Criteria for same and different judgments and visual comparison strategies of four-year-olds.

4-year-olds made same and different judgments about pairs of stimuli requiring detailed comparison in 2 conditions: a judgment-only condition and a justification condition in which children explained the reasons for their judgments. The systematic comparison strategies revealed in the justifications indicated that all children had definite criteria for "same" and "different" although about two-thirds of the children used a criterion that differed from the adult criterion. Judgments were more accurate in the justification than in the judgment-only condition, suggesting that overt verbalizations and gestures may provide a beneficial external support for completion of a child's own visual comparison strategy.