Abstract
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.
Highlights
Humans and many animals use their two ears to localize sounds within their surroundings
Studies reported a remarkable precision of the binaural system, with threshold interaural time differences (ITDs) orders of magnitude smaller than temporal difference detection thresholds for all other sensory modalities
Precise and systematic studies have been conducted to determine threshold ITDs (Zwislocki and Feldman, 1956; Klumpp and Eady, 1956; Mills, 1958) and it has been consistently reported that the lowest ITD detection thresholds are very close to 10 ls
Summary
Humans and many animals use their two ears to localize sounds within their surroundings. The cue that facilitates the most accurate sound localization (as small as 1 in azimuth) is the ITD (Mills, 1958). Studies reported a remarkable precision of the binaural system, with threshold ITDs orders of magnitude smaller than temporal difference detection thresholds for all other sensory modalities (see, e.g., Klemm, 1920, who introduced a new “unit” to describe threshold ITDs, which we call the microsecond). Precise and systematic studies have been conducted to determine threshold ITDs (Zwislocki and Feldman, 1956; Klumpp and Eady, 1956; Mills, 1958) and it has been consistently reported that the lowest ITD detection thresholds are very close to 10 ls
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