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Using the sounds of hearing.

The human ear serves as both a detector and a generator of sound. Tiny hair cells in the inner ear convert incoming acoustic vibrations into nerve signals. But as the cells move in response to sound waves, they themselves produce faint sounds, which are known as otoacoustic emissions. By listening to these feeble signals, researchers can study in remarkable detail how the inner ear works. Now, detection of these emissions shows promise as a means of evaluating a wide range of common hearing problems involving damage to hair cells.

"It gives scientists a chance to listen to what's going on inside the ear," says Brenda Lonsbury-Martin of the University of Miami (Fla.) Ear Institute. The technique also makes it easy for hearing specialists and physicians to begin assessing hearing difficulties without having to ask anything of their patients. Such a test would be especially useful for screening infants and young children.

To detect otoacoustic emissions, researchers insert a miniature probe -- which looks somewhat like a hearing aid and contains a sound source and a sensitive microphone -- into the outer ear canal. The sound source generates either a click or a tone, and the microphone picks up the resulting ear-generated sound. In an ear with normal hearing, the faint output sound is nearly identical to the input sound.

"In damaged ears or in ears with hearing difficulties, we see a systematic degradation of this response," Lonsbury-Martin says. From such data, "the hope is that we'll be able to predict what the hearing level is and what the hearing problems are without having to ask the patient to try to describe the problem."

This type of test may prove particularly valuable because many hearing difficulties involve damage to hair cells. Such damage can be caused by exposure to prolonged or excessively loud noise, various drugs, and bacterial and viral infections. "These cells are very fragile, and they're very susceptible to all of the agents that damage hearing:' Lonsbury-Martin says. "'It just happens that what we listen to are these cells."
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Title Annotation:otoacoustic emissions used to evaluate hearing problems
Author:Peterson, Ivars
Publication:Science News
Article Type:Brief Article
Date:Feb 27, 1993
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