Hearing impairment

Any alteration of hearing capacity. Hearing impairment can be of various degrees, including mild, moderate, severe, profound, or total. The degree of impairment typically is categorized by the loss of hearing sensitivity, that is, how loud sounds must be for a listener to hear them. The degree of impairment can refer either to the loss of hearing sensitivity for individual pitches of sounds for each ear separately, or to an overall loss of hearing sensitivity for both ears. Hearing impairment is further defined as unilateral if present in only one ear, and as bilateral if present in both ears.

Hearing impairment may be present at birth or acquired later in life. Congenital hearing loss greatly interferes with normal language and speech development if it is bilateral and of severe or greater magnitude over the pitch range that covers speech sounds. Acquired hearing loss can occur gradually or suddenly at any time of life and therefore can also be defined in relation to the development of language and speech. Hearing impairment is often termed prelingual, perilingual, or postlingual if the hearing loss occurred prior to, during, or after the development of language and speech.

The term deafness has two meanings. If it refers only to a total lack of hearing function, a lowercase d is used. If it refers to an individual with a bilateral hearing loss who does not use oral language and speech, an uppercase D is used.

Hearing loss can be classified by the part of the auditory system that is defective. Conductive hearing loss results from abnormalities or diseases of the outer or middle ear; sensorineural hearing loss results from abnormalities or diseases of the inner ear or auditory nerve; and central hearing impairment results from abnormalities or diseases of the auditory portions of the central nervous system. Combined conductive and sensorineural hearing loss is referred to as mixed hearing loss. See also Audiometry; Ear (vertebrate).

Conductive hearing loss impairs sensitivity to sound; if the sound is amplified, the impairment can usually be overcome. See also Acoustic noise; Loudness.

In sensorineural hearing loss, the abnormality can affect different portions of the inner ear so that often hearing sensitivity may be normal or nearly so for low-pitched tones but falls off sharply for higher tones. In addition, what is heard may be distorted. The speech of the hearing-impaired person may deteriorate over time because the high-pitched speech sounds cannot be heard. See also Speech disorders.

In most cases of sensorineural or mixed hearing loss, both sensitivity and clarity are impaired, so the perceived sound is weak and distorted. A hearing aid that amplifies sound fails to correct the distortion, and so the difficulty of understanding speech is only partially remedied. Speech deteriorates for adults who suffer this type of hearing loss after speech has developed normally. For children born with severe or profound bilateral sensorineural hearing loss, special education is required for the acquisition of speech and language. See also Hearing aid.

Other symptoms characterize sensorineural hearing loss. Tinnitus—head noise or ringing in the ears that is heard with no related acoustic stimulus—may occur continuously or intermittently, and is described as a rushing or roaring noise. Vertigo and nausea may accompany the hearing deficit if the abnormality affects the vestibular system, as in Ménière's disease. In double hearing, or diplacusis, a single tone is heard at a different pitch in each ear, or simple tones may sound fuzzy or rough. Loudness recruitment, an abnormal increase in perceived loudness as a sound is intensified, may be associated with a low tolerance for loud noises.

Prevention is the best approach to possible loss. Immunization for viral and bacterial diseases, early medical intervention for upper respiratory infections or earaches, keeping both nostrils open when blowing the nose, control of allergies, avoidance of ototoxic drugs, and reduced exposure to loud sounds are desirable preventive measures. Routine hearing tests are also advisable.

Antibiotic control of ear infections is a common treatment for conductive hearing loss, and surgical procedures are also available. Many of these procedures for conductive hearing loss allow hearing to return to normal.

Measures to correct sensorineural deafness are varied. Tranquilizing and antivertiginous drugs, vasodilative agents, and low-salt diets are among the treatments prescribed for the symptomatic management of Ménière's disease, but they have met with only moderate success. The cochlear implant seeks to restore hearing in the completely deaf ear by direct electrical stimulation of the auditory nerve, thereby producing an auditory sensation that can represent environmental sounds and certain speech sounds. Success is not universal, but some with postlingual deafness have improved substantially.

Nonmedical aural rehabilitation for persons with hearing impairment includes the use of hearing aids, special auditory training to use this amplification, and instruction in speech reading (lip reading). Devices that convert sound to skin sensations are sometimes useful when hearing aids fail to provide any benefit.

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Definition

Hearing impairment is the temporary or permanent loss of some or all hearing in one or both ears.

Description

There are three types of hearing impairment that occur in young children:

• conductive hearing loss, a usually temporary interference with the reception of sound from the outer ear to the middle or inner ear
• sensorineural hearing impairment, a permanent abnormality of the cochlear hair cells of the inner ear, the auditory nerve, or the auditory center of the brain
• mixed hearing impairment, a combination of conductive and sensorineural impairments

Hearing impairments also are classified as prelingual (occurring before a child learns to speak) and post-lingual (occurring after the child has acquired language).

Normal hearing in children is defined as the ability to hear sounds in the range of 0–25 decibels (dB). Hearing impairments are classified in the following degrees:

• Mild, in which a child hears sounds from 26–40 dB. Speech and conversation are usually unaffected but distant sounds may be difficult to hear.
• Moderate, in which a child hears sounds from 41–70 dB. The ability to form sounds and hear normal conversation is affected.
• Severe, in which a child hears sounds from 71–90 dB. The child requires a hearing aid to hear conversations.
• Profound, in which a child can only hear sounds above 90 dB. A hearing aid may help but the child will not be able to articulate words normally.

Demographics

Temporary and permanent hearing impairments are not uncommon among children.

Conductive hearing impairment is most often caused by otitis media, an infection of the middle ear. This is very common in children between the ages of six months and four years. About 20 percent of children have an episode of acute otitis media every year. It affects boys and girls equally. Otitis media is more common among children of Eskimo or Native American descent and among children whose parents smoke. The condition is less common in children over the age of eight. Chronic secretory otitis media, also called otitis media with effusion or suppurative otitis media, is the most common cause of temporary hearing impairment in children under eight. It is more common in boys and rare in children over age eight.

About 12,000 American infants annually are born with some degree of hearing impairment. Although congenital (present at birth) deafness is the rarest form of deafness, it is the most common congenital abnormality in newborns. Three out of every 1,000 children are born with significant hearing impairment. About 65 percent of these children are born deaf and an additional 12 percent become deaf before the age of three. In the United States 14.9 percent of children aged six to 19 have measurable hearing impairment in one or both ears.

Noise-induced hearing impairment is increasing in the United States. It is not uncommon for teenagers to become permanently hearing impaired in the high-frequency range above 4,000 hertz.

Causes and Symptoms

Conductive Hearing Impairment

Children develop otitis media because the eustachian tubes that connect the middle ear with the back of the mouth and equalize air pressure and drain fluid are small and easily obstructed. Acute otitis media can result from a respiratory infection such as a cold that causes an inflammation that blocks a eustachian tube. The fluid that builds up in the middle ear is susceptible to bacterial and viral infection. If the blockage persists it causes chronic secretory otitis media, the most common cause of conductive hearing impairment in children.

A painful earache and temporary hearing impairment in one ear are common symptoms of acute otitis media. The symptoms of secretory otitis media develop gradually and fluctuate. They are usually worse in the winter. Symptoms of partial hearing loss from secretory otitis media may go unnoticed for some time and may include the following symptoms:

• immature speech
• behavioral problems resulting from frustration at not being able to hear well
• sitting close to the television or turning up the volume
• poor school performance

Otitis media sometimes runs in families, indicating that there may be a hereditary component. Second-hand smoke also is a risk factor for otitis media. Conductive hearing impairment from middle ear infections may be associated with other medical conditions including the following problems:

• asthma or allergic rhinitis
• cleft palate, which impairs drainage of the middle ears through the eustachian tubes (Some 30% of children with cleft palate have conductive hearing loss.)
• other head or facial abnormalities
• Down syndrome, which is characterized by narrow ear canals resulting in susceptibility to middle ear infections (About 80% of children with Down syndrome have some hearing impairment.)

Another cause of conductive hearing impairment is an excessive build-up of earwax that prevents sound waves from reaching the eardrum. Although earwax, produced by glands in the outer ear canal, normally works its way out of the ear, sometimes excessive amounts build-up and harden in the outer ear canal, gradually impairing hearing.

Sensorineural Hearing Impairment

Sensorineural hearing impairments result from abnormal development or disorders of the cochlea, the spiral cavity of the inner ear, disorders of the auditory nerve that transmits electrical impulses from the inner ear to the brain, or abnormalities of the auditory center of the brain. Such conditions have a variety of causes. For example, more than 70 known inherited disorders account for about one-half of all severe sensorineural hearing impairments; however, 90 percent of children with congenital hearing impairment are born to parents with normal hearing. In addition, the following problems are associated with sensorineural hearing impairment:

• craniofacial anomalies
• Down syndrome, in many of which cases the child has some immune deficiency that leads to frequent ear infections resulting in hearing loss
• problems during or shortly after birth that may damage the inner ear or auditory nerve
• low birth weigh, below 3.5 lb (1.6 kg)
• incubator noise affecting premature infants
• neonatal exposure to aminoglycoside antibiotics
• bacterial infections such as meningitis during infancy
• cytomegalovirus (CMV) infection during childhood
• accidents involving head injuries

High-frequency hearing impairment in teenagers most often results from exposure to loud noise such as amplified music.

While about 50 percent of congenital hearing impairments have no known cause, prenatal risk factors for congenital hearing impairment include:

• rubella (German measles) (More than 50% of children born to mothers who contracted rubella during the first ten weeks of pregnancy suffer from congenital malformations.)
• CMV, the most common viral infection in fetuses, a leading cause of congenital deafness (CMV affects 1% or 40,000 newborns annually; about 8,000 of these newborns have birth defects.)
• other infections, including toxoplasmosis, herpes, syphilis, or flu
• drug or alcohol consumption
• drugs that are ototoxins

Symptoms of congenital deafness in newborns include:

• lack of response to loud noises
• lack of response to voices or noise when sleeping in a quiet room
• failure to calm down at the sound of the mother's voice
• failure to make normal baby sounds including cooing by six weeks of age
• failure to look for the source of a noise by three to six months of alie
• failure to play with noisy toys, such as a rattle, by four to eight months
• failure to babble by about six months of age

Symptoms that a baby or young child may have a hearing impairment include:

• lack of reaction to loud noises
• failure to imitate sounds
• lack of response to the child's name during the first year of life
• failure to vocalize (to imitate simple words, enjoy games that involve speech, or talk in two-word sentences during the second year)
• failure to understand simple directions during the third year

When to Call the Doctor

A physician should be consulted immediately if a parent suspects that a child has a hearing impairment.

Diagnosis

Parents are usually the first to suspect a hearing impairment in their child. Early detection of and intervention for hearing impairments are crucial for preventing or minimizing developmental and educational delays. Hearing-impaired children who are identified and receive early intervention before six months of age develop significantly better language skills than children identified after six months of age. However, in the United States, the average age of diagnosis is at two years of age, and significant hearing impairments have gone undiagnosed in children as old as six.

Newborn hearing tests often are administered only if an infant is considered at risk for congenital deafness. However, routine screening of sleeping newborns is on the increase. If a problem is detected, additional tests are used to determine the type and severity of the impairment. Tests used are as follows:

• An evoked otoacoustic emissions (OAE) test that detects an echo emitted by the inner ear in response to sound; the echo is produced only if the inner ear is healthy and functioning normally.
• An automated auditory brainstem response (ABR) test, or brainstem auditory-evoked response (BAER) test, in which brainstem responses to sounds are monitored through small electrodes taped to the child's head.

Pediatricians may examine a child's ears with a viewing instrument called an otoscope. Age-appropriate hearing tests may be performed routinely throughout childhood. Test administrators who suspect a hearing impairment may cover their mouths to prevent the child from lip reading, also called speech reading. Types of hearing tests include:

• behavioral tests that measure the quietest sound that the child can hear and the ability to understand words
• speech discrimination tests for children with simple vocabularies
• the McCormick toy discrimination test for three-yearolds, in which the child is asked to identify words that sound similar, such as tree and key
• a simple form of audiometry that assesses frequency perception through earphones
• tympanometry, in which a probe inserted into the ear measures sound waves bouncing off the eardrum
• acoustical impedance tests to identify middle ear problems including otitis media

Treatment

Conductive Hearing Impairment

Acute otitis media may be treated with antibiotics. Secretory otitis media usually disappears without treatment. However, a procedure called myringotomy or tympanostomy may be used for recurrent acute otitis media or secretory otitis media that persists for several months. A small plastic tube is inserted through the eardrum to drain fluid and equalize the air pressure between the middle ear and the ear canal. The tube usually falls out within six to 12 months and the hole in the eardrum closes. Myringotomy is an outpatient procedure performed under general anesthesia.

Excessive earwax usually can be removed at home, following a doctor's instructions. Special drops are used to soften the wax, and the ears are flushed with water. If necessary a doctor may remove earwax using suction or a metal probe.

Sensorineural Hearing Impairment

Sensorineural hearing impairment and congenital deafness are incurable. However, any residual hearing can be maximized with a hearing aid. Many types of hearing aids are available for children as young as three months. A postauricular hearing aid fits behind the ear and is connected to a plastic mold that is custom-fitted for the child's ear. These must be replaced as the child grows.

An older child with sufficient residual hearing can use an in-the-ear or in-the-canal hearing aid, in which the entire apparatus fits inside the ear. Hearing aids may be programmed to match a child's particular type of hearing loss. A transposer can change high-pitched sounds that are inaudible to many hearing-impaired children into lower-pitched sounds.

Cochlear implants may be used in children who are profoundly deaf and thus are not candidates for hearing aids. Electrodes are surgically implanted into the cochlea through a hole drilled in the mastoid bone. Cochlear implants rely on three external components: a microphone to pick up sound, a speech processor to select and arrange the sounds, and a transmitter and receiver/stimulator that converts the signals from the processor into electrical impulses. The electrodes in the cochlea collect the impulses from the stimulator and send them to the brain. Although they do not restore normal hearing, cochlear implants can provide substantial improvement in speech recognition and production, as well as the ability to hear and identify common sounds such as doorbells. Most children receive implants between the ages of two and six. As of 2002 about 10,000 American children had cochlear implants. Children with cochlear implants have been found to be at an increased risk for bacterial meningitis.

Various educational approaches are employed for children with hearing impairments:

• lip reading and sign language, particularly for children with severe hearing impairment
• a bilingual-bicultural (bi-bi) approach that considers the deaf community as a separate culture with its own language (American Sign Language [ASL])
• the auditory-oral approach, which relies on powerful hearing aids or cochlear implants, supplemented with lip reading, and uses spoken rather than sign language
• the auditory-verbal (A-V) approach, which relies on enhanced residual hearing and one-on-one teaching to develop auditory skills without lip reading or sign language
• cued speech, a simple visual phonetic-based system of eight handshapes, each representing several consonant sounds, and four positions around the mouth, each representing several vowel sounds
• the total communication approach, which uses multiple methods of communication, including hearing amplification, gestures, lip reading, finger spelling, and one of several English-based sign languages known collectively as Manually Coded English (MCE)

Prognosis

Symptoms of acute otitis media usually disappear within a few days, although a ruptured eardrum may take several weeks to heal. Sometimes hearing is affected for three months or more until all of the fluid has drained from the ear. Following a myringotomy hearing in the affected ear usually returns to normal, often within a few days. As a child grows the eustachian tubes widen and stiffen, allowing air to enter and fluid to drain from the middle ear more efficiently. However, recurrent or chronic otitis media can result in ongoing moderate hearing impairment, often at a stage in which hearing is essential for language development.

Children who receive early intervention for hearing impairments can develop at nearly the same rate as other children. However, even a minor hearing impairment can significantly affect a baby's ability to understand and communicate and to acquire speech and language. The effects of hearing impairment on learning depend on the following:

• the severity of the impairment
• the affected frequency range
• the age at which the impairment occurred
• how early the impairment was detected
• how early treatment was initiated

Prevention

Couples with family histories of congenital deafness may seek genetic counseling to assess the risks for their children. If they have not already had rubella, women should be vaccinated before becoming pregnant. During pregnancy women should take only drugs that are known to be safe for the fetus.

It is very important for the hearing-impaired to protect residual hearing from loud noise. Teenagers should be encouraged to avoid very loud music. Those at risk for hearing impairment from other loud noises should be encouraged to wear earplugs.

Parental Concerns

Hearing is very important for the development of emotional relationships between a child and the family. Families of hearing-impaired children must find additional means of connecting emotionally. Support groups often are very helpful for hearing-impaired children and their families.

Because hearing impairments may delay speech and language acquisition, interfere with cognitive development, and disrupt progress in school, the educational decisions that parents make for their child are of special significance. About 50 percent of all children with congenital deafness attend regular schools; the other 50 percent receive some type of specialized schooling.

See also Cochlear implants.

Resources

Books

Kurtzer-White, Ellen, and David Luterman, eds. Early Childhood Deafness. Washington, DC: AG Bell, 2001.

Niparko, John, et al. Cochlear Implants: Principles and Practices. Washington, DC: AG Bell, 2000.

Olsen, Wayne, ed. Mayo Clinic on Hearing. Rochester, MN: Mayo Clinic Health Information, 2003.

Roush, Jackson. Screening for Hearing Loss and Otitis Media in Children. Washington, DC: AG Bell, 2001.

Organizations

Alexander Graham Bell Association for the Deaf and Hard of Hearing (AG Bell). 3417 Volta Place, NW, Washington, DC 20007. Web site: www.agbell.org.

American Speech-Language-Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. Web site: .

Deafness Research Foundation. 1050 17th St., NW, Suite 701, Washington, DC 20036. Web site: www.drf.org.

Web Sites

"FDA Public Health Web Notification: Risk of Bacterial Meningitis in Children with Cochlear Implants." U.S. Food and Drug Administration, September 25, 2003. Available online at www.fda.gov/cdrh/safety/cochlear.html (accessed December 28, 2004).

Gordon-Langbein, Amie. "Facts About Hearing Loss in Children." Alexander Graham Bell. Available online at www.agbell.org/information/brochures_faq.cfm (accessed December 28, 2004).

"So Your Child has a Hearing Loss: Next Steps for Parents."

Alexander Graham Bell. Available online at www.agbell.org/information/brochures_parent_so.cfm (accessed December 28, 2004).

[Article by: Margaret Alic, PhD]

This entry consists of the following articles:

• Hearing Impairment: School Programs
• Hearing Impairment: Teaching Methods

Partial or complete loss of hearing; see also deafness.

A reduction in the acuity to detect and recognize sound.

See also: Deaf culture for the social movement.

Deafness is a disability wherein the ability to detect certain frequencies of sound is completely or partially impaired. When applied to humans, the term hearing impaired is rejected by the majority of deaf people where the terms deaf and hard-of-hearing are preferred.

Contents 1 Definition 2 Classification 2.1 Conductive and sensorineural hearing impairments 2.1.1 Conductive hearing loss 2.1.2 Sensorineural hearing loss 2.1.3 Mixed hearing loss 2.2 Quantification of hearing loss 2.3 Age of onset 2.3.1 Pre-lingual deafness 2.3.2 Post-lingual deafness 2.4 Unilateral and bilateral hearing impairment 3 Causes 3.1 Environmental situations 3.2 Neurological disorders 4 Treatments 5 Deaf culture 6 Sign language 6.1 History 6.2 Sign language in the present 7 Historical deaf people 8 See also 9 References

Definition

Hearing sensitivity is indicated by the quietest sound that an animal can detect, called the hearing threshold. In the case of humans and some animals, this threshold can be accurately measured by a behavioral audiogram. A record is made of the quietest sound that consistently prompts a response from the listener. The test is carried out for sounds of different frequencies. There are also electro-physiological tests that can be performed without requiring a behavioral response.

Normal hearing thresholds within any given species are not the same for all frequencies. If different frequencies of sound are played at the same amplitude, some will be perceived as loud, and others quiet or even completely inaudible. Generally, if the gain or amplitude is increased, a sound is more likely to be perceived. Ordinarily, when animals use sound to communicate, hearing in that type of animal is most sensitive for the frequencies produced by calls, or in the case of humans, speech. All levels of the auditory system contribute to this sensitivity toward certain frequencies, from the outer ear's physical characteristics to the nerves and tracts that convey the nerve impulses of the auditory portion of the brain.

A hearing loss exists when an animal has diminished sensitivity to the sounds normally heard by its species. In humans, the term hearing impairment is 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 that must be made above the usual level before the listener can detect it. In profound deafness, even the loudest sounds that can be produced by an audiometer (an instrument used to measure hearing) may not be detected.

Another aspect to 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.^[1]

Classification

This section includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations. (September 2009)

There are two different types of hearing impairments, conductive hearing impairment and sensorineural hearing impairment. A third type is a combination of the two called mixed hearing loss. Hearing impairments are categorized by their type - conductive, sensorineural or both, by their severity, and by the age of onset. Furthermore, a hearing impairment may exist in only one ear (unilateral) or in both ears (bilateral).

Conductive and sensorineural hearing impairments

Main article: Conductive hearing loss

Main article: Sensorineural hearing loss

Conductive hearing loss

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; hammer, anvil and stapes may result in conductive hearing loss. The mobility of the ossicles may be impaired of different reasons and disruption of the ossicular chain due to trauma, infection or anchylosis may also result in hearing loss.

Many of these conditions can be helped with surgery, and an air conduction hearing aid is often a good choice of treatment. However, in some cases such an aid is not possible to use. The most obvious reason is if the patient does not have any ear canals. Where to place the ear mould? A more common reason is in patients with chronic ear infections that drain continuously or start to drain when the ear canal is obstructed with an air conduction hearing aid mould. In these patients a direct bone conduction hearing device could be an excellent solution. An implant made out of titanium is placed in the bone behind the external ear and allowed to osseointegrate and an impedance-matched hearing aid can be attached. At present there are two such hearing aids on the market; the Baha 3 by Cochlear BAS and the Ponto by Oticon Medical.

Sensorineural hearing loss

A sensorineural hearing loss is one resulting from 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. As we grow older the hair cells degenerate and lose their function, and our hearing deteriorates. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has an impaired hearing. Impaired hearing is the most common physical handicap in the industrialized world.

Another common reason for hearing loss due to hair cell damage is noise-induced hearing loss. These types of hearing loss are often most pronounced in the high frequency range. This will often interfere with speech understanding, as it is in the high frequency range that we find the consonant sounds that are most important especially in noisy surroundings. Head trauma, ear infections, tumours and ototoxic drugs such as gentamycine are other reasons for sensorineural hearing loss.

Hair cells that are damaged cannot be replaced with any surgical procedure, even if research with stem cell treatment is presently going on in many institutions. The clinical application of this will however not yet be available for many years. Protection from noise exposure is at present the only way to reduce the hair cell damage. Conventional air conduction hearing aids are often prescribed for patients with sensorineural hearing loss. The outcome with modern types of hearing aids is often excellent, but speech understanding could still be a problem in demanding situations.

Total or near total sensorineural deafness could be the result of congenital malformations, head trauma or inner ear infection. In patients with total or near total deafness, an air conduction aid could not be used even if the drum and middle ear are normal. For these patients a cochlear implant could be a treatment option. This means that a thin electrode is placed into the cochlea and is stimulated electrically through a small microprocessor under the skin behind that ear.

Mixed hearing loss

Mixed hearing loss is a combination of the two types discussed above. Chronic ear infection that is a fairly common diagnosis could result in a defect ear drum and/or middle ear ossicle damages. 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, but 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.

Quantification of hearing loss

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
• Moderate: between 41 and 55 dB HL
• Moderately severe: between 56 and 70 dB HL
• Severe: between 71 and 90 dB HL
• Profound: 91 dB HL or greater

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 a EU funded project Hearcom. The RNID version is available over the phone (0844 800 3838, only available in the UK), on the web and as an app on the iPhone.

Age of onset

The age at which hearing loss occurs is crucial for the acquisition of a spoken language.

Pre-lingual deafness

Main article: Prelingual deafness

Prelingual deafness is hearing impairment that is sustained prior to the acquisition of language, which can occur as a result of a congenital condition or through hearing loss in early infancy. Prelingual deafness impairs an individual's ability to acquire a spoken language, but children born into signing families rarely have delays in language development. Most pre-lingual 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.

Post-lingual deafness

Main article: Post-lingual deafness

Post-lingual deafness is hearing impairment that is sustained after the acquisition of language, which can occur as a result of 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 and learning lip reading.

Post-lingual deafness is far more common than pre-lingual deafness.

Unilateral and bilateral hearing impairment

Patients 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. See also: "cocktail party effect", House Ear Institute's Hearing In Noise Test.

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.^[2] 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.

Causes

Environmental situations

Deafness can be caused by environmental situations such as noise, trauma, or other ear defections. Dangerous Decibels, a group that is attempting to help reduce deafness, states that anything over 85 decibels, which is about the level of a busy city, will damage hearing.^[3] Listening to loud noises for long periods of time does not make the eardrum less sensitive, over-exposure to noise actually over-stimulates the hair cells in the cochlea, which in turn damages them and sends corrupted signals via the VIII nerve to your brain resulting in a ringing sound you may experience, called tinnitus. These corrupted signals are the reason it is difficult to hear, and that is why over exposure to noise results in a sensorineural hearing loss mostly between 2–8 kHz (these are the region of hair cells mostly affected), and it is not due to the 'fact' that your eardrum or tympanic membrane are somewhat over stimulated(if this were true over exposure to noise would result in a conductive hearing loss because it is affecting the middle ear mechanisms). Going through a trauma, like a car accident, can cause hearing loss due to the noise of the incident or an injury to the ear. If the middle ear or inner ear is damaged during the accident then hearing will degenerate because the sound wave cannot make it to the brain to be interpreted into sound. Other environmental factors that can cause deafness are nasal allergies. Nasal allergies cause mucus to build up in the throat and the nose, which will block the eustachian tubes and make it difficult for sound waves to make it into the inner ear.

Neurological disorders

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 there is no possible way at present to repair them. 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 infected 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 infected person will become completely deaf in one or both ears. There is no cure for MS.^[4] A stroke occurs if there is a clot in the brain, and blood is unable to get to a section of the brain. Within minutes the oxygen-deprived cells begin to die, causing serious damage to the human body. Depending on what nerves are damaged, one of the side effects can be deafness.^[5]

Treatments

The most common hearing loss treatment is a type of surgical procedure that will remove a blockage in the outer ear. This is almost always effective and will treat conductive hearing loss however surgery is only possible if the cause of the hearing loss can be identified. If not, a hearing aid can be used to amplify sound to make it clearer and more defined. The newest treatment for ANSD and sensorineural hearing loss is a cochlear implant. The cochlear implant is surgically installed to connect to the auditory nerve. The implant has a membrane that vibrates when sound hits it and sends signals to the nerve which then transmits the stimulus to the brain. The cochlear implant has only one membrane compared to the human ear’s three membranes. This means that sound will not be as clear using the cochlear when juxtaposed to normal hearing, but sounds can still be identified and responses can be made.

Deaf culture

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.”^[6] Deaf culture is not about contemplating what deaf people cannot do and how to fix their problems. That is called a "pathological view of the deaf". 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.”^[7] There is more to deaf culture than meets the eye and has to be “experienced” to full comprehend it.^[7]

Sign language

History

Abbe Charles-Michel de l'Épée was the first person to open a deaf school. L’Épée taught French sign language to children, and started the spread of many deaf schools across Europe. Thomas Gallaudet was traveling to England to start a deaf school. His inspiration was a nine-year-old girl who lived next door. Seeing her conquer her struggles made Gallaudet want to teach and see other children conquer their own disabilities. Gallaudet witnessed a demonstration of deaf teaching skills from Sicard, Massieu, and Clerc, the masters of teaching deaf children at the time. After the demonstration of Gallaudet studied under the French masters and perfected his own teaching skills. Once he was done learning Gallaudet and Clerc traveled to the United States and opened the first deaf school in Hartford Connecticut. American Sign Language, or ASL, started to evolve from primarily LSf, French sign language, and other outside influences.^[8]

Sign language in the present

Sign language consists of different hand signals to mean different words. It also has signs for the alphabet which is primarily used to spell names. Sign language also uses: facial expressions, body language, hand shape, hand position, hand movement, and gestures, all of these things affect the meaning or sincerity of the signs that are used. Sign language is offered at most major schools and is recognized as its own language. Sign language makes deaf culture possible. Deaf people can communicate in their own way and do not have to rely on reading lips or technology to help them, if they choose not to.

Historical deaf people

• Trix Bruce - Actor
• Thomas Edison - inventor
• Helen Keller - American author and activist
• Johnnie Ray - Singer
• Pete Townshend - Musician
• Ludwig Van Beethoven - Classical Composer

See also

• Sound pressure - has a table of sound levels

References

Wikimedia Commons has media related to: Hearing impairment

1. ^ eBook: Current Diagnosis & Treatment in Otolaryngology: Head & Neck Surgery, Lalwani, Anil K. (Ed.) Chapter 44: Audiologic Testing by Brady M. Klaves, PhD, Jennifer McKee Bold, AuD, Access Medicine
2. ^ Lieu JE. Speech-language and educational consequences of unilateral hearing loss in children. Arch Otolaryngol Head Neck Surg. 2004: 130(5);524-30
3. ^ "Dangerous Decibels". Dangerous Decibels. http://www.dangerousdecibels.org/. Retrieved 2012-01-10. 
4. ^ "Multiple Sclerosis". MayoClinic.com. 11. http://www.mayoclinic.com/health/multiple-sclerosis/DS00188. Retrieved 2 December 2011. 
5. ^ "Stroke". MayoClinic.com. 1. http://www.mayoclinic.com/health/stroke/DS00150. Retrieved 2 December 2011. 
6. ^ Deaf Heritage: A Narrative History of Deaf America by Jack Gannon (National Association of the Deaf, 1981)
7. ^ ^{a b} Drolsbaugh, Mark. "Everything You've Wanted to Know About Deaf Culture (And Then Some)". Deaf Culture Online. Archived from the original on 13 February 2011. http://web.archive.org/web/20110213211737/http://www.deaf-culture-online.com/index.html. Retrieved 28 November 2011. 
8. ^ Frishberg, Nancy (September 1975). "Arbitrariness and Iconicity: Historical Change in American Sign Language". Language 51 (3): 696. 

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