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Driving performance in mild dementia Tallman, Karen S.

Abstract

The automobile driving performance of 18 mildly demented subjects was compared to that of 18 normal elderly and 18 mid-age controls. Driving tasks were grouped according to a three-level hierarchical model that characterizes driving as a problem solving skill involving (a) low-level vehicle control skills, (b) intermediate level manoeuvring skills in response to on-road events, and (c) higher level driving-related judgemental abilities. Driving simulator measures of brake reaction time and steering accuracy were selected to represent the lowest level of hierarchy. A Motor Vehicle Branch (MVB) road test and a test of emergency braking distance indexed the intermediate level. Driving-related judgment was assessed by evaluating the accuracy of subjects' appraisals of their own driving skills, and by examining whether the demented subjects evidenced an increased level of driving avoidance that might be commensurate with the extent of their driving deficits. Overall the demented subjects performed significantly less well than did controls on the driving behaviour measures. Particularly striking were their deficits at the highest and lowest levels of the hierarchical task analysis. They were markedly impaired on the driving simulator tasks and they showed a clear tendency to over-estimate their driving competence relative to their actual performance. However, from a practical standpoint it was noted that despite significant group differences at the intermediate level, the overlap in performance scores between the demented and the normal elderly was considerable for these in-car tasks. Also, although the mildly demented subjects had significantly more demerit points on the MVB road test than did the elderly controls, nearly 70% were able to pass the licensing exam. Mildly demented drivers might best be characterized as having marginal driving abilities, a fact which may pose considerable challenges to clinicians and policy makers. A second component of the study involved evaluation of the correlations between the driving measures and several common psychometric tests of attention, perception, and psychomotor speed. After group membership was accounted for, the psychometric tests failed to add precision to the prediction of driving performance.

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