Adult age differences in task switching.

Age differences in 2 components of task-set switching speed were investigated in 118 adults aged 20 to 80 years using task-set homogeneous (e.g., AAAA... ) and task-set heterogeneous (e.g., AABBAABB... ) blocks.General switch costs were defined as latency differences between heterogeneous and homogeneous blocks, whereas specific switch costs were defined as differences between switch and nonswitch trials within heterogeneous blocks.Both types of costs generalized over verbal, figural, and numeric stimulus materials; were more highly correlated to fluid than to crystallized abilities; and were not eliminated after 6 sessions of practice, indicating that they reflect basic and domain-general aspects of cognitive control.Most important, age-associated increments in costs were significantly greater for general than for specific switch costs, suggesting that the ability to efficiently maintain and coordinate 2 alternating task sets in working memory instead of 1 is more negatively affected by advancing age than the ability to execute the task switch itself.Cognitive control processes are generally seen as responsible for the regulation and organization of behavioral activity (Baddeley, 1986;Norman & Shallice, 1986).Influenced by the neuropsychological research tradition, developmental researchers have become increasingly interested in the role of cognitive control processes for the regulation of behavior and in their relationship to agerelated decrements in fluid intelligence or the mechanics of cognition (e.g., Baltes, 1993).Theoretical considerations about aging models of cognitive control are dominated by the frontal lobe hypothesis of aging, which assumes that age-related decline in intellectual functioning is associated with age-based changes in the frontal lobe (Dempster, 1992;Duncan, 1995; Prull, Gabrieli, & Bunge, in press).This line of thinking has been primarily influenced by clinical observations of behavioral deficits in frontal lobe patients (Reitan & Wolfson, 1994;Shallice & Burgess, 1993;Tranel, Anderson, & Benton, 1994).Deficits in frontal lobe patients were observed with psychometric tests assumed to require