THE EFFECTS ON COMODULATION MASKING RELEASE OF SYSTEMATIC VARIATIONS IN ON-FREQUENCY AND OFF-FREQUENCY MASKER MODULATION PATTERNS

Detection thresholds were obtained for a 500-Hz tone added to a masker comprised of an amplitude-modulated tone centered at the signal frequ ency (on-frequency masker) and an array of amplitude modulated tones c entered at 300, 700, 800, 900, 1000, and 1100 Hz (off-frequency masker s). The shapes of the amplitude modulation patterns of the on- and off -frequency maskers were either matched or mismatched. In the shape-mat ched conditions the on- and off-frequency masker modulation patterns w ere the same, either sinusoidally or square-wave amplitude modulated. In the shape-mismatched conditions, the on-frequency masker was sinuso idaly amplitude modulated and the off-frequency maskers were square-wa ve amplitude modulated. The rate of modulation was either 10 or 20 Hz, and the duty cycle of square-wave modulation was systematically varie d. The relative phases of the on- and off-frequency modulators were ei ther in-phase, out-of-phase, or random-phase. Comodulation masking rel ease (CMR) was defined as the difference between thresholds in the in- phase and random-phase conditions. CMRs as large as 12 dB were obtaine d for the shape-matched as well as the shape-mismatched conditions. Th resholds in the out-of-phase condition were on average 2.6 dB higher t han those in the random-phase condition. Results are consistent with a cued listening model where off-frequency modulation minima trigger sa mpling at the output of the auditory filter centered on the signal fre quency. (C) 1996 Acoustical Society of America.