Classification in young and retarded children: the primacy of overall similarity relations.

Previous studies have shown that young normal children use similarity relations as a predominant basis for classification, whereas older children use dimensional relations. Experiment 1 shows that similarity relations are systematically used by normal preschoolers and by retarded preadolescents for classification. Experiment 2 suggests that their tendency to use similarity relations is not merely a matter of preference, but that these children have difficulty learning to use dimensional relations. Still, experiment 3 demonstrates that dimensional relations have some psychological reality for preschoolers and for retarded children despite the dominance of overall similarity and despite the relative inaccessibility of dimensional relations. The research affords a finer specification of the development of classification skills and highlights the relation between intelligence and psychological stimulus structure.