Light Source Distance Affects Perceived Audiovisual Simultaneity

Distance of sound and light sources affects the proximal stimulation and some of these changes can influence the perceived timing of stimuli. Sound source distance causes attenuation and transmission delay. Light source distance causes decreased retinal size and lower stimulus energy. These modifications could have opposite influences on the perception of simultaneity, however it is often assumed that the effect of distance on simultaneity perception is primarily due to the distance of the sound source. Here we compare the magnitude of the effect of audio and visual source distance on perceived simultaneity when distances are presented interleaved or blocked during the course of the experiment. Participants performed temporal order judgments of audiovisual stimuli presented from speakers and LEDs located at 1 and 16 m. Sounds and lights sources could be either co-located or dislocated as the distances of the sound and light sources were combined. The four distance conditions were either presented interleaved or blocked throughout the course of the experiment. As expected, we find that sound source distance requires beeps to be presented earlier to appear simultaneous with flashes. We also find that light source distance requires flashes to be presented earlier to appear simultaneous with beeps. Interestingly, the effect of sound source distance is higher with blocked presentation whereas the effect of light source distance is larger than sound source distance (but opposite in sign) when the four distance conditions are presented randomly interleaved. This effect can be related to peripheral viewing of the light sources in the interleaved condition and it suggests that scenes with audio-visual events at several distances could be perceived simultaneously without the need for a perceptual mechanism that use distance cues to maintain perceptual synchrony.