The interpretation of social interactions between people is important in many daily situations. In this talk, we will present the results of 2 studies examining the visual perception of other people interacting. The first study used functional brain imaging to investigate the brain regions involved in the incidental visual processing of social interactions; that is, the processing of the body movements outside the observers’ focus of attention. The second study used a visual search paradigm to test whether people are better able to find interacting than non-interacting people in a crowd.
In the first study, we measured brain activation while participants (N = 33) were presented with point-light dyads portraying communicative interactions or individual actions. These types of stimuli allowed us to investigate the role of motion in processing social interactions by removing form cues. Participants in our study discriminated the brightness of two crosses also on the screen, thus excluding the body movements from the participant’s task-related focus of attention. To investigate brain regions that may process the spatial and temporal relationships between the point-light displays, we either reversed the facing direction of one agent or spatially scrambled the local motion of the points. Incidental processing of communicative interactions elicited activation in right anterior STS only when the two agents were facing each other. Controlling for differences in local motion by subtracting brain activation to scrambled versions of the point-light displays revealed significant activation in parietal cortex for communicative interactions, as well as left amygdala and brain stem/cerebellum. Our results complement previous studies and suggest that additional brain regions may be recruited to incidentally process the spatial and temporal contingencies that distinguish people acting together from people acting individually.
Our second study focussed on deliberate visual processing of communicative interactions in the observer’s focus of attention. Participants viewed arrays of the same point-light dyads used in our first study, but here they searched for an interacting dyad amongst a set of independently acting dyads, or for an independently acting dyad amongst a set of interacting dyads, by judging whether a target dyad was present or absent (targets were present on half the trials). In each of two experiments (N=32 and N=49), participants were faster and more accurate to detect the presence of interacting than independently acting target dyads. Moreover, visual search for interacting target dyads was more efficient than for independently acting target dyads, as indicated by shallower search slopes (increase in response time with increasing number of distractors) for the former as for the latter. In the second experiment, we measured the eye movements of the participants using an eye tracker. The analyses of the eye tracking data are ongoing. Based on the results from our first study and on search performance, we expect that fixation duration on communicative-dyad targets will be shorter than on independent-dyad targets, because less attentional focus (as measured by fixation duration) is needed to process social interactions.