Genetic and environmental influences on two measures of speed of information processing and their relation to psychometric intelligence: Evidence from the German observational study of adult twins

Speed of information processing, as measured by reaction times (RTs) in elementary cognitive tasks (ECTs), has been found to be an important correlate of human psychometric intelligence. While the heritability of psychometric intelligence is well understood, we know only a little about genetic and environmental influences on ECT performance, particularly about genetic and environmental contributions to ECT-intelligence relation. These questions were studied by employing two widely used ECTs (Sternberg's memory scanning and Posner's letter-matching task) as well as two psychometric intelligence tests (Advanced Progressive Matrices and Leistungs-Pruf System) in a large sample of 169 monozygotic (MZ) and 131 dizygotic (DZ) twin pairs. As expected, RTs correlated negatively with psychometric intelligence. Moreover, heritability estimates were substantial for both psychometric intelligence and RTs in ECTs. Finally, multivariate genetic analyses suggested that most of the phenotypic correlation between mental speed and intelligence is due to genetic factors.