Detection of dynamically varying interaural time differences

Humans are highly sensitive to Interaural Time Differences (ITDs) in stimuli presented via headphones. For broadband noise stimuli of long durations, ITD detection thresholds can be as low as 10 to 15 ms. When the stimulus duration is shortened, thresholds increase by about a factor 2 for a tenfold decrease in duration.

ITD thresholds also increase, when the probe carrying an ITD is surrounded by diotic fringes. When a 5-ms probe is combined with preceding or trailing fringes, the effect of a fringe preceding the probe is stronger than that of a trailing fringe for fringe durations <35 ms. The effect of fringes surrounding the probe is equal to the addition of the effects of the individual fringes.

In this contribution, we present behavioral data for the same experimental condition, called dynamically varying ITD detection, but for a wider range of probe and fringe durations. Probe durations varied between 5 and 400 ms, and fringe durations had values of 5, 20, 100 or 200 ms. In contrast to earlier findings, we observed for most duration combinations a stronger effect of the trailing fringe than of the preceding fringe.

For these configurations, the effect of surrounding fringes was dominated by the trailing fringe. Only for the combination of 5-ms fringes with 5-ms probes did we see the clear dominance of the preceding fringe. These results are not easy to align with the concept of onset emphasis often used to explain binaural localization data for short stimuli.

In fact the data seem to be difficult to predict with a purely signal-driven model of perception and thus form an interesting challenge for modeling human localization.