Detectability of simultaneously masked signals as a function of signal bandwidth for different signal delays.

The improvement in signal detectability as signal onset is delayed from masker onset was measured as a function of signal bandwidth for wideband and notched-noise maskers. The signal was centered at 2500 Hz. In two conditions, the 20-ms signal was gated 1 or 250 ms after the onset of a 420-ms masker. Although there were marked individual differences, the signal was consistently more difficult to detect in the short-delay than in the long-delay condition. The difference in detectability decreased as signal bandwidth increased and was similar in magnitude across the masker types. This result indicates that an across-channel process contributes to the improvement in detectability as the signal delay is increased, because the masking components at the signal frequency in the wideband masker exerted very little influence on the size of the effect. In a third condition, the signal was gated 1 ms after the onset of a 23-ms masker. The signal was hardest to detect in this burst condition, and performance varied differently as a function of signal bandwidth in this than in the other two conditions, particularly for the notched-noise maskers. This outcome suggests the presence of a second across-channel process that is sensitive to masker offsets, especially when there are no masking components at the signal frequency. Finally, the pattern of results obtained across the three conditions using the wideband masker was consistent with the idea that the critical bandwidth narrows as the signal is delayed from masker onset.