Role of Peripheral Nonlinearities in Comodulation Masking Release

The detection of a signal in the presence of a masker at the signal frequency (on-frequency masker, OFM) is enhanced when one or more additional offfrequency maskers (flanking band, FB) are presented, but only if the FB and OFM are coherently modulated. This phenomenon, known as comodulation masking release (CMR), has been traditionally attributed to across-channel processing. However, it was also argued that part of the effect might be due to the processing within the auditory channel at the signal frequency. Withinchannel effects were usually discussed in relation to a possible excitatory interaction of FB, OFM and signal within the auditory filter at the signal frequency. However, the FB might also suppress the excitation evoked by the OFM (Oxenham and Plack 1998). Suppression can also be regarded as a within-channel cue, since it is an effect related to the nonlinear response of the auditory filter centred at the signal frequency (Ernst and Verhey 2005). The first two experiments of the present study investigated the role of suppression in CMR experiments with large spectral distances between OFM and FB. CMR was measured with various combinations of level and centre frequencies of OFM and FB. In order to determine the amount of CMR due to nonlinear properties of the basilar membrane, the data are simulated with a suppression model. The model is a modified version of the model proposed by Plack et al. (2002). They showed that a combination of the dual-resonance nonlinear (DRNL) filter (Meddis et al. 2001) and a temporal window (TW, e.g. Oxenham 2001) was able to describe two-tone suppression as observed in psychoacoustical experiments. In addition to the simulations with a within-channel model, an experiment is performed that was hypothesized to distinguish between withinchannel and across-channel processes in CMR experiments (Dau et al. 2005). Grose and Hall (1993) showed that onset asynchrony can abolish CMR. Dau et al. (2005) extended the experiment of Grose and Hall (1993) using different spectral distances between the OFM and the FBs. They