The relationship between quiet threshold and the forward-masking temporal effect.

Abstract

Research in our laboratory has shown that the temporal effect (TE) in simultaneous masking is consistent with a decrease in gain, possibly mediated by the medial olivocochlear reflex (MOCR). The TE in simultaneous masking is a decrease in threshold signal-to-masker ratio for a signal at masker onset when a precursor is added. This work has been extended to a forward-masking paradigm. A growth of masking (GOM) function is measured with a short-duration off-frequency masker (which should not activate the MOCR) and a 4-kHz signal. Then the masker level is fixed at a point on the lower leg of the GOM function, and threshold is measured with a long-duration precursor which is intended to activate the MOCR. The estimated input-output function is compared for a precursor at and well below the signal frequency. The difference in thresholds is the TE, which is also a measure of the change in gain. In simultaneous masking, the size of the TE decreases with increasing quiet threshold. In the present study, this relationship was examined for the forward-masking TE. The TE was measured as a function of precursor level for listeners who had a range of quiet thresholds, including listeners with mild cochlear hearing impairment. [Research supported by a grant from NIH(NIDCD) R01 DC008327.]