Intentional and incidental memory in organically mentally retarded, familial retarded, and nonretarded individuals.

Groups of organically mentally retarded, familial retarded, and nonretarded subjects were compared on two tasks of intentional memory and one of incidental memory. With mental age being covaried, the familial group did better than the organic group on both tasks of intentional memory. However, the performance of both retarded groups was inferior to that of the nonretarded children. The three groups did not differ on incidental learning. The finding of differences between organically retarded and familial retarded persons supports the view that etiology needs to be considered when studying cognitive functioning in mentally retarded persons. The differences between the familial retarded and nonretarded groups appear to be in contradiction to the similar structure hypothesis of mental retardation.