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 beca me easier to hear when the masker duration was increased. The signal w as a 1000-Hz tone, 4 ms in duration; the masker was a wideband noise h aving a spectral notch 1400 Hz wide centered at 1000 Hz. Compared to p erformance with a 22-ms burst masker, average detection threshold acro ss five subjects improved by 15 dB when a 150-ms masker ''fringe'' pre ceded 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 contrala teral to the signal/burst complex. However, when the fringe was presen ted to both ears and the signal/burst complex to just one ear, the for ward fringe was about as helpful as when the stimuli were presented mo notically, but the benefit of the backward fringe was substantially re duced. The backward-fringe advantage was restored by reducing the leve l, or delaying the onset, of the contralateral component of the fringe . The results suggest that the forward-fringe advantage is a robust ph enomenon that is largely insensitive to input to the contralateral ear . In contrast, the backward-fringe advantage appears to be a fragile e ffect that can be affected by inputs from both ears.