Self-suppression in a locally active nonlinear model of the cochlea: a quasilinear approach

Mechanical input-output functions of the cochlea for pure-tone stimuli are nonlinear for frequencies around the characteristic frequency. To simulate these functions, a long-wave model of the cochlea containing a saturating pressure generator (located at the site of the outer hair cells) is solved in the frequency domain with a quasilinear method. In this method distortion products in the basilar-membrane (BM) response are treated as perturbations and the nonlinear pressure waveform is approximated by the first-order Fourier component. Because the saturating pressure generator forms part of a feedback loop the solution of the model is achieved in a number of iteration steps. Model results show flattening of the BM response at higher input pressures; this property, called self-suppression, is due to saturation of the pressure generator. The resulting input-output functions display the main features of experimental curves. The third-order distortion product in the BM velocity is always more than 25 dB below the primary BM velocity and does not influence the results of the computation; this justifies the use of the quasilinear method.