Comparison of mentally retarded and nonretarded persons' organization of semantic memory.

The production frequency of exemplars for 16 categories was obtained from institutionalized mentally retarded adults and compared with those of nonretarded children, adolescents, and adults and with typicality ratings given by the same retarded subjects previously. The production frequency of exemplars by retarded and nonretarded persons was remarkably similar and varied more as a function of specific category than of mental development. Production frequency and typicality ratings of the retarded persons were less reliable. There is a striking similarity in the structure of the semantic memory of retarded and nonretarded persons.