Interaural fluctuations and the detection of interaural incoherence. II. Brief duration noises.

Listeners detected a small amount of interaural incoherence in reproducible noises with narrow bandwidths and a center frequency of 500 Hz. The durations of the noise stimuli were 100, 50, or 25 ms, and every one of the noises had the same value of interaural coherence, namely 0.992. When the nominal noise bandwidth was 14 Hz, the ability to detect incoherence was found to depend strongly on the size of the fluctuations in interaural phase and level for durations of 100 and 50 ms. For the duration of 25 ms, performance did not appear to depend entirely on fluctuations. Instead, listeners sometimes recognized incoherence on the basis of laterality. However, when the nominal bandwidth was doubled, leading to a greater number of fluctuations, detection performance at 25 ms resembled that at 50 ms for the smaller bandwidth. It is concluded that the detection of a small amount of interaural incoherence is mediated by fluctuations in phase and level for brief stimulus durations, so long as such fluctuations exist physically. This conclusion presents a promising alternative to models of binaural detection that are based on the short-term cross-correlation in the stimulus.