Perceptual effects of fluctuating envelopes

Abstract

Signal/masker envelope fluctuations have important effects on detection and discrimination. Narrowband Gaussian noise (GN) forward maskers yield higher masked thresholds for detecting pure tones than do low-fluctuation noise (LFN) forward maskers. The increased residual masking is due to inherent fluctuations in the temporal envelope of GN producing listener uncertainty. This uncertainty persists for longer durations for hearing-impaired (HI) than for normal-hearing (NH) listeners. In addition to listener uncertainty, amplitude-modulation (AM) forward masking may contribute to masking that occurs in complex listening tasks. In a recent study of AM forward masking, an unmodulated GN masker yielded more masking than an unmodulated LFN, suggesting that inherent envelope fluctuations were responsible for the amount of AM forward masking measured across listener groups. Contrary to predictions, there were no differences in AM forward masking between NH and HI listeners, revealing little effect of hearing loss on recovery from AM forward masking for this task. Considering the combination of listener uncertainty and AM forward masking, the persistence of masker envelope fluctuation effects likely lead HI listeners to experience sluggish recovery from prior rapid envelope fluctuations compared to NH listeners. Together, these findings may have implications for speech understanding in modulated or interrupted conditions. [Support: NIH-DC008306.]