Is Concept Formation An Age-Independent Process?

We present the results of a study examining the effects of category learning on the performance of five year-old children and adults on similarity judgment and same-different tasks. Participants in the learning condition learned to distinguish two kinds of invented alien stimuli by hearing an interactive story over the course of two days, at the end of which they performed three tasks. A comparison of their performance with control participants revealed a marked expansion effect in both children and adults, with learning groups judging between-category pairs to be more different than control groups did. There was no compression effect (within-category pairs were not judged as more similar by learning than control groups). We hypothesize that expansion occurred because distinguishing pairs of stimuli was difficult, as indicated by a high error rate on the same-different task for both child and adult participants.