Objective and subjective measures of pure-tone stream segregation based on interaural time differences

Abstract

The effect of interaural time differences (ITDs) on stream segregation for successive tone bursts was investigated. Obligatory stream segregation was inferred from the threshold for detecting a rhythmic irregularity in an otherwise isochronous sequence of interleaved “A” and “B” tones (task 1). Subjective stream segregation was evaluated by requiring listeners to indicate whether they heard one or two streams during presentation of a 30-s long sequence (task 2). The A and B tones had equal but opposite ITDs and had the same or different frequencies of 500 and/or 707 Hz. The ITDs ranged from 0 to 2 ms in study 1, and from 0 to 0.5 ms in study 2. Sensitivity on task 1 was poor in both studies when A and B had different frequencies, and was little affected by ITD. Thresholds for the same-frequency conditions worsened somewhat with increasing ITD up to 0.5 ms and then (for study 1) flattened off. There was a small increase in subjective streaming as the ITD was increased up to 0.5 ms, but little streaming for larger ITDs (study 1). We conclude that ITD, at most, has weak effects in producing obligatory and subjective stream segregation.