Minimal group membership biases early neural processing of emotional expressions.

Mere affiliation with a social group alters people's perception of other individuals. One suggested mechanism behind such influence is that group membership triggers divergent visual facial representations for in-group and out-group members, which could constrain face processing. Here, using electroencephalography (EEG) under functional magnetic resonance imagery (fMRI) during a group categorization task, we investigated the impact of mere affiliation to an arbitrary group on the processing of emotional faces. The results indicate that in- and out-group members trigger differential event-related potential activity, appearing 150 ms after presentation of group membership information, which correlated with medial prefrontal fMRI activity. Additionally, EEG activity in the earliest stages of face processing (30-100 ms after expression onset) dissociated unexpected group-related emotions (in-group anger and out-group joy) from expected ones and correlated with temporo-parietal junction fMRI activity. We discuss the possibility that such dissociation may result from top-down influences from divergent representations for in-group and out-group members. Taken together, the present results suggest that mere membership in an arbitrary group polarized expectations which constrain the first steps of face processing.