Features of across-frequency envelope coherence critical for comodulation masking release.

The masking release associated with coherent amplitude modulation of the masker is dependent on the degree of envelope coherence across frequency, with the largest masking release for stimuli with perfectly comodulated envelopes. Experiments described here tested the hypothesis that the effects of reducing envelope coherence depend on the unique envelope features of the on-signal masker as compared to the flanking maskers. Maskers were amplitude-modulated tones (Experiments 1 and 3) or amplitude-modulated bands of noise (Experiment 2), and the signal was a tone; across-frequency masker coherence was manipulated to assess the effects of introducing additional modulation minima in either the on-signal or flanking masker envelopes of otherwise coherently modulated maskers. In all three experiments, the detrimental effect of disrupted modulation coherence was more severe when additional modulation minima were introduced in the flanking as compared to on-signal masker envelopes. This was the case for both ipsilateral and contralateral flanking masker presentations, indicating that within-channel cues were not responsible for this finding. Results are consistent with the interpretation that the cue underlying comodulation masking release is based on dynamic spectral features of the stimulus, with transient spectral peaks at the signal frequency reflecting addition of a signal.