Reaction time (RT) data from the Minnesota Twin Study of Adult Development and Aging were used to investigate genetic and environmental influences on intraindividual variability in RT. The sample was 738 individuals (aged 27 to 95 years), including 185 monozygotic (MZ) and 131 disygotic (DZ) twin pairs. Two RT factors were created: decision time and movement time. Age-corrected heritability estimates were 40% for mean RT; 21% for intraindividual variability in movement time; and 0% for intraindividual variability in decision time. Multivariate analysis indicated that all genetic variance in the RT measures was shared among measures; environmental variance was specific to each RT measure.
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Received 12 September 2005; accepted 7 January 2006. The Minnesota Twin Study of Adult Development and Aging was supported by NIA grant AG06886. Analytical work was supported by a fellowship from the American Philosophical Society. Address correspondence to Deborah Finkel, PhD, Indiana University Southeast, 4201 Grant Line Road, New Albany, IN 47150, USA. E-mail: email@example.com