How do listeners detect interaural incoherence?

Abstract

Listeners are remarkably sensitive to interaural incoherence. They can easily distinguish between a coherence of 1.00 and a coherence of 0.99. Interaural incoherence leads to the sensation of apparent source width; it is also held to be responsible for the masking level difference and for the creation of binaural pitch. However, incoherence per se is only a statistical description of signals; it is not indicative of any particular auditory binaural property. To discover the relevant binaural attribute(s), three-interval oddity experiments were performed using narrow-band noises that were perfectly coherent or slightly incoherent. The listener’s task was to identify the incoherent noise. First, it was shown that different frozen noises with identical values of incoherence could often differ greatly in detectability. Subsequent experiments studied the detectability of incoherent frozen noises that were were particularly strong or particularly weak according to selected binaural difference functions. These functions tested different rules for combining interaural phase differences (IPD) and interaural level differences (ILD)—either weighted sums of squares or rules that combine IPD and ILD to form a fluctuating lateralized image. The goal was to discover the best predictor of incoherence detectability. [Work supported by the NIDCD Grant DC 00181.]