The cognitive and neural mechanisms underlying norm-enforcement behaviors under social observation.

Abundant evidence has revealed that social observation could enhance people's norm-enforcement behaviors to norm violators. However, whether such enhancement is strategically reputation-based without changes on awareness of social norms or it is accompanied with strengthened perception of norm violations remains unclear. We aimed to test these two hypotheses using a modified Ultimatum Game (UG). Participants played the UG as responders in the fMRI scanner after being instructed the rules of the game and how the observers monitored their performances during the task. Behavioral results showed that unfair offers were perceived more unfair (decreased fairness ratings) and rejected more often under the condition with social observation than that without observation (the control condition). The changes in fairness ratings predicted the increase of rejection rates between two conditions, which provided more evidence for the latter hypothesis. Neural results demonstrated that right insula and anterior cingulate cortex associated with processing norm violations and/or negative emotions were more activated in response to unfair treatments under social observation relative to the control condition. Furthermore, bilateral anterior insula, anterior cingulate cortex, and right amygdala (an emotional processing structure) showed increased activations with the reduction of fairness ratings under social observation. Besides, compared to the control condition, rejecting unfair trials under social observation induced more left anterior insula activation. These findings indicated that the increase of norm-enforcement behaviors in the UG under social observation was more than a behavioral strategy for social desirability, but a result of enhanced sensitivity to fairness norm violations and unfairness-related negative feelings.