Book excerpt: "The empirical study of aging and cognition has progressed tremendously over the past 50-plus years. Much of the original research had its roots in the medical realm as investigators sought to characterize cognitive deficits associated with aging. For the most part, this research adhered to a biomedical model, in which aging was considered akin to a disease, and the focus was on understanding patterns of decline that were assumed to be an inevitable part of getting older (Hess & Blanchard-Fields, 1996). Indeed, aging was often studied by comparing patterns of decline to those associated with atypical populations with specific diseases or cortical lesions/insults (e.g., West, 1996). The study of aging and cognitive change made its way into mainstream experimental psychology in the 1960s and 1970s as researchers focused more on understanding normal aging through the lens of verbal learning and cognitive psychology (for reviews, see Kausler, 1982, 1991). One of the great advantages of these perspectives was the availability of sophisticated models to characterize memory and cognitive functions, and associated methods for assessing specific processes within these models. In these traditions, aging was usually studied by introducing a two-level age variable into traditional experimental designs that consisted of groups of young and older adults. The former groups typically comprised university undergraduates, whereas the latter groups usually encompassed a much wider age range of community-dwelling volunteers"--