Recovery time of the temporary threshold shift for delayed evoked otoacoustic emissions and tone bursts

The recovery time of temporary threshold shift after 1-kHz tone bursts delayed evoked otoacoustic emissions (DEOE) after the same stimulus were studied after auditory fatigue (AF) with a pure tone (0.75 kHz, 10 min, 95 dB HL) in 20 normal-hearing subjects aged 19-23 years. Close similarities were observed in the two experimental conditions. Since DEOE are transmitted to the outer ear via structures independent of the fibers of the afferent acoustic pathway and their synapses, it may be supposed that changes in the motile activity of the outer hair cells caused by AF could be partly responsible for their production and could constitute an active intracochlear mechanism taking part in this phenomenon. It may also be supposed that the effects of this active mechanism could be superimposed on those produced by a passive intracochlear mechanism consisting of the traveling wave induced in the basilar membrane by the perilymph owing to the movements of the stapes.