Motor action reduces temporal asynchrony between perceived visual changes

Perceiving a visual object requires binding sensory estimates of its various physical attributes. This process can be facilitated if changes of different attributes are perceived with little asynchronies when they are physically aligned, which is not always the case as revealed by temporal order judgment or perceptual synchronization tasks of visual attributes changes. In this study, we analyzed the effect of performing a motor action on the perceived relative timing between changes of position and color of a visual target by using a temporal order judgment (TOJ) task. Results showed that in the perceptual condition, the change of color must precede (-37.9 ms) the change of position in order to perceive a synchronous change of both target's visual attributes. This physical asynchrony vanished when the same changes took place near the end of a manual reaching action executed towards the visual target (-3.3 ms). The reduction of asynchrony was, however, not observed when participants performed TOJ of visual attributes change in the presence of concomitant tactile information (-36 ms) but with no action. The perceptual relative timing between visual changes was also unaffected when the timing was obtained by comparing each visual change to tactile information resulting from motor action (-33.5 ms) or external stimulation (-27.8 ms). Altogether, these results suggest that signals associated with the organization of a motor action, but not sensory information itself, contribute to reduce the differential delays when processing visual attributes of a single object. Furthermore, the effect of action was not observed when judging relative timing of object-related (visual) versus object-unrelated (tactile) sensory information.