Individual differences in the aging memory : Mediation accounts, moderators, and contextual factors

Sammanfattning: Within the field of cognitive aging, mediation accounts propose that age affects cognitive abilities through a mediator variable. Most of these mediation accounts are developed based on studies with cross-sectional designs. We had access to data from Betula, a longitudinal population-based multi-cohort project, and tested, in Study I, the well-known processing speed account (general age-related slowing of mental processing speed affects cognitive abilities negatively) (Salthouse, 1996). Interestingly, no support was found for the speed account. In Study II, a second mediation theory was tested, the common cause account (Lindenberger & Baltes, 1994). This notion suggests a link between sensory and cognitive abilities, where both abilities decline with age in a similar fashion because of a third factor, a common cause. Again, no support for a major account of cognitive decline was found. In Study III, interactions including vascular health and genetic status (APOE status) as potential interacting predictors of cognitive development were examined. A difference in the distribution of interaction effects on episodic and semantic memory development was found. Study IV, finally, consisted of a comparison of cognitive aging in two very different countries, Bangladesh (Poverty and Health in Ageing) and Sweden (Betula). The findings were surprising since chronological age, in Bangladesh, did not exert much effect on declarative memory in older people, in contrast to Betula and most other aging studies, predominantly performed in the Western world. Results from these four studies are discussed with respect to theoretical implications and methodological considerations. Recommendations for future research focus are made and implications for explanatory models of cognitive aging are elaborated on.