Difference thresholds for interaural delay

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Abstract
Cross−correlational models of binaural interaction postulate an interaural delay line in which neural impulses arising in one ear are delayed relative to those from the other. For localization based on interaural differences of time, accuracy is limited by the resolving power of this hypothetical delay line. The present study sought to determine whether the delay line is organized in such a way as to provide a foveal area of best acuity, as exists in spatial vision. Thus, threshold increments of interaural time difference (Δt)’s were determined as a function of overall delay (t). Stimuli were acoustic transients of either low (0.1 to 2 kHz) or high (3−4 kHz) frequency content, ranging in level from 18 to 68 dB SPL. The overall delay ranged from 0 to 500 μsec. In general, the functions that relate Δt to t were found to rise gradually with lowest thresholds occurring for the lower−frequency and higher−level clicks. In exception were the results from weak high−frequency clicks, which showed a marked and sudden rise at large values of t. Ignoring the sudden rises in these latter cases, the resolution of the delay line is best described by a shallow decay in acuity over the range of delay tested, and though accuracy is best in the center, clearly no sharp delineation exists in sound localization as in vision. Subject Classification: 65.62, 65.75.

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