Masker fringe and binaural detection

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Abstract
Yost [J. Acoust. Soc. Am. 78, 901-907 (1985)] found that the detectability of a 30-ms dichotic signal (S.pi.) in a 30-ms diotic noise (No) was not affected by the presence of a 500-ms dichotic forward fringe (N.pi.). Kollmeier and Gilkey [J. Acoust. Soc. Am. 87, 1709-1719, (1990)] performed a somewhat different experiment and varied the onset time of a 25-ms S.pi. signal in a 750-ms noise that switched, after 375-ms, from N.pi. to No. In contrast to Yost, they found that the N.pi. segment of the noise reduced the detectability of the signal even when the signal was temporally delayed well into the No segment of the noise and suggested that the N.pi. segment of noise acted as a forward masker. To resolve this apparent conflict, the present study investigated the detectability of a brief S.pi. signal in the presence of an No masker of the same duration as the signal. The masker was preceded by quiet or an N.pi. forward fringe and followed by quiet, an No, or N.pi. backward fringe. The present study differs from most previous studies of the effects of the masker fringe in that the onset time of the signal was systematically varied to examine how masking changes during the time course of the complex fringe-masker-fringe stimulus. The results failed to replicate those of Yost in that an N.pi. forward fringe reduced the detectability of the signal, and agreed with those of Kollmeier and Gilkey in that thresholds were elevated well after the offset of the N.pi. segment of the noise. The addition of an N.pi. backward fringe was also shown to reduce the detectability of the signal. Possible reasons for differences between the results of the present study and those of Yost are evaluated. Results are discussed in the context of models of binaural detection.

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