Basilar Membrane Responses to Simultaneous Presentations of White Noise and a Single Tone

Abstract

One of the fundamental problems in auditory physiology and psychophysics is the detection of tones in noise. In spite of its importance, little is known about its mechanical basis, namely the response of the basilar membrane (BM) to the simultaneous presentation of broadband noise and a pure tone. BM responses to simultaneous presentations of white noise and a single tone were recorded at the base of the chinchilla cochlea using a displacement-sensitive heterodyne laser interferometer. The characteristic frequency (CF) of this region was in the 8-10 kHz range. Fourier analysis showed that the response of the BM to a single tone whose frequency is near or at CF decreases in proportion to the level of the white noise stimulus. Mechanical suppression was larger for softer single tones than for louder ones. Suppression also depended on the tone frequency, being less pronounced as the frequency of the stimulus was set away from CF. In fact, suppression of tones whose frequency was more than 0.5 octaves away from CF - in the linear region of the cochlea - was nonexistent. The results of these experiments were modeled using a nonlinear model of the human cochlea. Suppression in this model was similar to the one observed in our experiments.