Modelling across–and within–channel mechanisms in comodulation masking release

The audibility of a target sound embedded in another masking sound can be improved by adding sound energy that is remote in frequency from both the masker and the target. This effect is known as comodulation masking release (CMR) [1] and is observed when the remote sound and the masker share coherent patterns of amplitude modulation. While a large body of data has been presented, the mechanisms underlying CMR are not clear. Neuronal suppression at a cochlear level, the detection of modulation beatings within auditory channels, and across-channel comparisons of temporal envelope information have been suggested to contribute to CMR. The present study extends an earlier model that includes an equalization-cancellation (EC) stage for the processing of modulations across the audio-frequency channels by a non-linear peripheral filtering stage. In the framework of the model, the combination and interaction of three main mechanisms were assessed: (i) suppression, (ii) within-auditory-channel cues related to amplitude modulations, and (iii) across-auditory-channel processes at higher, retro-cochlear stages. Experiments are presented to examine the relative role of these mechanisms. In particular, the influence of level and effects of auditory grouping on CMR were investigated.