The effects of spatial relations and motion information in social scene perception

A body of research shows that the human visual system hosts a network specialized in processing social interactions-i.e., physical/communicative exchanges between people. This network largely overlaps with regions involved in motion perception. Current views propose that, since motion is an intrinsic component of social interaction, it is necessary to trigger social-interaction selectivity. However, the relationship between social-interaction perception and motion perception remains unclear. We took advantage of two existing functional MRI datasets collected in the same participants, to identify the social-interaction network, and study how it responds to static versus dynamic visual social scenes. Results showed that scenes showing interacting face-to-face (vs. back-to-back) people elicited greater activity in the extrastriate body area (EBA) and posterior superior temporal sulcus (pSTS). This facingness effect was observed for both static and dynamic stimuli, indicating that motion is not required to trigger social-interaction selectivity. However, neural activity was stronger for dynamic (vs. static) stimuli, implying that motion enhances the network's responsiveness. Moreover, the facingness effect was stronger in left hemisphere areas. Thus, while social perception has traditionally been associated with the right hemisphere, the present findings highlight a critical role for left visual areas, raising new questions about their function in social perception.