Monetary payoffs modulate reciprocity expectations in outcome evaluations: An event-related potential study.

Choosing cooperation or aggression relies on reciprocity preferences which refer to the tendency of an individual to return cooperative or aggressive action for cooperative or aggressive action (i.e., positive or negative reciprocity preference). The reciprocity preference is positively correlated with reciprocity expectation, wherein individuals with stronger reciprocity preferences may have higher expectations than future cooperative or aggressive behavior should be delivered by beneficiaries (positive reciprocity expectation) or victims (negative reciprocity expectation). Although previous studies have demonstrated that the presence of monetary payoffs enhances reciprocity preferences, the modulation of monetary payoffs in reciprocity expectations remains unclear. Using event-related potentials (ERPs), we examined how monetary payoffs modulated reciprocity expectations by adopting the Chicken game. Participants were asked to choose between cooperation and aggression with a putative opponent in the Chicken game involving the monetary (vs. non-monetary) payoffs. Participants' electroencephalogram (EEG) was recorded when they saw the opponent's cooperative or aggressive decision. Results showed that compared to the non-monetary payoff trials, the feedback-related negativity (FRN) effect in response to the opponent's decisions was stronger following the participant's aggressive decision in the monetary payoff trials, whereas P3 was insensitive to monetary payoffs. These findings suggest that monetary payoffs heighten expectations of negative reciprocity at the earlier and automatic outcome processing stage.