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.