Distortion product emissions from a cochlear model with nonlinear mechanoelectrical transduction in outer hair cells

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A model of cochlear mechanics is described in which force-producing outer hair cells (OHC) are embedded in a passive cochlear partition. The OHC mechanoelectrical transduction current is nonlinearly modulated by reticular-lamina (RL) motion, and the resulting change in OHC membrane voltage produces contraction between the RL and the basilar membrane (BM). Model parameters were chosen to produce a tonotopic map typical of a human cochlea. Time-domain simulations showed compressive BM displacement responses typical of mammalian cochleae. Distortion product (DP) otoacoustic emissions at 2f(1)-f(2) are plotted as isolevel contours against primary levels (L(1),L(2)) for various primary frequencies f(1) and f(2) (f(1)<f(2)). The L(1) at which the DP reaches its maximum level increases as L(2) increases, and the slope of the "optimal" linear path decreases as f(2)/f(1) increases. When primary levels and f(2) are fixed, DP level is band passed against f(1). In the presence of a suppressor, DP level generally decreases as suppressor level increases and as suppressor frequency gets closer to f(2); however, there are exceptions. These results, being similar to data from human ears, suggest that the model could be used for testing hypotheses regarding DP generation and propagation in human cochleae.