Onset- and offset-specific effects in interaural level difference discrimination

The relative sensitivity of human listeners to interaural level differences (ILDs) carried by the onsets, offsets, and interior portions of brief sounds was examined. Stimuli consisted of single 4000-Hz Gabor clicks (Gaussian-windowed tone bursts) or trains of 16 such clicks repeating at an interclick interval (ICI) of 2 or 5 ms. In separate conditions, ILDs favored the right ear by a constant amount for all clicks (condition RRRR) or a changing amount that was maximal at sound onset (condition R000), offset (condition 000R), both onset and offset (condition R00R), or at the temporal midpoint of the stimulus (condition 0RR0). ILD increases and decreases were implemented as linear decibel sweeps across four clicks to minimize transient distortion. Threshold ILDs were determined adaptively for each of these conditions and for single clicks. Thresholds were similar for ILDs presented near sound onset or offset (condition R000 vs 000R) but lower when ILDs were carried by both onset and offset clicks (condition R00R) than for ILDs carried by interior clicks alone (condition 0RR0). The results suggest that similar sensitivity to onset and offset ILD does not reflect uniform temporal weighting; instead, ILD sensitivity favors onsets and offsets over the interior portions of sounds.