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Human cognition alters naturally over time, affecting memory, executive function, processing speed, and language. Research helps reveal why these changes occur-and can point to strategies for maintaining healthy cognitive skills across the lifespan.
Cognitive aging encompasses a very wide range of processes, including speed, working memory, executive functions, memory, and linguistic abilities and knowledge. Longitudinal age declines in cognition are gradual and, in general, are not statistically significant until after age 60 (Schaie, 2005). Declines vary by cognitive domain, with many domains suggesting decrements and others, like language, suggesting stability (Salthouse, 2004). Changes attributed to age decline are in some cases moderated by changes in the cognitive environment as an effect of birth cohort or generation (Zelinski and Kennison, 2007).
There are also important individual differences that affect prediction of performance (Zelinski and Gilewski, 2003). Nevertheless, cognitive skills in healthy older adults appear to be modifiable by engagement in aerobic exercise and direct training, and transferable to untrained cognitive tasks (Hertzog et al., 2009). The potentially negative impact of cognitive aging in successful performance of everyday activities additionally may be reduced by compensatory factors, though this is not well understood.
Cognitive Processes That Show Declines
Many of the processes that have been examined in cognitive aging are not independent of one another. Though it has been suggested that very basic processes, like cognitive slowing, explain most of the declines observed in older people (Salthouse, 2004), the history of cognitive aging research suggests that one process does not account for all of them. Declines associated with normal aging are observed in the basic processes of speed, working memory, and executive control as well as in more complex cognitive domains.
Speed, working memory, and executive control processes
Processing speed, or the rate at which rapid perception and execution of decisions occur, declines with age (Salthouse, 1996). Slowing with age has implications for older adults' ability to execute more complex tasks, such as noticing and responding to a sudden change in road conditions while driving, or being able to quickly retrieve a specific word in the course of a conversation. Theories have suggested that slowing effects should increase multiplicatively with age, so that older adults are disproportionately affected compared to younger adults as tasks increase in difficulty...