds, which cause vibrations of the tympanic membrane. These vibrations move along the ossicles of the middle ear, to be transmitted to the inner ear. The stapes is connected to the oval window, so when the stapes transmits vibrations, this causes movement of perilymph that is in the inner ear. The movement of the perilymph is transmitted via the scala vestibuli and the scala tympani, to the round window, where it induces movement of the secondary tympanic membrane. This results in the movement of the endolymph of the cochlear duct, causing pressure on the tectorial membrane, which then induces pressure on the sensory hairs, stimulating the receptor cells within the cochlear duct to send impulses to the spiral ganglion. The axons of the spiral ganglion form part of the vestibulocochlear nerve.
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Anatomy of human ear:
Human ear, organ of hearing and equilibrium, detects and analyzes sounds by transduction (or the conversion of sound waves into electrochemical impulses) and maintains the sense of balance (equilibrium). The human ear, like that of other mammals, contains sense organs that serve two quite different functions: that of hearing and that of postural equilibrium and coordination of head and eye movements. Anatomically the ear has three distinguishable parts: the outer, middle, and inner ear. The outer ear consists of the visible portion called the auricle, or pinna, which projects from the side of the head, and the short external auditory canal, the inner end of which is closed by the tympanic membrane, commonly called the eardrum. The function of the outer ear is to collect sound waves and guide them to the tympanic membrane. The middle ear is a narrow, air-filled cavity in the temporal bone. It is spanned by a chain of three tiny bones—the malleus (hammer), incus (anvil), and stapes (stirrup), collectively called the auditory ossicles. This ossicular chain conducts sound from the tympanic membrane to the inner ear, which has been known since the time of Galen as the labyrinth. It is a complicated system of fluid-filled passages and cavities located deep within the rock-hard petrous portion of the temporal bone. The inner ear consists of two functional units: the vestibular apparatus, consisting of the vestibule and semicircular canals, which contains the sensory organs of postural equilibrium; and the snail-shell-like cochlea, which contains the sensory organ of hearing. These sensory organs are highly specialized endings of the eighth cranial nerve, also called the vestibulocochlear nerve.
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Physiology of hearing:
The function of the external and middle ear is to amplify sound to facilitate conversion of the mechanical energy of the sound wave into an electrical signal by the inner ear hair cells, a process called mechanotransduction. Sound waves enter the external auditory canal and set the tympanic membrane (eardrum) in motion, which in turn moves the malleus, incus, and stapes of the middle ear. Movement of the footplate of the stapes causes pressure changes in the fluid-filled inner ear, eliciting a traveling wave in the basilar membrane of the cochlea. The tympanic membrane and the ossicular chain in the middle ear serve as an impedance-matching mechanism, improving the efficiency of energy transfer from air to the fluid-filled inner ear. Stereocilia of the hair cells of the organ of Corti, which rests on the basilar membrane, are in contact with the tectorial membrane and are deformed by the traveling wave. The vibrations cause the fluid in cochlea to move the hair cells. When these hair cells move, they produce electrical signals that travel along your auditory nerve to your brain, where they’re converted into meaningful information such as language or music. A point of maximal displacement of the basilar membrane is determined by the frequency of the stimulating tone. High-frequency tones cause maximal displacement of the basilar membrane near the base of the cochlea, whereas for low-frequency sounds, the point of maximal displacement is toward the apex of the cochlea. The inner and outer hair cells of the organ of Corti have different innervation patterns, but both are mechanoreceptors. The afferent innervation relates principally to the inner hair cells, and the efferent innervation relates principally to outer hair cells. The motility of the outer hair cells alters the micromechanics of the inner hair cells, creating a cochlear amplifier, which explains the exquisite sensitivity and frequency selectivity of the cochlea. Beginning in the cochlea, the frequency specificity is maintained at each point of the central auditory pathway: dorsal and ventral cochlear nuclei, trapezoid body, superior olivary complex, lateral lemniscus, inferior colliculus, medial geniculate body, and auditory cortex. At low frequencies, individual auditory nerve fibers can respond more or less synchronously with the stimulating tone. At higher frequencies, phase-locking occurs so that neurons alternate in response to particular phases of the cycle of the sound wave. Intensity is encoded by the amount of neural activity in individual neurons, the number of neurons that are active, and the specific neurons that are activated. There is evidence that the right and left ears as well as the central nervous system may process speech asymmetrically. Generally, a sound is processed symmetrically from the peripheral to the central auditory system. However, a “right ear advantage” exists for dichotic listening tasks, in which subjects are asked to report on competing sounds presented to each ear. In most individuals, a perceptual right ear advantage for consonant-vowel syllables, stop consonants, and words also exists. Similarly, whereas central auditory processing for sounds is symmetric with minimal lateral specialization for the most part, speech processing is lateralized. There is specialization of the left auditory cortex for speech recognition and production, and of the right hemisphere for emotional and tonal aspects of speech. Left hemisphere dominance for speech is found in 95–98% of right-handed persons and 70–80% of left-handed persons.
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The mechanism of hearing is depicted in the figure below:
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Let us deal with the sound conducting mechanism. The range of audible sound is approximately 10 octaves from somewhere between 16 and 32 Hz (cycles per second) to somewhere between 16,000 and 20,000 Hz. The sensitivity is low at the extremes but becomes much more sensitive above 128 Hz up to about 4,000 Hz when it again becomes rapidly less sensitive. The range of maximum sensitivity and audibility diminishes with age. The head itself acts as a natural barrier between the two ears and thus a sound source at one side will produce a more intense stimulus of the ear nearest to it and incidentally the sound will also arrive there sooner, thus helping to provide a mechanism for sound localization based on intensity and time of arrival differences of sound. High frequency hearing is more necessary than low frequency hearing for this purpose and this explains why sound localization becomes difficult with a high frequency hearing loss. The head in humans is large in comparison to the size of the pinna so the role of the pinna is less than in some other mammals. Nonetheless, its crinkled shape catches higher frequency sounds and funnels them into the ear canal. It also blocks some higher frequency sound from behind, helping to identify whether the sound comes from the front or the back. The ear canal acts as a resonating tube and actually amplifies sounds at between 3000 and 4,000 Hz adding to the sensitivity (and susceptibility to damage) of the ear at these frequencies. The ear is very sensitive and responds to sounds of very low intensity, to vibrations which are hardly greater than the natural random movement of molecules of air. To do this the air pressure on both sides of the tympanic membrane must be equal. Anyone who has their ear blocked even by the small pressure change of a rapid elevator ride knows the truth of this. The Eustachian tube provides the means of the pressure equalization. It does this by opening for short periods, with every 3rd or 4th swallow; if it were open all the time one would hear one’s own every breath. Because the lining membrane of the middle ear is a respiratory membrane, it can absorb some gases, so if the Eustachian tube is closed for too long it absorbs carbon dioxide and oxygen from the air in the middle ear, thus producing a negative pressure. This may produce pain (as experienced if the Eustachian tube is not unblocked during descent of an aeroplane). The middle ear cavity itself is quite small and the mastoid air cells act as an air reservoir cushioning the effects of pressure change. If negative pressure lasts too long, fluid is secreted by the middle ear, producing a conductive hearing loss. The outer and middle ears serve to amplify the sound signal. The pinna presents a fairly large surface area and funnels sound to the smaller tympanic membrane; in turn the surface of the tympanic membrane is itself much larger than that of the stapes foot plate, so there is a hydraulic amplification: a small movement over a large area is converted to a larger movement of a smaller area. In addition, the ossicular chain is a system of levers which serve to amplify the sound. The outer and middle ears amplify sound on its passage from the exterior to the inner ear by about 30 dB.
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The function of the inner ear is to transduce vibration into nervous impulses. While doing so, it also produces a frequency (or pitch) and intensity (or loudness) analysis of the sound. Nerve fibres can fire at a rate of just under 200 times per second. Sound level information is conveyed to the brain by the rate of nerve firing, for example, by a group of nerves each firing at a rate at less than 200 pulses per second. They can also fire in locked phase with acoustic signals up to about 5 kHz. At frequencies below 5 kHz, groups of nerve fibres firing in lock phase with an acoustic signal convey information about frequency to the brain. Above about 5 kHz frequency information conveyed to the brain is based upon the place of stimulation on the basilar membrane. As an aside, music translated up into the frequency range above 5 kHz does not sound musical. As mentioned above each place along the length of the basilar membrane has its own characteristic frequency, with the highest frequency response at the basal end and lowest frequency response at the apical end. Also any sound introduced at the oval window by motion of the stapes is transmitted along the basilar membrane as a travelling wave until all of its frequency components reach their respective places of resonance where they stop and travel no further. For example, a 1 kHz tone induces resonance at about the middle of the basilar membrane. Any frequency components lower than 1 kHz must travel more than half the length of the basilar membrane, whereas high frequency components, greater than 1 kHz must travel less than half the length of the basilar membrane. Evidently the brain must suppress high frequency information in favour of low frequency information as the travelling wave on the basilar membrane passes through places of high frequency resonant response. An explanation is thus provided for the observation that low frequency sounds, for example traffic noise, are very effective in masking high frequency sounds, for example the fricatives of speech, making telephones near busy streets difficult to use.
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Ordinarily, when airborne sound strikes the surface of a body of water, almost all of its energy is reflected and only about 0.1 percent passes into the water. In the ear this would represent a transmission loss of 30 decibels, enough to seriously limit the ear’s performance, were it not for the transformer action of the middle ear. Vibration is poorly transmitted at the interface between two media which differ greatly in characteristic impedance (product of density of the medium and speed of sound within it), as for example air (middle ear) and water (inner ear). The ear has evolved a complex mechanism to overcome this impedance mis-match, known as the sound conducting mechanism. The matching of impedances is accomplished in two ways, primarily by the reduction in area between the tympanic membrane and the stapes footplate and secondarily by the mechanical advantage of the lever formed by the malleus and incus. Although the total area of the tympanic membrane is about 69 square millimetres (0.1 square inch), the area of its central portion that is free to move has been estimated at about 43 square millimetres. The sound energy that causes this area of the membrane to vibrate is transmitted and concentrated in the 3.2-square-millimetre area of the stapes footplate. Thus, the pressure is increased at least 13 times. The mechanical advantage of the ossicular lever (which exists because the handle of the malleus is longer than the long projection of the incus) amounts to about 1.3. The total increase in pressure at the footplate is, therefore, not less than 17-fold, depending on the area of the tympanic membrane that is actually vibrating. At frequencies in the range of 3,000 to 5,000 hertz, the increase may be even greater because of the resonant properties of the ear canal. The ossicular chain not only concentrates sound in a small area but also applies sound preferentially to one window of the cochlea, the oval window. If the oval and round windows were exposed equally to airborne sound crossing the middle ear, the vibrations in the perilymph of the scala vestibuli would be opposed by those in the perilymph of the scala tympani, and little effective movement of the basilar membrane would result. As it is, sound is delivered selectively to the oval window, and the round window moves in reciprocal fashion, bulging outward in response to an inward movement of the stapes footplate and inward when the stapes moves away from the oval window. The passage of vibrations through the air across the middle ear from the tympanic membrane to the round window is of negligible importance. Thanks to these mechanical features of the middle ear, the hair cells of the normal cochlea are able to respond, at the threshold of hearing for frequencies to which the ear is most sensitive, to vibrations of the tympanic membrane on the order of 1 angstrom (0.0000001 millimeters) in amplitude. On the other hand, when the ossicular chain is immobilized by disease, as in otosclerosis, which causes the stapes footplate to become fixed in the oval window, the threshold of hearing may increase by as much as 60 decibels (1,000-fold), which represents a significant degree of impairment. Bypassing the ossicular chain through the surgical creation of a new window, as can be accomplished with the fenestration operation, can restore hearing to within 25 to 30 decibels of the normal. Only if the fixed stapes is removed (stapedectomy) and replaced by a tiny artificial stapes can normal hearing be approached. Fortunately, operations performed on the middle ear have been perfected so that defects causing conductive impairment often can be corrected and a useful level of hearing restored.
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My view:
Sound is transmitted as air conduction up to tympanic membrane, then as solid conduction in bony ossicles and then as liquid conduction via cochlear fluid. So there is air-solid interface and solid-liquid interface rather than direct air-liquid interface. Vibration is poorly transmitted at the interface between two media which differ greatly in characteristic impedance (product of density of the medium and speed of sound within it); here there are two interfaces, so double impedance mismatch.
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Function of the muscles of the middle ear:
The muscles of the middle ear, the tensor tympani and the stapedius, can influence the transmission of sound by the ossicular chain. Contraction of the tensor tympani pulls the handle of the malleus inward and, as the name of the muscle suggests, tenses the tympanic membrane. Contraction of the stapedius pulls the stapes footplate outward from the oval window and thereby reduces the intensity of sound reaching the cochlea. The stapedius responds reflexly with quick contraction to sounds of high intensity applied either to the same ear or to the opposite ear. The reflex has been likened to the blink of the eye or the constriction of the pupil of the eye in response to light and is thought to have protective value. Unfortunately, the contractions of the middle-ear muscles are not instantaneous, so that they do not protect the cochlea against damage by sudden intense noise, such as that of an explosion or of gunfire. They also fatigue rather quickly and thus offer little protection against injury sustained from high-level noise, such as that experienced in rock concerts and many industrial workplaces.
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Cochlea:
The cochlea is a snail-shaped formation that enables sound transmission via a sensorineural route, rather than through a conductive pathway. The cochlea is a complex structure, consisting of three layers of fluid. The scala vestibuli and scala media are separated by Reissner’s Membrane whereas the scala media and scala tympani are divided by the basilar membrane. The diagram below illustrates the complex layout of the compartments and their divisions:
The cochlea has three fluid-filled sections, and supports a fluid wave driven by pressure across the basilar membrane separating two of the sections. Strikingly, one section, called the cochlear duct or scala media, contains endolymph, a fluid similar in composition to the intracellular fluid found inside cells. The organ of Corti is located in this duct on the basilar membrane, and transforms mechanical waves to electric signals in neurons. The other two sections are known as the scala tympani and the scala vestibuli; these are located within the bony labyrinth, which is filled with fluid called perilymph, similar in composition to cerebrospinal fluid. The chemical difference between the fluids endolymph and perilymph fluids is important for the function of the inner ear due to electrical potential differences between potassium and calcium ions.
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The basilar membrane widens as it progresses from base to apex. Therefore, the base (the thinnest part) has a greater stiffness than the apex. This means that the amplitude of a sound wave travelling through the basilar membrane varies as it travels through the cochlea. When a vibration is carried through the cochlea, the fluid within the three compartments causes the basilar membrane to respond in a wave-like manner. This wave is referred to as a ‘travelling wave’; this term means that the basilar membrane does not simply vibrate as one unit from the base towards the apex. When a sound is presented to the human ear, the time taken for the wave to travel through the cochlea is only 5 milliseconds. When low-frequency travelling waves pass through the cochlea, the wave increases in amplitude gradually, then decays almost immediately. The placement of vibration on the cochlea depends upon the frequency of the presented stimuli. For example, lower frequencies mostly stimulate the apex, in comparison to higher frequencies, which stimulate the base of the cochlea. This attribute of the physiology of the basilar membrane can be illustrated in the form of a place–frequency map:
Simplified schematic of the basilar membrane, showing the change in characteristic frequency from base to apex.
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The basilar membrane supports the organ of Corti, which sits within the scala media. The organ of Corti comprises both outer and inner hair cells. The total number of outer hair cells in the cochlea has been estimated at 12,000 and the number of inner hair cells at 3,500. Although there are about 30,000 fibres in the cochlear nerve, there is considerable overlap in the innervation of the outer hair cells. A single fibre may supply endings to many hair cells, which thus share a “party line.” Furthermore, a single hair cell may receive nerve endings from many fibres. The actual distribution of nerve fibres in the organ of Corti has not been worked out in detail, but it is known that the inner hair cells receive the lion’s share of afferent fibre endings without the overlapping and sharing of fibres that are characteristic of the outer hair cells. Hair cells are columnar cells, each with a bundle of 100-200 specialized cilia at the top, for which they are named. There are two types of hair cells. Inner hair cells are the mechanoreceptors for hearing: they transduce the vibration of sound into electrical activity in nerve fibers, which is transmitted to the brain. Outer hair cells are a motor structure. Sound energy causes changes in the shape of these cells, which serves to amplify sound vibrations in a frequency specific manner. Lightly resting atop the longest cilia of the inner hair cells is the tectorial membrane, which moves back and forth with each cycle of sound, tilting the cilia, which is what elicits the hair cells’ electrical responses. Inner hair cells, like the photoreceptor cells of the eye, show a graded response, instead of the spikes typical of other neurons. These graded potentials are not bound by the “all or none” properties of an action potential. Hair cells are very sensitive, due to the unique nature of endolymph encouraging K+ influx into hair cells. Cilia are in endolymph, but hair cell body is in perilymph. There is a high concentration of potassium ions (K+) in endolymph, which is maintained by ion pumps in the stria vascularis. The senses of hearing and equilibrium depend on hair cells which can detect motions of atomic dimensions and respond more than 100,000 times a second. Biophysical studies suggest that mechanical forces control the opening and closing of transduction channels by acting through elastic components in each hair cell’s mechanoreceptive hair bundle. Other ion channels, as well as the mechanical and hydrodynamic properties of hair bundles, tune individual hair cells to particular frequencies of stimulation.
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Outer hair cells act like a biological amplifier/attenuator, boosting soft sounds and dampening loud sounds. Inner hair cells transfer sound information to the auditory nerve. Outer hair cells deteriorate over time so that only about 70% are intact by 70 years of age. This can result in reduced hearing of high pitch sounds. Hearing aids are usually very beneficial in compensating for this type of hearing loss. Exposure to excessive noise can accelerate damage to outer hair cells causing a greater magnitude of hearing loss. Appropriate hearing protection should be used when in the presence of excessively loud sound to reduce damage to sensory hearing cells. Hearing aids are usually very beneficial in compensating for this type of hearing loss. Damage to inner hair cells can occur due to excessive noise, ear disease or degenerative conditions. Hearing aids are most effective at compensating for reduced function of outer hair cells, which is the most common type of permanent hearing loss. If the function of inner hair cells is very poor then a cochlear implant may provide better hearing ability.
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The ear has evolved a very intriguing mechanism to cope with the large range in sound intensity encountered in the environment. Only the inner hair cells initiate nervous impulses which are heard as sound. They are not particularly sensitive but they are rugged and they are placed at the inner edge of the basilar membrane which is relatively immobile. The point where the basilar membrane vibrates most is about its middle so that the inner hair cells are spared the most violent vibration of very intense sound. The question then arises, how do the inner hair cells respond to slight or moderate amounts of stimulation? Here the outer hair cells play a major role. When they are stimulated by the travelling wave they respond actively and physically contract. They have muscle proteins in their wall and literally shorten. Because they are attached both to the Reissner’s membrane and the basilar membrane, this produces an additional shear movement of the membranous labyrinth, which amplifies the travelling wave at the point of maximal stimulation. This amplified movement is transmitted to the inner hair cells which then respond. If the amount of movement of the basilar membrane is slight, the amount of outer hair cell contracture adds significantly to the basilar cell movement; if the amount of movement is large the contracture adds nothing to the already great displacement of the membranous labyrinth. If the outer hair cells are damaged they no longer contract in response to slight sounds and the inner hair cells are not stimulated. This produces a hearing loss for low intensity sound. If the sound is more intense, the inner hair cells are stimulated directly and they respond normally so that the ability to hear louder sounds remain unimpaired. This is a common phenomenon known as loudness recruitment. The inner hair cells are much “tougher” than outer hair cells and much less likely to be damaged by ageing, noise or most ototoxic drugs, so ageing, noise and ototoxic drugs usually only produce hearing loss but not deafness. It was noted earlier that the ear is most sensitive to sounds between approximately 3000 and 4000 Hz, in part because of the amplifying mechanism of the ear canal. Thus, the most intense stimulus is produced at these frequencies and the outer hair cells which respond to these frequencies are most at risk from damage. Prolonged exposure to loud sounds damages these hair cells and thus explains the hearing loss from noise which occurs first at 3 to 4 kHz.
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Synopsis of physiology of hearing is depicted in the figure below:
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Central auditory processing:
The nervous impulses are carried along the 8th cranial nerve (vestibulocochlear nerve) from the cochlea to the brain stem. Here the nerve fibres reach nuclei where they relay with other nerve fibres. The fibres from each auditory nerve split, some passing to one side of the brain, others remaining on the same side. Thus, as auditory stimuli pass up each side of the brain from both ears, unilateral hearing loss cannot be caused by a brain lesion. The fibres pass up the hind brain to the mid brain and the cerebral cortex. Evidence of orderly spatial representations of the organ of Corti at the lower levels of the auditory pathway has been reported by many investigators. These patterns seem to be in accord with the place theory of the cochlear analysis of sound. Physiological evidence of tuning of the auditory system also has been obtained by recording with the electrical potentials from individual neurons at various levels. Most neurons of the auditory pathway show a “best frequency”—i.e., a frequency to which the individual neuron responds at minimal intensity. This finding is entirely compatible with experimental evidence of frequency tuning of the hair cells. With each increase in the intensity of the sound stimulus, the neuron is able to respond to a wider band of frequencies, thus reflecting the broad tuning of the basilar membrane. With sounds of lower frequency, the rate of impulses fired by the neuron reflects the stimulus frequency, and the response often reveals phase-locking with the stimulus; that is, the nerve fibres are stimulated at regularly recurring intervals, corresponding to a particular position or phase, of each sound wave. Increased intensity of stimulation causes a more rapid rate of responding. In general, the pitch of a sound tends to be coded in terms of which neurons are responding, and its loudness is determined by the rate of response and the total number of neurons activated. Although extensive studies have been made of the responses of single cortical neurons, the data do not yet fit any comprehensive theory of auditory analysis. Experiments in animals have indicated that the cortex is not even necessary for frequency recognition, which can be carried out at lower levels, but that it is essential for the recognition of temporal patterns of sound. It appears likely, therefore, that in humans the cortex is reserved for the analysis of more complex auditory stimuli, such as speech and music, for which the temporal sequence of sounds is equally important. Presumably it is also at the cortical level that the meaning of sounds is interpreted and behaviour is adjusted in accordance with their significance. Such functions were formerly attributed to an “auditory association area” immediately surrounding the primary area, but they probably should be thought of as involving much more of the cerebral cortex, thanks to the multiple, parallel interconnections between the various areas.
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The brain works hard:
Many people find it challenging to follow conversations in some places, like in a noisy restaurant. This is because speech is made up of a large number of different sounds, put together in very rapid flow. Our brain constantly prioritises and organises all these sounds for us. When it comes to hearing, it may come as a surprise to learn that the brain works harder than the ears. This is why in noisy environments, such as in a crowded restaurant, it can be very frustrating just trying to follow conversation. Even people with no hearing loss can find this challenging. Ordinarily your brain will be able to sort through all information you apply your attention to through a cognitive process: Put simply, the brain organises the sound environment, selects the desired source and follows it. For people with hearing loss, however, the brain has to work much harder to make sense of sound because the input it receives from the ears is softer, less detailed, and/or unclear
Some sounds are heard better than others:
The high-pitched consonant sounds like f, s and t are easily drowned out by louder, low pitched vowel sounds like a, o and u. This results in a person with hearing loss complaining that they can hear that others are talking, but not what they are saying.
The ability to block out unwanted sounds:
In a crowded noisy room a young person with normal hearing can tune in and out conversations at will. This is known technically as the cocktail party effect. The brain quite automatically adjusts time of arrival and intensity differences of sound from different signal sources so that the one which is wanted passes to the cortex and all others which do not meet these criteria are suppressed by feedback loops. This requires good high frequency peripheral hearing, two ears and an additional central mechanism. Even in the presence of normal bilateral peripheral hearing, the elderly lose part of the central mechanism and find it difficult to listen in crowded rooms. This is compounded if there is some hearing loss.
On and Off Sounds:
Hearing has an alerting function especially to warning signals of all kinds. There are brain cells which respond only to the onset of a sound and others which respond only to the switching off of the sound, i.e. a change. Think only of being in an air conditioned room when the air conditioner turns on, one notices it. After a while it blends into the background and is ignored. When it switches off, again one notices it for a short time and then too the absence of sound blends into the background. These cells allow the ear to respond to acoustic change – one adjusts to constant sound – change is immediately noticeable. This is true too with machinery and a trained ear notices change.
Interaction of Sound Stimuli with other parts of the Brain:
Sound stimuli produce interaction with other parts of the brain to provide appropriate responses. Thus, a warning signal will produce an immediate general reaction leading to escape, a quickening of the heart rate, a tensing of the muscle and a readiness to move. A baby’s cry will alert the mother in a way it does not alert others. The sound of martial music may lead to bracing movement of those to whom it is being played and induce fear and cowering in the hearts and minds of those at whom it is being played. Certain sounds can evoke anger, others pleasure. The point is that the sensations produced by hearing are blended into the body mechanism in the central nervous system to make them part of the whole milieu in which we live.
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Sound localization:
A normal human can localize quite accurately the source of the sound. One knows from what direction the sound is coming; one knows where to turn one’s head to look for a speaker; as one knows where to look for an aeroplane or a bird. There are specific neurones which deal with this in the mid brain. The localization of sounds from a stationary source in the horizontal plane is known to depend on the recognition of minute differences in the intensity and time of arrival of the sound at the two ears. A sound straight in front of the head is heard at the same time by both ears. A sound to the side of the head is heard approximately 0.0005 seconds later by the ear furthest away. A sound halfway to one side is heard approximately 0.0003 seconds later. This is the interaural time difference (ITD) cue and is measured by signal processing in the two central auditory pathways that begin after the cochlea and pass through the brainstem and mid-brain. A sound that arrives at the right ear a few microseconds sooner than it does at the left or that sounds a few decibels louder in that ear is recognized as coming from the right. In a real-life situation the head may also be turned to pinpoint the sound by facing it and thus cancelling these differences. For low-frequency tones a difference in phase at the two ears is the criterion for localization, but for higher frequencies the difference in loudness caused by the sound shadow of the head becomes all-important. Such comparisons and discriminations appear to be carried out at brain stem and midbrain levels of the central auditory pathway. Sound streams arriving from below the head, above the head, and over behind the head (the vertical plane) are localised again by signal processing in the central auditory pathways. The cues this time however are the notches/peaks that are added to the sound arriving at the ears by the complex shapes of the pinna. Different notches/peaks are added to sounds coming from below compared to sounds coming from above, and compared to sounds coming from behind. The most significant notches are added to sounds in the 4 kHz to 10 kHz range. Localization of sound that emanates from a moving source is a more complicated task for the nervous system and apparently involves the cerebral cortex and short-term memory. Experiments in animals have shown that injury to the auditory area of the cortex on one side of the brain interferes with the localization of a moving sound source on the opposite side of the body.
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Air conduction and bone conduction:
Air conduction means sound waves move through the air in the external auditory canal and hit the tympanic membrane (eardrum) and cause the tympanic membrane to move. When the tympanic membrane moves, this movement is transmitted to the 3 bones called the malleus, the incus, and the stapes. Movement of the stapes causes pressure waves in the fluid-filled inner ear. Bone conduction occurs when a sound wave or other source of vibration causes the bones of the skull to vibrate. These vibrations are transmitted to the fluid surrounding the cochlea and hearing results. When the handle of a vibrating tuning fork is placed on a bony prominence such as the forehead or mastoid process behind the ear, its note is clearly audible. Similarly, the ticking of a watch held between the teeth can be distinctly heard. When the external canals are closed with the fingers, the sound becomes louder, indicating that it is not entering the ear by the usual channel. Instead, it is producing vibrations of the skull that are passed on to the inner ear, either directly or indirectly, through the bone.
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Bone conduction is the conduction of sound to the inner ear through the bones of the skull. Bone conduction transmission can be used with individuals with normal or impaired hearing. Bone conduction is one reason why a person’s voice sounds different to them when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own voices to be lower and fuller than others do, and a recording of one’s own voice frequently sounds higher than one expects it to sound. Musicians may use bone conduction while tuning stringed instruments to a tuning fork. After the fork starts vibrating placing it in the mouth with the stem between the back teeth ensures that one continues to hear the note via bone conduction, and both hands are free to do the tuning.
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Vibration of the skull results in auditory sensation. This is a way to somewhat bypass the outer and middle ears to stimulate the cochlea. Von Bekesy is credited with the discovery that at the level of the cochlea, phase shifted bone-conduction signals cancel out air conduction signals. Bone-conduction works because all of the bones of the skull are connected; including the temporal bone, which in turn stimulates the cochlea. The higher audible frequencies cause the skull to vibrate in segments, and these vibrations are transmitted to the cochlear fluids by direct compression of the otic capsule, the bony case enclosing the inner ear. Because the round window membrane is more freely mobile than the stapes footplate, the vibrations set up in the perilymph of the scala vestibuli are not cancelled out by those in the scala tympani, and the resultant movements of the basilar membrane can stimulate the organ of Corti. This type of transmission is known as compression bone conduction. At lower frequencies—i.e., 1,500 hertz and below—the skull moves as a rigid body. The ossicles are less affected and move less freely than the cochlea and the margins of the oval window because of their inertia, their suspension in the middle-ear cavity, and their loose coupling to the skull. The result is that the oval window moves with respect to the footplate of the stapes, which gives the same effect as if the stapes itself were vibrating. This form of transmission is known as inertial bone conduction. In otosclerosis the fixed stapes interferes with inertial, but not with compressional, bone conduction.
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Direct stimulation of the cochlea by a vibrator through bone conduction is routinely employed in audiological evaluations to distinguish hearing losses attributable to the outer and/or middle ear defects from those of sensorineural impairments. Bone conduction is the basis of some of the oldest, simplest, and most useful tests in the repertoire of the otologist. These tests employ tuning forks to distinguish between conductive impairment, which affects the middle ear and is amenable to surgery, and sensorineural impairment, which affects the inner ear and the cochlear nerve and for which surgery usually is not indicated. Bone conduction hearing aids are useful in cases of conductive hearing loss. In persons with middle-ear disease, hearing aids with special vibrators are sometimes used to deliver sound to the mastoid process (the part of the temporal bone behind the ear), which is then conducted by bone to the inner ear. Bone conduction is also being used in new methods of tinnitus therapy, both for masking and long-term residual inhibition. Conventional bone conduction hearing aids and bone conduction audiometry assume that (1) the frequency response of the skull to vibration is relatively flat across the range of interest, and (2) that there is little attenuation across the skull, allowing binaural perception from a single transducer on one side of the head. While this is largely the case below 5 kHz, which is the range of most interest for perception of unmodified speech, there is great variability both in frequency response and attenuation across the skull in the higher frequencies. An understanding of this complex response to bone conducted vibration is of less importance for deep insertion transcranial hearing aids, but is important for technologies using high audio (10-20 kHz) and ultrasound (> 20 kHz) for remediation of hearing loss and tinnitus.
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Normal hearing:
A healthy hearing system can recognise both low pitch sounds (a double-bass or traffic) and high pitch (a violin or the twittering of birds). In technical terms, that means frequencies between around 20 and 20,000 Hertz. What’s more, it can process very quiet sounds (the buzzing of a mosquito) and extremely loud sounds (a jet engine starting). This equates to volumes between 0 and more than 120 decibels.
Understanding speech:
Our brain is particularly adept at understanding language, which it can cope with in all its various facets and in every situation. Whether we are sitting in a café, on the phone or in a lecture, our brain filters out a flood of irrelevant sounds to concentrate on those that we need to hear. It is thanks to this facility that we are able to focus on a single instrument in a symphony orchestra, or participate in intimate conversations in a noisy environment.
Spatial hearing:
Our brain hears sounds 360 degrees around the head – at every angle around our head. Our brain can differentiate between front and back, up and down. This lets us tell where a sound is coming from, how big a room is or whether there is an obstruction in the area.
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Hearing standard:
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The figure below shows range of frequencies and hearing levels of average human speech:
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Human hearing extends in frequency from 20-20,000 Hz, and in amplitude from 0 dB to 130 dB or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to -5 or even -10 dB. 130 dB represents the threshold of pain. But the ear doesn’t hear all frequencies equally well; hearing sensitivity peaks around 3000 Hz. There are many qualities of human hearing besides frequency range and amplitude that can’t easily be measured quantitatively. But for many practical purposes, normative hearing is defined by a frequency versus amplitude graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies. Because of the cumulative impact of age and exposure to noise and other acoustic insults, ‘typical’ hearing may not be normative.
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The absolute threshold of hearing (ATH) is the minimum sound level of a pure tone that an average human ear with normal hearing can hear with no other sound present. The absolute threshold relates to the sound that can just be heard by the organism. The absolute threshold is not a discrete point, and is therefore classed as the point at which a sound elicits a response a specified percentage of the time. This is also known as the auditory threshold. The threshold of hearing is generally reported as the RMS sound pressure of 20 micropascals, corresponding to a sound intensity of 0.98 pW/m2 at 1 atmosphere and 25 °C. It is approximately the quietest sound a young human with undamaged hearing can detect at 1,000 Hz. The threshold of hearing is frequency-dependent and it has been shown that the ear’s sensitivity is best at frequencies between 1 kHz and 5 kHz, where the threshold reaches as low as −9 dB SPL.
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Temporal summation is the relationship between stimulus duration and intensity when the presentation time is less than 1 second. Auditory sensitivity changes when the duration of a sound becomes less than 1 second. The threshold intensity decreases by about 10 dB when the duration of a tone burst is increased from 20 to 200 ms. For example, suppose that the quietest sound a subject can hear is 16 dB SPL if the sound is presented at a duration of 200 ms. If the same sound is then presented for a duration of only 20 ms, the quietest sound that can now be heard by the subject goes up to 26 dB SPL. In other words, if a signal is shortened by a factor of 10 then the level of that signal must be increased by as much as 10 dB to be heard by the subject. The ear operates as an energy detector that samples the amount of energy present within a certain time frame. A certain amount of energy is needed within a time frame to reach the threshold. This can be done by using a higher intensity for less time or by using a lower intensity for more time. Sensitivity to sound improves as the signal duration increases up to about 200 to 300 ms, after that the threshold remains constant.
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The human ear is capable of hearing many of the sounds produced in nature, but certainly not all. Some low frequencies like a heartbeat of 1 or 2 Hz cannot be heard, just like sonar sounds produced by dolphins which are too high. Any frequency that is below the human range is known as infrasound. It is so low that it may be detected by a creature with big ears, such as an Elephant. In fact, recent research indicates that elephants also communicate with infrasound. Ultrasound, on the other hand, is above the range of the human ear. Bats, whales, porpoises, and dolphins use ultrasound for navigation. Most bats can detect frequencies as high as 100,000 Hz!
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Can some people have super hearing?
Hearing isn’t like other senses; if a light is too bright we can always close our eyes or turn away, but our hearing is always ‘on’, even when we are asleep, and super-sensitivity would be quite impairing. We would be surrounded by such a cacophony of sound we wouldn’t hear anything very well. Some people, however, are more sensitive to particular aspects of sound. We do have people we refer to as golden ears, people who have much better hearing than others, but they can be very sensitive to some aspects of sound but not necessarily to others. Golden ears may be able to hear very, very soft sounds, or sounds at high frequencies, or may be able to detect minute timing differences in how sounds arrive at each ear, but we don’t often see people who have above average ability on all those aspects of hearing. You can be good at some and not others. In fact, the closest we get to ‘super-hearing’ is at birth. That’s when the peripheral nervous system, the ear and the cochlea are in the best shape that they’re ever going to be in your whole life. However our ears only play part of the role in hearing, most of the really complex work is actually done by the brain. For this reason our basic hearing ability isn’t developed until sometime between the ages of 5 and 10 years when auditory brain areas become fully developed. Depending on our exposure to noise, hearing sensitivity can start to decline in our twenties. From thirty it can be a slippery slope down to hearing impairment. The softest sound we can hear corresponds to air vibration as small as one tenth the diameter of an atom. Our brain can automatically detect differences in sound on the order of 10 millionths of a second. We all possess this extraordinary sensitivity but the physiology mechanisms that give us this amazing ability are very fragile, so loud noise exposure, or certain types of brief loud sounds, like explosions, can irreversibly damage those inner hair cells of the ear. Once they’re damaged they don’t regenerate and that’s why you have general decay of hearing as you get older.
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Hearing loss:
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International symbol of deafness and hearing loss:
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Hearing loss, also known as hearing impairment, is a partial or total inability to hear. A deaf person has little to no hearing. Hearing loss may occur in one or both ears. In children hearing problems can affect the ability to learn language and in adults it can cause work related difficulties. In some people, particularly older people, hearing loss can result in loneliness. Hearing loss can be temporary or permanent.
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A person who is not able to hear as well as someone with normal hearing having hearing thresholds of 25 dB or more in one or both ears – is said to have hearing loss. Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear. Hearing loss may be mild, moderate, severe or profound. It can affect one ear or both ears, and leads to difficulty in hearing conversational speech or loud sounds. ‘Hard of hearing’ refers to people with hearing loss ranging from mild to severe. They usually communicate through spoken language and can benefit from hearing aids, cochlear implants and other assistive devices as well as captioning. People with more significant hearing losses may benefit from cochlear implants. ‘Deaf’ people mostly have profound hearing loss, which implies very little or no hearing. They often use sign language for communication.
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Hearing loss refers to a diminished ability to hear sounds like other people do, while deafness refers to the inability to understand speech through hearing even when sound is amplified. Profound deafness means the person cannot hear anything at all; they are unable to detect sound, even at the highest volume possible. In profound deafness, even the loudest sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, are heard. Use of the terms “hearing impaired,” “deaf-mute,” or “deaf and dumb” to describe deaf and hard of hearing people is discouraged by advocacy organizations as they are offensive to many deaf and hard of hearing people.
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Things to Know about Hearing Loss:
• Hearing loss is a major public health issue that is the third most common physical condition after arthritis and heart disease in elderly.
• Gradual hearing loss can affect people of all ages — varying from mild to profound. Hearing loss is a sudden or gradual decrease in how well you can hear. Depending on the cause, it can be mild or severe, temporary or permanent.
• Degrees of hearing loss: mild, moderate, severe, profound.
• Congenital hearing loss means you are born without hearing, while gradual hearing loss happens over time.
• Hearing loss is an invisible condition; we cannot see hearing loss, only its effects. Because the presence of a hearing loss is not visible, these effects may be attributed to aloofness, confusion, or personality changes.
• In adults, the most common causes of hearing loss are noise and aging. There is a strong relationship between age and reported hearing loss.
• In age-related hearing loss, known as presbycusis, changes in the inner ear that happen as you get older cause a slow but steady hearing loss. The loss may be mild or severe, and it is always permanent.
• In older people, a hearing loss is often confused with, or complicates, such conditions as dementia.
• Noise-induced hearing loss may happen slowly over time or suddenly. Being exposed to everyday noises, such as listening to very loud music, being in a noisy work environment, or using a lawn mower, can lead to hearing loss over many years.
• Sudden, noise-induced hearing loss from gunfire and explosions is the number one disability caused by combat in current wars.
• More often than not tinnitus (or ringing in the ears) will accompany the hearing loss and may be just as debilitating as the hearing loss itself.
• Other causes of hearing loss include earwax buildup, an object in the ear, injury to the ear or head, ear infection, a ruptured eardrum, and other conditions that affect the middle or inner ear.
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What is prelingual deafness?
Prelingual deafness refers to the inability to hear properly or at all before the patient learnt how to utter or understand speech. In such cases the individual was born with a congenital condition or lost their hearing very early in life, during infancy. People with prelingual deafness have never acquired speech with sound. In the majority of cases, people with prelingual deafness have hearing parents and siblings, and were born into families who did not know sign language. Consequently, they also tend to have slow language development. The very few who were born into signing families tend not to have delays in language development. If cochlear implants are placed in prelingual deaf children before they are four years old, they will usually acquire oral language successfully. Oral language and the ability to use social cues are very closely interrelated. That is why children with hearing loss, especially those with severe symptoms, may not only experience delayed language development, but their social development will take longer too. Consequently, prelingual deaf children can become socially isolated, unless they attend a school with other prelingual deaf children which has a well-run special needs department.
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Childhood hearing loss:
The interaction between a person and his or her surrounding environment is mediated through sensory experiences. The sense of hearing, in particular, fundamentally facilitates communication and fosters social interaction. Hearing is the key to learning spoken language and is important for the cognitive development of children. Population-based studies in Europe and North America have identified a consistent prevalence of approximately 0.1% of children having a hearing loss of more than 40 decibels (dB) through review of health or education records, or both. Other international studies using different methods or criteria (such as screenings, questionnaires, and less severe decibel thresholds) have reported much higher estimates. The prevalence of congenital and early-onset hearing loss in most developed countries is estimated to range between 2-4 infants with moderate-severe hearing loss in every 1000 births. In contrast, only limited information is available on developing regions, including the Middle East especially in the Arab countries, where the prevalence is estimated to be markedly higher than in Israel or European and North American countries. In developing countries, more than 10 infants in every 1000 births are estimated to be affected by a severe profound hearing loss. Of the 62 million deaf children younger than 15 years old worldwide, two-thirds reside in developing countries. Hearing is critical for the development of speech, language, communication skills, and learning. The earlier that hearing loss occurs in a child’s life, the more serious is the effect on the child’s development. Similarly, the earlier the hearing loss is identified and intervention begun, the more likely it is that the delays in speech and language development will be diminished. Recent research indicates that children identified with hearing loss who begin services before 6 months old develop language (spoken or signed) on a par with their hearing peers. Since hearing loss in infants is silent and hidden, great emphasis is placed on the importance of early detection, reliable diagnosis, and timely intervention. Even children who have mild or unilateral permanent hearing loss may experience difficulties with speech understanding, especially in a noisy environment, as well as problems with educational and psycho-social development. Children with hearing loss frequently experience speech-language deficits and exhibit lower academic achievement and poorer social-emotional development than their peers with normal hearing. The period from birth to 3-5 years is often considered as the “critical period” for the development of normal speech and language. Normal hearing in the first six months of life is also considered critical for normal speech and language skills. Hence, early identification and appropriate intervention within the first six months of life have been demonstrated to prevent or reduce many of the adverse consequences and to facilitate language acquisition. Consequently, in developed countries with a high standard of health care, primary services include the early detection of congenital hearing loss and the initiation of auditory rehabilitation before six months of age.
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What is post-lingual deafness?
Most people with some kind of hearing loss have post-lingual deafness. They had acquired spoken language before their hearing was diminished. Losing their sense of hearing may have been caused by a medication side-effect, trauma, infection, or a disease. In most cases, the person lost their hearing gradually; household members, friends and teachers may have noticed something was wrong before they themselves acknowledged the disability. Depending on the severity of hearing loss, the patient may have had to use hearing aids, had a cochlear implant inserted, or learnt how to lip-read. People who experience hearing loss face different challenges, depending on when it occurred and how long it took to develop. They have to become familiar with new equipment, perhaps undergo surgery, learn sign language and lip reading, and use various communication devices. A feeling of isolation is a common problem, which can sometimes lead to depression and loneliness; add to that the process of coming to terms with a disability. It is also a challenge for household members, loved ones and close friends, who have to adapt to the person’s hearing loss. Miscommunication can place a strain on relationships, a strain not only for the person with the hearing impairment, but also people around them. If the hearing loss is gradual and has not yet been diagnosed, family members may mistakenly believe that the patient is becoming more distant.
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Epidemiology and prevalence of hearing loss:
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Hearing loss (adult onset) per 100,000 people worldwide in 2004:
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Globally hearing loss affects about 10% of the population to some degree. Over 5% of the world’s population – 360 million people – has disabling hearing loss (328 million adults and 32 million children). Disabling hearing loss refers to hearing loss greater than 40 decibels (dB) in the better hearing ear in adults and a hearing loss greater than 30 dB in the better hearing ear in children. The majority of people with disabling hearing loss live in low- and middle-income countries. Approximately one-third of people over 65 years of age are affected by disabling hearing loss. The prevalence in this age group is greatest in South Asia, Asia Pacific and sub-Saharan Africa.
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The Global Burden of Disease Hearing Loss Expert Group has recently proposed a modified classification of hearing impairment. According to this classification, about 538 million people older than 5 years have disabling hearing impairment. Although this classification still employs the better-ear hearing threshold, in decibels, averaged over frequencies of 0.5, 1, 2 and 4 kHz, it changes the threshold for disabling hearing impairment to 35 dB for all age groups and equates “unilateral hearing impairment” with “bilateral mild hearing impairment”. It also recalibrates the hearing scale in equal steps of 15 dB in an attempt to reflect crucial shifts in hearing perception more accurately. This new classification is consistent with the International classification of functioning, disability and health and with the increasing evidence that difficulties in language development may arise in children with a hearing loss of less than 35 dB.
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According to the National Institute on Deafness and Other Communication Disorders (NIDCD), one in eight, or 30 million people in the United States 12 years or older has hearing loss in both ears. Roughly 25 million Americans has experienced tinnitus lasting at least five minutes in the past year, and fewer than 30 percent of adults ages 70 and older with hearing loss has ever used hearing aids. Hearing loss is the third most prevalent chronic condition in older Americans, after hypertension and arthritis; between 25% and 40% of the population aged 65 years or older is hearing impaired. The prevalence rises with age, ranging from 40% to 66% in patients older than 75 years and more than 80% in patients older than 85 years. Alternative definitions of hearing loss would raise estimates of prevalence even higher. In addition, the impact of hearing loss on society will increase not only because the population is aging, but also because the prevalence of age-adjusted hearing loss has increased significantly since the 1960s.
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Types and causes of hearing loss:
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Classification of hearing loss:
Hearing loss is categorized by type, severity, and configuration. Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). Hearing loss can be temporary or permanent, sudden onset or insidious.
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When describing hearing impairment, three attributes are considered:
1. Type of hearing loss (part of the hearing mechanism that is affected).
2. Degree/severity of hearing loss (range and volume of sounds that are not heard).
3. Configuration (range of pitches or frequencies at which the loss has occurred).
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Types of hearing loss:
A hearing loss can be classified as a conductive, sensorineural, mixed hearing loss, central deafness or auditory processing disorder, based on the anatomic location of the problem (site of lesion). Hearing loss can result from disorders of the auricle, external auditory canal, middle ear, inner ear, or central auditory pathways. In general, lesions in the auricle, external auditory canal, or middle ear that impede the transmission of sound from the external environment to the inner ear cause conductive hearing loss, whereas lesions that impair mechanotransduction in the inner ear or transmission of the electrical signal along the eighth nerve to the brain cause sensorineural hearing loss. A hearing loss may also be labelled as unilateral or bilateral, depending on whether the loss is in one (unilateral) or both (bilateral) ears. The degree and configuration of hearing loss might be the same in both ears (symmetrical hearing loss) or it could be different for each ear (asymmetrical hearing loss).
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What is unilateral and bilateral deafness?
Unilateral deafness refers to just one ear, while bilateral means a hearing impairment in both. People with unilateral hearing impairment may find it hard to carry on a conversation if the other person is on their “deaf” side. Pinpointing where a sound is coming from may be more difficult, compared to those who can hear well with both ears. Understanding what others are saying when there is a lot of noise about may be hard. When there is no background noise, or very little, a person with unilateral deafness has virtually the same aural communicative abilities as somebody with normal hearing in both ears. Babies born with unilateral deafness tend to have speech developmental delays. They may find it harder to concentrate when they go to school. Social activities may be more challenging than it is for children with no hearing problems.
In a nutshell:
People with unilateral hearing loss have difficulty in:
•hearing conversation on their impaired side
•localizing sound
•understanding speech in the presence of background noise.
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Conductive hearing loss:
Conductive hearing loss is characterized by an obstruction to air conduction that prevents the proper transmission of sound waves through the external auditory canal and/or the middle ear. It is marked by an almost equal loss of all frequencies. The auricle (pinna), external acoustic canal, tympanic membrane, or bones of the middle ear may be dysfunctional. Conductive hearing loss may be congenital or caused by trauma, severe otitis media, otosclerosis, neoplasms, or atresia of the ear canal. Some conductive hearing loss can be treated surgically with tympanoplasty or stapedectomy, and the use of hearing aids and assistive listening devices may also be beneficial.
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Sensorineural hearing loss:
Sensorineural hearing loss occurs when the sensory receptors of the inner ear are dysfunctional. Sensorineural deafness is a lack of sound perception caused by a defect in the cochlea and/or the auditory division of the vestibulocochlear nerve. This type of hearing loss is more common than conductive hearing loss and is typically irreversible. It tends to be unevenly distributed, with greater loss at higher frequencies. Sensorineural hearing loss may result from congenital malformation of the inner ear, intense noise, trauma, viral infections, ototoxic drugs (e.g., cisplatin, salicylates, loop diuretics), fractures of the temporal bone, meningitis, ménière’s disease, cochlear otosclerosis, aging (i.e., presbycusis), or genetic predisposition, either alone or in combination with environmental factors. Sensorineural hearing loss may also result from any neoplastic, vascular, demyelinating, infectious, or degenerative disease or trauma affecting the central auditory pathways. HIV leads to both peripheral and central auditory system pathology and is associated with sensorineural hearing impairment. Many patients with sensorineural hearing loss can be habilitated or rehabilitated with the use of hearing aids. Patients with profound bilateral sensorineural hearing loss (e.g., at least 90 dB) who derive no benefit from conventional hearing aids may be appropriate candidates for the cochlear implant device, which bypasses the damaged structures of the cochlea and stimulates the function of the auditory nerve. Auditory brainstem implants, which are similar to multichannel cochlear implants, are used in patients with neurofibromatosis type 2 following vestibular schwannoma removal, especially those individuals who have lost integrity of the auditory nerves.
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This is how you hear in sensorineural hearing loss:
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A table comparing sensorineural to conductive hearing loss
| Criteria | Sensorineural hearing loss | Conductive hearing loss |
| Anatomical site | Inner ear, cranial nerve VIII, or central processing centers | Middle ear (ossicular chain), tympanic membrane, or external ear |
| Weber test | Sound localizes to normal ear in unilateral SNHL | Sound localizes to affected ear (ear with conductive loss) in unilateral cases |
| Rinne test | Positive Rinne; air conduction > bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged). | Negative Rinne; bone conduction > air conduction (bone/air gap) |
Other, more complex, tests of auditory function are required to distinguish the different types of hearing loss. Bone conduction thresholds can differentiate sensorineural hearing loss from conductive hearing loss. Other tests, such as oto-acoustic emissions, acoustic stapedial reflexes, speech audiometry and evoked response audiometry are needed to distinguish sensory, neural and auditory processing hearing impairments.
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Sensorineural hearing loss is caused by lesions of either the inner ear (sensory) or the auditory (8th) nerve (neural). This distinction is important because sensory hearing loss is sometimes reversible and is seldom life threatening. A neural hearing loss is rarely recoverable and may be due to a potentially life-threatening brain tumor—commonly a cerebellopontine angle tumor.
Differences between Sensory and Neural Hearing Losses:
| Test | Sensory Hearing Loss | Neural Hearing Loss |
| Speech discrimination | Moderate decrement | Severe decrement |
| Discrimination with increasing sound intensity | Usually improves up to a point, depending on the severity and distribution of loss of sensory elements | Deteriorates |
| Recruitment | Present | Absent |
| Acoustic reflex decay | Absent or mild | Present |
| Waveforms in auditory brain stem responses | Well-formed, with normal latencies | Absent or with abnormally long latencies |
| Otoacoustic emissions | Absent | Present |
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Mixed hearing loss:
A finding of conductive and sensory hearing loss in combination is termed mixed hearing loss. Mixed hearing losses are due to pathology of both the middle and inner ear, as can occur in otosclerosis involving the ossicles and the cochlea, head trauma, chronic otitis media, cholesteatoma, middle ear tumors, and some inner ear malformations. Trauma resulting in temporal bone fractures may be associated with conductive, sensorineural, and mixed hearing loss.
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Central deafness:
Damage to the brain can lead to a central deafness. The peripheral ear and the auditory nerve may function well but the central connections are damaged by tumour, trauma or other disease and the patient is unable to hear. Primary diseases of the central nervous system can present with hearing impairment. Characteristically, a reduction in clarity of hearing and speech comprehension is much greater than the loss of the ability to hear pure tone. Auditory testing shows normal otoacoustic emissions (OAE) and an abnormal auditory brainstem response (ABR).
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Auditory processing disorder (APD):
Auditory processing disorder is not a hearing loss as such but a difficulty perceiving sound. This is not an actual hearing loss but gives rise to significant difficulties in hearing. One kind of auditory processing disorder is King-Kopetzky syndrome, which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests. APD is a deficit in neural processing of auditory stimuli that is not due to higher order language, cognitive, or related factors. However, APD may lead to or be associated with difficulties in higher order language, learning, and communication functions. This type of auditory problem affects more complex auditory processes, such as understanding speech when there is background noise. The results of hearing sensitivity and physiological tests, such as otoacoustic emissions (OAE) and auditory brainstem response (ABR) are normal in children with a auditory processing disorder.
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Severity/degree of hearing loss:
The level of severity of hearing loss is defined as follows:
| -10 to 15 dB HL | Normal Hearing |
| 16-25 dB HL | Slight Hearing Loss |
| 26-40 dB HL | Mild Hearing Loss |
| 41-55 dB HL | Moderate Hearing Loss |
| 56-70 dB HL | Moderate-Severe Hearing Loss |
| 71-90 dB HL | Severe Hearing Loss |
| >90 dB HL | Profound Hearing Loss |
(Average threshold level for 0.5, 1 and 2 kHz)
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Hearing loss of 100 dB is nearly equivalent to complete deafness for that particular frequency. A score of 0 dB is normal. It is possible to have scores less than 0, which indicates better-than-average hearing.
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Another classification of levels of deafness:
There are four levels of deafness (possibly 5 in some countries), they are:
•Mild deafness or mild hearing impairment – the patient can only detect sounds from between 25 to 29 decibels (dB). They may find it hard to understand everything other people are saying, especially if there is a lot of background noise.
•Moderate deafness or moderate hearing impairment – the patient can only detect sounds from between 40dB and 69dB. Following a conversation just from hearing is very difficult without using a hearing aid.
•Severe deafness – the person only hears sounds above 70db to 89dB. A severely deaf person must either lip-read or use sign language in order to communicate, even if they have a hearing aid.
•Profound deafness – anybody who cannot hear a sound below 90dB is profoundly deaf; some profoundly deaf people cannot hear anything at all, at any level of decibels. Communication is done with sign language and/or lip-reading. Obviously, if the hearing impaired deaf person can read and write, they may also communicate by reading and writing.
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Configuration of hearing loss:
The configuration, or shape, of the hearing loss refers to the pattern of hearing loss across frequencies (tones), as illustrated in a graph called an audiogram. For example, a hearing loss that only affects the high tones would be described as a high-frequency loss. Its configuration would show good hearing in the low tones and poor hearing in the high tones. On the other hand, if only the low frequencies are affected, the configuration would show poorer hearing for low tones and better hearing for high tones. Some hearing loss configurations are flat, indicating the same amount of hearing loss for low and high tones.
There are four general configurations of hearing loss:
1. Flat: thresholds essentially equal across test frequencies.
2. Sloping: lower (better) thresholds in low-frequency regions and higher (poorer) thresholds in high-frequency regions.
3. Rising: higher (poorer) thresholds in low-frequency regions and lower (better) thresholds in higher-frequency regions.
4. Trough-shaped (“cookie-bite” or “U” shaped): greatest hearing loss in the mid-frequency range, with lower (better) thresholds in low- and high-frequency regions.
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The shape of an audiogram shows the relative configuration of the hearing loss, such as a Carhart notch for otosclerosis, ‘noise’ notch for noise-induced damage, high frequency rolloff for presbycusis, or a flat audiogram for conductive hearing loss. In conjunction with speech audiometry, it may indicate central auditory processing disorder, or the presence of a schwannoma or other tumor.
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Causes of hearing loss:
The causes of hearing loss and deafness can be divided into congenital causes and acquired causes.
Congenital causes:
Congenital causes may lead to hearing loss being present at or acquired soon after birth. Hearing loss can be caused by hereditary and non-hereditary genetic factors or by certain complications during pregnancy and childbirth, including:
•maternal rubella, syphilis or certain other infections during pregnancy;
•low birth weight;
•birth asphyxia (a lack of oxygen at the time of birth);
•inappropriate use of particular drugs during pregnancy, such as aminoglycosides, cytotoxic drugs, antimalarial drugs and diuretics;
•severe jaundice in the neonatal period, which can damage the hearing nerve in a newborn infant.
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Acquired causes:
Acquired causes may lead to hearing loss at any age, such as:
•infectious diseases such as meningitis, measles and mumps;
•chronic ear infections;
•collection of fluid in the ear (otitis media);
•use of particular drugs, such as some antibiotic and antimalarial medicines;
•injury to the head or ear;
•excessive noise, including occupational noise such as that from machinery and explosions, and recreational noise such as that from personal audio devices, concerts, nightclubs, bars and sporting events;
•ageing, in particular due to degeneration of sensory cells;
•wax or foreign bodies blocking the ear canal.
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Causes of temporary deafness:
Some of the causes of temporary deafness include:
•Wax – the ear canal secretes cerumen, a waxy substance that helps to protect and lubricate the tissues. A build-up of wax can block the ear canal, leading to short-term conductive deafness.
•Foreign object – similarly to ear wax, a foreign object stuck inside the ear canal (such as the tip of a cotton bud) can temporarily cause hearing loss.
•Excess mucus – the common cold, a bout of flu, hay fever or other allergies can cause an excess of mucus that may block the Eustachian tubes of the ear.
•Ear infections – including otitis externa (infection of the outer ear) and otitis media (infection of the middle ear). Fluid and pus don’t allow the full conduction of sound.
•Drugs – certain drugs, including aminoglycosides and chloroquine, can cause temporary deafness in susceptible people.
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The most common causes of hearing loss are age and overexposure to loud noise.
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Presbycusis:
Presbycusis (also spelled presbyacusis, from Greek presbys “old” + akousis “hearing”), or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging (nosocusis and sociocusis) is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult. Presbycusis is the most common cause of hearing loss, afflicting one out of three persons by age 65, and one out of two by age 75. Presbycusis is the second most common illness next to arthritis in aged people. In the study published online in the journal JAMA Otolaryngology-Head & Neck Surgery, the researchers examined if the rate of age-related hearing loss is constant in the older old – 80 years and older. They found that Presbycusis, or age-related hearing loss (ARHL), affects approximately two-thirds of adults older than 70 years and four-fifths of adults older than 85. There is urgency to increase hearing aid use among the older population because untreated hearing loss is associated with higher risks for social isolation, depression, dementia, inability to work, reduced physical activity, and falls.
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In the early stages, it is characterized by symmetric, gentle to sharply sloping high-frequency hearing loss as seen in the figure above. With progression, the hearing loss involves all frequencies. More importantly, the hearing impairment is associated with significant loss in clarity. There is a loss of discrimination for phonemes, recruitment (abnormal growth of loudness), and particular difficulty in understanding speech in noisy environments such as at restaurants and social events. Hearing aids are helpful in enhancing the signal-to-noise ratio by amplifying sounds that are close to the listener. Although hearing aids are able to amplify sounds, they cannot restore the clarity of hearing. Thus, amplification with hearing aids may provide only limited rehabilitation once the word recognition score deteriorates below 50%. Cochlear implants are the treatment of choice when hearing aids prove inadequate, even when hearing loss is incomplete.
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Sensory presbyacusis is caused by loss of sensory elements in the basal (high-frequency) end of the cochlea with preservation of neurons. These patients have symmetrical, high-frequency sensorineural hearing loss. Pathology shows loss of hair cells. Neural presbyacusis is caused by loss of cochlear neurons. These patients have poorer discrimination than patients with sensory presbyacusis. Striatal presbyacusis is caused by loss of the stria vascularis with aging. Patients have a flat or slightly sloping hearing loss with good speech discrimination. Mixed presbyacusis is also possible. Cochlear conductive presbyacusis is caused by thickening of the basilar membrane caused by deposition of basophilic substance. This diagnosis is made on post-mortem. Because presbycusis occurs in some individuals as they age but not in others, genetic or environmental factors must also play a role in its development. Medical conditions that are common in the elderly, such as diabetes and stroke, may also increase the risk of hearing loss with aging
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Noise-induced hearing loss (NIHL):
Approximately 10% of the population worldwide suffer from hearing loss and about half of these cases can be attributed to auditory damage caused by exposure to intense noise. Hearing may deteriorate gradually from chronic and repeated noise exposure, such as loud music or background noise, or suddenly, from an acute, high intensity noise incident including gunshots and airhorns. In both types, loud sound over-stimulates delicate hearing cells, leading to the permanent injury or death of the cells. When the ear is exposed to excessive sound levels or loud sounds over time, the overstimulation of the hair cells leads to heavy production of reactive oxygen species, leading to oxidative cell death. Recent studies have investigated additional mechanisms of NIHL involving delayed or disabled electrochemical transmission of nerve impulses from the hair cell to and along the auditory nerve. Once lost, hearing cannot be restored in humans. Noise-induced hearing loss (NIHL) is defined as a hearing impairment resulting from exposure to high decibel sound that may exhibit as loss of a narrow range of frequencies, impaired cognitive perception of sound or other impairment, including hyperacusis or tinnitus. Long term exposure to sound levels over 85 dB can cause permanent hearing loss. Noise is defined as unwanted sound. Environmental noise consists of all the unwanted sounds in our communities except that which originates in the workplace. Environmental noise pollution, a form of air pollution, is a threat to health and well-being. It is more severe and widespread than ever before, and it will continue to increase in magnitude and severity because of population growth, urbanization, and the associated growth in the use of increasingly powerful, varied, and highly mobile sources of noise. It will also continue to grow because of sustained growth in highway, rail, and air traffic, which remain major sources of environmental noise. The potential health effects of noise pollution are numerous, pervasive, persistent, and medically and socially significant. Noise produces direct and cumulative adverse effects that impair health and that degrade residential, social, working, and learning environments with corresponding real (economic) and intangible (well-being) losses. It interferes with sleep, concentration, communication, and recreation. The aim of enlightened governmental controls should be to protect citizens from the adverse effects of airborne pollution, including those produced by noise. People have the right to choose the nature of their acoustical environment; it should not be imposed by others.
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WHO highlights serious threat posed by exposure to recreational noise. Some 1.1 billion teenagers and young adults are at risk of hearing loss due to the unsafe use of personal audio devices, including smartphones, and exposure to damaging levels of sound at noisy entertainment venues such as nightclubs, bars and sporting events. Hearing loss has potentially devastating consequences for physical and mental health, education and employment.
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Comparing loudness of common sounds:
What kind of decibel levels are you exposed to during a typical day?
To give you an idea, compare noises around you to these specific sounds and their corresponding decibel levels:
Sound levels of common noises:
| Decibels | Noise source |
| Safe range | |
| 30 | Whisper |
| 60 | Normal conversation |
| 78 | Washing machine |
| Risk range | |
| 80 to 90 | Heavy city traffic, power lawn mower |
| 90 | Motorcycle |
| 100 | Snowmobile, hand drill |
| 110 | Chain saw, rock concert |
| Injury range | |
| 120 | Ambulance siren |
| 140 (pain threshold) | Jet engine at take-off |
| 165 | 12-guage shotgun blast |
| 180 | Rocket launch |
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Maximum sound-exposure durations:
Below are the maximum noise levels on the job to which you may be exposed without hearing protection, and for how long.
| Sound level, decibels | Duration, daily |
| 90 | 8 hours |
| 92 | 6 hours |
| 95 | 4 hours |
| 97 | 3 hours |
| 100 | 2 hours |
| 102 | 1.5 hours |
| 105 | 1 hour |
| 110 | 30 minutes |
| 115 | 15 minutes or less |
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How many decibels are too loud?
A continuous noise level of 85 dB will result in hearing damage and either cause permanent or temporary hearing loss. This is the sound level of heavy road traffic. Compressed air hammers have a sound level of about 100 dB and rock concerts almost always reach 110-120 dB – the same sound intensity can easily be produced in headsets when you listen to your stereo. Not to mention the noise levels in many schools and kindergartens! Various governmental, industry and standards organizations set noise standards. The U.S. Environmental Protection Agency has identified the level of 70 dB (40% louder to twice as loud as normal conversation; typical level of TV, radio, stereo; city street noise) for 24‑hour exposure as the level necessary to protect the public from hearing loss and other disruptive effects from noise, such as sleep disturbance, stress-related problems, learning detriment, etc. Noise levels are typically in the 65 to 75 dB range for those living near airports of freeways and may result in hearing damage if sufficient time is spent outdoors.
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Common causes of NIHL:
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Noise exposure and intense sounds can cause two main types of hearing loss, namely temporary threshold shift and permanent threshold shift. Temporary threshold shift is mostly experienced as a temporary dullness in your hearing after exposure to loud noises. Your hearing will subsequently recover – depending on how loud the noises have been and how long you have been exposed to them. Permanent threshold shift is first experienced 48 hours after exposure to excessive noise. Permanent threshold shift can occur if you have been regularly exposed to excessive noise for long periods of time. It can also occur if you are exposed to very high sound levels for a short period of time. Exposure to noise and high sound levels can also result in Tinnitus – a constant sound in your ears or head.
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Audiometric testing is the only diagnostic evaluation relevant to diagnosis of noise-induced hearing loss (NIHL).
Noise-induced hearing loss (NIHL) typically manifests as elevated hearing thresholds (i.e. less sensitivity or muting) between 3000 and 6000 Hz, centered at 4000 Hz. As noise damage progresses, damage spreads to affect lower and higher frequencies. On an audiogram, the resulting configuration has a distinctive notch, called a ‘noise’ notch. As aging and other effects contribute to higher frequency loss (6–8 kHz on an audiogram), this notch may be obscured and entirely disappear.
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Prevention is the single defense against noise induced hearing loss. The best, first option for protecting hearing is lowering the volume of sound at its source. Secondly, limiting the time of exposure to loud noise can reduce injury. Finally, physical protection from the noise can reduce its impact. Government regulations are designed to limit occupational exposure to dangerously loud noise. The largest burden of NIHL, has been through occupational exposures; however, noise-induced hearing loss can also be due to unsafe recreational, residential, social, and military service-related noise exposures. It is estimated that 15% of young people are exposed to sufficient leisure noises (i.e. concerts, sporting events, daily activities, personal listening devices, etc.) to cause NIHL. There is not a limited list of noise sources that can cause hearing loss. Rather, it is important to understand that excessive decibel levels of any source over time can cause hearing loss.
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Hearing Aids in NIHL:
Hearing aids can be set to limit noise and thus can be set up so that they do not contribute to additional hearing loss. For someone whose life is affected by noise induced hearing loss, a hearing aid may be a very reasonable thing to consider.
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Prevention of hearing loss:
It is estimated that half of cases of hearing loss are preventable.
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Approach to patient with hearing loss:
Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiology technician. Otolaryngologists are trained in the medical and surgical management and treatment of patients with diseases and disorders of the ear, nose, throat (ENT), and related structures of the head and neck. They are commonly referred to as ENT surgeons.
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Hearing impairment in babies:
The following signs may indicate a hearing problem (but not always):
•Before the age of four months, the baby does not turn his/her head towards a noise
•By the age of 12 months, the baby still does not utter a single word
•The baby does not appear to be startled by a loud noise
•The baby responds to you when he/she can see you, but much less so (or not at all) when you are out of sight and call out their name
•The baby seems to be aware of some sounds only
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Hearing impairment in toddlers and children:
The following signs may indicate a hearing problem (but not always):
•The child is behind the others of his/her age in oral communication
•The child keeps saying “What?” or “Pardon?”
•The child talks in a very loud voice, and tends to produce louder-than-normal noises
•When the child speaks, his/her utterances are not clear
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Symptoms of hearing loss in adults:
The time to see a specialist is as soon as you start experiencing signs of hearing loss:
•You’re turning up the TV or radio volume louder than usual
•You have ringing in your ears
•You have trouble distinguishing conversations from background noise
•Your family and friends have to repeat themselves
•You have difficulty hearing on the telephone
•You notice a difference between the right and left ear
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Primary symptoms of presbycusis:
•sounds or speech becoming dull, muffled or attenuated
•need for increased volume on television, radio, music and other audio sources
•difficulty using the telephone
•loss of directionality of sound
•difficulty understanding speech, especially women and children
•difficulty in speech discrimination against background noise (cocktail party effect)
Secondary symptoms:
•hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, resulting from “recruitment”
•tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present
•vertigo and disequilibrium
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Evaluation of a patient with auditory complaints is to determine (1) the nature of the hearing impairment (conductive vs. sensorineural vs. mixed), (2) the severity of the impairment (mild, moderate, severe, or profound), (3) the anatomy of the impairment (external ear, middle ear, inner ear, or central auditory pathway), and (4) the etiology. The history should elicit characteristics of the hearing loss, including the duration of deafness, unilateral versus bilateral involvement, nature of onset (sudden vs. insidious), and rate of progression (rapid vs. slow). Symptoms of tinnitus, vertigo, imbalance, aural fullness, otorrhea, headache, facial nerve dysfunction, and head and neck paresthesias should be noted. Information regarding head trauma, exposure to ototoxins, occupational or recreational noise exposure, and family history of hearing impairment may also be important. A sudden onset of unilateral hearing loss, with or without tinnitus, may represent a viral infection of the inner ear, vestibular schwannoma, or a stroke. Patients with unilateral hearing loss (sensory or conductive) usually complain of reduced hearing, poor sound localization, and difficulty hearing clearly with background noise. Gradual progression of a hearing deficit is common with otosclerosis, noise-induced hearing loss, vestibular schwannoma, or Ménière’s disease. Small vestibular schwannomas typically present with asymmetric hearing impairment, tinnitus, and imbalance (rarely vertigo); cranial neuropathy, in particular of the trigeminal or facial nerve, may accompany larger tumors. In addition to hearing loss, Ménière’s disease may be associated with episodic vertigo, tinnitus, and aural fullness. Hearing loss with otorrhea is most likely due to chronic otitis media or cholesteatoma.
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Examination should include the auricle, external ear canal, and tympanic membrane. The external ear canal of the elderly is often dry and fragile; it is preferable to clean cerumen with wall-mounted suction or cerumen loops and to avoid irrigation. In examining the eardrum, the topography of the tympanic membrane is more important than the presence or absence of the light reflex. In addition to the pars tensa (the lower two-thirds of the tympanic membrane), the pars flaccida (upper one-third of the tympanic membrane) above the short process of the malleus should also be examined for retraction pockets that may be evidence of chronic Eustachian tube dysfunction or cholesteatoma. Insufflation of the ear canal is necessary to assess tympanic membrane mobility and compliance. Careful inspection of the nose, nasopharynx, and upper respiratory tract is indicated. Unilateral serous effusion should prompt a fiberoptic examination of the nasopharynx to exclude neoplasms. Cranial nerves should be evaluated with special attention to facial and trigeminal nerves, which are commonly affected with tumors involving the cerebellopontine angle.
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Tuning-fork tests:
The Rinne and Weber tuning fork tests, with a 512-Hz tuning fork, are used to screen for hearing loss, differentiate conductive from sensorineural hearing losses, and confirm the findings of audiologic evaluation. The Rinne test compares the ability to hear by air conduction with the ability to hear by bone conduction. The tines of a vibrating tuning fork are held near the opening of the external auditory canal, and then the stem is placed on the mastoid process; for direct contact, it may be placed on teeth or dentures. The patient is asked to indicate whether the tone is louder by air conduction or bone conduction. Normally, and in the presence of sensorineural hearing loss, a tone is heard louder by air conduction than by bone conduction; however, with conductive hearing loss of ≥30 dB, the bone-conduction stimulus is perceived as louder than the air-conduction stimulus. For the Weber test, the stem of a vibrating tuning fork is placed on the head in the midline and the patient is asked whether the tone is heard in both ears or better in one ear than in the other. With a unilateral conductive hearing loss, the tone is perceived in the affected ear. With a unilateral sensorineural hearing loss, the tone is perceived in the unaffected ear. A 5-dB difference in hearing between the two ears is required for lateralization.
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Hearing loss differs from vision loss:
As with the eye, the ear’s performance is affected by ageing. However, bad vision gradually makes reading harder as the letters get smaller, but hearing loss is different. Hearing loss can make certain syllables and sounds harder to hear. For example, high-pitched consonants like f, s and t are easily drowned out by louder, low-pitched vowels like a, o and u. This results in a person with hearing loss complaining that they can hear others are talking, but not what they are saying.
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The figure below compares visual and hearing impairment:
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Hearing Testing and Screening in Young Children:
Rationale for screening:
•Hearing loss is not confined to those with risk factors – approximately 40% of all children ultimately identified with sensorineural hearing loss do not have an established risk factor; therefore, universal screening is recommended.
•Hearing screening allows hearing loss to be identified at a younger age. There is evidence that this is beneficial because early detection and management improve outcomes in terms of speech, language and education.
•The critical age for commencing intervention may be as early as 6 months.
•Parents may quickly recognise a baby as having severe or profound hearing loss, but moderate hearing loss or high-frequency hearing loss may go unnoticed for several years unless formally tested.
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Neonatal hearing screening tests:
1. Otoacoustic emissions (OAE):
OAE are low-level sounds produced by the sensory hair cells of the cochlea (primarily the outer hair cells of the inner ear) as part of the normal hearing process. Hair cells that are normally functioning emit acoustic energy, which can be recorded by placing a small probe (containing a microphone) attached to a soft ear tip in the external ear canal opening. The earphone delivers test signals into the ear canal that evoke an acoustic response from the hair cells, and the responses are recorded by a second microphone in the probe. These responses are called evoked otoacoustic emissions. OAE screeners display the results of the test as either pass or refer, requiring no test interpretation by staff. The test takes a few minutes.
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2. Automated auditory brainstem responses (AABR) test:
The stimulus (either clicks or tones) is presented using earphones or an ear canal probe, and the electrophysiological response from the brainstem is detected by scalp electrodes. Automated devices allow screening to be performed by non-specialists. This test takes 15 minutes. The loudness of the clicks is set to a particular level. If this does not produce a response, further diagnostic testing will be required. The AABR test measures not only the integrity of the inner ear, but also the auditory pathway. It can therefore detect the rare condition of auditory neuropathy in children who are deaf but have normal otoacoustic emissions (because the cochlea is normal).
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Both OAE and AABR testing are best done when the child is asleep, as the response to be detected is very small and can be hidden if there is a lot of movement. Older babies and young children can be taught to respond to sounds through play. These tests, known as visual response audiometry and play audiometry, can better determine the child’s range of hearing.
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The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:
•When they enter school
•At ages 6, 8, and 10
•At least once during middle school
•At least once during high school
There is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptoms.
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Hearing tests for adults:
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Screening tests:
Routine screening may be helpful because it is difficult to diagnose hearing loss in the primary care setting. The onset of presbycusis is insidious and patients themselves are frequently unaware of their hearing loss. Physicians may overlook presbycusis in a quiet examination room, since the symptoms of early presbycusis are more apparent in settings with background noise. In addition, the diagnosis of hearing loss must be confirmed with formal audiometric testing, which is the diagnostic criterion standard.
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Many simple tests for hearing loss have been used as a routine part of the physical examination, but they are difficult to implement in systematic screening programs because they cannot be standardized. For example, the Whispered Voice Test is performed by examiners who whisper words from behind the patient at varying distances. The degree of hearing loss is reflected by the furthest distance from which patients may still reliably reproduce what is whispered. Attempts to standardize the test have been made (e.g., by whispering only after full expiration), but there is no reliable way to control the loudness of the whispers, and robust descriptions of interobserver variability and test-retest reliability are lacking. Screening with a vibrating tuning fork or the sounds of an examiner’s fingers rubbing also has been proposed. Judgments about hearing loss generally rely on measuring the threshold distance beyond which the sounds cannot be heard. Alternatively, the hearing thresholds of the patient and the examiner can be compared by placing the vibrating tuning fork on each person’s mastoid process (Schwabach test). Again, although reasonable test accuracy has been reported in small series, the intrinsically subjective nature of these tests is a serious limitation.
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Audioscope:
The physiologic test uses an audioscope, a hand-held, combination of otoscope and audiometer that delivers a 25- to 40-dB pure tone at 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz, the most commonly tested frequencies needed to hear speech. The audioscope is held directly in the external auditory (ear) canal with a probe tip sealing the canal. Tones are presented at each frequency, and the listener is asked to indicate whether he or she can hear the tone. Minimal training is required. Patients unable to hear a predetermined series of tones may then be referred for formal evaluation. In addition to screening for hearing loss, the audioscope also allows for direct inspection of the ear canal to assess external ear abnormalities, such as cerumen, otitis, and foreign bodies.
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Laboratory assessment of hearing:
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Audiologic Assessment:
The minimum audiologic assessment for hearing loss should include the measurement of pure tone air-conduction and bone-conduction thresholds, speech reception threshold, word recognition score, tympanometry, acoustic reflexes, and acoustic reflex decay. This test battery provides a screening evaluation of the entire auditory system and allows one to determine whether further differentiation of a sensory (cochlear) from a neural (retrocochlear) hearing loss is indicated. Pure tone audiometry assesses hearing acuity for pure tones. The test is administered by an audiologist and is performed in a sound attenuated chamber. The pure tone stimulus is delivered with an audiometer, an electronic device that allows the presentation of specific frequencies (generally between 250 and 8000 Hz) at specific intensities. The intensity range is usually 100 decibels in steps of 5 decibels. The “zero dB” level represents normal hearing for young adults under favourable, noise-free laboratory conditions. Air- and bone-conduction thresholds are established for each ear. Air-conduction thresholds are determined by presenting the stimulus in air with the use of headphones. Bone-conduction thresholds are determined by placing the stem of a vibrating tuning fork or an oscillator of an audiometer in contact with the head. In the presence of a hearing loss, broad-spectrum noise is presented to the nontest ear for masking purposes so that responses are based on perception from the ear under test. The responses are measured in decibels. An audiogram is a plot of intensity in decibels of hearing threshold versus frequency. In “conventional” audiometry, the child (5+ yrs.) presses a button or raises a hand each time he or she hears a sound. For younger children, examiners introduce reward [e.g. visual reinforcement audiometry (VRA): 7-30 months.] and/or play [e.g. conditioned play audiometry (CPA): 30 months. – 5 yrs.] “incentives” into testing. As the child responds to the presented tones and thresholds are determined and marked across the audiogram, the graph fills in to present a picture of the child’s hearing ability.
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In pure-tone audiometry (PTA) each ear is tested separately, while the other is shielded against sound. The person being tested wears an earphone or sits in front of a loudspeaker in a quiet test chamber, with instructions to give a hand signal whenever a brief tone is sounded. The audiologist proceeds to determine the lowest intensity for each frequency at which the person reports being just able to hear the tone 50 percent of the time. For example, one who hears the tone of 4,000 hertz only half the time at the 40-decibel setting has a 40-decibel hearing level for that frequency—i.e., a threshold 40 decibels above the normal threshold. A graph showing the hearing level for each ear by octaves and half octaves across the frequency range of 125 to 8,000 hertz is called an audiogram. The shape of the audiogram for an individual who is hard-of-hearing can provide the otologist or audiologist with important information for determining the nature and cause of the hearing defect. (The audiologist is primarily concerned with measuring the degree of hearing impairment; the otologist diagnoses and treats defects and diseases of the ear by medical or surgical means.)
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Various terms used in audiometry:
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Cross hearing and interaural attenuation:
When sound is applied to one ear the contralateral cochlea can also be stimulated to varying degrees, via vibrations through the bone of the skull. When the stimuli presented to the test ear stimulates the cochlea of the non-test ear, this is known as cross hearing. Whenever it is suspected that cross hearing has occurred it is best to use masking. This is done by temporarily elevating the threshold of the non-test ear, by presenting a masking noise at a predetermined level. This prevents the non-test ear from detecting the test signal presented to the test ear. The threshold of the test ear is measured at the same time as presenting the masking noise to the non-test ear. Thus, thresholds obtained when masking has been applied, provide an accurate representation of the true hearing threshold level of the test ear. A reduction or loss of energy occurs with cross hearing, which is referred to as interaural attenuation (IA) or transcranial transmission loss.
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The audiometry implications:
• When air conduction tests show a hearing loss, but there is no loss identified with bone conduction tests, there may be a conductive loss.
• When both air and bone conduction results show hearing loss at the same level, the loss is considered sensorineural.
• If different degrees of hearing loss are found via air and bone conduction testing, the loss is mixed.
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Pure tone audiometry establishes the presence and severity of hearing impairment, unilateral versus bilateral involvement, and the type of hearing loss. Conductive hearing losses with a large mass component, as is often seen in middle ear effusions, produce elevation of thresholds that predominate in the higher frequencies. Conductive hearing losses with a large stiffness component, as in fixation of the footplate of the stapes in early otosclerosis, produce threshold elevations in the lower frequencies. Often, the conductive hearing loss involves all frequencies, suggesting involvement of both stiffness and mass. In general, sensorineural hearing losses such as presbycusis affect higher frequencies more than lower frequencies. An exception is Ménière’s disease, which is characteristically associated with low-frequency sensorineural hearing loss. Noise-induced hearing loss has an unusual pattern of hearing impairment in which the loss at 4000 Hz is greater than at higher frequencies. Vestibular schwannomas characteristically affect the higher frequencies, but any pattern of hearing loss can be observed. Presbycusis usually manifests as a bilateral and symmetric sensorineural hearing loss. Usually, the higher frequencies are most severely affected. Otosclerosis results in an audiogram with significant loss at all frequencies, often of around 40 dB (HL). A deficiency particularly around 2 kHz (termed a Carhart notch in the audiogram) is characteristic of either otosclerosis or a congenital ossicular anomaly.
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Speech audiometry:
Speech recognition requires greater synchronous neural firing than is necessary for appreciation of pure tones. Speech audiometry tests the clarity with which one hears. The speech reception threshold (SRT) is defined as the intensity at which speech is recognized as a meaningful symbol and is obtained by presenting two-syllable words with an equal accent on each syllable. The intensity at which the patient can repeat 50% of the words correctly is the SRT. Once the SRT is determined, discrimination or word recognition ability is tested by presenting one-syllable words at 25–40 dB above the SRT. The words are phonetically balanced in that the phonemes (speech sounds) occur in the list of words at the same frequency that they occur in ordinary conversational English. An individual with normal hearing or conductive hearing loss can repeat 88–100% of the phonetically balanced words correctly. Patients with a sensorineural hearing loss have variable loss of discrimination. As a general rule, neural lesions produce greater deficits in discrimination than do cochlear lesions. For example, in a patient with mild asymmetric sensorineural hearing loss, a clue to the diagnosis of vestibular schwannoma is the presence of greater than expected deterioration in discrimination ability. Deterioration in discrimination ability at higher intensities above the SRT also suggests a lesion in the eighth nerve or central auditory pathways.
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Evoked Responses:
Electrocochleography measures the earliest evoked potentials generated in the cochlea and the auditory nerve. Receptor potentials recorded include the cochlear microphonic, generated by the outer hair cells of the organ of Corti, and the summating potential, generated by the inner hair cells in response to sound. The whole nerve action potential representing the composite firing of the first-order neurons can also be recorded during electrocochleography. Clinically, the test is useful in the diagnosis of Ménière’s disease, where an elevation of the ratio of summating potential to action potential is seen. Brainstem auditory evoked responses (BAERs), also known as auditory brainstem responses (ABRs), are useful in differentiating the site of sensorineural hearing loss. In response to sound, five distinct electrical potentials arising from different stations along the peripheral and central auditory pathway can be identified using computer averaging from scalp surface electrodes. BAERs are valuable in situations in which patients cannot or will not give reliable voluntary thresholds. They are also used to assess the integrity of the auditory nerve and brainstem in various clinical situations, including intraoperative monitoring, and in determination of brain death. Bone-conduction auditory brainstem response or BCABR is a type of auditory evoked response that records neural response from EEG with stimulus transmitted through bone conduction. Bone-conduction auditory brainstem response (BCABR) are similar to air conduction auditory brainstem responses, with the main difference being that the signal is transmitted via bone-conduction instead of air. The goal of bone ABR is to estimate cochlear function and to help identify the type of hearing loss present. Responses to air and bone-conduction ABRs are compared (for the same intensity and stimuli). The vestibular-evoked myogenic potential (VEMP) test elicits a vestibulocolic reflex whose afferent limb arises from acoustically sensitive cells in the saccule, with signals conducted via the inferior vestibular nerve. VEMP is a biphasic, short-latency response recorded from the tonically contracted sternocleidomastoid muscle in response to loud auditory clicks or tones. VEMPs may be diminished or absent in patients with early and late Ménière’s disease, vestibular neuritis, benign paroxysmal positional vertigo, and vestibular schwannoma. On the other hand, the threshold for VEMPs may be lower in cases of superior canal dehiscence, other inner ear dehiscence, and perilymphatic fistula.
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Imaging Studies:
The choice of radiologic tests is largely determined by whether the goal is to evaluate the bony anatomy of the external, middle, and inner ear or to image the auditory nerve and brain. Axial and coronal CT of the temporal bone with fine 0.3- to 0.6-mm cuts is ideal for determining the caliber of the external auditory canal, integrity of the ossicular chain, and presence of middle ear or mastoid disease; it can also detect inner ear malformations. CT is also ideal for the detection of bone erosion with chronic otitis media and cholesteatoma. MRI is superior to CT for imaging of auditory nerve, retrocochlear pathology such as vestibular schwannoma, meningioma, other lesions of the cerebellopontine angle, demyelinating lesions of the brainstem, and brain tumors. Both CT and MRI are equally capable of identifying inner ear malformations and assessing cochlear patency for preoperative evaluation of patients for cochlear implantation.
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Treatment of hearing loss:
An otolaryngologist is a doctor who specializes in diagnosing and treating diseases of the ear, nose, and throat. An otolaryngologist will try to find out why you’re having trouble hearing and offer treatment options. He or she may also refer you to another hearing professional, an audiologist. An audiologist has specialized training in identifying and measuring the type and degree of hearing loss and recommending treatment options. Audiologists also may be licensed to fit hearing aids. Another source of hearing aids is a hearing aid specialist, who is licensed by a state to conduct and evaluate basic hearing tests, offer counselling, and fit and test hearing aids. Treatment depends on the specific cause if known as well as the extent, type and configuration of the hearing loss. Most hearing loss, that resulting from age and noise, is progressive and irreversible, and there are currently no approved or recommended treatments; management is by hearing aid. A few specific kinds of hearing loss are amenable to surgical treatment. In other cases, treatment is addressed to underlying pathologies, but any hearing loss incurred may be permanent.
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Treatment of hearing loss in primary care clinic:
Cerumen Impaction:
Several otologic abnormalities can be identified and treated by the primary care physician. Cerumen impaction may result in substantial hearing loss and can be found in up to 30% of elderly patients with hearing loss. If physical inspection of the external auditory canal reveals cerumen impaction, the cerumen may be removed by several techniques. A small cerumen curette, if available, may be used to remove the cerumen if the practitioner is comfortable and familiar with this technique. Alternatively, gentle warm water irrigation may be used to loosen and remove the cerumen if the patient has no history of tympanic membrane perforation or ear surgery. Hydrogen peroxide–containing solutions can be prescribed to loosen firm cerumen impactions if the patient has no history of tympanic membrane perforation or ear surgery. Deep cerumen impactions may be resistant to these manoeuvres and the patient can be referred to an otolaryngologist for safe removal of the cerumen under microscopic examination.
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Chronic Otitis Media:
Chronic otitis media with effusion is a common problem in older adults. This condition, also known as serous otitis since the middle ear becomes filled with a serous fluid, may result in discomfort and a conductive hearing loss. I am unable to identify any randomized, placebo-controlled trials that documented the efficacy of antibiotic therapy or other treatments in older adults with this condition. In children, systematic reviews of randomized placebo-controlled trials suggest that antibiotics and oral steroids both shorten the course of disease, but that decongestants and antihistamines had no significant effect on effusion clearance. Serous otitis may persist for weeks or months, and such patients should be referred to an otolaryngologist either for more aggressive treatment (e.g., surgical aspiration of fluid) or to rule out an underlying disorder with resultant obstruction of the Eustachian tube (e.g., nasopharyngeal carcinoma).
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Treatment of hearing loss by hearing specialist:
Referrals for hearing loss are best directed to audiologists, otolaryngologists, or both. Audiologists have expertise in hearing testing, use of assistive listening devices (e.g., telephone amplifiers, infrared systems, pocket talkers, and visual/tactile alerts for the doorbell, telephone, and smoke alarm), and the selection and fitting of hearing aids. Otolaryngologists have specialty training in a range of disorders in the head and neck, which include the medical and surgical treatment of otologic problems. The first step in the clinical workup of hearing loss is formal audiometric testing by an audiologist. The audiometric tests are performed in a sound-protected environment. These tests include a standard test battery consisting of pure-tone audiometry that assesses the patient’s threshold of hearing for tones from low frequency (250 Hz) to high frequency (8 kHz); word recognition tests that measure the percentage of monosyllabic words that a patient can repeat (discrimination scores); the speech reception threshold that measures the lowest intensity level at which a patient can repeat 50% of spondaic words (i.e., 2-syllable words with equal emphasis on each syllable, such as baseball, cowboy, and pancake); and bone-conduction testing, acoustic reflexes, and tympanometry, which primarily target the presence or absence of specific disorders, such as otosclerosis, acoustic neuromas, or otitis media.
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Otolaryngology Treatments:
In general, conductive hearing losses are amenable to surgical correction, whereas sensorineural hearing losses are usually managed medically. Atresia of the ear canal can be surgically repaired, often with significant improvement in hearing. Tympanic membrane perforations due to chronic otitis media or trauma can be repaired with an outpatient tympanoplasty. Likewise, conductive hearing loss associated with otosclerosis can be treated by stapedectomy, which is successful in >95% of cases. Tympanostomy tubes allow the prompt return of normal hearing in individuals with middle ear effusions. For persistent chronic otitis media with effusions, the use of myringotomy (incision in the tympanic membrane) and pressure-equalization tubes are routinely used to aspirate the contents and aerate the middle ear cleft, which immediately restores hearing. It also is important for the otolaryngologist to examine the patient’s nasopharynx to rule out both benign (e.g., allergic disease) and malignant (e.g., nasopharyngeal carcinoma) underlying conditions that might obstruct the eustachian tube and predispose the patient to otitis media. Small tympanic membrane perforations from recent traumatic events or otitis media frequently heal spontaneously. However, large persisting perforations may cause substantial conductive hearing loss and predispose patients to recurrent otitis. Surgical repair of the perforation with fascial grafts (tympanoplasty) has an extremely high success rate. Ossicular chain discontinuities also may result from trauma or long-standing ear infections and are readily treated with ossicular chain reconstructions using transposed ossicles or surgical implants.
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Otosclerosis/Stapes Surgery:
Otosclerosis is usually inherited in an autosomal dominant pattern with variable penetrance. This means that you have a 50% chance of getting the gene for otosclerosis if one parent has it, but that not everyone with the gene develops symptoms. Otosclerosis occurs when there is an excess growth of bone around the connections of the ossicles and particularly at the site where the stapes meets the inner ear. Any of the ossicles can be involved by otosclerosis, but the stapes is most commonly involved. In order to restore the mobility of the ossicles a stapedectomy or stapedotomy is performed. In these procedures the stapes, the last of the three bones in the middle ear, is partially or completely replaced by prosthesis. This allows for transmission of the sound waves to the inner ear and can dramatically improve hearing. Cochlear implantation has been performed as initial treatment and following stapedectomy with good results.
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Hearing aids [vide infra]:
Hearing aids are devices that work to improve the hearing and speech comprehension of those with hearing loss. It works by amplifying the sound vibrations in the ear so that one can understand what is being said around them. The use of this technological device may or may not have an effect on one’s sociability. Some people feel as if they cannot live without one because they say it is the only thing that keeps them engaged with the public. Others dislike hearing aids very much because they feel wearing them is embarrassing or weird. Due to their low-esteem, they avoid hearing aid usage altogether and would rather remain quiet and to themselves in a social environment.
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Profound sensorineural hearing loss (defined as >80 dB of loss in the better ear), or true deafness, is increasingly amenable to treatment with cochlear implantation. Rapid technological advances in implant technology in the past 2 decades have led to successful rehabilitation of these patients who previously had no reasonable alternative forms of treatment. Much of the literature has focused on the effectiveness of treatment in the pediatric population, but recent findings from systematic reviews and prospective cohorts suggest that cochlear implantation results in such substantial improvements in quality of life, and patient preference states that implantation is cost-effective in the adult patient as well.
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Sudden Sensorineural Hearing Loss:
Early intervention by the astute primary care physician may halt or reverse two forms of sensorineural hearing loss: unilateral sudden sensorineural hearing loss (or sudden deafness) and hearing loss caused by ototoxicity. The etiology of sudden sensorineural hearing loss is not yet clear. A variety of mechanisms ranging from viral infections to microcirculatory injuries to immune-mediated disorders have been proposed, although expert opinion is that viral infection may be the most important contributor. However, 2 recent randomized trials failed to show benefit from antiviral agents. To date, the only treatment to show efficacy in placebo-controlled trials has been glucocorticoid administration. In an earlier randomized trial, nearly twice as many patients (61% vs. 32%) receiving glucocorticoids experienced at least partial recovery of hearing as those receiving placebo. In a randomized controlled study, intratympanic injection of dexamethasone is shown to effectively improve hearing in patients with severe or profound SSNHL after treatment failure with standard therapy and is not associated with major side effects. A study by Narozny (2004) concluded that hyperbaric oxygen therapy (consisting of exposure to 100% oxygen at a pressure of 250 kPa for a total of 60 minutes) in a multi-place hyperbaric chamber with high doses of glucocorticoids improves the results of conventional sudden sensorineural hearing loss treatment; the best results are achieved if the treatment is started as early as possible. To document the hearing loss, and to rule out masquerading retrocochlear processes such as acoustic neuromas, these patients should be referred urgently for specialty care.
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Ototoxicity:
The ototoxic effects of antibiotics and antineoplastic agents are well documented. The aminoglycosides and platinum compounds are particularly ototoxic, but a variety of other agents have been implicated as well in case reports. When known ototoxic agents need to be administered, ultra high-frequency audiometry is available for early detection of ototoxicity in adult populations, but currently no guidelines are available on the use of ultra-high-frequency audiometry. Because high-frequency hearing loss usually precedes loss in the normal range, early detection of such loss may lead to modifications in treatment that prevent clinically important hearing loss. A frequently overlooked ototoxic agent is aspirin. Little is known about what level of dosage causes ototoxicity, but it is generally believed that 80 mg of aspirin on a daily basis is safe. Fortunately, in most cases, the resulting tinnitus and hearing loss are temporary and reversible with cessation of aspirin.
Partial Listing of Ototoxic Medications:
Antibiotics: aminoglycosides, erythromycin, and vancomycin
Antineoplastics: cisplatin, carboplatin, and vincristine sulfate
Loop diuretics: furosemide, ethacrynic acid
Anti-inflammatory: aspirin and quinine
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Stem cell transplant and gene therapy:
While hearing aids and cochlear implants can provide good recovery of hearing function, the development of a biological method to repair the damaged cochlea has the potential to restore normal hearing without any type of prosthesis. One approach to restore hearing might be to surgically place stem cells within the cochlea in such a way that they would fuse with the remaining cochlear structures and develop and function as hair cells. Scientists believe this is a viable approach because, unlike most organs that are destroyed by disease, the inner ear remains structurally intact—only the hair cells are lost. By mimicking the steps involved in the formation of embryonic mouse ears, Stanford scientists have produced stem cells in the laboratory that look and act very much like hair cells, the sensory cells that normally reside in the inner ear. If they can generate hair cells in the millions, it could lead to significant scientific and clinical advances along the path to curing deafness in the future. A promising source of creating hair cells comes from induced pluripotent stem cells (iPS)—adult cells, taken for example from a patient’s own skin that have been genetically reprogrammed to revert back to stem cells. This breakthrough process represents a major opportunity to eventually treat a patient with his or her own cells. Recent research, reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils, using stem cells. Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement. About 10 years ago a gene called Atoh1 was discovered which acts as a “switch” to turn on hair cell growth. In mammals the Atoh1 switch is turned off following birth but in birds and amphibians it remains on into adulthood. That is why birds and other non-mammals are able to readily regenerate inner ear damage and age-related hearing loss does not occur in birds. It was discovered that when Atoh1 is artificially switched on in the cells that support hair cells (called “supporting cells”) it instructs them to divide and form new hair cells. This led researchers to investigate whether Atoh1 could be used as a gene therapy to treat certain types of profound hearing loss. A 2008 study has shown that gene therapy targeting Atoh1 can cause hair cell growth and attract neuronal processes in embryonic mice. Some hope that a similar treatment will one day ameliorate hearing loss in humans.
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Assistive Listening Devices (ALD):
ALD’s are electronic devices, other than hearing aids, that help you hear better in tough listening situations. Some ALD’s help you hear more clearly while others alert you to something that requires your attention. Amplification Systems help you hear more clearly. Examples include the headsets worn in movie theaters and houses of worship, and amplified telephones. Alert (Notification) Systems notify you when some event occurs such as the ringing of the doorbell or phone. If you need just a little help with hearing, there are a number of low-cost listening devices to aid you. They include apps that let you amplify sound with your smart phone and earbuds, and portable wireless devices that let you listen to your TV and other audio devices with earphones. You can also find amplified, flashing, or vibrating versions of basic household items such as telephones, alarm clocks, and doorbells. Some ALDs are part of hearing assistive technology systems (HATS) and discussed later on.
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Lip reading and sign language:
Hearing loss can sometimes affect your speech, as well as your ability to understand other people. Many people with significant hearing loss learn to communicate in other ways instead of, or as well as, spoken English. For people who experience hearing loss after they’ve learnt to talk, lip-reading can be a very useful skill. Lip-reading is where you watch a person’s mouth movements while they’re speaking, to understand what they’re saying. For people born with a hearing impairment, lip-reading is much more difficult. Those who are born with a hearing impairment often learn sign language, such as British Sign Language (BSL), which is a form of communication that uses hand movements and facial expressions to convey meaning. BSL is completely different from spoken English and has its own grammar and syntax (word order).
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Introduction to hearing aid:
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The first hearing aids were ear trumpets, and were created in the 17th century. Some of the first hearing aids were external hearing aids. External hearing aids directed sounds in front of the ear and blocked all other noises. The apparatus would fit behind or in the ear. The movement toward modern hearing aids began with the creation of the telephone, and the first electric hearing aid was created in 1898. By the late 20th century, digital hearing aids were commercially available. The invention of the carbon microphone, transmitters, digital signal processing chip or DSP, and the development of computer technology helped transform the hearing aid to its present form.
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Hearing aid is an electronic device usually worn in or behind the ear of a hearing-impaired person for amplifying sound to help hear better. A hearing aid essentially amplifies sound. By making it louder it can increase transmission of sound in conductive hearing loss or stimulate the remaining tiny hairs within the inner ear in sensorineural hearing loss. The electronic hearing aid, or more correctly the electroacoustic hearing aid, detects sound in the environment, amplifies it and then delivers into the ear canal. These electronic aids should not be confused with surgically implanted prosthetic devices. The modern hearing aid is a small device that can be inserted and removed at will and also disabled when necessary. It is the successor of the out-dated hearing aids that had a large box and cumbersome wires for amplifying sound electronically. Four of five people with hearing loss do not use hearing aids. Most people don’t realize that the majority of hearing losses can be treated with hearing aids. Untreated hearing loss can cause embarrassment, social stress, tension, and fatigue. This is true not only for the person with the hearing loss but also for family members, friends, and colleagues.
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There’s a tired old joke in television sit-coms where people shout at a deaf person (usually a deaf, elderly person) to make themselves heard. What happens if you shout at a deaf person is that you transmit sound waves of greater amplitude (volume) and energy into their ear canal. Their cochlear hair cells are more likely to detect these more energetic sound waves and, consequently, they’re more likely to hear you. Old-style ear trumpets work a slightly different way. Effectively, they make the outer ear much bigger and concentrate the energy in incoming sounds into a smaller area. That increases the pressure that sounds make on the eardrum and, again, improves the person’s chances of hearing. While shouting louder and using ear trumpets are crude mechanical solutions to the problem of hearing loss, a hearing aid is a much more sophisticated electrical solution. A hearing aid is simply an electronic sound amplifier. You’ve seen people on stage speak into a microphone and have their voices hugely amplified by giant loudspeakers so crowds can hear them. A hearing aid works exactly the same way, except that the microphone, amplifier, and loudspeaker (and the battery that powers them) are built into a small, discreet, plastic package worn behind the ear or just inside the ear canal. Speaker of hearing aid is also called receiver. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations.
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The hearing aid is a small wearable amplifier. It is just an amplifier-nothing more. The hearing aid only amplifies the sound that you are hearing. Interpreting the sounds i.e. identifying and understanding the meaning of the spoken words is basically a function of the brain and the hearing aid is not expected to enhance the power of understanding the meaning of the speech. However, by making the speech louder and making the speech sounds more audible, it does help the auditory system (i.e. the mechanism of hearing) in the brain to hear the sound. The brain can interpret the speech only after it has heard it. The hearing aid, by making the speech louder, helps the brain in hearing and consequently understanding speech. In many types of deafness, especially in very old people, the brain’s power of understanding speech becomes defective and in such persons, the hearing aid only partially helps the user. Your expectations from the hearing aid must be realistic. The hearing aid will not make you understand speech, it will help you only to hear the speech. Only the portion of your hearing handicap that is attributable to loss of hearing sensitivity, will be corrected by the hearing aid (provided it is selected properly). A perfect selection of the hearing aid is very important for the hearing aid to be effective.
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Hearing aids differ by:
•design
•technology used to achieve amplification (i.e., analog vs. digital)
•special features
Some hearing aids also have earmolds or earpieces to direct the flow of sound into the ear and enhance sound quality. The selection of hearing aids is based on the type and severity of hearing loss, listening needs, and lifestyle.
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To achieve the best results from a hearing aid, you should meet with a certified audiologist to learn what a hearing aid can and cannot do and how best to operate it. It is important to understand how hearing aids work and how to select, operate, and care for them. On the basis of the hearing test results, the audiologist can determine whether hearing aids will help. Hearing aids are particularly useful in improving the hearing and speech comprehension of people with sensorineural hearing loss. When choosing a hearing aid, the audiologist will consider your hearing ability, work and home activities, physical limitations, medical conditions, and cosmetic preferences. For many people, cost is also an important factor. You and your audiologist must decide whether one or two hearing aids will be best for you. Wearing two hearing aids may help balance sounds, improve your understanding of words in noisy situations, and make it easier to locate the source of sounds. Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. This process is called “fitting” and is performed by audiologists. The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting. Devices similar to hearing aids include the bone anchored hearing aid, and cochlear implant. Successful hearing aid users are those who are motivated to improve their communication by improving their listening and hearing. They have worked with their audiologist to learn what they can expect from hearing aids. That is, they understand what a hearing aid can and cannot do and how best to operate it.
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Hearing aid basic:
All hearing aids have a microphone, processors, receiver, and battery compartment. Sound enters the microphone, is amplified and shaped by the processor, converted back into sound by the receiver, and directed out to the ear canal.
In the ear hearing aid:
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Behind the ear hearing aid:
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Conventional hearing aids have a few controls some of which are user-operable and others are dispenser-operable. The dispenser- operable controls are the trimmers with which you should not fiddle at all. These trimmers modify the quality of the sound coming out from the hearing aid. The user-operable controls are the volume control by which you can adjust the loudness of the hearing aid and a switch called M-MT-T switch. Some hearing aids have a separate on-off switch also but in some aids the on-off function is incorporated in the volume control or M-MT-T switch. When the on-off function is built in the M-MT-T switch, then the switch is labelled as the O-T-M switch where “O” is the setting for the “off” function. The hearing aid is switched off when put in the “O” setting. The “M” setting is for normal use; in the M-setting the hearing aid microphone picks up sounds from the surroundings and sends it to the amplifier. The “T”-setting is for using the telephone or for activating the telecoil in the hearing aid such that it can pick up sound signals in places where an induction coil has been installed like in some theatre halls or class-rooms of deaf schools. When the hearing aid is set to T, the microphone does not pick up any sound from the surroundings. The MT setting enables the user to use the telephone as well as the microphone together. E.g. if the user desires to talk to someone through the telephone but at the same time also wants to converse with other people in the room. However, modern sophisticated digital hearing aids are often devoid of user-operable controls. A volume control or M/T switch may or may not be present as these hearing aids are usually automatic and except for switching the hearing aid “on” or “off” the user does not have to do any adjustments. Some modern hearing aids called “multi-program hearing aids” have a toggle switch for changing over from one listening program to another. Try to be conversant with handling of the user-operable switches when you buy the hearing aid.
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What kind of hearing aid is best for me?
A variety of styles are available, so it is important to work with your audiologist to evaluate your needs. The best hearing aid will depend on the nature of your home life, your work environment, and your leisure activities. It is also critical that your hearing aid be adjusted and programmed to provide the best performance given your needs. Using hearing aids successfully takes time and patience. Hearing aids will not restore normal hearing or eliminate background noise. Adjusting to a hearing aid is a gradual process that involves learning to listen in a variety of environments and becoming accustomed to hearing different sounds. Try to become familiar with hearing aids under non-stressful circumstances a few hours at a time. Programs are available to help users master new listening techniques and develop skills to manage hearing loss. Contact your audiologist for further information about programs that may suit your individual needs.
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Persons with deafness usually have a number of hearing deficiencies combined together. Our faculty of hearing involves the following viz. auditory acuity (i.e. sensitivity of hearing), auditory localization (i.e. determining the direction from which the sound is coming), auditory awareness, auditory discrimination (i.e. differentiation between the different sounds), auditory attention (i.e. being especially attentive for certain sounds), auditory synthesis, auditory memory (i.e. storing in memory the meaning of the different sounds and retrieving it from auditory memory when the same sound is heard) etc. Even the faculty of hearing in presence of background noise is a very specialized auditory function that takes place partially in the ear but mainly in the brain. Of all these different faculties of hearing, the hearing aid basically corrects only the deficiency of auditory sensitivity (hearing acuity), not the other hearing faculties as the other faculties are all functions of the brain. In many patients of deafness (especially in sensorineural and in central deafness), not only the hearing acuity, but also the other faculties of hearing are deranged. In these cases, only a part of the auditory deficiency is corrected by the hearing aid. Moreover, the hearing aid does not amplify the full range of frequencies that the human ear is capable of hearing. The hearing aid amplifies just the speech frequencies i.e. from about 300 to 5000Hz whereas the normal human ear can hear sounds from approx. 20 to 20,000 Hz. Even with the best of hearing aids, some difficulty of hearing like discriminating between the different sounds, partial difficulty of hearing in presence of loud background noise may persist. This has to be made up by your motivation and increased attention while listening. Hearing through the aid is different from natural hearing but with regular use you are expected to adapt yourself to this artificially amplified hearing. This adaptation usually requires a few weeks of regular usage.
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Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible. Two primary issues minimize the effectiveness of hearing aids:
•When the primary auditory cortex does not receive regular stimulation, this part of the brain loses cells which process sound. Cell loss increases as the degree of hearing loss increases.
•Damage to the hair cells of the inner ear results in sensorineural hearing loss, which affects the ability to discriminate between sounds. This often manifests as a decreased ability to understand speech, and simply amplifying speech (as a hearing aid does) is often insufficient to improve speech perception.
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The Basics of Hearing Aid Selection:
Hearing aid selection is a complex part of hearing rehabilitation. The selection process follows the clinician’s assessment of a patient’s candidacy for amplification, and precedes the hearing aid fitting, verification, and validation processes. When the decision in favor of treating the particular case in point is made, the clinician is confronted with multiple decisions to customize the client’s treatment with amplification. The clinical challenge is to weigh the many factors in the selection process to achieve an optimum fitting. It is a fact that there is not just one possible hearing aid fitting per patient. Therefore, patients and clinicians usually have many choices in the selection of treatment. Essentially, the patient’s goals, the clinician’s assessments, and all of the potential fittings somehow must merge during the fitting process to arrive at the most successful rehabilitation outcome. It should be obvious that many experienced professionals have developed their own way for accomplishing this objective, and these methods may deviate substantially from the methods presented here. From a purely pragmatic point of view, how do you as a hearing care professional decide what hearing aid to fit a patient with? An everyday three-part categorization may provide a practical framework for the selection process used in most practices:
1. Clinical Considerations
a. Type of hearing loss (sensorineural, conductive, or mixed);
b. Degree of hearing loss (mild, moderate, severe, or profound);
c. Sensitivity to sounds, tolerance/recruitment problems, and dynamic range;
d. Psychological attitude toward correction (e.g., motivation and the primary motivator);
e. Contraindications for correction.
2. Physical Conditions of the Patient
a. Shape and size of ears and ear canal;
b. Manual dexterity and finger sensitivity;
c. Mental acuity.
3. Patient Wishes/Preferences
a. Cosmetic;
b. Needs assessment;
c. Appropriate circuit choices (digital, programmable, etc.);
d. Appropriate controls [e.g., AGC (automatic gain control), VC (volume control), remote control, directional microphones, etc.].
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Indications for Hearing Aid:
Any individual who has a hearing loss that cannot be helped by medical or surgical means is a candidate of hearing aid.
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The type of fitting:
Whether it is monoaural (one aid only), binaural (one aid for each ear), binaural with y connection (one aid but two receivers, one for each ear) or the CROS type. CROS (contralateral routing of signals) is microphone is fitted on the side of the deaf ear and the sound thus picked up is passed to the receiver placed in the better ear. This is useful for persons with one ear severely impaired & helps in sound localisation coming from the side of the deaf ear. Now bone-anchored hearing aids (BAHA) are being preferred for single-sided deafness & have replaced the use of CROS aids.
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On the day you pick up your hearing aids, your audiologist will:
• Check to ensure that your hearing aids fit comfortably
• Evaluate your hearing aids to be sure they are set (programmed) for your hearing needs
• Show you how to insert and remove your hearing aids
• Teach you how to insert and remove the batteries and clean and care for your hearing aids
• Teach you how to use your hearing aid on the phone
• Discuss hearing assistive technology that may be helpful to you
• Schedule you to return for a follow-up visit
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Expectations of consumer from hearing aids:
Since you are considering the purchase of hearing aids, it’s important for you to establish reasonable expectations from these highly sophisticated, miniature devices. Acquiring hearing aids is not merely a simple act of going to a store and purchasing a product. Rather, it is a complex process – one that evolves over time and begins with the hearing-impaired individual accepting the realization that hearing impairment has detrimental effects on interpersonal relationships and safety. The hearing impaired person’s motivation to hear well is the single most important factor in determining the success of the hearing aid fitting. It is important to realize that you will not experience the exact same benefits from your hearing aids as your neighbor does. This individuality is a critical component, and your expectations should be based on you, your type and degree of hearing loss, your past experiences, and the improvements you personally receive from amplification. Most unreasonable expectation would be to expect normal or perfect hearing.
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Have realistic expectations for hearing aids:
When wearing hearing aids in quiet environments, your hearing should improve. Your hearing in moderate background noise should improve. Your hearing with background noise is not going to be as good as your hearing in a quiet environment. Your hearing with loud background noise should not be worse than without the hearing aids. Soft speech should be audible, average speech should be comfortable, and loud speech should not be uncomfortable. Your ear molds should not hurt — if they do, they should be modified or remade. Your voice will sound different to you but it should not be objectionable. If it is, your hearing professional should reprogram your hearing aid or modify the fit. There should be no feedback — whistling — when the hearing aids are properly seated in your ears, unless you have your hand or an object close against them. If the feedback managers are good quality and working properly, whistling is virtually nonexistent. Your hearing aids should allow you to listen with less effort. Your hearing aids require time to get used to. Performance will improve as you gradually become accustomed to amplification. Just like with a new eyeglass prescription, your brain must reprogram to a new way of hearing. Your hearing aids will not restore your hearing capabilities to “normal’’ or pre-existing levels. Hearing aids do not eliminate background noise — only earplugs are designed to do that. You may be aware of soft sounds that were previously not audible. Examples include your footsteps, the refrigerator running, the rubbing of a nylon jacket, the clock ticking, chewing your food and brushing your hair. Identifying the “new” sounds helps you adapt to hearing them once again. If you only wear one hearing aid and have hearing loss in both ears, you will never hear well in situations where there is background noise. No two people have the same hearing loss or the same hearing aid experience. Just because one person is unhappy with their hearing aids does not mean you will be unhappy. Remember, when you are wearing hearing aids for the first time, you are using a hearing instrument to hear with an impaired hearing system — your ears — in a very noisy world. It may have taken a long time to lose your hearing and it will take you time, practice and patience to get used to hearing again. If you are having a difficult time adjusting to your hearing aids, make sure you go back to your hearing professional for help. If your expectations are realistic and you are still not satisfied, try a different model or seek another hearing aid professional.
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Is there an adjustment period to wearing hearing aids?
You’ll need time to learn how to; insert and remove the hearing aids from your ears, learn to adjust the volume control (some hearing aids have volume controls, other are automatic), learn how to clean them, learn how to open and close the battery door, learn to change the battery, get accustomed to placing the hearing aids in a dry-aid kit for the times when they are not in your ears. As you can see, there is a lot to learn, and people learn at different speeds. It can take up to four months for you to get accustomed to your hearing aids and to really get the most out of them. You will notice small changes right from the start, but it’s important to be patient. If you have questions or concerns about your progress, be sure to call your hearing professional for help. Hearing aids often need to be adjusted several times during the trial period. This is a team effort, so do not be afraid to speak up. When you first begin to use hearing aids, your brain will be startled to receive signals it has been missing. The brain needs time to become familiar again with the high-frequency sounds of speech and environmental noises. Re-acclimating your brain to true sound, after years of distortion caused by hearing loss, is like priming a pump. You’ve got to stay with it long enough for the water to flow. Once it is flowing – and it will flow – the hardest part is over. Your perceptions will improve over time, as the true sounds of everyday life are re-introduced to your consciousness after not being heard for years. At first, all sounds will seem loud. The true pitch of the telephone, the sound of your clothes rustling as you walk, the whoosh of your air conditioner or the hum of your refrigerator motor will seem loud in relation to other sounds. These sounds will become part of your subconscious again as your brain begins to prioritize them. It’s a good idea to begin with a schedule in which you wear your hearing aids part time and gradually work up to wearing them from the time you rise until the time you go to bed. Most importantly, expect to enjoy the sounds of life again! Your hearing aids are a key ingredient to staying active and improving the quality of your life. You will once again enjoy social events, leisure activities, and conversations with your family, friends, and co-workers. Your hearing aids will also help you hear sounds to keep you safe and well.
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Your hearing aids may squeal (also called “whistle,” or “feedback”) under some circumstances. If a hearing aid is somewhat functioning and has a good battery in it, this squeal (acoustic feedback) will occur when the hearing aid is cupped in the hand. Most users find that this helps determine the status of the battery and it is a good sign! However, you should be able to wear your hearing aids at a comfortable loudness level and not experience this squeal. If you do not have a volume control on your aids, they will squeal when you place them in your ears – until you get them placed comfortably. Sometimes, your aids will squeal if you press the phone too tightly to your ear. Report these events to your audiologist/HIS and determine what is normal, what is abnormal, and what can be done to reduce unnecessary acoustic feedback.
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Binaural hearing aid:
There are many benefits to binaural (two ear) hearing, including being better able to understand speech in noise, and being better able to localize sound. It is very important to understand that if you have two ears with hearing loss, and you only wear a hearing aid on one ear, you will still have significant hearing problems, even under the best of circumstances. A reasonably good analogy is to consider wearing a single eye glass (monocle) for a two-eye vision problem, such as being near-sighted or far-sighted – it simply will not work well for very long! In cases where only one ear is affected, a single hearing aid can restore balanced hearing. More than 50% of people with hearing impairment are affected in both ears and so wear two hearing aids.
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It is well known in the psychoacoustics and audiology literature that to understand sound in very difficult listening situations (i.e., noise), the human brain must compare and contrast sound from the left and right sides. The variation in interaural timing differences (ITDs) and interaural loudness differences (ILDs) from both sides (as well as other factors in binaural summation and binaural squelch) provides enormous information and allows the brain to know where to attend/focus and what to focus on. When reliably and clearly transmitted and perceived, these same factors (ITDs, ILDs) allow the brain to assign meaning to sounds. That is, understanding speech-in-noise is not specifically about loudness, per se, but involves many factors to include:
•Signal-to-noise ratio (how loud the signal of interest is above the noise floor),
•Audibility (are all speech sounds present),
•Preservation of acoustic speech cues, and
•Most importantly, the brain’s ability to compare and contrast information from the left and right side to first identify left and right differences (with respect to ILD and ITD) and to assign meaning to sound. That is, for the brain to maximally understand speech in noise, the brain requires input from the left and right side.
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Some benefits of wearing two hearing aids include:
• Better localization – the ability to tell where sounds are coming from
•Better hearing in background noise
•Better sound quality (“mono” versus “stereo”)
•Better hearing for soft sounds such as children’s voices and sounds of nature
•Less strain on you while listening – with only one hearing aid you may often strain to hear various sounds and become fatigued, with two hearing aids listening is more relaxed
•Listening balance – you won’t be turning your “good” ear to hear.
•Higher success and satisfaction – studies indicate people who wear two hearing aids are much more satisfied with their hearing aids.
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Hearing aid impersonation:
Hearing aid impersonation means electronic devices that mimic hearing aid.
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Personal Sound Amplification Product (PSAPs):
Personal Sound Amplification Products, also known as “Personal Sound Amplification Devices,” or by the acronym PSAP, are defined by the U.S. Food and Drug Administration as wearable electronic products that are intended to amplify sounds for people who are not hearing impaired. They are not hearing aids, which the FDA describes as intended to compensate for impaired hearing. According to Dr. Mann of the FDA, choosing a PSAP as a substitute for a hearing aid can lead to more damage to your hearing. Because they do not require a medical prescription and professional fitting, PSAPs have been described as the audio version of reading glasses. As such, PSAPs are suggested for use by hunters listening for prey, for bird watching, assistance hearing distant conversations or performances and amplifying the sound of a television in a quiet room, for example. Of note, even reading glasses are regulated under the FDA. Companies such as Soundhawk, Etymotic, Advanced bionics, and Able Planet offer PSAPs that leverage technology and personalization. PSAP models differ significantly in price and functionality. Some devices simply amplify sound. Others contain directional microphones, equalizers to adjust the audio signal gain and filter noise. PSAPs have grown in popularity among people with hearing impairment, in part because they are less expensive than custom hearing aids, although apathy, vanity and difficulty scheduling appointments with audiologists also have been cited as reasons for low hearing aid adoption. Because they do not require medical examination and fitting, PSAPs range from as little as 50 to several hundred dollars in price, while custom hearing aids cost about $1400 on average and are not covered by Medicare and many insurance plans. According to the National Institute of Deafness and Other Communication Diseases, of the 36 million Americans who might benefit from a hearing aid, only about 20 percent actually use one. However, a 2010 survey indicates that fewer than 18 percent of PSAPs were used as a substitute for custom hearing aids and concludes that the majority of PSAP users would have lived with their hearing loss because of the higher price of hearing aids. Many PSAPs are sold direct to the consumer through online stores, at pharmacies and through many drugstore and retail store chains.
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Some PSAPs available in market:
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Difference between PSAP and digital hearing aids:
Both PSAPs and hearing aids are small electronic devices that fit into the ear and amplify sound. PSAPs are mostly off-the-shelf amplifiers for people with normal hearing who need a little boost in volume in certain settings (such as hunting and bird watching). Hearing aids contain a much higher level of technology prescribed to treat a diagnosed hearing loss. PSAPs are not regulated under the Food, Drug and Cosmetic Act because they are not intended to treat, diagnose or cure hearing impairment and do not alter the structure or function of the body. As a result, there is no regulatory classification, product code or definition for these products. However, the FDA does regulate PSAPs under certain provisions of the Radiation Control for Health and Safety Act of 1968, covering electronic products such as sound amplification equipment that emits sonic vibrations.
Hearing aids and PSAP’s have the same four basic components:
1. A Microphone, to convert acoustical sound energy into electrical energy
2. An Amplifier, to increase the electrical signal strength
3. A Speaker, to convert the electrical signal back into acoustical energy
4. A Battery, or source of power for the device
The difference is that hearing aids are classified as medical devices whereas PSAP’s are classified as electronic devices. Unlike a hearing aid, a PSAP is not intended to compensate for impaired hearing and must be labelled accordingly. Probably the biggest concern for people using PSAP’s is the level of the sound entering the ear. Exposure to loud sounds can damage the ear. Hearing aids are programmed to limit the maximum level of sound. Another difference between hearing aids and most PSAP’s is that hearing aids amplify the frequency of sound, based on a person’s loss. In other words, the hearing aids of a person with high frequency hearing loss will have high frequencies amplified more than the low frequencies. Most PSAP’s will amplify all frequencies by the same amount. Still another difference is that most, if not all, hearing aids today have two or more microphones strategically placed to help reduce background noise. Most PSAP’s have only one microphone so the ability to filter background noise is limited. An internet search of PSAP’s will show the cost in the range of $10 to $600. The cost for a hearing aid will vary from about $1000 – $2700 (this cost may or may not include professional services). The technology used in PSAP’s is improving. One PSAP product that deserves attention is the Soundhawk. The cost is $299 but it requires the use of a smartphone for tuning and volume settings. Newer hearing aids also have the ability to be tuned using a smartphone.
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Research by Cheng and McPherson in 2000 examined several PSAPs using real-ear measurements, and found the devices often provided too much low frequency gain and insufficient high frequency gain. This configuration made the devices inappropriate for many users with a high frequency hearing loss. A 2008 study by Callaway and Punch obtained similar results across a range of PSAPs, but did find that higher-end PSAP models (those above $300) were able to more closely match NAL-NL1 prescriptive targets and appropriately amplify sound. Subjectively, patients have reported no discernable difference between environmental sounds and music amplified through a mid-range PSAP and a traditional BTE hearing aid. However, there was significant preference for speech amplified through the hearing aid versus the PSAP. These studies suggest that PSAPs may be appropriately fit to some types of hearing losses, but further data is required before that assumption can be made.
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Why buy PSAP:
Recent research regarding the low rate of hearing aid adoption has examined the issues of affordability, device performance, and patient outcomes. While results have differed slightly between studies, it is apparent that the issue of affordability plays a significant role in the decision to purchase hearing aids. Obtaining hearing aids from a licensed hearing aid dispenser can cost upwards of $1,000 for two basic devices (in a bundled-service model) with costs rising in excess of $6,000 for the inclusion of more advanced features. Confounding the affordability dilemma is the lack of standardization regarding third-party coverage of hearing aids, with many insurance companies—including traditional Medicare—refusing to pay for the devices. During periods of recession, hearing aid sales have been shown to dip significantly, indicating hearing healthcare may be seen as a luxury in times of economic duress. Given this information, it would seem logical for the hearing aid industry to attempt to reduce prices; however, hearing aid prices have previously shown to be fairly inelastic, with a reduction in prices not resulting in an increase in sales. Additionally, in countries where hearing aids are provided to patients at low or no cost, hearing aid adoption rates show only slight improvement over those in the United States.
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Complicating matters is the recent introduction of a third class of amplification products called hearables. These devices, borrowing their name from the trend of wearable devices, are very similar to PSAPs. Most of the devices are wireless in-the-ear style headphones that combine the functionality of wireless headphones with additional features, including heart rate monitors, media storage, Bluetooth-compatibility, and equalizer settings allowing users to alter the sound quality of incoming audio signals. Some of these devices are not just intended to be worn when listening to music, but can be worn for extended periods of time to alter how we hear environmental sounds and monitor our surroundings. With most hearables entering the market at around $500, these devices are almost identical to some high-end PSAPs, and their unregulated status may only further confuse the average consumer.
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From the market’s perspective, hearing aids are normally more expensive, better quality, and designed for people hearing impaired people; personal sound amplifiers are generally inexpensive with few features. Some PSAPs are designed with hearing impaired people in mind and many are not. Some people are strongly against using PSAPs for people with hearing loss and their reasons can be summarized as follow:
1. Using a PSAP may cause delay in diagnosis of potentially treatable conditions and lead to serious consequences.
2. PSAP may damage your ears if not used properly.
3. PSAP may not fit your needs as well as HA.
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Smart PSAP:
The now ubiquitous smartphone has opened the door for change, allowing the creation of a new category of personal sound amplification products: Smart PSAPs. Smart PSAPs can be personalized by using smartphone to the needs of the user, by the user.
What makes a smart PSAP different from a regular PSAP?
Smart PSAPs provide amplification and signal processing in a way that improves listening performance in the situations that matter to the listener, while also being useful in situations that we all encounter every day. These situations might include talking on the phone, attending a meeting or having dinner with friends. By allowing the user to make changes to the perception of sound, and by including a wireless, remote microphone, these devices allow the listener to listen effectively at a distance, for example, with comfort and a sound that is desirable and enjoyable. Smart PSAPs provide cutting edge signal processing features like directional microphones, digital noise reduction, wind-noise management and flexible amplification similar to that found in high-end hearing aids. But smart PSAPs don’t look like hearing aids, are not intended to replace hearing aids and do things that hearing aids cannot.
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Smart phone work as hearing aid:
“Hearing aid” application for smartphones / tablets:
Computer programs allowing to create a hearing aid on the basis of a PC, tablet or smartphone currently gain popularity. Modern mobile devices have all the necessary components to implement this: hardware (an ordinary microphone and headphones may be used) and a high-performance microprocessor that carries digital sound processing according to a given algorithm. Application configuration is carried out by the user himself in accordance with the individual features of his hearing ability. The computational power of modern mobile devices is sufficient to produce the best sound quality. This, coupled with software application settings (for example, profile selection according to a sound environment) provides for high comfort and convenience of use. In comparison with the digital hearing aid, mobile applications have the following advantages:
•ease of use (no need to use additional devices, batteries and so on.);
•high wearing comfort;
•complete invisibility (smartphone is not associated with a hearing aid!);
•user-friendly interface of software settings;
•high sampling frequency (44.1 kHz) providing for excellent sound quality;
•Fast switching between the external headset and phone microphone;
•acoustic gain is up to 30 dB (with a standard headset);
•low delay in audio processing (from 6.3 to 15.7 ms – depending on the mobile device model);
•No need to get used to it, when changing mobile devices;
•No loss of settings when switching from one gadget to another and back again;
•High duration of the battery;
•free distribution of applications.
It should be clearly understood that “hearing aid” application for smartphone / tablet cannot be considered a complete substitution of a digital hearing aid, since the latter:
•is a medical device (exposed to the relevant procedures of testing and certification);
•is designed for use by doctor’s prescription;
•is adjusted using audiometry procedures.
Functionality of hearing aid applications may involve hearing test (in situ audiometry) too. However, the results of the test are used only to adjust the device for comfortable working with the application. The procedure of hearing testing in any way cannot claim to replace audiometry test carried by medical specialist, cannot be a basis for diagnosis.
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India’s first ever smartphone-based hearing aid app launched:
The Q+ app claims to harness the processing power of your smartphone to use it as a complete and fully-functional hearing mechanism. Quadio Devices, a Pune based startup, has introduced an app which combines the components already present on with your smartphone such as the microphone, the processor and headset to emulate what they claim is a fully functional hearing mechanism. The app is designed to use the results from a simple, interactive hearing test to calibrate and customise the listening experience of a hearing impaired user. With the Q+ app, one can easily follow conversations using the phone headset in both quiet and noisy environments. There are different modes offered by the app, which optimise hearing in different situations, like in a restaurant, or while driving. It also has a mode which makes it easier to watch TV, or watch videos. According to the company, the hearing test in the app is calibrated for accuracy, as per ANSI standards of audiometry. The company estimates that about 120 million people in India have hearing problems and less than 1 percent actually use any kind of hearing solution. That’s a pretty large potential market. As of now the app is as good as a mid level physical hearing aid but the developers plan on making the app as good as a high end hearing device, which costs about Rs 100,000 or more in the market. The startup aims to increase the penetration of hearing solutions by increasing affordability and reach of the technology. “The flexibility of controls offered by a smartphone app is much more than that offered by conventional hearing aids and, along with the affordability of smartphones, the reach of app store, and the inbuilt test, this gets us closer to achieving our objective,” said Anurag Sharma, Co-Founder and CTO. The app is available for free on Google Play, and iTunes and according to Neeraj Dotel, CEO, Quadio Devices, the app comes in two versions a Pro and Lite. As an introductory offer both are free for the first two months initially while after this period, the full (or Pro) version of the app can be unlocked by paying a one-time fee of Rs. 500. The Lite version is to be ad supported.
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Hearing aid lookalike:
Devices in ear which look like hearing aid:
1. An inductive earpiece—stage actors often use these to help with cues and missed lines during performances.
2. An anti-seizure device—sound can trigger certain forms of seizures. A German-engineered device called the Epitect fits inside the ear and can detect and warn of an impending seizure, but more closely resembles a more traditional hearing aid with a component that hangs behind the ear.
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Technology of hearing aid:
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Hearing aids are electronic devices that collect sound, amplify it, and direct the amplified sound into the ear. While the style of hearing aid may vary, all hearing aids have similar components:
• A microphone to pick up sound
• An amplifier to make sounds louder
• A receiver (miniature loudspeaker) to deliver the amplified sound into the ear
• Batteries for power
Some hearing aids also have earmolds (or dome ear pieces) to direct the flow of sound into the ear and enhance sound quality.
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In all hearing aids you’ll find 5 basic components: microphones, an amplifier, a loudspeaker, a battery and a computer chip that is programmed by the hearing care professional to suit individual needs. Although all hearing aids have a similar construction, there can be significant differences in the quality of sound capture and speech understanding between different devices. The higher the quality of the hearing aid, the more natural the listening experience will be. This is because they offer features like bandwidth, automatic volume regulation, noise management and feedback suppression.
The most advanced hearing aids also have a wide range of personalisation options and the ability to connect wirelessly to a number of devices, such as mobile phones. You’ll find the most advanced technology in the newer hearing aid models, and these improvements come at a cost. But you can feel assured that there are hearing aids available to suit all tastes and budgets. A hearing care professional can recommend a model based on the result of a hearing test and a conversation about your lifestyle and budget.
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Sound processing:
The first electrical hearing aid used the carbon microphone of the telephone and was introduced in 1896. The vacuum tube made electronic amplification possible, but early versions of amplified hearing aids were too heavy to carry around. Miniaturizations of vacuum tubes lead to portable models, and after World War II, wearable models using miniature tubes. The transistor invented in 1948 was well suited to the hearing aid application due to low power and small size; hearing aids were an early adopter of transistors. Analog hearing aids (i.e., the older type of technology that consisted of components such as transistors, resistors, and capacitors, etc.) were essentially limited to making incoming sounds louder, frequencing shaping (i.e., shaping the degree to which sounds were amplified based on the degree of hearing loss), and compressing the large intensity range of sounds into the reduced range of hearing in those with hearing loss. The advent of programmable hearing aids in the mid-to-late 1980s enabled multiple hearing aid settings (memories) for different listening environments, while at about the same time dual microphone technology was incorporated into hearing aids. This combination of features allowed for greater flexibility for the hearing aid user. For example, when listening in quiet the user could have the hearing aid set for listening to sounds coming from all directions, while in noisy settings the listener could use a different memory setting whereby the hearing aid was programmed with a different frequency response and the microphones amplifying signals from in front (where the talker typically would be positioned), while attenuating the noise from behind the hearing aid user. The development of integrated circuits allowed further improvement of the capabilities of wearable aids, including implementation of digital signal processing techniques and programmability for the individual user’s needs. The implementation of digital processing in hearing aids in the 1990s resulted in many additional benefits. These included: miniaturization of hearing aids (yet not relinquishing power); distinguishing between speech/noise; decreasing the annoying whistling/feedback that was sometimes experienced; and, in turn, being able to fit individuals with normal hearing in the low frequencies with what we now refer to as open-fit hearing aids, thereby decreasing/eliminating the occlusion effect (i.e., the feeling where one’s voice sounds as if he or she is talking in a barrel). In recent years, hearing aid wireless connectivity has come to fruition with its numerous benefits. Hearing aid wireless connectivity includes data and possibly audio transmission between hearing aids, as well as the ability of hearing aids to communicate directly with electronic devices (such as the cell phone, TV, MP3 player, computer, etc.), allowing for direct reception from the sound source. In today’s digital hearing aids, the acoustic (natural) sound from the microphone is converted into digits (0, 1), processed within the hearing aid, and then reconverted into an analogue signal for the listener.
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Hearing Aid Gain:
All hearing aids have the same basic parts. The microphone picks up sounds and sends them to an amplifier that makes them louder. The hearing aid will make some pitches of sound louder than others, depending on the shape of the hearing loss. Your audiologist uses the hearing aid’s internal controls or computer programming to adjust the sound for your needs. The graph below shows how much a hearing aid increases the loudness of sounds at different pitches or frequencies. The increase in loudness is called “gain”. For milder hearing losses, a small amount of gain is needed. A severe hearing loss needs more gain. When the amount of hearing loss is different across frequencies, the audiologist must adjust the gain of the hearing aid differently for different frequencies.
In the figure above gain ranges from 40-65 dB for a relatively flat hearing loss (shown here using a solid line). Very little gain is provided for the low pitches in the case of a high pitch hearing loss (shown here using a dashed line).
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NAL-NL1 and NAL-NL2
NAL-NL1 is a software program to prescribe hearing aids using the NAL-NL1 selection procedure. The National Acoustic Laboratories and the Cooperative Research Centre for Cochlear Implant, Speech and Hearing Research have derived a prescription formula that specifies the required performance characteristics for non-linear hearing aids, and have developed a software program that makes it easy for clinicians to use the new procedure. NAL-NL2 is the second generation of prescription procedures from The National Acoustic Laboratories (NAL) for fitting wide dynamic range compression (WDRC) instruments. Like its predecessor NAL-NL1, NAL-NL2 aims at making speech intelligible and overall loudness comfortable. This aim is mainly driven by a belief that these factors are most important for hearing aid users, but is also driven by the fact that less information is available about how to adjust gain to optimise other parameters that affect prescription such as localisation, tonal quality, detection of environmental sounds, and naturalness. In both formulas, the objective is achieved by combining a speech intelligibility model and a loudness model in an adaptive computer-controlled optimisation process. Adjustments have further been made to the theoretical component of NAL-NL2 that are directed by empirical data collected during the past decade with NAL-NL1
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Digital and analog hearing aid:
Hearing aids are of 4 technical types:
(1) digital aids,
(2) programmable analogue aids,
(3) the conventional analogue non-programmable aids, and
(4) the non-programmable digital hearing aids.
1. The 100% digital hearing aids, which can be programmed digitally and use digital technology for amplification of the sound is the most sophisticated form of hearing aid available today. The costly high-tech hearing aids i.e. the digital/programmable ones use technologically advanced mechanisms for amplification of the sound and hence the amplified sound appears to be clearer and distortion-free to you as compared to that of the analogue/non-programmable (i.e. conventional) hearing aids. It is available in behind-the-ear (BTE) and inside-the-ear (ITE/ITC/CIC) models. In some types of hearing loss, digital hearing aids are the only option available to the patient. The cheap conventional hearing aids are useless in these special cases. If you have been successful in finding out an honest, knowledgeable and ethical dispenser, he will guide you properly on this aspect.
2. The programmable analogue hearing aids use more or less the same age old technology of sound amplification but the amplification can be tailored through a computer according to your hearing loss in the different frequencies i.e. amplification can be made more for those sounds where you have more deafness and amplification can be reduced for those sounds where your hearing is better. This helps you to hear better and makes the hearing aid more comfortable for you. These are a type of hearing aids where at the touch of a button (a toggle switch) in the hearing aid or in a remote control, the amplification character of the hearing aid can be changed to suit a particular acoustic environment. If you have a hearing aid with 3 programs you may have one setting for a quiet bedroom, one setting for a crowded market place and one setting for hearing a telephone. You may switch over from one program to another depending on where you are placed. The hearing aid will customise the sound output accordingly and give you the best hearing for that environment.
3. The non-programmable conventional analogue hearing aids amplify all sounds over the entire frequency range. There is very little scope of tailoring the amplification according to the hearing loss of the patient in these analogue non – programmable hearing aids. Minor adjustments can definitely be done by manipulating the trimmers but the adjustments possible are much less as compared to the programmable hearing aids.
4. The non-programmable digital hearing aids use digital technology for amplification of the sound signal but the hearing aids are not digitally programmable i.e. their amplification parameters cannot be adjusted exactly according to the user’s requirements through the computer. Limited adjustments can be done by manipulating the trimmers on the hearing aids. The high or low frequencies can be slightly emphasised or reduced by suitable trimmer adjustments. Trimmers are small dispenser-operable mechanical control knobs in the hearing aid.
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The programmable digital hearing aids and even the programmable analogue (non-digital) hearing aids offer the facility of adjusting the amplification according to the needs of the user. Hence, hearing is much better and comfortable with digital or with programmable variety of analogue hearing aids as the amplification is precisely tailored according to your individual needs and requirements in these hearing aids. Moreover, later on the amplification parameters can also be changed in tune with changes in your hearing loss and according to your changed requirements. Hence, with programmable hearing aids you usually do not need to change your hearing aid if your hearing partially deteriorates later on. Just a reprograming through a computer can be done by your hearing aid dispenser to suit your increased hearing requirements.
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Analog hearing aid:
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The analogue amplifier works with transistors, which amplify the sound and capacitors and resistors, which determine the filter and compressor characteristics. Even a slight distortion of the current running through the analogue amplifier (which is quite frequent due to minor changes in the electronics of the capacitors and transistors) is heard as distortion of the sound. Noise created by the electronics of the analogue hearing aid (caused mainly by the random movements of the electrons in the resistors) is heard as noise as it directly affects the signal. This is the limitation of analogue circuits. Analog hearing aids work by making continuous sound waves louder, amplify all sounds (speech and noise). Some analog hearing aids are programmable, containing a microchip which stores multiple program settings for various listening environments. Using these settings, the user can change their hearing aid settings to switch from a quiet environment such as a library, to noisy places such as a restaurant, to an amplified environment such as a baseball stadium or concert hall. These programs can be changed by the user by pushing a button on the hearing aid.
Advantages of analog hearing aids:
•Generally cost less than digital hearing aids
•Are sometimes more powerful than digital hearing aids
•Long time hearing aid users sometimes prefer analog over digital
Conventional analog hearing aids are designed with a particular frequency response based on your audiogram. The audiologist tells the manufacturer what settings to install. Although there are some adjustments, the aid essentially amplifies all sounds (speech and noise) in the same way. This technology is the least expensive, and it can be appropriate for many different types of hearing loss.
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Digital Hearing Aids (DHA):
The 100% digital multiband hearing aids give you advantages which cannot be provided by any conventional hearing aid. Until 10 years back, hearing aids were limited by their analogue technology, which led to compromises in sound quality. In any analogue system, the sound is first converted into an electrical wave by the microphone, then passed through the amplifier, and then converted back into a sound wave by the receiver. All these stages result in a certain amount of sound distortion added to the original sound signal. With digital technology, the sound signal from the microphone is converted into a numerical code and then calculated. All of the required sound parameters – the intensity, the frequency characteristics, the details of your deafness from your audiogram and especially your hearing needs, are taken into account in the calculation process. By the time the sound reaches your ear, the sound is custom-tailored to your unique hearing needs, with clear CD quality. The microchip in the sophisticated digital hearing aid carries out thousands of calculations every second to sample (i.e. analyse ) incoming speech sounds as well as the ambient noise and then deliver the amplified sound to the user’s (i.e. patient’s) ear such that the user hears the desired sound (speech) most comfortably and clearly.
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Digital hearing aids take the continuous sound wave and break it up into very small, discrete bits of information. This is called digitizing the signal and all digital hearing aids do this. The very fact that a hearing device is digital does not make it better than a comparable analog hearing aid device. Beyond just digitizing the sound prior to amplification, there are differences in exactly how various digital hearing aid devices amplify or process sound. The more sophisticated digital hearing aids are able to amplify the softest sounds of speech while at the same time subtracting out certain types of unwanted noises. Digital signal processing allows hearing aid designers to write computer programs, called algorithms that can be customized to each individual’s hearing loss. In addition, digital hearing aids enable important features — such as directional microphone arrays, and multiple user programs to be placed into cosmetically appealing device. It is this potential that makes digital hearing devices so promising for so many hearing losses. Selecting the type of hearing aid that is right for your hearing loss and unique listening needs requires the guidance of a professional well versed in all of variations of hearing instrument technology. Today, over 90 % of all hearing aids sold are digital.
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In digital signal processing (technically known as DSP), the sound parameters are encoded into a sequence of numbers. Digital processing is done by calculations on the sequence of numbers that are passing through the processor. A 10 times amplification is achieved through multiplication of each number in the sequence by a factor of 10 before reconversion. Filtering to cut-off unwanted sounds is achieved through other calculations. In the conversion, a binary number system is applied, creating a stream of bits. This stream runs through the processor, which makes calculations and modifies it accordingly. The net result of these manipulations emerges after reconversion in a Digital-to-Analogue converter and presents an analogue signal to the receiver. The receiver finally transforms the signal into sound. This is a very brief idea of how the analogue and digital hearing aids work. Digital hearing aids aren’t superior to analog ones because they amplify sounds better—analog aids may, in fact, do that job just as well—but because they turn sounds into digital information that can be enhanced to make speech that’s easier to understand, music that’s more pleasant to listen to, and so on.
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How digital hearing aid works:
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Digital hearing aids give us the ultimate in hearing aid technology that is available today featuring:
1. Programmability i.e. setting amplification parameters according to your individual requirements. An example will clarify this. If you have a deafness for high frequency sounds only, you will be able to hear that people are talking to you but you will not be able to make out what they are saying. This happens because the consonant sounds that give us the intelligibility of speech are mostly high frequency sounds (from 2000 to 8000Hz) ; so if you have selective high frequency deafness, you will only be able to hear the loud vowel sounds and miss the faint consonant sounds. If you use a conventional hearing aid that cannot be programmed in accordance to this hearing loss, the low frequency (vowel) sounds and the background noise (which mainly consists of low frequency sounds) will get over-amplified (i.e. will become very loud) and mask the faint consonant sounds and thereby further reduce your speech intelligibility. You will hear the sounds very loudly but not understand what is being spoken. In multichannel digital hearing aids, by proper programming, only those high frequency sounds where you have the deafness can be selectively amplified without amplifying the low frequency sounds. This increases your understanding of speech i.e. enhances speech intelligibility. Digital hearing aid technology provides us the opportunity for finer control over a wide range of acoustic parameters and hence has more potential for accurate and very precise fitting to the individual hearing loss.
Multiple and automatic programming:
Different listening environments often call for different settings within hearing aids in order to maximise their effectiveness. For example, when listening to music, the user would prefer to turn off features that may misinterpret elements of the music as noise. When in a quiet room, a wearer will not need the benefit directional microphones and noise reduction to the same extent they would in a crowd at the football. Advanced hearing aids allow the user to change the settings by pressing a small button on the device. The most advanced hearing aids will even listen to the environment and change the hearing aids settings automatically, without the wearer needing to touch or think about their hearing aids.
2. CD quality sound processing with very clear distortion-free sound.
3. Sophisticated signal processing for speech enhancement and reduction of background noise.
Monitoring the background noise and amplifying the speech sounds accordingly. The sophisticated digital hearing aids have sensors that sample i.e. analyse the background noise thousands of time every second and try to amplify the speech sounds in such a way that the background noise is much less disturbing and speech more clearer to the user. The high end sophisticated digital hearing aids automatically sense the acoustic environment and change the hearing aid’s sound output spontaneously and instantly according to the changes in the acoustic environment. They are smarter than the Multi-program hearing aids as the user does not have to operate a toggle switch when he goes from one acoustic environment to another.
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Noise reduction:
One of the problems with older hearing aids was that they amplified all sounds equally – whether the source of the sound is the person who the wearer is listening to, or background noises, such as traffic, air conditioners, or ambient noise from a crowded room. This led to discomfort and did not help the user to follow conversations in difficult environments. Now digital hearing aids can actually tell the difference between speech and background noise and do this individually for every frequency band. The hearing aid then amplifies the speech sounds and reduces the amplification of background noise. Now consider the size of a hearing aid and the number of computations that it must perform every few milliseconds across up to 48 frequency bands and then deliver the enhanced sound into the ear canal. The results of noise management include greater listening comfort and clarity.
Other features that reduce noise include:
•Directional microphone: The directional microphone prioritizes noise that comes in from the sides and back are unimportant, and amplifies the sound from the front.
•Multiple channels: In order to reduce unavoidable ambient noise like the whirring of fans or humming of machines, many hearing aids are equipped with multiple channels. Several channels that pick up ambient sound are reduced, while other channels that amplify speech or voice sounds are prioritized.
•Wind noise manager: Because wind can create a lot of noise for someone wearing a hearing aid, many devices are equipped with electronic features that are able to reduce extra sound created by blowing wind.
•Wide dynamic range compression: This feature helps increase softer sounds more than louder sounds, so that listeners can hear voices and soft conversations, which are often lower in volume than unnecessary background or atmospheric noise. When a hearing aid uses compression, the circuit amplifies or boosts softer sounds more than louder sounds. If a hearing aid circuit has wide dynamic range compression, it automatically adjusts the amount of gain so that soft sounds will be made louder and loud sounds won’t be distorted or too loud. This kind of circuit may help children hear conversations at different listening distances.
4. Fully automatic control – for comfortable, natural loudness.
5. Digital Processor making 32,000 or more calculations per second for producing the exact quality and intensity of the sound output which is best suited for that particular user at the particular listening environment in which the user is placed. The nature and extent of your hearing loss as obtained from the audiological tests, your hearing preferences and the nature of the ambient i.e. environmental noise are all taken into account by the microprocessor chip of your hearing aid to calculate the sound output which will be best suited for you. If the digital hearing aid is programed properly (which of course is mandatory for the success of the aid) it will produce one type of amplified sound if the user is in a traffic crossing and another type of sound output when the user is placed in a concert hall or in a quiet bedroom. If two different users having two different types of hearing losses are placed in the same listening environment, the same digital hearing aids will produce different types of sound output for the two users, if of course the aid is programed differently according to the hearing loss of the two different users. This does not happen with the non-digital conventional hearing aids.
6. Some of the digital hearing aids are equipped with fine-scale noise canceller which continually monitors the speech to noise ratio (SNR) in multiple bands where noise is interfering with speech. It then intelligently adjusts gain in each band separately according to the intensity of the ambient noise and produces a sound output where background noise is very minimum or even absent.
7. Sound classification: This categorizes the sounds you can hear into music, speech, noise or whatever and amplifies them (or reduces them) selectively. Sophisticated digital hearing aids effectively figure out what kind of environment you’re in (concert hall, noisy restaurant, lecture theater with distant speaker, or whatever) and apply a different amplification pattern to the sounds you’re hearing. Effectively, they’re working like sophisticated programmable analog aids but switching themselves automatically according to the environment you’re in.
8. Feedback reduction: Hearing aid users have to suffer two kinds of feedback: acoustic and mechanical. Electrically amplified sound suffers from acoustic feedback: if you turn the volume up too much, the amplified sound enters the microphone with the original sound, gets amplified, enters the microphone again, and so on until you hear a horrible, deafening whistle. Digital hearing aids can tackle it more effectively than analog aids (where the only solution is to turn down the volume). Digital hearing aids can also remove mechanical feedback noise from such things as jaw movements.
And all these advanced functions can be carried out in a very small piece of hardware that can even be hidden completely in your ear canal. A microchip as efficient as the processor of a Pentium computer does numerous calculations very very fast and ultimately produces a sound which is not only very close to the original sound but also most suited for your type of hearing loss.
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Various technologies used in digital hearing aid:
We live in a digital world—and hearing instruments are no exception. Not only does digital signal processing result in more accurate hearing, it can be adjusted to individual needs in a way older analog hearing instruments never could. Digital signal processing has brought tremendous advances in hearing health. New technologies can improve sound clarity and speech intelligibility, reduce noise, and even connect you with wireless devices like cell phones, TVs and MP3 players. Most importantly, digital hearing aids are custom programmed so they can be “fine-tuned” to your personal hearing needs. Here are some of the many technologies digital hearing instruments may offer:
| Technology | What it does |
| Digital Signal Processing | Converts the incoming sound into digital values for processing, then converts them back into sound pressure waves that stimulate your auditory system. Processing a signal digitally allows the hearing aid to enhance the original sounds to improve the sound quality and helps reduce noise and feedback (whistling). |
| Automatic Gain Control (AGC) |
Automatically changes how much sounds at different frequencies are amplified. This is very individual, as the range of frequencies you can hear will be different from other people. AGC helps make softer speech sounds audible while controlling how much unwanted loud sounds are amplified. |
| Noise Reduction | Reduces annoying noise that can get in the way of conversational speech. This is done by analyzing the incoming sound and separating speech from steady background noises (like a refrigerator or fan). The speech is amplified and the noise is decreased to provide comfort and better speech understanding. |
| Impulse Noise Reduction | Reduces sudden, loud sounds like the clinking of silverware or jangling of keys, without modifying other sounds that may contain important speech cues. |
| Soft Noise Reduction (Expansion) | Keeps soft sounds quiet by providing less amplification for sounds that are quieter than conversational speech. This improves the quality of sound from the hearing device when worn in quiet situations. |
| Wind Noise Reduction | Prevents noise caused by wind from being over amplified. This improves the quality of amplified sound in outdoor environments. |
| Adaptive Feedback Cancellation | Detects sudden feedback (whistling or squeal) in a hearing device then removes it by applying a cancelling signal. If the cause of the feedback changes, the cancelling signal will automatically adapt. Adaptive Feedback Cancellers are designed to manage transitory feedback (e.g. feedback that happens when you place a hand or telephone next to your ear). This doesn’t resolve on-going feedback, which might be due to a poorly fitted earmold or hearing device. |
| Omni Microphone | Emphasizes sounds equally from all directions. All hearing devices have omni microphone capability. |
| Directional Microphones | Emphasizes sounds coming from the front; de-emphasize sounds coming from the sides and behind. Since most conversations occur when you’re facing a speaker, directional microphones help you focus on that source. Directional technology is available on all but the very smallest custom models which are limited by size constraints. |
| Automatic Directional Microphones | Allows a hearing device to automatically switch from an omni microphone setting to a directional microphone setting when the system predicts better performance with the directional settings. |
| Adaptive Directional Microphones | Allows the hearing device to dynamically change directional settings to provide maximum reduction towards the location of the dominant noise source. |
| Listening Memory/ Program | Provides settings designed for a particular listening situation. Most hearing devices have two to four listening memories/ programs (e.g. listening in noise, telephone use, etc.). Changing programs or memories is done by pressing a button on the hearing device or with a remote control. Some hearing devices have a “Universal” listening memory that works well in a variety of situations and automatically adapts without having to push a button. Multiple listening memories are not available in some smaller models due to space limitations. |
| Wireless Connectivity | This broad term can refer to many different features: communication between hearing devices (‘binaural coordination’), communication between hearing devices and external audio sources (e.g. mobile phones, TVs, etc.), the ability to control devices remotely (‘remote control’), and the ability for hearing care professionals to program devices without wires. Wireless connectivity features are available for select products and models. |
| Open Fit | A style designed to keep the ear canal as open as possible to prevent the occluded – or ‘stuffed up’ – feeling associated with wearing a hearing device. This can be done with large vents (e.g. custom devices or earmolds for behind-the-ear style instruments) or by moving the majority of the hearing device components behind the ear, leaving the ear canal as open as possible (e.g. thin tube behind-the-ear or receiver-in-the-canal style devices). This style is well suited for those with Mild to Moderate hearing loss. |
| Telecoil | Transmits electromagnetic signals from the handset of a telephone to the hearing device. Because the sound is transmitted as an electromagnetic signal, telecoils can help prevent feedback. Telecoils are not available in some smaller models due to space limitations. |
| Volume Control | Allows you to adjust the volume manually using a control on the hearing aid. Volume controls are not available on some smaller models due to space limitations. |
| Remote Control | Allows you to adjust the volume and memory/program selection without touching the hearing device. Remote controls are available for select products and models. |
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A digital hearing aid is the right choice provided you can afford it. The next choice should be a very well- programmed analogue hearing aid followed by the conventional non-programmable analogue hearing aids. The term “programmable” means that the amplification characteristics can be adjusted according to the hearing loss of the person for different types of sound. If this adjustment can be done through the computer, the hearing aid is called “digitally programmable”. In 100% digital hearing aids, the amplification can be programmed through a computer and the amplification of sound is done by a digital amplifier, whereas in the digitally programmable analogue hearing aids, the amplification can be programmed by the computer but the sound is amplified by an analogue amplifier. However, if you have a profound i.e. near total deafness with low speech discrimination scores, the sophisticated high-priced digital hearing aids may not be the correct choice for you as you will not be able to utilise the advantages of the digital hearing aids that you are paying for. A high powered (technically termed as strong-class) conventional hearing aid will be adequate to provide the limited benefit that you will derive from the hearing aid. An honest and ethical hearing aid dispenser will be the right person to guide you on this.
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The figure below summarises how sound amplification differ in analog and digital hearing aid:
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What is the difference between analog and digital hearing aids?
Analog hearing aids make continuous sound waves louder. These hearing aids essentially amplify all sounds (e.g., speech and noise) in the same way. Some analog hearing aids are programmable. They have a microchip which allows the aid to have settings programmed for different listening environments, such as in a quiet place, like at a library, or in a noisy place like in a restaurant, or in a large area like a soccer field. The analog programmable hearing aids can store multiple programs for the various environments. As the listening environment changes, hearing aid settings may be changed by pushing a button on the hearing aid. Analog hearing aids are becoming less and less common. Digital hearing aids have all the features of analog programmable aids, but they convert sound waves into digital signals and produce an exact duplication of sound. Computer chips in digital hearing aids analyze speech and other environmental sounds. The digital hearing aids allow for more complex processing of sound during the amplification process which may improve their performance in certain situations (for example, background noise and whistle reduction). They also have greater flexibility in hearing aid programming so that the sound they transmit can be matched to the needs for a specific pattern of hearing loss. Digital hearing aids also provide multiple program memories. Most individuals who seek hearing help are offered a choice of only digital technology these days.
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Digital hearing aids can cost twice as much as analog ones, but are they worth it?
That’s obviously a very subjective question. To some people, the very discreet nature of a CIC hearing aid is the most important consideration, irrespective of whether it is analog or digital and even if a larger, more intrusive BTE hearing aid would provide better performance. But comparing like for like, analog for digital, which gives the best overall performance in varied listening environments?
Various studies have been done:
•In 1999 Professor Stig Arlinger (one of the pioneers of digital hearing aids) and Erica Billermark of Linköping University studied about 30 people who had switched to digital hearing aids one year before. They found people used their hearing aids twice as much compared to their previous analog aids and their ability to recognize speech gradually improved by up to 25 percent.
• In 2001, David H. Kirkwood noted that “More than three-quarters of respondents to the [Hearing] Journal’s eighth annual dispenser survey reported that their patients were more satisfied with digital signal processing (DSP) instruments than with other advanced non-digital hearing aids,” with high satisfaction on sound quality, understanding speech in noisy environments, listening comfort, and preventing feedback.
•In 2003, Donald Schum and Randi Pogash did a blind comparison (in which patients had to test different aids without knowing which was which) and found 74 percent preferred second-generation digital aids to less advanced digital or analog ones.
• In 2005, Sergei Kochkin of the Better Hearing Institute compared customer satisfaction with digital and analog aids and found a preference for digital in almost every respect, including overall customer satisfaction (77% / 66%), clearness of tone (80% / 68%), ability to hear soft sounds (70% / 56%), feedback (63% / 46%), use in noisy situations (57% / 42%), and almost every type of listening environment.
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Hearing aid technology has progressed dramatically over the past 10 years. The introduction of digital signal processing (DSP) into hearing aids in 1996 allowed advanced signal processing algorithms to be implemented. In 2005, 93% of the hearing aids sold in the United States contained DSP technology. More than half of those hearing aids included directional microphones and providing verifiable improvements to speech understanding in noise. Open-canal products have increased in popularity because feedback cancellation allowed for of improved comfort and the elimination of occlusion problems, even though the amount of gain provided by these devices is limited by the acoustics of the design.
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Basically, the modern trends in DHA are aimed at:
•creation of waterproof devices;
•making ITE models smaller and lighter;
•Introduction of non-trivial solutions (for example, in models Alera of ReSound company the external microphone is located in the auricle, for the implementation of the natural abilities of the person to focus and strengthen the sound);
•improving the electronics and sound processing algorithms.
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CROS (contralateral routing of signals) and BiCROS hearing aids:
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CROS hearing aids are suitable if you have hearing in one ear only. They pick up sounds from the side with no hearing and transmit it to your better ear. BiCROS aids amplify sound from both sides and feed it into the ear that has better hearing. Audiologists traditionally fitted CROS or BiCROS hearing aids on spectacles to hide all the wiring. However, thanks to today’s wireless technology, this is no longer necessary. CROS hearing aids are recommended for people who only have hearing in one ear. They work by picking up sounds from the side that doesn’t have hearing and transmitting them to the ear that’s able to hear. The sound is sometimes transmitted through wires, although wireless models are available. BiCROS hearing aids work in a similar way to CROS hearing aids, but they amplify the noise entering the ear that’s able to hear. They’re useful for people who don’t have any hearing in one ear, with some hearing loss in the other ear.
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Using this technology, a hearing aid-like device on the user’s deaf side uses its microphone to pick up sound from that side and sends it to another instrument at the better ear. The sound is then inserted into the good ear. The CROS implementation is for a user who has relatively normal hearing in the good side and has hearing that can’t be aided on the bad side. The receiving BTE device on the bad side transmits the sound to a device on the good side. The user hears the amplified sound from the bad side in their good ear. The users hears the sound from the good side naturally in their good ear, without amplification. The BiCROS implementation is for a user with little or no hearing on one side and with some hearing loss in their better ear. It works just like the CROS implementation, except that the device on the good side is actually a fully capable hearing aid for hearing sounds from the good side that is also capable of receiving the sound transmitted from the CROS aid on the other side. Transmission in a CROS or BiCROS configuration can be via wire around the back of the neck or wirelessly via radio. The main advantages of CROS technology are: you can hear sounds coming from your deaf side better (even though you’re hearing them in your better ear, and 2) you can get some cues about the location of the sound. Primary disadvantages are: 1) the extra sound from the bad side may, at times, interfere with your ability to understand what you’re hearing from your good side, and 2) CROS technology certainly can’t restore natural localization and noise reduction, since that requires two ears, and CROS only inserts sound into one ear. CROS technology may be a help for some people with unilateral hearing. BiCROS may help those whose good ear is also somewhat impaired.
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Note:
Remember whatever we have discussed in technology of hearing aid whether digital or analog is about conventional air conduction hearing aid. Bone conduction hearing aid will be discussed later on.
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HATS:
What are hearing assistive technology systems (HATS)?
Hearing assistive technology systems (HATS) are devices that can help you function better in your day-to-day communication situations. HATS can be used with or without hearing aids or cochlear implants to make hearing easier—and thereby reduce stress and fatigue.
Hearing aids + HATS = better listening and better communication!
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The following situations are difficult for all listeners, but they are especially difficult for people with hearing loss:
1. Distance between the listener and the sound source:
The farther away you are from a speaker, of course, the harder it is to hear the speaker. This is because the intensity, or loudness, of a sound fades rapidly as it travels over distance. So, while you may have no difficulty hearing someone in close range, you may have considerable difficulty hearing the same person across the room.
2. Competing noise in the environment:
Most rooms have background noise that competes with the spoken message or sound we want to hear. Examples of background noise include ventilation systems, others talking, paper shuffling, computers, radios, TVs, outside traffic or construction, and activities in adjacent rooms. Background noise can make hearing very challenging. For optimum hearing, speech should be at least 20–25 decibels (dB) louder than any competing noise. This is called the signal-to-noise ratio, or S/N ratio.
3. Poor room acoustics/reverberation:
A room’s acoustics are the quality of sound maintained in the room, and they can affect your ability to hear effectively. Sound waves bounce off hard surfaces like windows, walls, and hard floors. This creates sound reflections and echoes (called “reverberation”). The result of excess reverberation is distorted speech. Large gyms, cathedrals, and open marble lobbies quickly come to mind when we think about reverberation. Reverberation also can occur in smaller spaces such as classrooms. We’ve all experienced how much easier it is to hear in rooms that are carpeted and have upholstered furniture (which absorbs noise) than in empty rooms with tile or cement floors.
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The figures above illustrate that sound pressure decreases markedly over distance, while background noise tends to be more constant. The degradation of sound pressure obeys inverse-square law so that sound intensity is inversely proportional to the square of the distance from the source of sound.
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There are three types of HATS, depending on the type of wave that is generated: FM radiowaves, infrared lightwaves, and magnetic inductive energy:
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1. FM (frequency modulated) Systems:
Hearing aids keep getting better. But hearing aids alone do not make listening easier in all situations. The things that can interfere with listening are background noises, distance from a sound and reverberation or echo. People with normal hearing also have problems hearing when listening from a distance. Background noise and echo are a problem for everyone. People with hearing loss have even more problems than people with normal hearing when trying to listen in these difficult situations. Some examples are listening in the car, at day care, playing outside or at the park, and watching television. The best way to hear better in all of these situations is to remove background noise and to have a short distance between the speaker and the listener. Background noises usually cannot be removed or changed. Because of this, there are devices designed to make it easier to hear in difficult situations. The device used most often today is the Frequency Modulated or FM system.
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The Parts of an FM System:
Microphones:
FM systems work like small radio stations. There is a small radio transmitter attached to a microphone and a small radio receiver. A parent or teacher wears the FM transmitter and microphone while the child wears the FM receiver.
Receivers:
The FM transmitter sends a low-power radio signal to the FM receiver. The receiver needs to be within about 50 feet of the transmitter to pick up the signal. The FM receiver gets the signal from the microphone and sends it to a personal hearing aid, cochlear implant processor or other device. Listening to the FM signal is like listening to someone talking from only 3 or 6 inches away.
The best method to improve the signal-to-noise ratio is an FM system, which locates the microphone near the mouth of the desired talker. FM systems have been found to provide a better signal to noise ratio even at larger speaker-to-talker distances in simulated testing conditions.
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2. Infrared Light system uses the same type of signal as your TV’s remote control. These invisible light waves fall just below the visible spectrum. The receiver, often a headphone, has a little “window” that catches the light waves and converts them back into sound. This window must be accessible to the light. It cannot be covered up or kept out of sight (as can the FM receiver). Large area systems are commonly used in movie theaters. Lightwaves do not penetrate walls so transmitters in adjoining theaters will not interfere with one another. Large area infrared light systems are more difficult to set up than other systems. The transmitters must be set at the correct angle and may require more than one, so the system can be more expensive as well.
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3. The Magnetic or Induction Loop system operates on a basic principle of physics that when electricity runs through a wire, it creates a magnetic field. In the induction loop system, a wire is laid around the perimeter of a room or activity area (like a museum exhibit). The transmitter, instead of sending the sound directly through the air as invisible waves, first pumps it through the wire, creating a magnetic field that fills the area within the perimeter of the wire. This signal can be picked up by a hearing aid with a T-coil or by a portable receiver. Once set up, it is ideal for anyone with a T-coil hearing aid. No additional receiver is necessary. Otherwise, like the other systems, a receiver is required. T-coil is discussed in the following section.
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Features Available in Hearing Aids:
Many hearing aids have optional features that can be built in to assist in different communication situations. Some options are:
1. Directional microphone:
Most people with hearing loss find that trying to follow a conversation in a noisy place can be a tremendous struggle. Logically, most conversations are with people who we are facing, while distracting background noise will come from the sides and behind us. A modern digital hearing aid can actually pinpoint the location of sounds. It does this by using more than one microphone and gauging the difference in time that it takes sounds to reach each microphone even though the microphones are only a few millimetres apart! It will then provide the greatest amplification to sounds coming from in front of the wearer and less amplification to sound coming from the sides and behind. Directional microphones can be extremely beneficial in difficult situations like restaurants and are the greatest factor in improving a wearer’s ability to follow conversations in noisy places. A directional microphone helps you converse in noisy environments by making the audio signal in front of you louder than the noise in the rear or from the sides. Most older hearing aids have only an omnidirectional microphone. An omnidirectional microphone amplifies sounds equally from all directions. In contrast, a directional microphone amplifies sounds from one direction more than sounds from other directions. This means that sounds originating from the direction the system is steered toward are amplified more than sounds coming from other directions. If the desired speech arrives from the direction of steering and the noise is from a different direction, then compared to an omnidirectional microphone, a directional microphone provides a better signal to noise ratio. Improving the signal-to-noise ratio improves speech understanding in noise. Directional microphones have been found to be the second best method to improve the signal-to-noise ratio (the best method was an FM system, which locates the microphone near the mouth of the desired talker). Many hearing aids now have both an omnidirectional and a directional microphone mode. This is because the wearer may not need or desire the noise-reducing properties of the directional microphone in a given situation. Typically, the omnidirectional microphone mode is used in quiet listening situations (e.g. living room) whereas the directional microphone is used in noisy listening situations (e.g. restaurant). The microphone mode is typically selected manually by the wearer. Some hearing aids automatically switch the microphone mode.
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2. T-coil:
T-coil stands for telephone coil or telecoil. It is a tiny coil of wire that fits in the hearing aid or cochlear implant. About 30% of the hearing aids in America contain T-coils. (You have one if your switch has a “T” setting.) It’s a great thing to have because it enhances the clarity of phone conversations and can also help out in certain public settings. When the switch is set to “T”, the microphone is turned off. It’s a principle of physics that whenever current runs through a wire, it generates a magnetic field around the wire. So when current runs through the small speaker in your telephone handset it generates a magnetic field that, in turn, generates (induces) a current in the T-coil of the hearing aid. The signal, which has bypassed the microphone in the hearing aid, is amplified and passed directly into the ear. The signal is very clear and since the microphone is not being used, there is no feedback and no pickup of room noise. This feature can also be used with other hearing assistive technology that is telecoil-compatible. They can be used with telephones, FM systems (with neck loops), and induction loop systems (also called “hearing loops”) that transmit sound to hearing aids from public address systems and TVs. In the UK and the Nordic countries, hearing loops are widely used in churches, shops, railway stations, and other public places. In the U.S.A., telecoils and hearing loops are gradually becoming more common.
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A T-coil consists of a metal core (or rod) around which ultra-fine wire is coiled. T-coils are also called induction coils because when the coil is placed in a magnetic field, an alternating electric current is induced in the wire. The T-coil detects magnetic energy and transduces (converts) it to electrical energy. In the United States, the Telecommunications Industry Association’s TIA-1083 standard, specifies how analog handsets can interact with telecoil devices, to ensure the optimal performance. Although T-coils are effectively a wide-band receiver, interference is unusual in most hearing loop situations. Interference can manifest as a buzzing sound, which varies in volume depending on the distance the wearer is from the source. Sources are electromagnetic fields, such as CRT computer monitors, older fluorescent lighting, some dimmer switches, many household electrical appliances and airplanes.
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Figure below shows a sign on a train station explaining people that the public announcement system uses a “Hearing Induction Loop” (audio induction loop). Hearing aid users can use a telecoil (T) switch to hear announcements directly through their hearing aid receiver.
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Say you were trying to listen to a lecturer using a hearing aid. You notice the hearing loop sign and switch your aid to T-mode. The lecturer begins speaking into a microphone hooked up to an amplifier. This amplifier connects not just to the speakers, but also to the hearing loop, transmitting an electromagnetic field. The hearing aid converts the electromagnetic field into an electrical signal, and through a processor, back into the voice of the lecturer. Suddenly the lecturer sounds loud and clear rather than muffled and washed out by other students’ conversations. Many churches do so because they know it’s good for their members. You can also use a telecoil to hear the TV, telephones, in meetings, in noisy restaurants, or in a noisy car if you supply the magnetic signal using an Assistive Listening Device (ALD) coupled with a room loop, a neckloop or silhouettes. One major advantage of a using a telecoil is that you can turn off your normal hearing aid microphone, and thus, not hear all the noise that might be around you. You only hear the magnetic signal, which doesn’t include all that noise, so you can hear it a lot better.
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M, T, and MT switch on hearing aid:
It allows hearing impaired people to hear more clearly. Most hearing aids have a ‘T’ or ‘MT’ switch which allows them to pick up the better sound from the wire. The hearing aid converts this signal into a sound suited to its user’s specific hearing requirements. Any hearing impaired person positioned within or near the wire and switch ‘T’ or ‘MT’ on hearing aid to the correct position, allowing to receive the sound from the wire. No matter how high the volume is, there will be no whistles sounds in when using in ‘T’ or ‘MT’ position.
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While Hearing Loops can be used one-on-one such as: a neck loop attached to a Walkman or telephone, or a home loop attached to a TV, they are the technology of choice when many people need to listen in a large venue with a sound system such as a house of worship, conference room, or auditorium. The loop signal is universally compatible (around the world) with all T-Coil equipped hearing aids. A Hearing Loop installed to the IEC standard will have excellent frequency response from 100 to 5 kHz, often beyond what most hearing aids are capable of amplifying. T-coils get their power from the loop signal and draw no, or nearly negligible power from the battery. Because hearing loops get their signal directly from the source (the speaker’s microphone or other audio output) there is no need to process the sound so there is no need for the loop to use digital processing, and take advantage of any digital processing that is being done by the hearing aid itself. And last but not least, in a looped venue the person with hearing difficulties need not self-identify as having difficulty understanding the spoken word, nor wear listening devices with unsightly and unhygienic headphones – all they need to do is discretely push the button on the hearing devices they are wearing to activate the telecoils.
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3. Direct audio input (DAI):
Many people who wear hearing aids every day are not aware that they could plug their hearing aids into a headphone socket. The sound quality is fantastic and it is particularly good for listening to music. The method of connecting into a headphone socket is referred to as ‘direct input’ and uses a ‘direct input’ lead and hearing aid connection known as a ‘hearing aid direct input shoe’. The majority of behind-the-ear hearing aids have a direct input facility. I would suggest asking your audiologist if your hearing aid has a direct input facility and if it has been activated. If your direct input is not turned on, it will take your audiologist a matter of moments to activate the relevant program. Direct audio input (DAI) allows the hearing aid to be directly connected to an external audio source like a CD player or an assistive listening device (ALD). By its very nature, DAI is susceptible to far less electromagnetic interference, and yields a better quality audio signal as opposed to using a T-coil with standard headphones. Some hearing aids have a direct audio input capability that allows you to plug in a remote microphone or an FM assistive listening system. This enables you to connect directly to a TV or other device, such as your computer, CD player, MP3 player, or radio. As you have noticed, your hearing aid doesn’t have a socket on it to allow you to connect in a cable. This is because the hearing aid would need to be larger to fit a socket plus ‘holes’ in the hearing aid itself would attract dirt, dust and condensation, none of which are good for hearing aids. Instead, you use a ‘shoe’ as a connecting interface between the hearing aid and the cable. The shoe clips onto the bottom of your hearing aid and has a small three-pin socket on the bottom which allows you to plug in a direct input lead. The direct input lead can then be connected to your audio source (iPod, MP3, tablet, TV, radio, CD player etc.).
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Hearing aid connectivity:
Hearing aid connectivity could be wired and wireless. Direct audio input is a type of wired connectivity. T-coil and Bluetooth are wireless connectivity. Wireless connectivity can refer to many different features: communication between hearing devices (‘binaural coordination’), communication between hearing devices and external audio sources (e.g. mobile phones, TVs, etc.), the ability to control devices remotely (‘remote control’), and the ability for hearing care professionals to program devices without wires. Wireless connectivity features are available for select products and models.
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Familiar Wireless Connections:
Wireless connectivity has been around for many years. Examples in everyday life include TV remote control devices and garage openers. Even in the hearing health-related field, wireless transmission devices have been available for many years through what is referred to as hearing assistive technology (HAT), such as a hearing loop, FM, or infrared systems.
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Bluetooth:
The 1980s saw much work devoted to developing wireless technology that could be standardized across the communications industry. In 1994, telecom vendor Ericsson invented what came to be known as Bluetooth® wireless technology. Bluetooth® is a standard that is managed by the Bluetooth Special Interest Group (SIG) which was formed in 1998, and which now has more than 25,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. Bluetooth® (BT) uses radio waves and operates within the 2.4 GHz range (i.e., in an ultra-high frequency range and consists of extremely shortwave lengths). BT uses an agreed upon standard transmission protocol. Within this framework, one can have a master BT device that can communicate with a maximum of seven devices. Typically, the master BT device is paired with another BT device. The specific bonding that is done is extremely secure such that no other device can pick up signals from either of these two devices—thus ensuring privacy. The typical transmission distance for BT devices is 15 to 30 feet. Please note that just because you might observe that a device is BT does not mean it can be paired to communicate with any BT device. For example, a BT garage opener can’t be paired with a BT cell phone as they have different transmission/reception codes.
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Binaural synchronization using NFMI:
The BT concept was intriguing to hearing aid manufacturers as they saw this as an opportunity to directly pair hearing aids with electronic devices—such as the TV, radio, phone, etc.—while overcoming some of the disadvantages inherent in typical hearing aid use. However, traditional BT technology requires a great deal of processing, resulting in significant battery drainage in the small hearing aid battery. Consequently, for a long time BT technology was unable to be incorporated into hearing aids. To address this, hearing aid manufacturers were clever and began to adopt alternate strategies to link hearing aids with outside sound sources as well as to each other. One of the first wireless connectivity adaptations was binaural synchronization using NFMI, a feature that allows hearing aids to communicate wirelessly with each other via data codes. This feature, incorporated by all major hearing aid manufacturers, allows for the synchronization in binaural hearing aids of aspects such as volume control and program changes. Another wireless connectivity feature is binaural streaming. In this case, the full audio stream is shared between the hearing aids. In order for this to be accomplished, each hearing aid has internal hardware that allows it to communicate with the other hearing aid via radio wave transmission. Prior to this ability to communicate wirelessly to each other, hearing aids adjusted internal parameters independently of each other, and consequently could be using different digital processing schemes or different timing characteristics. Binaural streaming allows for the hearing aid algorithms to be linked so that the two hearing aids can carry out the same signal processing paradigms at the same time. For example, in the presence of noise, both hearing aids can transition synchronously from the omnidirectional mode (used in quiet settings) to the directional mode (amplifying more from where the speech signal is coming from and attenuating background noise emanating from a different direction). This ability to synchronize as well as stream a full audio signal between the two hearing aids allows for an even greater benefit of directionality, as it incorporates not just the two microphones per ear (i.e., both microphones in each hearing aid), but a network of four microphones across the two hearing aids. This creates a more advanced beam of the target signal, and greater speech understanding in the presence of noise as well as decreased listening effort. Another application of binaural synchronization/streaming is the hearing aid user’s ability to listen to a telephone conversation in both ears. In this case, the telephone signal is routed from the hearing aid adjacent to the phone to the hearing aid on the opposite side. This not only allows for the unique ability to hear telephone conversation in both ears, but the possibility (depending on how the hearing aids have been set) to turn off the microphone of the second hearing aid, thus, reducing background noise in the opposite hearing aid and making the overall phone listening experience much easier. Other benefits of binaural synchronization/streaming include enhanced comfort and listening in windy situations as well as enhanced reception of the talker when the latter is seated in the back of the car and the hearing aid user is in the front seat and facing the opposite direction. In the latter situation, the hearing aids might be able to adjust simultaneously to enhance reception for the speaker from the rear, while minimizing car noise arising from in front.
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Bluetooth hearing aids:
Hearing aids with Bluetooth connectivity make it possible to stay connected to a number of electronic devices, including phones, televisions and tablets. Hearing aids of the past often limited the wearer’s access to many personal audio devices such as mobile phones and music players. For example, in order to use a music player while jogging, the hearing aid wearer had to remove his hearing aids to accommodate a pair of earbuds. However, today’s wireless hearing aids make it possible for the hearing impaired individual to connect with personal electronic devices and stream signals directly to the hearing aid through the use of Bluetooth.
Are there Bluetooth hearing aids?
A full implementation of the Bluetooth standard requires a greater power supply than can be generated within the small footprint of a hearing aid battery, so actual “Bluetooth hearing aids” are not currently on the market. However, manufacturers of wireless hearing aids long ago created a clever solution for accessing this prevalent wireless standard. Wireless hearing aids can use compatible assistive listening devices, often called streamers, to provide a communication link between the wireless technology in the hearing aids and any Bluetooth-enabled device. More recently, Apple has patented a specific Bluetooth connectivity with hearing aids so that certain hearing aids can communicate directly with the iOS platform that runs iPhone, iPad and iPod Touch devices. This technology is designed to allow the devices direct connection without extreme stress on the battery power. Several hearing aid manufacturers have released hearing aids that implement this Bluetooth technology, marketed as Made for iPhone™.
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Hearing Aids and External Technology:
In addition to wireless connectivity between hearing aids, hearing aids can now connect wirelessly to external technology—such as cell phones, television, etc. As mentioned earlier, for a long time BT transmission could not be incorporated into hearing aids because of its significant processing requirements. To overcome this limitation, hearing aid manufacturers developed alternative transmission schemes. One such technique involved the incorporation of an intermediary BT device—usually worn around the neck. The larger size of these intermediary devices and, in turn, larger batteries— as compared to hearing aids—allowed for the incorporation of BT processing. In this adaptation, the intermediary BT device is paired with an electronic device (cell phone, MP3 player, TV), be it one that has BT built into the device or one in which a BT transmitter is connected to the device. An advantage to this strategy is that much of the power consumption required for wireless streaming can be absorbed by the battery in the intermediary device. Once the electronic device and intermediary have been paired, the signal can be transmitted via BT from the sound source to the intermediary, and from there to the hearing aid via another form of signal transmission. The latter transformation is required because traditional BT does not allow for transmission around and across the head.
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Non-Bluetooth connectivity:
Two other forms of radio frequency (RF) transmission were implemented for the purpose of communicating to and between hearing aids. One form is known as Near-Field Magnetic Induction (NFMI). The most common approach to wireless communication in hearing aids is near-field magnetic induction (NFMI). Wireless communication through NFMI uses technology similar to a traditional telecoil. The range of frequencies used in hearing aids for NFMI data transmission typically falls between 3 and 15 MHz. NFMI is designed to contain transmission energy within a localized magnetic field. The magnetic field energy resonates around the communication system, consequently, the transmission distance of NFMI is extremely limited—no more than one meter. This form of transmission can successfully be used for binaural processing in hearing aids, or, for transmission from the BT intermediary device to the hearing aids. Since the transmission distance is so limited, it requires that the intermediary device to be close by—such as wearing it on the neck or perhaps as a remote device on the arm. Figure A below illustrates the stages of wireless audio streaming for near-field (NFMI) wireless streaming. A second form of transmission involves a 900 MHz audio stream that can transmit up to 15 feet (and is often referred to as far-field wireless transmission), yet, its properties still allow for hearing aid-to-hearing aid transmission around and across the head. The audio stream is converted to a 900 MHz signal/emitted from a proprietary transmitter connected to the electronic media device, and, in turn, transmitted to the hearing aids which it has previously been paired. Figure B below illustrates transmission of far-field wireless signals, one of which consists of 900 MHz signals, from the sound source to the hearing aids. Figure B below also illustrates direct BT transmission from various electronic devices to a hearing aid. However unlike the other far-field transmission hearing aid systems that rely on 900 MHz transmission, hearing aids that incorporate BT 4.0 do not require the purchase of proprietary transmitters to be connected to electronic devices.
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In fact, hearing aids have been using NFMI for decades, to synchronize and control the signal quality of both units by pushing buttons on either one of the ear’s units to control both. Many modern hearing aids have added Bluetooth, in order to stream music from smartphones in addition to their normal hearing aid function.
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Continued Evolution of Bluetooth Transmission:
Recently, the communication industry developed a new Bluetooth standard (version 4.0) which has a low-energy option, one which has significantly less processing requirement—such that it no longer poses a significant hearing aid battery drain. Two hearing aid manufacturers (Starkey, ReSound) have incorporated chips with BT 4.0—along with their own proprietary 2.4 GHz transmission codes—into some of their hearing aid lines.
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BT 4.0 has enabled hearing aids to communicate directly with cell phones, as well as with other BT enabled devices such as an iPad or iPod, without the need for an intermediary device. It is expected that other hearing aid manufacturers will also implement this mode of transmission within their hearing aid lines.
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Smart Phones now performing the task of wireless streamers:
Up until 2014, someone wanting to connect their hearing aids wireless to their phone, tablet or music player would have been required to purchase an optional wireless streamer with their hearing aids. Now, since the launch of the ground-breaking ReSound LiNX, it is possible to have your smartphone (iPhone) manage these tasks. The GN ReSound LiNX™ is the first hearing aid to earn the “made for iPhone” label. This means that the audio from an iPhone can be directly transmitted to both hearing aids without the use of a streamer. So wearers can manage streaming and functions such as volume and program settings from an easy to use App on their iPhone or iPad. Initially, BT cell phone pairing was available with only iPhones, but recently Starkey added android phone capability. It should be noted that although hearing aids with BT 4.0 can be paired with both iPhones and android phones, at the present time there is a significant difference. Hearing aids paired with the iPhone via BT can receive both audio (such as music) and data streams, while pairing with android phones allows only for data stream transmission. Therefore, android cell phones presently can only serve as remote control/hearing aid programming units (since these aspects rely only on data streams), but they can’t be used to directly stream audio to the hearing aids. Hence, an intermediary device is required if audio streams are to be transmitted from the android phone to the hearing aid. As technology advances even android phones would directly stream audio into hearing aids.
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Advantages of this mode of wireless connectivity are that:
• they do not require the purchase of proprietary transmitters (cutting down expenses),
• they do not require any worn intermediary device,
• they are not subject to electromagnetic field interference from extraneous electric components such as might occur when using the t-coil of a hearing aid, and,
• when paired with iPhones, they can receive a high quality audio signal directly from the source (be it a cell phone, iPod, or iPad).
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IRIS—for long distance wireless transmission:
The 900-MHz implementation of wireless hearing aids features a wireless technology developed by Starkey Laboratories, called Iris. The term calls to mind the eye and connotes the ability to transmit and receive data across a long distance. The Iris wireless system is designed to offer long-distance audio streaming, wireless programming, and binaural signal processing, without need for an intermediate relay. For wireless audio streaming, a wireless media device, SURFLink Media, connects to the patient’s television or other media source and streams stereo audio directly to the hearing aids—up to 20 feet away. When a hearing aid enters the range of the media device, it can be programmed to detect that streaming device automatically and accept the new audio input. For instance, if a patient returned home from work, her hearing aids could immediately begin streaming audio from the television when she entered the front door; or the option to manually initiate audio streaming is also available. An unlimited number of hearing aids can access a single SURFLink media device, without the need for pairing. If used in a group living environment, everyone wearing hearing aids with the Iris wireless technology can access the television’s audio by simply walking into the same room as the television. Disconnecting from the audio stream is as easy as leaving the room or tapping the memory button on the hearing aid.
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Benefits of Hearing Aid Wireless Connectivity:
In addition to the binaural synchronization/streaming, there are numerous advantages of hearing aid wireless connectivity:
• Remote control of one’s hearing aids, either via BT (e.g., via a cell phone) or an intermediary device (streamer).
This is especially useful if: the hearing aids are too small to accommodate external controls; or, an individual has dexterity issues or difficulty lifting their arms to touch the button on the hearing aid
• Can be paired to various hearing-related applications that one can download to a cell phone or iPad/tablet
• Ability to connect wirelessly to the cell phone for ease of phone calls—including the ability to make hands-free phone calls
• Wireless connectivity to cell phones, iPad/tablets, MP3 players, computers can optimize the listening experience to music and videos
• The use of remote BT microphones that can be paired with an intermediary device or directly with a BT-enabled hearing aid, can enable similar functionality to an FM system such as: a) clipping a microphone to the clothing of the talker—be it a lecturer or passenger in a car; b) placing the microphone on a table in a noisy restaurant; or c) a coach communicating with an athlete who has a hearing loss during the course of a game. However, the effective listening distance is much less than with traditional FM systems (30 feet versus 200 or more feet).
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What about Hearing Aids without Wireless Connectivity?
There are many people who do not have hearing aids with wireless connectivity. ClearSounds has developed the Quattro 4.0 solution to meet the various hearing needs of these individuals. The Quattro is a BT-enabled device that can be paired with multiple BT devices, and, in turn, transmit the audio stream via a neckloop to one’s hearing aids, or even a headset for those who do not have hearing aids (such as individuals who have normal hearing but have a central auditory processing disorder). Similar to the hearing aids discussed above, the Quattro can be paired with a cell phone or to various electronic devices (such as a TV or computer) via ClearSounds’ BT transmitters connected to the output of these devices and paired with the Quattro.
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Even with the advent of such remarkable technology as wireless digital connectivity, t-coils still play an important role in assisting individuals with hearing loss in difficult listening settings such as places of worship, (movie) theaters, libraries, etc., through their ability to interface with hearing loops, or with neckloops used with FM or Infrared systems. There are also intermediary devices that have built-in t-coils, thus, allowing an individual to wear very small sized hearing aids, yet, still having t-coil connectivity. It is truly a remarkable time for those with hearing loss. Never would have they imagined that they would actually be able to hear better in certain settings than their normal hearing family, friends and colleagues. To be able to hear the phone in both ears, listen to the television at settings too soft for even normal hearing individuals, hear someone speak softly at 30 feet away, and understand what someone is saying in a noisy restaurant while normal hearing individuals might be struggling, is truly remarkable.
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Ready to buy new hearing aids?
Be sure it includes Bluetooth as well as Telecoil Wireless Technology. There is some confusion among hearing professionals regarding Blue Tooth and Hearing Induction Loops. The misunderstanding that is that Bluetooth and hearing loop technology are mutually exclusive when in fact they complement each other and have tremendous capability to improve quality of life for the user. Hearing aid users can take advantage of both: many benefits from Bluetooth wireless technology watching TV at home while using their cellphone or on Sunday morning when they happily switch to their telecoil in church.
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Telecoil vs. wireless digital connectivity:
Telecoils have been used in hearing aids for a long time as wireless non-digital connectivity. The main advantages of telecoils include blocking environmental noise and improving the signal to noise ratio – all without the risk of acoustic feedback. One of the most common applications of telecoil use is for the telephone. By receiving the electromagnetic signal directly from the telephone handset without the activation of the hearing aid microphone, there is no chance of feedback. At the same time, this transmission reduces the level of environment noise for the listener, and makes it easier for the user to concentrate on the conversation. Telecoils are also advantageous for use with loop systems in large, public venues where listening may be exceptionally difficult. These environments are typically characterized by background noise, reverberation, and significant distance of the listener from the sound source. When a loop system is installed in a venue such as a church or theater, the broadcasted sound will be sent directly to the hearing aids via the telecoil, thereby improving the signal to noise ratio. Telecoils are advantageous in these looping environments due to their ease of use, with no pairing required to tap into the broadcasted signal. The telecoil program can be activated by a simple press of the program button or by switching to the telecoil (T) setting. Adding to the attractiveness of telecoils is their relatively low cost. Like most kinds of technology, there are situations which may be more advantageous or disadvantageous for telecoil use. First, telecoils are optimized for speech signals, so music may sound distorted. This is due to the fact that music is often comprised of higher frequencies than the telecoil bandwidth can handle. Second, the orientation of the telecoil is important to achieve a good signal with the telephone or in a looping environment. Telecoils obtain the best signal when they are oriented at a 90 degree angle from the loop or coil. Thus, telecoils are best oriented horizontally for telephone use and vertically for looping systems. Depending on the orientation of the telecoil in the hearing aid, the user may need to position the telephone handset differently in order to get the best signal. Third, the use of telecoils in venues necessitates installation of a fixed loop in that space. The loop cannot be easily moved to other locations, and the signal strength is limited to the confines of the loop. For example, if the loop is installed for a TV in the living room, when the user leaves the living room the signal strength will decrease dramatically. Lastly, loop systems may experience interference from other electronics, which can be perceived by the hearing aid user as a buzzing sound.
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In recent years, digital wireless hearing aids and accessories have become more and more popular. Bluetooth 4.0, Bluetooth streamer or smart phone working as streamer are examples of wireless digital connectivity. One of the main advantages of digital wireless technology is that it renders more options for phone use than were previously available. Digital wireless communication between hearing aids in a binaural pair has led to features such as ReSound’s Comfort Phone, which reduces the hearing aid gain for the non-phone ear. This automatically decreases ambient noise, making it easier for the user to focus on the phone conversation. Another advantage of digital wireless technology is the possibility of streaming the phone signal to both hearing aids simultaneously. Recent research indicates that binaural streaming of the phone signal results in better speech recognition performance and improved listening ease and comfort, as compared to monaural listening via telecoil. Digital wireless technology enables hands-free communication abilities on the phone, and ensures privacy due to the precise pairing protocol necessary for connection to the hearing aids. In addition, the wider frequency response and low likelihood of interference enables digital wireless hearing aid accessories to provide excellent sound quality for both speech and music. Binaural streaming of music from the phone directly to the user’s hearing aids is a reality with this technology. Disadvantages of digital wireless technology include its relatively higher cost as compared to telecoil technology. Further, there is no common standard for digital wireless transmission in large public venues, as different hearing aid manufacturers may use different digital wireless technology. Finally, the accessories need to be paired to the hearing aids, which may cause a certain degree of inconvenience.
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Both telecoil and digital wireless technology have distinct advantages and disadvantages. In certain situations, one type of technology will be preferred. Fortunately, telecoil and digital wireless technology are not mutually exclusive. Both types of wireless technology can be incorporated in most modern hearing aids, allowing the user to more fully enjoy the benefits of improved signal to noise ratio in various settings.
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Wireless Connectivity with SoundGate:
A hearing instrument isn’t the only important instrument in your life. Mobile phones, MP3 players, PCs, and television are likely part of your everyday routine. SoundGate helps you hear them all—right through your hearing aids. Your hearing instruments already help you hear sounds coming from different sources. But imagine if your favorite music wasn’t playing from 10 feet away — it’s streaming directly into your hearing aids. That’s the concept behind the SoundGate device. It’s like having personal speakers for your ears. The heart of our wireless system, SoundGate is the digital “go-between” connecting external devices with your hearing instruments. It’s a small, portable accessory (streamer) that turns your hearing aids into personal “speakers” for the TV, your phone, or in assistive listening environments. SoundGate allows you to connect with any device that’s already Bluetooth® enabled – like your mobile phone or a digital audio player. But you can connect to other audio sources that aren’t Bluetooth®-compatible using SoundGate and optional accessories. It’s possible to change programs and volume levels with a discrete click of a button instead of reaching for the controls on your hearing aids themselves.
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Wireless hearing aids:
Recent digital hearing aids include wireless hearing aids. One hearing aid can transmit to the other side so that pressing one aid’s program button simultaneously changes the other aid, so that both aids change background settings simultaneously. FM listening systems are now emerging with wireless receivers integrated with the use of hearing aids. A separate wireless microphone can be given to a partner to wear in a restaurant, in the car, during leisure time, in the shopping mall, at lectures, or during religious services. The voice is transmitted wirelessly to the hearing aids eliminating the effects of distance and background noise. FM systems have shown to give the best speech understanding in noise of all available technologies. FM systems can also be hooked up to a TV or a stereo. 2.4 gigahertz Bluetooth connectivity is the most recent innovation in wireless interfacing for hearing instruments to audio sources such as TV streamers or Bluetooth enabled mobile phones. Current hearing aids generally do not stream directly via Bluetooth but rather do so through a secondary streaming device (usually worn around the neck or in a pocket), this Bluetooth enabled secondary device then streams wirelessly to the hearing aid but can only do so over a short distance. This technology can be applied to ready-to-wear devices (BTE, Mini BTE, RIE, etc.) or to custom made devices that fit directly into the ear. In developed countries FM systems are considered a cornerstone in the treatment of hearing loss in children. More and more adults discover the benefits of wireless FM systems as well, especially since transmitters with different microphone settings and Bluetooth for wireless cell phone communication have become available. Many theatres and lecture halls are now equipped with assistive listening systems that transmit the sound directly from the stage; audience members can borrow suitable receivers and hear the program without background noise. In some theatres and churches FM transmitters are available that work with the personal FM receivers of hearing instruments.
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Advantages of wireless hearing aids:
Sound quality:
Wireless technology allows two hearing aids to operate together as one complete system, instead of acting as two independent devices. The sound input to both hearing aids is shared and decisions about the digital sound processing are based on the combined information. For example, if one hearing aid is being triggered for directional mode, both hearing aids would likely switch into that mode at the same time. The data transfer rates for wireless hearing aids are measured in nanoseconds, which is much faster than human brain can detect. For the wearer, the adjustments are perceived in real time. Sound processing is therefore synchronized between the two hearing aids, thus improving sound quality for the wearer.
Localization:
You were born with two ears for a reason. Binaural hearing equips us to locate the source of sound quickly because the brain analyzes timing and level differences that are received from each side of the head. Localization is one of the reasons your hearing care professional will recommend two hearing aids to compensate for hearing loss that affects both ears. Traditional hearing aids process sound independently, according to the hearing loss in each ear. This can cause the wearer difficulty in pinpointing the sources of sound because the timing and level differences are often lost. Wireless hearing aids address this problem by working together to compare timing and level differences for sounds received at the microphone of each device, thus preserving the natural localization cues our ears provide.
Convenience:
Wireless capability may also result in hearing aid features that improve convenience. Some wireless hearing aids may be set up so that when a user pushes a program button or changes the volume control on one hearing device, the change is automatically implemented on the other side. Another feature made possible by wireless communication is the selection of a program button in one hearing aid and a volume control in the other hearing aid of the matched set. This arrangement requires less space for buttons on each device and reduces the amount of required changes by half. When the volume or program needs to be adjusted, the user only needs to touch one hearing aid and be confident that the other hearing aid will change automatically to match.
Connectivity:
Wireless hearing aids are often capable of wirelessly communicating with external devices as well as with each other. There are a variety of technologies that make this possible, the most common of which are electromagnetic fields, frequency modulation (FM) and Bluetooth. Some of these technologies have been around awhile, like the use of electromagnetic fields that can be picked up by an antenna in your hearing aid called a telecoil. With the advancements in wireless hearing aids, telecoil can be used to a greater advantage. A telecoil in a wireless hearing aid may be able to pick up the signal from a phone that’s placed near one hearing aid and then stream the signal to the other hearing aid. Not only does this feature allow the wearer to hear the caller in through both hearing aids, it effectively excludes any ambient noise in the room. Electromagnetic fields can also be created in a room by installing what is called an induction loop around the perimeter. Anyone in the room who is wearing an equipped hearing aid can easily switch to telecoil for ease of listening. Many public spaces use this technology to ensure access for all individuals with hearing loss. There are usually headphones provided for those who have difficulty hearing but do not have hearing aids. Traditional FM systems are composed of a transmitter (a microphone) that is worn by the person speaking and a receiver that has to be attached to the hearing aid(s) of the wearer. In wireless hearing aids, the FM receiver may be embedded in the processor so that an external receiver is not needed. With the FM receiver built into many wireless hearing aids, it has become much more convenient to use. An FM transmitter may be carried with you to a business meeting, dinner out with your family or a lecture hall. The transmitter becomes an extension of your hearing aid microphones, vastly improving your ability to hear in many complex listening environments. FM systems are essential in classrooms for children with hearing loss. With a lapel-worn transmitter, the teacher’s voice can be clearly delivered to the child (or children) with hearing aids while the teacher is walking around the room. The Bluetooth standard is a fairly new technology that has the potential to impact hearing aids in a big way. Most wireless hearing aids on the market are able to pair with Bluetooth devices by utilizing an intermediary device. This device, or streamer, can translate the Bluetooth signal into a signal that can be picked up by an FM receiver or telecoil. For example, your wireless hearing aid may be connected to a streamer that is then connected via Bluetooth to your cell phone. When you have a phone call, the streamer would indicate the incoming call and allow you to activate the relay of the audio signal directly to your hearing aid. Introduced in the spring of 2014, the newest Bluetooth-compatible hearing aids are able to directly communicate with Apple’s latest iPhone devices.
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Hearing devices that can pick up wireless signals put us all in touch again, regardless of the means. Wireless transmission of sound data between two hearing aids benefits hearing aid users every day with better sound quality, improved localization, convenience and vastly increased connectivity.
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Synopsis of hearing aid connectivity is depicted in the figure below:
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Connecting to computers for hearing aid users:
Why connect a hearing aid to a computer?
Hearing aid users have accentuated problems when listening to sound from loudspeakers. When using computers there are often even more problems than usual caused by the combination of ‘less than perfect sound’ together with noise from disk drives, printers as well as from the rest of the family etc. Consequently, a hearing aid user may well have turned up the volume on their computer, so connecting directly might be much appreciated by those around them!
There are four options to consider for improving the sound quality from a PC for a hearing aid user. Which option you choose will depend on the connections on your computer and/or what additional equipment you have available.
1. Connecting into a suitable headphone socket
a. Using the ‘T’ pick-up on your hearing aid(s) with an inductive device.
b. Stereo sound using the direct input facility on the hearing aids
c. Mono sound for single direct input hearing aid wearers
2. Connecting to an amplifier unit which does have a suitable headphone socket
3. Connecting to a Connevans ATU30 auditory trainer
4. Connecting into a Connevans fmGenie or CRM-220 radio aid system
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Television:
Better TV Sound for those with Hearing Loss:
1. Audio Settings:
Many older adults experience high-frequency sensorineural hearing loss, which can affect the clarity of the program. An increase in volume alone will not help. If that’s the case, try lowering the bass and lower mid-range and boosting the upper midrange and higher frequencies, where voices are typically found, to compensate.
2. Wireless Headphones and Headsets:
Some TVs are outfitted with two-way Bluetooth, which lets you send the sound straight to a pair of wireless headphones. If your set lacks this feature, you can purchase a system with a transmitter that plugs into your TV and a set of headphones with a built-in receiver. The headphones typically work using infrared (IR) or radio frequencies (RF). Some models, such as Sennheiser’s RS 195, have a speech-enhancement mode that boosts the dialogue while lowering background noise. There are also stethoscope-style headphones, called stethosets or TV listeners, designed to enhance TV sound for those with hearing loss. They, too, work by boosting the frequencies common to dialogue. TV Ears is probably the best-known manufacturer, though other companies, including Sennheiser, make stethoset-style systems. These generally use a small base unit with a transmitter you connect to the TV and a pair of horseshoe-shaped earphones with a receiver. For homes with more than one person suffering from hearing loss, you can also find TV speakers outfitted with the same technology.
3. Sound Bar Speakers:
Sound bar speakers are a great way to improve TV sound and a few claim to have built-in voice-enhancement technologies. For example, the Sonos Playbar speaker has a “Speech Enhancement” setting that reportedly boosts the audio frequencies associated with the human voice. Sony’s HT-ST7 7.1-channel sound bar speaker and subwoofer combo has a “voice” button to boost dialogue levels. And recently a new model from Zvox– AccuVoice AV200 TV Speaker—that’s designed specifically to improve dialogue intelligibility is available. According to the company, the AccuVoice feature tries to mimic the function of a hearing aid by isolating voice frequencies and lifting them out of background sounds.
4. Room Loops:
For those who already use a hearing aid, a room loop (also known as an induction loop) is another option. This technology is often deployed in Broadway theaters and movie houses, but it can be set up on a smaller scale in your home. By connecting an amplifier to your TV’s audio output and running a wire around the perimeter of the room, you distribute electromagnetic TV signals that can be picked up by a tiny receiver (called a T coil or telephone coil) built into most hearing aids. One benefit to this approach is that multiple listeners can tune in, provided they each have a compatible receiver in their hearing aids. Another plus: You get good reception no matter where you are in the room, so you don’t have to worry about moving around.
5. TV Listening Systems:
TV listening systems are wireless systems that transmit the sound from a TV (or other sound source such as a stereo or computer) to a receiver. A small transmitter sits on top of the TV and gathers the sound from either a small microphone placed over the speaker or from a cable plugged into the “audio out” socket on the back of the TV. Like other wireless systems, the sound is converted to radio waves, infrared light, or magnetic energy, transmitted through the air, and picked up by the receiver. The headset has its own volume control and is independent from that of the TV’s speakers. The headset can be turned up loudly while the TV’s volume is set at a comfortable level for others in the room, or even turned all the way down. Different systems have different advantages. The FM listening system permits you to walk into another room or go outside and still hear the sound but it is subject to outside interference and interference from other nearby TV systems. The infrared light system, on the other hand, does not penetrate walls but does allow you to have more than one system operating in the house without risk of interference.
6. Closed Captions:
As a last resort, you can always turn on the closed caption function in the settings on your TV or cable box and read the dialogue as it scrolls across your screen.
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Ultrasonic Speakers could be a Breakthrough for those with Hearing Loss:
HyperSound Clear speakers improve clarity and speech via ultrasound beams. HyperSound Clear speakers emit sound in a controlled, narrow beam. Attached to TVs and other electronics, the speakers are designed to improve clarity and speech intelligibility for those with hearing loss. While typical speakers create audio waves that can be several feet long, HyperSounds emit ultrasonic waves with lengths of about 2/15 of an inch. The waves’ small size means the speakers can focus them in a particular direction. It’s like a flashlight beam, compared with light from a bare bulb. HyperSounds’ audio can be heard best by listeners positioned in the beam’s path. The ultrasonic waves carry an audio signal that’s converted back into sound, maintaining its focused direction, when the wave hits air molecules. Research is on for a speaker that can be integrated into a TV or computer screen, or a car dashboard, to focus sound on people in front of it.
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Bone conduction hearing aids:
So far we discussed air conduction hearing aids, their technology and their connectivity. Now I will discuss bone conduction hearing aids.
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Hearing aids can be divided into two groups, distinguished by the principle of how sound is transmitted to the cochlea. The largest group is that consisting of air conduction (AC) hearing aids, with the other type being bone conduction (BC) hearing aids. The BC hearing aids are useful to a relatively small population of hearing impaired people, but nevertheless for this group often are the only satisfactory solution. Bone conduction hearing aids vibrate in response to the sounds going into the microphone. The part of the hearing aid that vibrates is held against the bone behind the ear (mastoid) by a headband. The vibrations pass through the mastoid bone to the cochlea and are converted into sound in the usual way. Bone conduction hearing aids are suitable if problems with your outer or middle ear are stopping sound from getting through. They send sound vibrations through the skull directly to the inner ear. They can be worn with a headband or attached to your glasses and some are surgically implanted.
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Bone conduction devices (BCD):
To categorize all existing BCDs for hearing rehabilitation, the first division was made into “direct-drive” BCDs and “skin-drive” BCDs as seen in the figure below. All direct-drive BCDs transmit vibrations directly to the skull bone, not through the skin. Skin-drive BCDs transmit vibrations through the skin, and can be divided into conventional and passive transcutaneous BCDs. A similar division could be made to direct-drive BCDs, which are divided into percutaneous and active transcutaneous devices. There is also a category of BCDs called in-the-mouth devices, which are neither direct-drive nor skin-drive BCDs, as they stimulate the ear by transmitting vibrations via a tooth and its relatively stiff root connected to the skull.
Figure above shows categorization of bone-conduction devices.
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Because of soft-tissue challenges with percutaneous implants, the trend in BCDs is towards transcutaneous semi-implantable devices, where the skin is kept intact. The four main challenges with transcutaneous solutions are related to sufficient power, firm and stable implant attachment, surgical invasiveness, and MRI compatibility. When comparing the hearing improvement with the different devices, the direct-drive BCDs, both percutaneous and active transcutaneous, provide the best hearing rehabilitation, mainly because of the direct stimulation of the bone (no vibrations through the skin).
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Conventional bone-conduction hearing aid:
Conventional bone conduction hearing aid consists of a transducer and amplifier attached to a headband or spectacle frame. It is designed to press firmly against the skull vault. These hearing aids have remained unpopular due to their poor aesthetics, discomfort due to constant pressure from the transducer, and poor sound quality at higher frequencies. In BAHA, sound transmission to the skull is direct. Therefore, it is possible to achieve the same hearing threshold as with transcutaneous conventional bone conduction but with a lower output of the transducer and therefore less distortion. A vibrator with a steel spring over the head or in heavy frames of eyeglasses pressed towards the bone behind the ear has been used to bring sound to the inner ear. This has, however, several disadvantages, such as discomfort and pain due to the pressure needed. The sound quality is also impaired as much of the sound energy is lost in the soft tissue over the skull bone, particularly for the higher sound frequencies important for speech understanding in noise.
The Spectacle bone conduction hearing aids:
The hearing aid mechanism is fitted inside the arms of the spectacle and there is nothing going inside the ear. It can be fitted only on those patients who have conductive deafness, with large air-bone gap i.e. patients with normal bone conduction hearing levels but poor air-conduction hearing levels.
The Google Glass device employs bone conduction technology for the relay of information to the user through a transducer that sits beside the user’s ear. The use of bone conduction means that any vocal content that is received by the Glass user is nearly inaudible to outsiders.
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Bone Anchored Hearing Aids (BAHA/Baha):
A Bone Anchored Hearing Aid (BAHA) transmits sound directly to the cochlea by vibrating the mastoid bone. A minor operation is needed to fix a screw to the skull, on which the hearing aid can be clipped on and off. A BAHA is removed at night and when you swim or take a shower. Unlike a bone conduction hearing aid, it’s not uncomfortable to wear and is used for patients with conductive hearing loss, or in some patients who have no hearing in one of their ears. Some people may benefit from newer types of implantable bone conduction hearing aids that are held onto the head with magnets instead of a connector through the skin. However, these are only available at some BAHA centres and may require a referral to a different BAHA centre. Baha is no longer referred as hearing aid; but referred as an auditory osseointegrated implant system.
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A bone anchored hearing aid (BAHA) is an auditory prosthetic based on bone conduction which can be surgically implanted. It is an option for patients without external ear canals, when conventional hearing aids with a mould in the ear cannot be used. The BAHA uses the skull as a pathway for sound to travel to the inner ear. For people with conductive hearing loss, the BAHA bypasses the external auditory canal and middle ear, stimulating the functioning cochlea. For people with unilateral hearing loss, the BAHA uses the skull to conduct the sound from the deaf side to the side with the functioning cochlea. Individuals under the age of two (five in the USA) typically wear the BAHA device on a Softband. This can be worn from the age of one month as babies tend to tolerate this arrangement very well. When the child’s skull bone is sufficiently thick, a titanium “post” can be surgically embedded into the skull with a small abutment exposed outside the skin. The BAHA sound processor sits on this abutment and transmits sound vibrations to the external abutment of the titanium implant. The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing. One important feature of the Baha is that, if a patient for whatever reason does not want to continue with the arrangement, it takes the surgeon less than a minute to remove it. The Baha does not restrict the wearer from any activities such as outdoor life, sporting activities etc. A BAHA can be connected to an FM system by attaching a miniaturized FM receiver to it. Two main brands manufacture BAHAs today – the original inventors Cochlear, and the hearing aid company Oticon.
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A woman having BAHA:
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The bone-anchored hearing device is composed of three main parts: a titanium implant, an external abutment, and a sound processor. The sound processor was also called a bone-anchored hearing aid, which is terminology that is still being used in some parts of the world. The sound processor actually behaves like a conventional air-conduction hearing aid. It picks up the sounds from the environment through a microphone, but unlike an air-conduction hearing aid where the sound is transmitted as acoustic energy, this sound is converted into mechanical vibrations and these vibrations are transmitted to the bone through the abutment into the implant which is imbedded in the temporal bone, and the sounds are then transmitted to the cochlea directly. The sound processor attaches to an abutment via the coupling. The abutment is then fixed to the implant by a screw. So the abutment is like a bridge between the sound processor and the titanium implant, which sits in the bone. The sounds vibrations are transmitted to the cochlea, bypassing the outer and middle ear. That is the key to direct bone conduction. Figure below is a picture of how the sound processor picks up the sounds and transmits the vibrations through the abutment, through the implant, into the bone, into the skull, and to the cochlea. That is what direct bone conduction is. There are several advantages with direct bone conduction. First of all, it works independently of the ear canal and middle ear. Because it is direct transmission, the sound is often clearer than the sound you get from a traditional hearing aid. Preoperative testing is possible, and the varying comfort is fairly high compared to a traditional bone-conduction hearing aid. The surgery is straightforward, and it is very safe.
It is a solution for conductive and mixed hearing losses and single-sided deafness. Those are the two main groups that this device will be suitable for.
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The bone-anchored sound processor bypasses the middle ear and stimulates the cochleae directly, overcoming the audiometric air-bone gap as seen in the figure below.
So if someone has an air-bone gap or a conductive element in their hearing loss, you will find that this device will actually help to overcome that air-bone gap. You are getting the sound right to the cochlea, at the inner ear thresholds by bypassing that air-bone gap. When you bypass the middle ear and the external ear, you do not really need a lot of gain when providing amplification that way. In traditional hearing aids, you really have to take into account and overcome the air-bone gap. With this device, you do not need that. You will need much less gain with a bone-anchored hearing aid or bone-anchored sound processor. You also get better sound quality because the sound transmission is direct and the ear canal can remain open. You can see that the device basically provides direct bone conduction. It bypasses the middle ear completely. The gain prescription is going to be based on how much amplification we need to actually provide to the cochlea, and that is not going to be a huge amount of gain. Also, the kind of amplification prescription you are going to use will be based on a linear amplification scheme. You do not need to use compression at all because there is no sensorineural hearing loss here. Of course, if there is a mixed hearing loss, the NAL–NL1 prescription formula is used for that to account for the sensorineural component. Again, there is going to be hardly any compression used in the amplification scheme.
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The other group of people who will benefit from this solution are people with single-sided deafness. The definition of that is profound, unilateral sensorineural hearing loss. By that you would have normal hearing of 20 dB or better in one ear with a profound sensorineural hearing loss in the impaired ear. The clinical aspects of single-sided deafness present as having difficulties communicating in group situations and in noisy situations. Patients will have difficulties localizing sounds. You can very well appreciate that because they have input coming from one cochlea. They may have difficulty understanding a person situated on the deaf side. In children, this can present itself as a major handicap in school. They may not have a lot of difficulty communicating one on one, listening to the TV or the radio, but they will have difficulties communicating in group situations. There is transcranial routing of the signal from the implanted side to the side with the good hearing. Because both cochleae are stimulated at the same time, when you implant this device on the side where there is profound sensorineural hearing loss, the transmissions will actually go to the other side via the bone, and the better side will pick up the sound, which is true transcranial routing of the signal. Sounds are picked up and converted to vibrations and the vibrations are transmitted to both sides. It works as a CROS hearing aid in that sense.
Figure above shows direct transcranial bone conduction, transmitting sounds to both cochleae. When we have the bone-anchored hearing aid, it actually transmits the sound not just to one cochlea, but to both cochleae.
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For single-sided deafness, we have to take into account the bone-conduction thresholds of the better side. Of course, FDA indications state that the better side has to have normal hearing, so you need to take into account the bone-conduction thresholds of that good ear. Clinics are increasingly fitting this device on patients who do have some mild to moderate hearing loss, and they are finding that it is still very beneficial. This device still provides enough gain to compensate for the mild hearing loss on the better hearing side. For single-sided deafness, another thing we have to take into consideration is the fact that you have a deaf ear on one side and a good ear on the other. We have to take into account the head-shadow effect. We know that when sounds are transmitted to the other side, some of the high frequencies are going to be lost, and we have to compensate for that. So we do provide more high-frequency amplification in single-sided deafness. The low frequencies have a longer wave length and can reach the other ear, so we do not really have to provide much low-frequency amplification. In some cases, we may have to bring down the gain for low frequencies. When we do that, these patients do very well. That is the gain rationale that we use for mixed, conductive and single-sided deafness.
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What is the difference between Baha and a cochlear implant?
The Baha relies on integrity of the inner ear, whereas a cochlear implant bypasses the inner ear with an array of electrodes surgically implanted in the cochlea. The electrodes receive acoustic signals that have been converted to electrical signals, which then stimulate the auditory nerve. A cochlear implant is appropriate for children and adults with bilateral severe-profound sensori-neural hearing loss who receive minimal benefit from traditional hearing aids.
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Benefits of BAHA:
By bypassing the outer or middle ear, BAHA can increase hearing in noisy situations and help localise sounds. In addition to improved speech understanding, it results in a natural sound with less distortion and feedback compared with conventional hearing aids. The ear canal is left open for comfort, and helps to reduce any problems caused by chronic ear infections or allergies. In patients with single-sided sensorineural deafness, BAHA sends the sound by the skull bone from the deaf side to the inner ear of the hearing side. This transfer of sound gives a 360° sound awareness. Certainly, there are obvious advantages of the BAHA over air conduction hearing aids when there is no external ear canal, such as in cases of congenital or acquired external canal absence. The expected outcome of BAHA surgery can be assessed preoperatively by using the head-band or test rod (sometimes also called the bite-bar), tremendously helping patient selection. Moreover, the absence of the interposed soft tissues in BAHA results in a better sound quality, requires less energy, and offers greater comfort than the traditional bone conduction hearing aids. Hakansson summarized the audiometric results from 122 patients with an average follow-up time of 5.6 years. They found the improved quality of life reported by their patients is a combination of improved audibility and quality of sound (warble tone threshold, speech reception threshold, and discrimination in noise), improved comfort, and relief from middle ear and ear canal diseases occasioned by conventional hearing aids.
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The processor is not waterproof, so you will have to remove it prior to showering or swimming. It should also be removed during contact sports, to avoid damage or loss. During these breaks you can use a special cover to hide the abutment. You should also remove the processor before going to bed. During hair treatments, always cover your abutment. You may use the special abutment cover provided with your sound processor. Make sure to protect or remove your sound processor during visits to the hairdresser or when applying hair products. You should also cover your abutment when using hair gel or hair spray.
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Middle ear implants (MEI):
These are surgically implanted devices that attach to the hearing bones and make them vibrate. They’re suitable for people who can’t use a hearing aid, but have hearing loss at a level where a BAHA would not help. Implantable hearing aids are designed to help increase the transmission of sound vibrations entering the inner ear. A middle ear implant (MEI) is a small device attached to one of the bones of the middle ear. Rather than amplifying the sound traveling to the eardrum, an MEI moves these bones directly. Middle ear implants are an option for people who either can’t tolerate or don’t benefit from hearing aids, but whose hearing loss isn’t severe enough for a cochlear implant. Here’s how it works: You wear an external microphone above your ear that picks up sound. The sound is converted into electrical signals, which travel through the skin to an implant that is attached to the tiny bones of the middle ear. The implant enhances the vibration of the middle ear bones and sends those amplified vibrations to the inner ear. Finally, the nerve signal is sent to the brain, where it is recognized as sound.
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What’s the difference between the MEI and a cochlear implant?
Cochlear implants are for those who suffer from severe to profound hearing loss. They are implanted directly in the inner ear, or cochlea, where they electronically stimulate the nerves through a series of electrodes. In contrast, the MIE is for hearing-impaired people with moderate to severe hearing loss. It provides an enhanced signal to the inner ear by directly vibrating the middle ear bones.
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Management of single-sided deafness (SSD):
SSD is defined as a condition where an individual has non-functional hearing in one ear and receives no clinical benefit from amplification in that ear, with the contralateral ear possessing normal audiometric function. Here normal audiometric function is hearing thresholds that are no poorer than 20 dB hearing level (HL) for pure-tone averages of 0.5, 1, 2, and 3 kHz. The non-functional ear can be, but is not limited to, a profound hearing loss. The key factor is that the poor or “bad” ear has not or will not receive benefit when traditional acoustic amplification is applied. The “good” ear must have a pure-tone average that is 20 dB or better across the pure-tone range. Before SSD was a recognized term, it was called unilateral sensorineural hearing loss, and it was usually in the profound category. The term single-sided deafness was actually coined by the company, Entific, when they started offering Baha for SSD. It has become very widely used in the industry to describe the condition of a complete sensorineural hearing loss in one ear. SSD is to be differentiated from someone who may have a conductive loss in one ear, as you would see in a patient with atresia or microtia. These patients typically have good cochlear function. People with SSD actually have such damage to the inner ear that traditional amplification does not provide them any benefit. SSD can be defined relative to a bone-conduction device such as Baha. The use of a Baha device for SSD is intended to improve speech recognition. SSD is an indication for a Baha for patients who suffer from unilateral sensorineural deafness on one ear, while the other ear has normal hearing of no worse than 20 dB.
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Learning of the central nervous system by “plasticity” or biological maturation over time does not improve the performance of monaural listening. In addition to conventional methods for improving the performance of the impaired ear, there are also hearing aids adapted to unilateral hearing loss which are of very limited effectiveness due to the fact that they don’t restore the stereo hearing ability.
•Contralateral Routing of Signals (CROS) hearing aids are hearing aids that take sound from the ear with poorer hearing and transmit to the ear with better hearing. There are several types of CROS hearing aid:
◦conventional CROS comprises a microphone placed near the impaired ear and an amplifier (hearing aid) near the normal ear. The two units are connected either by a wire behind the neck or by wireless transmission. The aid appears as two behind-the-ear hearing aids and is sometimes incorporated into eyeglasses.
◦CIC transcranial CROS comprises a bone conduction hearing aid completely in the ear canal (CIC). A high-power conventional air conduction hearing aid fits deeply into the patient’s deaf ear. Vibration of the bony walls of the ear canal and middle ear stimulates the normal ear by means of bone conduction through the skull.
◦BAHA transcranial CROS: a surgically implanted abutment transmits sound from the deaf ear by direct bone conduction and stimulates the cochlea of the normal hearing ear.
◦SoundBite Intraoral bone conduction which uses bone conduction via the teeth. One component resembles a conventional behind-the-ear hearing aid that wirelessly connects to a second component worn in the mouth that resembles a conventional dental appliance.
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CROS vs. BAHA for unilateral deafness (SSD):
Patients with unilateral deafness have difficulty with sound localization and reduced clarity of hearing in background noise. They may benefit from a CROS (contralateral routing of signal) hearing aid in which a microphone is placed on the hearing-impaired side and the sound is transmitted to the receiver placed on the contralateral ear. The same result may be obtained with a bone-anchored hearing aid (BAHA), in which a hearing aid clamps to a screw integrated into the skull on the hearing-impaired side. Like the CROS hearing aid, the BAHA transfers the acoustic signal to the contralateral hearing ear, but it does so by vibrating the skull. Patients with profound deafness on one side and some hearing loss in the better ear are candidates for a BICROS hearing aid; it differs from the CROS hearing aid in that the patient wears a hearing aid, and not simply a receiver, in the better ear. The Bone anchored device offers significant advantages to the traditional CROS hearing aid. The device is placed behind the ear leaving the canal open. It is worn under the hair and is not perceptible to others. Because it is held in place by a clip and directly integrated with the skull bone, there is no need for a head band and pressure against the skin of the head. In recent clinical trials patients prefer the sound and speech clarity achieved with the bone anchored device versus the CROS and versus the unaided condition. Neither system (CROS or BAHA) provides true binaural hearing in cases of SSD, as only one cochlea is stimulated. Unfortunately, while CROS and BAHA devices provide benefit, they do not restore hearing in the deaf ear. Only cochlear implants can restore hearing. Increasingly, cochlear implants are being investigated for the treatment of patients with single-sided deafness; early reports show great promise in not only restoring hearing but also improving sound localization and performance in background noise. In Germany and Canada, cochlear implants have been used with great success to mostly restore the stereo hearing ability, minimizing the impacts of the SSD and the quality of life of the patient.
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Conventional hearing aid vs. implantable hearing aid:
Hearing aids have fundamental disadvantages: (1) stigmatization of the patient; (2) the sound is often found to be unsatisfactory due to the limited frequency range and undesired distortion; (3) in many patients, the ear canal fitting device generally necessary leads to an occlusion effect; (4) acoustic feedback when amplification is high. Conventional hearing aids transmit sound into the ear canal via a small microphone. This sound has the disadvantage of requiring high output sound pressure levels for its transmission. This along with the necessary miniaturization of the loudspeaker as well as the resonances and reflections in the closed ear canal contribute to the disadvantages mentioned. In contrast, implantable hearing aids do not make sound signals but micromechanical vibrations. An implantable hearing aid has an electromechanical transducer instead of the loudspeaker of a conventional hearing aid. The hearing signal does not leave the transducer as sound but as a mechanical vibration which is directly coupled to the auditory system bypassing the air. This implantable hearing aid is either coupled to the tympanic membrane, the ossicular chain, the perilymph of the inner ear, or the skull. An implantable hearing aid is expected to have: (1) Better sound fidelity than a hearing aid (2) No ear canal fitting device, free ear canal (3) No feedback (4) Invisibility.
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Hearing aid styles:
Hearing aids can differ based on whether they are digital or analog, worn primarily behind the ear or inside it, and are open fit or closed fit. Each of these variations has advantages for some hearing aid wearers, but not others. Learning about the different types of hearing aids available can help you determine which works best for your lifestyle and hearing needs.
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Hearing aids have been available in four styles: body, eyeglass, behind-the-ear (BTE), and in-the-ear (ITE). Included in the category of ITE hearing aids are in-the-canal (ITC) and completely-in-the-canal (CIC) styles. While body and eyeglass style hearing aids were regularly used 40-50 years ago, they comprise only about 1% of all hearing aids marketed today. Instead, most individuals choose ITE (approximately 80%) or BTE (approximately 20%) style hearing aids. This transition in style, use, and preference is occurring for a number of reasons, including the reduction in the size of the components, durability, and cosmetic concerns on the part of the consumer.
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Brief mention of Body Worn Hearing Aids:
This was the first type of hearing aid invented by Harvey Fletcher while working at Bell Laboratories. Body aids consist of a case and an earmold, attached by a wire. The case contains the electronic amplifier components, controls and battery while the earmold typically contains a miniature loudspeaker. The case is typically about the size of a pack of playing cards and is carried in a pocket or on a belt. These are available in analogue or digital technology for one or both ears depending upon hearing loss. Some but not all can be set up separately for individual ears. Wires from a body worn unit are connected to moulded ear pieces. The unit can be worn in a pocket, on the belt or clipped to clothing depending upon its design. This style is an option for people with poor dexterity and who require a high powered hearing aid. These may be useful if you have a visual impairment or find it hard to use small switches or buttons. Without the size constraints of smaller hearing devices, body worn aid designs can provide large amplification and long battery life at a lower cost. Body aids are still marketed in emerging markets because of their lower cost.
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Eye glass hearing aids are mentioned in bone conduction hearing aids.
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There are two basic types of hearing aids. The first type, hearing aids worn in the ear (ITE styles), are usually custom-fit, based on an impression that is taken by the hearing care professional at the time of the hearing aid consultation. These styles are typically available in different skin tones to camouflage with the outer ear. The second type, behind the ear hearing aids (BTE styles) sit behind or on top of the outer ear with tubing that routes the sound down into the ear canal via a custom-fit earmold or an ear tip that doesn’t block the entire ear canal opening. BTE styles are available in different colors to match hair or skin tone, as well as flashier designs to highlight personal flair. Different sizes of hearing aids accommodate different features, exterior control options and battery sizes. Larger hearing aids, whether ITE or BTE style, accommodate more buttons, more interior circuitry and larger batteries that may be needed for to meet power consumption requirements. While many people choose discreet ITE and BTE styles that largely go unnoticed when worn, others enjoy showing off what they’ve chosen! When selecting hearing aids, individuals should consider not only appearance, but also dexterity and lifestyle preferences.
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The term in-the-ear hearing aid will be used to generically refer to ITE (in-the-ear), ITC (in-the-canal) and CIC (completely-in-the-canal) hearing aids; unless a specific one of the three types is stated and discussed. This general term is intended to contrast to BTE (behind-the-ear) hearing aids. This distinction is made because there are significant differences in construction between the generic categories of in-the-ear and behind-the-ear hearing aids. The major difference in construction between custom in-the-ear hearing aids and BTE hearing aids is the obvious difference between the two types in the methods of housing the electronic amplifiers and the transducers, such as microphones, receiver and telecoils. BTE hearing aids are generally manufactured on a production line and have identical internal construction for a specific model of hearing aid. Custom in-the-ear hearing aids, on the other hand, are individually handcrafted at final assembly, though most of the faceplate circuit subassemblies are made on a production line with standardized layouts. This means that transducers for in-the-ear hearing aids are fitted into the shell wherever space allows.
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Different Styles of Hearing Aids:
In-the-Canal (ITC) and Completely-in-the-Canal (CIC) Aids
These aids are contained in a tiny case that fits partly or completely into the ear canal. They are the smallest aids available and offer some cosmetic and listening advantages.
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In-the-Ear (ITE) Aids
All parts of the aid are contained in a shell that fills in the outer part of the ear. These aids are larger than canal aids and, for some people, may be easier to handle than smaller aids.
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Behind-the-Ear (BTE) Aids
All parts of the aid are contained in a small plastic case that rests behind the ear. The case is connected to an earmold by a piece of clear tubing. This style is often chosen for young children for safety and growth reasons.
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Behind-the-Ear Aid: Open Fitting
A small plastic case rests behind the ear, and a very fine clear tube runs into the ear canal. Inside the ear canal, a small, soft silicone dome or a molded, highly vented acrylic tip holds the tube in place. These aids offer cosmetic and listening advantages and are used typically for adults.
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Receiver-in-Canal Aids
These aids look very similar to the behind-the-ear hearing aid with a unique difference: the speaker of the hearing aid is placed inside the ear canal, and thin electrical wires replace the acoustic tube of the BTE aid. These aids also offer cosmetic and listening advantages and are typically used for adults.
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Typical ITE:
The ITE style hearing aid fits directly into the external ear. The circuitry is housed primarily in the concha (external) portion of the ear. Due to the miniaturization of the component parts (including the microphone, receiver and battery), it is possible to make hearing aids small enough to fill only a portion of the concha (ITC) or fit deeply into the ear canal (CIC). All three of these styles have typically been considered to be more modern and cosmetically appealing. However, modern BTE hearing aids have become smaller and at times are less noticeable than some ITC hearing aids. In-the-Ear (ITE) hearing aids fit completely in the outer ear and are used for mild to severe hearing loss. The case, which holds the components, is made of hard plastic. ITE aids can accommodate added technical mechanisms such as a telecoil, a small magnetic coil contained in the hearing aid that improves sound transmission during telephone calls. ITE aids can be damaged by earwax and ear drainage, and their small size can cause adjustment problems and feedback. They are not usually worn by children because the casings need to be replaced as the ear grows. A Completely-in-Canal (CIC) hearing aid is largely concealed in the ear canal and is used for mild to moderately severe hearing loss. Because of their small size, canal aids may be difficult for the user to adjust and remove, and may not be able to hold additional devices, such as a telecoil. Other features of in-the-ear instruments are as follows:
•More secure fit, and easier insertion and removal than with BTEs.
•Improved cosmetic benefits with smaller styles (CIC, ITC).
•Less wind noise in the smaller styles than with BTEs.
•Directional microphone technology available for most styles, excluding CICs.
•Deep microphone and receiver placement with CICs may result in increased battery life and high frequency amplification compared with other styles.
•All components are integrated into a one-piece shell, which may be easier to handle and operate than for BTE styles.
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In the ear aids (ITE) devices fit in the outer ear bowl (called the concha); they are sometimes visible when standing face to face with someone. ITE hearing aids are custom made to fit each individual’s ear. They can be used in mild to some severe hearing losses. Feedback, a squealing/whistling caused by sound (particularly high frequency sound) leaking and being amplified again, may be a problem for severe hearing losses. Some modern circuits are able to provide feedback regulation or cancellation to assist with this. Venting may also cause feedback. However, different vent styles and sizes can be used to influence and prevent feedback. Traditionally, ITEs have not been recommended for young children because their fit could not be as easily modified as the earmold for a BTE, and thus the aid had to be replaced frequently as the child grew. However, there are new ITEs made from a silicone type material that mitigates the need for costly replacements. ITE hearing aids can be connected wirelessly to FM systems, for instance with a body-worn FM receiver with induction neck-loop which transmits the audio signal from the FM transmitter inductively to the telecoil inside the hearing instrument. In the canal (ITC) aids are smaller, filling only the bottom half of the external ear. The aid cannot be seen when face to face with the wearer. Mini in canal (MIC) or completely in canal (CIC) aids are generally not visible unless the viewer looks directly into the wearer’s ear. These aids are intended for mild to moderately severe losses. CICs are usually not recommended for people with good low-frequency hearing, as the occlusion effect is much more noticeable. In-the-ear hearing aids are typically more expensive than behind-the-ear counterparts of equal functionality, because they are custom fitted to the patient’s ear. In fitting, an audiologist takes a physical impression (mold) of the ear. The mold is scanned by a specialized CAD system, resulting in a 3D model of the outer ear. During modelling, the venting tube is inserted. The digitally modelled shell is printed using a rapid prototyping technique such as stereolithography. Finally, the aid is assembled and shipped to the audiologist after a quality check.
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Invisible in canal hearing aids (IIC) style of hearing aids fits inside the ear canal completely, leaving little to no trace of an installed hearing aid visible. This is because it fits deeper in the canal than other types, so that it is out of view even when looking directly into the ear bowl (concha). A comfortable fit is achieved because the shell of the aid is custom-made to the individual ear canal after taking a mould. Invisible hearing aid types use venting and their deep placement in the ear canal to give a more natural experience of hearing. Unlike other hearing aid types, with the IIC aid the majority of the ear is not blocked (occluded) by a large plastic shell. This means that sound can be collected more naturally by the shape of the ear, and can travel down into the ear canal as it would with unassisted hearing. Depending on their size, some models allow the wearer to use a mobile phone as a remote control to alter memory and volume settings, instead of taking the IIC out to do this. IIC types are most suitable for users up to middle age, but are not suitable for more elderly people.
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Typical BTE:
Behind-the-Ear (BTE) hearing aids are worn behind the ear and are connected to a plastic earmold that fits inside the outer ear. The components are held in a case behind the ear. Sound travels through the earmold into the ear. BTE aids are used by people of all ages for mild to profound hearing loss. Poorly fitting BTE earmolds may cause feedback, a whistle sound caused by the fit of the hearing aid or by buildup of earwax or fluid. Some BTE models do not use a custom earpiece; instead the rubber tubing is inserted directly into the ear. The case is typically flesh colored, but can be obtained in many colors and/or patterns. Other features include:
•BTEs may be the most appropriate choice for young children, as only the earmold needs to be replaced periodically as the child grows and the ear changes in dimension.
•Typically, BTEs are the most powerful hearing aid style available, and may be the best option for persons with severe-to-profound hearing loss.
•FM and direct auditory input is routinely available as an optional or standard feature.
•Telecoil circuitry is often more powerful than with ITEs.
•Non-occluding earmolds may be used with BTE hearing aids, if a medical condition exists or if the patient reports a “plugged” sensation when wearing other hearing aid styles.
•Directional microphone technology available with most BTE styles and models.
•Larger battery sizes used in BTEs may be easier to handle than smaller styles for those with limited manual dexterity or vision deficits.
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In BTE hearing aid, the sound from the instrument can be routed acoustically or electrically to the ear. If the sound is routed electrically, the speaker (receiver) is located in the earmold or an open-fit dome, while acoustically coupled instruments use a plastic tube to deliver the sound from the case’s loudspeaker to the earmold. BTEs can be used for mild to profound hearing loss. As the electrical components are located outside the ear, the chance of moisture and earwax damaging the components is reduced, which can increase the durability of the instrument. BTEs are also easily connected to assistive listening devices, such as FM systems, to directly integrate sound sources with the instrument. BTE aids are commonly worn by children who need a durable type of hearing aid. A new type of BTE aid called the mini BTE (or “on-the-ear”) aid. It also fits behind/on the ear, but is smaller. A very thin, almost invisible tube is used to connect the aid to the ear canal. Mini BTEs may have a comfortable ear piece for insertion (“open fit”), but may also use a traditional earmold. Mini BTEs allow not only reduced occlusion or “plugged up” sensations in the ear canal, but also increase comfort, reduce feedback and address cosmetic concerns for many users. BTE hearing instruments that place the loudspeaker directly in the ear without a fitted earmold are often referred to as “Receiver in the Canal” instruments. These instruments use soft ear inserts, typically of silicone, to position the loudspeaker in the patient’s ear. Some of the advantages with this approach include improved sound quality, reduced case size, “open-fit” technology, and immediate patient fitting.
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The figure below shows various types of in the ear (ITE) and behind the ear (BTE) hearing aids:
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Ear Mold:
If you decide to pursue hearing aids, the hearing aid dispenser will take a mold or cast of your ear. The mold allows the hearing aid manufacturer to customize the hearing aid or ear mold to your ears. This procedure will take 5 to 10 minutes and in few cases, may cause minimal discomfort. This usually ensures a comfortable fit and reduces the possibility of feedback. If you are purchasing a mini-behind-the-ear device with a thin tube this step will not be necessary. An ear mold will be required if you purchase completely-in-the canal (CIC), in-the-ear (ITE), in-the-canal (ITC), or larger behind-the-ear models. Ear-molds of ITE, ITC or CIC are also called hearing aid shell. Earmolds are made from a variety of hard (firm) and soft (pliable) materials. Most hearing aids are worn with an earmould that is made of plastic or silicone. To make a hearing aid, an audiologist or hearing aid dispenser will make an imprint of the patient’s ear by pouring silicon material into the ear. Once it hardens, the silicon imprint is removed from the ear and sent to the manufacturer to make the hearing aid. The imprint is used to make a silicon mold, which is filled with acrylic and hardened in an ultraviolet oven. This creates the shell of the hearing aid. Holes are drilled into the hearing aid, and the electrical components — volume control, microphone and speaker — are placed inside. A group of wires is attached to all of the different electronic parts and the battery is installed. When the hearing aid is finished, it is polished smooth and then analyzed to make sure that it fits the patient’s hearing prescription. The earmould holds the hearing aid securely in place and carries the sound from the hearing aid into your ear. Earmolds help in transmission of sound from the hearing aid receiver to the ear. An impression of your ear canal will be made so your earmould will be the perfect size and shape for you. They can be made of different materials and colours. It is custom-made for each individual. Non-hearing aid users may use earmolds, too. Custom earmolds are a great way to protect your hearing from loud sounds at work or at play. Musicians, stock car racers and even some professional football teams use earmolds with an acoustical chamber which blocks most noise while still allowing the wearer to understand speech. Some swimmers use specialized ear molds designed to keep water out of their ear canal.
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Types of BTE:
The popularity of behind-the-ear (BTE) hearing aids has soared in the last few years. The latest industry statistics showed that more than 50% of hearing aids sold in the United States during 2007 were BTEs. A key reason for the renewed interest in BTEs is that this style of hearing aid has undergone a substantial metamorphosis. Along with the smaller size, today’s BTEs are more stylish, more cosmetically appealing, and more functionally versatile. At the same time, the manner to which current BTEs are coupled has led to a plethora of names and terms that may confuse even the most experienced clinicians.
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Six Basic BTE Couplings:
Today’s BTE couplings can be broadly grouped by two distinct dimensions: one involving the “diameter of the tubing” and one involving the “openness” of the fittings. Using these two dimensions and adding thin-wire fittings, one can classify today’s BTE couplings into six categories as seen in the figure above. A thin-wire open fitting is also known as RIC (receiver in canal) or RITE (receiver in the ear). To maintain the openness of the ear canal, the receiver of a thin-wire (RIC/RITE) hearing aid must be smaller than the diameter of the ear canal to leave it unoccluded for a majority of its wearers. The ear-insert, in which the receiver is encased, must remain small as well.
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Open-ear vs. Occluded-ear Fittings:
In general, the main reason for choosing an open-ear fitting, among many possible reasons, is the minimization or total elimination of the occlusion effect (OE). The reduction of OE is possible because the unoccluded ear canal in an open-ear fitting allows the low-frequency SPL that is generated during vocalization to escape the ear canal. It is commonly accepted that the accumulation of low-frequency SPL during vocalization is the main source of the “hollow voice” complaint. Kuk et al has estimated that the average objective occlusion effect with a typical occluding earmold is about 20 dB. In addition, each 1 mm vent diameter leads to a reduction of the OE by about 4 dB. This means that, for the average ear to be completely clear of the OE, the equivalent vent diameter of the earmold should be larger than 5 mm. This vent size is almost impossible for a standard custom ITE hearing aid, or a typical earmold, to achieve. True open-ear fitting is the only possible option to achieve a complete elimination of the objective OE. On the other hand, an open-ear fitting has its challenges and caveats.
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What is occlusion and why is it a problem?
Occlusion is the sensation of hearing distorted, muffled sounds experienced when an object blocks the ear canal. It is a common complaint among hearing aid users, who often find that the presence of the hearing aid, or hearing aid ear mold, in their ear canal distorts not only outside sounds but also the sound of their own voice.
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What is an open fitting?
Because the new generation of open-fit products has been so strongly associated with thin-tube and receiver-in-the-ear styles, many consider any device falling into either of these categories to be “open fit.” However, either of these types of hearing aids can also be fit with either a custom micromold or occluding plastic dome, thereby making them anything but open. A more useful way to define open fitting is in terms of low frequency acoustics: If low frequency energy can pass freely in and out of the ear canal when the hearing aid is worn, then it is an open fitting. Defined in this way, any style of existing or not-yet-invented hearing aid can be an open fitting as long as it meets the criterion of allowing low frequencies to enter and leave the ear canal unhindered.
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Open fit hearing aids:
Advantages of open fitting is that self-generated low frequency sound can escape from the ear canal, thus avoiding the perception of a boomy-sounding own voice or unbearably loud crunching when chewing. Low frequency sounds that are audible to the user can also enter the ear, preserving important cues to localization and contributing to natural sound quality for users with good low frequency hearing. Another significant effect of open fitting is an enhancement of real-ear gain in the region of the unaided ear canal resonance. Improvements in feedback management have allowed hearing aid manufacturers to develop devices that do not obstruct the natural passage of sound through the ear canal. Previously, wearers of hearing aids would complain of a “talking in a barrel” sensation, like you can experience when using your fingers to block your ears and listening to the sound of your own voice. Open fit hearing aids have very thin tubes that enter the ear canal and smaller cases that rest behind the ear, making them barely visible. Additionally, hearing aids that sit within the ear canal can now have greater ventilation. The end result is far more comfort and clarity for the hearing aid wearer of today. The main reason for the surge in popularity of open fitting is that current open-fit products offer solutions to the “side effects” of hearing aids for those with mild-to-moderate high frequency hearing losses, which tip their cost/benefit analyses in favor of amplification. In addition to their cosmetic appeal, open-fit hearing aids are generally physically comfortable to wear and eliminate occlusion-related complaints. Conversely, because of the increased possibility of feedback, and because an open fit allows low frequency sounds to leak out of the ear canal, they are limited to mild to moderate high-frequency losses. They cannot be used in severe to profound hearing loss. While the design approach is attractive to a general hearing aid user, open-fit devices can by their design have problems when connected to Assistive Listening Devices (ALD’s). This problem has been addressed by manufacturers, who provide assistive listening devices that can be paired with the hearing aid.
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Standard-tube vs. Thin-tube Fittings:
The main advantage of using a thin tube (inner diameter of 0.8 mm) instead of the traditional #13 tube (inner diameter of 1.9 mm) is the cosmetic appeal of a thin tube. A thin-tube BTE is less visible and has increased patient acceptance. The drawback of a thin tube is its reduced high-frequency output when compared to the standard #13 tube. _
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RIC pros and cons:
In behind-the-ear and in-the-ear hearing aids, the device’s components are all held in the same case: either behind the ear or in the ear. RIC hearing aids, on the other hand, separate the components into two major sections. A case behind the ear holds the aid’s amplifier and microphone, while a small bud that contains the receiver is used inside the ear canal. A small tube connects the receiver to the case. Separation of the receiver into its own compartment has several advantages. Feedback and occlusion tend to be much less of a problem with RIC devices than they are with other hearing aids. With the ear canal open, wearers generally report a more natural sound which is judged to be more comfortable. This type of device a great choice for listeners with mild to moderate hearing issues because it amplifies high-pitched tones exceptionally well. There is also a physical advantage to the RIC’s split configuration. Separating the two components allows the device to remain very small, making it unobtrusive and easy to hide. Its small size also allows it to fit very comfortably in and on the ear. No device is perfect, and RIC aids do have some disadvantages. Frequent repairs to the receiver are one drawback to the receiver in canal because the receiver end is vulnerable to moisture in the ear canal. Amazingly, the potential for loss is another drawback. Because they are so small and lightweight it can take some time for the user to realize that the hearing aid is missing. Compared to other hearing aid styles, receiver in canal designs are average to above average in cost.
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| Hearing aids styles pros and cons: | |||
| Type | Pros | Cons | |
| Behind-the-ear (BTE) with earmould–For mild to severe hearing loss. | Fits widest range of hearing loss. Earmould fits snugly while the rest of the aid sits behind the ear. Most versatile and reliable type of hearing aid. | Most visible type of hearing aid. Ear might feel plugged-up, but vents in mould can relieve this and are fitted when appropriate. | |
| Behind-the-ear (BTE) open-fit–For mild to moderate hearing loss. | Has a small, soft earpiece at the tip of the tubing instead of an earmould, which will make you feel less plugged-up. Comfortable (not too heavy on the ear) and less visible than an earmould. It can give you a very natural sound. | Needs to be inserted correctly otherwise can become loose. | |
| Receiver-in-the-canal (RIC) digital aids–For mild to severe hearing loss. | All the benefits of an open-fit hearing aid but can be fitted with more amplification. Often smaller than BTE aids because some parts sit inside the ear. | Vulnerable to wax and sweat, which can affect the sound in the receiver. | |
| In-the-canal (ITC) and in-the-ear (ITE) digital aids–For mild to some severe hearing loss. | Both have working parts in the earmould, or a small compartment clipped to it, so the whole aid fits in the ear. ITC aids are less visible than ITEs, but neither has parts behind the ear. | Tend to need repairing more often than behind-the-ear aids. | |
| Completely-in-the-canal (CIC) or invisible hearing aids–For mild to moderate hearing loss | Smallest type of hearing aid. Almost invisible as working parts are in the earmould; fits further into the ear canal than ITE/ITC aids. | Unlikely to be suitable if you have frequent ear infections. Ear might feel plugged-up unless it is vented. Small tube is particularly vulnerable to becoming plugged with sweat and wax, which may cause temporary malfunction. Can be tricky to use if you can’t manage small switches or buttons. How hidden it is will depend on the shape of your ear. | |
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Comparison of various hearing aid styles:
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Synopsis of classification of hearing aids is depicted in the figure below:
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Personal, user, self, or consumer programmable:
The personal programmable, consumer programmable, consumer adjustable, or self-programmable hearing aid allows the consumer to adjust their own hearing aid settings to their own preference using their own PC. Personal programmable hearing aid manufacturers or dealers can also remotely adjust these types of hearing aids for the customer. Available in all hearing aid styles, these hearing aids differ from traditional hearing aids only in that they are adjustable by the consumer.
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Extended Wear Hearing Aids:
Extended wear hearing aids are hearing devices that are non-surgically placed in the ear canal by a hearing professional. The extended wear hearing aid represents the first “invisible” hearing device. These devices are worn for 1–3 months at a time without removal. They are made of soft material designed to contour to each user and can be used by people with mild to moderately severe hearing loss. Their close proximity to the ear drum results in improved sound directionality and localization, reduced feedback, and improved high frequency gain. While traditional BTE or ITC hearing aids require daily insertion and removal, extended wear hearing aids are worn continuously and then replaced with a new device. Users can change volume and settings without the aid of a hearing professional. The devices are very useful for active individuals because their design protects against moisture and earwax and can be worn while exercising, showering, etc. Because the device’s placement within the ear canal makes them invisible to observers, extended wear hearing aids are popular with those who are self-conscious about the aesthetics of BTE or ITC hearing aid models. As with other hearing devices, compatibility is based on an individual’s hearing loss, ear size and shape, medical conditions, and lifestyle. The disadvantages include regular removal and reinsertion of the device when the battery dies, inability to go underwater, earplugs when showering, and for some discomfort with the fit since it is inserted deeply in the ear canal, the only part of the body where skin rests directly on top of bone.
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Disposable hearing aids:
Disposable hearing aids are hearing aids that have a non-replaceable battery. These aids are designed to use power sparingly, so that the battery lasts longer than batteries used in traditional hearing aids. Disposable hearing aids are meant to remove the task of battery replacement and other maintenance chores (adjustment or cleanings). Disposable hearing aids are sometimes recommended for people who have mild to moderate hearing loss. The battery inside a disposable hearing aid usually lasts for about 12 weeks, after which time the hearing aid is thrown away and replaced. Disposable hearing aids tend to be expensive in the long term and are only available privately. Disposable hearing aids have been a failure.
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Are smaller hearing aids better?
Many people believe that small hearing aids that fit in your ear are pricier, more up-to-date and ‘better’ – but in fact, any size and type of hearing aid can be the modern, digital kind. Some smaller hearing aids can be difficult to manipulate if you have poor eyesight or dexterity. They can sometimes be a bit harder to keep clean and can be more affected by heat and moisture, as the mechanics of the hearing aid sit in the ear canal. They are usually only suited to people with mild to moderate hearing loss.
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Cosmetics Still Matter:
It has been shown that hearing instrument adoption rates even for those with moderate-to-severe losses are quite low (below 50%) for consumers not yet 65 years of age. This finding points toward a significant and continuing age stigma among non-adopters of hearing aids, even in this era of micro BTE and RIE hearing aids. Comments made by survey respondents such as “Hearing aids are a public admission of hearing loss,” as well as hearing aids are “noticeable” and “embarrassing,” suggest a perceived connotation of disability and aging is associated with hearing aids. In the MarkeTrak VIII survey, a slightly different tack in the questions posed was taken. Whereas non-adopters had been asked in previous surveys what was keeping them from acquiring hearing aids, MarkeTrak VIII asked them to indicate financial, hearing aid related, listening utility, and psychosocial factors that would influence them to adopt hearing aids within the next 2 years. The strongest influencer in terms of psychosocial factors (#15 in a list of 53 factors) was that the hearing aid should be nearly invisible. Given that finding, it makes sense for hearing instrument manufacturers to continue to focus design efforts on creating products that are unnoticeable to others. While a small BTE with a thin tube or wire to the ear canal may satisfy this demand for some consumers, not all find this style sufficiently inconspicuous. The most invisible style of hearing aid until recent years has been the completely-in-the-canal (CIC) device. The faceplate of a CIC is at least adjacent to, and sometimes 1 or 2 mm inside, the opening of the ear canal. It should also terminate within 5 mm of the tympanic membrane. Although considered to be cosmetically appealing, CICs typically remain visible to the casual observer if the ear is exposed. Advances in technology have enabled the design and manufacture of an even smaller style of hearing instrument, the ultra-cosmetic invisible-in-the-canal (IIC). Because the IIC can be built smaller, its faceplate can be recessed even farther into the ear canal than a CIC. The goal for an IIC is for the faceplate to reside between the opening and the first bend of the ear canal rather than near the opening. Due to the recessed nature of the faceplate, the hearing instrument is essentially invisible.
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Numerous studies have shown that there is a lot of stigma attached to hearing aids and hearing aid users. Audiologists often tend to focus on audibility first and cosmetics second, but the hearing aid user might have it the other way around. The concern about appearance has to be taken seriously, since the hearing aids will be of no use, if the hearing-impaired person is so concerned about his or her appearance that they will not wear them. The primary concern of a hearing-impaired individual can be found in the questions he or she asks e.g. are the questions concerned around the solution provided or around the size and visibility of the device.
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The Hearing Aid as Fashion Statement:
This hearing aid looks more like an earring. Its tiny triangular body comes in exuberant colors like sunset orange, racing green or cabernet red; a slender wisp of wire uncoils gracefully from the body to an earpod no bigger than a teardrop. But it is indeed a hearing appliance, made by the Danish company Oticon. It is called Delta, after its triangular housing that contains the microphones and signal-processing electronics. Introduced in May 2016, the device is designed for people typically in their 40’s, 50’s or older who are starting to lose the ability to hear high-pitched sounds but hate doing anything about it. This new design is appealing to people who traditionally are reluctant to seek help” for hearing loss.
The figure above shows The Delta hearing aid by Oticon, in a leopard skin pattern. The device is designed not to cover the ear canal.
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Communicator
For someone who is unable to fit a conventional hearing aid into their ear, maybe because of poor dexterity, a communicator may be a good option. This is a simple analogue amplifier that uses ear pieces like a doctor’s stethoscope in both ears. It is set up the same for both ears and is suitable for up to moderate/severe hearing losses.
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Audiology Services:
The majority of hearing loss is sensorineural. In mild-to-severe loss, the most effective treatment is hearing amplification with hearing aids. In a seminal randomized clinical trial of 194 elderly veterans, patients randomly assigned to receive a hearing aid experienced significant improvements in social and emotional function, communication function, and depression after 4 months, compared with patients in the control group. The authors subsequently found that the improvements were sustained 1 year after being fit with a hearing aid. These findings were confirmed by a cross-over trial involving 180 older patients, comparing a hearing aid, an assistive listening device, and in combination. The most significant improvements in emotional and social function were noted with the hearing aid. More recently, in a 4-arm, randomized trial of 60 older veterans comparing 2 types of hearing aids and 2 types of control arms, substantial improvements in quality-of-life measures, communication function, patient preferences, and adherence were noted for patients using hearing aids, with particular preference for a programmable hearing aid with a directional microphone. However, treatment effectiveness is not guaranteed even if patients receive hearing aids. Nonadherence to use of hearing aids is high. Several authors have conservatively estimated that up to 30% of patients who receive hearing aids do not use their aids. As patients age, handling the hearing aid can become increasingly difficult. Older patients experience more problems with inserting the earmold into the ear, switching on and off the hearing aid, changing the battery, cleaning the earmold, and changing the volume. These difficulties are among the most common explanations for failure to wear a hearing aid. Among a group of 138 hearing aid users who were older than 90 years, 33% to 79% experienced difficulty with any or all of these tasks. However, age (or any other predetermined variable) has not yet been identified as an accurate predictor of hearing aid use. In a group of 87 elderly male veterans, variables such as subjective functional handicap, age, education, and number of medications had no consistent correlation with hearing aid use.
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A number of hearing aid technologies have been a focus of study, including digital sound processing. Despite the promise of this technology, to date, little evidence is available to show that digital hearing aids result in improved hearing, since no trials involving digital technology have used adequate concurrent control groups. Valente et al have suggested that features, such as directional microphones confound existing comparisons between digital and analog hearing aids. Another recent study found that expectations strongly influence outcomes in patients who receive digital aids. The investigators provided digital aids to the entire cohort, but they led half of the patients to believe that they received analog aids. Significantly lower satisfaction rates were observed in these patients. Since digital hearing aids cost substantially more than analog hearing aids, they cannot yet be considered cost-effective. However, advances in digital technology may lower cost and improve effectiveness and thereby improve the cost-effectiveness ratio.
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The size and shape of hearing aids may influence satisfaction. In one randomized study, 244 elderly patients were fitted with either behind-the-ear, in-the-ear, or in-the-canal hearing aids. The in-the-ear aid was rated as the easiest to manipulate, but surprisingly, cosmetic judgments were unaffected by the size of the hearing aid. Another study of 40 patients compared patient satisfaction with behind-the-ear vs. in-the-canal hearing aids. Patients with in-the-canal hearing aids used their aids more frequently than patients with behind-the-ear aids. In both studies, patients with behind-the-ear aids reported significantly more “undesirable experiences” (operational difficulties, ear discomfort, and negative sound experiences).
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Audiologists also commonly use assistive listening devices in auditory rehabilitation. I am unaware of randomized controlled trials demonstrating that assistive listening devices have benefit over placebo. However, these devices have face validity and are commonly accepted and prescribed by audiologists. In patients with moderate hearing loss, devices such as infrared systems and telephone amplifiers may supplement the use of hearing aids. For patients with profound hearing loss in whom conventional amplification is unsuccessful, frequency-modulated systems, consisting of a microphone placed near the source of sound, a transmitter, and a receiver worn by the patient, are commonly used. In addition, visual and/or tactile alerts for the doorbell, telephone, and smoke detector have been used in place of hearing aids.
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Hearing aids are effective and well tolerated in patients with conductive hearing losses. Patients with mild, moderate, and severe sensorineural hearing losses are regularly rehabilitated with hearing aids of varying configuration and strength. Hearing aids have been improved to provide greater fidelity and have been miniaturized. The current generation of hearing aids can be placed entirely within the ear canal, thus reducing any stigma associated with their use. In general, the more severe the hearing impairment, the larger the hearing aid required for auditory rehabilitation. Digital hearing aids lend themselves to individual programming, and multiple and directional microphones at the ear level may be helpful in noisy surroundings. Because all hearing aids amplify noise as well as speech, the only absolute solution to the problem of noise is to place the microphone closer to the speaker than the noise source. This arrangement is not possible with a self-contained, cosmetically acceptable device. A significant limitation of rehabilitation with a hearing aid is that although it is able to enhance detection of sound with amplification, it cannot restore clarity of hearing that is lost with presbycusis.
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Hearing aids for Children:
Interventions for most infants and young children with hearing loss are primarily focused on the following goals:
•Preventing or reducing the communication problems that typically accompany early hearing loss.
•Improving the child’s ability to hear.
•Facilitating family support and confidence in parenting a child with a hearing loss.
Interventions focused on developing a child’s communication skills and abilities differ according to the type of communication approach that will be used by the child and family. Communication approach options for young children with hearing loss range from sign language alone to auditory/verbal (spoken language) or various combination approaches. Often parents must make an initial decision about a communication approach soon after their child has been diagnosed with a hearing loss. Parents also must choose a means for improving their child’s access to sound. The assistive devices most commonly used to amplify sound are hearing aids. Other assistive devices include FM systems and tactile aids. Some children with severe to profound hearing loss who have demonstrated little benefit from conventional hearing aids may receive a cochlear implant, an electronic device that is surgically placed in the inner ear. An aural rehabilitation consultation is considered medically necessary as part of the hearing impairment evaluation.
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When can my child be fit with hearing aids?
Infants as young as 4 weeks can be fit with hearing aids and hearing assistive technology systems.
What kind of hearing aid is best for my child?
It is important to work with your audiologist and early intervention team to evaluate your child’s needs. Since very young children cannot adjust their own hearing aids, the hearing aid selected for infants must be easily manipulated and monitored by parents and caregivers. As your child grows and develops and can respond to more sophisticated tests, hearing aids are adjusted accordingly. Therefore, hearing aids that can be easily adjusted for frequency response, amount of amplification, and maximum limits of amplification are desirable. These devices are typically digital hearing aids. It is important to know that, as a child grows, the ear grows too. This means that earmolds will need to be remade on a regularly scheduled basis—more often when children are very young and less often as children get older and their ears grow more slowly. In educational and home settings, children frequently connect their hearing aids to hearing assistive technology systems. Therefore, the hearing aid prescribed should have special features (telecoil and direct audio input capability) that will allow for this connection. Several types of hearing aids are available; the appropriate type depends on your child’s individual needs and skills.
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The behind-the-ear (BTE) hearing aid is the type of hearing aid most commonly recommended for infants and young children for a number of reasons, including:
1. It accommodates various earmold types.
2. The earmold detaches and can be easily remade as the child grows.
3. The earmold is easy to handle and can be easily cleaned.
4. Parents and caregivers can easily do a listening check and make adjustments.
5. It can accommodate a wide variety of hearing losses.
6. It can be made with direct audio input or a telecoil, so it can be used with other listening devices.
7. The earmolds are made of a soft material that is safer and more comfortable for tiny ears.
In-the-ear (ITE) styles are usually reserved for adults and older children. Once you have selected a hearing aid, the audiologist will carefully set the hearing aid using the results of your child’s hearing tests.
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How is a hearing aid tested on a baby or a young child?
The best way to test hearing aid benefit is to see how the hearing aid is working in a person’s ear. Audiologists measure hearing aid gain in the ear by using a probe microphone system. A small, soft tube is placed in the child’s ear next to the earmold. The tube is attached to a microphone. The probe microphone measures the amount of sound coming out of the hearing aid while it is on the ear. Children have much smaller ears than adults, so it important to take measures on each child’s ear to make sure hearing aids are set correctly. It can be difficult to test babies and young children using regular probe microphone tests. Babies may not keep the probe tube in their ear for more than a few minutes. They may not be able to sit quietly enough to test the hearing aid when it is on their ear. A special test called the Real-Ear-to-Coupler Difference (RECD) can be used instead. The audiologist makes a quick probe-microphone measure with just the child’s earmold in his or her ear. The hearing aid can be tested in a separate testing box. The hearing aid can be adjusted for the child and the child does not have to keep the probe microphone in their ear for more than a few minutes. The RECD is one of the most recent tests designed for babies and young children. It is considered regular practice for pediatric audiologists when working with babies. Research studies have shown that the RECD test is safe for babies younger than 6 months of age. The most important goal of hearing aid testing is to make sure speech is loud enough for the child to hear. Probe-microphone testing helps the audiologist judge how much speech will be heard through the hearing aid. This is called aided audibility. Using measures of aided audibility, the audiologist can compare different hearing aid settings and different listening situations. The differences between audibility with and without the hearing aid also can be compared.
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It is very important that children with hearing loss use their hearing aids as much as possible. A child who has been wearing hearing aids consistently since infancy will probably wear them without resistance. Children who have not been consistent hearing aid wearers may be more of a challenge. Start by putting the hearing aids on your child while you are engaged in a fun activity and increase the amount of time until your child is wearing the hearing aids during all waking hours. Young children should learn that only an adult should put the hearing aids on and take the hearing aids off. Older children may be more interested in their hearing aids if they are able to provide input into the color of their earmold or hearing aid. There are several ways to secure the hearing aids to your child’s ears. Some ideas include two-sided toupee tape, Huggie AidsTM, lightweight caps and headbands, fishing line and a safety pin, and hearing aid clips. Your audiologist will help you find the best method for your child.
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Misconceptions of mild hearing loss:
The hearing loss classification by Clark (1981) is used worldwide and defines a mild hearing loss as having thresholds between 26 and 40 dB HL. Mild hearing losses are clouded by the misnomer that is used to classify these levels of hearing impairment. The term ‘mild’ suggests little to no experienced impairment or handicap, resulting in a low priority for rehabilitation and amplification on the part of the patient, the consequences of which can be very high. In reality individuals with mild hearing losses often experience difficulties understanding speech especially in the presence of competing signals. There are five main reasons for hearing-impaired individuals with sensorineural hearing loss having problems hearing. They are decreased audibility, reduced dynamic range, reduced frequency resolution, reduced temporal resolution and increased listening fatigue. Reduced audibility, reduced dynamic range and increased listening fatigue affects individuals with all levels of sensorineural hearing losses, even those with mild levels of hearing loss, whereas reduced frequency resolution and temporal resolution are believed to affect mostly increased levels of hearing loss.
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The mild terminology is misleading as important speech sounds become inaudible with a mild hearing loss. People with a mild hearing loss are likely to hear some sounds, but not others or part of others. In particular the softer phonemes, which are usually consonants, may not be heard. It is especially the fricatives that become inaudible with a mild hearing loss, the /f/, /s/, /th/ and /k/. The reason for this is twofold, these phonemes are weaker and they are high frequency phonemes, which is the frequency area most commonly affected by impairment. The high-frequency components of speech are weaker than the low-frequency components and because the loudness of speech mostly originates from the low-frequency components, people with high frequency hearing loss may not realize that they are hearing less of the speech signal, even when they cannot understand speech in many situations. Statements like “speech is loud enough, but not clear enough” and “if only people would not mumble” are common.
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A sensorineural hearing loss increases the threshold of hearing much more than it increases the threshold of loudness discomfort, resulting in the range between the hearing threshold and the loudness discomfort being decreased. This means that for hearing-impaired individuals even with a mild hearing loss, weak to moderate sounds are not audible while loud sounds stay audible.
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With hearing loss listening and understanding requires more work to understand particularly in noise. Hearing-impaired people report increased concentration effort, attention and focus, compared to individuals without hearing loss. Increased listening fatigue is likely to be a side effect of even a mild hearing loss. Increased listening fatigue is however like decreased audibility often not being noticed by the person with a mild hearing loss him- or herself. The terminology mild hearing loss is in other words a misnomer. Mild hearing losses do not have mild consequences. A consequence of mild hearing loss is reduced audibility resulting in reduced speech intelligibility in general, but especially in noise and over distance. Another consequence is increased listening fatigue with the risk of affecting social life.
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Many people with mild hearing losses are unaware of their hearing loss:
There are significantly more people with mild hearing losses as compared to people with moderate, severe and profound hearing losses (World Health Organization, 2000). However, within the group of hearing- impaired individuals, people with mild hearing losses are the least likely to own hearing aids. There are many reasons for this, one being that many people with mild hearing impairment are unaware of their hearing loss.
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Do people with mild high frequency hearing loss need hearing aids?
High frequency hearing loss (sometimes called “Partial Deafness”) occurs when the hair cells in the cochlea are missing or damaged. When the cochlea hears sounds, high-frequency sounds are perceived in the bottom of the cochlea and low-frequency sounds are in the top. Because of this, it’s common for hearing loss to happen in the high-frequencies before it happens in the low frequencies. When this occurs, and the cochlea is still able to understand some low-frequency sounds but no high-frequency sounds, the hearing loss is called “high frequency hearing loss”. This means that someone with high frequency hearing loss will be able to hear sounds like the roll of thunder, but will have difficulty hearing with sounds like the letters F, S, or K, and female voices. There are lots of different reasons why high frequency hearing loss occurs, including exposure to noise, ageing, or genetics.
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It is also important to note that different professionals will have a different take on what is classed as a high frequency. Low and high frequencies are measures on an audiogram and there are some professionals that will class a level of 2,000 Hz (2kHz) as being a high frequency. The stated range for high frequency actually runs from 2,000 Hz all the way through to 8,000 Hz. When you take on board that many people consider 1,000 Hz to be the mid-level of frequencies, it is easy to see that there is a wide range of sounds that can be classed as being at a high frequency.
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To a person with high-frequency hearing loss, other people sound like they’re mumbling. That’s because those with the condition have a hard time hearing sounds in the 2,000 to 8,000 Hertz range. In human speech that includes consonants like f, h or s. Some examples include female voices, birds and doorbells. High-frequency hearing loss can adversely affect a person’s quality of life by causing anxiety, depression and social isolation. Technically speaking, high-frequency hearing loss results when the sensory hearing cells in the ear’s cochlea die or becoming damaged. The cells’ job is translating external noise into electrical impulses that the brain then interprets as sound. There are a number of causes of high frequency hearing loss. Noise is a major factor, causing permanent irreversible hearing loss. Aging also causes high-frequency hearing loss, but does so gradually. High frequency hearing loss can also run in families. Certain ototoxic drugs, can damage hearing, as well. Some diseases can cause high frequency hearing loss.
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It has been proved beyond doubt that central auditory processing is best when there is equal input from both ears in all the frequencies. Even if in one particular octave there is a difference in the hearing threshold level between the two ears the central auditory processing of sound cues with that particular frequency will be comparatively poor. If central auditory processing is poor, the subject will have poor speech understanding in challenging acoustic environments. Though a mild or mild to moderate hearing loss limited to the higher frequencies only with normal hearing in the low and middle frequencies is usually passed off as NEAR NORMAL HEARING and clinicians often ask such patients to refrain from using hearing aids, yet even a mild deafness in the high frequencies is far from normal and the subject with such hearing deficit is bound to have problems in understanding speech when he is in difficult hearing situations and in challenging acoustic environments even though he may not want to accept or realise it.
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A person with a mild high frequency hearing loss only in the high frequencies of even about 40 dB has a significant problem in understanding speech as he misses the high frequency consonant sounds not only because he has a mild hearing loss in the high frequencies but also because the high frequency consonant sounds are spoken softly. In normal human speech, high frequency consonant sounds are pronounced about 30dB softer (i.e., lower in intensity) than the low frequency vowel sounds. Hence the handicap of a person having a 40dB high frequency hearing loss is not just a hearing loss of 40dB but much more (say 40 + 30 dB as the high frequency consonant sounds which provide intelligibility to the speech are pronounced at much lesser intensity). So the handicap of a person with a 40dB high frequency hearing loss is actually much more than 40dB.
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When a person has a high frequency hearing loss even if it is mild, there is usually a concomitant cochlear outer hair cell damage which in turn jeopardizes cochlear processing of sounds of those particular frequencies. Cochlear processing involves selective amplification, frequency resolution, temporal resolution, temporal summation etc which are very important requirements for clear hearing and speech understanding. The function of the cochlea is not mere amplification of the sound but much more than that. The cochlea processes and cleans the sound so that a very clean image of the sound in the form of action potentials reaches the central auditory system for more efficient processing in the brain. When there is even a minor localized damage of the cochlea, this function is lost for those frequencies. Selective amplification which is a specific cochlear function means higher gain (amplification) for soft sounds (say input sounds of 30dB or lower) but lower gain (very slight or no amplification) of loud sounds (say input sounds of 80dB). Without this, recruitment will take place and hearing will become uncomfortable. Similarly, frequency resolution and temporal resolution will also be improper for those frequencies leading to poor speech understanding. These problems will be there but the subject may not realize it adequately but is definitely handicapped especially in difficult hearing situations. By doing an audiometry test we are measuring only the hearing threshold for those frequencies, we are not testing these specialized cochlear functions and so the handicap appears lesser to us on paper but the actual handicap is much more than what is revealed by the audiometric thresholds. A sophisticated digital hearing aid if programmed perfectly can mimic many of the cochlear functions and provide near natural and comfortable hearing in these types of so called MILD hearing loss.
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Another important aspect is there regarding central auditory processing. The brain is tonotopic as regards processing of the different frequencies. If the brain is deprived of certain frequencies even partially, the functionality of those areas is reduced or is replaced by other functions. Stimulating these areas later on by amplification is not expected to yield the desired results and central processing will be poor if the amplification is provided late. Hence amplification should be provided as soon as the hearing loss is detected. And what is most important in such cases where there is just a minor cochlear damage limited to just a few frequencies, is that the hearing handicap may not be very perceptible and so the patient is not so much bothered and so ignores it, even though he is bound to have a problem but dysfunction of central auditory processing induced by the hearing impairment will have permanent and more serious handicapping effects with deleterious results that cannot be corrected later on even by providing amplification.
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A study had carried out speech discrimination scores (SDS) in two groups of patients having a similar mild high frequency hearing loss, five years after the hearing loss had been audiometrically detected. The patients who had been fitted with a hearing aid immediately on detection of the hearing loss had better SDS after 5 years than the patients who had not been fitted the hearing aids even though the hearing thresholds had not deteriorated in five years. Other studies have suggested that perfectly programed suitable digital hearing aids gives better SDS scores when fitted early proving that central auditory processing deteriorates if the deafness, however mild, is not corrected early.
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Those in the legal profession esp. judges and lawyers work in acoustically challenged noisy environments do not afford to miss a single word. They will be immensely benefitted with digital hearing aids for high frequency hearing loss.
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What to consider when fitting mild hearing losses:
People with mild hearing losses on average experience fewer hearing loss related problems in their daily life, than people with more severe hearing losses. For this reason they also on average get less hearing aid benefit. However, they DO gain benefit from amplification and this is a key message that the audiologist has to pass on to the hearing-impaired individual. As hearing-impaired individuals with mild hearing losses on average have less potential for hearing aid benefit it is even more important to optimize their hearing aid benefit and minimize the potential disadvantages. Occlusion effect is one potential disadvantage of hearing aids, but with the launch of open fittings back in 2003 this is no longer an issue as open solutions now are multiple.
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First use of hearing aid:
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What Questions should you ask before buying Hearing Aids?
Before you buy a hearing aid, ask your audiologist these important questions:
• Are there any medical or surgical considerations or corrections for my hearing loss?
• Which design is best for my hearing loss?
• What is the total cost of the hearing aid?
• Is there a trial period to test the hearing aids? What fees are nonrefundable if they are returned after the trial period?
• How long is the warranty? Can it be extended?
• Does the warranty cover future maintenance and repairs?
• Can the audiologist make adjustments and provide servicing and minor repairs? Will loaner aids be provided when repairs are needed?
• What instruction does the audiologist provide?
• Can assistive devices such as a telecoil be used with the hearing aids?
• What problems might I experience while adjusting to my hearing aids?
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Become familiar with your hearing aid.
Your audiologist will teach you to use and care for your hearing aids. Also, be sure to practice:
◦putting in and taking out the aids
◦adjusting volume control
◦cleaning
◦ identifying right and left aids
◦replacing the batteries with the audiologist present.
–The hearing aids may be uncomfortable.
Ask the audiologist how long you should wear your hearing aids during the adjustment period. Also, ask how to test them in situations where you have problems hearing, and how to adjust the volume and/or program for sounds that are too loud or too soft.
–Your own voice may sound too loud.
This is called the occlusion effect and is very common for new hearing aid users. Your audiologist may or may not be able to correct this problem; however, most people get used to it over time.
–Your hearing aid may “whistle.”
When this happens, you are experiencing feedback, which is caused by the fit of the hearing aid or by the buildup of earwax or fluid. See your audiologist for adjustments.
–You may hear background noise.
Keep in mind that a hearing aid does not completely separate the sounds you want to hear from the ones you do not want to hear, but there may also be a problem with the hearing aid. Discuss this with your audiologist.
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Some Hearing-Aid features worth noting:
• Digital noise reduction improves listener comfort and sound quality in noisy environments. For many, it also may improve speech understanding in noise.
• Low-battery indicator sound—most newer hearing aids have this.
• Wax guards help keep hearing aids free of ear wax, which can cause malfunctions and is a major complaint of our survey respondents. Ask the hearing-aid dispenser to teach you how to remove and replace the wax guard, and how often you’ll need to change it.
• Automatic volume control (compression) provides more amplification for low sound levels than high sound levels, which prevents high sound levels from being intrusively loud. Most aids had this feature.
• Vents are tiny tunnels in ear molds or the one-piece hearing aids that sit in the ear. They minimize the stuffed-up sensation, and can contribute to improved speech understanding, depending on the vent size.
• Manual volume control lets you make adjustments in a given environment. Some hearing aids have a self-learning feature that automatically adjusts amplification based on how they’re typically used.
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Features in Behind-the-Ear Models Only:
• Bluetooth capability for hands-free use of cell and regular phones, and streaming TV.
• Direct audio input allows the aid to be connected by cable to FM systems (effectively, mini-radio stations used in an enclosed space, specifically for hearing-aid users); MP3 players; and other audio devices.
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Learn how to use your hearing aid:
There are various things you need to know about your new hearing aids.
•Familiarise yourself with your specific model and practise putting your hearing aids in and taking them out.
•If you have two hearing aids, they are often colour coded to make sure you put the aid in the correct ear. RED is always for the RIGHT ear and BLUE for the LEFT ear.
Hearing aid controls:
Practise using the controls on your hearing aids and adjusting the volume (if you have a control for this) in a comfortable and quiet environment. Hearing aid controls vary from model to model. You should refer to the specific instructions that came with your aids. Although controls do vary you will sometimes see O for off, M for microphone and a T setting. The normal setting for using your hearing aid is M. Most hearing aids have a T setting. This allows you to use special listening equipment such as induction loops or telephones that are hearing aid compatible. Your audiologist or hearing aid dispenser will show you how to switch to the T setting.
Volume:
Many hearing aids have a volume control. This is usually a wheel, but it can be a small lever. To increase the volume, push the wheel or lever upwards. Push the wheel or lever down to make the volume quieter. Some hearing aids adjust the volume automatically. With these aids, there is no volume control for you to adjust as it is all done internally by the hearing aid.
Programmes:
Many digital hearing aids have different programmes or settings for different listening situations. The programmes let you change how the hearing aid behaves when you go into different situations, such as into a noisy situation or when listening to music. The types of programme depend on the model of hearing aid and how it has been set up. Your audiologist or hearing aid dispenser will explain what you can do and how to switch between listening programmes. If you wear two hearing aids, your audiologist or hearing aid dispenser will help you make sure that you get the right sound balance between the two sides.
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Tips to help you adjust to your New Hearing Aids:
The most important thing you can do to save your residual hearing is to wear your hearing aids. Hearing aids can improve your life in many ways, but it can also be hard to adjust to them. Learn some tricks to fully enjoy and utilize your new hearing aids. While hearing aids can greatly improve your hearing, they are foreign to your ears when you first start wearing them. They can take some getting used to. It’s estimated that one in eight hearing aids is never used, due to unrealistic expectations of how they will work from the beginning.
Here are a few things to keep in mind to make the transition easier as you settle into your new hearing life:
1. There is an adjustment period:
If you waited a few years to get a hearing aid, you will start hearing sounds you haven’t heard in a long time. It will take some time to get used to hearing them again. It also takes time to adjust to sounds that are amplified directly in your ear. It can take anywhere from 30 to 90 days for your brain to adjust to your new hearing aid, so don’t give up. Follow the adjustment regimen recommended by your audiologist, and start hearing better.
2. Hearing aids are a little uncomfortable at first:
New hearing aids are similar to new shoes or new glasses. They don’t feel familiar, and take some getting used to. Your audiologist can make adjustments to your hearing aid to make sure the fit is perfect for you, but give yourself time to get used to them. What is a little uncomfortable at first will quickly become normal, and your improved hearing will be worth it.
3. It may feel too noisy at first:
Hearing aids amplify the sounds around you, allowing you to hear sounds you missed before. They can seem noisy and overwhelming at first, because you haven’t heard these sounds in a long time. Your audiologist will work with you to manage the new sounds. They will probably recommend wearing the new hearing aids in quiet environments first, working up to noisy environments over a few weeks. With a little time, your brain will adjust to the new sounds, and soon enough, it will all feel normal. Hearing aids open up a world of sounds that weren’t available before. At first it can be a little overwhelming. Your brain is adjusting to hearing sounds that have been missing for a long time, but you are meant to hear it all! Give yourself a little bit of time to get used to your new hearing aids, and soon it will all sound just the way it should.
4. You may have difficulty understanding speech:
Some hearing aids can direct hearing in a particular direction, but even the best hearing aids in the world can’t completely separate speech sounds from other sounds in the environment. Even people with normal hearing sometimes have trouble hearing speech and following conversations in loud places. This complaint is common among new hearing aid wearers, and it is something they quickly learn to adjust to.
5. What to do about feedback:
Feedback occurs in hearing aids that don’t fit properly, or are clogged with earwax. Hearing aids should fit snugly, and ill-fitting hearing aids can cause sound to “leak” out of the ear. This “leak” is what causes feedback. A leak can be corrected with a quick visit to your audiologist to adjust the fit of your hearing aid, or to clean up the earwax.
6. Eliminating static (noise):
Hearing aids shouldn’t produce static if they are working properly. So if your hearing aid has static, take it in to your audiologist for a checkup. Static in hearing aids can be something as simple as dirt buildup, or a low battery, or something more complicated like an amplifier problem. Your audiologist will be able to diagnose the problem, and can work with you to get it corrected, so your hearing is undisturbed and as normal as possible.
7. At first, only wear them for a few hours a day.
If you need to, it’s okay to only wear your new devices in comfortable situations and environments for the first few days. Professionals recommend that you eventually try to wear them during your waking hours. The more sounds you are able to recognize and filter out as well as identify as bothersome can help your hearing healthcare professional make adjustments in your follow-up visits. Also, the more you wear your hearing aids, even in quiet situations when you are at home, the more sounds you will be able to detect and filter so that when you are in a noisy environment, your brain will have been able to acclimate faster.
8. Start out in a quiet room.
On the first day, sit in a quiet room in your house and start getting used to your rediscovered ability to hear faint sounds, like the ticking of a clock or a car driving by outside. These might seem unnaturally loud at first because your brain isn’t used to hearing them. It’s all a part of your brain’s adjustment and won’t last long. Some hearing healthcare professionals encourage you to write things down that you are noticing that may be bothersome to you. Before you return to your next follow-up visit, glance at your list and you may notice that some of those sounds aren’t bothersome any longer. If you find that some still are, those are the ones to report to your hearing healthcare professional to be adjusted at your follow-up visit.
9. Don’t play with the volume too much.
It’s likely that your hearing aids adjust to different listening situations automatically, so they shouldn’t need to be manually adjusted very often. If you do turn them up, don’t make the volume too loud. Don’t try to make your devices do what fully-functioning ears can’t do, like hear faint sounds from very far away; they don’t work that way, and you can damage your hearing more by doing that.
10. Practice talking to people in groups.
Start having conversations with your close friends and family, as familiar voices are the easiest to identify. Hearing still requires active listening, which means making sure you face the speaker and look right at them while they’re talking. This will help your brain reconnect the dots between sounds, vocal patterns, and nonverbal body language.
11. Ask your friends or family to set the television to a “normal” volume.
Now that you have your new hearing aids, you shouldn’t need to turn the television up louder than a person with normal hearing would. Ask someone else to help you find an appropriate volume, and try to use that setting consistently.
12. Watch with captions or subtitles.
Listening to and reading words at the same time is a great way to help retrain your brain to connect sounds and language. Turn on your television’s closed captioning and enable subtitles when you watch a movie.
13. Do not expect your family doctor to be knowledgeable about hearing loss, brands of hearing aids and whether or not you need them. Data shows that only 13% of physicians screen for hearing loss.
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Adjustment:
Hearing aids are incapable of truly correcting a hearing loss; they are an aid to make sounds more accessible.
Three primary issues minimize the effectiveness of hearing aids:
•The occlusion effect is a common complaint, especially for new users. Though if the aids are worn regularly, most people will become acclimated after a few weeks. If the effect persists, an audiologist or Hearing Instrument Specialist can sometimes further tune the hearing aid(s).
•The compression effect: The amplification needed to make quiet sounds audible, if applied to loud sounds would damage the inner ear (cochlea). Louder sounds are therefore reduced giving a smaller audible volume range and hence inherent distortion. Hearing protection is also provided by an overall cap to the sound pressure. Also of protective value is impulse noise suppression, available in some high-end aids.
•The initial fitting appointment is rarely sufficient, and multiple follow-up visits are often necessary. Most audiologists or Hearing Instrument Specialists will recommend an up-to-date audiogram at the time of purchase and at subsequent fittings.
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Evaluation:
There are several ways of evaluating how well a hearing aid compensates for hearing loss. One approach is audiometry which measures a subject’s hearing levels in laboratory conditions. The threshold of audibility for various sounds and intensities is measured in a variety of conditions. Although audiometric tests may attempt to mimic real-world conditions, the patient’s own every day experiences may differ. An alternative approach is self-report assessment, where the patient reports their experience with the hearing aid.
Hearing aid outcome can be represented by three dimensions:
1. hearing aid usage
2. aided speech recognition
3. benefit/satisfaction
The most reliable method for assessing the correct adjustment of a hearing aid is through real ear measurement. Real ear measurements (or probe microphone measurements) are an assessment of the characteristics of hearing aid amplification near the ear drum using a silicone probe tube microphone.
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How to put on hearing aid:
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Identify the left/right hearing aid
It is important to distinguish between the left and the right hearing aid as they might be shaped and programmed differently.
A BLUE shell, text or dot identifies the LEFT instrument.
A RED shell, text or dot identifies the RIGHT instrument.
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How to insert an in-the-ear hearing aid:
Gently swing the battery door fully open, but do not force it
Remove the sticker from the new battery
Place the battery into the empty compartment.
The + sign on the battery should face up.
For maximum power, allow the battery to be aired for 60 seconds before placing it into the empty compartment.
The MultiTool can be used for battery change. Use the magnetic end to remove and insert batteries. The MultiTool is provided by your hearing care professional.
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Turning the Hearing Aid ON
Close the battery door completely. You should notice a click. The hearing aid is now ON.
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Inserting Your Hearing Aid
Your hearing aid has been programmed individually for your right or left ear. You will see a color marking on your hearing aid. This can help you distinguish between the left (blue) and right (red) hearing aids.
When inserting the right hearing aid, hold it with the right hand. When inserting the left hearing aid, hold it with the left hand.
Hold your hearing aid between your thumb and index finger with the microphone on top. If your hearing aid has a pull-out string, this must be on the bottom. Vent is also at bottom.
Hold the hearing aid with the coloured dot face up. Place the tip of the hearing aid in your ear canal.
Gently pull your ear outwards and push the hearing aid into the ear canal, twisting slightly if necessary. Follow the natural contour of the ear canal
It takes patience and practice to insert your earmold correctly.
Initially use mirror at the time of insertion.
If you have difficulty, please consult your hearing care professional.
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Removing Your Hearing Aid
Use your thumb to push up against the bottom (back part) of your ear to loosen the hearing aid
Grasp the hearing aid at its edge between your thumb and forefinger. Gently remove it from your ear.
If your hearing aid has a removal (pull-out) string, pull it gently
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Turning the Hearing Aid OFF
Place your fingernail underneath the front edge of the battery door and lift to open. The hearing aid is now OFF.
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How to put on a miniRITE or RITE (RIC) hearing aid
1. Place the hearing aid behind your ear.
2. Hold the bend of the speaker wire between your thumb and index finger. The earpiece should point towards the ear canal opening.
3. Gently push the earpiece into your ear canal until the speaker wire sits close against the side of your head.
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How to put on a miniBTE or BTE13 hearing aid with thin tube
Putting on your hearing aid with a thin tube correctly every time takes practice. Learn about it here.
1. Place the hearing aid behind your ear.
2. Hold the bend of the tube between your thumb and index finger. The earpiece should point towards the ear canal opening.
3. Gently push the earpiece into your ear canal until the thin tube sits close against the side of your head.
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How to put on a miniBTE, BTE13 and BTE13 SP hearing aid with hook
1. Gently pull your ear outwards and press the mould in the direction of the ear canal, twisting slightly.
2. Place the hearing instrument behind your ear
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Batteries of hearing aid:
Hearing aids come in many different sizes and styles. Because there are various sizes of hearing aids with different features, the amount of power needed for the device to run differs. Larger hearing aids generally require larger hearing aid batteries. Additionally, hearing aids used for individuals with severe or profound hearing losses typically require larger batteries because more power is needed to help them operate. The most commonly used batteries for hearing aids are called zinc-air batteries. These batteries operate from 1.35 to 1.45 volts. Small silver discs, zinc-air batteries are not rechargeable, and must be discarded after use. Hearing aid batteries come in five sizes. The right one for you depends on the style and size of your hearing aids. The hearing aid industry has color-and-number-coded the packaging of batteries to make buying replacements easy-choose 5-red, 10-yellow, 13-orange, 312-brown, or 675-blue. The sticky tab on the back of the battery is also color-coded.
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There are five sizes of hearing aid batteries available on the market. The sizes, from smallest to largest, are 5, 10, 312, 13 and 675. Size 5 hearing aid batteries are very rare. The four most common hearing aid battery sizes are all smaller than the diameter of a dime:
•Size 10 – 5.8 mm wide by 3.6 mm high
•Size 312 – 7.9 mm wide by 3.6 mm high
•Size 13 – 7.9 mm wide by 5.4 mm high
•Size 675 – 11.6 mm wide by 5.4 mm high
Because size differences may appear trivial to the regular eye or can be difficult to remember, battery packaging is generally color-coded to making finding and purchasing the correct ones easier. Size 5 batteries are labelled red, size 10 batteries are labelled with yellow, size 312 are marked in brown, size 13 are packaged in orange and size 675 are usually designated using blue.
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How do zinc-air hearing aid batteries work?
Unlike common household batteries such as AA, AAA and 9-volt, zinc-air batteries are activated by the oxygen in the air. Without oxygen, zinc-air batteries can’t power hearing aids. Before a hearing aid battery is inserted, a sticker must be removed from the back. This sticky tab keeps the battery fresh, and protects the zinc inside the battery from being activated. Once the tab is removed, tiny holes in the battery casing allow molecules of oxygen to enter. The holes are big enough to let oxygen in, but small enough to prevent battery fluid from seeping out. A filter behind the holes also helps thwart leakage. Remember, once you remove the tab, there’s no turning back! Resealing the battery will not stop the activation process and save it. So, be sure to keep the tab intact until you’re ready to use the battery. Because oxygen must pass through fine holes and a filter, it’s absorbed slowly. That’s why it’s important to wait a full minute before you insert the battery and close the battery door after you’ve removed the tab. If you don’t wait, the battery may not absorb enough oxygen to properly power your hearing aids.
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How long do hearing aid batteries last?
Battery life varies with hearing aid styles. Some hearing instruments require more power to function at optimum levels. Digital hearing aids contain sophisticated circuitry to deliver near-to-natural hearing in a variety of environments, and this requires more power than analog hearing aids need. Typically, wearers of digital hearing aids can expect a battery to last from 5 to 7 days. If you experience shorter battery life, your hearing care professional can check the battery contacts in your hearing aids, as well as, test for battery drain. Most batteries have a “shelf-life” of about three years.
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Get the best performance from hearing aid batteries:
To enjoy maximum battery life, store batteries at room temperature. Heat exposure can shorten the life of hearing aid batteries, as can a humid environment, such as a bathroom or refrigerator. It is not recommended to carry batteries in a pocket or handbag where they can mingle with metal items like loose change or keys-doing so can short-circuit your hearing aid batteries. For optimum performance, open the battery compartments in your hearing aids whenever you’re not wearing them. This limits battery drain and helps alleviate moisture build-up. Turning your hearing aids off when not in use can also help extend battery life.
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Why is my hearing aid not working despite having a new battery?
There could be several reasons for this. Here are some things to check:
•Not enough time for battery to be activated/”charged” after removal of the tab.
•Dented battery surface causes poor contact with battery terminal of the hearing aid.
•Battery is dead (even if it is brand new). This is very rare. Can as well happen when not activated correctly!! Built up dirt on the battery terminal of the hearing aid causes poor contact.
•The battery does not fit into the battery door of the hearing aid (some battery doors are designed with a smaller cavity where the battery negative housing is placed).
lf hearing aid does not work properly after replacing with a new battery (wait two minute after removing the tab before use), take your hearing aid to your hearing care provider for further troubleshooting.
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When might a hearing aid battery expand and leak?
If the discharged battery is left in the hearing aid after end of life, humidity can influence the battery chemistry and lead to swelling, especially in extreme weather conditions such as a tropical environment. Once a battery is at the end of its life, it should be removed from the hearing aid.
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Why does my hearing aid battery suddenly last a shorter time?
Statistics show that, in most of the cases, the reasons for a short running time are not necessarily production faults, but rather:
•Environmental influences (e.g. humidity, temperature).
•Personal hearing habits have changed (longer period of use per day, higher noise level, new features of the hearing aid are being used).
•The hearing aid was in use longer than usual (e.g. night at the theater).
•The hearing aid is new, or the type or brand of the hearing aid has changed.
•The new hearing aid has additional features that require more energy.
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Improper handling can also reduce the running time of the hearing aid battery, for example:
•The battery tab is removed and activation period as too short!! It has to be at least 1 minute before it is inserted into the hearing aid.
•The hearing aid is not switched off over night or after a long period of non-use.
•The battery loses capacity due to a short circuit when mishandled (e.g. through contact with metal objects).
•The battery is stored in a warm environment (e.g. in parked car in the sun).
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There are two ‘NEVERs’ with batteries. NEVER keep batteries with your medicines, as you might accidentally ingest one. NEVER allow young children to handle batteries, as they might ingest them. All hearing aid batteries are toxic if swallowed. Keep them in a safe place and be sure to recycle your batteries properly.
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Power one ACCU plus rechargeable hearing aid batteries (cells):
The rechargeable hearing aid cells are available in the sizes p10accu, p13accu, p312accu and p675accu. They can be used in most hearing aids of the relevant size. In order to charge the ACCU plus cells, several power one charging solutions can be used. These fast chargeable batteries are ecologically sound. Please ensure that the mating surfaces of the power one ACCU plus and inside the appliance are kept clean. For best results and product life, please avoid deep discharging or short circuiting the battery at all times. The batteries should be stored at a room temperature of 20-25 degrees without their product life being affected. Physically determined rechargeable hearing aid batteries (NiMH-technology) have a lower energy density compared with zinc air hearing aid batteries (primary cells). This is expressed through a lower capacity, which is consistent with just approx. 1/10 of the capacity of primary cells. In exchange the rechargeable hearing aid cells could be recharged approx. 500 times. If ACCU capacity is sufficient for one day of hearing aid use, the same hearing aid with zinc air batteries reaches at least 10 days running time.
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Maintenance and care of hearing aid:
Few consumer purchases have any faster rate of depreciation and limited resale value than hearing aids. Stated differently, from an economic standpoint your hearing aids are of no value to anyone but you. For this reason and because they’re expensive to replace, it makes good sense to service them on a regular basis. Systematic maintenance will reduce repair costs, lessen the number of “down” times, and most importantly extend the life of your hearing aids. What follows is a brief list of maintenance procedures that will help you to accomplish this:
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Clean your Hearing Aids Daily:
This is best accomplished by first wiping the hearing aids with a dry cloth or tissue to remove wax, oil and moisture from the surface. Do not use water, cleaning fluids, solvents or alcohol, as these could damage your hearing aids. Then lightly dry-brush all components using the wax removal techniques, and remove wax from the receiver and vent tubes. This cleaning should be done daily, preferably at bedtime. Most hearing aids come with a filter or other device to stop wax getting into the hearing aid. Check the wax filter and replace it if necessary once in 3 months.
Using the MultiTool for cleaning:
The MultiTool is a versatile tool that should be used to ensure the best care, cleaning and performance of your hearing aids: Replace the brush when necessary. Simply pull it out of the tool and insert a new fresh brush. Press the new one firmly into the handle. MultiTool brushes can be purchased from your hearing care professional.
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Proper Storage:
Keep hearing aids away from heat and moisture. Place hearing aids in a safe, convenient and protected location, being certain to disengage the battery door. Sticking hearing aids in pockets or at the bottom of purses without a protective container exposes them to dirt and dust that can eventually do damage. Dust-free carrying cases are provided with nearly all new hearing aids. You should have this case available when necessary. If moisture build-up is a concern, store the hearing aids in a closed container with an absorbent dry-pack available from your provider.
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Schedule Regular and Periodic servicing:
In-office cleaning and servicing are usually included free with your purchase of hearing aids and you should take advantage of this service from your hearing healthcare provider. Servicing should be done at least every three months (like servicing an expensive car). Hearing aids should be checked for power loss, dirty contact points, plugged vents and openings, and so forth. A more comprehensive servicing should be performed at least annually. This should include electroacoustic analysis (test box evaluation to ensure maintenance of original manufacturer’s performance specifications). BTE wearers should also have the tubing replaced at this time (if not needed at 6 months). There may be a modest charge for this more comprehensive servicing but it’s worth it. Residents of drier climates will need more frequent tubing changes than those living in more moist environments. Next to daily cleaning, regular in-office servicing is the most important maintenance you can obtain.
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Ear hygiene:
Always pay attention to proper ear hygiene so that your hearing aids can provide the best performance. Your ears must always be free of earwax and debris, e.g. dry skin or infections. You can get products to help keep the ear or earpieces clean from your hearing care professional. They will be able to examine your ear and hearing aids thoroughly for any blockages caused by ear wax, or debris and check that the hearing aids are functioning properly.
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Avoid impacts:
Avoid dropping the hearing aid on hard surfaces. This can happen while cleaning or changing the battery. Take care when inserting or removing your hearing aid. When handling your hearing aids, it is a good idea to hold them over a soft surface to avoid damage if you drop them. I recommend that you put a soft cloth on the table. Keep your hearing aids in their presentation case or in a drying kit when you are not using them.
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Cost and lifespan of hearing aid:
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Hearing aid pricing:
Hearing aids are sometimes described as tiny computers for your ears. Because of the sophisticated technology and miniature size, hearing aid prices can range from less than $1000 to as much as $4,000 per ear for the very best technology. Features, size and level of personalization can all account for differences in cost. It’s time to do something about a public health crisis affecting too many older adults suffering in silence because they can’t afford hearing aids. Nearly half of adults who are 75 and older suffer hearing loss, yet a majority just can’t afford to do anything about it. A national study shows hearing aids aren’t affordable for most people who need them. According to the study, about 30 million people in the US have hearing loss of some form. In 2013, the average retail price of a hearing aid was $4,700.
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The purchase price of a single hearing aid is generally anywhere from $800 to $4000 per ear, so the total for two hearing aids, as most people require, ranges $1600 to $8000. The price of a hearing aid typically includes the cost of the hearing examination, the device consultation and fitting time (including post-fitting adjustments), follow-up appointments, cleanings and a device warranty that can range from one to three years. The warranty often covers all repairs and includes a one-time replacement policy if you lose the hearing aid during the first year. The price may also include a year’s worth of hearing aid batteries.
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Why is there such a large range of pricing for hearing aids?
There are two main factors that affect the purchase price of the hearing aid: the style of the hearing aid and the technology of the hearing aid.
Style:
The hearing aid style can range from devices that are small enough to fit completely in your ear canal or discreetly tuck behind your ear to larger devices that sit on top of the ear or fill up the outer part of the ear canal. Generally speaking, the smaller custom devices are the most expensive because of the labor and precision required to create them in the exact shape of your ear canal.
Technology:
All hearing aids have a basic level of sound processing technology that will automatically adjust for sound coming in and account for your hearing loss. The more advanced hearing aids have the best technologies available for feedback reduction, hearing in noise solutions, wireless capabilities and other features to improve the listening experience. Generally speaking, the more advanced the technology in a hearing aid, the more expensive the device.
When you combine the user need for advanced technology in the smallest custom sizes, you will see prices along the higher range, and vice versa.
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Why do Hearing Aids cost so much?
If you’re looking to purchase a custom-fitted, quality pair from an audiologist, you can expect to pay anywhere from about $2,200 to more than $7,000 a pair for devices with the latest tech, such as the ability to wirelessly stream sound from your television and link up to your smartphone. According to a survey recently published by the Hearing Review, the average price of a mid-level pair of aids hovers between $4,400 and $4,500. The same survey found that the average prices of both high-end and mid-level aids have dropped since 2005. The price of most budget-oriented aids has remained steady. No matter how you look at it, hearing aids are expensive. So why exactly do they cost what they do? Experts say you are not only buying a high-tech device that requires extensive research, but also likely paying for services from highly trained hearing specialists during the life span of your hearing aids. On the manufacturing end, materials such as microprocessors and microphones may be about 10 percent of the final cost for some hearing aids. Research may account for as much as triple the cost of materials. Between electrical engineers, audiologists, computer programmers and musicologists, an immense amount of technical knowledge is required to produce these miniature devices. Once made, the hearing aids must then be marketed and sold, an expense that also includes the cost of staff responsible for training the audiologists and other hearing specialists in their use.
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Using the average price of $4,400 for a pair of hearing aids, the costs are broken down as shown below. Please note that these figures are estimates drawn from a variety of sources, including discussions and correspondence with audiologists, manufacturers and industry experts.
Overall cost — $4,400
Costs for the manufacturer:
•Materials — $440
•Research — $1,320
Other retailer costs:
•Rent/overhead — $473
•Testing/diagnostic machines — $352
•Licenses/insurance — $132
•Salaries — $660
•Marketing — $330
•Continuing education/training — $220
•Potential profit for the retailer (pretax) — $473
Approximate product cost for retailer — $1,760
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At hearing clinics and other outlets, aids sell for approximately 2-1/2 times the wholesale price. Many factors contribute to the markup. When customers visit an audiologist in an office — where rent and overhead can be 10 to 15 percent — they spend time learning about their condition, going over various products available and then getting fitted — often requiring a hearing-test booth and a sound box for calibration. These high-tech machines need to be replaced every few years and can account for about 8 percent of the total cost. But even before the customers walk in the door, the audiologist needs to purchase licenses and insurance, about 3 percent for some practices. Customers frequently return for adjustments, cleaning and seminars, all of which take time and are usually included in the price of the hearing aids. Salaries can account for 10 to 20 percent of the cost, depending on the size and scope of the practice. Like any business, there are marketing activities to attract and retain customers, accounting for 5 to 10 percent, as well as continuing-education requirements and staff training, which make up 5 percent of the total. It all adds up quickly for the audiologist, who in a good year may take home from 10 to 15 percent of a practice’s revenue — and that’s before taxes and interest payments. You can buy a hearing aid anywhere, but it will only be as good as the person fitting it.
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Hearing Aid Recycling Program (HARP):
The World Health Organization estimates that 360 million people worldwide have disabling hearing loss. Yet, current annual production of hearing aids meets less than 10% of the global need. Do you know someone who has difficulty hearing but is unable to afford hearing aids? The UWSHC Hearing Aid Recycling Program (HARP) provides free or low-cost reconditioned behind-the-ear hearing aids, ear molds, and batteries to individuals with low-incomes. This program is supported by generous donations from community members, Epic Systems Corporation, Starkey Hearing Technologies, the UW-Madison Student Academy of Audiology, and the former Sertoma Club of Madison. The Hearing Aid Recycling Program (HARP) enables to provide affordable, refurbished hearing aids for individuals with limited financial resources.
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What is the average lifespan of a hearing aid?
Five to seven years depending on the age and usage of the person. Expect to purchase new hearing aids every 5 years. This may come as a surprise, particularly if you just purchased a set of digital hearing aids! However, hearing aid technology changes rapidly, just like computers, and new technology may benefit you greatly. Some people may keep the same pair of hearing aids for 10 to 12 years, particularly if their hearing loss remains stable over time and if they do a great job with maintenance, but the average life expectancy is about five years. Some hearing aids are replaced not necessarily as a result of being worn out but due to changes in a person’s hearing or because the individual may desire hearing aids of improved technology. In any case, you’re well-advised to consider 5 years as the average life span of most hearing aids. All things considered, proper maintenance will help to extend the longevity of hearing aids to their optimum potential.
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How do I determine if it is time to replace my old hearing aids?
-If your hearing aid whistles, or
-If the hearing aid no longer fits in the ear properly (whistles), or
-If the hearing aid is being sent for repair every 6 months to 1-year, or
-If you are dissatisfied with performance of current hearing aid.
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Factors impacting how long hearing aids last:
1. Materials used to make hearing aids
2. Frequency of cleaning
3. Where hearing aids are worn
4. How hearing aids are stored
5. Hearing aid style
6. An individual’s body physiology
7. Frequency of maintenance
8. Technological advancements
9. Individual hearing needs
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Why not buy hearing devices online or through mail order?
Kochkin and colleagues at the Better Hearing Institute surveyed more than 2000 hearing aid users about their fitting experience and level of satisfaction. The outcome was straightforward: those users who were fitted using a clinically validated hearing aid fitting protocol had greater satisfaction with their hearing aids. In other words, those patients who were given appropriate support and service by a licensed hearing aid professional actually heard better! Another finding from Kochkin’s research was that a typical hearing aid user will need about three visits after purchase to get a hearing device properly adjusted, and some wearers will need more. You will not be able to get that type of service through the mail.
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Specifically, of those hearing aid users who received a comprehensive clinical protocol:
•81 percent would repurchase the same brand of hearing aids
•85 percent were satisfied with how the hearing aids worked in multiple listening environments
•94 percent would recommend the professional they worked with to a friend
•99 percent were satisfied with the benefit they received from the hearing aids
•97 percent would recommend hearing aids to a friend
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Alternatively, when an incomplete fitting and adjustment method is used, such as what might be offered to those who order hearing aids from the internet:
•14 percent would repurchase the same brand of hearing aids
•14 percent were satisfied with how the hearing aids worked in multiple listening environments
•39 percent would recommend the professional they worked with to a friend
•12 percent were satisfied with the benefit they received from the hearing aids
•56 percent would recommend hearing aids to a friend
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Problems with hearing aid:
Eight main issues: 1) Batteries, 2) ear wax, 3) ear mold/venting issues, 4) moisture/ corrosion/dirt/intermittence, 5) telephone use, 6) feedback, 7) static/noise, and (8) prevention.
1. Issues with batteries include the following: Dead and defective batteries, getting the most out of your batteries, batteries in backwards, spent batteries, defective batteries, short battery life, conserving battery life, safety issues with batteries.
2. Issues with ear wax include: earwax obstruction, preventing wax build-up, when and how to remove wax.
3. Ear mold and venting issues include (comfort & sound quality): ear discomfort, causes of ear discomfort, correcting a hearing aid fitting problem, plugged up vents.
4. Moisture, corrosion, dirt & related intermittence: moisture problems, resolving moisture problems, effects of moisture, dirty volume control, dirty battery, problem of oily skin.
5. Telephone issues: poor telephone reception, telecoil circuit, successful use of the telecoil circuit, other tips for improved telephone listening.
6. Feedback issues: hearing aid squeal (acoustic feedback), acceptable versus unacceptable feedback, earwax and feedback, solving the feedback problem, feedback with new hearing aids, feedback and telephone use.
7. Static and other unwanted sounds: wind noise, background noise.
8. Preventive hearing aid maintenance: Spare set of hearing aids, hearing aid disuse and longevity.
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Hearing aids are electronic devices that are greatly beneficial to millions of people. Like any piece of technology, they can stop functioning at any time. Consider that hearing aids are usually worn for long hours each day, which places stress on electrical components and battery power. They exist in relatively hostile conditions of moisture, warm temperatures (especially with certain styles) and substances such as earwax, skin acids and oils. These substances may be healthy for the ear but are potentially corrosive to hearing aids. Additionally, these substances can block sound delivery pathways making the hearing aid perform poorly. For these reasons, no matter how well they’re made, sooner or later they will stop working. Hearing aid failure is often unpredictable and sometimes occurs at the most critical and inopportune times, such as in the middle of an important business meeting. Hearing aid failure can be upsetting in such cases and even in less critical situations, a hearing aid that quits working can produce considerable frustration. At the very least, hearing aid breakdown is annoying. Like your automobile, any number of problems can go wrong with a hearing aid, but for the most part, easy and relatively inexpensive remedies are available. I will discuss some of the problems with hearing aid in detail.
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Earwax issues:
The medical term for earwax is cerumen, a naturally occurring substance in the outer ear. It’s produced by a gland in the outer ear roughly one-third of the way down the ear canal. The product of this gland is a pasty substance, usually light brown or tan in color and bitter in taste. Ingredients for a good batch of earwax include oil and sweat mixed with dirt and dead skin cells. It’s hard to believe something so unappealing can be so important to your ears’ good health, yet being sticky and smelly is exactly why a normal amount of ear wax is beneficial. Consider these attributes:
1. Earwax is a natural barrier which prevents dirt and bacteria from entering the innermost parts of your ears. Because it is sticky, it collects microscopic debris which finds its way into your ear canal, much like fly paper traps insects. Without this defensive barrier, your inner ear would be at risk.
2. It acts as a moisturizer and protective coating for your ear canal. Without earwax, your outer ear might be itchy and flaky, which puts it at greater risk for becoming irritated and infected.
3. It acts as an insect repellent. The smell of earwax keeps bugs away, while the stickiness traps those which accidentally venture inside.
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A leading cause of hearing aid failure is wax blockage. On average, men experience more wax buildup than women. Some women, however, can produce large amounts of cerumen, as can children. For reasons not clearly understood, some individuals generate little or no wax. If you’re presently unaware of the wax condition in your ears, your physician or hearing healthcare provider can readily inform you of this after examination with an otoscope (ear light). Hearing aid wearers must continually be on the lookout for adverse effects of earwax. When hearing aids are inserted into the ear canals, (or earmolds in the case of BTE hearing aids), they can slide alongside or directly into accumulated wax. The fresher the wax, the softer and more easily it can get pushed into the sound bore (receiver) of an aid. A thin smear of earwax over the receiver (sound) tube will shut the hearing aid down instantly. The first defense against wax build-up is regular cleaning of your ear canals by a physician or audiologist, or as simple as it sounds, in a shower by direct spray into the canals. The cautions here are to be careful of the water pressure, and be certain you don’t have a hole in your eardrum, or any other condition which might prevent such easy management of earwax. The second defense against wax blockage is utilization of some type of wax guard for your hearing aid. There are a number of commercially available products which suit this purpose. Many manufacturers now provide such a device on their hearing aids. Directly, or under magnification, you can look into the sound opening of the hearing aid to see if a wax guard is there. These common devices include “spring,” “Band-Aid” or “trap-door” style guards. All such devices should be discussed with your hearing health care provider who can explain service requirements.
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Whomever dispensed your hearing aids does not have the primary responsibility to keep them free of earwax. You need to develop a daily habit of inspecting the end of the hearing aid where the sound comes out and looking for wax blockage. If accumulation is noticed, this wax can be readily removed in most cases by the hearing aid wearer with tools provided by the hearing healthcare professional. Remember, periodic check-ups (every 3-6 months) with your hearing health care professional are recommended. After you have been fit with hearing aids, be sure your hearing healthcare professional demonstrates how to clean your hearing aids using tools which normally come with the purchase of hearing aids. The best time to inspect hearing aids for wax is at the end of the day. At this time, any accumulated wax will still be soft and more easily removed. If you use the Band-Aid style guard, you can wipe across it gently. After a few days if you observe the cushion separating from the adhesive backing, remove it altogether and replace. If used properly, you’ll never need to clean out the receiver (loud speaker) which is the rubber housing hole at the tip of an aid. If your hearing aids have the wire coil in them, you may use a device known as a wax loop. This is merely a wire looped around the end of a piece of plastic. Gently insert it into the receiver tube, turn it one full rotation, then remove. Avoid picking or poking. Clean any debris from the loop. Nightly cleaning has the added advantage of keeping the receiver tube open for more adequate ventilation and drying. Review this procedure carefully and thoroughly with your hearing healthcare provider so that inadvertently you don’t damage your hearing aids by cramming the wax loop into the wrong opening (such as the microphone port on the face of the hearing aid) or too deeply into the receiver port which can damage the speaker diaphragm. Additionally, a wax tool that is a little too large to fit readily into the receiver tube can push the tube itself down into the shell of the hearing aid. This will damage the aid, often causing it to squeal, resulting in needed repairs. Wax should also be removed from hearing aid vents. This is the other port in the hearing aid next to the receiver (loud speaker) port. It can be identified because vents are longer, they do not have a rubber housing through the channel, and often run the length of the earpiece or earmold. This also means they’re not as easily cleaned. Some people have resorted to the use of wires of various gauges to ream out vents. Wire should be used with caution as it can crack the shell. Large vents are less likely to get plugged up and much easier to clean. Pipe cleaners work extremely well for large vents, such as ITEs, and light gauge fishing line for vents in CICs. Your provider will have suggestions for obtaining these and other suitable tools for cleaning. Sometimes, wax build-up becomes dry and flaky before it’s removed. When this happens, a good brushing of the hearing aid openings can be helpful in addition to use of the wire loop. When brushing, always hold the hearing aid upside down so that wax particles fall out of, rather than down into, the hearing aid. Also, keep your brush clean so that wax particles which collect in the bristles from previous brushing aren’t injected inadvertently into the openings.
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Ear-mold and venting issues: (Comfort and sound quality issues):
Ear Discomfort:
Like pressure on the feet from a tight fitting pair of new shoes, hearing aids can occasionally be uncomfortable. Unlike feet, however, such discomfort in the ear is not tolerated well. Hearing aid-related ear pain can distract from intended amplification. Discomfort associated with hearing aid use usually has a specific anatomical site of origin but a widespread reaction. That is, a tight-fitting earmold may cause specific tenderness in one spot in the ear canal but in time the sensation can radiate. Additionally, accumulation of earwax and moisture may result in periodic ear discomfort.
Causes of Ear Discomfort:
The most common cause of ear discomfort is an ill-fitting earmold (in the case of BTE) or hearing aid shell (in the case of ITE, ITC or CIC). Earpieces are fabricated from impressions taken of your ear. Usually they’ll fit precisely. They’re designed to fit snugly but not uncomfortably. It should be realized, however, that your degree of hearing loss will have a bearing on the tightness. Severe hearing losses must have a tight fit to prevent feedback (whistling). There are two causes for ear discomfort which can result from a poorly fitting hearing aid or earmold. Either the earpiece was made improperly or incorrectly positioned in the ear. Ear impressions can and usually do provide exact replicas of the ear canal. This is because most hearing healthcare providers are experienced in taking ear impressions. Occasionally, however, impressions can be distorted during preparation, while in transit to the laboratory or during fabrication. Another factor affecting comfort has to do with jaw movement. In some cases ear pain is caused or aggravated by movement of the jaw when earpieces are in place. For many, movement of the jaw can have significant influence on the shape of the canal. This is really quite normal. The effects of jaw movement can be felt by placing the “pinkie” finger deep in the ear canal while moving the jaw. (Try it while you’re reading this). This movement arises from the joint of the lower jaw called, technically, the temporomandibular joint, or simply TMJ. Even though earmolds may have reflected accurate impressions of the canal, the resulting earpieces may not “give” when the jaw and ear canal are moving, as when talking or chewing. If you suspect a poorly fitting earmold or hearing aid due to influences of the TMJ, you should discuss this matter with your hearing care professional and seek a solution within the usual 30 day trial period. Never accept hearing aids which cause you discomfort or which hurt. The second most common cause of ear discomfort is the earpiece which is placed incorrectly in the ear. Earmolds that have been accurately fabricated can cause ear pain if not inserted correctly. When placing the earmold or hearing aid in the ear, you must make certain the device is seated into its exact position or it can create pressure points in the canal. Difficulty with correct placement is a common problem, especially for new wearers. Those who use behind-the-ear (BTE) hearing aids, for example, must make sure the entire earmold is properly placed. A common problem here is when the earmold is inserted into the canal, and the uppermost portion isn’t tucked into the groove of skin at the top of the ear. This incomplete placement can shift the angle of the earmold just enough to create a tender spot down in the canal. ITE wearers can have the same problem. With mini-BTE hearing aids there is less of a problem since you are only inserting a thin tube in your ear with a canal placement device or receiver at the end of the tube. Those who try CIC aids may experience some fitting and placement problems initially. The deeper a hearing aid is placed in the canal, the more sensitive the canal tissue. Some wearers are simply reluctant to push an aid fully into the canal, fearful that doing so will cause pain. This is understandable. Also, there can be concern the aid can be pushed too deeply into the canal and cause damage. This also is a logical concern. However, ear canals tend to be carrot-shaped (that is, the deeper into the canal, the narrower the opening) and the aid cannot be pushed without discomfort beyond its appropriate location. With detailed instruction from your hearing healthcare provider and with practice, however, you will soon get a “feel” for the exact location of the hearing aid and should be able to insert it correctly with confidence and without discomfort. If the hearing aids are difficult to insert, repeated “fiddling” can also cause discomfort. Special earmold lubricant is available to assist in the insertion. If placement difficulties aren’t easily resolved, practicing proper insertion of the hearing aid in the presence and under the watchful eye of your hearing healthcare provider is helpful and reassuring. It’s helpful here to note that in most situations of poor fit, satisfactory corrections can be made right in the office. Also, please be aware that most wearers don’t experience these initial difficulties at all and “hit the ground running” with new hearing aids. Often people forget hearing aid is in their ears.
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Plugged Up Vents:
A vent in an earmold or hearing aid is simply an open passageway or tube that extends from the front of the earpiece to the tip. It almost always exits the tip very close to the sound opening (receiver tube). Except in the case of more significant hearing loss, a vent will always be present. The diameter of the vent may be either large or small. In general, hearing aids fit to people with mild loss will have large vents while those fit to individuals with more severe losses will have smaller vents. They’re usually placed in earmolds or hearing aid shells by manufacturers. They can also be placed there or modified by your provider. Vents should always be kept open to perform their intended function. Again, if you have a vent on your hearing aid the hearing healthcare professional should instruct you on how to properly clean them.
Purposes for Vents:
Vents are placed in earpieces for three important reasons. First, they allow sounds that you may hear normally to enter the ear canal directly without being amplified. You don’t want to block the ear to sounds which you hear normally. Vents that serve this purpose are usually fairly large and obvious. This type of vent is very helpful if your hearing loss affects only higher frequencies. The second purpose of venting is to reduce amplification of unwanted sounds. Often these are low-pitched tones which you may already hear normally. Experienced and sometimes even new wearers will report hearing better when their provider enlarges the vent by drilling. This diminishes low-pitch bothersome background sounds. Hearing aids and earmolds fit to those with more severe loss will require smaller vents. A third purpose of venting, perhaps the most important in some fittings, is to decrease the acoustic effects of your own voice. You’ll readily identify this as the objectionable sounds of your own voice while the ears are blocked off. This is called the “occlusion effect”. It’s the “my voice sounds like I’m talking in a barrel” effect.
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The figure above shows recommended vent diameters (in mm) based on the hearing loss at 500 Hz (in dB HL). You can see that as severity of hearing loss increases, vent diameter reduces. For an open-ear fitting, the hearing loss at 1000 Hz should not exceed 60-70 dB HL so that sufficient gain may be provided.
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Moisture Problems:
Handling moisture problems will depend on what type of hearing aids you own. The use of water to remove wax or dirt from any part of the hearing aid itself is inadvisable. Moisture is a natural enemy to electronic devices. The use of a dry cloth or tissue to wipe clean the outside surface of the hearing aid is the only recommended cleaning practice. With regard to BTE style hearing aids, earmolds used with these aids must be removed from the hearing aids before cleaning. They can be soaked in a solution of soap and warm water, gently scrubbed clean and then completely dried before re-connecting to the hearing aid. Two methods we recommend for drying is a handheld, forced-air blower which simply pumps air through the tubing or a can of compressed air (typically used to blow dust off computer keyboards). Failure to dry earmolds will risk moisture seepage into the aid. Another useful tool in keeping moisture from being a problem is regular use of a dehumidifier. Commercial versions are available and very reasonably priced. The device is simply a container for your hearing aid with a built-in, moisture-absorbing chemical. The hearing aids are placed in the container anytime they’re not being worn. The device absorbs accumulated moisture and leaves the hearing aids dry. The chemical eventually becomes saturated with moisture but can be recharged by heating it in a warm oven. Be sure to follow the manufacturer’s instructions.
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Ear canals can produce a degree of moisture which can affect hearing aid performance. Like the problem of earwax, the amount of moisture present in human ear canals can vary widely from person to person. Your activity level and climatic conditions in which hearing aids are worn are two of the more common variables affecting moisture build-up. People with high levels of physical activity who perspire easily can be more prone to moisture problems than those who lead a more sedentary life. Moreover, a moisture problem can be further aggravated by conditions of high humidity. Moisture build-up can result from either internal or external sources. Internal sources are those related to the condition of the auditory canal while the latter refers to liquids which arise from outside the ear, as those, for example, associated with rain or severe perspiration. While BTE-type hearing aids, if maintained properly, can outlast in-the-shell types, they tend to have the worst problem with moisture. Water vapors arising from the canal condense in the connecting tube. When these vapors reach a region outside the canal of slightly cooler temperature, condensation converts to small droplets of water which appear as tiny bubbles in the tube. The accumulation of enough water droplets can be sufficient to close the tube and shut down amplification. Externally-produced moisture surprisingly is less of a problem. Rain water, unless very severe or persistent, usually runs around the ear and off the head with little or no adverse effects. A worse condition, especially for BTE use, exists for the person who perspires a lot. With such individuals, beads of perspiration form in the hair along the top of the hearing aid. In time, this moisture can seep into the cracks and openings along the upper surface of the hearing aid and eventually affect operation. Hearing aids of the type worn in the ear have less difficulty with moisture build-up. Externally produced moisture with in-the-shell- type hearing aids tends to flow around rather than into the ear as a rule. Also, the further the aid is placed inside the canal, the less the problem as moisture from the canal lining has less of an opportunity to get into the receiver tube. Therefore, CIC’s are the least affected by internal and external moisture. It should be noted that hearing aid failure due to moisture is not always easy to diagnose. Except for water vapor forming in the tube of BTE hearing aids which is readily visible, moisture is difficult to observe. If hearing aid stoppage is found to be unrelated to the more obvious causes, such as faulty batteries or wax blockage, then moisture build-up should be suspected. The use of drying procedures previously described should help isolate this problem. Also, perhaps with the help of your hearing healthcare provider, you could check your daily routine.
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Acoustic Feedback and other Audible Artifacts in Hearing Aids:
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Acoustic feedback:
Acoustic feedback has been described as “whistling,” “howling,” “screeching,” “screaming,” “squealing,” “whining,” “ringing,” “humming,” “buzzing,” “oscillating” and by various other names. A hearing aid will make the sound of “eeee” when the ear mold doesn’t fit in the ear tightly. If no one is wearing the hearing aid, but if it is still on, then it will “eee” too. The high-pitched whistling of a hearing aid experiencing acoustic feedback is an irritating sound for the hearing aid wearer and for nearby individuals. Suppressing these irritating squealing noises is not easy. Thus dealing with acoustic feedback is still a prevalent problem that plagues clinicians and wearers alike. Though specific figures are considered by manufacturers to be proprietary information, industry experts estimate that as many as 10% to 15% of in-the-ear hearing aid products are likely to be returned to the factory within the first 90 days after manufacture for feedback-related problems. Obviously this adds to the overall cost of hearing aids to the dispenser, and anything that can be done to help reduce these returns will ultimately benefit the wearer.
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Before starting a detailed discussion of feedback, an important point should be made concerning terminology. Acoustic feedback in a hearing aid fitting produces a form of instability and the resulting audible oscillation. It is caused by a sound wave from the output leaking back to the input. Though all acoustic feedback of the correct phase and magnitude produces an undesired form of oscillation in a hearing aid, not all oscillation is due to acoustic feedback. In precise terms the objectionable audible sound produced by a hearing aid due to acoustic feedback should be called audible oscillation due to acoustic feedback. Through common usage, this more accurate term has generally been abbreviated simply to acoustic feedback, though in reality acoustic feedback is the cause of the problem and not the audible effect. However, to comply with common usage the term acoustic feedback will be used consistently throughout the text to refer to the unpleasant and undesired squealing and screeching that occurs in a hearing aid and which is caused by the leakage of amplified output sound back to the microphone.
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In this age of ubiquitous electronic amplification, it is often observed that if a speaker using a public address system in a conference room or an auditorium stands too close to the loudspeaker, then a loud and obnoxious squeal may occur. This is acoustic feedback. A portion of the sound coming from the loudspeaker has been picked up by the microphone, has been amplified, and then radiated back into the room. This situation is shown diagrammatically in the figure below. Part of this amplified signal is picked up by the microphone, is re-amplified, and is subsequently re-radiated into the room where it is again picked up by the microphone, and so forth. This repeating cycle of sound amplification, radiation and pickup continues until the system is no longer stable and oscillation occurs. The audible manifestation of this instability is a loud and overwhelming squeal. This sound is obnoxious and is irritating to both the speaker and the audience.
Figure above shows acoustic feedback in a public address system.
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Thus acoustic feedback is a circle of amplification, where amplified sound is continuously re-amplified to the point at which a tonal squeal occurs. The specific tonality of the squeal is determined by the electronic characteristics of the amplifier combined with the acoustic characteristics of the microphone, the room and the loudspeaker. Due to the varied dimensions, and the reflection and absorption characteristics of different structures, different rooms produce squeals with different tonal characteristics. Though the obvious and most common manifestation of acoustic feedback is a squeal, feedback in itself is sometimes desirable. Electronic feedback may be intentionally created in a circuit in order to achieve desired results. For example, electronic feedback may be used to create tones for use in test equipment, such as audiometers. To accomplish this, a signal is deliberately fed back around an amplifier in a controlled fashion to create an electrical tone similar to that resulting from acoustic feedback. Changes in the values of the components in the electronic circuit are used to change the frequency of the tone, in order to create a range of test frequencies.
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Though the above example of acoustic feedback was applied to a public address system, the same principle applies on a smaller scale to a hearing aid. Amplified sound transmitted to the ear canal from the receiver is radiated out through the vent, or via various other pathways (such as acoustic leakage between the earmold or hearing aid shell and the wall of the ear canal via a pathway called slit-leak), back to the microphone. Then it is amplified and re-radiated out of the ear canal, where it is picked up again by the microphone, re-amplified and so forth. Figure below shows a schematic representation of the acoustic feedback pathway in an ITE hearing aid that can lead to acoustic feedback.
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Figure below illustrates an ITE hearing aid in place in the ear, showing potential acoustic leakage pathways.
ITE hearing aid placed in the ear, showing potential acoustic feedback pathways through the vent and through slit leakage.
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Though slit-leak and an adequate seal to the ear are very important, acoustic feedback caused by slit-leak and venting may or may not be present. The problem created by this leakage also depends on the amount of gain provided by the hearing aid. If the gain is quite low there may not be enough sound radiated out through leakage pathways to cause acoustic feedback. Thus, the effect of any venting in this instance will only be to reduce low frequency amplification. The probability of acoustic feedback is greater in a hearing aid than with a public address system because the microphone and receiver in a hearing aid are in fixed locations very close to each other. Also, it is generally not possible to move the microphone further away from the receiver to prevent feedback, as may be done with a public address system.
In summary, it can be seen from this fundamental description of feedback that several conditions have to exist for acoustic feedback to occur and be sustained in a hearing aid:
1. Some of the sound radiated from the receiver has to leak out of the ear canal and be picked up by the microphone,
2. Amplification has to occur,
3. The amplified sound has to be re-radiated from the receiver and ear canal back to the microphone.
Thus far, this description of acoustic feedback has been very basic and qualitative to ensure that you have a fundamental understanding of the mechanism which results in the familiar squeal heard from a hearing aid. From this generalized description, it would appear that acoustic feedback could occur at any frequency. However, as is well-known by hearing aid wearers and clinicians, feedback usually occurs at a frequency which gives the audible acoustic screech a distinctly tonal quality. Most wearers also empirically note that the pitch of feedback may be altered by changing the acoustic conditions surrounding the hearing aid. For example, moving a cupped hand nearer to or further away from a hearing aid usually changes the pitch of the audible squealing sound. Thus, though the theoretical potential exists for feedback to occur at any frequency, in reality, it only occurs at one or two frequencies. The reason for this is determined by the acoustics of the feedback environment and relates primarily to the phase of the signal passing through the hearing aid circuit.
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Acoustic feedback is well-known and continues to be a major concern for those wearing hearing aids. This is caused by the leakage of sound from the hearing aid speaker (receiver) back to the microphone . This sound wave leakage from the output back to the input produces a form of instability, resulting in an audible oscillation. In essence, amplified sound is returned to the microphone and this open loop circle of sound transmission is continuously amplified to the point at which a tonal squeal occurs. This is an undesired acoustic coupling between the hearing aid speaker and the microphone. The consequence of acoustic feedback is to limit the maximum amplification that can be used in the hearing aid without making it unstable. This level is often referred to as maximum stable gain (MSG). MSG has also been referred to in the literature as Actual Feedback Limit, maximum feedback-free gain, maximum available gain, critical gain, or open loop gain (OLG), and probably in other ways as well. Perhaps OLG should not be used because it is defined as a specific technique to measure the MSG.
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The acoustic feedback can be categorized into three general types:
1. External acoustic feedback: caused by some factor related to the fitting and not due to malfunction within the hearing aid. Examples of circumstances which may cause external acoustic feedback include very high gain, a vent with a large diameter or uncontrolled acoustic slit-leakage. This is the most common type of acoustic feedback.
2. Internal acoustic feedback: caused by leakage and subsequent audible oscillation within the hearing aid because of internal malfunction.
3. Miscellaneous audible non-feedback sounds: caused by factors interacting with the hearing aid which may lead to acoustic manifestations. This is not acoustic feedback, but is often mistakenly confused with it.
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External acoustic feedback is caused by the leakage of sound from the receiver back to the microphone. It is caused by an interaction of a number of acoustical and mechanical factors which are inter-related in the fitting of a hearing aid. The presence of feedback can be caused by something as simple as the earmold or shell being seated improperly in the ear, which can result in undesired sound leakage and thus acoustic feedback. The impact of leakage on causing acoustic feedback is related to a number of factors. These factors include:
1. Residual volume of the ear canal. Decreasing the residual volume of the ear canal will raise the sound pressure in the remaining cavity and can initiate feedback. As a rough rule of thumb, every time the residual volume is reduced by one-half, the sound pressure increases by 6 dB.
2. Type of hearing aid. The smaller models of hearing aid, such as an ITC or CIC, place the microphone and receiver close to each other internally due to their small case size and also produce a shorter pathway between their external ports. This proximity produces a higher susceptibility to feedback.
3. Presence and configuration of venting. The larger the diameter of the vent, the more sound leaks out of the canal back to the microphone.
4. Amount of slit leakage. The larger the slit leakage present, the easier sound leaks out of the canal back to the microphone.
5. Fit of the hearing aid in the ear. The looser the fit in the ear, the more slit leakage will be present.
6. Length and diameter of the canal area of the shell or earmold. The longer the length of the canal portion of the hearing aid, the better the hearing aid seals to the ear and reduces the potential for feedback. The smaller the diameter of the canal portion with respect to the ear canal, the looser the fit and the more slit leakage will be present
7. Wearer’s pinna size and shape. The larger the pinna and the more it bends back towards the head, the more sound from venting or slit leakage is liable to be reflected back to the microphone.
8. Gain and frequency response of the hearing aid. The higher the overall gain, particularly the high frequency gain, the more prone a hearing aid is to have feedback.
9. Orientation of the hearing aid or earmold in the ear. If the receiver tube of the hearing aid or sound outlet bore of an earmold points towards the wall of the ear canal instead of at the eardrum, sound can more easily be reflected out of the ear and cause feedback.
10. Eardrum impedance. A stiffer eardrum is more likely to cause feedback than a more compliant one, due to more efficient reflection from the surface of the membrane.
11. The setting of the gain control. The higher the gain control setting, the more likely the possibility of feedback.
All these factors influence the occurrence of acoustic feedback and the frequency at which it occurs. Coughing, chewing, sneezing, yawning, talking, tilting the head, bringing a hand up to the face, use of the telephone, the proximity of reflective surfaces and placing a hat on the head can also initiate feedback in a hearing aid which borders on having an unstable feedback environment. Because of these variables, acoustic feedback can be a very elusive phenomenon. It can occur at different frequencies with the same hearing aid at different times and under different acoustic conditions. The audible pitch of the feedback may vary smoothly as acoustic conditions change, or it may jump between different frequencies. Feedback may even occur at more than one frequency at the same time.
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Acceptable versus Unacceptable Feedback:
We want to emphasize that acoustic feedback is a natural phenomenon of amplifiers and not of concern, in and of itself. Feedback is to be expected, for example, when a hearing aid is “on” and held in a cupped hand. It does no damage to use feedback in this way to tell if the hearing aid is working. Similarly, it’s usually not a problem to purposely cup the hand to the ear and listen for the “beep” as the hand is moved toward and away from the ear. Many wearers test the hearing aid in this way to be sure it’s on. Others will rotate the volume control to the position of feedback during adjustment. Here again, this is no problem. These are all examples of predictable and acceptable feedback. Unacceptable feedback is the type that spontaneously rings without warning or provocation; that happens, for example, while you’re chewing, brushing your hair, scratching the side of your head or tilting your head downward. This latter movement causes a slight shift in the position of the hearing aid, sometimes just enough to allow sound to leak out. The squeal associated with all of these activities can be vexing not only to you but to those around you. Feedback of the unacceptable kind also occurs when you try to turn the volume of the hearing aid up to a more desirable level but cannot because the aid starts to squeal. At this volume position, with you attempting to extract the last decibel of sound possible, the aid is on the verge of feedback and will squeal at the least little disturbance. These are examples of feedback which you will not want to tolerate. Almost all of them can be corrected with help from your hearing healthcare professional.
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Acoustic feedback typically occurs at or close to the high frequency peaks in the hearing aid frequency response since these peaks occur at the frequency of the greatest gain. Feedback typically occurs in the region of high frequencies between 2000 Hz and 5000 Hz. It is often initiated by the large amount of high frequency gain typically used to successfully fit high frequency sensorineural hearing loss. It should be noted that a hearing aid that has moderate gain and a relatively flat frequency response is less likely to cause feedback than a hearing aid with greater gain and an emphasized high frequency response. Since acoustic feedback is initiated by excessive high frequency gain, the higher the overall gain, the more likely feedback is to occur. Specifically, the higher the gain in the high frequencies, the more likely feedback is to occur. When discussing acoustic feedback with wearers, it may be helpful to counsel them that there are certain situations in which feedback may be inevitable. These include improper insertion of an ITE hearing aid or BTE earmold into the ear; turning the gain control to maximum setting; or cupping a hand around the hearing aid.
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Causes of external acoustic feedback:
The most common problems with feedback are those related to the hearing aid fitting. In most cases, external acoustic feedback results from one or more of the causes outlined in figure below.
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Earwax and Feedback:
Feedback can occur anytime sound is deflected toward the microphone. Normal eardrums tend to absorb energy so that if an earpiece is reasonably snug, leakage is minimal and feedback doesn’t occur. Earwax, on the other hand, seems to absorb very little sound and will bounce the sound right back out of the canal toward the microphone. Therefore, individuals who experience unexplained feedback should have their ears checked for wax build-up.
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Causes of internal acoustic feedback:
The second general category of acoustic feedback encompasses problems occurring due to malfunction of the hearing aid. These malfunctions are generally technical problems which require the aid be returned to the factory for service. However, a clinician can sometimes perform minor repairs in the office to resolve a problem without having to return the aid to the manufacturer.
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Causes of other undesired audible sounds in hearing aids:
The preceding sections have described the causes of acoustic feedback from the point of view of the hearing aid and the fitting of the hearing aid. But it is important to also discuss other types of undesired audible sounds that occur in hearing aids. This is important in order to distinguish various sounds from each other and to assist the clinician in separating symptoms and causes when troubleshooting oscillation and feedback problems. All of these types of problems, whether caused by feedback or not, may manifest themselves as various types of audible noises, such as “howling”, “whistling”, “sizzling”, “roaring” or “buzzing sounds” that come from the hearing aid. Often these sounds are described generically by the wearer as feedback. Unfortunately, from the clinician’s viewpoint, there is usually little that can be done to the hearing aid to correct problems within this category. In almost all cases it is either necessary to remain clear of an environment that causes these problems, or to return the hearing aid to the factory for service.
Other forms of oscillation in hearing aids that may be encountered are listed below:
1. Electrical feedback
2. Electromagnetic feedback
3. Electromagnetic pickup
4. Class D output stage oscillations
5. Oscillations due to battery problems
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Electronic solutions to reduce acoustic feedback:
Understanding the nature of acoustic feedback leads to an understanding of the numerous solutions to help solve the problem. One general method of resolving feedback is through electronic modifications via circuit adjustments. Electronic methods of feedback reduction include:
1. Overall gain reduction
2. Reduction of high frequency gain
3. Electronic damping of high frequency peaks
4. Bandpass filtering
5. Notch filtering
6. Frequency shifting
7. Phase shifting
8. Frequency warbling
9. Adaptive cancellation filters
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Feedback Cancellation:
Historically, one of the greatest complaints and a source of embarrassment for hearing aid wearers is related to feedback – the whistling sound created when amplified sound is picked up by the hearing aids microphone, causing squealing or whistling. Sound travels in waves. The digital hearing aid can now detect the frequency of and the wave shape that is causing the feedback and counteract it with a mirror image of that feedback within fractions of a second, which cancels the feedback. So, there will be no annoying and embarrassing whistling from your hearing aid.
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Acoustic solutions to reduce acoustic feedback:
Acoustic feedback may be reduced or eliminated by alteration of the physical conditions causing feedback. These might include modifications of the earmold or hearing aid case. For example, lengthening the canal portion of an earmold or in-the-ear hearing aid will change the feedback pathway and may be enough to reduce or prevent feedback. Reducing the size of the vent may reduce the amount of feedback at the critical frequency and may eliminate audible oscillations.
Acoustic methods of feedback reduction or prevention include:
1. Elimination of the vent or reduction of its diameter
2. Ensuring a tight seal to the ear
3. High frequency gain reduction
4. Acoustic damping of receiver peaks
5. Use of dual receivers
6. Acoustic notch filtering
7. Modification of the canal tip
8. Physical separation of the microphone and receiver
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Beware the Digital Enigma!
Frequency response adjustments – They may solve your feedback, but can be disastrous for your speech understanding! There are times that feedback can be solved in other ways than getting a better acoustic seal, but these are sometimes at the expense of hearing well. With digital hearing aids, there are automatic feedback controls, and also adjustments that the hearing aid fitter can make to reduce feedback, but these are not always in the best interest of clear hearing. In some (but not all) digital hearing aids, the feedback control methods involve some manner of cutting high frequency amplification. The most common adjustment to control feedback involves decreasing the high frequencies of a hearing aid. This is the easiest way to stop feedback, but it could be at the expense of your hearing ability! If the cause of your feedback is poor fit or ear wax, and your hearing aid fitter does not consider that cause, they may say “no problem”, and reduce the high frequencies in the programming. This can solve the immediate problem, but it can be detrimental to your ability to understand speech. If your hearing aid professional adjusts the hearing aid for feedback and you still hear as well as before the adjustment, that is good. But if you find yourself straining for clarity after the adjustment, discuss the possibility with them that you may have a fit problem. Before you have your hearing aids reprogrammed to control the feedback, try some of the temporary solutions above for loose fit, such as pressing the hearing aid into your ear to see if the feedback stops.
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Feedback when using a Telephone:
Feedback occurs most often when some object is placed next to the hearing aid. This object can be a telephone, your own hand or even a nearby wall or other flat surface. Acoustic feedback while using the telephone is a problem for hearing aid wearers. The problem is particularly difficult when using a hearing aid or earmold containing venting. Placing the telephone receiver near the ear forms a reflective surface that directs sound from the vent or from slit leak back to the microphone and can immediately initiates feedback. Reducing the gain control setting to prevent acoustic feedback is not always satisfactory, since this also reduces audibility and thus defeats the intended use of the hearing aid. Solutions to allow acoustic use of the telephone without incurring feedback are generally not particularly satisfactory.
Possible solutions for using the telephone without incurring feedback may include:
1. Use of a telephone coil. This eliminates the microphone as a source of acoustic feedback.
2. Use of direct audio input (DAI), with the appropriate adapter system for the telephone. This also eliminates the microphone as a source of acoustic feedback.
3. Use of a programmable hearing aid that reduces the bandwidth of the hearing aid to match the telephone frequency response and reduce the high frequency gain.
4. Use of circuitry that automatically alters the phase of the signal through the hearing aid to prevent violation of the Nyquist Stability Criterion when the telephone is brought close to the ear. The Nyquist Stability Criterion is a unique method for determining stability of a closed loop system.
5. Use of various self-adhesive foam rings or snap-on plastic extension devices that fasten over the telephone receiver to block ambient noise and acoustically seal the telephone to the ear.
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What’s wrong with my hearing aid?
Hearing aid is a complex technological devices that isn’t infallible. Like other complex devices, you are likely to experience a glitch with your hearing aids at least once or twice during their lifetime because they are not completely flawless hearing loss solutions. Maybe your hearing aid won’t turn on, there’s no sound or it’s whistling. Those are just a few common hearing aid issues that you’ll have to sort out. The malfunction could be due to many things – some of them easier to fix than others.
Here are some common hearing aid glitches as well as their possible causes and solutions:
1. Your hearing aid seems to be dead.
It sounds silly, but in the hustle and bustle of daily life, sometimes people forget to turn their hearing aids on! If that isn’t the case, here are a few more possible issues:
•Your hearing aid needs to be set to the microphone (M) setting.
•The battery might not be inserted correctly
•The battery compartment may not be closed completely.
•Perhaps your battery is dead and needs to be replaced.
•The earmold might be blocked by wax and need to be cleaned.
•The wax filter may need to be cleaned, or the microphone opening may be clogged and need to be cleaned with a brush.
•The tubing may be blocked or bent, so check and replace it if necessary.
If none of these are the case, you should take your hearing aid to be inspected by your audiologist, who can help diagnose the problem.
2. Sound is distorted.
•Your battery might be nearly dead. It seems odd, but sound can be distorted when the battery is too weak.
•The volume on your device might be too high.
•Your hearing aid may be switched to telecoil (T), rather than M
•The battery might be corroded or dirty. You can wipe it with a dry cloth, if necessary.
•The battery contacts in your device may be corroded or need to be wiped clean with a dry cloth.
3. Sound is quieter than usual.
•The hearing aid tubing might be frayed, cracked or have moisture damage. Check to see if it needs to be replaced.
•Your earmold might be blocked with wax. Try cleaning it with a soft cloth.
•The battery level may be too low and battery needs to be replaced.
•The opening of the microphone is possibly blocked. If you are unable to carefully clean it yourself, bring it to your hearing health care professional for assistance.
4. Your hearing aid is whistling or howling.
•Your earmold might be inserted wrong. Try reinserting it to see if the problem goes away.
•The volume might be too high.
•Your battery may need to be replaced.
•The tubing might be too lose or cracked.
• There could be wax issue.
If your earmold causes discomfort or pain or does not seem to fit properly, visit your audiologist to have it checked and possibly be fitted for a new one.
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Tinnitus and hearing aid:
Tinnitus is defined as the perception of a sound when there is no sound in the environment. It may have a buzzing, roaring, or ringing quality and may be pulsatile (synchronous with the heartbeat). Tinnitus is often associated with either a conductive or sensorineural hearing loss. The prevalence of tinnitus has been estimated as 15% of the world population. Hearing loss is a risk factor for tinnitus, and the prevalence increases to 33% in individuals aged over 60 years. The pathophysiology of tinnitus is not well understood. Tinnitus is not a disease but a symptom that can result from a number of underlying causes. One of the most common causes is noise-induced hearing loss. Other causes include: ear infections, disease of the heart or blood vessels, Ménière’s disease, brain tumors, emotional stress, exposure to certain medications, a previous head injury, and earwax. It is more common in those with depression. The cause of the tinnitus can usually be determined by finding the cause of the associated hearing loss. Tinnitus may be the first symptom of a serious condition such as a vestibular schwannoma. Pulsatile tinnitus requires evaluation of the vascular system of the head to exclude vascular tumors.
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While the specific mechanism causing tinnitus is unclear, tinnitus researchers agree that you are more likely to experience tinnitus if you also have a hearing loss. The damage to the tiny hair cells in the inner ear, whether it be caused by loud noise exposure, medications, or aging can lead to an increased likelihood of developing tinnitus. The pitch of a person’s tinnitus is usually around the same frequency (or pitch) where there is the most hearing loss. If you have a high-frequency hearing loss, it is likely you hear a high-pitched (high-frequency) ringing or buzzing. It is thought that the brain is trying to “make up for” the fact that there is little acoustic stimulation at that pitch by producing it’s own sound. Tinnitus is the brain’s reaction to the information it’s not getting from the ear (in the setting of hearing loss). Most individuals find a hearing aid to be beneficial in reducing tinnitus because it is providing some ‘good sound’ to the ear (and, therefore, the brain). What is likely occurring is that the brain benefited from the hearing aid, and the tinnitus was more noticeable with the aid out.
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How can hearing aids help?
Hearing aids can help mask the ringing commonly heard in tinnitus. Hearing aids have come a long way in their technology. While previously they worked to amplify sounds, with new advancements and better fittings hearing aids can successfully alleviate tinnitus, too. Hearing aids have also become slimmer and less obvious, so they aren’t as noticeable as they once were. If you have a hearing loss, a hearing aid can help with managing tinnitus by offering sound therapy in the following ways:
• increase the information available to the brain by amplifying background sounds making the tinnitus seem less audible.
• improve communication with others, therefore reducing stress levels.
• helping to compensate for your hearing loss.
• helping you to become accustomed to tinnitus sounds as they aren’t as noticeable anymore
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Studies have shown robust evidence promoting hearing aid fitting as an effective treatment option of tinnitus control. The provision of hearing aids decreased the severity of tinnitus in 69% of bilaterally aided patients and 67% of unilateral aided patients. Similarly, research undertaken by Del Bo et al, (2006) showed successful results for 22 patients fitted with open-fit hearing aids in alleviating symptomatic tinnitus perception. One of the main reasons why open-fit hearing aids have been successful in tinnitus patients is because they do not significantly occlude the ear canal, which can aggravate tinnitus symptoms and, therefore, do not interfere with external sound transmission. They provide sufficient amplification in patients with a mild-moderate hearing loss, have an in-built noise reducing control, and are perceived as highly comfortable.
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Unfortunately, most single-sided deafness (SSD) devices are not able to help tinnitus. There is no cure for tinnitus although some patients do benefit from using hearing aids or maskers in the ear that has ringing. In SSD, the hearing loss is usually so severe that these devices are not strong enough to stimulate the ear. Similarly, SSD devices are not designed to actually stimulate the affected ear and would not be strong enough to impact the tinnitus. Currently, the only option for very severe tinnitus and single-sided deafness is cochlear implantation. This is only in the clinical trial stage at select clinics. Early research suggests that this technology may hold promise for individuals with severe-to-profound hearing loss and severe tinnitus because the cochlear implant provides stimulation directly to the hearing nerve.
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Hearing aid and consumer: some studies:
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Consumer satisfaction with hearing aids is slowly increasing: a 2010 study:
The top 10 factors related to overall customer satisfaction with overall hearing aid satisfaction (correlation in parentheses) are:
1. Overall benefit (0.71)
2. Clarity of sound (0.70)
3. Value (performance of the hearing aid relative to price) (0.68)
4. Natural sounding (0.66)
5. Reliability of the hearing aid (0.65)
6. Richness or fidelity of sound (0.65)
7. Use in noisy situations (0.63)
8. Ability to hear in small groups (0.63)
9. Comfort with loud sounds (0.60)
10. Sound of voice (occlusion) (0.60)
These are the factors that tend to co-vary the most with overall satisfaction. The implication is that incremental improvements in these areas will drive improvements in overall satisfaction.
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Consumer Reports:
Hearing Aid is only part of Hearing Restoration Process:
If you’ve heard that hearing aids don’t work, you’ve heard wrong. But you’ve also heard wrong if you think the answer to hearing loss is simply sticking a hearing aid in your ear, an in-depth study by Consumer Reports shows. The study had three components. Consumer Reports followed 12 people with hearing loss for six months as they shopped for and used their hearing aids. It conducted a national survey of 1,100 people who bought a hearing aid in the last three years and lab-tested 44 different hearing aids. The bottom line: If you suffer hearing loss, the brand of hearing aid you select is far less important than the process of hearing restoration. The reason so many hearing aids end up in drawers is people don’t understand the adapting you need to do to get the most out of them. Expectations have to be tempered. Hearing aids aren’t like glasses. You can’t suddenly put them on and hear as you did before. The brain has to adapt. People who lose the ability to hear quiet sounds expect a hearing aid will fix that, and they are disappointed. They think that if they just get a better hearing aid it will address this problem. But part of the process is learning that a hearing aid will help but will not restore normal hearing. Self-motivated individuals don’t just stick their hearing aids in their ears and go home. They go out right away and test them in different situations: at parties, in theaters, in front of the TV, in quiet conversations, at restaurants, and in crowds. They make note of the situations where they have the most difficulty, and then work with their hearing professional on improving their hearing in these situations. There are many issues involved in hearing rehabilitation. It is not just information and learning, but also psychosocial issues of adjustment. People have different personalities and react differently to the challenges posed by hearing loss. Hearing rehabilitation is much more than getting fitted with the proper hearing aid. The one factor that always emerges from hearing-rehabilitation studies is the time people spend practicing. A lot of people, depending on their personality, will not be deterred, and they will spend time doing what needs to be done. Others will be intimidated and will withdraw from communication situations. For them, it might be better to have formal training materials. Consumer Reports warns that not all hearing professionals are equal. Audiologists generally must have a doctoral degree (usually the AuD), pass national tests, and have extensive clinical training. Hearing-aid specialists have from six months to two years of supervised training or a two-year college degree, and in most states must pass licensing tests. However, the study found that both types of hearing professionals made mistakes in fitting the hearing aids that the 12 shoppers bought. About two-thirds of the time, they ended up with the wrong hearing aid settings. Which hearing aid was best? The testers from Consumer Reports found that the behind-the-ear, open-fit models worked best for the vast majority of people. But they weren’t cheap; these models range in price from $1,850 to $2,700 apiece. Consumer Reports did not compare brands, but it did test some nonprescription hearing aids. These were inexpensive, but Consumer Reports gave them low marks.
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Self-Report Assessment of Hearing Aid Outcome:
Hearing aid benefit can be defined as the difference between unaided and aided performance measured either objectively or subjectively. Hearing aid benefit can be measured objectively by comparing aided and unaided measures of speech recognition ability, as one example. Hearing aid benefit can also be measured subjectively through the use of self-report measures. Because objective tests are completed using a pre-defined external standard, they are almost exclusively tests that take place within the laboratory. Therefore, self-report measures of outcome are a useful method of determining real-world benefits of hearing aid performance. Another separate dimension of outcome is hearing aid satisfaction. Satisfaction differs from benefit in that satisfaction is not necessarily performance driven. For example, a patient can have a significant degree of benefit as measured on any aided and unaided tests, but report dissatisfaction as measured on a satisfaction scale. An important question to address at this time is, “Why do we need self-report measures of real-world outcome?” According to Cox (2003) there are at least three reasons to use self-report measures of benefit and satisfaction.
1. First, for largely economic reasons, health care is becoming more consumer driven. In this evolving system, the consumer decides what treatment is selected and when it is complete. The major indices of quality of service are self-report of outcome and satisfaction. Consumer-driven health care places an added emphasis on the patient’s point of view. Therefore, it is critical to measure the real-world benefit and satisfaction of hearing aid use. Because today’s patients are more savvy and informed, thanks in part to easily accessible information on the Internet, they want to know how much benefit they are receiving in everyday listening situations. Using a self-report of hearing aid outcome is simply the right thing to do.
2. A second reason why self-report measures of outcome are gaining importance is related to the fact that many of these real-world experiences simply cannot be measured effectively in laboratory conditions. The traditional hearing aid outcome measures clinicians have used in the past like speech recognition in quiet and in noise, do not capture the true experiences of hearing aid use in everyday listening situations. In order to quantify the true impact hearing loss and its associated treatment have on activity limitations, lifestyles, etc., self-report measures of outcome should be used.
3. Third, even when laboratory conditions are used to simulate real-world listening situations they do not always resemble the patient’s impression of the actual real-life situation. According to Cox (2003), self-report outcome measures are increasing in use, because they give us a scientifically defensible way to validly measure the real-life success of the hearing aid fitting. Finally, an evidence-based practice paradigm requires clinicians to demonstrate that their hearing aid fittings are providing benefit in real-world conditions. For this reason, self-reports of outcome are the new “gold standard” for measuring and reporting success.
It is widely accepted that self-reports of outcome reflect the real-world listening experiences of patients. In an evidence-based practice paradigm, the use of self-report assessments of real world outcome is the new “gold standard” and should be used to measure treatment effectiveness. As health care continues to become more consumer driven, it is imperative for audiologists to account for changes in communication as a result of using hearing aids. It is widely accepted that self-reports of hearing aid outcome reflect these changes.
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Use of Hearing Aids by Adults with Hearing Loss: a study:
The chart above displays time trends in the use of hearing aids for adults (20–69 years) and older adults (70+ years). The number of persons with hearing loss is calculated based on National Health and Nutrition Examination Survey (NHANES) hearing exam estimates of the number of people with a pure-tone average (PTA) of thresholds at frequencies of 1000, 2000, 3000, and 4000 Hertz greater than or equal to 35 decibels (dB) hearing level (HL) in either one or both ears. The number of persons who respond that they have ever worn a hearing aid is obtained annually from the National Health Interview Survey (NHIS). The 2020 target lines represent the goals recommended by the Hearing Health group to the Federal Interagency Working Group for Healthy People 2010.
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How Physical Limitations impact Hearing Aid choice:
An individual’s physical limitations must also be considered before selecting the appropriate hearing aids.
1. Some hearing aids can be firmly attached with acoustically tuned head bands (great for skiing), with sports clips (for kayaking, water-skiing, hiking back-country), and with clips to eyeglasses or collars (used for individuals with dementia).
2. Some hearing aids pick up sounds from behind or to the side.
–If the user is confined to a wheelchair, rear facing microphones are terrific to hear the caregiver.
–If the user is a realtor who drives clients who ride “shotgun” and/or in the back seat, two manufacturers provide adaptive microphones who identify the primary talker and “zoom” to that person.
3. Some hearing aids are far better suited to individuals who spend lots of time on the phone or on the computer.
4. Reduced manual dexterity may result in the inability to deal with changing batteries or even inserting the hearing aid.
5. Individuals who use oxygen with a cannula find it difficult to fit behind the ear hearing aids and the oxygen tube simultaneously. They are better fit with custom, in the ear or in the canal hearing aids.
6. “Technically challenged” and those resistant to any manual controls on a hearing aid should inquire about the vast number of automatic features to eliminate the need for manual controls.
7. Those with ear malformations will be glad to find a large array of features to keep the hearing aids in place.
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Have a Spare Set of Hearing Aids:
It’s also apparent that despite your best efforts, without warning, your hearing aids can fail from time to time. If you’re a person who’s totally dependent on your hearing aids in order to communicate, you might want to consider the purchase of backup hearing aids for use in emergencies. Maintaining two sets of hearing aids may initially cost more. It could be argued, however, that two sets used more or less alternately will last twice as long as one set used full time. So, spare aids may not cost more in the long run. It’s like the wisdom of owning two pairs of shoes versus only one pair. For some wearers, this works. Also, the availability of spare hearing aids removes the anxiety that might accompany this loss. Some hearing healthcare providers provide loaner aids which may or may not be suitable to your personal needs but is worth inquiring about. How can you judge whether you should have spare hearing aids? The best test we know is an honest answer to the following question: Does the mere thought of even a temporary loss of the use of your hearing aids create in you the slightest tinge of anxiety? If it does, then you probably should have a spare set. Actually, the availability of “spares” is something we all insist upon with commonly used devices we consider vital. (Our cars have spare tires, for example, so we can avoid panicking when a tire fails.) In our experience, people with severe hearing loss will regularly maintain a backup set of hearing aids, especially when the livelihood of such individuals is dependent on good hearing. Furthermore, the federal government for decades has issued to eligible military veterans two complete sets of hearing aids so that good hearing won’t be interrupted by temporary breakdowns. You may be one who would also like the extra security of backup aids in case yours go in for repair. Backup hearing-aids can be the still-functioning old set that you just replaced with new ones, or where money is of lesser concern, they can be hearing aids of more current vintage. If you choose to purchase or otherwise have available a set of spare hearing aids, try to ensure that they take the same size battery as your regular ones. This will lend itself to far more convenience than having to store and maintain two different kinds of fresh batteries.
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Compatibility of hearing aids:
Compatibility of hearing aid means hearing aid can work together with other devices without problems or conflict, and in fact can act in concert with other devices. Connectivity of hearing aid refers to many different features: communication between hearing aids, communication between hearing aids and external audio sources (e.g. mobile phones, TVs, etc.), the ability to control aids remotely, and the ability for hearing care professionals to program hearing aids without wires. Although connectivity and compatibility are distinct features, they do overlap while discussing hearing aids.
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I will discuss hearing aid compatibility with following devices:
1. Smartphones
2. Headphones
3. Eye glasses
4. Stethoscope
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Hearing aid compatibility (HAC) of cell phone:
The FCC defines Hearing Aid Compatibility (HAC) for cell phones in terms of two parameters; radio-frequency (RF) emissions and telecoil coupling. HAC-compliant device packages are marked with “M” or “T” ratings. The M-rating refers to the microphone mode. The T-rating refers to the telecoil mode. Only phones that meet HAC compliance will be labelled as such. If you see a “M3”, “M4”, “T3” or “T4” on the box then the phone has been designated as HAC compliant. Cell phones that comply with the FCC’s hearing aid compatibility rule must receive a minimum rating of M3 for RF emissions and T3 for telecoil coupling.
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The FCC’s hearing aid compatibility requirements address hearing aids that operate in either of two modes – acoustic coupling (“M” rating) or inductive coupling (“T” rating).
Acoustic coupling:
Hearing aids operating in acoustic coupling mode receive through a microphone and then amplify all sounds surrounding the user, including both desired sounds, such as a telephone’s audio signal, and unwanted ambient noise. If you plan to listen to your phone by placing the receiver up to the hearing aid microphone, you will be using acoustic coupling. This is very common practice for individuals with mild or moderate hearing loss. This allows the listener to hear ambient or background noise as well as the telephone signal through the hearing aid microphone.
Inductive coupling:
Hearing aids operating in inductive coupling mode turn off the microphone to avoid amplifying unwanted ambient noise, instead using a telecoil to receive only audio signal-based magnetic fields generated by inductive coupling-capable telephones.
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Are all cell phones hearing aid compatible?
Not all cell phones are hearing aid compatible. However, wireless manufacturers and service providers do offer many wireless devices that are HAC. The FCC has set minimum requirements for the number of HAC cell phones both manufacturers and service providers must offer. If you have a hearing aid or cochlear implant, you should look for wireless devices with hearing aid compatibility features.
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Adjust the hearing aid using a smart phone, tablet, or handheld device:
iPhone®, iPad®, and Android™ developers are working with hearing aid manufacturers to create seamless connectivity between hearing aids and smartphones. This will give hearing aid users the ability to adjust their instruments’ settings using Apps on an iPhone, iPad, or Android powered device. Currently, many hearing aid manufacturers offer smartphone Apps for their devices.
•Siemens has released an App for android devices. The Siemens miniTek Remote App turns a smartphone into a remote control to adjust the settings of the hearing aids.
•GN Resound has released a similar App called ReSound Control™.
•GN Resound has also released the Smart App for Resound LiNX™ hearing aids.
•Phonak has released an App for treating tinnitus called The Tinnitus Balance App.
•Oticon has released the Alta Diary App and the ConnectLine App for smart phones and tablets. The Alta Diary App enables the Alta user to rate various listening situations and send the audiologist feedback. The ConnectLine App allows users to stream the audio of an iPhone directly to both hearing aids.
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Best smartphones for your hearing aid in 2014:
Here are four smartphones that work with hearing aids. All come with an M3 and T4 HAC rating.
HTC One:
This is a top-rated smartphone for the hearing impaired, widely praised by a range of reviewers for call quality and features. It’s also been given great marks for its lack of voice distortion and natural tone.
Nokia Lumia 1020:
Nokia’s Lumia 1020 has an impressive list of features, though it does get mixed reviews for call clarity.
LG E988 Optimus G Pro LTE:
This smartphone is described as a “phablet” (phone/tablet) due to its massive 5.5-inch screen. Rates highly for call and voice quality.
iPhone 5:
The iPhone 5 also has an M3 and T4 rating—the iconic brand still going strong.
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In a nutshell smartphone-hearing aid relationship work in various ways:
1. Smartphone itself work as hearing aid
2. Smartphone work as a streamer between other audio sources and hearing aid
3. Smartphone can directly connect with hearing aid via Bluetooth and T-coil
4. Smartphone can have good acoustic coupling with hearing aid (HAC M3 rating or more)
5. Smartphone apps can program hearing aids
6. Smartphone can act as remote control of hearing aids
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Headphones:
Headphones and Hearing Aids–Can you wear both?
There’s really two parts to this question:
1. Can you physically wear headphones with hearing aids?
2. Will headphones make my hearing loss worse?
The answer is: it depends on your hearing aid and it depends on your headphones.
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The three main types of headphones that work well with hearing aids are:
1. Bone Conduction Headphones
Best for: in-the-ear (ITE), in-the-canal (ITC), completely-in-canal (CIC), invisible-in-the-canal (IIC)
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2. On-ear Headphones
Best for: completely-in-canal (CIC), invisible-in-the-canal (IIC)
*Can also be used for: in-the-ear (ITE), in-the-canal (ITC), behind-the-ear (BTE), receiver-in-canal (RIC)
3. Over-ear Headphones
Best for: in-the-ear (ITE), in-the-canal (ITC), behind-the-ear (BTE), receiver-in-canal (RIC)
Can also be used for: completely-in-canal (CIC), invisible-in-the-canal (IIC)
On-ear headphones (or supra-aural, left) sit on the ear, while over-ear headphones (or circum-aural, right) sit over the ear.
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A few more things you should know about wearing headphones with hearing aids. A lot of people are going to tell you that you shouldn’t wear headphones because they are a primary cause for hearing loss, especially in younger generations. Unfortunately this is only partially true.
Yes, headphones can cause hearing loss. No, they don’t have to…if you use them properly.
•If wearing your hearing aids with headphones, be careful to turn the music down, as the music will be amplified.
•If the headphones push on the hearing aid or sit too closely to the hearing aid, you may experience feedback, a whistling noise coming from the hearing aid. This is an indicator that you either need to re-position the headphones or unable to wear those headphones with your hearing aids.
•Noise cancelling or noise isolating headphones should be your primary choice. The biggest problem with headphones is that people turn the volume up a lot higher than it needs to be primarily because of background noise (i.e. people talking on the bus, loud co-workers, etc.). Noise isolating and noise cancelling headphones help to remove the background noise so you don’t crank up the volume to dangerous levels. Regardless, you should always use a simple sound volume meter app that tells you exactly how loud your music really is. You should aim to be lower than 85 dB if you are listening to music for an extended period of time.
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Can a hearing aid wearer use headphones?
No, it’s not a good idea. Hearing aid users will have problems if they try to use conventional headphones – they will almost certainly be uncomfortable worn over hearing aids with probably distorted or unclear sound. You will have to use T coil or Hearing Aid Direct Audio Input.
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Using headphones over a hearing aid is neither comfortable nor will give good sound quality, a personal inductive listening product will give a much better sound. Headphones do not work well with hearing aids but hearing aid users can use their hearing aid ‘T’ pickup coil by using a personal inductive listening device. Connevans offer three types of personal inductive listening devices. Mono inductive neck loops, stereo inductive silhouette earhooks and stereo inductive silent headphones. All three types are used with any equipment which provides a suitable output for driving personal stereo headphones, they simply plug directly into the headphone socket. Typical equipment with suitable headphone sockets are iPods, personal radios, CD players, talking book machines etc. For most hearing aids when ‘T’ is selected the microphone becomes dead; meaning problems of feedback are eliminated and hearing aid(s) might be able to be used louder than usual. Some people prefer to have sound from both their loop programme and their microphone combined, so they are still aware of the world around them – discuss which would be best for you with your audiologist. The neck loops are the most straightforward to use, however the silhouette earhooks and silent headphones are more position sensitive (you need to experiment by moving them slightly to get the best signal). A neck loop is best suited to both the casual user and those who do not enjoy coping with gadgets. The silhouettes give a good signal but are more fiddly to wear they are sometimes not liked by those with glasses. The silent headphones are sometimes preferred for their more conventional look.
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A better option for listening to music with your Hearing Aids:
With the improvement in hearing aid and wireless technology, hearing aids can now become your headphones. There is no longer a need to figure out how to wear headphones over your hearing aids, or take your hearing aids out completely to listen to music with headphones. With wireless hearing aids, you can connect your Bluetooth iPod or iPhone directly to your hearing aid with no wires! This lets you listen to music through your hearing aids, just as if they were headphones themselves. And the best part is, you’re already wearing your hearing aids so all you have to do is push play!
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Eye glasses:
During the late 1950s through 1970s, before in-the-ear aids became common (and in an era when thick-rimmed eyeglasses were popular), people who wore both glasses and hearing aids frequently chose a type of hearing aid that was built into the temple pieces of the spectacles. However, the combination of glasses and hearing aids was inflexible: the range of frame styles was limited, and the user had to wear both hearing aids and glasses at once or wear neither. Today, people who use both glasses and hearing aids can use in-the-ear types, or rest a BTE neatly alongside the arm of the glasses. Behind the ear hearing aids may cause some discomfort if not sited correctly but that in no way means that they are not a good choice for glasses wearers. Many people who suffer from both hearing and visual problems would like to hide one of them and feel uneasy when their aid is visible. That is why some opt for very small and discreet hearing aids or choose contact lenses instead of spectacles. While this may be convenient for certain people, it is not a universal solution. There are different options for comfortably wearing both glasses and hearing aids depending on preference, type of hearing loss and hearing aid and glasses frames. Wearing glasses with behind the ear hearing aids is not problematic if you are cautious when putting them on. First, you need to put your glasses on and then the hearing aid, you can use a mirror to adjust them if necessary. When you need to take off your spectacles, it is better to do so by pulling them forward rather than to the side to avoid dislodging the hearing aid. You can also use special clips and straps such as SafeNSound to connect the frames and the hearing aid so they are secured together. That option is especially suitable for children and the elderly. There are still some specialized situations where hearing aids built into the frame of eyeglasses can be useful, such as when a person has hearing loss mainly in one ear: sound from a microphone on the “bad” side can be sent through the frame to the side with better hearing. This can also be achieved by using CROS or bi-CROS style hearing aids, which are now wireless in sending sound to the better side.
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Spectacle hearing aids:
It’s possible to have your hearing aids and glasses built into one unit. However, this generally isn’t ideal because if your hearing aids need repairing or you need a new glasses prescription, you could be left with neither hearing nor visual aids in the interim. With some spectacle aids, the frame has to be adapted or cut, meaning that the glasses can’t be returned to their original state. Once the hearing aid has been fitted to the frames, some opticians are reluctant to change the lenses in the glasses as they are worried about damaging the hearing aid. Also, the hearing aids can’t be removed and worn separately. Due to low demand, the technology in spectacle hearing aids can be slightly behind normal hearing aid technology, despite costing about the same. However, one instance where spectacle hearing aids can work really well is if you have conductive hearing loss. This is because the bone conductor is mounted onto the arm of the glasses and creates pressure on the mastoid bone behind the ear, transferring it directly to the cochlea in the inner ear. They can also be useful for people who have mild to moderate hearing loss, but are unable to wear any device in or around the ear due to allergy or infection. Spectacle aids come in two forms, bone conduction spectacles and air conduction spectacles.
Directional spectacles:
These ‘hearing glasses’ incorporate a directional microphone capability: four microphones on each side of the frame effectively work as two directional microphones, which are able to discern between sound coming from the front and sound coming from the sides or back of the user. This improves the signal-to-noise ratio by allowing for amplification of the sound coming from the front, the direction in which the user is looking, and active noise control for sounds coming from the sides or behind. Only very recently has the technology required become small enough to be fitted in the frame of the glasses. As a recent addition to the market, this new hearing aid is currently available only in the Netherlands and Belgium.
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Eyeglass-hearing aid relationship can work in various ways:
1. Eyeglass can work as bone conduction hearing aid
2. Eyeglass can become a style of wearing hearing aid
3. Eyeglass can be worn over hearing aids
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Stethoscopes:
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal or human body. It typically has a small disc-shaped resonator that is placed against the chest, and two tubes connected to earpieces. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins. In combination with a sphygmomanometer, it is commonly used for measurements of blood pressure.
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Acoustic stethoscope:
The acoustic stethoscope operates on the transmission of sound from the chest piece, via air-filled hollow tubes, to the listener’s ears. The chest piece usually consists of two parts that can be placed against the patient for sensing sound: the bell (hollow cup) and the diaphragm (disc). The bell transmits lower frequency sounds, while the diaphragm transmits higher frequency sounds. When the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves that travel to the listener’s ear. When the diaphragm is placed against the patient’s skin, body sounds vibrate the diaphragm, creating acoustic pressure waves which then travel to the listener’s ears. The human body then translates these pressure waves into sound and allows the listener to “hear” what they are examining. One problem with acoustic stethoscopes is that the sound level was extremely low.
Electronic stethoscope:
An electronic stethoscope overcomes the low sound levels by electronically amplifying body sounds. However, amplification of stethoscope contact artifacts, and component cutoffs (frequency response thresholds of electronic stethoscope microphones, pre-amps, amps, and speakers) limit electronically amplified stethoscopes’ overall utility by amplifying mid-range sounds, while simultaneously attenuating high- and low- frequency range sounds. Currently, a number of companies offer electronic stethoscopes. Electronic stethoscopes utilize advanced technology to overcome these low sound levels by electronically amplifying body sounds. Electronic stethoscopes require conversion of acoustic sound waves obtained through the chest piece into electronic signals which are then transmitted through uniquely designed circuitry and processed for optimal listening. The circuitry consists of components that allow the energy to be amplified and optimized for listening at various frequencies. The circuitry also allows the sound energy to be digitized, encoded and decoded, to have the ambient noise reduced or eliminated, and sent through speakers or headphones. The fact that sounds are transmitted electronically allows electronic stethoscopes to offer features such as audio or serial data output, wireless transmission, and recording of sound clips.
Digitizing Stethoscopes:
A few of the electronic stethoscopes on the market are called “digitizing stethoscopes” because they convert the audio sound to a digital signal. These stethoscopes can transmit serialized audio data that can be shared real time (synchronously) and/or in a store and forward fashion (asynchronously). These units work by detecting sound through the electronic stethoscope sensor, converting that sound energy to electricity and running it through circuitry which can amplify it, filter it by frequency, and finally convert the data from analog to a digital.
Amplifying Stethoscopes:
Simple electronic stethoscopes are also called amplifying stethoscopes. On average amplified stethoscopes amplify between 15-50 dB gain depending upon the product. There are several brands of amplified stethoscopes available such as: E-Scope II, Welch Allyn Master Elite, and the 3M Littman, Electromax.
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Common objections against electronic stethoscope:
•Electronic stethoscopes are expensive.
•Unless you have a hearing problem, you should be able to hear just fine without one.
•Physicians have gone without electronic stethoscopes for almost two hundred years — why switch now?
The amplification of average electronic stethoscope is up to 18 times greater than the best non-electronic acoustic stethoscope. And the ambient noise reduction technology cancels out an average of 75% of distracting room noise. In an ideal situation, could you pick up all the murmurs you might hear with the electronic Model with a conventional acoustic stethoscope? Sure — but there are no ideal situations. Hospitals are noisy, it’s sometimes difficult to position patients properly to listen to their heart and lungs, and doctors are often rushed. At the very least, the electronic stethoscope provides an added level of assurance that you haven’t missed any significant findings.
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Hearing impaired professionals are in need of a means to detect heart and breath sounds and to measure blood pressure during their routine medical duties. Hearing aids are designed for enhancement of voice sounds that have a frequency range from approximately 300Hz to 5000Hz. Some hearing aids can be programmed for lower frequencies. However, even with this additional low frequency response, hearing aids still are not be able to reproduce the heart and lung sounds adequately for diagnostic purposes. Also, some individuals may have hearing loss in the range for heart and lung sounds that is not compensated by their hearing aid. Voice sounds range between 300-5000Hz while heart sounds are between 20-650Hz. The first and second heart sounds, which are essential to hear, range between 70-120Hz. The third and fourth heart sounds are in the 40-60Hz range. No hearing aid presently on the market will reproduce a sound low enough to allow hearing the third or fourth heart sound.
Do I need amplification?
Heart and lung sounds are low frequency, lower than most speech sounds. And lower than the audiogram usually tests. Most speech sounds are from 300Hz to 5000Hz and upwards. Heart sounds are between 20-650Hz, lung sounds 70-4000Hz, most below 2000Hz. So those of us with only a high-frequency hearing loss may be able to use normal stethoscopes safely. If your hearing loss is significant at low frequencies, you will need an electronic stethoscope. Once you’ve established whether you need amplification or not, your choice of stethoscope will also depend on whether or not you’re happy to take your hearing aids out or would prefer to keep them in when you use a stethoscope.
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I want to emphasize that hearing aids and acoustic stethoscope are incompatible; you cannot wear standard stethoscope over hearing aid because you will not hear anything pertaining to heart or lung. There are two reasons for incompatibility of acoustic stethoscope and hearing aid.
1. Eartips of acoustic stethoscope cannot fit snugly over hearing aids, there is always sound leakage. As such acoustic stethoscope’s sound level is extremely low and leakage will worsen it.
2. Hearing aid primarily amplifies speech and not very low frequency heart sounds.
So remove hearing aid if you are using it for high frequency hearing loss, and then use standard stethoscope.
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Stethoscope use without adaptations:
If you’re happy to take your hearing aids out to auscultate and have good low-frequency hearing, you’re fine using a standard stethoscope. If you have poor low-frequency hearing, you’ll need an electronic stethoscope and unless your hearing impairment is too great, you can simply take out your hearing aids when you use the stethoscope. CICs can be a bit fiddly so some people work with one in and one out. Remember, using a stethoscope in only one ear, sounds will only be half as loud. Open fit BTEs can be uncomfortable to flip in and out. Normal BTE moulds can be flipped out easily, leaving the hearing aid hooked over your ear. If the aids keep slipping off, you can use toupee tape or little stickies to stick the aids to your head or ear at the beginning of the day. This is the most straightforward option as it’s sometimes tricky setting up an electronic stethoscope along with hearing aids. Why complicate things if you don’t need to?
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Stethoscope-hearing aid interface:
You’ve reached the point of deciding you don’t want to remove your hearing aids.
What are your options?
1. Ideally you’ll have open fit or vents allowing you to bypass your hearing aids using adapted eartips or custom ear moulds or headphones.
2. If pushed, and with caution, you may be able to connect your hearing aids or implants to the stethoscope using telecoil, direct audio input or an FM or Bluetooth assisted listening device.
3. Don’t discount the “not quite removing my hearing aid” options:
•Some people work with one hearing aid in, one out.
•Flip out your ear moulds leaving BTEs hooked over your ears
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Custom moulds and adapted eartips of stethoscopes:
There are several ways you can adapt a stethoscope to use with some hearing aids, or even adapt the hearing aid to hold a normal stethoscope eartip.
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Special eartips such as Steth-O-Mates can be used with CIC and sometimes ITE aids. It is sometimes difficult keeping them in the correct position and people occasionally find them uncomfortable. It may be more tricky to get them to stay in place over ITEs and they may be more likely to buckle or give feedback. But Steth-O-Mates don’t cost much and are convenient to use so worth a try. The smaller size fit over CICs and larger over ITE. Specify your make of stethoscope to get the right screw fitting. Hearing aid moulds can sometimes be adapted to allow you to use a stethoscope with normal eartips. This may be as simple as carving out a hollow over the vent on your moulds to fit your stethoscope eartips. Or take off the stethoscope eartips and fit the stethoscope tube to vents in the ear moulds. Moulds can also be made that are attached permanently to your stethoscope and worn over CIC and possibly ITE hearing aids (e.g. Westone.) If you have open fitting hearing aids, you may not need to do anything: you may be comfortable using normal ear pieces over the domes. Of course check you can hear through the stethoscope and the domes aren’t occluding the stethoscope ear tips. And check the domes and fine tubing aren’t being damaged. If the spring in other stethoscope arms is so strong you find it uncomfortable, try the Thinklabs ds32a+ which has adjustable arms.
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Don’t forget, hearing aids don’t usually reproduce the low frequencies well. So if you’re using earpieces, custom moulds or headphones over hearing aids you also need vents in your ear moulds or open fitting. Even then you may not hear heart and lung sounds well.
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Connecting Hearing aid and implant accessories to electronic stethoscope:
In some circumstances, we may use our hearing instruments’ accessories such as telecoil (T-switch) or direct audio input (patch cord.) Or even stream wirelessly using FM or Bluetooth. Hearing aids usually have a poor low frequency response. Cochlear implants vary, some extending to lower frequencies than others. So connecting electronic stethoscope to hearing aid or implant must be done cautiously. You may need a programme on the aids or processors specifically for stethoscope use. Cardionics advises “increasing the gain of low frequency improves heart sounds … and you will need to disable automatic noise reduction.” But this still won’t address hearing aids’ and implants’ limitations due to poor low-frequency response. Heart and lung sounds might be distorted or may not be transmitted at all. If your hearing aids have telecoils (a T-switch), you can use a headphone “silhouette” similar to the “T-link” you may already use with a mobile phone. Hook it over your ear(s) and switch your hearing aids to T setting. Cardionics still supply single and dual headphone silhouettes though they no longer recommend them, describing both silhouettes and direct audio input as a “last resort.” HATIS also makes silhouttes and their Epic has been used with electronic stethoscopes. This was before Cardionics raised their concerns. Headphone silhouettes can be used with cochlear implants with BTE processors, depending on the implant’s low frequency response. If the stethoscope has a suitable output socket you can connect it directly to your processor by a patch cord or to BTEs via “shoes.” This may work with the Cardionics and Thinklabs stethoscopes but the Littmann socket isn’t suitable. You can make a wired connection from the Cardionics or Thinklabs stethoscopes to an FM ALD or Bluetooth streamer. If your hearing aids or implants have FM or Bluetooth capability, this transmits wirelessly to your hearing aids/implants. If not, you link the ALD to your hearing aids by telecoil or direct audio input. It seems to work for some and not others and you may have to experiment with different configurations, programmes and stethoscopes to set it up. If you are using an ALD or streamer a lot of the time anyway, this setup may be little trouble as you simply switch from one source to another.
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Stethoscope comparison table:
| Can be used with: | Acoustic stethoscope | Littmann 3100 & 3200 | Thinklabs (One and ds32a+) | Cardionics Vi-Scope | Cardionics E-Scope |
| *Adapted earpieces or custom ear moulds | YES | YES | Moulds – possibly. Adapted eartips – NO | YES | YES |
| *Headphones | NO | NO | YES | YES | YES (hearing impaired model) |
| *Telecoil DAI or FM/Bluetooth systems | NO | NO | YES | YES | YES |
| *Visual display | NO | NO | YES – iPhone/iPod | YES – integral | NO |
| *Electronic record | NO | YES -3200 | YES | YES | Maybe (needs software?) |
| *Teaching – 2 headsets | NO | NO | YES | YES | YES |
| Comments | Thinklabs supplies cable | Concerns about quality of link with headphones and accessories. Cardionics also supply headphones. Cardionics are no longer supplying this but some may still be available. |
Unavailable routinely in UK. Cardionics can supply headphones silhouettes and cables |
* Not supplied with the stethoscope unless indicated
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1. Don’t forget, hearing aids don’t usually reproduce the low frequencies well. So if you’re using earpieces, custom moulds or headphones over hearing aids you also need vents in your ear moulds or open fitting.
2. Certain electronic stethoscopes can link to hearing aids using accessories such as the T switch, direct audio input (DAI) cables or even FM or Bluetooth if your hearing aids have these facilities. However it is better to use earpieces or headphones if possible to avoid the problem of poor low frequency reproduction.
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Headphones to hear heart sounds:
As explained, heart sounds in particular are lower frequency than most speech sounds. Even as low as 20Hz. Like hearing aids, headphones are designed to reproduce speech clearly. They’re also designed for music so may have a better low frequency response than hearing aids. Even so, many headphones don’t perform well enough at the very low frequencies and won’t reproduce some heart sounds. So it is essential you check the specifications of any headphones you buy. Cardionics supplies headphones to use with their E-scope and Vi-scope stethoscopes, so these can be relied on to have a good low-frequency response. Cardionics also supply full size headphones, the Koss UR40 lightweight headphones, that some people with BTEs find more comfortable and that will reduce some background noise. For very noisy situations such as in ambulances, helicopters and even noisy emergency departments, Cardionics supply an amplified stethoscope with aviation-style headphones. If the headphone plug doesn’t match the stethoscope output socket (for example the Thinklabs stethoscope has a 2.5mm socket) you can buy an adapter. Depending on quality, this may attenuate the signal. You may need a higher quality adapter or to rewire the plug. Don’t forget, hearing aids don’t usually reproduce the low frequencies well. So if you’re using earpieces, custom moulds or headphones over hearing aids you also need vents in your ear moulds or open fitting.
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Thinklabs ‘One’ electronic stethoscope:
Thinklabs One electronic stethoscope addresses the specialized needs and unique challenges of hearing impaired medical professionals. Because One offers unparalled amplification, connectivity and adaptability, you can create a custom solution for auscultation that meets your individual needs. With a standard 3.5 mm jack, One connects to any headphones and because it has over 100x amplification, One is loud enough to compensate for hearing deficits. It will blow you away with maximum bass response – which is critical in listening to heart and lung sounds. Use One with headphones that offer strong bass.
One electronic stethoscope work in two ways:
1. Streamer connects to Thinklabs One via a cable included with the stethoscope. Streamer connects to close-fit hearing aid.
2. Open fit allows sound to enter the ear, headphone bass can transmit directly, which is helpful at low frequencies.
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Using One with a Streamer:
One works with streamers to deliver sound directly to your hearing aids. The streamer, manufactured by your hearing aid company, transmits sound to your closed-fit hearing aid. One plugs into the streamer, worn around the neck, which then transmits wirelessly to hearing aids. Many users find this to be an elegant auscultation solution. Simply connect One to the streamer via the cable provided by Thinklabs. Work with your audiologist to program your hearing aids for strong bass output. Just plug One into a streamer and you’re ready to practice! Please note: a streamer is not recommended for use with open-fit hearing aids, as much of the audio is lost. Again, results vary greatly from person to person so we encourage you to work with your audiologist for optimal results. Bluetooth transmitter could not be paired with the streamer to eliminate the cable between One and the streamer as sound quality is diminished by adding another radio hop to the system and adds unnecessary complexity to the setup.
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Listening to One with Cochlear implants:
One has a standard 3.5mm headphone jack, the same as cell phones, music players and similar devices. Cochlear implant wearers may simply choose to wear over-ear headphones, or they can utilize the Personal Audio Cable provided by Cochlear to connect One with the sound processor in the CI system. If you wear the Nucleus 6 Cochlear Implants, you can use the Cochlear MiniMicrophone, which transmits wirelessly to the CI. In this case, One is connected by a cable to the MiniMic, which then transmits wirelessly to the CI. Wearers of older models can connect to One using the personal audio cable. Using external devices with CIs is very specific to each individual user’s hearing, CI settings and other factors. The Cochlear MiniMic is also compatible with ReSound and Beltone hearing aids.
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Cardionics recommends that users of the Phonak and other BTE hearing aids should not directly connect the E-Scope with their BTE hearing aids and attempt to use them for diagnostic auscultation. Provided the user has adequate low frequency hearing, the E-Scope Clinical Model or the E-Scope Belt-Clip Model may be used by hearing impaired clinicians or nurses either by inserting the ear tips in their ears, or placing the headset speakers over their ears with their ear molds removed. An alternative method would be to use an “open fit” type BTE type hearing aid and place the headset speakers from the E-Scope Belt-Clip Model over their ears. The final determination regarding the suitability of using the E-Scope with a BTE hearing aid in the recommended manner above should be made by an audiologist or other competent medical professional.
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Stethoscope hearing aid:
These hearing aids are designed for medical practitioners with hearing loss who use stethoscopes. The hearing aid is built into the speaker of the stethoscope, which amplifies the sound.
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The figure below guides hearing impaired medical professional to use stethoscope (standard/electronic) to hear heart/lung sounds with/without using hearing aids:
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Cochlear implant (CI):
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In the event that the hearing aid provides inadequate rehabilitation, cochlear implants may be appropriate. Criteria for implantation include severe to profound hearing loss with open-set sentence cognition of ≤40% under best aided conditions. Worldwide, more than 300,000 hearing-impaired individuals have received cochlear implants. Cochlear implants are neural prostheses that convert sound energy to electrical energy and can be used to stimulate the auditory division of the eighth nerve directly. In most cases of profound hearing impairment, the auditory hair cells are lost but the ganglionic cells of the auditory division of the eighth nerve are preserved. Cochlear implants consist of electrodes that are inserted into the cochlea through the round window, speech processors that extract acoustical elements of speech for conversion to electrical currents, and a means of transmitting the electrical energy through the skin. Patients with implants experience sound that helps with speech reading, allows open-set word recognition, and helps in modulating the person’s own voice. Usually, within the first 3–6 months after implantation, adult patients can understand speech without visual cues. With the current generation of multichannel cochlear implants, nearly 75% of patients are able to converse on the telephone.
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A cochlear implant is composed of an external microphone and speech processor worn on the ear and a receiver implanted underneath the temporalis muscle. The internal receiver is attached to an electrode that is placed surgically in the cochlea.
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Cochlear implants (CIs) are indicated for bilateral (both ears) sensorineural hearing loss (hearing loss due to inner ear or inner ear nerve damage). However, there is now a recognized role for CI in patients who have nonserviceable hearing loss in the candidate ear and advanced—but still ‘aidable’—hearing loss in the good ear. If the deaf ear has been without hearing for more than 20 years, it is likely that the implant will not restore levels of understandable speech that could be achieved in patients with a shorter term of deafness. Inserting a cochlear implant destroys any residual hearing in the operated ear so that cochlear implant is not an option with some residual hearing. Cochlear implants (CIs) in the setting of SSD with fairly normal hearing on the other side would be considered ‘off label’, meaning that it is not an indication that the FDA has approved. However CIs have been used in SSD in other countries. A 2013 study on efficacy of cochlear implants in children showed that the majority of deaf children who received cochlear implants before 18 months of age had language skills similar to their hearing peers. Younger age of implantation had a positive correlation to better spoken language skills.
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Hybrid CI:
The U.S. FDA recently approved the first hybrid cochlear implant for the treatment of high-frequency hearing loss. Patients with presbyacusis typically have normal low frequency hearing, while suffering from high-frequency hearing loss associated with loss of clarity that cannot always be adequately rehabilitated with a hearing aid. However, these patients are not candidates for conventional cochlear implants because they have too much residual hearing. The hybrid implant has been specifically designed for this patient population; it has a shorter electrode than a conventional cochlear implant and can be introduced into the cochlea atraumatically, thus preserving low-frequency hearing. Individuals with a hybrid implant use their own natural low frequency “acoustic” hearing and rely on the implant for providing “electrical” high-frequency hearing. Patients who have received the hybrid implant perform better on speech testing in both quiet and noisy backgrounds.
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EAS:
Electric acoustic stimulation (EAS) is the use of a hearing aid and a cochlear implant together in the same ear. The hearing aid acoustically amplifies low frequencies, while the cochlear implant electrically stimulates the middle and high frequencies. The inner ear processes acoustic and electric stimuli simultaneously. The results of international studies have shown a highly synergistic effect between hearing aid and cochlear implant technology, particularly evident in speech understanding in noise, pitch discrimination and music appreciation. An ideal treatment for high frequency hearing loss is Electric Acoustic Stimulation. It’s the only type of hearing implant that combines both electric stimulation, which is sending electrical pulses directly to the nerve cells in the inner ear like a cochlear implant does, and acoustic amplification, like a hearing aid. This combination of stimulation is ideal for someone with high frequency hearing loss because it helps to reproduce the high-frequency sounds with electric stimulation, while using acoustic amplification to take care of the low-frequency residual hearing. The electric stimulation is necessary to reproduce the high-frequency sounds because it can stimulate the cochlea even when no hair cells are present. It’s done with a cochlear implant and an electrode array designed specifically for high-frequency hearing loss. But, because some hair cells in the low-frequency region still work (called “residual hearing”), the goal is to take full advantage of each and every one of these remaining hair cells. This is done with a solution that’s much different from a CI, and very straightforward: turning up the volume. Like a hearing aid, the EAS system sends amplified sounds to the cochlea along the ear’s natural hearing path. This way, both the high-frequency and low-frequency hearing losses each get unique and targeted treatment to provide the best possible hearing.
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Hearing Aids vs. Cochlear Implants for those with Severe Hearing Loss:
If hearing aid fitting has been assertive and well-managed, and if the child still cannot learn spoken language naturally, cannot use the telephone, and/or cannot converse with relative ease under the direction of an auditory-verbal therapist in partnership with parent, then the CI is likely the device of first choice. While there are no guarantees when one opts for a cochlear implant, the chances are extraordinarily high that one with profound deafness will derive immeasurably greater benefit from implants than from hearing aids. Assuming that all amplification options have been exhausted, how well a child hears or does not hear normal conversation should be the primary reason for contacting a cochlear implant center and/or pursuing cochlear implantation. For those with profound hearing loss, the CI is likely the prosthetic device of preferred choice…so as to learn natural auditory-verbal communication. For those with severe-profound hearing loss, most will do better with implants. For those with severe hearing loss, hearing aids are typically the preferred choice of prosthetic devices providing aided thresholds in the 30-35 dB range (or better) can be attained at least in the low-to-mid frequency range as a result of assertive amplification and ongoing effective audiological management.
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Although cochlear implants (CI) and hearing aids (HA) serve the same purpose there are differences between them. Hearing aids deliver amplified sound to the damaged cochlea. Depending on the type of loss, be it the common-ski slope shaped hearing chart (high frequencies are most severely impacted) or reverse-slope loss (low frequencies are impacted), a hearing aid can be programmed to shape the amplification of sound to match the loss. Sound is still being delivered to damaged nerves, so HAs are limited in ability to aid severe and profound loss beyond environmental sounds and vowels in speech. The use of a hearing aid at the severe and profound level can be deceptive in the perceived benefit due to the fact you “can still hear.” Modern hearing aids can do lots of processing, including compensating for hearing loss that varies at different frequencies, and improving performance in noise. But in the end, they can only present the sound to you by yelling in your ear. The signal is still processed by the damaged cochlea and sent to the brain with its added distortion. Even with substantial amplification, you may not hear very much, and you become tired and strained due to the loud sounds being presented to your ear. Cochlear implants operate very differently than hearing aids. A cochlear implant bypasses the damaged hair cells by delivering electrical current directly to the cochlear, or auditory, nerve. A cochlear implant presents a wide range of frequencies, regardless of the pre-implantation hearing loss. The primary benefit of a hearing aid over a cochlear implant is in the area of low frequencies. Low frequencies are detected at the apex (inner-most area) of the cochlea. Current implant technology limits the insertion depth of the electrode into the cochlea, limiting access to the lower frequencies below 250 Hz. Those who are able to use a hearing aid in one ear and an implant in the other are encouraged to do so for this reason. Users who rely solely on an implant to hear generally find that they gain access to/perceive low frequencies via harmonics once the brain has learned to translate the electrode signal. People who transition from HAs to CIs generally find that compensation techniques such as lip-reading become easier. Eventually, you may reach the point where you require very little compensation. With hearing aids, many people try to increase the volume as much as possible. With a severe or profound hearing loss, this may provide some cues to aid in reading lips and interpolating contextual cues. Cochlear implants provide plenty of sound, so that you don’t need to have high volumes blasted into your ear just to get those sounds. Your job is to learn how to interpret them so that it becomes second nature. Many types of hearing loss involve more loss at high frequencies. This is particularly unfortunate because much of the important information in speech resides in those high frequencies. Hard consonants and sibilant sounds all have a lot of high-frequency content. If you don’t hear at those frequencies, it sounds like everybody mumbles unintelligibly. Hearing aids, especially those fit for severe and profound loss, are prone to feedback (whistling.) Eating, talking, and chewing gum all affect hearing due to the loosening/tightening of the ear canal around the ear mold. Cochlear implant users do not experience either issue. No ear mold or amplified sound is involved in the process. The lack of an ear mold is a comfort bonus as well.
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Caveat:
There are some problems that will be similar for both hearing aid and implant users, such as having the CI coil or the BTE aid frequently getting knocked off while the child is in a car seat. Another similarity is that understanding speech within background noise remains problematic for people with hearing loss, regardless of prosthetic device employed. Still another similarity is that understanding speech over distance remains severely limited with either device, so that FM systems are typically needed for the classroom or other large-room settings. As with any auditory-verbal therapy situation, for both hearing aid and cochlear implant users, wide individual differences remain in terms of device effectiveness.
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Cochlear implant vs. CROS/BAHA for SSD:
Self-report and behavioural data confirm that individuals with SSD experience difficulties with listening to sounds on the side of their impaired ear and in determining the location of sounds in space. Current treatment options for SSD primarily aim to improve access to sounds arriving at the impaired ear by utilising the intact hearing in the contra-lateral ear. Sounds at the impaired ear are transmitted to the non-impaired ear either via a wireless link and a conventional acoustic coupling (CROS) or by conduction via the cranial bones (BAHA). Individually, both systems have been found to be efficacious compared to an unaided condition in improving speech perception in noise but the systems do not improve the ability to localise sounds. Cochlear implantation in SSD can restore the ability to localise sounds by providing access to the inter-aural cues which underpin accurate localisation and thus has the potential to support useful aspects of binaural hearing. Recent published evidence has suggested that cochlear implantation in individuals with a single-sided deafness can restore access to the binaural cues which underpin the ability to localise sounds and segregate speech from other interfering sounds.
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Auditory brainstem implant (ABI):
For individuals who have had both eighth nerves destroyed by trauma or bilateral vestibular schwannomas (e.g., neurofibromatosis type 2), brainstem auditory implants placed near the cochlear nucleus may provide auditory rehabilitation. An auditory brainstem implant (ABI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf, due to retrocochlear hearing impairment (due to illness or injury damaging the cochlea or auditory nerve, and so precluding the use of a cochlear implant). The auditory brainstem implant uses technology similar to that of the cochlear implant, but instead of electrical stimulation being used to stimulate the cochlea, it is used to stimulate the brainstem of the recipient. Only about one thousand five hundred recipients have been implanted with an auditory brainstem implant, due to the nature of the surgery required to implant the device (as it requires brain surgery to implant the device). In the United States ABIs were previously only approved for adults (18 & over) and only for patients with neurofibromatosis type II (NF2). In January 2013, the US FDA approved a clinical trial of auditory brainstem implants for children. In Europe, ABIs have been used in children and adults, and in patients with NF2 as well as other auditory complications, such as auditory nerve aplasia and cochlea ossification. An ABI will not fully restore your hearing, but it can usually restore some degree of hearing and can make lip-reading easier.
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The benefits of wearing hearing aid:
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Hearing aid and residual hearing:
Residual hearing refers to the hearing that remains after a person has experienced a hearing loss. Hearing aids primarily improve how well people use their residual hearing. They provide valuable sensory stimulation to the auditory system that otherwise might deteriorate over time. Another question people may have after visiting an audiologist and learning they have a hearing loss is whether their affected ear will become “lazy” if they don’t get a hearing aid. It may. Ears function like an arm or leg – lack of use can result in both physical and functional loss. An ear is a body organ that needs to work. Sensory organs that are not stimulated are vulnerable to various levels of physical atrophy and/or dysfunction. Therefore, when prescribed by an audiologist, amplification should be used to reduce the physical and physiological impact of sensory deprivation. While hearing aids do not physically repair damaged ears and hearing, they may slow the process of sensorineural hearing loss and auditory processing problems by helping to prevent auditory deprivation.
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Individuals with untreated hearing loss are more likely to report depression, anxiety and paranoia, and in addition, are less likely to participate in organized social activities when compared with those who wear hearing aids. Hearing aid use is associated with significant improvement in social, psychological, emotional, and physical aspects of the lives of hearing impaired persons with all degrees of hearing loss. This includes improvements in their relationships at home, their sense of independence, and their social as well in sexual functioning. According to a MarkeTrak VIII survey done in 2011, 75 percent of hearing aid users reported overall improved quality of life, including factors such as personal and work relationships, physical health and self-confidence. They might also help you to enjoy listening to music and the TV again, at a volume that’s comfortable for those around you. According to a survey by Action on Hearing Loss, people who use hearing aids are generally very satisfied with them. More than half of those questioned described being fitted with a hearing aid as “a relief” and most of them felt their lives had improved because they “felt more involved”.
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Hearing aid and Quality of life:
There is an extensive body of research concerning the impact of hearing loss on quality of life. When we talk of quality of life, the benefits of healthy hearing are not limited to enhancing the aesthetic pleasure of acoustic sounds in a person’s environment. Indeed, hearing loss has been shown to have a negative effect on nearly every dimension of the human experience, including: physical health, emotional and mental health, perceptions of mental acuity, social skills, family relationships, and self-esteem, not to mention work and school performance. In a review of the literature, Bridget Shield, PhD, a professor of acoustics at London South Bank University, has shown that hearing loss is related to unemployment and underemployment. However, research in this area has focused primarily on people with severe to profound hearing loss. The literature has historically been less clear regarding the impact of the full spectrum of hearing loss and how it impacts effectiveness in the workforce. In a 2005 Better Hearing Institute (BHI) study of more than 40,000 households, hearing loss was shown to reduce average household income by up to $23,000 a year depending on the degree of hearing loss. However, the use of hearing aids was shown to mitigate the effects of hearing loss by 50%. The BHI estimated that people with hearing loss in the workforce could be losing more than $100 billion a year in income. This reduction in earnings not only damages the quality of life of the person with hearing loss, but it also has a detrimental impact on society as a whole due to reduced productivity and losses in tax revenues.
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Are there limitations with hearing aids?
•Hearing aids DO NOT restore normal hearing. In contrast, eyeglasses can restore 20/20 vision.
•Hearing aids amplify all sounds, including background noise that you do not wish to hear.
•Hearing aids require an adjustment period that may take several months. Follow-up visits with the licensed hearing aid dispenser are necessary to take full advantage of the hearing aids.
•When you begin to use hearing aids, many sounds, including your own voice, might seem too loud.
•You will need to learn how to adjust the settings for hearing aids with more complicated technology.
•Hearing aids can be expensive.
To overcome the potential limitations with hearing aids, inclusion of aural rehabilitation during the process of your hearing aid purchase can be helpful. Aural rehabilitation may assist in maximizing the benefits of hearing aids and developing strategies to deal with hearing aid limitations.
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Limitation of hearing aids vis-à-vis Bluetooth:
The reason that digital wireless technology is not in every hearing aid today is because of power consumption. Currently, a Bluetooth chip requires over 30 mW to transmit and receive audio. Most hearing aids require less than 1 mW of power in total, so adding a Bluetooth chip would increase the power consumption dramatically and reduce the battery life of the hearing aid. Until this power problem is solved, Bluetooth chips will not likely be added as a component within a hearing aid. Yanz suggested an interim solution of a general-purpose relay device with a large battery that sits near the hearing aid, receives Bluetooth signals, and then relays them to the hearing aid using a wireless technology that requires less power than Bluetooth. This solution would trade lower hearing aid power consumption for the need of an accessory but would provide the widespread connectivity described earlier if the usability were designed to be simple. As digital wireless chips continue to be designed smaller and lower in power, these limitations will disappear, and it is likely that the majority of hearing aids will have wireless receivers embedded in them in the same way that the majority of hearing aids today have DSPs. When this happens, hearing aids will contain new ear-to-ear algorithms and will be connected to almost any audio source that the wearer wants to hear. The engineering challenge will be to make connecting to these sources as easy as possible for the hearing aid wearer.
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Caution while using hearing aids:
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X-ray, CT, MR, PET scanning and Electrotherapy:
Remove your hearing aid for example during X-ray, CT / MR / PET scanning electrotherapy or surgery as your hearing aid may be damaged when exposed to strong fields. External hearing aids are included in the category of electronically-activated devices that may be found in patients referred for MR procedures. Exposure to the magnetic fields used for MR examinations can damage these devices. Therefore, a patient or other individual with an external hearing aid must not enter the MR system room. Fortunately, most external hearing aids can be readily identified and removed from the patient or individual to prevent damage associated with the MRI environment. Other hearing devices may have external components as well as pieces that are surgically implanted. Hearing devices with external and internal components may be especially problematic for patients and individuals in relative to the use of MR procedures. Accordingly, patients and individuals with these particular hearing devices may not be allowed into the MR environment because of the risk of damage to the components. The manufacturers of these devices should be contacted for current MRI labelling information.
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MRI and cochlear implant:
An MRI is a diagnostic tool to obtain images of organs and tissues using a very powerful magnetic field measured in tesla (T). MRIs can range in strength from 0.2T to 7.0T, with 1.5T being the most common. Cochlear implants are a proven medical option for infants as young as 12 months old with profound hearing loss in both ears, children aged two and older with severe-to-profound hearing loss, and adults with moderate-to-profound hearing loss in both ears. They are electronic devices that bypass damaged hair cells in the inner ear, or cochlea, and stimulate the hearing nerve directly. Inside each cochlear implant is a magnet. Of radiology professionals surveyed, 97 percent do not recommend conducting MRI scans on patients with magnets in their bodies. Now we have a key safety feature to ensure MRI compatibility for its implants: a removable magnet. The removable magnet ensures customer safety and comfort if an MRI is needed and an alternative imaging option is not available. The magnet is easy to remove and replace with a minor procedure if needed.
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Hearing aid remote control devices and the pacemaker patient: Two studies of 2001:
Signals from cellular phones and electronic surveillance equipment have already been shown to interfere with pacemaker function in this way. Applying proper caution, some instructional booklets for hearing aid remote control devices (RCDs) have also included a warning that pacemaker patients should not operate an RCD very close to their pacemaker, such as in a breast pocket. Such warnings are only precautionary because the potential of RCDs to interfere with pacemaker function has never been demonstrated. On the contrary, there is a general presumption of safety regarding RCDs, which is based on their necessary conformance with standards applicable to all Class I medical devices. These studies found no instances of inappropriate pacing or of inhibition of pacing with any of the remote control devices that authors tested, even when the device was placed close to the pacemaker or the leads in a “worst case scenario.” However, use of the electromagnetic or FM RCD in close proximity to the pacemakers and their programmers did interfere with the telemetry between the pacer programmer and the pacemaker, and in some models even delayed programming or confirmation of programming of the pacemaker. Programming or confirmation, however, always took place as soon as the hearing aid remote was de-activated. When a rhythm stripper was used to record non-telemetered EGG activity from the anterior chest itself, significant distortion resulted in the ECG signal when the FM or the electromagnetic RCD was operated near the pacemaker. In general, the results of these studies do not indicate that use of remote control devices for programmable hearing aids poses any threat to the normal functioning of an implanted cardiac pacemaker. However, both studies show that there may be problems with evaluating or programming a pacemaker while a remote control device is being activated to adjust a hearing aid. Since this eventuality is a real one, information about this type of interference should be made available to both patient and physician to preclude confusion or possible erroneous suspicion of pacemaker malfunction during a routine pacemaker check-up.
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Electromagnetic interference produced by a hearing aid device on electrocardiogram recording: a 2008 study:
An 85-year-old male was implanted with a single-chamber permanent pacemaker because of atrial fibrillation with slow ventricular response. The patient had a chronic hearing impairment and decided to buy a hearing aid device. The MyLink device (MyLink, Phonak, Stafa, Switzerland) is a multifrequency FM transmitter/receiver (169.40-176.00 MHz and 214.00-220.00 MHz) with a neck-loop antenna that is designed to be used in combination with a second FM transmitter, which detects sound, produced by an audio source or person, and transmits this information to the MyLink wearer. These transmissions are subsequently converted by the MyLink and sent to the patient’s existing hearing aids wirelessly. Given the proximity of the receiver to the left-sided pacemaker pocket, a concern about possible interaction was brought to our attention. Normal functioning of the pacemaker was observed during the test. However, potent electromagnetic interference on electrocardiogram (ECG) recording was induced when the MyLink loop antenna was placed on top or near the ECG electrodes.
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Caution must be taken with active implants (pacemaker or implantable defibrillator):
If your hearing aid has a wireless transmission, keep the hearing aid at least 15 cm away from the implant, e.g. do not carry it in a breast pocket. Your Autophone magnet or MultiTool (which has a built-in magnet) should be kept more than 30 cm away from the implant, e.g. do not carry it in a breast pocket. In general, please follow the guidelines recommended by the manufacturers of implantable defibrillators and pacemakers on use with mobile phones.
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Hearing aids may fail if radio frequencies are sold:
A government auction of radio frequencies could render thousands of hearing aids and implants useless, a charity has claimed. The National Deaf Children’s Society (NDCS) said the auction to mobile phone companies could leave an inadequate protection zone between the frequency range used by technology such as hearing aids, cochlear implants and radio aid and the band up for offer. Many hearing devices operate within the 2.40 to 2.485 GHz frequency range. Ofcom is the communications regulator in the UK. Ofcom is proposing to auction the 2.35 to 2.39 GHz frequencies, leaving a 10 MHz protection zone between the two bands. The NDCS said this “might not be enough” to prevent interference from mobile telephone networks using 4G, and warned that “at worst” the use of these frequencies could cause equipment to malfunction or fail altogether. During the small scale test, one hearing aid lost a programme, two digital streamers stopped working completely and several radio aids experienced a 33% reduction in range. An Ofcom spokesman said: “We take the needs of people with hearing impairments, both children and adults, extremely seriously. We have carried out careful tests of listening devices and sought evidence from across the deaf community to help ensure these devices won’t be affected by future mobile signals.” While these airwaves are already used in other countries, with no reported interference to any listening devices, Ofcom have asked manufacturers to carry out further tests at their specialist facility to ensure their devices work as they should.
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Disadvantages of Hearing Aids:
Of course most people would find fewer disadvantages to wearing hearing aids, as there really aren’t that many, but of the potential shortcomings that do exist, the following are the most notable:
1. High Price
Yes, it is true that hearing aids can be costly, with a top-of-the-line brand new model costing about $2,000 per pair. However, some would argue that a couple thousand is a nominal price to pay when you consider how much you can improve your quality of life by having your hearing restored to comfortable levels.
2. Potential Discomfort
If you choose the wrong configuration type or style, or the custom mould is not fitted properly, you could encounter some discomfort. However, this is usually an easy fix as a simple visit to your audiologist will get you on track with a more suitable model. Then there is also the potential for social discomfort when wearing the hearing aids in public, particularly if you’re conscientious about letting other people know that you’re wearing them.
3. Maintenance Issues
Finally, keep in mind that you may have to perform maintenance on your hearing aids from time to time. This may include removing any built up ear wax from the casing. Fortunately, most hearing aids come with a cleaning kit and instructions on how to maintain the device.
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Hearing Aid: Frequently Asked Questions (FAQ):
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1. Which hearing aid will work best for me?
The hearing aid that will work best for you depends on the kind and severity of your hearing loss. If you have a hearing loss in both of your ears, two hearing aids are generally recommended because two aids provide a more natural signal to the brain. Hearing in both ears also will help you understand speech and locate where the sound is coming from. You and your audiologist should select a hearing aid that best suits your needs and lifestyle. Price is also a key consideration because hearing aids range from hundreds to several thousand dollars. Similar to other equipment purchases, style and features affect cost. However, don’t use price alone to determine the best hearing aid for you. Just because one hearing aid is more expensive than another does not necessarily mean that it will better suit your needs. A hearing aid will not restore your normal hearing. With practice, however, a hearing aid will increase your awareness of sounds and their sources. You will want to wear your hearing aid regularly, so select one that is convenient and easy for you to use. Other features to consider include parts or services covered by the warranty, estimated schedule and costs for maintenance and repair, options and upgrade opportunities, and the hearing aid company’s reputation for quality and customer service.
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2. Is it okay for me to sleep in my hearing aids?
When going to bed for the night, you should remove your hearing aids and open the battery door to help conserve battery life and allow air to enter in hearing aid to prevent moisture build-up. There are exceptions. When I was working in Saudi Arabia as a doctor with bilateral hearing loss due to otosclerosis, I used to wear hearing aid in one ear and sleep on side with ear having hearing aid on the top. I used to get night calls for emergency and this method helped me attend night calls.
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3. Can I wear my hearing aids when I take a shower, bath, or when I swim?
Even with the water resistance capabilities of modern hearing aids, I recommend you remove your hearing aids prior to any aquatic activity.
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4. Will wearing my BTE or RITE (RIC) hearing aid interfere with my glasses?
No, it should not. Many people wear both hearing aids and glasses. First, you need to put your glasses on and then the hearing aid, you can use a mirror to adjust them if necessary. Make sure that when you remove your glasses, you use both hands, one on each bow by your temple, and pull them straight forward. Avoid pulling your glasses roughly off to one side – this may cause the hearing aid on the opposite side to become dislodged.
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5. How often should I have my hearing evaluated?
Hearing evaluations are recommended annually just like eye exams. Hearing evaluations are especially recommended if there is a family history of hearing loss, history of noise exposure or if you are noticing any changes in your hearing. A baseline hearing evaluation is recommended at any age.
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6. Why do so many people have hearing aids that they complain about or do not use?
There can be a variety of reasons why hearing aids are not effective or used. Sometimes the hearing aids are not appropriate for the individual’s hearing needs. The style, circuitry, or options may not be the optimal choice for this person. The hearing aids may not be programmed correctly. Occasionally, the cosmetic appeal of the hearing aids takes precedence over its function of improving hearing. The expectations of the hearing aid wearer also need to be realistic. Hearing aids will not restore normal hearing, but they can greatly improve the ability to hear and communicate in a variety of situations. The choice of the best hearing aids depends on many factors and can often be confusing. Qualified audiologists are experts in choosing the most appropriate hearing assistance and providing support and counselling throughout the adjustment period.
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7. Is there a hearing aid that can eliminate background noise?
No hearing aid can completely eliminate background noise, but they can lessen the effects of non-speech noise.
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8. Will I hear normally as soon as I start using the hearing aid?
No, it will take some time. If you are sufficiently motivated you will achieve this faster. In the initial stages, the sound usually appears a little different on using the hearing aid. This happens because your brain has come to accept your impaired hearing as normal and anything else as abnormal. Moreover it becomes a little difficult for the brain to identify new amplified sounds through the hearing aid which you had not been hearing for some years. It is believed (but not fully proved) that the brain forgets how to process sounds that it had not heard for some time. So when the hearing aid re-introduces these sounds to the brain, the brain being unable to recognize it, perceives it as noise. In about 6 weeks’ time , the brain re-learns these sounds and can then interpret these long-forgotten sounds provided you give some effort in getting used to this new form of hearing. So the first few weeks are a little frustrating to the new hearing aid user. You must be able to bear with this. It can take several weeks to completely adjust to your new hearing aids. This adjustment period is essential to get the maximum benefit from your hearing aids, but remember that you’ll be enjoying more of the sounds you love very soon.
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9. Will my hearing worsen if I use the hearing aid?
No, not at all. If your hearing aid has been properly selected by a responsible and knowledgeable person, taking into account all details of your audiogram, there will be no harm whatsoever to your hearing.
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10. Will using the hearing aid stop any further deterioration of my hearing?
No, if you are having a progressive deafness, the hearing aid cannot stop or check the deterioration of your hearing. The hearing aid is just an amplifier and it can never alter or influence the disease process. The disease usually follows its own course and cannot be either stopped or increased by the hearing aid. If due to the progress of disease, the hearing deteriorates, the amplification parameters of the hearing aid can be adjusted (at least partially) to suit your requirements of increased amplification. This facility is better with programmable hearing aids.
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11. Will I become dependent on the hearing aid if I use one and not be able to hear at all without the aid later on?
The hearing aid will definitely improve your hearing and it is desirable that you use the hearing aid always. However when you want to hear without the hearing aid, your hearing will be exactly as before; using the hearing aid will not worsen your natural hearing at all.
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12. Will a costlier hearing aid give me better hearing?
Not always. You will sometimes find that your are doing quite well even with comparatively cheap hearing aids. However the digital hearing aids are expected to give you clearer sound. The benefit you derive from the hearing aid depends primarily on the how perfectly the selection and programming of the hearing aid has been done, not on the cost only. Even if you buy the very costly multichannel digital hearing aids, your hearing will not be satisfactory if the hearing aid has not been programmed properly. The insight, dedication and experience of the person dispensing the aid matters a lot. Do not go by cost alone and do not have any misconceptions that a costlier hearing aid will suit you better.
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13. Will my giddiness (vertigo) be corrected if I use a hearing aid?
No, the hearing aid has nothing to do with your balance system.
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14. Is it better to use a digital hearing aid?
Yes, the digital hearing aids offer a lot of advantages which are already discussed in this article. The digital aids are smaller in size and a lot of electronic jugglery can be packed in a much smaller space. Hence even in very small CICs and BTEs a lot of special features and higher amplification can be obtained in hearing aids using digital technology. Even if the hearing profile changes drastically later on, there is much more scope of adjusting the hearing aid according to the changed hearing loss. Understanding of speech is much better with digital aids as many of the digital aids contain separate speech processors for different frequency bands by virtue of which the faint consonant sounds (which provide the intelligibility of speech) can be enhanced over the loud vowels. Feedback in hearing aid is annoying whistling sound that can be selectively filtered off in digital aids. Feedback manager is a special feature in most digital hearing aids. Most of the digital hearing aids can sense the environmental (i.e. the ambient) noise and automatically adjust the volume so that you do not have to fiddle with the volume control every now and then. Some of these aids have special features like selective programmes for different hearing situations like hearing a concert, hearing in traffic, and hearing in closed spaces etc.
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15. What are the common problems one encounters while using the hearing aid?
The common problems are: – (a) It may appear to you that your ear is blocked and you are hearing inside a barrel, (b) sudden loud sounds may be very disturbing and annoying in the initial stages (c) the background noise in the room i.e. the ambient room noise may appear disturbing and (d) the speech sounds especially the vowel sounds may appear loud in contrast to the faint consonant sounds (e) your own voice may appear a little different. Most of these problems can (at least partially) be corrected by your dispenser by making a vent in the ear mould, re-programming the hearing and other methods but to get the best out of your hearing aid and to override these teething troubles, you must also be sufficiently motivated and try to adapt to this new form of hearing. Moreover, with time as you get acclimatised to the hearing aid, these minor problems disappear.
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16. Does the brand of hearing aid make a difference?
The brand of hearing aid is less important than processing features, and most importantly, working with a qualified professional who can guide you in selecting the appropriate device and them programming it optimally for your hearing abilities and challenges. There are hundreds of hearing aid companies and many have similar capabilities, but selecting appropriate features and then utilizing them appropriately will ultimately impact outcomes more than the manufacturer.
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17. What should I do with my old hearing aids after I purchase new ones?
Some people like to keep their old hearing aids as backups. Others often look to trade them in for upgraded technology, and some hearing aid providers do accept and offer trade ins. Personally, I like to encourage people to donate them. Any make and model can be donated. The donated hearing aids are repaired, reconditioned and then used to help give the gift of hearing to someone in need.
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Common Misconceptions about the Hearing aids:
A misconception is a view or opinion that is incorrect because it is based on faulty thinking or facts that are incorrect. A hearing loss can be an invisible disability which only adds to the confusion. The problem with misconceptions is that they usually only further the frustration level of both the hearing impaired individual and others around them.
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Myth: Hearing aids function much the same as eyeglasses.
Fact: This is a misconception. Most people who wear glasses get close to 20/20 vision when they wear them. Hearing aids do not restore hearing in the same way. They amplify unwanted environmental sounds as well as those the person wants to hear.
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Myth: When someone loses hearing, he or she automatically becomes a good lip (speech) reader.
Fact: The fact is that people vary in their ability to speech-read. Most people need formal instruction through speech-reading classes. Also, speech-reading is useless when one cannot clearly see the speaker’s face. A really good speech reader can usually get only about 40 percent of what is being said. Like hearing aids, speech reading skills are helpful, but are not a final solution
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Myth: Sign Language is for everyone with hearing loss.
Fact: All too often sign language is recommended for people who are hard of hearing or an interpreter is brought in to sign for them. The majority of people who have hearing loss do not use sign language and are not interested in learning it. It requires time and effort to learn sign language and, for most people who are hard of hearing, their family members, co-workers, and friends do not know or use sign language, so it would not be helpful when communicating with them. The first choice for most people who have hearing loss should always be to do what is necessary to capitalize on their residual hearing through amplification systems and effective communication behavior.
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Myth: Increasing the volume of your voice will help the hearing impaired individual to understand better.
Fact: Increasing the volume is only part of the solution; clarity is also important. And there is a point where increasing the volume begins to distort the quality of sound. To obtain sufficient clarity, people with residual hearing may require sound to be transmitted from a microphone directly to their ear via an assistive listening system. Sitting close to the speaker can assist the listener (it facilitates lip reading) but is not a substitute for an assistive listening system. Yelling and over-articulating does not help because these distort the natural rhythm of speech and make lip reading more difficult. A person who can hear normally cannot determine whether the sound is adequate for a person with hearing loss.
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Myth: If you only have hearing loss in one ear, you can still hear normally.
Fact: Normal hearing requires both ears. People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in hearing conversation on their impaired side, localizing sound and understanding speech in the presence of background noise. Since most types of types of hearing loss affect both ears, it’s possible that your perception of a “normal ear” really just means one ear is better than the other. When in fact you may an asymmetrical hearing loss meaning one ear hears better than the other but both are below normal.
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Myth: Your hearing loss cannot be helped.
Fact: In the past, many people with hearing loss in one ear, with a high frequency hearing loss, or with nerve damage have all been told they cannot be helped, often by their family practice physician. This might have been true many years ago, but with modern advances in technology, nearly 95% of people with a sensorineural hearing loss can be helped with hearing aids.
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Myth: It’s okay to wait to get hearing aids.
Fact: The longer you wait, the harder your hearing loss will be to treat. That’s because the part of your brain that processes sound isn’t being stimulated, and so the brain stops recognizing sound. Fortunately, our brains can “relearn” to hear, thanks to neuroplasticity. In other words, you have to teach your brain to hear again, by wearing the hearing aids regularly and the sooner the better.
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Myth: Hearing aids are only for people with severe hearing loss.
Fact: Reduced audibility, reduced dynamic range and increased listening fatigue affects individuals with all levels of sensorineural hearing losses, even those with mild levels of hearing loss. A consequence of mild hearing loss is reduced audibility resulting in reduced speech intelligibility in general, but especially in noise and over distance. I recommend digital hearing aid to people with mild to moderate hearing loss to improve their hearing in difficult hearing situations & challenging acoustic environments, and in professions where you cannot afford to miss a single word; and to prevent deterioration of central auditory processing.
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Myth: Hearing aids can’t help with tinnitus.
Fact: Hearing aid increase the information available to the brain by amplifying background sounds making the tinnitus seem less audible. Nowadays, some hearing aids come with a special tinnitus program that provides background noise or other features to help minimize the effects of tinnitus. By reducing the effect of the tinnitus while simultaneously increasing hearing, especially through digital streaming to both ears, this technology can make an enormous difference. Studies have shown robust evidence promoting hearing aid fitting as an effective treatment option of tinnitus control.
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Myth: Hearing loss affects only “old people” and is merely a sign of aging.
Fact: Actually the prevalence of hearing loss is the reverse of what most people think. The majority (65%) of people with hearing loss are younger than age 65. Hearing loss affects all age groups.
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Myth: If I had a hearing loss, my family doctor would have told me.
Fact: Not true! Only 13% of physicians routinely screen for hearing loss. Since most people with hearing impairments hear well in a quiet environment hear well in a quiet environment like a doctor’s office, it can be virtually impossible for your physician to recognize the extent of your problem. Without special training, and an understanding of the nature of hearing loss, it may be difficult for your doctor to even realize you have a hearing problem.
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Myth: Deaf people are not permitted to drive.
Fact: Deaf people may use special devices to alert them to sirens or other noises, or panoramic mirrors to enable improved visibility. Many countries allow deaf people to drive, although at least 26 countries do not allow deaf citizens to hold a driver’s license.
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Myth: A hearing aid will damage your hearing.
Fact: A properly fitted and maintained hearing aid will not damage your hearing.
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Research and technological innovation vis-à-vis hearing aids:
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Researchers are looking at ways to apply new signal processing strategies to the design of hearing aids. Signal processing is the method used to modify normal sound waves into amplified sound that is the best possible match to the remaining hearing for a hearing aid user. NIDCD-funded researchers also are studying how hearing aids can enhance speech signals to improve understanding. In addition, researchers are investigating the use of computer-aided technology to design and manufacture better hearing aids. Researchers also are seeking ways to improve sound transmission and to reduce noise interference, feedback, and the occlusion effect. Additional studies focus on the best ways to select and fit hearing aids in children and other groups whose hearing ability is hard to test.
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Novel algorithm by which sounds are sorted out to improve hearing aid:
Scientists at the Massachusetts Institute of Technology have been researching how the human ear distinguishes between sounds with subtle differences. Several years ago MIT researchers Dennis Freeman and Roozbeh Ghaffari identified that the tectorial membrane – a small string of gel material less than an inch long and thinner than a single strand of human hair – also plays a role in this process. They discovered that sound waves that move up and down travel along the basilar membrane while those that move side to side travel along the tectorial membrane. Together, the two membranes can work to activate enough hair cells so that individual sounds are detected, but not so many that sounds can’t be distinguished from each other. The tectorial membrane consists of three specialized proteins, making them the ideal targets of genetic studies of hearing. One of those proteins is called beta-tectorin (encoded by the TectB gene), which was the focus of Ghaffari, Aranyosi and Freeman’s recent Nature Communications paper. The researchers collaborated with biologist Guy Richardson of the University of Sussex and found that in mice with the TectB gene missing, sound waves did not travel as fast or as far along the tectorial membrane as waves in normal tectorial membranes. When the tectorial membrane is not functioning properly in these mice, sounds stimulate a smaller number of hair cells, making the ear less sensitive and overly selective. Hearing aids today are not able to focus on specific sounds but rather amplify all of the sounds input into them, both signal and noise. Most hearing aids consist of a microphone that receives sound waves from the environment, and a loudspeaker that amplifies them and sends them into the middle and inner ear. Over the decades, refinements have been made to the basic design, but no one has been able to overcome a fundamental problem: Instead of selectively amplifying one person’s voice, all sounds are amplified, including background noise. Freeman believes that by incorporating the interactions between the tectorial membrane and basilar membrane traveling waves, this new model could improve our understanding of hearing mechanisms and lead to hearing aids with enhanced signal processing. Such a device could help tune in to a specific range of frequencies, for example, those of the person’s voice that you want to listen to. Only those sounds would be amplified. Researchers are really trying to figure out the algorithm by which sounds are sorted, because if they could figure that out, they could put it into a machine. Researchers hope that further study of this mechanism may lead to new hearing aids and other assistive devices that are much more effective than the models currently on the market.
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Oticon’s new Hearing Aid with better speech understanding and internet connectivity:
Developed by manufacturer Oticon, OPN™ is a world-first, linking the hearing aid, via an app, to the user’s emails, social media, doorbell, home alarm system, baby monitor and other devices. The technology can considerably improve quality of life for the user, and is regarded as the closest sound to natural hearing. Powered by the Velox™ platform, the newest BrainHearing™ solution from Oticon employs an “open sound” approach to manage multiple speech and noise sources, even in complex listening situations. The company says the new OpenSound Navigator™ scans the environment 100 times per second to analyze and balance every sound individually. With this open sound experience, Oticon reports that it makes traditional directionality, designed to focus on the main sound in front and suppress background sounds, a thing of the past. Users can now focus on a conversation while staying attentive to people and things around them, and switch focus quickly and easily. Oticon Opn is the first hearing aid proven to make it easier on the brain. Testing also shows that Opn increases speech understanding, the parameter most important to users, by 30% over other Oticon hearing solutions. Designed specifically for hearing aids, Oticon reports that the Velox platform is a powerhouse of ground breaking features. The tiny chip is said to have the speed needed to manage multiple sound sources, analyzing and processing sound data 50 times faster than before. A 64-band frequency resolution enables a more precise sound analysis and better sound quality to support the brain’s ability to make sense of sound. Opn offers TwinLink™ technology, two wireless communication systems in one hearing solution. Power-efficient near-field magnetic communication (NFMI) in one dedicated system is optimized for binaural ear-to-ear communication. Users enjoy high quality sound for better listening in all environments with very low power consumption. A second dedicated system uses 2.4GHz Bluetooth direct streaming for wireless streamer-free communication to smartphones and other devices. Developed specifically for hearing aids, this variant of Bluetooth uses significantly less battery power when streaming. The free, downloadable Oticon ON App allows users discreet control of their Opn hearing aids as well as other internet-connected solutions. Oticon Opn connects to the Internet via If This Then That (IFTTT.com), a web service that automates other web-based functions to make life easier. Users can connect to a wide range of IFTTT-enabled devices used in everyday life such as door bells, baby monitors, and thermostats. Opn provides users with a solution that will enable them to use their hearing aids with a growing number of IFTTT-compatible products and services as they become available. Opn makes it easier for people with hearing loss to communicate and stay socially active, with less listening effort and more ability to remember what is being said. And now, they can even connect their hearing aids to the internet. New Oticon Opn hearing solutions are available in the popular discreet miniRITE™.
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SoundSense hearing aid vibrates to warn hearing impaired users of loud sounds:
This concept combines microphone and separate motor that vibrates to notify users. A new prototype hearing aid has been developed that can vibrate to alert wearers of sounds above a certain level. Called SoundSense, the small microphone built into the hearing aid also has a separate motor which vibrates when noise exceeds normal levels, such as when a fire alarm sounds or police siren. Created by US firm Furenexo, the device could be priced at around $25 (around £20) and has been designed to help “build the confidence of individuals who cannot hear and empower them to venture out into unfamiliar environments”.
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New EarLens Laser-based Hearing Aid:
The US Food and Drug Administration (FDA) announced that it is allowing the marketing of a new hearing aid that uses a laser diode and direct vibration of the eardrum to amplify sound: the EarLens Contact Hearing Device (CHD), which is manufactured by EarLens Corporation of Menlo Park, Calif. The FDA reports that the combination of laser light pulses and a custom-fit device component that comes in direct contact with the eardrum is designed to use the patient’s own eardrum as a speaker and enables amplification over a wider range of frequencies for some hearing impaired persons. The EarLens CHD is indicated for use by adults with mild to severe sensorineural hearing impairment. The EarLens CHD consists of two parts: a tympanic membrane transducer (TMT), which is non-surgically placed deeply into the ear canal on the eardrum, and a behind-the-ear (BTE) audio processor that sits on the outer ear and is connected to an ear tip that is placed in the ear canal. External sound waves received by the BTE processor are converted to electronic signals, digitally processed, amplified and sent to the ear tip, which contains a laser diode. There, the electronic signals of amplified sound are converted to pulses of light. The laser light pulses then shines onto a photodetector in the TMT, which converts the light back into electronic signals, transmitting sound vibrations directly to the eardrum by direct contact. The EarLens CHD differs from traditional air conduction hearing aids in several ways. The TMT component is custom-molded to the patient’s eardrum and contains a driver mechanism that directly stimulates the eardrum, enabling efficient amplification of sound (functional gain). Clinical data supporting the safety and effectiveness of the EarLens CHD included several assessments over a 4-month period, such as residual hearing stability, improved word recognition, functional amplification gain, and the ability to hear sentences in background noise compared to listening without any amplification. Studies showed that after 30 days of device use, the 48 subjects experienced, on average, a 33% improvement in word recognition. Users also experienced a clinically significant functional gain of 30.5 dB on average in the high frequency range (2,000-10,000 Hz), with an average of 30-40 dB of functional gain noted at 6,000 Hz and above and a maximum of 68 dB at 9,000-10,000 Hz, which is not typically achieved with conventional air-conduction hearing aids. EarLens doesn’t fit cleanly into what most dispensing professionals consider a “hearing aid”; it does not amplify sound by air conduction, but instead mechanically stimulates the eardrum using light as the transmission medium. The device has the potential to substantially reduce or eliminate feedback (i.e., there is no traditional “sound loop” feedback mechanism as found in hearing aids), and as noted above, may also be able to provide a wide range of gain in addition to ultra-wide frequency range.
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The figure below shows comparison of normal, hearing aid and EarLens hearing:
EarLens is using 3D printing technology to improve design flexibility and support faster time-to-market.
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Solar Powered Hearing Aids:
A company called Solar Ear has developed the first hearing aid battery that can be recharged by light. It lasts for 2 to 3 years and works with about 80 per cent of hearing aids. The units are manufactured for countries in the developing world, and costs are supported by the World Health Organization.
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Insects are helping us develop the future of hearing aids:
Both mammals and insects have the equivalent problem when it comes to hearing: the conversion and amplification of sound waves into information the brain can use. What researchers are identifying is that the mechanism insects use to solve this problem is in many ways more proficient than our own. The organs of hearing in an insect are more compact and more sensitive to a greater range of frequencies, allowing the insect to detect sounds humans are unable to hear. Insects also can sense the directionality and distance of sound in ways more accurate than the human ear. Hearing aid design has historically been directed by the way humans hear, and hearing aids have tended to supply straightforward amplification of incoming sound and transmission to the middle ear. But researchers are now asking a different question. Finding inspiration from the natural world, they’re questioning how nature—and its hundreds of millions of years of evolution—has attempted to solve the problem of detecting and perceiving sound. By investigating the hearing mechanism of assorted insects, such as flies, grasshoppers, and butterflies, researchers can borrow the best from each to generate a brand new mechanism that can be utilized in the design of new and improved miniature microphones.
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The human ear is a miracle of mechanical evolution. It allows us to hear an astonishing range of sounds and to communicate and navigate in the world. It’s also easy to damage and difficult to repair. Hearing aids are still large, uncomfortable and as yet unable to deliver the rich and wonderful sounds we take for granted. Yet there may be a new way for us to replace damaged hearing from an unlikely source – the insect world. Crickets create sound by rubbing their wings together. The secret to their loud calls is that their wings are corrugated in specific patterns which makes them very stiff, which in turn makes them very loud when they are rubbed together. Using laser vibration systems and advanced computer modelling simulations (more often used to study aerodynamics), we can replicate this idea by tailoring the stiffness of a speaker surface. This creates a simple and efficient way to make tiny speakers very loud indeed. Insect inspiration doesn’t stop with small speakers, however. Hearing aids have traditionally been designed to operate in distinct stages. Sound signals are picked up by a microphone and then electrically amplified. Unwanted sounds are filtered out using digital processors and finally a speaker delivers high intensity sound into the ear canal. In each of these processes we may be able to learn from insects.
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Among the best studied insects in bio-acoustics is the locust, which has two large “tympanal” membranes used for hearing on either side of its chest. These membranes vibrate with sound and transfer the resulting signals to the nervous system, much a like a human eardrum. Recently researchers observed this membrane doing more than just vibrating up and down. Upon careful dissection, they found that it had a regular variation in thickness. While this may not sound particularly interesting at first, when they played sound to it they were amazed. It produced a tsunami-like vibration with the peak of the wave directly at the location of the nerve cells. In effect, this simple variation in thickness allowed for huge amplifications of the sound energy. The process of amplification in mammals is achieved with fragile middle ear bones, something locusts are achieving by simply varying the thickness of their ear drum. So we may be able to similarly design microphones with inbuilt passive amplification based on this idea. The process of filtering incoming sounds with a hearing aid requires quite sophisticated electronics, which directly impact the device’s size and battery life. Here again the locust may help. Along with amplifying the sound waves, the tympanal membranes also filter out a range of frequencies. Researchers recently found a South American species of katydid or bush cricket that may well perform the same task. The katydid has a tiny structure less than a millimetre in size in each of its forelegs that is capable of separating different frequencies into location specific vibrations, very similar in function to the human cochlea. If we could somehow encompass this mechanical frequency separation into the microphone itself, we may be able to harness its automatic filtering properties. Interestingly, some insects are even making us question what exactly a microphone can be. Mosquitoes and fruit flies, as examples, have tiny antennae on their heads which are microscopic in size yet are very sensitive to sound. While research into these features is tentative, it could direct us in unexplored directions of microphone design. A group of researchers have developed a microscopic microphone that mimics the hearing ability of an Ormia ochracea fly. It has an incredible ability to accurately locate sound, something that most insects antenna able to do whatsoever. The idea is not ready for market yet, but researchers say that this technology could prove useful in developing automatically-adaptive directional microphones in the next generation of hearing aids.
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Insect-inspired miniature directional microphones:
Researchers from University of Strathclyde in Glasgow, Scotland, and the MRC/CSO Institute for Hearing Research (IHR) at Glasgow Royal Infirmary, will be evaluating hearing aids furnished with a new kind of miniature microphone inspired by insects.
The hope is that the new hearing aids will achieve three things:
1. More energy-efficient microphones and electronics that will eventually result in smaller hearing aids, lower power usage, and extended battery life.
2. The capability to more precisely locate the source and distance of sound.
3. The ability to focus on specific sounds while wiping out background noise.
Researchers will also be experimenting with 3D printing techniques to improve the design and ergonomics of the new hearing aids.
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Biology, medicine and engineering have traditionally been quite separate disciplines. But by combining them, we can develop new engineering solutions based on discoveries that may have been made many years ago. So while bio-inspired hearing aids may not be about to arrive on the shelves, this innovative new field of study could find more and more ways to address the needs of people with hearing loss. And there’s plenty more inspiration that could come from our miniature mechanical specialists, the insects.
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New developments in digital technology of hearing aids:
Hearing aids have advanced significantly over the past decade, primarily due to the maturing of digital technology. The next decade should see an even greater number of innovations to hearing aid technology. Both incremental and radical innovations in digital hearing aids will be driven by research advances in the following fields: (1) wireless technology, (2) digital chip technology, (3) hearing science, and (4) cognitive science.
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Future Treatment Approaches for Hearing Loss:
In future hearing loss will become less defined by diagnostic measures, such as the audiogram, and more defined by the mechanism of the loss. Today, hearing aids are primarily fit to the audiogram of the hearing aid wearer, yet the nature of an individual’s hearing loss is more complex than that simple description. Pure-tone thresholds do not identify whether a sensorineural hearing loss is caused by damage to the outer hair cells, the inner hair cells or a mixture of both. A rule of thumb has typically been that hearing loss up to approximately 60 dB HL is from outer hair cell loss, and greater levels of loss are a result of additional damage to inner hair cells. In all likelihood, even losses below 60 dB HL contain a mixture of inner and outer hair cell damage. Additional mechanisms of hearing loss include changes to the endocochlear potential. Schmiedt et al have suggested that presbycusis might result from damage to the cochlear lateral wall, reducing the voltage within the cochlea and altering the function of the hair cells. In this case, the hair cells are not damaged, just altered in function, and amplification will not cause auditory nerves to respond at the same level as they would with a healthy cochlea or a cochlea suffering from damage to inner or outer hair cell loss. Clearly, in order to best treat the hearing loss of patients, the physiology of their hearing loss must be understood. To do so, additional diagnostic procedures are needed, from which the mechanism of hearing loss can be estimated. For example, the amount of compression at a specific frequency region can be estimated using a masked-threshold technique, which might provide information on the health of outer hair cells in that frequency region. Otoacoustic emissions (OAEs) have been demonstrated to be correlated with compression as well, where the growth of OAEs with increasing stimulus level matched the growth of loudness with stimulus level. Because the slope of the loudness growth function has been assumed to be related to the state of outer hair cell health, this measure of OAE response might also be useful in estimating the residual compression. Such information could be used to alter hearing aid signal processing or to design new algorithms based on a better understanding of the mechanism of someone’s hearing loss. Of course, this will work only for less severe losses where OAEs can be measured.
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Another improvement is that patients with the same diagnostic characteristics of hearing loss, and maybe even the same mechanism of loss, will no longer be treated as having the same needs. Although the general approach of the industry is to treat hearing aid wearers the same if they have identical loss, the reality is that they respond differently to the same treatment. This might be in part because they have different mechanisms of hearing loss, but could also be because they have other differences as well. These other differences between patients include dexterity, lifestyle, speech understanding ability, and cognitive ability. Each of these differences could result in one patient’s requiring different technology than another patient who has similar levels of hearing loss. These individual differences might require different treatments to hearing impairment. Different hearing aid technologies and feature settings could be applied as we better understand the individual differences of the patients better and what their corresponding needs are. For example, the finding that intelligence quotient test scores have been positively correlated with speech understanding’s benefit from fast-acting compression suggests that different compressor time constants might be prescribed for patients with different cognitive ability. The increased commonplace use of mobile and home computing will allow individual needs to be met with innovative therapies integrated with hearing aid solutions. Some patients will require more assistance in adapting to their hearing aids than others, and home-administered therapies such as Listening and Communication Enhancement (LACE) could become a common method to assist patients in optimizing their use of their hearing aid technology. LACE trains users to improve their hearing with their hearing aids and adapts itself to the performance of the user. If the patient improves quickly, then LACE adjusts its difficulty quickly; if the patient has more difficulty adapting to the hearing aid and has difficulty with the tasks in LACE, then the program adjusts its difficulty slowly. One can imagine that hearing aids will adapt over time as patients adapt to their new technology in the same way that LACE training adapts the difficulty of its tests to the subject’s performance. Combined with the intelligent algorithms in hearing aids discussed earlier, hearing aids become systems that are designed to refine their treatment to the individual needs of the user.
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My theory of sound and speech:
Sound is transmission of energy in air manifested as vibration of air molecules in a circular fashion which generate sound waves. Energy transmitted by sound is directly proportional to square of frequency (pitch) and square of amplitude (loudness/intensity) of wave, when all other factors are same as shown by me in the thought experiment below:
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Let us perform thought experiment:
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There are two sound waves, A with frequency 1 Hz and B with frequency 10,000 Hz, both having same amplitude 1 meter.
This figure shows how air molecules move in circular fashion to propagate sound wave. You can see that amplitude of sound wave is akin to radius (R) of a circle. Wave A has molecules moving 2 X Pi X R (circumference of a circle) meter in one second i.e. 2Pi meter in one second. Wave B has molecules moving 2Pi meter, 10,000 times in one second as it has frequency of 10,000 Hz. That amounts to 2Pi X 10,000 meter in one second. So velocity of wave B molecules is 10,000 times faster than wave A molecules. Since kinetic energy is proportional to square of velocity (1/2 mV2), energy carried by wave B is 10,000 X 10,000 = 100000000 times more than wave A. In other words, when all other factors are same, energy of sound wave is proportional to square of frequency.
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There are two sound waves, A with amplitude 1 meter and B with amplitude 10,000 meter, both having same frequency of one Hz. Wave A molecules move 2Pi meter in one second and wave B molecules move 2Pi X 10,000 meter in one second. So velocity of wave B molecules is 10,000 times faster than wave A molecules. Since kinetic energy is proportional to square of velocity, energy carried by wave B is 10,000 X 10,000 = 100000000 times more than wave A. In other words, when all other factors are same, energy of sound wave is proportional to square of amplitude.
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Summing frequency and amplitude of sound wave, energy carried by sound wave is proportional to square of frequency and square of amplitude when all other factors are same. Remember, square of a number is just multiplying it by itself. When two different sound waves are compared, the ratio of their energy is proportional to ratio of their frequencies squared multiplied by ratio of their amplitudes squared as seen in the figure below.
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This is a thought experiment. In reality, for typical sound waves, the maximum displacement of the molecules in the air is only a hundred or a thousand times larger than the molecules themselves — and we don’t have technologies for tracking individual molecules. For the sake of simplicity, change in potential energies of vibrating molecules is not discussed in thought experiment. Mechanical waves in a continuous media can be thought of as an infinite collection of infinitesimal coupled harmonic oscillators. On average, half the energy in a simple harmonic oscillator is kinetic and half is elastic (potential). The time-averaged total energy in then either twice the average kinetic energy or twice the average potential energy.
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Since frequency remains same while transmission, energy consumed by frictional resistance reduce amplitude as time progresses, so loudness of sound decreases as it moves away from sound source obeying inverse square law. High frequency sound may carry low energy if amplitude is low. Low frequency sound may carry high energy if amplitude is high. High frequency high amplitude sound always carry high energy. Low frequency low amplitude sound always carry low energy. How far you can hear and how clear you can hear depend not only on sound energy carried but also on absorption, reflection, diffraction and bending of sound waves by various objects in environment that are dependent on many factors including wavelength of sound waves. Low frequency waves (high wavelength waves) tend to pass through bigger object with lesser absorption or reflection. So in this kind of situation, even if the environment has many obstructing matter, low frequency can travel farther than high frequency although having lower energy than high frequency waves provided amplitude is same. So there is disproportionate degradation of high-frequency information as speech sound travels in environment full of various objects. Also, we have different hearing sensitivities to different frequencies. So besides strength of sound energy, all these other factors interplay to accomplish hearing in us. Speech is generation of sound waves by vocal cords of larynx using airflow from lungs, modified by vocal tract resonance. Our body energy is used to generate speech sound wave energy. Energy used to generate speech shows a flat response so that same energy is given to all frequencies. Therefore both high frequency consonants and low frequency vowels are given same energy. Therefore high frequency consonants are spoken softly and low frequency vowels are spoken loudly as both carry same energy as they leave our vocal tract. Remember, sound energy is directly proportional to square of frequency and square of amplitude. For the same energy, when frequency is high amplitude will be low, and when frequency is low amplitude will be high. That is why in normal human speech, high frequency consonant sounds are pronounced about 30dB softer (i.e., lower in intensity) than the low frequency vowel sounds. So in a normal speech of an individual, high frequency sounds are spoken softly (lower intensity/loudness) and low frequency sounds are spoken loudly (high intensity). So far so good!!! However in high frequency sensorineural hearing loss due to aging/noise, softly spoken high frequency consonant sounds like f, s and t are easily drowned out by louder, low pitched vowel sounds like a, o and u. The consonant sounds that give us the intelligibility of speech are mostly high frequency sounds (from 2000 to 8000Hz); so if you have selective high frequency hearing loss, you will only be able to hear the loud vowel sounds and miss the faint consonant sounds. This results in a person with high frequency hearing loss complaining that they can hear that others are talking, but not what they are saying. In other words, in high frequency sensorineural hearing loss, clarity of speech is lost. Additionally, they would have difficulty hearing the high-pitched voices of women and children. Additionally, the brain suppresses high frequency information in favour of low frequency information as the travelling wave on the basilar membrane passes through places of high frequency resonance area before it reaches low frequency resonance area. All these factors would make even mild high frequency hearing loss troublesome reducing intelligibility and clarity of speech. A person with a mild high frequency hearing loss has a significant problem in understanding speech as he misses the high frequency consonant sounds not only because he has a mild hearing loss in the high frequencies but also because the high frequency consonant sounds are spoken softly. Additionally there is disproportionate degradation of high-frequency consonants as speech sound travels in environment having many objects. Digital hearing aid which selectively increases gain of high frequency may help if only outer hair cells are damaged.
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Moral of the story:
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1. As far as hearing is concerned, sound is a wave of pressure fluctuation transmitted in air from sound source to ear. Air molecules do not travel with the sound wave but merely vibrate in a circular fashion. A higher wave frequency simply means that the air pressure fluctuation switches back and forth more quickly. The level of air pressure in each fluctuation, the wave’s amplitude, determines how loud the sound is. The effect of frictional resistance is to reduce the amplitude as time progresses, so loudness of sound decreases as it moves away from sound source. The speed of sound is approximately 343 m/s in air. Sound travels in solid bony ossicles of middle ear and liquid of cochlea in inner ear as vibration of molecules albeit with faster speed. Cochlea converts these mechanical vibrations in to electrical impulses to be conveyed to brain.
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2. Human hearing extends in frequency (pitch) from 20 to 20,000 Hz, and in amplitude (intensity/loudness) from 0 dB to 130 dB or more. Human speech ranges from 300 to 5,000 Hz. Speech is produced by fundamental frequencies (vocal cord) plus odd harmonics resonance pattern (vocal tract) and, therefore, the ability to hear complex sounds rather than only pure tones is important for understanding speech.
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3. The smallest sound pressure level (SPL) at which sound can be perceived by humans is 20 micropascals. This gives the first point (zero decibel) of the audiogram sound intensity level. This is the faintest sound the human ear can detect and labelled as 0 dB. On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times louder is 10 dB. A sound 100 times louder than near total silence is 20 dB. A sound 1000 times louder than near total silence is 30 dB. Normal human conversation is at 60 dB and whisper is at 30 dB. On the decibel scale, the range of human hearing extends from 0 dB, which represents a level that is all but inaudible, to about 130 dB, the level at which sound becomes painful. Many experts agree that continual exposure to more than 85 decibels may cause noise induced hearing loss.
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4. The human ear is not equally sensitive across frequency range. Audible sensitivity is low at the extremes but becomes much more sensitive between 1000 Hz and 5000 Hz, where the threshold reaches as low as −9 dB SPL. Since ear is most sensitive to sounds between approximately 3000 and 4000 Hz the outer hair cells which respond to these frequencies are most at risk from damage due to prolonged intense stimulus, therefore prolonged exposure to loud sounds damages these hair cells and thus explains the hearing loss from noise which occurs first at 3000 to 4000 Hz.
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5. The ear operates as an energy detector that samples the amount of energy present within a certain time frame of sound reception. A certain amount of energy is needed within a time frame to reach the threshold. This can be done by using a higher intensity for less time or by using a lower intensity for more time. Sensitivity to sound improves as the signal duration increases up to about 200 to 300 ms, after that the threshold remains constant.
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6. The outer and middle ears amplify sound on its passage from the exterior to the inner ear by about 30 dB.
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7. Sound localization depends on the recognition of minute differences in the intensity, phase and time of arrival of the sound at the two ears. High frequency hearing is more necessary than low frequency hearing for sound localisation and this explains why sound localization becomes difficult with a high frequency hearing loss.
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8. Outer hair cells act like a biological amplifier/attenuator, boosting soft sounds and dampening loud sounds. Inner hair cells transfer sound information to the auditory nerve. If the outer hair cells are damaged they no longer contract in response to slight sounds and the inner hair cells are not stimulated. This produces a hearing loss for low intensity sound. If the sound is more intense, the inner hair cells are stimulated directly and they respond normally so that the ability to hear louder sounds remain unimpaired. This is a common phenomenon known as loudness recruitment. Conductive hearing loss does not exhibit loudness recruitment. The inner hair cells are much “tougher” than outer hair cells and much less likely to be damaged by ageing, noise or most ototoxic drugs; so ageing, noise and ototoxic drugs usually only produce hearing loss but not deafness. Hearing aids are most effective at compensating for reduced function of outer hair cells, which is the most common type of permanent hearing loss. If the function of inner hair cells is very poor then a cochlear implant may provide better hearing ability.
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9. A person who is not able to hear as well as someone with normal hearing, having hearing thresholds of 25 dB or more in one or both ears for audible frequencies is said to have hearing loss. Hearing loss is categorized by type (part of hearing mechanism), severity (degree of loss), and configuration (frequency affected). Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral); it can be temporary or permanent; and it can be sudden onset or insidious. Unilateral hearing loss is equal to bilateral mild hearing loss. The least audiologic assessment for hearing loss should include the measurement of pure tone air-conduction & bone-conduction thresholds, and speech reception threshold.
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10. Globally hearing loss affects about 10% of the population to some degree. It is estimated that half of cases of hearing loss are preventable. Over 5% of the world’s population i.e. 360 million people has disabling hearing loss of sufficient magnitude to require a hearing aid. Disabling hearing loss refers to hearing loss greater than 35 decibels (dB) in the better hearing ear. The most common causes of hearing loss are age and overexposure to loud noise. Presbycusis or age-related hearing loss affect one out of three persons by age 65, and one out of two by age 75.
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11. About half of all hearing loss cases can be attributed to auditory damage caused by exposure to intense noise. Some 1.1 billion teenagers and young adults are at risk of hearing loss due to the unsafe use of personal audio devices including smartphones, and exposure to damaging levels of sound at noisy entertainment venues such as nightclubs, bars and sporting events.
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12. Hearing is critical for the development of speech, language, communication skills, and learning in children; therefore the earlier the hearing loss is identified and intervention begun, the better it is for speech and language development. Since hearing loss in infants is silent and hidden, great emphasis is placed on the importance of early detection, reliable diagnosis, and timely intervention.
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13. Hearing loss isn’t just an ear issue; it’s a quality of life and health issue. Hearing loss has been shown to have a negative effect on nearly every dimension of the human experience including: physical health, emotional and mental health, perceptions of mental acuity, social skills, family relationships, and self-esteem, not to mention work and school performance. A decrease in hearing sensitivity is associated with diminished cognitive function, shorter life span, unemployment, poorer mental health, and social withdrawal and isolation. People with hearing loss in the workforce could be losing more than $100 billion a year in income. This reduction in earnings not only damages the quality of life of the person with hearing loss, but it also has a detrimental impact on society as a whole due to reduced productivity and losses in tax revenues.
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14. Hearing aid is an electronic device usually worn in or behind the ear of a hearing-impaired person to amplifying sound to help hear better. By making sound louder and more energetic, it can increase transmission of sound in conductive hearing loss or stimulate the remaining hair cells within the inner ear in sensorineural hearing loss. Hearing aid basically corrects only the deficiency of auditory sensitivity (hearing acuity), not the other hearing faculties. Hearing aid will neither restore normal hearing nor eliminate background noise nor improve speech discrimination. Hearing aid amplifies just the speech frequencies i.e. from about 300 to 5000Hz whereas the normal human ear can hear sounds from 20 to 20,000 Hz. Hearing aids will help you hear better but not perfectly. Any individual who has a hearing loss that cannot be helped by medical or surgical means is a candidate of hearing aid.
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15. Hearing aids are divided into three groups, distinguished by the principle of how sound is transmitted to the cochlea or auditory nerve. The largest group is that consisting of air conduction hearing aids (conventional hearing aid); the other types being bone conduction hearing aids (bone anchored hearing aid BAHA, middle ear implant MEI) and nerve conduction hearing aid (cochlear implant). Hearing aids also differ based on whether they are digital or analog, whether they are worn primarily behind the ear (BTE) or inside it (ITE), whether they are removable or implantable and whether they are open fit or closed fit. Open fitting means low frequency sound can pass freely in and out of the ear canal when the hearing aid is worn. The more severe the hearing impairment, the larger the hearing aid required and closer the fitting becomes for auditory rehabilitation.
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16. Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. This process is called “fitting” and is performed by audiologists.
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17. More than 50% of people with hearing impairment are affected in both ears and must wear two hearing aids for better understanding of speech in noise, and better localization sound.
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18. Digital hearing aids aren’t superior to analog ones because they amplify sounds better—analog aids may in fact do that job just as well—but because they turn sounds into digital information that can be enhanced to make speech that’s easier to understand, music that’s more pleasant to listen to, and additionally reduce background noise and feedback sound. The microchip in the sophisticated digital hearing aid carries out thousands of calculations every second to sample (i.e. analyse ) incoming speech sounds as well as the ambient noise and then deliver the amplified sound to the user’s (i.e. patient’s) ear such that the user hears the desired sound (speech) most comfortably and clearly. The more sophisticated digital hearing aids are able to amplify the softest sounds of speech while at the same time subtracting out certain types of unwanted noises. Digital works better than analog hearing aid in all different types of hearing loss except for profoundly deaf individual with low speech discrimination scores where the sophisticated high-priced digital hearing aids may not be the correct choice as the patient will not be able to utilise the advantages of the digital hearing aids that they are paying for. A high powered (strong-class) conventional analog hearing aid will be adequate to provide the limited benefit from the hearing aid in such an individual.
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19. Hearing aids primarily improve how well people use their residual hearing in sensorineural hearing loss. Also the most important thing you can do to save your residual hearing is to wear your hearing aids.
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20. About 95 percent people with hearing loss can be treated with hearing aids and individuals who treat their hearing loss early have shown significant benefit. Hearing aids help process incoming sound making it easier for your brain to understand them. Other benefits of hearing aids include reduced mental fatigue, decreased feelings of social isolation and depression, improved ability to do several things at once, improved memory, attention and focus, as well as improved communication skills. Various trials showed that hearing aids use showed significant improvements in social and emotional function, communication function, and depression and quality of life.
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21. Infants as young as 4 weeks can be fit with hearing aids and hearing assistive technology systems. The behind-the-ear (BTE) hearing aid is the type of hearing aid most commonly recommended for infants and young children for a number of reasons.
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22. My theory of sound and speech:
Sound is transmission of energy in air manifested as vibration of air molecules in a circular fashion which generate sound waves. Energy transmitted by sound is directly proportional to square of frequency (pitch) and square of amplitude (loudness/intensity) of wave, when all other factors are same as proved by me in the thought experiment. Since frequency remains same while transmission, energy consumed by frictional resistance reduce amplitude as time progresses, so loudness of sound decreases as it moves away from sound source. High frequency sound may carry low energy if amplitude is low. Low frequency sound may carry high energy if amplitude is high. High frequency high amplitude sound always carry high energy. Low frequency low amplitude sound always carry low energy. How far you can hear and how clear you can hear depend not only on sound energy carried but also on absorption, reflection, diffraction and bending of sound waves by various objects in environment that are dependent on many factors including wavelength of sound waves. Low frequency waves (high wavelength waves) tend to pass through bigger object with lesser absorption or reflection. So in this kind of situation, even if the environment has many obstructing matter, low frequency can travel farther than high frequency although having lower energy than high frequency waves provided amplitude is same. So there is disproportionate degradation of high-frequency information as speech sound travels in environment. Also, we have different hearing sensitivities to different frequencies. So besides strength of sound energy, all these other factors interplay to accomplish hearing in us. Speech is generation of sound waves by vocal cords of larynx using airflow from lungs, modified by vocal tract resonance. Our body energy is used to generate speech sound wave energy. Energy used to generate speech shows a flat response so that same energy is given to all frequencies. Therefore both high frequency consonants and low frequency vowels are given same energy. Therefore high frequency consonants are spoken softly and low frequency vowels are spoken loudly as both carry same energy as they leave our vocal tract. Remember, sound energy is directly proportional to square of frequency and square of amplitude. For the same energy, when frequency is high amplitude will be low, and when frequency is low amplitude will be high. That is why in normal human speech, high frequency consonant sounds are pronounced about 30dB softer (i.e., lower in intensity) than the low frequency vowel sounds. So in a normal speech of an individual, high frequency sounds are spoken softly (lower intensity/loudness) and low frequency sounds are spoken loudly (high intensity). So far so good!!! However in high frequency sensorineural hearing loss due to aging/noise, softly spoken high frequency consonant sounds like f, s and t are easily drowned out by louder, low pitched vowel sounds like a, o and u. The consonant sounds that give us the intelligibility of speech are mostly high frequency sounds (from 2000 to 8000Hz); so if you have selective high frequency hearing loss, you will only be able to hear the loud vowel sounds and miss the faint consonant sounds. This results in a person with high frequency hearing loss complaining that they can hear that others are talking, but not what they are saying. In other words, in high frequency sensorineural hearing loss, clarity of speech is lost. Additionally, they would have difficulty hearing the high-pitched voices of women and children. Additionally, the brain suppresses high frequency information in favour of low frequency information as the travelling wave on the basilar membrane passes through places of high frequency resonance area before it reaches low frequency resonance area. All these factors would make even mild high frequency hearing loss troublesome reducing intelligibility and clarity of speech. A person with a mild high frequency hearing loss has a significant problem in understanding speech as he misses the high frequency consonant sounds not only because he has a mild hearing loss in the high frequencies but also because the high frequency consonant sounds are spoken softly. Additionally there is disproportionate degradation of high-frequency consonants as speech sound travels in environment. Digital hearing aid which selectively increases gain of high frequency may help if only outer hair cells are damaged.
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23. Since brain suppresses high frequency information in favour of low frequency information as the travelling wave on the basilar membrane passes through places of high frequency resonance area before it reaches low frequency resonance area, low frequency sounds for example traffic noise are very effective in masking high frequency sounds for example the fricatives of speech, making telephones near busy streets difficult to use in people with normal hearing. The background noise of low frequency would mask consonants of high frequency resulting in poor speech clarity in noisy environment in people with normal hearing. This effect is greatly exacerbated in people with mild high frequency hearing loss because as such there is mild hearing loss in the high frequencies plus high frequency consonant sounds are spoken softly. So speech hearing is greatly impaired in noisy environment among people with only mild high frequency loss. The mild terminology is misleading as important speech sounds become inaudible with a mild hearing loss. Although mild to moderate hearing loss limited to the higher frequencies only with normal hearing in the low and middle frequencies is usually passed off as near normal hearing by people, and clinicians often ask such patients to refrain from using hearing aids, I recommend digital hearing aid to such people to improve their hearing in difficult hearing situations & challenging acoustic environments, and in professions where you cannot afford to miss a single word; and to prevent deterioration of central auditory processing.
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24. Current annual production of hearing aids meets less than 10% of the global need.
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25. No matter how you look at it, hearing aids are expensive. Nearly half of adults who are 75 and older suffer hearing loss, yet a majority just can’t afford to do anything about it in the U.S. However in countries where hearing aids are provided to patients at low or no cost, hearing aid adoption rates show only slight improvement proving the point that cost is not the most important factor for use of hearing aid.
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26. On average, people wait 4.8 years between first noticing their hearing loss and finally taking action in developed nations.
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27. Statistics from developed nations show only one out of five individuals who could benefit from the use of hearing aids actually pursue treatment and even fewer take advantage of other forms of assistive listening devices. Factors suggested as reasons for lack of hearing aid use include cost, ignorance, low availability, perceived lack of benefit, denial of hearing loss and stigma associated with hearing loss & use of hearing aids. Individuals with hearing loss may also forego treatment simply because they don’t believe that their hearing loss is significantly impacting their lives. The single most important factor that prevents hearing impaired person to use hearing aid is noticeability of hearing aid amounting to public admission of disability and aging. Audiologists often tend to focus on audibility first and cosmetics second, but the hearing aid user might have it the other way around. The concern about appearance has to be taken seriously, since the hearing aids will be of no use, if the hearing-impaired person is so concerned about his or her appearance that they will not wear them.
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28. Non-adherence to use of hearing aids is high. Several authors have conservatively estimated that up to 30% of patients who receive hearing aids do not use their aids due to various reasons including unrealistic expectations of how they will work from the beginning. If you suffer hearing loss, the brand of hearing aid you select is far less important than the process of hearing restoration. The reason so many hearing aids end up in drawers is people don’t understand the adapting you need to do to get the most out of them. The brain has to adapt. Hearing rehabilitation is much more than getting fitted with the proper hearing aid. The one factor that always emerges from hearing rehabilitation studies is the time people spend practicing. Hearing aid will work only if you work for it. Also, those patients who were given appropriate support and service by a licensed hearing aid professional actually heard better!
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29. You can buy a hearing aid anywhere, but it will only be as good as the person fitting it. Hearing aid professionals make mistakes in fitting the hearing aids so that about two-thirds of the time, they end up with the wrong hearing aid settings. This is the most shocking statistics about hearing aid.
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30. Your hearing aids are of no value to anyone but you. For this reason and because they’re expensive to replace, it makes good sense to clean them daily, store them properly, and service them on a regular basis to reduce cost of repair and extend life of hearing aid. Remember heat, moisture, ear-wax, dirt and dust are enemies of hearing aid.
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31. It’s important to wait a full minute before you insert the battery and close the battery door after you’ve removed the tab. If you don’t wait, the battery may not absorb enough oxygen to properly power your hearing aids.
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32. One of the greatest complaints and source of embarrassment for hearing aid wearers is related to feedback. Acoustic feedback is the unpleasant and undesired squealing and screeching that occurs in a hearing aid and it is caused by the leakage of amplified output sound back to the microphone. Most common causes of acoustic feedback are very high gain, a vent with a large diameter, acoustic slit-leakage (loose fitting) and ear-wax. When your hearing aid professional adjusts the hearing aid for feedback, make sure that you still hear as well as before the adjustment because frequency response adjustments may solve your feedback, but at the cost of your hearing ability. Reducing the gain control setting to prevent acoustic feedback is not always satisfactory, since this also reduces audibility and thus defeats the intended use of the hearing aid.
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33. Hearing assistive technology systems (HATS) can be used with or without hearing aids or cochlear implants to make hearing easier—and thereby reduce stress and fatigue. Assistive Listening Devices (ALD) are electronic devices, other than hearing aids, that help you hear better in tough listening situations. The things that can interfere with listening are background noises, distance from sound source and reverberation or echo. People with hearing loss have more problems than people with normal hearing when trying to listen in these difficult situations. The best method to improve the signal-to-noise ratio is an FM system, which locates the microphone near the mouth of the desired talker. Listening to the FM signal is like listening to someone talking from only 3 or 6 inches away. FM listening systems are now emerging with wireless receivers integrated with the use of hearing aids. A separate wireless microphone can be given to a partner to wear in a restaurant, in the car, during leisure time, in the shopping mall, at lectures, or during religious services. The voice is transmitted wirelessly to the hearing aids eliminating the effects of distance and background noise. FM systems have shown to give the best speech understanding in noise of all available technologies. FM systems can also be hooked up to a TV or a stereo. Directional microphones have been found to be the second best method to improve the signal-to-noise ratio next to FM system. T-coils in hearing aids can be used with telephones, FM systems (with neck loops), and induction loop systems (also called “hearing loops”) that transmit sound to hearing aids from public address systems and TVs. The signal from T-coil is very clear and since the microphone is not being used, there is no feedback and no pickup of room noise.
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34. Compatibility of hearing aid means hearing aid can work together with other devices without problems or conflict, and in fact can act in concert with other devices. Connectivity of hearing aid refers to many different features: communication between hearing aids, communication between hearing aids and external audio sources (e.g. mobile phones, TVs, etc.), the ability to control aids remotely, and the ability for hearing care professionals to program hearing aids without wires. Although connectivity and compatibility are distinct features, they do overlap while discussing hearing aids.
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35. Wireless hearing aids benefits hearing aid user with better sound quality, improved localization, convenience and vastly increased connectivity.
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36. While buying a new digital hearing aid, make sure that it includes T-coil, Bluetooth and FM connectivity.
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37. Hearing impaired people wearing hearing aids can even hear better than normal people in certain settings. They are able to hear phone in both ears, listen to the television at settings too soft for even normal hearing individuals, hear someone speak softly at 30 feet away, and understand what someone is saying in a noisy restaurant while normal hearing individuals might be struggling.
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38. Hearing aid impersonation means electronic devices that mimic hearing aid. Personal sound amplification products (PSAPs) are hearing aid impersonation. About18 percent of PSAPs are used as a substitute for custom hearing aids simply because of cheap cost. The disadvantages of PSAPs are (1) Most PSAP’s will amplify all frequencies by the same amount while hearing aids amplify the frequency of sound based on a person’s hearing loss, (2) Hearing aids are programmed to limit the maximum level of sound while exposure to loud sounds can damage the ear in PSAP, (3) PSAP may cause delay in diagnosis of potentially treatable conditions and may damage your ears if not used properly.
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39. Smartphone app combines the components already present on your smartphone such as the microphone, the processor and the headset to emulate a hearing aid. It cannot be considered a substitution of digital hearing aid. But in a country like India where about 120 million people have hearing problems and less than 1 percent actually use any kind of hearing solution, such solution may help hearing impaired people.
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40. Bone anchored hearing aid (BAHA) has as an important part in hearing rehabilitation due to excellent sound quality and high output power. It is a solution for conductive and mixed hearing losses and single-sided deafness (SSD). An implantable hearing aid like BAHA is expected to have: (1) Better sound fidelity than a conventional air conduction hearing aid (2) No ear canal fitting device, free ear canal (3) No feedback (4) Invisibility.
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41. Cochlear implants (CIs) are indicated for bilateral or unilateral (some countries) very severe to profound sensorineural hearing loss. A cochlear implant bypasses the damaged cochlear hair cells by delivering electrical current directly to the auditory nerve while hearing aids deliver amplified sound to the damaged cochlea. The majority of deaf children who received cochlear implants before 18 months of age had language skills similar to their hearing peers. Younger age of implantation had a positive correlation to better spoken language skills.
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42. Although cochlear implant is better than hearing aid in many aspects for very severe to profound sensorineural hearing loss, the primary benefit of a hearing aid over a cochlear implant is in the area of low frequencies. Low frequencies are detected at the apex (inner most area) of the cochlea. Current cochlear implant technology limits the insertion depth of the electrode into the cochlea, limiting access to the lower frequencies below 250 Hz. Those who are able to use a hearing aid in one ear and an implant in the other are encouraged to do so for this reason.
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43. Medical professional having only high-frequency hearing loss may be able to use standard stethoscopes safely. I want to emphasize that hearing aids and acoustic stethoscope are incompatible; you cannot wear standard stethoscope over hearing aid. So remove hearing aid and then use standard acoustic stethoscope. If they have poor low-frequency hearing, they need an electronic stethoscope and unless hearing impairment is too great, they can simply take out hearing aids when they use electronic stethoscope or some people work with one in and one out. Remember, using a stethoscope in only one ear, sounds will only be half as loud. The amplification of average electronic stethoscope is up to 18 times greater than the best acoustic stethoscope and the ambient noise reduction technology cancels out an average of 75% of distracting room noise. On average electronic stethoscopes amplify between 15-50 dB gain depending upon the product. If you want to keep hearing aid in place and use electronic stethoscope, then you will have to use custom moulds, adapted eartips of stethoscopes, and open fitting to allow amplified low frequency heart and lung sound to reach eardrum as hearing aids don’t usually reproduce the low frequencies well. This is bypassing hearing aid. You may also use electronic stethoscope with headphones over open fitting as headphones have a better low frequency response than hearing aids. For medical professionals having very severe to profound low frequency hearing loss, connecting close-fit hearing aid to electronic stethoscope using T-coil, direct audio input, FM, Bluetooth or streamer may help although not optimally due to poor low-frequency response of hearing aids.
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44. Using headphones over a hearing aid is neither comfortable nor will give good sound quality. You will have to use hearing aid T-coil or Direct Audio Input to connect to headphones. A better option is to connect hearing aid via Bluetooth to other audio sources so that hearing aids can now become your headphones.
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45. The organs of hearing in an insect are more compact and more sensitive to a greater range of frequencies, allowing the insect to detect sounds humans are unable to hear. Insects can also sense the directionality and distance of sound in ways more accurate than the human ear. In hearing aids, sound signals are picked up by a microphone and then electrically amplified. Unwanted sounds are filtered out using digital processors and finally a speaker (receiver) delivers high intensity sound into the ear canal. In each of these processes we may be able to learn from insects. Biology, medicine and engineering have traditionally been quite separate disciplines. But by combining them, we can develop new hearing solutions inspired by insect hearing mechanisms.
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46. Future hearing aids will not be tailored according to audiogram report but according to physiology of hearing loss and considering dexterity, lifestyle, speech understanding ability, and cognitive ability of an individual. For example, different compressor time constants might be prescribed for patients with different IQ.
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Dr. Rajiv Desai. MD.
September 29, 2016
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Postscript:
When a person with hearing loss cannot hear properly and other people around him are unaware of his hearing loss, they assume that he thinks very high of himself and does not listen to what other say. Erroneously a person with hearing loss is labelled as arrogant. Hearing aid can bring humility in purported arrogant individual.
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