Effect of duration on amplitude-modulation masking (L)

Detection thresholds for a signal sinusoidal amplitude modulation (SAM) were measured in the presence of an additional, masking SAM. Signal and masker modulations were applied synchronously to a gated white noise carrier. The masker modulation frequency was fixed at 16 Hz and the signal modulation frequency ranged from 2 to 256 Hz. Modulation masking patterns were measured in three listeners for stimulus durations of 500, 1000, and 2000 ms. The results showed that modulation masking was reduced or abolished at signal modulation frequencies of 2, 14, and 18 Hz when stimulus duration was increased from 500 to 2000 ms. The effect at 2 Hz suggests that fringe effects in modulation masking previously reported by Bacon and Grantham [S. P. Bacon and D. W. Grantham, J. Acoust. Soc. Am. 91, 3451-3455 (1992)] were at least partly due to an increase in masker modulation duration. The reduction in modulation masking observed at signal modulation frequencies of 14 and 18 Hz was similar to that at 2 Hz, suggesting that listeners use a low-frequency temporal envelope beat cue (in this case at 2 Hz) when the distance between the signal and masker modulations is small. (C) 2002 Acoustical Society of America.