Attentional blocks are not responsible for age-related slowing.

Reaction time (RT) data in two tasks from a total of 784 adults between 18 and 87 years of age were analyzed to determine the relation between age and parameters of the intra-individual RT distribution. Although the absolute magnitude of the age differences was greatest for the slowest RTs in each individual's RT distribution, there was little or no independent age-related variance in the slowest RTs after controlling for the variance in the fastest RTs. Furthermore, the relation between RT and measures of motor speed, perceptual speed, working memory, and accuracy in several cognitive tasks was of nearly the same magnitude when only the fastest responses were considered as when both fast and slow responses were considered. These results imply that age-related slowing is associated with a shift (and expansion) in the entire RT distribution, and is not attributable to a selective influence on the individual's slowest responses.