Social comparison, in which people evaluate their opinions and abilities by comparing them with the opinions and abilities of others, is a central feature of human social life. Previous work has highlighted the importance of social comparison in reward processing. However, the time-course of the social comparison effect in outcome evaluation remains largely unknown. The purpose of this study was to explore to what extent brain activity is modulated by social comparison between an individual and their anonymous partner. Event-related potentials (ERPs) were measured while the participants viewed their own and their partner's gain and loss outcomes based on their performance in a dot estimation task. Analysis of ERPs revealed that the feedback-related negativity (FRN) amplitude differences between gains and losses were not modulated by social comparison. In contrast, the P300 was larger for gains and showed an effect of social comparison independent of feedback valence. A late component, the late positive potential (LPP), was also modulated by social comparison, but it was insensitive to feedback valence. The data suggest that social comparison modulates outcome evaluation at several points in the information processing stream. Social comparison has no effect on the early coarse evaluation stage, but modulates the late cognitive/affective appraisal and re-appraisal processes. These findings provide neurophysiological evidence for the importance of social comparisons in outcome evaluations by the human brain.
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