Fourteen-month-old infants infer the continuous identity of objects on the basis of nonvisible causal properties.

Research on object cognition in infancy suggests that children from (at latest) 1 year of age are capable of individuating objects according to property/kind information. It remains unclear from previous work, however, whether infants in such studies truly apply sortal (kind) concepts or whether they merely track objects on the basis of superficial surface features. To clarify this question, we examined infants' flexibility in tracking property changes. In particular, we investigated which property changes infants see as diagnostic for kind changes and whether they can dynamically adapt this view as a function of prior knowledge. Fourteen-month-old infants were presented with a salient property transformation indicating a category change (i.e., a rabbit was placed in a box but a carrot was retrieved from it). Prior to the test, half of the infants saw how a stuffed animal could be transformed into another object by a simple mechanism. The other infants were unaware of this transformation. Only infants of the naive group interpreted the property change observed in the subsequent test as diagnostic for a change in identity and thus expected two objects to be present in the box. The results are discussed in the light of psychological essentialism, which can explain why infants treat some classes of property changes but not others as diagnostic for changes in identity.