Infants' understanding of numerical transformations

This research explored infants' understanding of transformations that change the numerosity of a set. Do infants know how the insertion or deletion of a single object affects the relative numerosity of two sets? Four age groups (14‐, 18‐, 24‐ and 28‐month‐olds) were tested on problems involving sets whose numerosities were never greater than 2. The children were encouraged to find the set with more objects, after watching the experimenter cover up two sets and then transform one of them by performing either an insertion or a deletion. On the start‐equal problems, the two sets had the same number of objects until the transformation was performed, so that when an object was inserted the transformed set always had more and when an object was deleted the untransformed set always had more. On the start‐unequal problems, the initial numerosities of the two sets were varied so that these relations between the type of transformation that was performed and the relative numerosities of the two sets no longer held. One set initially had two objects in it and the other set had none. Insertions were performed on the smaller set, so that it still had less than the untransformed set; and deletions were performed on the larger set, so that it still had more than the untransformed set. Performance improved significantly across the four ages tested. However, every age group showed some understanding of the transformations. These results add to the growing body of evidence for an understanding of numerical relationships in infancy.