Infants’ Physical World

Investigations of infants’ physical world over the past 20 years have revealed two main findings. First, even very young infants possess expectations about physical events. Second, these expectations undergo significant developments during the first year of life, as infants form event categories, such as occlusion, containment, and covering events, and identify the variables relevant for predicting outcomes in each category. A new account of infants’ physical reasoning integrates these findings. Predictions from the account are examined in changeblindness and teaching experiments. KEYWORDS—infant cognition; physical reasoning; explanationbased learning Over the past 20 years, my collaborators and I have been studying how infants use their developing physical knowledge to predict and interpret the outcomes of events. This article focuses on infants’ knowledge about three event categories: occlusion events, which are events in which an object is placed or moves behind a nearer object, or occluder; containment events, which are events in which an object is placed inside a container; and covering events, which are events in which a rigid cover is lowered over an object (Baillargeon & Wang, 2002). I first summarize two relevant bodies of developmental findings, and then point out discrepancies between these findings. Next, I outline a new account of infants’ physical reasoning that attempts to make sense of these discrepancies. Finally, I describe new lines of research that test predictions from this account. All of the research reviewed here used the violation-of-expectation method. In a typical experiment, infants see an expected event, which is consistent with the expectation examined in the experiment, and an unexpected event, which violates this expectation. With appropriate controls, evidence that infants look reliably longer at the unexpected than at the expected event indicates that they possess the expectation under investigation, detect the violation in the unexpected event, and respond to this violation with increased attention.