Otoacoustic emissions (OAE) are inaudible sounds emitted by the cochlea when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate. The vibration produces an inaudible sound that echoes back into the middle ear. The sound can be measured with a small probe inserted into the ear canal. Persons with normal hearing produce emissions. Those with hearing loss greater than 25-30 dB do not.
An otoacoustic emission (OAE) is a sound which is generated from within the inner ear. Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.
Broadly speaking, there are two types of otoacoustic emissions: spontaneous otoacoustic emissions (SOAEs), which can occur without external stimulation, and evoked otoacoustic emissions (EOAEs), which require an evoking stimulus.OAEs are considered to be related to the amplification function of the cochlea. In the absence of external stimulation, the activity of the cochlear amplifier increases, leading to the production of sound. Several lines of evidence suggest that, in mammals, outer hair cells are the elements that enhance cochlear sensitivity and frequency selectivity and hence act as the energy sources for amplification. One theory is that they act to increase the discriminability of signal variations in continuous noise by lowering the masking effect of its cochlear ampliﬁcation.
Spontaneous otoacoustic emissions (SOAE)s are sounds that are emitted from the ear without external stimulation and are measurable with sensitive microphones in the external ear canal. At least one SOAE can be detected in app. 35-50% of the population. Evoked otoacoustic emissions are currently evoked using three different methodologies.