The effects of aging on fluid mental abilities of 90 mentally retarded adults from three settings were investigated in a cross-sectional study. To test the hypothesis that the early adult retarded show the same decline in fluid abilities as the non-retarded, the Raven Progressive Matrices, Porteus Mazes and a paired-associate memory test were administered to subjects ranging in age from 19 to 43 yr., all of whom had received WAIS IQs in the mildly retarded range when in their late teens. Scores on the three tests correlated negatively with the teenage WAIS Verbal IQ but positively with the teenage Performance IQ. Contrary to studies of normal adults, the older retarded subjects did somewhat better than the younger ones. Significant differences between age groups emerged only on the paired-associate scores. The results raise the possibility that fluid mental abilities show a later decline in the mildly retarded than in the non-retarded.
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