Intracochlear pressures resulting from brief high intensity stimuli

Abstract

A previous study has shown similar hearing loss and cochlear injury from exposures to impulses differing in peak pressure, but having the same energy and Fourier pressure spectrum. Nonlinear processes in the middle ear or transmission through the external and middle ear may render different stimuli more similar once they reach the cochlea, thus accounting for the equivalent injury observed. In order to explore this possibility, pressures in the basal turn of the cochleas of eight anesthetized chinchillas were measured for impulses presented at levels between 88‐and 147‐dB peak. This included the impulses used in the previous injury study. While nonlinearities were noted at the higher intensities, there was a remarkable preservation of the pressure‐time histories. In addition to these impulse stimuli, intracochlear pressures were measured using brief tone pips whose envelope was Gaussian. Frequencies of 700, 1375, 2000, 2700, and 4100 Hz were chosen to span the frequency response of the speaker. With these stimuli, nonlinearities appeared as both harmonic and subharmonic distortion as the intensities increased.