COCHLEAR MECHANICS AND NEURAL ENCODING

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The work proposed is intended to lead toward a comprehensive mathematical model for cochlear function that can include the effects of: 1) active and nonlinear cochlear mechanical phenomena; 2) spike-dependent recovery phenomena; and 3) depletion and other intra-cochlear adaptation phenomena. The cochlear mechanical modeling proposed would include both the active (but linear) mechanisms and the nonlinear (but passive) mechanisms, combined within a unified two-dimensional cochlea and middle ear model. Spike-dependent recovery effects would be studied using a Markov Chain model introduced by Gaumond, who showed that the probability of an auditory nerve spike discharge could be accurately represented as the product of a function of time since last spike only, multiplied by a function of stimulus only. Extensions to this work using stochastic point process concepts will provide improved methods for estimating the spike-dependent and stimulus-dependent factors affecting spike discharges. Experiments proposed would emphasize the study of auditory nerve discharges in the gerbil. Objectives of these studies would be: 1) to demonstrate for the gerbil the existence of propagating intermodulation distortion signals; 2) to evaluate the recovery-correction method of Gaumond for a large number of nerve fibers under a wide range of stimulus conditions; and 3) to obtain Excitation Function Estimates (EFE) under stimulus conditions intended to test the predictions of mechanical and transduction models. This work should help to provide a conceptual framework for the integration of experimental findings from direct as well as non-invasive studies of the cochlea. Improvements in our understanding of the mechanisms and the encoding function of the cochlea should help to provide a firmer basis for the characterization of peripheral auditory misfunction, and for the design of prosthetic devices and hearing aids. Development of new methods for nerve spike analysis, incidental to the primary objectives of this proposal, should prove valuable to other researchers of the auditory system and may also be applicable to studies of other parts of the nervous system.