Smallest perceivable interaural time differences.

It is well-established that the smallest discrimination thresholds for interaural time differences (ITDs) are near 10 μs for normal hearing listeners. However, little is known about the hearing and training status of the test subjects from past studies. Previous studies also did not explicitly focus on the identification of the optimal stimulus and measurement technique to obtain the smallest threshold ITDs. Therefore, the first goal of the current study was to identify the stimulus and experimental method that maximizes ITD sensitivity. The second goal was to provide a precise threshold ITD reference value for both well-trained and un-trained normal hearing listeners using the optimal stimulus and method. The stimulus that yielded the lowest threshold ITD was Gaussian noise, band-pass filtered from 20 to 1400 Hz, presented at 70 dB sound pressure level. The best method was a two-interval procedure with an interstimulus interval of 50 ms. The average threshold ITD for this condition at the 75% correct level was 6.9 μs for nine trained listeners and 18.1 μs for 52 un-trained listeners.