Signal threshold as a function of the relative modulation depth between on-frequency and flanking masker components

It is apparent that the mechanism underlying comodulation masking release (CMR) relies on the existence of temporal fluctuations in the masker envelope. This raises the question of how much fluctuation is necessary to facilitate CMR. The present experiment addresses this question by measuring psychometric functions relating signal threshold to depth of flanker band modulation using sinusoidally amplitude-modulated pure tones as masker components. In the first set of conditions, the on-frequency component had a constant modulation depth of 100%, while the depth of the flanking components was varied between 100% and 0%. As expected, signal threshold improved monotonically as depth of flanker band modulation increased. In the second set of conditions, the on-frequency component had a constant modulation depth of 63%, while the depth of the flanking components was either 100%, 63%, or 0%. Results to date suggest that signal threshold is lowest when the flanking components have the same depth of modulation as the on-frequency component. [Research supported by AFOSR.]