INTENSITY-DEPENDENT PEAK SHIFT IN COCHLEAR TRANSFER-FUNCTIONS AT THE CELLULAR-LEVEL, ITS ELIMINATION BY SOUND EXPOSURE, AND ITS POSSIBLE UNDERLYING MECHANISMS

Our systematic study of cochlear transfer functions has confirmed earl ier results that, in a normal cochlea, the cochlear AC responses at an y given cochlear location do not have a fixed best frequency at which the response is maximal. The best frequency depends on sound intensity , shifting to lower frequencies as the intensity is increased. This ph enomenon may account for the so called 'half-octave shift' of maximum cochlear damage relative to the frequency of the damaging sound observ ed in studies of auditory noise exposure. Our experimental results com bined with the results of others and with our model studies bring us t o the conclusion that, at Low to moderate sound intensities, the depen dence of the best frequency on sound intensity is due to an effect of the active feedback, which decreases as sound intensity increases. Con sequently, the feedback, when present, must shift the best frequency u pward.