Behavior Genetics

, Volume 34, Issue 1, pp 41-50

First online:

A Genetic Investigation of the Covariation Among Inspection Time, Choice Reaction Time, and IQ Subtest Scores

  • Michelle LucianoAffiliated withQueensland Institute of Medical Research
  • , Margaret J. WrightAffiliated withQueensland Institute of Medical Research
  • , Gina M. GeffenAffiliated withUniversity of Queensland
  • , Laurie B. GeffenAffiliated withUniversity of Queensland
  • , Glen A. SmithAffiliated withQueensland Institute of Medical Research
  • , Nicholas G. MartinAffiliated withQueensland Institute of Medical Research

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Information processing speed, as measured by elementary cognitive tasks, is correlated with higher order cognitive ability so that increased speed relates to improved cognitive performance. The question of whether the genetic variation in Inspection Time (IT) and Choice Reaction Time (CRT) is associated with IQ through a unitary factor was addressed in this multivariate genetic study of IT, CRT, and IQ subtest scores. The sample included 184 MZ and 206 DZ twin pairs with a mean age of 16.2 years (range 15–18 years). They were administered a visual (π-figure) IT task, a two-choice RT task, five computerized subtests of the Multidimensional Aptitude Battery, and the digit symbol substitution subtest from the WAIS-R. The data supported a factor model comprising a general, three group (verbal ability, visuospatial ability, broad speediness), and specific genetic factor structure, a shared environmental factor influencing all tests but IT, plus unique environmental factors that were largely specific to individual measures. The general genetic factor displayed factor loadings ranging between 0.35 and 0.66 for the IQ subtests, with IT and CRT loadings of −0.47 and −0.24, respectively. Results indicate that a unitary factor is insufficient to describe the entire relationship between cognitive speed measures and all IQ subtests, with independent genetic effects explaining further covariation between processing speed (especially CRT) and Digit Symbol.

Inspection time Choice RT IQ subtests processing speed multivariate genetic modeling