Group environment modulates how third parties assess unfairly shared losses and unfairly shared gains: neural signatures from ERPs and EEG oscillations.

Introduction: Through its long-term evolution and development, human society has gradually formed stable and effective norms to maintain normal social production and social activities. Altruistic punishment is indispensable in maintaining social norms. Altruistic punishment includes second-party and third-party punishment, and third-party punishment refers to punishing violators by unbiased bystanders who have not suffered damage to their interests. Cooperation is an important form of human social interaction. Third parties play an essential role in maintaining social cooperation. Third parties' behaviors in maintaining cooperative norms may be related to their social environment.

Method: We used the prisoner's dilemma (PD) game and distinguished between the gain and loss contexts of the economy to explore how the group environment modulates the cognitive neural mechanisms and psychological processing of the third-party punishment decision. Twenty-six college students (M_age = 19.88 ± 1.58) participated in the experiment; data from four participants were excluded from analyses of the EEG data due to large artifacts.

Results: The behavioral results show that the degree of punishment from the third party in a loss context was greater than in a gain context. ERP analysis results show that the third party applied a lower P300 in the loss context. The loss context induced a greater N100 than the gain context in the individual environment. At the same time, alpha-band power activated by the individual environment was greater than that activated by the group environment under the gain context.

Conclusion: These results suggest that a third party maintaining the norms of social cooperation in different contexts will adjust punishment decisions according to the environment, and this process is mainly dominated by the negative emotions caused by environment.