Neural representations of observed interpersonal synchrony/asynchrony in the social perception network.

The visual perception of individuals is thought to be mediated by a network of regions in occipitotemporal cortex that supports specialized processing of faces, bodies, and actions. In comparison, we know relatively little about the neural mechanisms that support the perception of multiple individuals and the interactions between them. The present study sought to elucidate the visual processing of social interactions by identifying which regions of the social perception network represent interpersonal synchrony. In an fMRI study with 32 human participants (26 female, 6 male), we used multi-voxel pattern analysis to investigate whether activity in face-selective, body-selective, and interaction-sensitive regions across the social perception network supports decoding of synchronous vs. asynchronous head-nodding and head-shaking. Several regions were found to support significant decoding of synchrony/asynchrony, including extrastriate body area, face-selective and interaction-sensitive mid/posterior right superior temporal sulcus, and occipital face area. We also saw robust cross-classification across actions in extrastriate body area, suggestive of movement-invariant representations of synchrony/asynchrony. Exploratory whole-brain analyses also identified a region of right fusiform cortex that responded more strongly to synchronous than to asynchronous motion. Critically, perceiving interpersonal synchrony/asynchrony requires the simultaneous extraction and integration of dynamic information from more than one person. Hence, the representation of synchrony/asynchrony cannot be attributed to augmented or additive processing of individual actors. Our findings therefore provide important new evidence that social interactions recruit dedicated visual processing within the social perception network that extends beyond that engaged by the faces and bodies of the constituent individuals. Significance statement The presence of interpersonal synchrony is a critical cue when appraising the nature and content of social interactions from third-person perspectives. However, little is known about its representation within the human visual system. Here, we use fMRI to reveal distributed representations of interpersonal synchrony/asynchrony in several regions of the social perception network, notably extrastriate body area and superior temporal sulcus. There is growing speculation that the perception of social interactions engages specialized visual processing beyond that recruited by the faces and bodies of the constituent individuals. Critically, perceiving interpersonal synchrony requires the simultaneous extraction and integration of dynamic information from more than one person. These results therefore provide key new evidence of dedicated multi-actor processing within the social perception network.