Moving toward versus away from another: how body motion direction changes the representation of bodies and actions in the visual cortex.

Representing multiple agents and their mutual relations is a prerequisite to understand social events. Using functional MRI on human adults, we show that visual areas dedicated to body-form and body-motion perception contribute to processing social events, by holding the representation of multiple moving bodies and encoding the spatial relations between them. In particular, seeing animations of human bodies facing and moving toward (vs. away from) each other, increased neural activity in the body-selective cortex (extrastriate body area -EBA) and posterior superior temporal sulcus for biological-motion perception (bm-pSTS). In those areas, representation of body postures and movements, as well as of the overall scene, was more accurate for facing-body (vs. non-facing body) stimuli. Effective connectivity analysis with Dynamic Causal Modeling revealed increased coupling between EBA and bm-pSTS during perception of facing-body stimuli. The attunement of human vision to multiple-body scenes involving perceptual cues of interaction such as face-to-face positioning and approaching behaviour, was further supported by the participants better performance in a match-to-sample task with facing-body vs. non-facing body stimuli. Thus, visuo-spatial cues of interaction in multiple-person scenarios affect the perceptual representation of body and body motion and, by promoting functional integration, streamline the process from body perception to action representation.