A minimal physical model of cochlear mechanics: Insights into active nonlinear feedback

Abstract

The remarkable sensitivity, compressive nonlinearity, and frequency selectivity of the mammalian cochlea arise from an active process that amplifies the passive mechanical response of the basilar membrane. Outer hair cells are widely regarded as the primary effectors of this active process in the basal regions of the cochlea. This active contribution progressively decreases with increasing stimulus level. Motivated by these observations, a minimal cochlear model is investigated in which each location is represented by a forced damped oscillator with an exponential displacement-dependent active feedback. The oscillators are coupled through the cochlear fluid and also by elastic and dissipative longitudinal interactions to form a one-dimensional distributed model. The model reproduces key features of cochlear mechanics, including level-dependent amplification, compressive nonlinearity, frequency selectivity, traveling-wave propagation, and phase accumulation. Comparison with a simplified cubic nonlinear model has been carried out. Even though the cubic nonlinearity describes the response for weak stimuli, at higher stimulus levels it deviates from the exponential model and fails to reproduce the gradual transition towards predominantly passive behavior. Longitudinal coupling broadens the frequency response, modifies the traveling wave profile, and increases phase accumulation. The proposed model provides a simple physical framework for understanding how local active processes and longitudinal mechanical interactions together shape the nonlinear response of the cochlea.