Across-channel processes in auditory masking

The peripheral auditory system is often modelled as containing an array of bandpass filters (called the auditory filters), each tuned to a different centre frequency. When a subject tries to detect, or discriminate changes in, a narrowband signal in noise, it has traditionally been assumed that performance is based on the output of the single audi toryfilter which gives the highest signal-to-masker ratio. However, recent experi mentsdemonstrate that outputs from other filters, tuned to frequencies remote from the signal frequency, can both enhance and degrade signal detection and discrimination. The enhancement takes place especially when the envelope of the masker fluctuates over time, and when the fluctuations are correlated across different frequency bands. This phenomenon is called comodulation masking release (CMR). In other situations, frequency components remote from the frequency of a signal may impair the discrimina tionof changes in that signal, especially changes in the modulation of the signal. This has been called modulation detection interference or modulation discrimination inter ference (MDI). Both CMR and MDI may depend partly on basic processes of audi torygrouping that are involved in assigning elements of complex sounds to perceptual streams. However, other processes are probably involved.