Preschool-aged children jointly consider others’ emotional expressions and prior knowledge to decide when to explore

Emotional expressions are abundant in children’s lives. What role do these expressions play in children’s learning? Here we ask whether preschool-aged children use others’ emotional expressions to infer the presence of unknown causal functions and guide their exploration accordingly. Children (3.0-4.9 years; N=112) learned about one salient causal function of a novel toy, and then saw an adult play with the toy. Children explored the toy more when the adult expressed surprise than when she expressed happiness (Experiment 1), but only when the adult already knew about the toy's salient function (Experiment 2). These results suggest that children selectively interpret others’ surprise as “vicarious prediction error” based on others’ knowledge, and use it to guide their own exploration and discovery.