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Psychol Sci. 2009 May;20(5):603-11. doi: 10.1111/j.1467-9280.2009.02331.x. Epub 2009 Apr 2.

Five-month-old infants have different expectations for solids and liquids.

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Psychology Department, Northwestern University, USA.


Many studies have established that 2-month-old infants have knowledge of solid objects' basic physical properties. Evidence about infants' understanding of nonsolid substances, however, is relatively sparse and equivocal. We present two experiments demonstrating that 5-month-old infants have distinct expectations for how solids and liquids behave. Experiment 1 showed that infants use the motion cues from the surface of a contained liquid or solid to predict whether it will pour or tumble from a cup if the cup is upended. Experiment 2 extended these findings to show that motion cues lead to distinct expectations about whether a new object will pass through or remain on top of a substance. Together, these experiments demonstrate that 5-month-old infants are able to use movement cues and solidity to discriminate a liquid from an object of similar appearance, providing the earliest evidence that infants can reason about nonsolid substances.

[Indexed for MEDLINE]

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