Spectro-temporal weighting of interaural time differences in speech

Numerous studies have demonstrated that the perceptual weighting of interaural time differences (ITDs) is non-uniform in time and frequency, leading to reports of spectral and temporal “dominance” regions. It is unclear however, how these dominance regions apply to spectro-temporally complex stimuli such as speech. The authors report spectro-temporal weighting functions for ITDs in a pair of naturally spoken speech tokens (“two” and “eight”). Each speech token was composed of two phonemes, and was partitioned into eight frequency regions over two time bins (one time bin for each phoneme). To derive lateralization weights, ITDs for each time-frequency bin were drawn independently from a normal distribution with a mean of 0 and a standard deviation of 200 μs, and listeners were asked to indicate whether the speech token was presented from the left or right. ITD thresholds were also obtained for each of the 16 time-frequency bins in isolation. The results suggest that spectral dominance regions apply to speech, and that ITDs carried by phonemes in the first position of the syllable contribute more strongly to lateralization judgments than ITDs carried by phonemes in the second position. The results also show that lateralization judgments are partially accounted for by ITD sensitivity across time-frequency bins.