Further analysis of behavioral measures of cochlear gain and gain reduction in listeners with normal hearing or minimal cochlear hearing loss

Abstract

This is a continuation of a study examining the relationship between cochlear hearing loss and psychoacoustic measures thought to be related to a cochlear function. In the listeners tested, audiometric thresholds for long tones ranged from well within the clinically normal range to just outside this range. Where thresholds were elevated, other clinical tests were consistent with a cochlear origin. Because the medial olivocochlear reflex decreases cochlear gain in response to sound, when possible, measures were made with short stimuli. Signal frequencies were from 1 to 8 kHz. One point on the lower leg of the input/output function was measured by finding threshold masker level for a masker almost one octave below the signal frequency needed to mask a signal at 5 dB SL. Gain reduction was estimated by presenting a pink broadband noise (BBN) precursor before the signal and masker and measuring the change in signal threshold as a function of the precursor level. Previous studies with listeners with normal hearing have shown that gain reduction begins at a low precursor level and grows compressively as the precursor level is increased. The current study is designed to determine whether this pattern changes when cochlear gain is permanently reduced. [Work supported by NIH(NIDCD)R01 DC008327 (EAS), the Purdue Office of the Executive Vice President for Research, and the Purdue Graduate School (WBS).]