One hundred and fourteen educable mentally retarded children divided equally into two groups by mental age (older vs. younger) were exposed to one of three different orienting instructions (incidental-semantic, intentional-control, or incidental-categorize) within an incidental learning paradigm. The experimental task consisted of 18 pictures representing six instances of each of three common taxonomic categories. Older subjects recalled significantly more pictures with better clustering than younger subjects. Subjects receiving incidental-categorize instructions recalled significantly more items and showed significantly more clustering than subjects receiving the other instructions. The superiority of the categorize condition was maintained during a 24-h follow-up session.
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