Short-term memory for pictures and words by mentally retarded and nonretarded persons.

Mentally retarded and nonretarded persons were compared in a Brown-Peterson short-term memory task for the retention of words and pictures over intervals up to 30 seconds. The retarded subjects forgot more rapidly over the initial 10 seconds. They also retained pictures better than they did words; the nonretarded subjects retained these stimuli equally well. The results were theoretically interpreted as reflecting a structural memory deficit in retarded individuals, who were viewed as having greater facility with an imaginal memory code than with a verbal code. Transforming information from one code to another may also have been more difficult for retarded persons.

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.