Psychometric functions for sentence recognition in sinusoidally amplitude-modulated noises.

Listeners' speech reception is better when speech is masked by a modulated masker compared to an unmodulated masker with the same long-term root-mean-square level. It has been suggested that listeners take advantage of brief periods of quiescence in a modulated masker to extract speech information. Two experiments examined the contribution of such "dip-listening" models. The first experiment estimated psychometric functions for speech intelligibility using sentences masked by sinusoidally modulated and unmodulated speech-shaped noises and the second experiment estimated detection thresholds for a tone pip added at the central dip in the masker. Modulation rates ranging from 1 to 64 Hz were tested. In experiment 1 the slopes of the psychometric functions were shallower for lower modulation rates and the pattern of speech reception thresholds as a function of modulation rate was nonmonotonic with a minimum near 16 Hz. In contrast, the detection thresholds from experiment 2 increased monotonically with modulation rate. The results suggest that the benefits of listening to speech in temporally fluctuating maskers cannot be solely ascribed to the temporal acuity of the auditory system.