Social contingency modulates the perceived distance between self and other.

Although social contingency, namely contingent reactions of other to one's own actions, critically affects attachment formation, can it also modulate the perceived distance between self and other? Previous studies have suggested a positive answer. However, these studies are criticized for not showing true top-down effects on perception because of pitfalls such as task demands. We show that social contingency reduced the perceived distance between self and other while avoiding pitfalls. According to Emmert's law, the perceived size of an afterimage increases with perceived distance. Thus, if social contingency modulates the perceived distance, the perceived size of afterimage should inevitably reflect it. The results showed that the size of the afterimages of a face that contingently responded to participants' actions was perceived as smaller than those of non-contingent and unresponsive faces. This effect was more salient with increasing viewing distances. Thus, prior knowledge of interaction with environment modulates online perceptual processing in size constancy, probably through its influence on perceived distance.