Age-Related Changes in Information Processing on Tasks of Perceptual Speed

The general slowing theory of cognitive aging claims that age-related decline in cognitive performance results from the global slowing of processing functions. This theory derives from evidence showing how tests of perceptual speed account for virtually all the age-related variance in many tasks. However, these tasks may reflect more than individual differences in general speediness, such as different strategies resulting from the different possible ways of understanding the task, differential memory abilities, or a speed-accuracy trade-off. Using verbal protocol analysis and eye tracking, different models for common tests of perceptual speed were evaluated. Participants completed the number comparison, digit-symbol, and backward digit span tasks in either a "think-aloud" or a silent control condition. In both conditions, participants' eye movements were recorded for number comparison and digit-symbol, and each participant was given one of three types of instructions for these two tests, one focusing the participant on speed, accuracy, or both. Overall, results show that the number of fixations during encoding potentially mediates age-related decline on these tasks, whereas other variables, such as fixation duration and switches between interest regions, did not correlate with age. The results have implications for theories of aging, as only one model, based on encoding delay, fully accounted for the observed results.