Young children can infer what speakers know based on their causal influence over listeners

A causal, mentalistic understanding of communication-a process by which a speaker's mind causes a change in a listener's mind-can support powerful inferences that go beyond observable data. If A struggles to activate a toy but succeeds after B whispers to A, you can infer that B knew how to activate it even without hearing what was said. Although humans are precocious communicators, much remains unknown about how we come to understand communication as a process by which speakers causally influence listeners. Extending prior work on children's forward inferences about communication-from speakers to listeners-the current work examined how children reason backwards from listeners' behaviors to recover speakers' knowledge. Children viewed two scenarios where a listener failed to activate a toy twice before finally succeeding. In one scenario the speaker communicated before a listener's success, whereas in the other scenario the speaker communicated before a listener's failure. Even 3-year-olds chose the former speaker as the one who knew how the toy works (Exp.1). However, when communication always preceded success but the scenarios differed in what would have happened without communication (i.e., the listener was poised to fail or succeed), a preference for the former speaker did not emerge until later (Exps.2-3). Importantly, across all experiments, children held no preference when speakers produced non-speech vocalizations. These results suggest that even young children have an abstract understanding of communication as a causal, mentalistic process, but their inferences are constrained by the causal cues available in context and continue to develop throughout early childhood.