Abstract: PURPOSE： Action and perception interact reciprocally in our daily life. Previous studies have found that action properties of a single object can affect visual perceptual processing. Here we investigated the modulation of action relations between two objects on visual size perception and its underlying neural mechanisms.
METHOD： We investigated this action-based effect by varying the action relations between the surrounding inducers and the central target of the Ebbinghaus illusion. In particular, the central target was always a ping-pong ball, and the surrounding inducers were four ping-pong bats or electric fans with their handles oriented left or right. During each trial, participants were required to adjust the size of a comparison circle to match the target circle without time limit. Immediately, they had to judge whether the surrounding inducers were ping-pong bats or electric fans.
RESULTS： The behavioral results showed that when the surrounding inducers were larger than the central target, the size illusion effect was significantly stronger when they were in a congruent condition (i.e., ping-pong bats and ping-pong ball) than when they were in an incongruent condition (i.e., electric fans and ping-pong ball), irrespective of handle orientation. However, when the surrounding inducers were smaller than the central target, significant modulation of action relations on size illusion effect was not observed. ROI analysis revealed that when the handles were oriented right, congruent condition elicited greater activation in left supramarginal gyrus (SMG) and insula than incongruent condition; right-oriented ping-pong bats condition induced larger activation in left insula and fusiform gyrus than left-oriented condition. Further DCM analysis showed that with handles oriented right, congruent condition significantly strengthened the connection from SMG to insula, and weakened the connection from SMG to fusiform gyrus, as well as decreased the inhibitory self-connection in insula relative to incongruent condition. The present study provides clear evidence that action relations between objects can affect visual size perception, which relies on both the forward connection from SMG to insula and the feedback connection from SMG to fusiform gyrus.
CONCLUSION: The findings confirm that action properties of objects shape visual perception, and suggest that fronto-parietal network and its connection to occipital region play a pivotal role in this process.

Key words: action relations, Ebbinghaus illusion, fMRI, DCM