Modulation masking: effects of modulation frequency, depth, and phase

Modulation thresholds were measured for a sinusoidally amplitude-modulated (SAM) broadband noise in the presence of a SAM broadband background noise with a modulation depth (mm) of 0.00, 0.25, or 0.50, where the condition mm = 0.00 corresponds to standard (unmasked) modulation detection. The modulation frequency of the masker was 4, 16, or 64 Hz; the modulation frequency of the signal ranged from 2-512 Hz. The greatest amount of modulation masking (masked threshold minus unmasked threshold) typically occurred when the signal frequency was near the masker frequency. The modulation masking patterns (amount of modulation masking versus signal frequency) for the 4-Hz masker were low pass, whereas the patterns for the 16- and 64-Hz maskers were somewhat bandpass (although not strictly so). In general, the greater the modulation depth of the masker, the greater the amount of modulation masking (although this trend was reversed for the 4-Hz masker at high signal frequencies). These modulation-masking data suggest that there are channels in the auditory system which are tuned for the detection of modulation frequency, much like there are channels (critical bands or auditory filters) tuned for the detection of spectral frequency.