Ruth Wilson, age 13, of Dotham, Ala., for her question:

WHAT CAUSES DEAFNESS?

Deafness is an inability to hear. This condition affects all age groups and its consequences range from minor to severe. About 16 million citizens in the United States have impaired hearing. Deafness is caused by a number of different conditions.

Four types of hearing loss may be described. The first, conductive hearing loss, is caused by diseases or obstructions in the outer or middle ear and usually can be helped by a hearing aid. Often conductive hearing losses can also be corrected through surgical or medical treatment.

The second kind of deafness, sensorineural hearing loss, results from damage to the sensory hair cells or the nerves of the inner ear and can range in severity from mild to profound deafness. Such loss occurs in certain sound frequencies more than in others, resulting in distorted sound perceptions even when the sound level is amplified. A hearing aid may not help a person with a sensorineural loss.

The third kind, mixed hearing loss, is caused by problems in both the outer or middle ear and the inner ear.

The fourth type of hearing loss, central hearing loss, is the result of damage to or impairment of the nerves or nuclei of the central nervous system.

Deafness in general can be caused by illness or accident, or it may be inherited. Continuous or frequent exposure to noise levels above 85 decibels can cause a progressive and eventually severe sensorineural hearing loss.

Until the Middle Ages, most people believed that deaf persons were incapable of learning language or of being educated in any way. By the 16th Century, however, a few educators began to reconsider the condition of deaf persons. By the 18th Century, special schools were established for deaf children.

Back in the 18th Century an educational problem developed that exists to this day. It is whether deaf children should be educated by oral (lip reading and speech) or manual (sign and finger spelling) methods.

Deafness does not affect a person's intellectual capacity or ability to learn. A child who sustains a hearing loss early in life, however, lacks the language stimulation experienced by children who can hear. Because of this delay in learning language, a deaf child's academic progress is often slower than that of hearing children.

The academic lag tends to be cumulative, so that a deaf adolescent may be four or more grade levels behind his or her hearing peers.

Increasingly, the philosophy of total communication is being used in schools and classes for deaf children. This philosophy encourages the combined use of whatever communication methods are appropriate to deaf children, including speech, lip reading, American sign Language, Manually Coded English, Cured Speech, finger spelling, art, electronic media, mime, gesture and reading and writing