Abstract:  Narcissism is a personality characteristic involving arrogance, a feeling of entitlement, and the willingness to exploit others. Narcissistic people tend to be self-centered, grandiose and sensitive to feedback from others. They are also extremely selfish, focusing solely on themselves, lacking regard for others, and showing deficits in pro-social behavior and emotional empathy. Research on Social Value Orientation (SVO) has found that proself people are less trusting and trustworthy than prosocial people. Because of his or her egoism and lack of emotional empathy, the narcissist may tend to not trust other people, especially unfamiliar ones. Relatedly, narcissism may also modulate the outcome evaluation of trust decisions. Previous social neuroscience research has revealed two ERP components related to outcome evaluation, including feedback related negativity (FRN) and P300. In this study, we aimed to investigate how narcissistic personality modulates outcome evaluation in the one-shot trust game. 38 healthy undergraduate participated in our experiment. To assess their narcissism and control for potential depression, all participants completed a brief version of narcissistic personality inventory (NPI-16) and Beck depression inventory-II (BDI-II) before the behavioral task. Participants then played the role of trustor in the one-shot trust game, while their electroencephalograms (EEGs) were recorded. In the trust game, each participant decide whether to trust or distrust different partners over 150 trials. The partners’ reciprocation strategies were pre-programed by the experimenter (the overall reciprocating rate was 50%). All participants were provided with post-decision feedback about the outcome of their decisions (gain or loss game points) in each trail. We analyzed their behavioral responses at the decision-making stage and ERP components at the outcome evaluation stage. Based on NPI-16 scores, 19 participants were classified as relatively low narcissists (scores below the 50th percentile), while the other 19 participants were classified as relatively high narcissists (scores above the 50th percentile); these two groups differed significantly in NPI-16 scores, but not significantly in BDI-II scores (depression). Behavioral results revealed that the high-narcissistic group made less trusting choices than did the low-narcissistic group in the trust game. ERP results indicated that the feedback-related negativity (FRN) was more negative going in response to loss feedback compared to gain feedback. This may indicate that participants typically experienced expectation violation when their trust was exploited. More importantly, the FRN difference wave (dFRN, loss-FRN minuses gain-FRN) was larger for the high narcissistic group than the low narcissistic group. Relatedly, the P300 amplitudes following outcome feedback were larger for the high narcissistic group than the low narcissistic group, especially at the frontalcentral site (FCz). Both dFRN and P300 effects suggested that more narcissistic people may be more sensitive to the outcome feedback of trust decisions. The present study provides preliminary evidence that individual differences in narcissism modulate trust decision- making and outcome evaluation.

Key words:  Trust game, narcissistic personality, outcome evaluation, differentiated feedback related negativity, P300