A dual filter model describing single-fiber responses to clicks in the normal and noise-damaged cochlea

This paper presents a composite model of the normal and noise-damaged guinea pig cochlea. The model incorporates a phenomenologically defined cochlear filter, and physiological descriptions of inner hair cell transduction, synaptic adaptation, and spike generation. The latter three model sections were taken from recent literature. The paper first deals with validation and evaluation of the model and adaptation of the relevant parameters to the guinea pig. Then the model is applied to explore to what extent changes in the cochlear filter can be held responsible for abnormal responses to clicks that were recorded in single auditory nerve fibers in noise-damaged animals. Focus is on those fibers in which the tip-to-tail sensitivity ratio of the frequency threshold curve (FTC) has decreased and/or in which the FTC tail has become hypersensitive. Inspired by this type of W-shaped FTC the mechanical response of the basilar membrane is phenomenologically modeled by two parallel filters, one responsible for the tip of the FTC, the other for its tail. Model simulations show that most abnormal temporal response properties can be explained by pathological alterations in the mechanical response. Residual discrepancies between model and experiment are identified which presumably point to pathological changes in other stages of cochlear processing.