Structural memory deficits of mentally retarded persons.

Short-term memory of mentally retarded and nonretarded persons was compared in four experiments on the Brown-Peterson task in an attempt to relate short-term memory deficit to control or structural processes. Type of stimulus, pictures and letters, was varied along with encoding time. On pictures, with liberal encoding time, rate of forgetting did not differ. Retarded groups forgot letters more rapidly after limited encoding time. Increases in encoding time improved retention for retarded persons, but this variable did not normalize forgetting rate. In a direct comparison, retarded persons retained pictures better than letters. The converse was true for nonretarded persons. Evidence for both encoding and storage deficiencies of retarded persons was found. Differences in memory were found under conditions that precluded the use of voluntary cognitive strategies. These differences were interpreted as evidence for structural memory deficits of retarded persons.