Conceptual organization and memory in nonretarded, mildly retarded, and moderately retarded adults.

Moderately retarded, mildly retarded, and nonretarded adults learned a list of 12 items from three categories to a criterion of 75% correct recall in a free-recall learning paradigm. Retention was measured 1 week later. The moderately retarded took more trials and had lower retention and clustering scores than the others. The mildly retarded took more trials and had lower retention than the nonretarded. The results violate Murdock's total time hypothesis (Cooper & Pantle, 1967) but support Mandler's (1967) contention that learning is enhanced by the mental capacity for organization.