ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pPP14. Stimulus-driven, time-varying weights for comodulation masking release.

Commun. and Digital Signal Processing Center, Dept. of Elec. and Comput. Eng., 409 DA, Northeastern Univ., 360 Huntington Ave., Boston, MA 02115-5096

Lei Ji Zhang

Mary Florentine

Northeastern Univ., Boston, MA 02115

This study tests the hypothesis that CMR is mediated by ``listening in the valleys'' [S. Buus, 1958--1965 (1985)]. Detectability was measured for signals consisting of 6 consecutive 25-ms, 1-kHz tone bursts presented in a 50-Hz wide masker or in maskers consisting of seven 50-Hz wide noises, one critical band apart, with either correlated or uncorrelated envelopes. Each burst varied randomly around masked threshold according to Gaussian distributions with 3- or 6-dB standard deviations. For each listener and condition, the responses from 5000 trials were sorted to construct conditional psychometric functions for d' as a function of burst energy for 10 ranges of short-term level of the on-frequency masker band during the burst. The slopes of these functions for three normal listeners decrease markedly with increasing short-term masker level for the correlated multiband masker, but are largely constant for the other maskers. This indicates that the weight applied to the signal channel is high when the masker level is low and vice versa for the correlated masker, but is approximately constant for single-band and uncorrelated mutliband maskers. This finding provides direct evidence that CMR is mediated by ``listening in the valleys.'' [Work supported by NIH-NIDCD R01DC00187.]