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deafness

deafness For most of us, the term ‘deafness’ conjures up a frightening image. Becoming deaf in the prime of life must be akin to becoming hard-of-hearing in old age, only infinitely more traumatic. We imagine ourselves turning desperately for help to an audiologist (a specialist in the assessment of hearing), or to a clinician specialized in the diagnosis and treatment of disorders of the ear (an otologist). Music, bird song, the warning sound of an approaching car: all of these, plus, most importantly, the possibility of engaging in spoken interaction with our fellows, are lost to us. Yet being deaf has always been much more than this. Throughout much of European history it meant to be an outcast: cut off not only from human society but, far worse, from the word of God.

Recently, a new ‘cultural construction of deafness’ has emerged. According to this view, to be ‘deaf’ is to identify with a community in which the dominant medium of communication is sign language, and with its own history, social institutions, and cultural forms. The medical understanding of deafness as hearing loss and the cultural understanding of deafness as social and linguistic difference coexist uneasily in modern societies.

Because of differences in the degree and nature of hearing loss, the overall incidence of deafness is difficult to estimate. However, it is likely that around 15% of the population have impaired hearing, which, in many cases, is accompanied by tinnitus (ringing in the ears) and balance problems. Deafness is associated with many hereditary and non-hereditary diseases and may also result from pre- or post-natal exposure to a variety of toxins and traumas. The degree of hearing loss can vary greatly, from a very slight impairment in one ear to total deafness in both ears.

Causes of deafness

Although tumours and other disorders may impair the function of the auditory nerve or of those areas of the brain that are responsible for our perception and recognition of sounds, most causes of deafness involve a defect in the ear and may be divided into two types. A conductive hearing loss results from conditions that interfere with the transmission of airborne sound through the external ear and the middle ear. These structures normally conduct sounds efficiently to the sensory apparatus within the cochlea of the inner ear. As sound waves pass through the external ear to the eardrum, their amplitude is increased as a result of the resonant properties of the outer ear and of the ear canal. Vibrations of the eardrum are then coupled by the middle ear ossicles, the three smallest bones in the body, to the fluid-filled cochlea. Conditions that impair sound transmission to the inner ear will therefore attenuate the incoming sound. Conductive hearing loss does not involve damage to the receptor cells or any other nerve cells in the auditory pathway.

The second major type of deafness to originate from abnormalities of the ear is known as a sensorineural hearing loss, which is sometimes referred to, albeit usually inaccurately, as ‘nerve deafness’. Sensorineural hearing loss most often arises from defects in the cochlea itself, but also describes the hearing deficit that results from damage to the auditory nerve.

Hearing sensitivity varies with sound frequency (or pitch) in a very characteristic way. Decreases in sensitivity at particular frequencies can provide valuable clues as to the nature of the hearing loss. Moreover, although sounds are most effectively conducted to the cochlea by the external and middle ear, they can also reach the cochlea by bone conduction if a vibrating object, such as a tuning fork, is applied to the skull. When airborne sounds are attenuated by disorders of the external ear or the middle ear, hearing by bone conduction should remain normal. On the other hand, sounds transmitted to the cochlea by bone conduction will be heard less well in cases of sensorineural deafness.

Abnormalities of the external ear that result in conductive hearing loss include obstruction of the ear canal, most commonly by wax, and inflammation of the skin surrounding the canal. The eardrum can be ruptured as a result of injury or middle ear disease. Build up of viscous fluid within the normally air-filled middle ear cavity can impede the mobility of the drum and the ossicles. This condition characterizes otitis media with effusion (glue ear) and is particularly prevalent in infants and young children. Damage to the middle ear ossicles may follow head injury. And in otosclerosis, bone growth between the third of these bones — the stapes or stirrup — and the membranous oval window that provides the entrance to the cochlea will immobilize the ossicles and reduce the amount of sound energy that is transmitted. Most forms of conductive hearing loss are characterized by more or less the same degree of deafness across all sound frequencies. In general, the causes of conductive hearing loss can be remedied by drugs or by surgery. Otherwise, hearing aids provide an effective means of amplifying the sound so that normal hearing can be restored.

In humans, each ear contains about 15 000 sensory hair cells, so named because of the bundle of fine hairs, the stereocilia, that project from their apical surfaces. These hair cells convert sound energy into electrical signals, which are conducted to the brain by the fibres of the auditory nerve. In birds, hair cell regeneration occurs following injury. However, if mammalian hair cells die, they are not replaced and so a permanent sensorineural hearing loss results. A variety of factors can cause the hair cells to die. One of these is ageing, and it is a sobering thought that one hair cell dies, without being replaced, approximately every two weeks. This condition, which is called presbyacusis, first affects those hair cells that are responsible for high frequency hearing, so the upper frequency limit of hearing progressively declines over a period of years. This leads to difficulties in distinguishing consonants, making it harder for the listener to understand what is being said.

Hair cells can also die as a result of certain infections and as a consequence of exposure to drugs, including therapeutic compounds with ‘ototoxic’ side-effects, such as the aminoglycoside antibiotics (see figure). However, the commonest cause of acquired sensorineural deafness is excessively loud noise. This used to be referred to as ‘boilermaker's disease’ because of the incidence of hearing loss among workers subjected, often without ear protectors, to intense industrial sounds. Noise-induced deafness affects all ages and may result from a history of exposure to gunfire, extensive wearing of personal stereos, or attending too many discos or rock concerts. As with ototoxic drugs, noise trauma involves damage to the stereocilia and, in more severe cases, destruction of the hair cells. High frequencies again tend to be affected first and the hearing loss may be restricted to frequencies around 4 kHz.

In addition to reduced or lost hearing over particular frequency ranges, people with sensorineural deafness often have problems understanding speech in noisy environments and experience an unusually rapid growth in loudness as sound intensity rises. In contrast to conductive hearing losses, surgery rarely helps in the treatment of sensorineural deafness. Hearing aids are therefore used to boost residual hearing, and in cases of total or near total deafness, a new technology, cochlear implantation, has been used successfully to bypass the damaged hair cells and to stimulate electrically what remains of the auditory nerve.

The deaf in society

The rehabilitation of the deaf is by no means restricted to attempts to restore or improve hearing, but also includes the utilization of non-verbal modes of communication. When speech seemed the single most important quality distinguishing man from beast, the question of how the ‘deaf and dumb’ were to be humanized loomed large. Many eighteenth-century texts contain examples of cures for deafness, of ‘deaf mutes’ spontaneously bursting into speech, of highly secret techniques for teaching speech to the deaf. In France, however, matters took a different turn. In 1760 the Abbé L'Epée, inspired by ideas taken from the philosophes and from John Locke, founded a school based on quite different assumptions. L'Epée distinguished speech from language, concluding that it was the minds, not the tongues, of deaf people that had to be united. To this end he studied the gestural form of communication that he found among the deaf, and used it to develop a sign-based form of education. Diderot, making a similar distinction between language and its oral expression, developed related ideas in more abstract form, particularly in his Lettre sur les sourds et muets à l'usage de ceux qui entendent et qui parlent. Inspired by this work, in the nineteenth century sign-based education spread rapidly, though more easily in some countries than in others.

Towards the end of the nineteenth century the tide turned. A leading figure in the re-establishment of speech-based education was Alexander Graham Bell, best known for his invention of the telephone. Bell had a deaf mother, worked initially as a teacher of the deaf, and subsequently married a deaf woman. Bell feared that the high rate of intermarriage among the deaf would ultimately lead to the ‘formation of a deaf variety of the human race’. He argued that both institutions and language (sign language) that facilitate formation of social relationships among the deaf should be banned by law. It did not go so far. But after the Congress of Milan on deaf education (1880) oralist approaches gradually became universal. Sign language and signing teachers were banished from schools for the deaf.

The turn of the nineteenth century saw the emergence of organized deaf clubs and national associations for the protection of the interests of the ‘deaf and dumb’. Today, older deaf people tell stories of their schooling: dominated by speech lessons, forced to sit on their hands, punished for signing. Few received any education worth the name, though some found their way into technical trades.

In 1960, and despite widespread scepticism, an American linguist, William Stokoe, embarked on a study of communication among deaf people. It gradually became clear that what was involved was no system of primitive gestures but true language, with all the properties of natural languages. The deaf need no longer be seen as a collection of deprived individuals handicapped by lack of (reflexive) communication. Research on sign language paved the way for sociological investigation of the deaf community and for historical research on the social life of deaf people. The fruits of these researches were to be an important resource: gradually, deaf people began to press for the recognition of sign languages and of their own minority status. Sign language gradually re-entered the schools. In 1980 an important milestone passed. The Swedish government recognized Swedish sign language as an official minority language, with deaf children now having the right to education in their ‘own’ language. Few countries have as yet followed suit, and in most countries oral and sign-based education are both to be found (together with a mixed form, Total Communication). Never-theless, where older deaf people are frequently ashamed to use sign language in the presence of hearing people, younger ones sign proudly. Productions in sign language are to be found on television and on the stage.

What does it mean to be deaf today? Few people deafened in middle age become proficient in sign language or identify strongly with deaf culture. What of the child born deaf? Ninety per cent are born to hearing parents. Do those parents try to rear their child to be as like them as possible, as indistinguishable as possible from its hearing peers? Or do they set out to master sign language as best they can, and help their child realize its identity as a culturally Deaf person? Some do one, some the other. Much depends on the advice they receive in those first months of fearsome uncertainty. There is no answer to the question of what it means to grow up deaf. All depends on the choices made by the family, on the child's own personality and attainments, on the educational, social, and cultural environment in which he or she grows up. But growing up deaf is still marked by conflict and uncertainty, for there is little sign of reconciliation between medical and cultural understandings of deafness or those who espouse them.

Stuart Blume, and Andrew J. King

Bibliography

Ballantyne, J. and and Martin, J. A. M. (1984). Deafness, (4th edn) Churchill Livingstone, Edinburgh.
Pickles, J. O. (1988). An introduction to the physiology of hearing, (2nd edn). Academic Press, London.
Sataloff, R. T. and and Sataloff, J. (1993). Hearing loss, (3rd edn) Marcel Dekker, New York.


See also ear, external; eustachian tube; hearing; hearing aid; tinnitus.

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deafness

deafness, partial or total lack of hearing. It may be present at birth (congenital) or may be acquired at any age thereafter. A person who cannot detect sound at an amplitude of 20 decibels in a frequency range of from 800 to 1,800 vibrations per second is said to be hard of hearing. The ear normally perceives sounds in the range of 20 to 20,000 vibrations per second. There are two principal kinds of deafness, conductive deafness and sensorineural deafness. In some cases of deafness both the conductive and the nerve mechanisms are disturbed.

Conductive Deafness

Conductive problems are those that disrupt the conduction of sound through the outer and middle ear (see ear), affecting hearing before the sound reaches the cochlea and the nerve receptors of the inner ear. Disturbances of the conductive mechanism are often temporary or curable. Most such cases are caused by otitis media, an infection that spreads to the middle ear from the upper respiratory tract; the condition usually responds to antibiotic therapy, but serious cases may require drainage of collected fluids through an incision in the eardrum (tympanum) or insertion of a tiny drainage tube. Foreign bodies or impacted wax can cause hearing loss and must be removed by a physician. In adults a predominant cause of conductive deafness is otosclerosis, a chronic hereditary condition in which spongy bone formation results in fixation of the stapes (the bone that connects the middle ear to the inner ear) and restricts its vibration. Important advances in surgical techniques have led to successful treatment of otosclerosis by replacing the stapes with a combination of grafted tissue, plastic, and wire appliances. Deafness can also be caused by perforation or rupture of the eardrum by a sudden loud noise, by physical puncture, or as a result of an infectious disease. In some such cases the eardrum can be repaired by grafting. Today there are many advanced medical techniques for treating infection of the mastoid and congenital malformations of the outer and middle ear that, if neglected, might result in deafness.

Sensorineural Deafness

Sensorineural deafness results from damage to the neural receptors of the inner ear (the hair cells, organ of Corti), the nerve pathways to the brain (notably the auditory nerve), or the area of the brain that receives sound information. Deafness of this type is usually permanent. It can be congenital or accompany other birth-related problems such as erythroblastosis fetalis (Rh incompatibility) or anoxia (lack of oxygen during delivery). Before vaccines were available, German measles (rubella) and common measles (rubeola) were leading causes; maternal cytomegalovirus and genital herpes simplex continue to be threats.

Tumors, injury, stroke, toxic substances (e.g., mercury), and certain over-the-counter and prescription drugs (e.g., streptomycin) are additional factors that can affect auditory pathways and the brain and lead to sensorineural deafness. Continued exposure to loud noise, as in certain industries or from loud music (see noise pollution), can result in damage to the inner ear, causing irreversible hearing loss. Presbycusis, or changes in hearing, especially of high frequencies, in adults has long been accepted as inevitable, but study of cultures where the phenomenon does not exist is bringing this into question. The hearing of patients with sensorineural deafness can sometimes be improved if the patient discontinues harmful medications or avoids exposure to loud noise, e.g., by wearing protective earplugs. In some cases, limited hearing has been restored by cochlear implants, tiny devices implanted into the inner ear that translate sound waves into electrical impulses that are then transmitted to the auditory nerve.

Mechanical and Educational Aids

Persons whose deafness cannot be relieved by medical or surgical means may be greatly helped by various types of electronic hearing aids. Those with hearing loss that cannot be relieved even by mechanical devices (i.e., those with sensorineural deafness) can have special training in speechreading (see lip reading). When deafness is present at birth or develops before a child has learned to speak, it is necessary also to provide specialized speech training and education in sign language, in which fingers and hands are the instruments of expression and communication. Schools and trained teachers for the hearing-impaired are now found in every large city in the world. Other aids for the hearing-impaired include specially trained "hearing dogs," customized telephones, and closed-caption television.

History of Education for the Deaf

Except for sporadic attempts by clerics in past centuries, there was no well-organized effort to help the hearing-impaired until the Abbé Charles Michel de l'Epée founded a school for the deaf in Paris in 1755. Samuel Heinicke established another one in Germany in 1778. The first public school for the deaf in the United States was founded (1817) in Hartford, Conn., by Thomas Hopkins Gallaudet; it is now called the American School for the Deaf. Alexander Graham Bell and his father, Alexander Melville Bell, did much to establish the study of speech on a scientific basis and to improve the methods of teaching the hearing-impaired. Educational and employment opportunities for the deaf have improved since passage of legislation in 1973 that prohibited discrimination against the handicapped by any institution receiving federal money and of the Americans with Disabilities Act in 1990.

Bibliography

See L. DiCarlo, The Deaf (1964); R. V. Harrison, The Biology of Hearing and Deafness (1988); A. P. Freeland, Deafness (1989).

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Deafness

111. Deafness

See also 132. EAR ; 198. HEARING

aerophone
a type of ear trumpet used by the deaf.
Ameslan
an acronym for the American Sign Language for the Deaf, a system of communication through gestures and hand signals.
anaudia
loss or absence of the power of hearing.
autophony
a form of deafness in which the sufferer hears only his own voice, and that very loudly. See also 266. MEDICAL SPECIALTIES .
dactylology, dactyliology
the technique of communicating through signs made with the fingers, as in the manual alphabet for the deaf.
deafmutism
the condition of lacking both hearing and speech. Also called surdomutism . deafmute , n.
manualism
the teaching of communication through the use of hand signals to the deaf. manualist , n.
oralism
1. the principles of the oral method of training the deaf, as lip reading.
2. the support or practice of these principles. Cf. manualism. oralist , n.
osteophone
a hearing device for the deaf that is placed against the upper teeth so it can transmit vibrations to the auditory nerve through the bones of the skull.
paracusis
defective sense of hearing. Also paracousia .
phonautography
a procedure for producing visible records of sound waves or speech sounds, especially to assist the deaf in using the telephone. Also called visible speech . phonautographic , adj.
surdism
Pathology. the degree of deafness that is sufficient to block the acquisition of speech by normal means.
surdomutism
deafmutism. surdomute , n.

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deafness

deafness (def-nis) n. partial or total loss of hearing in one or both ears. conductive d. deafness that is due to a defect in the conduction of sound from the external ear to the inner ear. This may be due to perforations of the eardrum, fluid or infection in the middle ear (see glue ear, otitis (media)), or disorders of the small bones in the middle ear (ossicles). sensorineural d. (perceptive d.) deafness that may be due to a lesion of the cochlea in the inner ear, the cochlear nerve, or the auditory centres in the brain. See also cochlear implant, hearing aid, hearing therapy, Rinne's test, Weber's test.

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deafness

deafness Partial or total hearing loss. Conductive deafness, faulty transmission of sound to the sensory organs, is usually due to infection or inherited abnormalities of the middle ear. Perceptive deafness may be hereditary or due to injury or disease of the cochlea, auditory nerve or hearing centres in the brain. Treatment ranges from removal of impacted wax to delicate microsurgery. Hearing aids, sign language, and lip-reading are techniques which help deaf people to communicate.

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Deafness

156. Deafness

  1. Aged P. Wemmicks deaf father. [Br. Lit.: Great Expectations ]
  2. Bell, Alexander Graham (18471922) telephone inventor; renowned for studies of deafness. [Am. Hist.: NCE, 265]
  3. Keller, Helen (18801968) overcame handicap of deafness as well as blindness. [Am. Hist.: NCE, 1462]
  4. Quasimodo rendered totally deaf by his occupation as bellringer at Notre Dame Cathedral. [Fr. Lit.: Victor Hugo The Hunchback of Notre Dame ]

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