Temporal factors and suppression effects in backward and forward masking

Abstract

The signal was a brief 10 ms 2-kHz sinusoid. The masker was a narrow band of noise of 40 dB spectrum level, 200 Hz wide, centered at the signal frequency. In some conditions, the presence of a 2nd band of noise of the same spectral level in the region of 2300-3700 Hz appeared to suppress the effects of the masker. Changes in the amount of suppression were examined as functions of the delay and duration of the suppressor. Adding the suppressor during the 50 ms interval nearest the signal produced changes in the signal threshold that were similar to those produced by reducing the level of the masker during this interval for both backward and forward masking. The operation of human peripheral processes common to both backward and forward masking was discussed. If the duration of the suppressor was increased beyond this 50 ms interval there was no effect on forward masking, but large additional reductions in backward masking. The operation of additional central processes in backward masking was discussed. For some observers, these additional processes appeared to operate over fairly long periods of time (250-500 ms). Such long durations were inconsistent with the estimates of integration time (.ltoreq. 200 ms) obtained for these same observers.