Model for cochlear echoes and tinnitus based on an observed electrical correlate.

Experiments in cat have revealed evidence of temporal correspondence between round-window recorded electrical potentials and delayed acoustical responses in the sealed ear canal at low sound levels. This would be difficult to explain if the acoustic response contained an appreciable component of delay due to a reverse travelling wave. An alternative interpretation is offered in which outer hair cells are assumed to undergo periodic volumetric changes correlated with their electrochemical activity. These volume changes would act on, and be divided between, the oval window, giving acoustic reemission and the basilar membrane, giving a secondary travelling wave. Owing to the active nature of the hair cell, the output is potentially greater than the input, so that when the secondary travelling wave exceeds the initial one, the amplitude will build up and continuous oscillation occurs, giving 'tinnitus'.