Mechanisms of within- and across- channel processing 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) and is observed when the remote sound and the masker share coherent patterns of amplitude modulation. Most ecologically relevant sounds, such as speech and animal vocalizations, have coherent amplitude modulation patterns across different frequency regions, suggesting that the detection and recognition advantages conveyed by such coherent modulations may play a fundamental role in our ability to deal with natural complex acoustic environments. While a large body of data has been presented, the mechanisms underlying CMR are not clear. This study proposes an auditory processing model that accounts for various aspects of CMR. The model includes an equalization-cancellation (EC) stage for the processing of stimulus information across the audio-frequency axis. The EC process, which is conceptually similar to the across-ear processing in binaural models, is assumed in the model to take place at the output of a modulation filterbank stage for each audio-frequency channel. This approach has been proven successful in several basic conditions of CMR (Piechowiak et al., 2007). In the present study, a modified version of the model is tested that includes a non-linear cochlear filtering stage, the dual resonance nonlinear filterbank (DRNL). It is investigated to what extent the within and across-frequency processes contributing to CMR depend on cochlear nonlinear processing.