ABSTRACT
Much of our current knowledge about how cognition changes across the adult life span comes from research that, paradoxically, is focused on stability. Developmental researchers investigating cognitive functioning in adulthood tend to examine adults’ level of performance, or total score, on a cognitive task on a single occasion. This type of measurement disregards any variability in performance while completing the task, and consequently assumes that the cognitive trait is stable in the short term, or from one week to the next. However, this assumption is in contrast with developmental theory. The life-span developmental perspective states that an individual is in constant fluctuation as a result of living in a dynamic environment (Nesselroade, 1991), and that stability is only a temporary break from the ongoing variations in functioning (Nesselroade & Featherman, 1997). Therefore, the study of developmental change has to include and expect both variability and stability in development (Nesselroade & Featherman, 1997). These arguments suggest that research investigating the level of cognitive performance in adulthood is not sufficient to fully characterize human cognitive development.
