“Otoacoustic emissions” are sounds that are produced by healthy ears in response to an external sound stimulation. First described by Kemp in 1978, normal hearing is regulated by a cochlear mechanism, present in the healthy outer hair cell, which magnifies the stimulus internally.

There are certain soft sounds, which a normal ear would produce in the response of the sounds which travel in. OAE or “Otoacoustic emission” testing is the recording of these emissions. Such echoes are not produced by a deaf ear.

Within the past 25 years, there has been going on lot of research in the field of ‘Audiology’, the identification of these emissions is also one of them.

When a sound enters the ear canal, it travels in a forward direction, vibrating the ear drum, ‘ossicular chain’, organ of ‘Corti’ and outer hair cells generating the OAE. The OAE travels in a reverse direction. A new study is conducted by Karl Grosh, a professor in the ‘U-M Departments of Mechanical Engineering and Biomedical Engineering’ in association with associate professor Tianying Ren.

During the experiment conducted in Ren’s lab, they found that contrary to the popular belief, these emissions don’t leave the air in the same fashion they entered.

Former scientists had concluded that as the sound wave travels in the ear, it leads to a backward-traveling wave going along the structure of the cochlea in the same way.

However this new study added that the sound waves coming out don’t simply flow along the basilar membrane of the cochlea, but travel through the inner ear fluid.

The inner ear structure called the cochlea is a snail-shell like structure which is divided in half by the basilar membrane, creating two chambers which are filled of a fluid. Both these chambers play a role in transmission of pressure and detecting the pressure impulses and thereby respond with electrical impulses which travel along the auditory nerve to the brain.

For this experiment, the interferometer was used, a device which is used to detect waves and sound evidence of forward moving waves, however there was no sign of backward moving ones. They devised a new method to pick up the tiniest vibration which could be thousand times smaller than an atom’s diameter.

Now they would develop new tools to shed more light on hear lose. New findings have given an understanding how these emissions are produced, giving a new insight to find out what wrong happens in a deaf ear.

Further identification of the disease or pathology that causes hearing loss and the treatment and the rehabilitation would gather a new direction with this study.

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