Binaural release from masking in forward-masked intensity discrimination: evidence for effects of selective attention.

In a forward-masked intensity discrimination task, we manipulated the perceived lateralization of the masker via variation of the interaural time difference (ITD). The maskers and targets were 500 Hz pure tones with a duration of 30 ms. Standards of 30 and 60 dB SPL were combined with 60 or 90 dB SPL maskers. As expected, the presentation of a forward masker perceived as lateralized to the other side of the head as the target resulted in a significantly smaller elevation of the intensity difference limen than a masker lateralized ipsilaterally. This binaural release from masking in forward-masked intensity discrimination cannot be explained by peripheral mechanisms because varying the ITD leaves the neural representation in the monaural channels (i.e., in the auditory nerve) unaltered. Instead, our results are compatible with the assumption that lateralization differences between masker and target promote object segregation and therefore facilitate object-based selective attention to the target.