Abstract
Sound travels more slowly than light. Perceptually, this is apparent in a thunderstorm. We can often see lightening seconds before we hear the thunder. While this timing difference is perceptually apparent for distant sources of sight and sound, it has been suggested that for proximate sources there is a perceptual compensation. Evidence for this is contradictory. Some data suggests that the point of subjective simultaneity between sight and sound does not vary as a function of viewing distance (Sugita & Suzuki, 2003, Nature 421: 911). Other data suggests that it does vary (Stone et al, 2001, Proc. R. Soc. Lond B 268, 31–38), which is inconsistent with a perceptual compensation for timing differences. We examined this issue by determining the temporal tuning of a cross modal interaction. In the stream / bounce illusion two translating dots move toward, become superimposed, and then move away from one another. They can be seen to either pass through, or to bounce off, one another. If a brief tone is sounded at an appropriate moment, observers are biased to see the dots as bouncing (Sekuler et al. 1997, Nature, 385, 308). We found that the appropriate timing for the tone varies as a function of viewing distance. In a two alternative forced choice perceptual pairing task, we also found that the point of subjective simultaneity varies as a function of viewing distance. Neither of these findings is consistent with perceptual compensation for the slower speed of sound relative to light.