Model for the Nonlinear Characteristics of Cochlear Potentials

Abstract

In an effort to clarify certain ideas about the nonlinear behavior of the cochlea, a simple nonlinear network was studied. The network was constructed to produce peak-clipping distortion similar to that seen in the cochlear microphonic (CM) of the basal turn of the cochlea. The interference between pairs of tones and the growth of combination tones as well as other manifestations of nonlinearity were similar for the ear and for the network. The degree of similarity between the output of the network and CM from the ear is shown by instantaneous waveforms and by input-output functions. An important finding of this paper is that the linearization effect of two-tone interference in the ear is a property of nonlinear systems, which occurs in the network also. The results also support recent theories that summating potential (SP) is produced by asymmetric nonlinearities in the ear.

Simple oscillator model of frequency dependence of cochlear two-tone suppression

“…This model is derived from the transmission line model so as to ignore the fluid coupling and reduce the system scale; it includes saturation feedback to reproduce the amplification, sharp tuning, and compressive nonlinearity. The saturation function has an important role in explaining the mechanics of 2TS [5,9,10]. Furthermore, it has been suggested that active OHC processes [22,23] that include a saturation property generate nonlinear dynamics in cochlear mechanics [8].…”

“…According to Refs. [9,10], suppression occurs via the saturation function. Therefore, in the simple oscillator model, the amount of feedback via the saturation function is reduced by the suppressor tone.…”

“…For tonic suppression, a saturation function approximated by a power series produces 2TS, where the output magnitude of one signal is suppressed when the input magnitude of another signal is increased [9,10]. The mathematical explanation of 2TS shows that the envelopes of the temporal responses to both the probe and suppressor tones are constant and do not depend on the input frequencies.…”

“…Thus, an AM signal is representative of phasic suppression in the BM. However, the 2TS mechanisms obtained from this transmission line model are more complicated than those obtained from the saturation function [5,9,10]. The reason for this is as follows.…”

Temporal aspects of suppression in distortion-product otoacoustic emissions

“…As stated earlier, these general trends are at least qualitatively similar to trends observed in both ANF and BM responses and support the use of DPOAEs to explore temporal aspects of suppression. Attempts to model suppression have found it difficult to simulate the frequency and level dependence asymmetry (e.g., Engebretson and Eldredge, 1968;Pfeiffer, 1970;Kim et al, 1973;Duifhuis, 1975;among others). The most successful models to date include a compressive nonlinearity of the BM, suggesting that the role of the OHCs is to compress the operating range of the cochlea into an optimum range for the IHCs (e.g., Neely and Kim, 1982;Zwicker, 1985;Yates et al, 1989;Geisler et al, 1990;among others).…”