Temporal weighting of binaural cues for sound localization

Abstract

Normal-hearing human listeners localize sound sources accurately and effortlessly across an effectively limitless variety of acoustic environments by responding to, among other cues, small differences in the timing and intensity of sound arriving at the two ears (interaural time differences [ITD] and interaural level differences [ILD]). This dissertation explores the temporal dynamics of normal sensitivity to these cues by assessing normal-hearing listeners' weighting of ITD or ILD cues over the duration of binaurally dynamic stimuli in a variety of psychophysical experiments. Experimental stimuli were rapidly amplitude-modulated signals mimicking those typical of echoic environments (e.g., rooms), including rapid sequences of filtered impulses carrying varied ITD or ILD over their duration, and pairs and trains of pairs of clicks carrying discrete ITD or ILD in first and second click of each pair. Consistent with past studies of the precedence effect in sound localization, onset dominance in lateralization and binaural adaptation, data demonstrated a prime salience of ILD and especially ITD at signal onset. Somewhat more surprisingly, data also indicated greater sensitivity to post-onset ILD than post-onset ITD (i.e., a weaker precedence effect for ILD). These psychophysical data were qualitatively consistent with outputs of a simple model that included peripheral auditory filtering effects, auditory nerve adaptation, and parallel computation of ITD and ILD. These investigations collectively suggest that accurate sound localization in ordinary listening environments depends on acute ITD and ILD sensitivity at signal onset, followed (on scale of a few to tens of milliseconds) by post-onset attenuation of ITD sensitivity and dependence on ILD for detection of changes in the environment (e.g., introduction of a novel source).