The effects on comodulation masking release of systemic variations in on- and off-frequency masker modulation...

Detection thresholds were obtained for a 500-Hz tone 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 shapes of the amplitude modulation patterns of the on- and off-frequency maskers were either matched or mismatched. In the shape-matched conditions the on- and off-frequency masker modulation patterns were the same, either sinusoidally or square-wave amplitude modulated. In the shape-mismatched conditions, the on-frequency masker was sinusoidally amplitude modulated and the off-frequency maskers were square-wave amplitude modulated. The rate of modulation was either 10 or 20 Hz, and the duty cycle of square-wave modulation was systemically varied. The relative phases of the on- and off-frequency modulators were either in-phase, out-of-phase, or random-phase. Comodulation masking release (CMR) was defined as the difference between thresholds in the in-phase and random-phase conditions. CMRs as large as 12 dB were obtained for the shape-matched as well as the shape-mismatched conditions. Thresholds in the out-of-phase condition were on average 2.6 dB higher than those in the random-phase condition. Results are consistent with a cued listening model where off-frequency modulation minima trigger sampling at the output of the auditory filter centered on the signal frequency.