BASILAR-MEMBRANE RESPONSES TO TONES AT THE BASE OF THE CHINCHILLA COCHLEA

Basilar-membrane responses to single tones were measured, using laser velocimetry, at a site of the chinchilla cochlea located 3.5 mm from i ts basal end. Responses to low-level (<10-20 dB SPL) characteristic-fr equency (CF) tones (9-10 kHz) grow linearly with stimulus intensity an d exhibit gains of 66-76 dB relative to stapes motion. At higher level s, CF responses grow monotonically at compressive rates, with input-ou tput slopes as low as 0.2 dB/dB in the intensity range 40-80 dB. Compr essive growth, which is significantly correlated with response sensiti vity, is evident even at stimulus levels higher than 100 dB. Responses become rapidly linear as stimulus frequency departs from CF. As a res ult, at stimulus levels >80 dB the largest responses are elicited by t ones with frequency about 0.4-0.5 octave below CF. For stimulus freque ncies well above CF, responses stop decreasing with increasing frequen cy: A plateau is reached. The compressive growth of responses with fre quency near CF is accompanied by intensity-dependent phase shifts. Dea th abolishes all nonlinearities, reduces sensitivity at CF by as much as 60-81 dB, and causes a relative phase lead at CF. (C) 1997 Acoustic al Society of America.