Hearing loss

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This article is about the deaf and hard of hearing medical condition. For other uses, see Deaf (disambiguation).
Hearing loss
Classification and external resources
International Symbol for Deafness.jpg
The international symbol of deafness or hard of hearing
ICD-10 H90H91
ICD-9 389
MedlinePlus 003044
eMedicine article/994159
MeSH D034381

Hearing loss, deafness, hard of hearing, anacusis, or hearing impairment (a term considered derogatory by many in the deaf community),[1] is a partial or total inability to hear.[2] In children it may affect the development of language and can cause work related difficulties for adults.[3]

It is caused by many factors, including: genetics, age, exposure to noise, illness, chemicals and physical trauma. Hearing testing may be used to determine the severity of the hearing loss. While the results are expressed in decibels, hearing loss is usually described as mild, mild-moderate, moderate, moderately severe, severe, or profound. Hearing loss is usually acquired by a person who at some point in life had no hearing impairment.

There are a number of measures that can prevent hearing loss and include avoidance of loud noise, chemical agents, and physical trauma. Testing for poor hearing is recommended for all newborns.[3] But, in some cases such as due to disease, illness, or genetics, it is impossible to reverse or prevent. Hearing aids are partially effective for many. Depending on the kind of hearing loss, hearing implants can be effective.[4]

Globally hearing loss affects about 10% of the population to some degree.[5] It caused moderate to severe disability in 124 million people as of 2004 (108 million of whom are in low and middle income countries).[6] Of these 65 million developed the condition during childhood.[7] It is one of the most common medical conditions presenting to physicians.[8] It is viewed by some in the deaf community as a condition, not an illness. Treatments such as cochlear implants have caused controversy in the deaf community.

Definition[edit]

Hearing loss exists when there is diminished sensitivity to the sounds normally heard.[7] The terms hearing impairment or hard of hearing are usually reserved for people who have relative insensitivity to sound in the speech frequencies. The severity of a hearing loss is categorized according to the increase in volume above the usual level necessary before the listener can detect it.

Deafness is defined as a degree of impairment such that a person is unable to understand speech even in the presence of amplification.[7] 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.

Speech perception[edit]

Another aspect of hearing involves the perceived clarity of a sound rather than its amplitude. In humans, that aspect is usually measured by tests of speech perception. These tests measure one's ability to understand speech, not to merely detect sound. There are very rare types of hearing impairments which affect speech understanding alone.[9]

Causes[edit]

The following are some of the major causes of hearing loss.

Age[edit]

There is a progressive loss of ability to hear high frequencies with increasing age known as presbycusis. For men, this can start as early as 25 and women at 30, but may even affect teenagers and children. Although genetically variable it is a normal concomitant of aging and is distinct from hearing losses caused by noise exposure, toxins or disease agents.[10]

Noise[edit]

Noise is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.[5]

Populations living near airports or freeways are exposed to levels of noise typically in the 65 to 75 dB(A) range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade hearing. The U.S. EPA and various states have set noise standards to protect people from these health risks. The EPA has identified the level of 70 dB(A) 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. (EPA, 1974).

Noise-induced hearing loss (NIHL) is typically centered at 3000, 4000, or 6000 Hz. As noise damage progresses, damage spreads to affect lower and higher frequencies. On an audiogram, the resulting configuration has a distinctive notch, sometimes referred to as 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.

Louder sounds cause damage in a shorter period of time. Estimation of a "safe" duration of exposure is possible using an exchange rate of 3 dB. As 3 dB represents a doubling of intensity of sound, duration of exposure must be cut in half to maintain the same energy dose. For example, the "safe" daily exposure amount at 85 dB A, known as an exposure action value, is 8 hours, while the "safe" exposure at 91 dB(A) is only 2 hours (National Institute for Occupational Safety and Health, 1998). Note that for some people, sound may be damaging at even lower levels than 85 dB A. Exposures to other ototoxins (such as pesticides, some medications including chemotherapy agents, solvents, etc.) can lead to greater susceptibility to noise damage, as well as causing their own damage. This is called a synergistic interaction.

Some American health and safety agencies (such as OSHA, the Occupational Safety and Health Administration, and MSHA, the Mine Safety and Health Administration), use an exchange rate of 5 dB.[11] While this exchange rate is simpler to use, it drastically underestimates the damage caused by very loud noise. For example, at 115 dB, a 3 dB exchange rate would limit exposure to about half a minute; the 5 dB exchange rate allows 15 minutes.

Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels include car stereos, children's toys, motor vehicles, crowds, lawn and maintenance equipment, power tools, gun use, musical instruments, and even hair dryers. Noise damage is cumulative; all sources of damage must be considered to assess risk. If one is exposed to loud sound (including music) at high levels or for extended durations (85 dB A or greater), then hearing impairment will occur. Sound levels increase with proximity; as the source is brought closer to the ear, the sound level increases.

In the USA, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure.[12]

Hearing loss has been described as primarily a condition of modern society.[13] In preindustrial times, humans had far less exposure to loud sounds and deafness appears to have been a rare condition.[14] This began to change with the event of machinery and electrical devices in the 18th-20th centuries. Studies have noted that baby boomers most often suffer hearing loss from recreational activities while their parents' generation were more affected by occupational (ie. workplace) noise. Military service in World War II, the Korean War, and the Vietnam War, has likely also caused hearing loss in large numbers of men from those generations, though proving hearing loss was a direct result of military service is problematic without entry and exit audiograms.[15]

Genetic[edit]

Hearing loss can be inherited. Around 75–80% of all cases are inherited by recessive genes, 20–25% are inherited by dominant genes, 1–2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance.[16]

When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Syndromic deafness occurs when there are other medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint.[16] Nonsyndromic deafness occurs when there are no other problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, which attributes to the vast majority of hereditary hearing loss.[16] Syndromic cases occur with diseases such as Usher syndrome, Stickler, Waardenburg syndrome, Alport's Syndrome, and Neurofibromatosis type 2. These are diseases that have deafness as one of the symptoms or a common feature associated with it. The genetics that correspond with these various diseases are very complicated and are difficult to explain scientifically because the cause is unknown. In nonsyndromic cases where deafness is the only ‘symptom’ seen in the individual it is easier to pinpoint the physical genes.

Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness.

  • The first gene mapped for non-syndromic deafness, DFNA1, involves a splice site mutation in the formin related homolog diaphanous 1 (DIAPH1). A single base change in a large Costa Rican family was identified as causative in a rare form of low frequency onset progressive hearing loss with autosomal dominant inheritance exhibiting variable age of onset and complete penetrance by age 30.[17]
  • The most common type of congenital hearing impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness.
  • The most common dominant syndromic forms of hearing impairment include Stickler syndrome and Waardenburg syndrome.
  • The most common recessive syndromic forms of hearing impairment are Pendred syndrome, Large vestibular aqueduct syndrome and Usher syndrome.
  • The congenital defect microtia can cause full or partial deafness depending upon the severity of the deformity and whether or not certain parts of the inner or middle ear are affected.
  • Mutations in PTPRQ Are a Cause of Autosomal-Recessive Nonsyndromic Hearing Impairment.[18]

Illness[edit]

  • Measles may cause auditory nerve damage
  • Meningitis may damage the auditory nerve or the cochlea
  • Autoimmune disease has only recently been recognized as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Wegener's granulomatosis is one of the autoimmune conditions that may precipitate hearing loss.
  • Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).
  • Presbycusis is a progressive hearing impairment accompanying age, typically affecting sensitivity to higher frequencies (above about 2 kHz).
  • Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing impairment and nasal infections that can spread to the middle ear.
  • People with HIV/AIDS frequently experience auditory system anomalies.
  • Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.
  • Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.
  • Premature birth causes sensorineural hearing loss approximately 5% of the time.
  • Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of infected children will eventually become deaf.
  • Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.
  • Medulloblastoma and other types of brain tumors can cause hearing loss, whether by the placement of the tumor around the Vestibulocochlear nerve, surgical resection, or platinum-based chemotherapy drugs such as cisplatin.
  • Superior canal dehiscence, a gap in the bone cover above the inner ear, can lead to low-frequency conductive hearing loss, autophony and vertigo

Neurological disorders[edit]

Neurological disorders such as multiple sclerosis and strokes can have an effect on hearing as well. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, a covering that protects the nerves. Once the myelin sheaths are destroyed they cannot be repaired. Without the myelin to protect the nerves, nerves become damaged, creating disorientation for the patient. This is a painful process and may end in the debilitation of the affected person until they are paralyzed and have one or more senses gone. One of those may be hearing. If the auditory nerve becomes damaged then the affected person will become completely deaf in one or both ears. There is no cure for MS.[19] Depending on what nerves are damaged from a stroke, one of the side effects can be deafness.[20] Charcot–Marie–Tooth disease variant 1E (CMT1E) is noted for demyelinating in addition to deafness.[21]

Medications[edit]

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamicin) and platinum based chemotherapeutics such as cisplatin.

Some medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics. The link between nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and hearing loss tends to be greater in women, especially those who take ibuprofen six or more times a week.[22] Others may cause permanent hearing loss.[23] On October 18, 2007, the U.S. Food and Drug Administration (FDA) announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors, which are used for erectile dysfunction.[24]

Chemicals[edit]

Main article: Ototoxicity

In addition to medications, hearing loss can also result from specific drugs; metals, such as lead; solvents, such as toluene (found in crude oil, gasoline[25] and automobile exhaust,[25] for example); and asphyxiants.[26] Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.[26]

Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system.[26] For some ototoxic chemical exposures, particularly styrene,[27] the risk of hearing loss can be higher than being exposed to noise alone. Controlling noise and using hearing protectors are insufficient for preventing hearing loss from these chemicals. However, taking antioxidants helps prevent ototoxic hearing loss, at least to a degree.[27] The following list provides an accurate catalogue of ototoxic chemicals:[26][27]

Physical trauma[edit]

There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.

People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent. I. King Jordan lost his hearing after suffering a skull fracture as a result of a motorcycle accident at age 21.[28]

Lesions to the auditory association cortex produced by physical trauma can result in deafness and other problems in auditory perception. The place where the lesion occurs on the auditory cortex plays an important role in what type of hearing deficit will occur in a person. A study conducted by Clarke et al. (2000) tested three subjects for the ability to identify a produced environmental sound, the source of the sound, and whether or not the source is moving. All three subjects had trauma to different parts of the auditory cortex, and each patient demonstrated a different set of auditory deficits, suggesting that different parts of the auditory cortex controlled different parts of the hearing process.[29] This means, lesion one part of auditory cortex and it could result in one or two deficits. It would take larger lesions at the right parts to produce deafness.

Neurobiological factors[edit]

From a neurobiological perspective, there are simply two reasons that could cause a person to be deaf: either there is something wrong with the mechanical portion of the process, meaning the ear, or there is something wrong with the neural portion of the process, meaning the brain.

The process of understanding how sound travels to the brain is imperative in understanding how and why these two reasons would cause a person to go deaf. The process is as follows: sound waves are transmitted to the outer ear, sound waves are conducted down to ear canal, bringing the sound waves to the eardrum where they vibrate, these vibrations are now passed through the 3 tiny ear bones in the middle, which cause the fluid to move in the inner ear, the fluid moves the hair cells, the movement of the hair cells cause the vibrations to be converted into nerve impulses, the nerve impulses are taken to the brain by the auditory nerve,[30] the auditory nerve takes the impulses to the medulla oblongata, the brainstem send the impulses to the midbrain, which finally goes to the auditory cortex of the temporal lobe to be interpreted as sound.[31]

This process is complex and involves several steps that depend on the previous step in order for the vibrations or nerve impulses to be passed on. This is why if anything goes wrong at either the mechanical or neural portion of the process, it could result in sound not being processed by the brain, hence, leading to deafness.

Diagnosis[edit]

a female medical professional is seated in front of a special sound-proof booth with a glass window, controlling diagnostic test equipment. Inside the booth a middle aged man can be seen wearing headphones and is looking straight ahead of himself, not at the audiologist, and appears to be concentrating on hearing something
An audiologist conducting an audiometric hearing test in a sound-proof testing booth

The severity of a hearing impairment is ranked according to the additional intensity above a nominal threshold that a sound must be before being detected by an individual; it is (measured in decibels of hearing loss, or dB HL). Hearing impairment may be ranked as mild, moderate, moderately severe, severe or profound as defined below:

  • Mild:
    • for adults: between 26 and 40 dB HL
    • for children: between 20 and 40 dB HL[7]
  • Moderate: between 41 and 54 dB HL[7]
  • Moderately severe: between 55 and 70 dB HL[7]
  • Severe: between 71 and 90 dB HL[7]
  • Profound: 91 dB HL or greater[7]
  • Totally Deaf: Have no hearing at all.

Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram.

For certain legal purposes such as insurance claims, hearing impairments are described in terms of percentages. Given that hearing impairments can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a recognized legal formula, it is possible to calculate a standardized "percentage of hearing loss" which is suitable for legal purposes only.

Another method for quantifying hearing impairments is a speech-in-noise test. As the name implies, a speech-in-noise test gives an indication of how well one can understand speech in a noisy environment. A person with a hearing loss will often be less able to understand speech, especially in noisy conditions. This is especially true for people who have a sensorineural loss – which is by far the most common type of hearing loss. As such, speech-in-noise tests can provide valuable information about a person's hearing ability, and can be used to detect the presence of a sensorineural hearing loss. A triple-digit speech-in-noise test was developed by RNID as part of an EU funded project Hearcom. The RNID version is available over the phone, on the web[32] and as an app on the iPhone.

Classification[edit]

Hearing impairments are categorized by their type, their severity, and the age of onset (before or after language is acquired). Furthermore, a hearing impairment may exist in only one ear (unilateral) or in both ears (bilateral). There are three main types of hearing impairments, conductive hearing impairment and sensorineural hearing impairment and a combination of the two called mixed hearing loss.[7]

Conductive hearing loss[edit]

A conductive hearing impairment is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The ear drum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the ear drum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.

Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons and disruption of the ossicular chain due to trauma, infection or anchylosis may also cause hearing loss.

Middle ear implants or bone conduction implants can help with this kind of hearing loss.[33]

Sensorineural hearing loss[edit]

A sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea, the nerve that transmits the impulses from the cochlea to the hearing centre in the brain or damage in the brain. The most common reason for sensorineural hearing impairment is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing. Cochlear implants can help with this kind of hearing loss.[4]

Mixed hearing loss[edit]

Mixed hearing loss is a combination of the two types discussed above. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. Surgery is often attempted but not always successful. On top of the conductive loss, a sensory component is often added. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone condition hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30–35 dB, an air conduction device could have problems overcoming this gap. A direct bone conduction aid like the Baha or the Ponto could, in this situation, be a good option. The active bone conduction hearing implant Bonebridge is also an option. This implant is invisible under the intact skin and therefore minimises the risk of skin irritations.[33]

Before language[edit]

Main article: Prelingual deafness

Prelingual deafness is hearing impairment that is sustained before the acquisition of language, which can occur due to a congenital condition or through hearing loss in early infancy. Prelingual deafness impairs an individual's ability to acquire a spoken language. Children born into signing families rarely have delays in language development, but most prelingual hearing impairment is acquired via either disease or trauma rather than genetically inherited, so families with deaf children nearly always lack previous experience with sign language. Cochlear implants allow prelingually deaf children to acquire an oral language with remarkable success if implantation is performed within the first 2–4 years.[34]

After language[edit]

Main article: Post-lingual deafness

Post-lingual deafness is hearing impairment that is sustained after the acquisition of language, which can occur due to disease, trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual and often detected by family and friends of affected individuals long before the patients themselves will acknowledge the disability.[citation needed] Common treatments include hearing aids, cochlear implants, middle ear implants, bone conduction implants, implants for electric-acoustic stimulation and learning lip reading. Post-lingual deafness is far more common than pre-lingual deafness. Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges, living with the adaptations that allow them to live independently.

Unilateral and bilateral[edit]

People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in:

  • hearing conversation on their impaired side
  • localizing sound
  • understanding speech in the presence of background noise.

In quiet conditions, speech discrimination is approximately the same for normal hearing and those with unilateral deafness; however, in noisy environments speech discrimination varies individually and ranges from mild to severe.

A similar effect can result from King-Kopetzky syndrome (also known as Auditory disability with normal hearing and obscure auditory dysfunction), which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests.

One reason for the hearing problems these patients often experience is due to the head shadow effect. Newborn children with no hearing on one side but one normal ear could still have problems.[35] Speech development could be delayed and difficulties to concentrate in school are common. More children with unilateral hearing loss have to repeat classes than their peers. Taking part in social activities could be a problem. Early aiding is therefore of utmost importance. Cochlear implants as well as bone conduction implants can help with single sided deafness.[36][37]

Screening[edit]

The United States Preventive Services Task Force recommends screening for all newborns.[3]

The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:[12]

There is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptoms.[38]

Prevention[edit]

It is estimated that half of cases of hearing loss are preventable.[7] A number of preventative strategies are effective including: immunization against rubella to reduce congenital infections, immunization against H. influenza and S. pneumoniae to reduce cases of otitis media, and avoiding or protecting against excessive noise exposure.[7] Education on the perils of hazardous noise exposure increases the use of hearing protectors.[39]

Management[edit]

There are a number of devices that can improve hearing in those who are hearing impaired or deaf or allow people with these conditions to manage better in their lives.

Hearing aids[edit]

Hearing aids are devices that work to improve the hearing and speech comprehension of those with hearing loss.[40] It works by magnifying the sound vibrations in the ear so that one can understand what is being said around them.[40] 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.[41]

Cochlear implants[edit]

Illustration of a cochlear implant

Cochlear implants improve outcomes in people with hearing loss in either one or both ears.[42] They work by artificial stimulation of the cochlear nerve by providing an electric impulse substitution for the firing of hair cells. They are expensive, and require programming along with extensive training for effectiveness.

Cochlear implant are at higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended.[43] People who have hearing impairments, especially those who develop a hearing problem in childhood or old age, may need support and technical adaptations as part of the rehabilitation process. Recent research shows variations in efficacy but some studies[44] show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech, particularly if supported by appropriate rehabilitation.

Assistive devices[edit]

Many hearing impaired individuals use assistive devices in their daily lives:

  • Individuals can communicate by telephone using telephone typewriters (TTY). Other common names are textphone, minicom and telecommunications device for the deaf (TDD). These devices look like typewriters or word processors and transmit typed text over regular telephone lines. This allows communication through visual messaging. TTYs can transmit messages to individuals who don’t have TTY by using the the National Relay service which is an operator that acts as a messenger to each caller.[45]
  • There are several new telecommunications relay service technologies including IP Relay and captioned telephone technologies. A deaf or hard of hearing person can communicate over the phone with a hearing person via a human translator. Wireless, Internet and mobile phone/SMS text messaging are beginning to take over the role of the TDD.
  • Real-time text technologies, involving streaming text that is continuously transmitted as it is typed or otherwise composed. This allows conversational use of text. Software programs are now available that automatically generate a closed-captioning of conversations. Examples include discussions in conference rooms, classroom lectures, and/or religious services. One such example of an available product is Auditory Sciences'Interact-AS product suite.[46]
  • Instant messaging software. In addition, AOL Instant Messenger provides a real-time text feature called Real-Time IM.[47][48]
  • Videophones and similar video technologies can be used for distance communication using sign language. Video conferencing technologies permit signed conversations as well as permitting a sign language–English interpreter to voice and sign conversations between a hearing impaired person and that person's hearing party, negating the use of a TTY device or computer keyboard.
  • Video relay service and video remote interpreting (VRI) services also use a third-party telecommunication service to allow a deaf or hard-of-hearing person to communicate quickly and conveniently with a hearing person, through a sign language interpreter.
  • Phone captioning is a service in which a hearing person's speech is captioned by a third party, enabling a hearing impaired person to conduct a conversation with a hearing person over the phone.[49]
  • For mobile phones, software apps are available to provide TDD/textphone functionality on some carriers/models to provide 2-way communications.
  • Hearing dogs are a specific type of assistance dog specifically selected and trained to assist the deaf and hearing impaired by alerting their handler to important sounds, such as doorbells, smoke alarms, ringing telephones, or alarm clocks.
  • Other assistive devices include those that use flashing lights to signal events such as a ringing telephone, a doorbell, or a fire alarm.
  • The advent of the Internet's World Wide Web and closed captioning has given the hearing impaired unprecedented access to information. Electronic mail and online chat have reduced the need for deaf and hard-of-hearing people to use a third-party Telecommunications Relay Service to communicate with the hearing and other hearing impaired people.
  • A person with hearing loss cannot always hear the phone or distinguish their own ringtone from another. A signalling transmitter can be attached to a phone that will cause a light or a vibration device to activate. Transmitters can also be used to activate visuals cues to represent fire alarms.[45]
  • Individuals with hearing loss require phones with amplifiers that have a higher power of amplification compared to a regular phone. The Hearing Aid Telephone Interconnect System is a hands free amplification which allows people amplify sound when using telephones, cell phones, computer and pay phones by the attachment of a portable unit.[45]

Wireless devices[edit]

A wireless device has two main components: a transmitter and a receiver. The transmitter broadcasts the captured sound, and the receiver detects the broadcast audio and enables the incoming audio stream to be connected to accommodations such as hearing aids or captioning systems.

Three types of wireless systems are commonly used: FM, audio induction loop, and InfraRed. Each system has advantages and benefits for particular uses. FM systems can be battery operated or plugged into an electrical outlet. FM system produce an analog audio signal, meaning they have extremely high fidelity. Many FM systems are very small in size, allowing them to be used in mobile situations. The audio induction loop permits the listener with hearing loss to be free of wearing a receiver provided that the listener has a hearing aid or cochlear implant processor with an accessory called a "telecoil". If the listener does not have a telecoil, then he or she must carry a receiver with an earpiece. As with FM systems, the infrared (IR) system also requires a receiver to be worn or carried by the listener. An advantage of IR wireless systems is that people in adjoining rooms cannot listen in on conversations, making it useful for situations where privacy and confidentiality are required. Another way to achieve confidentiality is to use a hardwired amplifier, which contains or is connected to a microphone and transmits no signal beyond the earpiece plugged directly it.

Classroom[edit]

For a classroom setting, children with hearing impairments often benefit from interventions. One simple example is providing favorable seating for the child. Having the student sit as close to the teacher as possible improves the student's ability to hear the teacher's voice and to more easily read the teacher's lips. When lecturing, teachers should try to look at the student as much as possible and limit unnecessary noise in the classroom. In particular, the teacher should avoid talking when their back is turned to the classroom, such as while writing on a whiteboard.

Some other approaches for classroom accommodations include pairing hearing impaired students with hearing students. This allows the hearing impaired student to ask the hearing student questions about concepts that they have not understood. The use of CART (Communication Access Real Time) systems, where an individual types a captioning of what the teacher is saying, is also beneficial.[50] The student views this captioning on their computer. Automated captioning systems are also becoming a popular option.[51] In an automated system software, instead of a person, is used to generate the captioning. Unlike CART systems, automated systems generally do not require an Internet connection and thus they can be used anywhere and anytime. Another advantage of automated systems over CART is that they are much lower in cost. However, automated systems are generally designed to only transcribe what the teacher is saying and to not transcribe what other students say. An automated system works best for situations where just the teacher is speaking, whereas a CART system will be preferred for situations where there is a lot of classroom discussion.

For those students who are completely deaf, one of the most common interventions is having the child communicate with others through an interpreter using sign language.[52]

Epidemiology[edit]

Disability-adjusted life year for hearing loss (adult onset) per 100,000 inhabitants in 2004.
  no data
  <250
  250–295
  295–340
  340–385
  385–430
  430–475
  475–520
  520–565
  565–610
  610–655
  655–700
  >700

Globally hearing loss affects about 10% of the population to some degree.[5] It caused moderate to severe disability in 124.2 million people as of 2004 (107.9 million of whom are in low and middle income countries).[6] Of these 65 million acquired the condition during childhood.[7] At birth ~3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems.[7]

Hearing loss increases with age. In those between 20 and 35 rates of hearing loss are 3% while in those 44 to 55 it is 11% and in those 65 to 85 it is 43%.[3]

History[edit]

Abbé Charles-Michel de l'Épée opened the first school for the deaf in Paris at the deaf school. The American Thomas Gallaudet witnessed a demonstration of deaf teaching skills from Épée's successor Abbé Sicard and two of the school's deaf faculty members, Laurent Clerc and Jean Massieu; accompanied by Clerc, he returned to the United States, where in 1817 they founded American School for the Deaf in Hartford, Connecticut. American Sign Language, or ASL, started to evolve from primarily LSF, and other outside influences.[53]

Society and culture[edit]

Main article: Deaf culture

Jack Gannon, a professor at Gallaudet University, said this about deaf culture. “Deaf culture is a set of learned behaviors and perceptions that shape the values and norms of deaf people based on their shared or common experiences.” Some doctors believe that being deaf makes a person more social. Dr. Bill Vicar, from ASL University, shared his experiences as a deaf person, "[deaf people] tend to congregate around the kitchen table rather than the living room sofa… our good-byes take nearly forever, and our hellos often consist of serious hugs. When two of us meet for the first time we tend to exchange detailed biographies."[54] Deaf culture is not about contemplating what deaf people cannot do and how to fix their problems, an approach known as the "pathological view of the deaf."[55] Instead deaf people celebrate what they can do. There is a strong sense of unity between deaf people as they share their experiences of suffering through a similar struggle. This celebration creates a unity between even deaf strangers. Dr. Bill Vicars expresses the power of this bond when stating, "if given the chance to become hearing most [deaf people] would choose to remain deaf."[56]

Views of treatments[edit]

There has been considerable controversy within the culturally deaf community over cochlear implants. For the most part, there is little objection to those who lost their hearing later in life, or culturally deaf adults choosing to be fitted with a cochlear implant.

Many in the deaf community strongly object to a deaf child being fitted with a cochlear implant (often on the advice of an audiologist); new parents may not have sufficient information on raising deaf children and placed in an oral-only program that emphasizes the ability to speak and listen over other forms of communication such as sign language or total communication. Other concerns include loss of deaf culture and limitations on hearing restoration.

Most parents and doctors tell children not to play sports or get involved in activities that can cause injuries to the head, for example soccer, hockey, or basketball. A child with a hearing loss may prefer to stay away from noisy places, such as rock concerts, football games, airports, etc., as this can cause noise overflow, a type of headache that occurs in many children and adults when they are near loud noises.

Sign language[edit]

Main article: Sign language

Sign languages convey meaning through manual communication and body language instead of acoustically conveyed sound patterns. This involves the simultaneous combination of hand shapes, orientation and movement of the hands, arms or body, and facial expressions to express a speaker's thoughts.

Government policies[edit]

Those who are hearing disabled do have access to a free and appropriate public education. If a child does qualify as being hearing impaired and receives an individualized education plan, the IEP team must consider, "the child's language and communication needs. The IEP must include opportunities for direct communication with peers and professionals. It must also include the student’s academic level, and finally must include the students full range of needs"[57] The government also distinguishes between deafness from hearing loss. The U.S. Department of Education states that deafness is hearing loss that is so severe that a person cannot process any type of oral information even if they have some sort of hearing-enhancing device. The U.S. Department of Education states that a hearing impairment is when a person's education is affected by how much that person is able to hear. This definition is not included under the term deafness. In order for a person to qualify for special services, they have to hear more than 20 decibels and their educational performance must be affected by their hearing loss. This is what the government has to say about governmental policies and individualized services.

Inclusion vs. pullout[edit]

Alexander Graham Bell with teachers and students of the Scott Circle School for deaf children, Washington, D.C., 1883

It is commonly misunderstood that least restrictive environment means mainstreaming or inclusion. Sometimes the resources available at the public schools do not match up to the resources at a residential school for the deaf. Many hearing parents choose to have their deaf child educated in the general education classroom as much as possible because they are told that mainstreaming is the least restrictive environment, which is not always the case. However, there are parents that live in Deaf communities who feel that the general education classroom is not the least restrictive environment for their child. These parents feel that placing their child in a residential school where all children are deaf may be more appropriate for their child because the staff tend to be more aware of the needs and struggles of deaf children. Another reason that these parents feel a residential school may be more appropriate is because in a general education classroom, the student will not be able to communicate with their classmates due to the language barrier.[citation needed]

In a residential school where all the children use the same language (whether it be a school using ASL, Total Communication or Oralism), students will be able to interact normally with other students, without having to worry about being criticized. An argument supporting inclusion, on the other hand, exposes the student to people who aren't just like them, preparing them for adult life. Through interacting, children with hearing disabilities can expose themselves to other cultures which in the future may be beneficial for them when it comes to finding jobs and living on their own in a society where their disability may put them in the minority. These are some reasons why a person may or may not want to put their child in an inclusion classroom.[57]

Myths[edit]

There are many myths regarding people with hearing losses including, but not limited to:

  1. Everyone who is deaf or hard of hearing uses sign language.
    • There are a variety of different sign systems used by deaf and hard of hearing individuals.[58]
    • Individuals who experience hearing loss later in life usually do not know sign language.[59]
    • People who are educated in the method of oralism or mainstream do not always know sign language.
  2. People who cannot hear are not allowed to drive.
    • Deaf people may use special devices to alert them to sirens or other noises, or panoramic mirrors to enable improved visibility.[60]
    • Many countries allow deaf people to drive, although at least 26 countries do not allow deaf citizens to hold a driver's license.[60]
  3. All forms of hearing loss can be solved by hearing aids or cochlear implants.
    • While many deaf and hard of hearing individuals do use hearing aids, others may not benefit from the use of a hearing aid.[58] One reason can be that they do not have any external ear canals in which to place the molds; another, that the hearing aids are not powerful enough.
    • For some deaf and hard of hearing individuals who experience distortion of incoming sounds, a cochlear implant may actually worsen the distortion.[58] A bone conduction hearing solution (BAHA) however, will never affect the hearing in a negative way, since it reroutes the sound through the skull.
  4. All deaf/hard of hearing people are experts in Deaf Culture.
    • Deaf people may have a variety of different beliefs, experiences, and methods of communication.[59]
    • This may be influenced by the age at which hearing was lost and the individual's personal background.[59]
  5. All deaf people want to be hearing.
    • While some individuals with hearing loss want to become hearing, this is not the case for everyone. Some take pride in their deafness or view themselves as a minority rather than a disability group.[61]
  6. People who can't hear can't use a phone.
    • Teletypewriters, Video phones and cell phone text messages are used by deaf people to communicate. A hearing person may use an ordinary telephone and a Telecommunications Relay Service to communicate with a deaf person.
    • Some people with moderate hearing loss may have enough hearing to use amplified telephones, even if they are culturally Deaf and depend primarily on sign language to communicate.
  7. Everyone who cannot hear can lip read.
    • Only about 30% of spoken English is visible on the lips.[58][59]
    • Lip reading requires not only good lighting, but also a good understanding of the oral language in question and may also depend on contextual knowledge about what is being said.[59]
  8. Most deaf people have deaf parents.
    • Less than 5% of deaf children in the United States have a deaf parent.[62]

Communication barriers[edit]

The most predominant forms of communication barriers originate from one's own personal self and they are directly the result of the hearing loss condition. These barriers are associated specifically with speech and language. In terms of speech, hearing loss has an effect on speech sound production, for example distortion caused by the omission of various letters from words. The pitch of their voice may sound too high or low and their volume may be louder or quieter than is intended. Resonance of voice is also affected, as it can be hypernasal or denasal. Prosody, which represents the patterns of stress and rhythm in the voice, will often become irregular. As a result of such changes to speech, the receiver during a conversation is likely to deem the communicator's speech unintelligible. The placement of improper stresses on syllables makes it more difficult for the receiver to clearly perceive and hear the intended words. Three major problems in terms of language are present for those with hearing loss. First, there are problems with language formation, where individuals may overuse nouns and verbs and they may improperly place words within a sentence. Second, the actual content of the language is troubling, for example the interpretation of synonyms and antonyms. This results in a limited vocabulary. The third major problem is associated with Pragmatics, which includes the inability of individuals to recognize that a message has been delivered to them, therefore resulting in inappropriate questions being asked. All of these speech and language barriers make it difficult for those with hearing loss to control their own speech and understand what others have to say, therefore making it quite hard to hold a conversation altogether.[63]

Communication with family[edit]

The communication limitations between people who are deaf and their hearing family members can often cause difficulties in family relationships, and affect the strength of relationships among individual family members. It was found that most people who are deaf have hearing parents, which means that the channel that the child and parents communicate through can be very different, often affecting their relationship in a negative way. If a parent communicates best verbally, and their child communicates best using sign language, this could result in ineffective communication between parents and children. Ineffective communication can potentially lead to fights caused by misunderstanding, less willingness to talk about life events and issues, and an overall weaker relationship. Even if individuals in the family made an effort to learn deaf communication techniques such as sign language, a deaf family member often will feel excluded from casual banter; such as the exchange of daily events and news at the dinner table. It is often difficult for people who are deaf to follow these conversations due to the fast paced and overlapping nature of these exchanges. This can cause a deaf individual to become frustrated and take part in less family conversations. This can potentially result in weaker relationships between the hearing individual and their immediate family members. This communication barrier can have a particularly negative effect on relationships with extended family members as well. Communication between a deaf individual and their extended family members can be very difficult due to the gap in verbal and non-verbal communication. This can cause the individuals to feel frustrated and unwilling to put effort into communicating effectively. The lack of effort put into communicating can result in anger, miscommunication, and unwillingness to build a strong relationship.[64]

Communication with peers and in the community[edit]

People who have hearing impairments can often experience many difficulties as a result of communication barriers among them and other hearing individuals in the community. Some major areas that can be impacted by this are involvement in extracurricular activities and social relationships. For young people, extracurricular activities are vehicles for physical, emotional, social, and intellectual development. However, it is often the case that communication barriers between people who are deaf and their hearing peers and coaches/club advisors limit them from getting involved. These communication barriers make it difficult for someone with a hearing impairment to understand directions, take advice, collaborate, and form bonding relationships with other team or club members. As a result, extracurricular activities such as sports teams, clubs, and volunteering are often not as enjoyable and beneficial for individuals who have hearing impairments, and they may engage in them less often. A lack of community involvement through extracurricular activities may also limit the individual’s social network. In general, it can be difficult for someone who is deaf to develop and maintain friendships with their hearing peers due to the communication gap that they experience. They can often miss the jokes, informal banter, and “messing around” that is associated with the formation of many friendships among young people. Conversations between people who are deaf and their hearing peers can often be limited and short due to their differences in communication methods and lack of knowledge on how to overcome these differences. Deaf individuals can often experience rejection by hearing peers who are not willing to make an effort to find their way around communication difficulties. Patience and motivation to overcome such communication barriers is required by both the hearing impaired and hearing individuals in order to establish and maintain good friendships.[64]

Many people tend to forget about the difficulties that deaf children encounter, as they view the deaf child differently from a deaf adult. Deaf children grow up being unable to fully communicate with their parents, siblings and other family members. Examples include being unable to tell their family what they have learned, what they did, asking for help, or even simply being unable to interact in daily conversation. Hearing impaired children have to learn sign language and to read lips at a young age, however they cannot communicate with others using it unless the others are educated in sign language as well. Children who are hearing impaired are faced with many complications while growing up, for example some children have to wear hearing aids and others require assistance from sign language (ASL) interpreters. The interpreters help them to communicate with other individuals until they develop the skills they need to efficiently communicate on their own. Although growing up for deaf children may entitle more difficulties than for other children, there are many support groups that allow deaf children to interact with other children. This is where they develop friendships. There are also classes for young children to learn sign language in an environment that has other children in their same situation and around their same age. These groups and classes can be very beneficial in providing the child with the proper knowledge and not to mention the societal interactions that they need in order to live a healthy, young, playful and carefree life that any child deserves.

Lee Meyerson, a Professor of Psychology at Arizona State University created three adjustment patterns that can help adults with hearing loss. The first one is to remain withdrawn into your own self. This provides a sense of safety and familiarity which can be a comforting way to lead your life. The second is to act “as if” one does not even have hearing loss. A positive attitude will help people to live a life with no barriers and thus, engage in optimal interaction. The final and third pattern is for the person to accept their hearing loss as a part of them without undervaluing oneself. This means understanding that one is forced to live life with this disability, however it is not the only thing that constitutes life’s meaning. Furthermore, many feel as if their inability to hear others during conversation is their fault. It's important that these individuals learn how to become more assertive individuals who do not lack fear when it comes to asking someone to repeat something or to speak a little louder. Although there is much fatigue and frustration that is produced from one’s inability to hear, it is important to learn from personal experiences in order to improve on one’s communication skills. In essence, these patterns will help adults with hearing loss deal with the communication barriers that are present.[41]

Communication in the workplace[edit]

In most instances, people who are deaf find themselves working with hearing colleagues, where they can often be cut off from the communication going on around them. Interpreters can be provided for meetings and workshops, however are seldom provided for everyday work interactions. Communication of important information needed for jobs typically comes in the form of written or verbal summaries, which do not convey subtle meanings such as tone of voice, side conversations during group discussions, and body language. This can result in confusion and misunderstanding for the worker who is deaf, therefore making it harder to do their job effectively. Additionally, deaf workers can be unintentionally left out of professional networks, informal gatherings, and casual conversations among their collogues. Information about informal rules and organizational culture in the workplace is often communicated though these types of interactions, which puts the worker who is deaf at a professional and personal disadvantage. This could sever their job performance due to lack of access to information and therefore, reduce their opportunity to form relationships with their co-workers. Additionally, these communication barriers can all affect a deaf person’s career development. Since being able to effectively communicate with one's co-workers and other people relevant to one's job is essential to managerial positions, people with hearing impairments can often be denied such opportunities.[64]

To avoid these situations in the workplace, individuals can take full-time or part-time sign language courses. In this way, they can become better able to communicate with the hearing impaired. Such courses teach the American Sign Language (ASL) language as most North Americans use this particular language to communicate. It is a visual language made up of specific gestures (signs), hand shapes, and facial expressions that contain their own unique grammatical rules and sentence structures [65] By completing sign language courses, it ensures that hearing impaired individuals feel a part of the workplace and have the ability to communicate with their co-workers and employer in the manner as other hearing employees do.

Communication in health care[edit]

Not only can communication barriers between deaf and hearing people affect family relationships, work, and school, but they can also have a very significant effect on a deaf individual’s health care. As a result of poor communication between the health care professional and the hearing impaired patient, many patients report that they are not properly informed about their disease and prognosis. [66] This lack of or poor communication could also lead to other issues such as misdiagnosis, poor assessments, mistreatment, and even possibly harm to patients. Poor communication in this setting is often the result of health care providers having the misconception that all people who are hearing impaired have the same type of hearing impairment, and require the same type of communication methods. In reality, there are many different types and range of hearing loss, and in order to communicate effectively a health care provider needs to understand that each individual with hearing loss has unique needs. This affects how individuals have been educated to communicate, as some communication methods work better depending on an individual’s severity of hearing loss. For example, assuming every hearing impaired patient knows American Sign Language would be incorrect because there are different types of sign language, each varying in signs and meanings. A patient could have been educated to use cued speech which is entirely different from ASL.[66] Therefore, in order to communicate effectively, a health care provider needs to understand that each individual has unique needs when communicating.

Although there are specific laws and rules to govern communication between health care professionals and people who are deaf, they are not always followed due to the health care professional’s insufficient knowledge of communication techniques. This lack of knowledge can lead them to make assumptions about communicating with someone who is deaf, which can in turn cause them to use an unsuitable form of communication. Acts in countries such as the Americans with Disabilities Act (ADA) state that all health care providers are required to provide reasonable communication accommodations when caring for patients who are deaf. These accommodations could include qualified sign language interpreters, CDIs, and technology such as Internet interpretation services. A qualified sign language interpreter will enhance communication between a deaf individual and a health care professional by interpreting not only a health professional’s verbal communication, but also their non-verbal such as expressions, perceptions, and body language. A Certified Deaf Interpreter (CDI) is a sign language interpreter who is also a member of the Deaf community.[67] They accompany a sign language interpreter and are useful for communication with deaf individuals who also have language or cognitive deficits. A CDI will transform what the health care professional communicates into basic, simple language. This method takes much longer, however it can also be more effective than other techniques. Internet interpretation services are convenient and less costly, but can potentially pose significant risks. They involve the use of a sign language interpreter over a video device rather than directly in the room. This can often be an inaccurate form of communication because the interpreter may not be licensed, is often unfamiliar with the patient and their signs, and can lack knowledge of medical terminology.[68]

Aside from utilizing interpreters, healthcare professionals can improve their communication with hearing impaired patients by educating themselves on common misconceptions and proper practices depending on the patient’s unique needs. For example, a common misconception is that over exaggerating words and speaking loudly will help the patient understand more clearly. However, many individuals with hearing loss depend on lip-reading to identify words. Over exaggerating words and raising your voice can distort the lips, making yourself even more difficult to understand. Another common mistake health care professionals make are the use of single words rather than full sentences. Although language should be kept simple and short, keeping context is important because certain homophonous words are difficult to distinguish just from lip-reading. Health care professionals can further improve their own communication with their patients by eliminating any background noise and positioning themselves in a way where their face is clearly visible to the patient. The healthcare professional should know how to use body language and facial expressions to properly communicate different feelings.[66]

Research[edit]

A 2005 study achieved successful regrowth of cochlea cells in guinea pigs.[69] However, the regrowth of cochlear hair cells does not imply the restoration of hearing sensitivity, as the sensory cells may or may not make connections with neurons that carry the signals from hair cells to the brain. 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.[70]

Recent research, reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils,[71] using stem cells. Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement.[72] The Hearing Health Foundation in the US has embarked on an ambitious project called the Hearing Restoration Project.[73] Also Action on Hearing loss in the UK is also aiming to restore hearing.[74]

Besides research studies seeking to improve hearing, such as the ones listed above, research studies on the deaf have also been carried out in order to understand more about audition. Pijil and Shwarz (2005) conducted their study on the deaf who lost their hearing later in life and, hence, used cochlear implants to hear. They discovered further evidence for rate coding of pitch, a system that codes for information for frequencies by the rate that neurons fire in the auditory system, especially for lower frequencies as they are coded by the frequencies that neurons fire from the basilar membrane in a synchronous manner. Their results showed that the subjects could identify different pitches that were proportional to the frequency stimulated by a single electrode. The lower frequencies were detected when the basilar membrane was stimulated, providing even further evidence for rate coding.[29]

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