Binaural Interaction in Backward Masking

The binaural auditory system exhibits certain advantages over the monaural system when detecting a tonal signal in a background of masking noise. These advantages have been described in detail and are referred to as masking-level differences (MLD). It has recently been suggested that these same advantages may be demonstrated in a binaural-masking experiment in which the signal and masker are not presented simultaneously. This suggestion is particularly puzzling since most explanations of MLD require addition or some other simple interaction of the signal and masker. In the present investigation, the size of the binaural advantage was measured in a backward-masking experiment in which the signal termination preceded the onset of the masker by 0, 4, 8, 12, or 20 msec. The results indicate that simultaneity of signal and masker is not required to show binaural improvement over monaural performance. [Research partially supported by the National Science Foundation and the National Institute of Mental Health.]