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 fro m masker onset was measured as a function of signal bandwidth for wide band 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 onse t of a 420-ms masker. Although there were marked individual difference s, the signal was consistently more difficult to detect in the short-d elay than in the long-delay condition. The difference in detectability decreased as signal bandwidth increased and was similar in magnitude across the two masker types. This result indicates that an across-chan nel process contributes to the improvement in detectability as the sig nal delay is increased, because the masking components at the signal f requency in the wideband masker exerted very little influence on the s ize of the effect. In a third condition, the signal was gated 1 ms aft er the onset of a 23-ms masker. The signal was hardest to detect in th is burst condition, and performance varied differently as a function o f signal bandwidth in this than in the other two conditions, particula rly 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 freque ncy. Finally, the pattern of results obtained across the three conditi ons using the wideband masker was consistent with the idea that the cr itical bandwidth narrows as the signal is delayed from masker onset. ( C) 1995 Acoustical Society of America.