Structural constraints on process explanations in cognitive aging.

Much of the current research in the area of cognitive aging has been focused on investigating specific processes presumed to be responsible for the age differences observed in particular cognitive tasks. A central thesis of this article is that age-related effects on cognitive variables seldom occur in isolation, and hence, they are best interpreted in the context of the structural interrelations that exist among variables and the relations of age on that organizational structure. Results from analyses of 2 separate data sets suggest that large proportions of the age-related effects across a wide range of cognitive variables are shared and that independent, or unique, age-related effects often contribute relatively little to the age differences observed in many cognitive variables. These findings imply that it is important to consider the structure within which a variable occurs when attempting to investigate the processes responsible for age-related differences on that variable.