Two-tone suppression in a cochlear model

Two-tone rate suppression is a nonlinear property of the cochlea in which the total neural firing rate in the region most sensitive to a probe tone is reduced by the addition of a second (suppressor) tone at a different frequency. A cochlear model featuring a cascade of adaptive-Q filter sections was investigated to determine its ability to reproduce two-tone suppression. It was found that the adaptive-Q filter sections are adequate to reproduce two-tone suppression when the suppressor is located higher in frequency than the probe tone but are not adequate to reproduce suppression for a suppressor lower in frequency than the probe. A modification to the cochlear model, in which the output signal level is adjusted in response to the estimated peak signal levels in the regions of the cochlear filter tip and tail, was much more accurate in reproducing two-tone suppression behavior. A speech example is also presented, and the implications of two-tone suppression in applications of the cochlear model are discussed