Visual capture of a stereo sound: Interactions between cue reliability, sound localization variability, and cross-modal bias

Multisensory interactions involve coordination and sometimes competition between multiple senses. Vision usually dominates audition in spatial judgments when light and sound stimuli are presented from two different physical locations. This study investigated the influence of vision on the perceived location of a phantom sound source placed in a stereo sound field using a pair of loudspeakers emitting identical signals that were delayed or attenuated relative to each other. Results show that although a similar horizontal range (+/-45°) was reported for timing-modulated and level-modulated signals, listeners' localization performance showed greater variability for the timing signals. When visual stimuli were presented simultaneously with the auditory stimuli, listeners showed stronger visual bias for timing-modulated signals than level-modulated and single-speaker control signals. Trial-to-trial errors remained relatively stable over time, suggesting that sound localization uncertainty has an immediate and long-lasting effect on the across-modal bias. Binaural signal analyses further reveal that interaural differences of time and intensity - the two primary cues for sound localization in the azimuthal plane - are inherently more ambiguous for signals placed using timing. These results suggest that binaural ambiguity is intrinsically linked with localization variability and the strength of cross-modal bias in sound localization.