ABSTRACT
It is well established that a decrease in cognitive performance is an inevitable consequence of growing old (Botwinick, 1973; Dustman, Emmerson, & Shearer, 1990). Behavioural slowing is the most significant aspect of the reduced cognitive performance that accompanies ageing. Almost all studies that have examined speed task performance have found older adults to be slower than their younger counterparts (Salthouse, 1985). This increased slowness of response is of major consequence for older individuals. For example, behavioural slowing affects the ability to drive a car, thus older adults are prone to higher accident rates and, as a result, pay higher insurance premiums. Slower movement speeds also contribute to higher accident rates at home and at work. Also, Hertzog (1989) has demonstrated that behavioural slowing in older adults is the major cause of their decline in intelligence. He has shown that the deterioration in mental abilities, typically found in older adults, may not reflect a loss of thinking but more a slowing of the rate of intelligent thought.
