Laser Interferometer Study Of Pitch Information Expression In Cochlear Basilar Membrane Vibration

The nature of pitch has been studied for over a thousand years.Problems of pitch extraction and pitch encoding have always been hot topics in hearing researches.How cochlea and auditory nerve cooperate to process pitch information,whether pitch is encoded in cochlea via place cues or in auditory nerve via timing cues and whether pitch is coded in terms of frequency or timing envelope are still unbeknown.Recently,some theoretical results from nonlinear dynamics suggest that cochlea may play a role in pitch extraction and encoding process.Pitch-shifting phenomena was investigated at the level of basilar membrane in the apical region of active guinea pig cochlea using a heterodyne interferometer system.This system's high resolution and good linearity allowed measurements to be performed in the cochlea region and us to discuss nonlinear effects on auditory periphery.Responses to the stimulus tones whose frequencies were designed above or below the characteristic frequency(CF)of probe section on the basilar membrane were recorded and analyzed in time domain.Several pitch-shifting lines were depicted and succeed in showing the second pitch-shifting effects.However,their shift patterns will change with the frequency of stimulus sounds.It is different from the discovery of the psychoacoustics experiments.An inverse shifting trend appears when the frequencies of stimuli below the CF of the probe point.These findings indicate that cochlea may participate in pitch analyzing and pitch perception process which are related to cochlea location.