Peripheral and central aspects of auditory across-frequency processing

Many natural sounds such as, e.g., speech show common level fluctuations across frequency. It is generally assumed that the auditory system uses this spectro-temporal information to group the frequency components into auditory objects although the exact physiological mechanism is still not fully understood. The aim of the present study is to disentangle the relative contribution of peripheral and central aspects of this across-frequency processing using psychophysical experiments and modelling. The study focuses on two different psychophysical phenomena which are thought to be related to the ability to compare information across frequency: comodulation masking release (CMR), i.e., a release from masking of a sinusoidal signal due to the addition of a comodulated off-frequency masker component to the masker component at the signal frequency, and comodulation detection difference (CDD), i.e., the reduced ability of the auditory system to detect a masked signal if masker and signal share the same envelope. The comparison between model predictions and experimental results indicates that a considerable amount of these effects can be accounted for by peripheral processing alone. This is confirmed by experimental results with confounding across-frequency information about the grouping of the different frequencies into auditory objects.