Voluntary or reluctant? Social influence in charitable giving: an ERP study.

Social information has substantial influences on prosocial behavior. In this study, we performed an event-related potential (ERP) experiment to examine the effect of social influence on giving. The participants were allowed to form an initial decision on how much money to donate to a charity provided the program's average donation amount and to make a second donation decision. Social influence varied in different directions (upward, downward and equal) by altering the relative donation amount between the average donation amount and the participants' first donation amount. The behavioral results showed that participants increased their donation amount in the upward condition and decreased it in the downward condition. The ERP results revealed that upward social information evoked larger feedback-related negativity (FRN) amplitudes and smaller P3 amplitudes than in the downward and equal conditions. Furthermore, the pressure ratings, rather than the happiness ratings, were associated with the FRN patterns across the three conditions. We argue that people in social situations are more likely to increase their donations owing to pressure than voluntary altruism. Our study provides the first ERP evidence that different directions of social information evoke different neural responses in time course processing.