Reputational concern has been suggested as an important determinant of human cooperative behavior and moral judgment in social interactions. Previous studies have examined how reputational concern or social distance alone influences moral decision-making. However, little is known about how reputational concern and social distance interact to affect moral decision-making, particularly about the underlying cognitive neural mechanism under proscriptive morality (i.e., harming behavior). In this study, participants were instructed to decide whether to deliver a certain intensity of painful electric shocks toward the target others (i.e., friends, acquaintances, or strangers) to receive the matched money for themselves, while the behavioral and neural responses were recorded. The behavioral results showed that participants made fewer electric shocks to friends than to both acquaintances and strangers, which suggested an obvious “egoistic altruism” tendency in anonymous situations [F(2, 58) = 11.06, p < 0.001, η2p = 0.28]. Participants spent more time making choices [F(2, 58) = 20.06, p < 0.001, η2p = 0.41] and experienced greater disgust [F(2, 58) = 5.21, p = 0.01, η2p = 0.21] in dilemmas involving acquaintances relative to those involving either friends or strangers, which showed an obvious “acquaintance effect”. However, these differences were weakened in public situations [F(2, 58) = 0.11, p = 0.16, see Figure 1]. Moreover, ERP results showed that the dilemmas involving acquaintances elicited a larger P260 component [F(2, 58) = 6.91, p = 0.002], which is associated with emotional responses, and late positive potential (LPP, 300~450 ms), which is associated with cognitive reasoning [F(2, 58) = 6.53, p = 0.003]. However, these differences in ERP indices were disappeared in public situations [F(2, 58) = 1.74, p = 0.19, see Figure 2]. The results supported the hypothesis that individuals follow the moral principle of egoistic altruism to conduct moral decision-making involving reputational concern and social distance. These findings suggest that the uncertainty of acquaintance relationships induces stronger negative emotions and cognitive load during moral decision-making, and reputational concern effectively weakens the aversion and dilemma conflict by weakening self-interest tendencies and interpersonal uncertainties.
