Measuring the use of a principle by retarded adolescents and nonretarded children on a Redundancy Series Test.

A series test composed of geometric figures placed in redundant patterns was designed to measure the ability of retarded adolescents to use of principle. It was administered to institutionalized and noninstitutionalized retarded adolescents and to nonretarded children from nursery school through fourth grade. Results revealed that four of the items accounted for most of the errors and that these four critical items were particularly sensitive to an inadequate scanning strategy. The retarded groups showed a mental age lag at least 1 year, 6 months and did not perform above chance on the critical items.