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The relation between cognitive rigidity and cognitive inertia was examined. Results showed that cognitive inertia was greater in individuals with mental retardation than in CA- but not MA-matched subjects without mental retardation. For individuals with mental retardation, cognitive inertia was positively correlated with CA. Results of comparisons of MA-matched individuals with and without mental retardation were not consistent with Kounin's (1941) theory. However, the current findings provided some support for Kounin's notion that there are age-related inherent structural differences that lead to greater rigidity in older adults.

Two experiments confirmed and extended earlier research (Ellis, Woodley-Zanthos, Dulaney,Palmer, 1989) showing that persons with mental retardation are more rigid than persons without mental retardation. In Experiment 1 subjects read Stroop words, practiced naming the colors of Stroop words, and then read the Stroop words again. Postpractice reading interference was related to amount of practice, and the interference effect was much greater in persons with mental retardation. We hypothesized that the practice led to automatization of a reading suppression response that had greater cognitive inertia for persons with mental retardation and, therefore, had a greater effect on postpractice reading for them. This cognitive inertia effect was shown to be quite durable in persons with mental retardation, lasting more than 3 months for 10 of 13 subjects. The effect disappeared within a month for persons without mental retardation.

A modified Stroop Color-Word Interference Test (Stroop, 1935) was used to assess automatic-effortful processing in persons with mental retardation and college students in three experiments. In Experiment 1, retarded persons experienced greater Stroop interference than did college students. This was attributed to a failure of control (effortful) processing needed to suppress the automatic reading responses of retarded subjects. In Experiments 2 and 3, all subjects practiced the Stroop color-naming task over three or four daily sessions. Changes in Stroop interference over practice were viewed as reflecting automatization of the suppression of the reading response. Both groups automatized the suppression response at about the same rate, but the automatized responses had far greater and more durable suppression effects for retarded subjects. This persistence of automatized responses, which were no longer adaptive, was described as cognitive inertia, a phenomenon similar to cognitive rigidity as defined by Kounin (1948).

Two experiments extended earlier research showing age- and intelligence-invariance in memory for spatial location. Second and sixth graders, college students, and mildly retarded persons relocated pictures after looking through a 100-picture book. There were no differences due to age, IQ, or instruction (intentional or incidental) in location memory; there were differences in picture recall. In a second experiment persons with Down syndrome, as a group, were less accurate in location memory than were college students, but many individuals performed as accurately. A 3-month follow-up on the subjects with Down syndrome revealed greater consistency in location memory than in recall. Overall, the results show that young children and mildly mentally retarded persons process spatial location information as well as do college students. Some, but not all, of the more severely mentally retarded persons had deficits in processing memory for location. All persons with mental retardation had deficits in effortful processing as reflected by free recall.