Peer presence increases adolescents' prosocial behavior by speeding the evaluation of rewards for others

Peer presence can elicit maladaptive adolescent decision-making, potentially by increasing sensitivity to the rewards one receives. It remains unknown whether peer presence also increases adolescents' sensitivity to others' rewards, which could have an adaptive effect in contexts allowing pro-social behaviors. Here, we combine social utility modeling and real-time decision process modeling to characterize how peer presence alters adolescents' processing of self and other rewards. We found that adolescents behaved selfishly when privately allocating rewards for themselves and a peer in an incentive-compatible task. In peer presence, however, adolescents became more altruistic. Real-time estimates of reward processing collected using computer mouse tracking showed that altruistic behavior was associated with relatively earlier processing of peer-rewards relative to self-rewards, such that peer presence sped peer-reward processing without altering self-reward processing. Our results indicate a causal mechanism through which peer presence prompts greater prosocial behavior by altering how adolescents process prosocial outcomes.