Social proof in the human brain: Electrophysiological signatures of agreement and disagreement with the majority.

Perceiving one's deviance from the majority usually instigates conformal adjustments of one's own behavior to that of the group. Using ERPs, we investigated the mechanisms by which agreeing and disagreeing with the majority are differentially represented in the human brain and affect subsequent cognitive processing. Replicating previous findings obtained in a slightly different paradigm, we found that learning about one's disagreement with the majority, as compared to learning about one's agreement with the majority, elicited a mediofrontal feedback negativity. Moreover, an enhanced posterior late positive complex was observed during the processing of agreement as compared to disagreement. Finally, when the to-be-judged faces were viewed for a second time, a stronger posterior P2 was observed for faces on whose judgment one had previously agreed with the majority than for those on which one had disagreed. We thus demonstrate that the brain places particular emphasis on the encoding of the rewarding experience of finding strong social proof for one's judgments. Likewise, having experienced agreement on the judgment of a certain item affects even the later reanalysis of this very item, as previous agreement increases early attention, as reflected in the P2. These findings corroborate and extend previous results and theories on the neurocognitive principles of social influence.