The aim of this thesis was to investigate inter-individual variability on cognitive task performance in normal older adults. In a review of the cognitive aging literature, the implications of a differential perspective were drawn out in order to establish a theoretical and methodological basis for an investigation into variability. A number of regularly occurring patterns, identified on the basis of available reports in the literature, were used to develop a model of variability (the shuttle model). The empirically-based model was located broadly within a neuropsychological framework, and derived explanatory power from the tenets of brain reserve capacity (BRC) theory. It served to describe the bulge in interindividual variability due to aging (the shuttle bulge), and the shifting occurrence of the bulge in relation to the age axis due to cohort and task-related influences (the shuttle shift). A two phase research study was conducted in order to test hypotheses derived from the model. Phase 1 comprised between-groups analyses of normative data covering a broad range of neuropsychological tests in the domains of attention, memory, language, visual and hand motor skills, in order to examine the progression of variability effects across the adult age range. Phase 2 constituted between and within-groups analyses of normative data from a more limited number of neuropsychological tests. It included the examination of raw score distributions and the characteristics of outliers, and was undertaken to explore more closely the nature of the variability phenomena detected in the first phase of the analysis. Taken together, the results of both phases of the investigation revealed statistically significant variability effects in support of the shuttle model. There was a consistent pattern of increased variability in association with older age regardless of functional modality; frequently, in association with later old age, there was also a subsequent decrease in variability (the shuttle bulge). The age of onset of the initial increase in variability occurred earlier or later (the shuttle shift) as a function of four factors: education, gender, task challenge and age-sensitivity of task. The finding of an earlier onset of variability effects for low education, male gender, high task challenge and high age-sensitivity of task was interpreted in terms of BRC threshold theory. The clinical and social implications of the outcome were discussed with special emphasis on the need for a differential perspective on aging, as a complement to the prevailing normative tradition. It was concluded that the shuttle model has considerable heuristic value. It presents an integrative framework for understanding existing variability data and provides clear indications for future research.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:rhodes/vital:3191 |
| Date | January 1998 |
| Creators | Jordan, Ann B |
| Publisher | Rhodes University, Faculty of Humanities, Psychology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Doctoral, PhD |
| Format | 504 leaves, pdf |
| Rights | Jordan, Ann B |
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