Response times to stimuli of increasing complexity as a function of ageing.

Twelve elderly and 12 young subjects were tested on a series of experiments with increasing complexity of perceptual-response mapping. As task complexity increased the differential slowing in performance between young and old increased and an ageXtask complexity interaction was observed. However, with practice this phenomenon disappeared leaving an apparent age lag constant. This slowing was due to increased central processing time rather than peripheral factors. No major differences in strategies were observed between the groups, though the old subjects tended to be less able to extract critical (useful) features from the display. Stimulus repetitions of a new kind were found where all characteristics of the stimulus (relevant and irrelevant) were important. Repetitions of coding rules rather than of particular signals or responses also facilitated RT. It was also found that later in practice old subjects were making fewer errors than the young, reversing earlier observations.