Abstract
Otoacoustic emissions are sounds produced by the inner ear. In humans, and other mammal species, all normal ears produce otoacoustic emissions in response to sound stimuli. Within the inner ear, a mechanism called the cochlear amplifier utilizes metabolic energy to enhance the sound-induced vibration of the basilar membrane. The enhanced basilar-membrane vibration forms the basis of normal hearing sensitivity. The operation of the cochlear amplifier is impaired by a variety of traumas, resulting in reduced basilar-membrane vibration and, thus, hearing loss. Impaired operation of the cochlear amplifier is associated with reduced or abolished otoacoustic emissions. Otoacoustic emissions and the action of the cochlear amplifier are both characterized by sharp frequency tuning and a high degree of nonlinearity. Thus, otoacoustic-emission generation is intimately related to the normal function of the cochlea, and appears to reflect the action of the cochlear amplifier. Otoacoustic emissions are in widespread use for the assessment of cochlear function in basic-science studies, and in clinical applications. Nevertheless, the cochlear processes underlying the enhancement of basilarmembrane motion and the generation of otoacoustic emissions are not well understood.
