The ear is both a receiver and transmitter of sound. We know that the ear receives sound - it is how we hear. The fact that the ear makes sound is less well known, being first discovered in the mid 1970s. These sounds are seldom audible but can be measured with a microphone placed in the ear canal. Of particular interest is that when you send a sound into the ear a sound comes back that is generated within the inner ear. This generation of sound is related to the mechanism by which the inner ear processes sound.
A common type of hearing loss involves impairment of the way the inner ear processes sound (for example, hearing loss due to aging). And this type of hearing loss means reduced or absent sound coming back out of the ear. These oto-acoustic (ear sounds) emissions, if measured, provide diagnostic information on the way the ear processes sound. In the audiology clinic, an otoacoustic emission test is part of a battery of tests that can be used to assess the type and degree of hearing loss.