Multisensory perception of natural versus unnatural motion.

Previous research has shown that visual perception is influenced by Newtonian constraints. Kominsky et al. showed humans detect unnatural motion, where objects break Newtonian constraints by moving at a faster speed after colliding with another object, faster than collisions that do not violate Newtonian constraints. These findings show that the perceptual system distinguishes between realistic and unrealistic causal events. However, real-world collisions are rarely silent. The present study extends this research by including sound at the collision point between two objects to evaluate how multisensory integration influences the perception of natural versus unnatural colliding events. Participants viewed an array of three simultaneous videos, each depicting two objects moving in a horizontal back and forth motion. Two of the videos showed the objects moving at the same speed while the third video was an oddball that either moved faster before the collision and slower after (natural target), or slower before the collision and faster after (unnatural target). A brief click was presented at the collision point of one or none of the videos. Participants were asked to indicate the oddball video via keypress. Replicating Kominsky et al., participants were faster when identifying unnatural target motion events compared with natural target motion events, both with and without sound. The findings also demonstrated lower accuracy rates for unnatural events compared with natural events, especially when a sound was added. These findings suggest that the addition of a sound could be distracting to participants, possibly due to limitations in attentional resources.