Abstract:
A model is proposed which provides a simple explanation for the noise-induced half-octave temporary threshold shift. The cochlear partition is modeled as a series of lightly coupled mechanical oscillators in which the outer hair cells are displacement responsive and the inner hair cells are velocity responsive. The outer hair cells are assumed to take an active role in providing negative damping in a region of stimulation of the cochlea at low-sound pressure levels. In the model, each oscillator is linear to very-high-sound-pressure levels except in a region of stimulation where the damping ratio varies with sound-pressure level. The model predicts that the passive viscous damping ratio of each oscillator is 1/[radical 2]. At low-sound-pressure levels negative structural damping reduces the total damping ratio to about 0.055. At high-sound-pressure levels negative damping ceases and the response in a region of high-level stimulation is then passive. The variable damping ratio provides an explanation for all cases of nonlinear cochlear response which have been investigated.