Previous research demonstrates that infants adapt and plan their actions based on object weight, but fewer studies have investigated how infants’ understanding of object weight shapes their understanding of physical events. The present study investigates 10-month-old infants’ understanding of the effect of object weight in support events—specifically, that object weight impacts whether a supporting surface will become compressed or not—and its relation to motor development. In Experiment 1, using an action task, we found that infants infer an object’s weight based on whether it compresses a supporting surface, as demonstrated by reaches to the light object following the support event. In Experiment 2, using a violation-of-expectation paradigm, we found that infants generate predictions for the outcome of support events involving heavy and light objects (i.e., they expect heavy, but not light, objects to compress a supporting surface), as demonstrated by longer looking to inconsistent events relative to consistent. Neither experiment found relations with infants’ motor development. These findings demonstrate that infants invoke a concept of object weight when interpreting and predicting the outcomes of physical events and that the ability to reason about object weight as a causal factor in physical events is relatively sophisticated in infancy.
Upshaw and Sommerville are with the Dept. of Psychology, University of Washington, Seattle, WA.