Heterogeneity of executive tasks has made it difficult to determine whether there are age-related declines in executive functioning. To address this issue, 112 individuals, 20-79 years old, took the California Trail Making Test (CTMT) and the California Stroop Test (CST), subtests of the Delis-Kaplan Executive Function Scale (D. C. Delis, E. Kaplan, & J. H. Kramer, in press) that include measurement of component skills embedded in the executive function tasks. Multiple regression analyses revealed that after controlling for component skills, age had a significant effect on the executive requirement of the CST, namely speed on the interference condition. Age did not affect switching performance on the letter-number condition of the CTMT. Additional analyses revealed that age was significantly associated with commission of certain types of errors. This study confirms the importance of partialing out components in the assessment of multidimensional cognitive tasks, particularly when making age comparisons. It also emphasizes specificity over generalizability when examining the impact of age on cognition.

Mental flexibility is required to track and systematically alternate between 2 response sets. In this study, 719 individuals, 20 to 89 years old, engaged in 3 different tasks that required verbal and nonverbal cognitive switching. Of importance, each task allowed for independent measurement of component skills that are embedded in the higher level tasks. When gender, education, Full Scale IQ, and component skills were partialed out by multiple regression analyses, significant age effects were revealed for each task. This study provides evidence that executive functions--and verbal and nonverbal cognitive switching in particular--are affected by age independently from age-related changes in component skills. The results are discussed in terms of theories of executive control and neurologic correlates across the adult life span.

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