出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/02/19 14:03:31」(JST)
| This article's introduction section may not adequately summarize its contents. To comply with Wikipedia's lead section guidelines, please consider modifying the lead to provide an accessible overview of the article's key points in such a way that it can stand on its own as a concise version of the article. (discuss). (March 2013) |
| Hearing loss | |
|---|---|
| Classification and external resources | |
The international symbol of deafness or hard of hearing
|
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| ICD-10 | H90–H91 |
| ICD-9 | 389 |
| MedlinePlus | 003044 |
| eMedicine | article/994159 |
| MeSH | D034381 |
Hearing impairment, hearing loss, or deafness, is a partial or total inability to hear.[1] It is one of the most common medical conditions presenting to physicians.[2] It is caused by many different factors, including, but not limited to, aging, exposure to noise, illness, or chemicals and physical trauma or any combination of these. Audiometry (hearing testing) may be used to determine the severity of the hearing impairment. While the results are expressed in decibels, a physical descriptor, hearing loss is usually described as mild, mild-moderate, moderate, moderately severe, severe, or profound. Conceptually, 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 be taken to prevent hearing loss, especially avoidance from exposure to noise, chemical agents, and physical trauma. But, in some cases such as due to disease, illness, or genetics, it is impossible to reverse or prevent. Technological advancements are being made continuously to improve the hearing of those who are hearing impaired. Hearing aids have become more advanced and smaller. There have been developments in the pharmacological management of hearing in response to insult from exposure to noise, chemical agents, or physical trauma.
Deafness, which can be functionally described, as the absence of usable hearing acquired either from birth or prelingually, is viewed by many of the deaf community as a condition, not an illness. Some of the newer technologies, such as cochlear implants that provide some hearing for the deaf, have caused controversy in the deaf community.
Hearing loss exists when there is diminished sensitivity to the sounds normally heard.[3] 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.[3] 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.
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.[4]
The following are some of the major causes of hearing loss.
There is a progressive loss of ability to hear high frequencies with increasing age known as presbycusis. This begins in early adulthood, but does not usually interfere with ability to understand conversation until much later. Although genetically variable it is a normal concomitant of aging and is distinct from hearing losses caused by noise exposure, toxins or disease agents.[5]
Noise is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.[6]
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.[7] 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, transportation, crowds, lawn and maintenance equipment, power tools, gun use, 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. Mainly, deafness or hard of hearing happens in the older.
In the USA, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure.[8]
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.[9]
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.[9] 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.[9] 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.
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.[12] Depending on what nerves are damaged from a stroke, one of the side effects can be deafness.[13] Charcot–Marie–Tooth disease variant 1E (CMT1E) is noted for demyelinating in addition to deafness.[14]
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. According to a study by researchers at Brigham and Woman's Hospital in Boston, 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.[15] Others may cause permanent hearing loss.[16] 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.[17]
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[18] and automobile exhaust,[18] for example); and asphyxiants.[19] Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.[19]
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.[19] For some ototoxic chemical exposures, particularly styrene,[20] 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.[20] The following list provides an accurate catalogue of ototoxic chemicals:[19][20]
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.[21]
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.[22] 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.
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,[23] 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.[24]
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.
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:
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[25] and as an app on the iPhone.
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.[3]
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.
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.
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.
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.[26]
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 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.
People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in:
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.[27] 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.
The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:[8]
There is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptoms.[28]
It is estimated that half of cases of hearing impairment and deafness are preventable.[3] 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.[3] Education on the perils of hazardous noise exposure increases the use of hearing protectors.[29]
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, which amplify the incoming sound, will improve hearing ability, but nothing can restore normal hearing.[why?][citation needed]
Cochlear implants improve outcomes in people with hearing loss in either one or both ears.[30] Cochlear implants artificially stimulate the cochlear nerve by providing an electric impulse substitution for the firing of hair cells. Cochlear implants are expensive, and require sophisticated programming in conjunction with extensive training for effectiveness. Cochlear implant recipients may be at higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended for those with cochlear implant.[31] 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[32] 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.
Many hearing impaired individuals use assistive devices in their daily lives:
Three types of wireless devices exist along with hard-wired devices. A wireless device used by people who use their residual hearing has two main components. One component sends the sound out to the listener, but is not directly connected to the listener with the hearing loss. The second component of the wireless system, the receiver, detects the sound and sends the sound to the ear of the person with the hearing loss. The three types of wireless devices are the FM system, the audio induction loop and the infra red system. Each system has advantages and benefits for particular uses.
The FM system can easily operate in many environments with battery power. It is thus mobile and does not usually require a sound expert for it to work properly. The listener with the hearing loss carries a receiver and an earpiece. Another wireless system is the audio induction loop which 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.
A third kind of wireless device for people with hearing loss is the infra red (IR) system, which also requires a receiver to be worn by the listener. Usually the emitter for the IR device, that is, the component that sends out the signal, uses an AC adaptor. The advantage of the IR wireless system 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 sends out no signal beyond the earpiece that is plugged directly into the amplifier. That amplifier of the hardwired device also has a microphone inside of it or plugged into it.
Inside the classroom, children with hearing impairments may also benefit from interventions. These include providing favorable seating for the child. This can be achieved by having the student sit as close to the teacher as possible so that they will be able to hear the teacher, or read their lips more easily. When lecturing, teachers should try to look at the student as much as possible and limit unnecessary noise in the classroom. If a student has a hearing aid, they are likely to hear a lot of unwanted noises.
Pairing hearing impaired students with hearing students is a common technique, allowing the non-hearing student to ask the hearing student questions about concepts that they have not understood. When teaching students with hearing impairments, overheads are commonly used, allowing the teacher to write, as well as maintain visual focus on the hearing impaired student. 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.[37]
Disability-adjusted life year for hearing loss (adult onset) per 100,000 inhabitants in 2004.
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no data
<250
250–295
295–340
340–385
385–430
430–475
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475–520
520–565
565–610
610–655
655–700
>700
|
Globally hearing loss affects about 10% of the population to some degree.[6] 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).[38] Of these 65 million acquired the condition during childhood.[3] At birth ~3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems.[3]
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."[39] 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."[40] 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."[41]
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 (voluntarily) 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 languages convey meaning by manual communication and body language instead of acoustically conveyed sound patterns. This can involve simultaneously combining hand shapes, orientation and movement of the hands, arms or body, and facial expressions to fluidly express a speaker's thoughts.
There is no single "sign language". Wherever communities of deaf people exist, sign languages develop. While they use space for grammar in a way that oral languages do not, sign languages exhibit the same linguistic properties and use the same language faculty as do oral languages. Hundreds of sign languages are in use around the world and are at the cores of local deaf cultures. Some sign languages have obtained some form of legal recognition, while others have no status at all. Deaf sign languages are not based on the spoken languages of their region, and often have very different syntax, partly but not entirely owing to their ability to use spatial relationships to express aspects of meaning. (See Sign languages' relationships with spoken languages.)
Abbe Charles-Michel de l'Épée was the first person to open a deaf school. L’Épée taught French Sign Language (LSF) 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, 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, and other outside influences.[42]
| The examples and perspective in this section deal primarily with the United States and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (December 2012) |
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"[43] 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.
There are mixed opinions on the subject between those who live in deaf communities, and those who have deaf family members who do not live in deaf communities. Deaf communities are those communities where only sign languages are typically used.
Many parents who have a child with a hearing impairment prefer their child to be in the least restrictive environment of their school. This may be because most children with hearing loss are born to hearing parents. This can also be because of the recent push for inclusion in the public schools.
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.
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.[43]
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There are many myths regarding people with hearing losses including, but not limited to:
A 2005 study achieved successful regrowth of cochlea cells in guinea pigs.[49] 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.[50]
Recent research, reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils,[51] using stem cells. Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement.[52] The Hearing Health Foundation in the US has embarked on an ambitious project called the Hearing Restoration Project.[53] Also Action on Hearing loss in the UK is also aiming to restore hearing.[54]
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 basiliar membrane was stimulated, providing even further evidence for rate coding.[22]
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| リンク元 | 「聴覚障害」「dysacusis」「hearing-impaired」 |
| 関連記事 | 「disorder」「hearing」 |