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Abstract Processing speed (PS), the rate at which an individual can perform basic cognitive tasks, and executive functions (EFs), cognitive abilities regulating thoughts and action, are key cognitive abilities related to important life outcomes. We investigated the relationship between PS and multiple EFs (a common factor and two factors specific to updating working memory and shifting mental sets) across adolescence ( M age = 17.26 years, SD = 0.68) and established adulthood ( M age 29.34 years, SD = 1.29). 797 individual twins (MZ = 428, DZ = 369) in the Colorado Longitudinal Twin Study completed 3 PS tasks and 6–9 EF tasks. PS age16 correlated strongly with PS age29 ( r = .90) and Common EF (cEF) at age 17 ( r = .70). Furthermore, cEF and Updating-Specific factors in late adolescence predicted new variance in PS age29 ( r s = 0.13 to 0.16), but PS age16 did not predict new variance in cEF in established adulthood. PS and cEF were highly heritable at both ages (a 2 > = 0.74) and genetically correlated at both time points ( r a = 0.70 to 0.73). PS was not significantly genetically correlated with the Updating- or Shifting-Specific factors in late adolescence, but was in established adulthood. Results indicate that PS and EFs are highly correlated yet distinct constructs. PS and EFs both demonstrate strong stability of genetic/environmental influences across nearly 15 years from late adolescence into established adulthood. It will be important for future developmental studies to understand why specific EF factors predict future variance in PS, but not the reverse.
Karhadkar et al. (Mon,) studied this question.