A systematic influence of stimulus type on audio-visual synchrony perception

In audio-visual synchrony perception, perceptual tolerance for relative delays is asymmetric, with greater tolerance found when the auditory component trails rather than leads the visual component. In synchronous-successive judgment paradigms, the curve indicating the proportion of "synchronous" responses is thus not symmetric around physical synchrony, but centers around a certain positive delay (audio following video), called the point of subjective simultaneity (PSS). Here we report an investigation of whether the causal interpretation of the audio-visual event by the observer influences synchrony perception. We estimated the PSS for an animation of Newton’s Cradle, showing a left-to-right pendulum movement, with three visual conditions: (1) the entire stimulus, (2) the left half, or (3) the right half. In conditions 1 and 2, the visual movement appears to cause the sound of the collision, whereas in condition 3 the visual movement appears to result from the sound of the collision. Using a procedure with ‘audio first,’ ‘video first,’ and ‘synchronous’ response alternatives, conditions 1 and 2 yielded positive PSSs, whereas for condition 3, perceptual synchrony coincided with physical synchrony. Such a shift in synchrony responses is in line with the interpretation that PSSs found in synchrony judgment experiments are influenced at least partially by the apparent causal relation between auditory and visual stimulus components.