All contexts are not created equal: Social stimuli win the competition for organizing reinforcement learning in 9-month-old infants.

Previous work has shown that infants as young as 8 months of age can use certain features of the environment, such as the shape or color of visual stimuli, as cues to organize simple inputs into hierarchical rule structures, a robust form of reinforcement learning that supports generalization of prior learning to new contexts. However, especially in cluttered naturalistic environments, there are an abundance of potential cues that can be used to structure learning into hierarchical rule structures. It is unclear how infants determine what features constitute a higher-order context to organize inputs into hierarchical rule structures. Here, we examine whether 9-month-old infants are biased to use social stimuli, relative to non-social stimuli, as a higher-order context to organize learning of simple visuospatial inputs into hierarchical rule sets. Infants were presented with four face/color-target location pairings, which could be learned most simply as individual associations. Alternatively, infants could use the faces or colorful backgrounds as a higher-order context to organize the inputs into simpler color-location or face-location rules, respectively. Infants were then given a generalization test designed to probe how they learned the initial pairings. The results indicated that infants appeared to use the faces as a higher-order context to organize simpler color-location rules, which then supported generalization of learning to new face contexts. These findings provide new evidence that infants are biased to organize reinforcement learning around social stimuli.