2-TONE SUPPRESSION OF BASILAR-MEMBRANE VIBRATIONS IN THE BASE OF THE GUINEA-PIG COCHLEA USING LOW-SIDE SUPPRESSORS

The responses of the basilar membrane (BM) in the basal section of the guinea pig cochlea were measured by laser interferometry, The stimuli were pairs of harmonically related tones, presented simultaneously. O ne tone, at the BM's characteristic frequency (CF) of about 17 kHz, wa s presented at a low intensity. The other tone, presented at various i ntensities, was a ''low-side'' suppressor, with a frequency of 0.2-8 k Hz. As observed by many others, the suppressor tone, when presented at high enough intensity, reduced the magnitude of the CF component of B M displacement, sometimes dramatically. However, regardless of whether the CF component was suppressed or not, the sum of the displacement a mplitudes of the CF and suppressor components was always greater than the displacement amplitude of the unsuppressed CF component. For suppr essor frequencies up to 4 kHz, the suppression was both tonic and phas ic, and synchronized to the suppressor period. For higher suppressor f requencies, principally tonic suppression was seen. (C) 1997 Acoustica l Society of America.