Threshold Interaural Time Differences under Optimal Conditions
* Presenting author
In the 1950s several studies have investigated human threshold ITDs with various stimuli and reported lowest thresholds to be near 10 μs. Despite the fact that these studies were partly preliminary reports and that they did not attempt to systematically find the smallest threshold ITD, they still serve as best available references. The goal of this study is to systematically determine the stimulus and the experimental paradigm that results in the smallest threshold ITD and to provide an accurate reference value. We varied seven stimulus and procedure parameters: stimulus waveform, stimulation level, stimulus duration, adaptive versus constant stimulus procedure, alternative-forced-choice (AFC) procedure, inter-stimulus pause duration, and complete waveform versus ongoing ITD. The condition yielding the lowest threshold ITD was Gaussian noise band-pass filtered from 20-1400 Hz, presented at 70 dB SPL, with a short inter-stimulus pause of 50 ms, and an interval duration of 0.5 s. The average threshold ITD for this condition at the 79% correct level was 8 μs.Compared to Klumpp and Eady (JASA 1956) the shorter inter-stimulus pause, shorter stimulus duration and extensive training are the most apparent factors that result in slightly lower thresholds in our study.