Comodulation masking release for regular and irregular modulators

The present study investigates whether the difference in comodulation masking release (CMR) for different modulator types is due to the different degrees of modulator regularity, as suggested in the literature, or results from different envelope distributions. Thresholds of a sinusoidal signal are measured in the presence of a noise masker which was either broadband or narrow band. A square-wave modulator with different degrees of regularity is used that preserves the envelope distribution. The measured CMR does not decrease as the regularity decreases. This finding argues against the hypothesis that the difference in CMR for different modulator types reported in the literature is due to differences in regularity. The data for the narrow-band conditions which either mimic the auditory frequency selectivity or preserve the modulation spectrum indicate that most of the CMR of the present study is due to within-channel cues. In agreement with this finding, within-channel models using either a peripheral nonlinearity or a modulation filterbank predict a CMR of a similar size. In contrast to the model predictions and the findings for the narrow-band conditions, the CMR for the broadband masker increases as the regularity decreases. This suggests that the CMR is not solely determined by the envelope distributions.