Earful of noise

Earful of noise DON'T turn a deaf ear if someone told you that ears not only receive sounds but also produce them. Now, a team of scientists led by Nicholas L Powers at the Hearing Research Laboratory in Stat.e University of New York, USA, has confirmed that the inner ear sometimes acts as a strong sound generator (Nature, Vo1375, No 6532).

These sounds -called spontaneous otoacoustic emissions -are found to be continuously generated within the ear and can sometimes be transmitted into the external environment. Interestingly, most individuals are unaware of the"soundgenerated within their ears; even though the emissions can be strong enough to be heard by other individuals standing nearby.

Powers and colleagues detected intense spontaneous sound emissions between 4 and 5 KHZ in the ear canal of Chinchilla laniger, a rodent. The fact that spontaneous emissions could be suppressed by external noise within a narrow frequency range suggests that these sound waves originated from a narrow region of the cochlea, the inner ear.

hearing ability of mammals. Resear- chers demonstrated that high intensity emissions vigorously activate the nerve fibres in the ear of C laniger. As a result, a 'line busy' signal is created which sig- nificantly degrades a neuron's ability to respond to sound, resulting in a loss of hearing.

Apparently, this hearing impair- ment due to inner 'biological noise' is distinctly different from the more usual kind caused by sensory cell destruction. While external noise pollution can be tackled by various preventive measures, the question looms large -how can inner biological noise be stopped from damaging the ear?

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