THE EFFECTS OF NOISE ON THE AUDITORY TRAN SDUCTION

The effects of noise on the auditory transduction and the temporary an d permanent threshold shifts (TTS and PTS) are reviewed in relation to the physiology, the morphology and the mechanics of the Corti's organ and especially of the outer hair cells. The modifications of the mech anical characteristics of the stereocilia: decrease of stiffness, shor tening of the rootlets, softening of the interciliary links... reduce the number of ionic channels which are opened during the mechanical ex citation of the Corti's organ. This reduction modifies greatly the beh avior of the <<cochlear amplifier>> which is located at the level of t he outer hair cells and is responsible for the auditory sensitivity at threshold and the frequency selectivity. Permanent damages to the ste reocilia of the hair cells following exposure to noise seem to be the main factor responsible for the apparition and the extent of the heari ng losses. The influence of several parameters: amplitude, duration, f requency..., on TTS and PTS are reviewed and the phenomenon of the hal f-octave shift is described.