Dynamic ITDs, Not ILDs, Underlie Binaural Detection of a Tone in Wideband Noise

Abstract

To examine the relative contributions of dynamic ITDs and ILDs in binaural detection, we developed a novel signal processing technique that selectively degrades different aspects of binaural stimuli. We applied this selective scrambling technique to the stimuli of a classic N0Sπ task: detecting an antiphasic 500-Hz signal in a diotic wideband noise. Data from five listeners revealed (1) selective scrambling of ILDs had little effect on binaural detection; (2) selective scrambling of ITDs significantly degraded detection; and (3) combined scrambling of ILDs and ITDs had the same effect as scrambling of ITDs only. We conclude that (1) dynamic ITDs dominate detection performance; (2) ILDs are largely irrelevant; and (3) interaural correlation is a poor predictor of detection. We describe two stimulus-based models, each reproduces all binaural aspects of the data quite well: (1) a single-parameter detection model using ITD variance as detection criterion; and (2) a crosscorrelator preceded by waveform compression. We propose that the observed sensitivity to ITDs and insensitivity to ILDs reflect enhanced temporal coding and limited dynamic range found in bushy cells, the monaural inputs to the binaural processor.