Detection of Interaural Time Differences in Short-Duration Low-Frequency Tones

Abstract

The detectability of interaural time differences (Δt) was investigated as a function of stimulus duration, level, and frequency. Temporally dichotic tone bursts of 250, 500, and 1000 Hz were presented in a two-interval forced choice, in such a way that the signal to one ear led by Δt μsec during either the first or second interval. The tone bursts were 10, 25, 50, 100, and 205 msec in duration and were gated with a rise-decay time of 2.5 msec. The levels used were 50 and 70 dB SPL. Threshold values of Δt were maximal for the shortest durations, then fell rapidly to asymptote in the region from 50 to 100 msec. In addition, thresholds decreased at higher frequencies. Finally, all conditions showed lower thresholds for 70 dB than for 50 dB. The data are fit by a model that treats increased duration as an increase in the number of samples of the interaural difference and describes the improvements found with higher frequencies and levels as a result of the steeper slopes of the displacement waveforms.