The effects of preceding sound on three measures related to gain reduction

Abstract

The medial olivocochlear reflex (MOCR) decreases the gain of the cochlear active process in response to sound. We have used psychoacoustic techniques to show behavioral effects of gain reduction, which could be consistent with the MOCR. We have used forward masking paradigms understood to measure frequency selectivity and the input/output function at the level of the cochlea using stimuli (masker and signal) that should be too short to evoke the MOCR. A precursor sound is then presented before these stimuli to evoke the MOCR. In previous studies, we have shown that a precursor: (1) increases signal threshold more after an off-frequency masker than the on-frequency one for forward maskers matched in effectiveness to increase signal threshold to 5 dB SL, (2) may increase on-frequency masker threshold required to mask a signal of 15-20 dB SL, and (3) may decrease suppression in forward masking. All of these effects would be consistent with a reduction in gain by the precursor, possibly by the MOCR. In the current study, these effects are all measured within the same listeners, using a more effective precursor than has been used in previous studies. The relationship between the measures will be discussed.