Co-modulation masking release: spectro-temporal pattern analysis in hearing

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 a sinusoidal signal in noise, it has traditionally been assumed that performance is based on the output of the single auditory filter which gives the highest signal-to-masker ratio. However, recent experiments demonstrate the ability to compare the outputs of different auditory filters to enhance signal detection. This enhancement takes place especially when the envelope of the masker fluctuates over time, and when the fluctuations are coherent or correlated across different frequency bands. This phenomenon is called comodulation masking release (CMR) and it demonstrates the ability of the auditory system to perform a highly flexible spectro-temporal pattern analysis. CMR appears to be reduced or absent in persons with cochlear hearing loss, and this may partly account for the difficulties experienced by these persons in understanding speech in noisy backgrounds.