Moral conformity: Neurocognitive mechanisms of social influence in dyadic harmful decisions.

Social influence, including obedience, compliance, and conformity, strongly shapes human behavior, particularly in moral contexts. While the neurocognitive mechanisms of obedience and compliance have been extensively studied, those underlying moral conformity remain underexplored. We conducted an experiment in which two agents sequentially decided whether to administer painful shocks to a victim in exchange for a shared monetary reward. We examined how the first agent's choice influenced the second agent's behavior and the neurocognitive processes involved. Key variables included personal and shared responsibility ratings, sense of agency, and three electroencephalography components: frontal-midline theta power (FMθ) during the partner's decision-a maker of auditory attention; FMθ during one's own decision-a marker of cognitive conflict; and centroparietal P3-LPP amplitude during shock observation-an index of empathic neural response. Results showed that the second agent's decisions were significantly influenced by first agent's choices, especially toward the antisocial direction. Greater FMθ during the auditory processing of the partner's choice was associated with higher overall conformity. FMθ during decision-making was lower when conforming prosocially compared with antisocially, while larger P3-LPP amplitudes to observed pain were associated with reduced antisocial conformity. Prosocial conformity was associated with greater feelings of personal and shared responsibility, higher subjective empathy, increased sense of agency, and reduced conflict during decision making. These findings show that people exhibit a clear tendency to align with others' moral decisions, and the effects of social influence are shaped by the moral valence of observed behavior. This suggests a distinction between processes of diffusion of responsibility in immoral contexts and shared responsibility in prosocial ones.