Stanley Sheft
William A. Yost
Parmly Hear. Inst., Loyola Univ. Chicago, 6525 N. Sheridan Rd., Chicago, IL 60626
Thresholds were measured for detecting amplitude modulation (AM) of a gated wideband noise signal that was either immediately preceded or followed by a modulated noise masker. The signal AM rate was 2.5, 5, 10, or 20 Hz and the masker AM rate ranged from 2.5 to 40 Hz. Signal duration was 200 or 400 ms and masker duration was 400 ms. The maximum elevation in signal AM detection thresholds due to the presence of masker modulation ranged across subjects from roughly 4 to 10 dB with the amount of masking generally greatest when the signal and masker AM rates were either close or the same. The extent of tuning in the modulation domain was broad in both the forward and backward masking conditions. When not modulated, the masker can be viewed as a fringe of the signal carrier. Separate conditions evaluated the effects of carrier fringes on signal AM detection. At low AM rates, the addition of either the forward or backward fringe benefitted AM detection. These results suggest that the decrement in low-rate AM detection due to carrier gating is not solely attributable to the neural onset response and short-term adaptation. [Work supported by NIH and NSF.]