Preverbal infants’ reactions to third-party punishments and rewards delivered towards fair and unfair agents

Rewarding individuals who distribute resources fairly and punishing those who distribute resources unfairly may be very important actions for fostering cooperation. This study investigates whether 9-month-olds have some expectations concerning such punishing and rewarding actions following distributive actions. Infants were shown simple animations and were tested using the violation-of-expectation paradigm. In Experiment 1, we found that infants looked longer when they saw a bystander delivering a corporal punishment to a ‘fair distributor’, who distributed equally the windfall resources to the possible recipients, rather than to the ‘unfair distributor’, who distributed the resources unequally. This pattern of looking times was reversed when, in Experiment 2, punishments were replaced with rewards. These findings reveal early-emerging expectations about punitive and reward motivations in third-party contexts and help to evaluate competing claims about the origins of a sense of fairness.