Deafness

Hearing specialists generally distinguish between a person who is deaf and a person who is hard of hearing. People who are hard of hearing can usually hear and understand at least some speech, especially when it is loud enough. However, they may be unable to hear some other sounds, such as doorbells or high musical notes. In addition, the quality of any sounds they do hear may be distorted.

Deaf children and children who are severely hard of hearing have tremendous difficulty learning to speak. Normally, children learn to speak by imitating the speech of others. However, deaf children cannot hear speech. A large number of deaf people never learn to speak well enough to be understood. Instead, they use sign language and other special techniques to communicate.

Hearing loss is the most common physical disability in the United States. At least 15 million Americans have a noticeable hearing loss, and about 2 million of these people are deaf.

Many deaf people earn college degrees, and most deaf men and women support themselves. Deafness need not hinder achievement in a wide variety of occupations. The famous German composer Ludwig van Beethoven wrote some of his finest music after he became deaf.

Conductive disorders result from interference with the transmission of sound through the outer ear or the middle ear. Sound normally enters the outer ear and passes down the ear canal to the tympanum (eardrum). This thin membrane vibrates in response to sound and activates three tiny bones, called ossicles, in the middle ear. The ossicles transmit the vibrations to the inner ear. Most cases of conductive hearing loss are due to diseases that prevent the ossicles from functioning properly.

Sensorineural disorders involve some defect in the inner ear or the auditory nerve, which leads from the inner ear to the brain. The inner ear contains the actual organ of hearing, called the organ of Corti. This organ converts the vibrations transmitted to the inner ear into electrical impulses, which the auditory nerve carries to the brain. Damage to any of these delicate tissues can be caused by a wide variety of factors, and it cannot be repaired.

The other major cause of conductive hearing loss is otosclerosis, a disease of the ossicles. In this disorder, a bony growth forms around the base of the stapes, the bone next to the inner ear. The growth keeps the stapes from moving and so prevents it from passing on vibrations to the inner ear. Physicians believe otosclerosis is hereditary. It may begin to affect hearing at any age but is usually not detected until the teen-age years or later.

Some diseases can cause sensorineural disorders. Meningitis and other diseases accompanied by a high fever can severely damage the inner ear and the auditory nerve. A disorder of the inner ear called Meniere's disease also causes hearing loss, especially among people over 40. This disorder, which affects millions of people, often disturbs the sense of balance.

Birth defects account for many cases of sensorineural deafness. Some people are born with inherited defects in their auditory (hearing) systems. Other inherited conditions may lead to hearing loss later in life.

A woman who has rubella during pregnancy may give birth to a child with a hearing loss. Rubella, especially if it strikes during the first three months of pregnancy, may interfere with the development of the child's ears and nervous system.

A condition called erythroblastosis fetalis can cause a child to be born with a hearing loss. The blood of some unborn children has a substance called the Rh factor, which is not in the mother's blood. The mother's body may produce substances that attack the Rh factor and damage the baby's auditory system.

Environmental factors, such as accidents and exposure to loud noise, can damage a person's hearing. A hard blow to the head can cause permanent hearing loss. Such injuries may affect the eardrum, the bones of the middle ear, or even parts of the inner ear. Exposure to loud noises can lead to serious hearing loss by damaging the organ of Corti. Extremely loud noises, such as explosions or gun blasts, can produce sudden deafness. In many of these cases, however, the victim eventually recovers much of the lost hearing.

Exposure to loud noise over a long period of time can gradually cause permanent loss of hearing. Many people who work in extremely noisy factories eventually suffer considerable hearing loss. Listening for long periods to the loud music played by many rock music bands can also damage hearing. In addition, many physicians believe that prolonged exposure to loud noises is a major cause of tinnitus (ringing in the ears). All loud sounds should be avoided if possible, or people should use ear plugs or other devices to muffle them.

Aging. Loss of hearing is common among older people. In the United States, two-thirds of people over 65 years of age experience some loss of hearing. From 3 million to 6 million elderly Americans have hearing problems severe enough to seriously impair their ability to communicate. Hearing loss in old age, called presbycusis, may result from illness or exposure to loud noise earlier in life. Some hearing specialists believe aging may also cause changes in the auditory system or in the brain that reduce hearing ability.

Testing for hearing disorders is usually done by trained experts called audiologists. The audiologist shown here is using a device called an audiometer to test a child's hearing. From The World Book™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. World Book photo by Dan Miller.

Audiologists can also measure hearing ability without the conscious participation of the person being tested. They perform these tests by measuring alterations in brain waves and other bodily responses to sound. Such responses make it possible to test an infant's hearing. A child's hearing should be tested within a few days after birth if premature birth or some other condition suggests a possible loss of hearing. Many schools conduct hearing tests annually. Children found to have a hearing loss are referred to a clinic for complete testing.

Medical treatment. Physicians can restore hearing partially or completely in many cases of conductive hearing loss. Doctors use penicillin and other antibiotics to treat otitis media. In severe cases of this infection, a small incision is made in the eardrum to drain fluids that have collected in the middle ear.

Some conductive disorders are treated by surgery. For example, a ruptured eardrum can be repaired surgically. An operation called stapes mobilization can restore the ability of the middle ear to transmit sound in patients suffering from otosclerosis. This operation frees the stapes from the bony growth that has trapped it. In some cases, the surgeon completely removes the stapes and replaces it with an artificial device. Such an operation is called a stapedectomy.

Most sensorineural disorders cannot be treated medically because damage to the inner ear or auditory nerve is permanent. However, a surgical operation called a cochlear implant can be helpful in some cases that involve damage to the cochlea, the part of the inner ear that contains the organ of Corti. In this operation, the surgeon implants a device that converts sounds into electric signals. These signals are picked up by the auditory nerve and transmitted to the brain. Such an operation may enable a profoundly deaf person to hear sounds and understand some speech. However, many physicians believe that the risks and cost of cochlear implants may outweigh their benefits.

Special aids and communication techniques. Many hearing-impaired people use electronic hearing aids to amplify sound. A hearing aid works much like a telephone. It converts sound to electrical energy, amplifies the energy, and then changes the energy back into sound. Hearing aids work for people with conductive disorders, but these devices may have only limited value in cases of sensorineural impairment. Amplification alone cannot make speech understandable to most victims of sensorineural disorders, but it may provide some improvement in hearing. An audiologist can recommend the proper hearing aid for a patient.

Many people who use a hearing aid also use speechreading and manual communication to help them communicate. Speechreading involves watching the movements of the speaker's mouth. In manual communication, people communicate primarily with their hands. Some deaf people rely entirely on speechreading and manual communication because a hearing aid cannot help them.

Manual communication usually involves both finger spelling, in which each letter of the alphabet is represented by a different hand signal, and sign languages, in which hand signals stand for objects and ideas. The chief sign languages used in the United States are Signed English and American Sign Language (also called ASL). Deaf people use manual communication to converse with people who understand finger spelling and sign language. They also communicate by speaking and lip reading, or by writing. Some use a method called cued speech, in which hand signals and lip movements are combined to represent the sounds of spoken words. In addition, deaf people sometimes use professional interpreters who hear normally and know manual communication.

Some deaf people also use other aids in their daily lives. For example, the American Humane Association trains dogs to serve as "hearing ear dogs" for the deaf. These dogs alert their masters to specific sounds, such as alarms, doorbells, and a baby's crying. Deaf individuals can make and receive telephone calls by using a special device called a TT (Text Telephone) also known as TTY or TDD. A TT is connected to a telephone by a special adapter. Both the caller and the person receiving the call must have a TT. The message is typed in at the caller's TT and typed out at the TT on the receiving end.

In addition, as required by the Americans with Disabilities Act of 1990, relay services have been established throughout the country. Relay services enable a deaf person who is using a TT and a telephone to communicate with another person who is only using a telephone. The person placing the call telephones a relay service operator, who calls the other party. During the conversation, the operator relays the message word for word between the parties.

Deaf people can enjoy TV and motion pictures if captions (printed dialogue) appear on the screen. The U.S. government sponsors Captioned Films for the Deaf, an agency that captions popular films and distributes them to deaf people. The Federal Communications Commission (FCC) has ordered television stations to caption weather warnings and all other emergency bulletins. The FCC also reserves part of the TV signal for the broadcasting of captions. In 1980, many television stations in the United States began closed captioning some of their programs over this part of the signal. Canadian stations began closed captioning in 1981.

Education and training. Many deaf children receive their elementary and high school education in special schools or in classes that have teachers specially trained to instruct them. Hard-of-hearing children may attend special classes, or they may enroll in regular classes and obtain expert assistance when needed. Many deaf and hard-of-hearing children have been placed in classrooms with children that have normal hearing. This practice is called mainstreaming.

Two main methods of training deaf children to communicate are the oralist method and total communication. In the oralist method, children are taught to speak and to lip-read. In total communication, they learn manual communication as well as speech and lip reading.

Deaf children can learn manual communication more easily than they can learn to speak. Supporters of the oralist method claim that children who learn manual communication will rely on it and never develop their potential for speech. However, supporters of total communication believe that deaf children should learn every means of communication--and use the methods that best meet their individual needs.

Teaching deaf children to speak requires special techniques. Normal speech development depends on hearing speech, but deaf children must use sight and touch to learn to speak. They watch their teacher make a vocal sound. They also touch the teacher's face and throat to feel the vibrations and the flow of breath involved in making the sound. Then they try to produce the same vibrations and breath effects themselves.

After deaf students graduate from high school, they may attend regular universities or go to special institutions of higher education. Gallaudet University, in Washington, D.C., is the world's only liberal arts college for deaf people. National Technical Institute for the Deaf, in Rochester, N.Y., also accepts only deaf students.

Treatment of hearing loss and education of deaf students enable deaf people to lead fulfilling lives. Deaf people can do almost any kind of work. But some have difficulty finding jobs suited to their education and training. Such organizations as the Alexander Graham Bell Association for the Deaf, the Convention of American Instructors of the Deaf, and the National Association of the Deaf promote the education, training, and employment of deaf people.

Contributor: John B. Christiansen, Ph.D., Prof. of Sociology, Gallaudet Univ.

Related articles include:

Audiology; Bell, Alexander Graham; Ear; Hearing Aid.

Turkington, Carol, and Sussman, A. E. The Encyclopedia of Deafness and Hearing Disorders. Facts on File, 1992.

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