Improving the detectability of a brief tone in noise using forward and backward masker fringes: monotic and dichotic presentations.

A brief tonal signal simultaneously masked by a brief noise burst became easier to hear when the masker duration was increased. The signal was a 1000-Hz tone, 4 ms in duration; the masker was a wideband noise having a spectral notch 1400 Hz wide centered at 1000 Hz. Compared to performance with a 22-ms burst masker, average detection threshold across five subjects improved by 15 dB when a 150-ms masker "fringe" preceded the signal (forward fringe), and by 9 dB when the masker fringe followed the signal (backward fringe). Little improvement was observed in either condition when the fringe was presented to the ear contralateral to the signal/burst complex. However, when the fringe was presented to both ears and the signal/burst complex to just one ear, the forward fringe was about as helpful as when the stimuli were presented monotically, but the benefit of the backward fringe was substantially reduced. The backward-fringe advantage was restored by reducing the level, or delaying the onset, of the contralateral component of the fringe. The results suggest that the forward-fringe advantage is a robust phenomenon that is largely insensitive to input to the contralateral ear. In contrast, the backward-fringe advantage appears to be a fragile effect that can be affected by inputs from both ears.