Phase effects in simultaneous and forward masking

Abstract

We estimated masked thresholds for a 20-ms (two 10-ms ramps), 1-kHz sinusoid as a function of its temporal relation to a 400-ms, 1-kHz sinusoid in the transition from simultaneous to forward masking conditions (signal center minus masker offset times of −200, −20, −10, −3.75, −2.40, −1.25, 0.00, 1.25, 2.40, 3.75, 10, and 20 ms). In simultaneous masking conditions, thresholds for signals presented in phase with the masker were lower than for signals added in quadrature, but there was no such phase effect in forward masking conditions. When there was partial overlap of signal and masker, the phase effect was apparent until +3.75-ms center-offset time, where the phase effect disappeared and thresholds decreased. Thresholds for just the portions of the 20-ms signal that occurred during the masker (simultaneous partial signals) and for the portions of the 20-ms signals after the masker (forward partial signals), generally were consistent with results for whole (20-ms) signals: when thresholds for the whole signal appeared to be determined by simultaneous masking, thresholds for the simultaneous partial signals matched those of the whole signal and also showed a phase effect, whereas thresholds for the forward partial signals were higher and showed no phase effect.