Temporal weighting for interaural time differences in low-frequency pure tones

Abstract

In contrast to envelope-based interaural time differences (ITD) at high frequencies, where sound onsets play a dominant role, the reliability and salience fine-structure ITD at low frequency (<1500 Hz) suggests uniform sensitivity to information across periods of an ongoing stimulus waveform. Several past studies, however, have demonstrated low-frequency ITD thresholds to improve sub-optimally with increasing sound duration [e.g. Houtgast & Plomp 1968, JASA 44:807-12], suggesting that the initial periods of a brief tone play a greater role in ITD processing than do later periods. Here, we measured the temporal profile of ITD sensitivity in pure tones ranging from 250-1000 Hz. Sounds were presented with ITD that either remained fixed over the sound duration (condition RR) or progressed linearly to eliminate the ITD cue from either the beginning (condition 0R) or end (R0) of the sound. Durations varied from 40-640 ms, including 20 ms ramps applied diotically to minimize envelope cues. ITD detection thresholds demonstrated (a) suboptimal improvement with duration and (b) greater sensitivity to ITD available early (R0) rather than late (0R) in the stimulus, a pattern nearly identical to that observed for high-frequency envelope ITD. [Supported by NIH R01 DC011548.]