Sound localization with unilaterally degraded spectral cues

Abstract

Two cues are thought to determine the apparent position of a sound, interaural time differences and the spectral patterning produced by the pinnae and upper body. The role of the spectral cues is the least well understood. One area of uncertainty is the extent to which cues from both ears are used. This study of the issue asked listeners to indicate the apparent positions of virtual sources synthesized from each listener’s own head-related transfer functions (HRTFs). Four types of stimuli were intermingled during a run: (1) all cues preserved, (2) spectral cues degraded at the ear on the side contralateral to the source, (3) degraded cues on the same side as the source, and (4) cues degraded binaurally. Cues were degraded either by smoothing, which preserved the major interaural level cues, or by replacing the natural HRTF with a constant average spectrum, which perturbed the natural interaural level cues. The results suggest that degrading contralateral cues has only a minor effect, while degrading either ipsilateral or binaural spectral cues causes significant localization errors. Results from the two degradation conditions were the same, suggesting that interaural level differences are relatively unimportant localization cues. [Work supported by NIH, NASA, and ONR.]