Toddlers' expectations of third-party punishments and rewards following an act of aggression.

Rewarding someone who defends the victim of an unjust aggression and punishing someone who chose not to defend her may be very important acts of reciprocation in social life. This study investigates whether 21-month-olds have some expectations concerning such punishing and rewarding actions. Infants were shown simple puppet shows and were tested using the violation-of-expectation paradigm. In Experiment 1, we found that infants looked longer when they saw a bystander puppet punishing the puppet who defended the victim rather than the puppet who did not defend her. This pattern of looking times was reversed when the punishing action was replaced with a rewarding action (Experiment 2). These findings reveal early-emerging expectations about punitive and reward motivations in third-party contexts, and provide some support for theoretical claims about the hardwiring of the human mind for cooperation and prosociality.