Interaural time discrimination as a function of stimulus frequency and duration

Abstract

A 200‐Hz‐wide noise (96 dB/octave skins), 75 dB SPL, was presented binaurally in a two‐interval forced‐choice task. Center frequency was 250, 500, 1000, 2000, or 4000 Hz. Signal duration was varied from 20 to 300 ms. In one interval an interaural delay of Δt was introduced to the waveform in the left channel; in the other interval the same delay was introduced to the waveform in the right channel. Observers indicated whether the direction of apparent movement produced by the two bursts was “left” or “right.” Threshold Δt (delay required for 75% correct responses) was 7–10 μs for the three lower‐frequency signals for all durations tested. For the higher‐frequency signals, performance improved with signal duration: threshold Δt decreased from about 100 μs to about 60 μs for both 2000‐Hz and 4000‐Hz signals as duration increased from 30 to 300 ms. Extreme variability of responses prevented us from obtaining psychometric functions at 20 ms at the high frequencies. The data support the conclusion that lateralization at low frequencies is based on fine‐structure, at high frequencies on envelope, of the stimulus. The data will be discussed in terms of binaural temporal processing.