Cognitive aging and the role of processing speed

As humans age, a decline in overall cognitive functioning occurs. Recent formulations of the process underlying age-associated cognitive decline suggest that decline in a few key domains explain much of cognitive aging. The processing resource approach suggests the primary domain underlying cognitive decline is speed. Slowing with age is well documented and some suggest that much of the decline in other areas of cognition can be explained as due to declines in speed. However, this is not universally supported. This study was designed to evaluate the processing resource theory of speed. The study was a secondary analysis of collected data. Participants were actively recruited from the Kaiser Permanente database in Southern California. They included 211 patients aged 65 through 89. Participants were given the Cognitive Assessment of Later Life Status (CALLS), a new telephone administered cognitive screening test. This test measures speed auditorily using simple and choice reaction time. Participants were also given a battery of neuropsychological tests. These tests were factor analyzed. The impact of speed on neuropsychological performance was evaluated by first calculating the correlations between the age measures and the neuropsychological factors. Speed was then controlled for using hierarchical regression to determine if it mediated the association between age and all neuropsychological factors. There was a significant negative correlation between age and choice reaction time. Age was significantly correlated with non-contextual verbal memory and set shifting and perceptual speed. Both of these significant associations remained after controlling for all of the speed variables. Support was not found for the processing resource theory. Exploratory analyses indicated that simple reaction time (right ear) was associated with attention and working memory. Both simple and choice reaction time were associated with language retrieval.