Abstract
The ability to perceive and understand social interactions between others is a fundamentally important cognitive skill, yet almost no research has investigated its brain basis. Here, we hypothesized that the posterior superior temporal sulcus (pSTS) – an area implicated in many other aspects of social perception – plays a key role in perception of social interactions. To test this hypothesis, we scanned subjects with fMRI while showing them point-light movies of two people interacting with each other (e.g. one person gesturing to another) versus point-light depictions of two people performing independent (non-interactive) movements (e.g. one biking, the other walking). Consistent with our hypothesis, in 6 of 8 subjects we found a region in pSTS that responded significantly more strongly during perception of social interactions than perception of “independent” actions. This region showed a significantly greater response to interaction than independent motions in independent data from the same subjects. We further tested the “interaction” selectivity of this pSTS region in independent data and found a significantly greater response to point-light interaction movies than i) movies showing the same motions but in which the characters performed their movements facing away from each other (p = .05), and ii) full-color movies of moving faces and bodies. These and other analyses suggest that the interaction-selective region in pSTS overlaps only slightly with regions showing selectivity for face perception and simple biological motion perception (identified in separate localizer scans). These results not only further implicate the pSTS in complex social perception but also suggest that there is a region in the pSTS specifically engaged in perceiving social interactions between others.