Interpersonal relationships modulate subjective ratings and electrophysiological responses of moral evaluations

This study explored how interpersonal relationships modulate moral evaluations in moral dilemmas. Participants rated moral acceptability in response to altruistic (prescriptive) and selfish (proscriptive) behavior conducted by allocators (i.e., a friend or stranger), toward the participants themselves or another stranger in a modified Dictator Game (Experiments 1 and 2). Event-related potential (ERP) data were recorded as participants observed the allocators' behavior (Experiment 2). Moral acceptability ratings showed that when the allocator was a friend, participants evaluated the friend's altruistic and selfish behavior toward another stranger as being less morally acceptable than when their friend showed the respective behavior toward the participants themselves. The ERP results showed that participants exhibited more negative medial frontal negativity (MFN) amplitude whether observing a friend's altruistic or selfish behavior toward a stranger (vs. participant oneself), indicating that friends' altruistic and selfish behaviors toward strangers (vs. participants) were processed as being less acceptable at the earlier and semi-automatic processing stage in brains. However, this effect did not emerge when the allocator was a stranger in subjective ratings and MFN results. In the later-occurring P3 component, no interpersonal relationship modulation occurred in moral evaluations. These findings suggest that interpersonal relationships affect moral evaluations from the second-party perspective.