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Generalized slowing in demented and cognitively-impaired-not-demented individuals Peters, Kevin Ross

Abstract

The purpose of the present investigation was to determine whether a widely accepted theory of normal cognitive aging can explain cognitive deficits in two groups of individuals with cognitive impairment. To answer this question, the Generalized Slowing Hypothesis (Birren, 1974; Cerrella, Poon, & Williams, 1980; Salthouse, 1980), which is that ageassociated declines in high-level cognition are mediated by reductions in processing speed, was examined in 16 dementia (M age = 69; SD = 13.01) and 35 Cognitively-Impaired-Not- Demented (CIND) patients (M age = 64; SD = 9.65). Participants were recruited from the Clinic for Alzheimer's Disease and Related Disorders at the University of British Columbia Hospital. The California Verbal Learning Test (CVLT) and Rey-Osterrieth Complex Figure (ROCF) were used as measures of high-level cognition. Processing speed was measured by three tests, each of which has been demonstrated to represent unique components of processing speed: Finger Tapping, Simple Reaction, and Card Sorting (Graf & Uttl, 1995). Hierarchical regression analyses were performed in order to determine the ability of age to predict performance on the CVLT and ROCF before and after statistically controlling for the influence due to the three measures of processing speed. The results obtained in this investigation did not provide support for generalized slowing of processing in these two patient groups. The attenuation in the ability of age to predict performance after partialling out the influence due to processing speed was above 60% only for the performance of the CIND group on the CVLT, which is slightly lower than the lowest magnitude of attentuation previously reported in healthy adults. The attenuation in the predictive ability of age for performance on the ROCF was only 43% in the CIND group, and it was only 27% for the performance on the CVLT in the dementia group. These findings, although preliminary, suggest that the cognitive deficits of dementia and CIND patients are not merely the consequence of an acceleration of normal aging. Clearly, more research, with larger sample sizes, needs to be conducted to examine the tenability of generalized slowing in these two patient groups.

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