Since the speed of sound is much slower than light, we sometimes hear a sound later than an accompanying light event (e.g., thunder and lightning at a far distance). However, Sugita and Suzuki (2003) reported that our brain coordinates a sound and its accompanying light to be perceived simultaneously within 20 m distance. Thus, the light accompanied with physically delayed sound is perceived simultaneously with the sound in near field. We aimed to test if this sound–light coordination occurs in a virtual-reality environment and investigate effects of binocular disparity and motion parallax. Six naive participants observed visual stimuli on a 120-inch screen in a darkroom and heard auditory stimuli from a headphone. A ball was presented in a textured corridor and its distance from the participant was varied from 3–20 m. The ball changed to be in red before or after a short (10 ms) white noise (time difference: −120, −60, −30, 0, +30, +60, +120 ms), and participants judged temporal order of the color-change and the sound. We varied visual depth cues (binocular disparity and motion parallax) in the virtual-reality environment, and measured the physical delay at which visual and auditory events were perceived simultaneously. In terms of the results, we did not find sound–light coordination without binocular disparity or motion parallax, but found it with both cues. These results suggest that binocular disparity and motion parallax are effective for sound–light coordination in virtual-reality environment, and richness of depth cues are important for the coordination.
Changes in the understanding of visual depth cues eight years after sight-recovery
