Visual biasing of auditory localization in azimuth and depth

Correctly integrating sensory information across different modalities is a vital task, yet there are illusions which cause the incorrect localization of multisensory stimuli. A common example of these phenomena is the "ventriloquism effect". In this illusion, the localization of auditory signals is biased by the presence of visual stimuli. For instance, when a light and sound are simultaneously presented, observers may erroneously locate the sound closer to the light than its actual position. While this phenomenon has been studied extensively in azimuth at a single depth, little is known about the interactions of stimuli at different depth planes. In the current experiment, virtual acoustics and stereo-image displays were used to test the integration of visual and auditory signals across azimuth and depth. The results suggest that greater variability in the localization of sounds in depth may lead to a greater bias from visual stimuli in depth than in azimuth. These results offer interesting implications for understanding multisensory integration.