Perception of intention in social interactions: an ERPs and eLORETA analysis applied to motor and social gestures

In interaction we need to understand intentions, emotions and attitudes from others’ behaviour. It has been suggested that some form of human social understanding is innate and automatic. According to direct access theories, the first steps of visual information processing offer us an informed direct grasp of the situation: we need to swiftly detect other human beings, attribute agency stance and recognise their intentions to effectively interact. This study aims at investigating early neural correlates of intentions perception in interaction. 20 volunteers without any history of psychiatric or neurological disorders participated to the study. EEG was recorder while participants observed dynamic visual stimuli (two static frames presented in close succession) showing realistic interactions. Stimuli depicted an arm executing a gesture addressed to a human interagent. The goal of gestures was varied across-conditions: in half of trials they conveyed a movement request (motor gestures), in other trials they conveyed a social interaction request (social gestures). ERPs and source reconstruction (eLORETA) were computed. Morphological analysis revealed a negative deflection sensitive to gesture category and peaking at about 350 ms. Peak amplitude and latency were statistically analysed by repeated measures ANOVA. Beside an electrode localization effect, amplitude analysis revealed a significant simple effect for gesture condition, with an ampler peak in response to social rather than motor gestures. Statistical non-parametric mapping attributed larger differences to orbitofrontal cortex (OFC) and anterior paracingulate cortex. Prefrontal structures have been included in affective-social networks but the parallel and serial timing of their activation is still a matter of debate. The study gives evidence for a larger activation of OFC in early stages of social perception in response to social-oriented gestures. Such activation may be related to social cues extraction and intentional processing.