Comodulation Masking Release Over a Three Octave Range

Cohen [1] published the only study showing comodulation masking release (CMR) for very widely spaced masker components. In that study, thresholds for a fixed flanking band (FB) and a variable signal-centred band (SCB) were measured for various signal frequencies. CMR was quantified by calculating the difference between the thresholds for the comodulated and uncorrelated conditions (CMR(U-C)). Another method of computing CMR is to subtract the thresholds for the comodulated and reference conditions (SCB only); the result is the CMR(R-C). The present study extended the Cohen study for spectral distances of two and three octaves, quantifying the CMR(R-C) and across-channel masking (ACM), defined as the difference between the thresholds in the uncorrelated and reference conditions. Only level differences between FB and SCB were considered for which Cohen obtained a CMR(U-C) of more than 4 dB. The study confirmed the finding of CMR(U-C) over a three octave range. CMR(R-C) was the same as CMR(U-C) for this spectral distance between SCB and FB. ACM was only found over a two octave range. For this spectral distance the average threshold in the presence of the FB alone was 7 dB above threshold in quiet indicating some within-channel influence of the FB which may account for the ACM.