Two-tone suppression in a locally active nonlinear model of the cochlea.

In auditory nerve, inner-hair cell and basilar-membrane responses, it has been found that the response to one tone can be suppressed by another tone. This phenomenon, called two-tone suppression, is examined on the level of the basilar membrane with a locally active long-wave model of the cochlea in which the active mechanism is nonlinear. The model is solved in the frequency domain by means of a quasi-linear solution method. Several phenomena, such as difference in growth of suppression for low-side and high-side suppressors and critical dependence of the phase of the probe response on suppressor parameters, have been replicated. The attenuation hypothesis which states that the presence of a suppressor has the same effect on the probe response as attenuation of probe level is shown to be insufficient in explaining the experimental data. This model, in which suppression is simply reduction of power amplification due to saturation of the active mechanism, is more successful in this respect.