Baby physics: expectations about liquid and sand in 5-month-old infants


Infants have expectations about physical properties of solid objects. However, evidence on infants’ understanding of nonsolid substances (e.g., water or sand) is sparse and equivocal. We conducted four habituation/dishabituation experiments demonstrating that 5-month-olds have distinct expectations for how objects and substances behave. Experiment 1 found that infants use motion cues from the surface of a contained liquid or solid to predict whether it would pass through or rest on a grid when the container was upended. Experiment 2 extended these findings to show that motion cues led to different expectations about whether a new object will pass through or remain on the top surface of a liquid or solid. Experiments 3 and 4 replaced the liquid with sand. We found that infants expected sand, like liquid, to go through a grid, but did not expect another object to pass through it. These findings begin to characterize infants’ understanding of substances.

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