What can Brinley plots tell us about cognitive aging?

The use of Brinley plots (the plotting of the mean response latencies of old adults against the mean latencies for younger adults) has recently become increasingly popular, not least because simple, coherent functions can be determined that account for a large proportion of the variance in performance across tasks. This has led some authors to question the need for a modular approach to cognitive aging and has led to attempts to replace such an approach with accounts based on global central nervous system factors. However, use of simulated data to test the efficacy of Brinley plots shows that their apparent success in predicting high levels of variance may be misleading in two ways: (a) Brinley type plots fail to detect occasions when data are generated specifically not to conform to a single function; and (b) the parameter values obtained differ significantly from the underlying functions used to generate the test data. It is suggested that high correlations between young and old reaction times across tasks that have been widely reported in the literature are not in themselves sufficient to support the strong claims made regarding global models of cognitive aging.