Infants use rational decision criteria for choosing among models of their input.

Previous work demonstrated that 9-month-olds who were familiarized with 3-syllable strings consistent with both a broader (AAB or ABA) and narrower (AAdi or AdiA) generalization made only the latter. Because the narrower generalization is a subset of the broader one, any example that is consistent with the broader generalization but not the narrower one should allow a rational learner to select the broader generalization. The current experiment asked whether infants show evidence of being such learners. Infants who heard the stimuli that previously led to the narrower generalization plus three counterexamples mixed into the last five stimuli made the broader generalization at test. A control condition ruled out the possibility that infants based their generalization on the last five familiarization stimuli. The new findings suggest that infants effectively consider multiple competing models for their input and use rational decision criteria for selecting among these models.