Temporal weighting functions for interaural time and level differences. VI. Effects of pulse rate on modulated envelopes.

Temporal weighting functions were measured for binaural lateralization of amplitude-modulated trains of narrowband clicks. When the envelope was one rise-fall cycle of a 20-Hz sinusoid and the interclick interval was 2 ms, temporal weighting functions revealed strong onset dominance in the form of maximal weight on the initial click, despite its low amplitude (-36 dB) relative to the envelope peak. Onset dominance was greater for lateralization based on interaural time differences compared to interaural level differences (ILDs), and was also reduced when the interclick interval was lengthened to 5 ms. At that rate, ILD weights appeared to follow the sound envelope, suggesting a level-dependent contribution of ILD that was not seen for interaural time differences. The overall results support the view that binaural cues are accessed via a brief temporal readout window aligned to sound onsets and other onset-like events, i.e., rising segments of the amplitude envelope. The process cannot be re-triggered for at least a few milliseconds, so that binaural processing of high-rate sounds is dominated by the overall sound onset, whereas for low-rate sounds, each pulse or cycle serves as its own onset.