ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3aPP6. The effects on comodulation masking release (CMR) of systematic variations in on- and off-frequency masker modulation patterns.

Emily Buss

Virginia M. Richards

Dept. of Psych., Univ. of Pennsylvania, Philadelphia, PA 19104

Detection thresholds were obtained for a 500-Hz tone signal added to a masker comprised of an amplitude modulated tone centered at the signal frequency (on-frequency masker) and an array of amplitude modulated tones centered at 300, 700, 800, 900, 1000, and 1100 Hz (off-frequency maskers). The on-frequency masker was a sinusoidally amplitude modulated tone, and the off-frequency maskers were square-wave modulated tones. On- and off-frequency modulators were either in-phase or of random phase relative to one another, and different conditions used square wave modulators with different duty cycles (0%--100%). The difference between thresholds obtained in the in-phase and random phase conditions (CMRs) were as large as 12 dB, comparable to the CMRs found with perfectly matched modulators. Thresholds in the random phase condition did not depend on duty cycle, but for the in-phase condition the plot of thresholds as a function of duty cycle is ``U'' shaped. The data are in rough agreement with ``cued-listening'' models of CMR in which the detection of the added tone is enhanced by the cue provided by the off-frequency masker minima. [Work supported by NIH.]