title: Genetic covariance among measures of information processing speed, working memory, and IQ.
abstract: The genetic relationship between lower (information processing speed), intermediate (working memory), and higher levels (complex cognitive processes as indexed by IQ) of mental ability was studied in a classical twin design comprising 166 monozygotic and 190 dizygotic twin pairs. Processing speed was measured by a choice reaction time (RT) task (2-, 4-, and 8-choice), working memory by a visual-spatial delayed response task, and IQ by the Multidimensional Aptitude Battery. Multivariate analysis, adjusted for test-retest reliability, showed the presence of a genetic factor influencing all variables and a genetic factor influencing 4- and 8-choice RTs, working memory, and IQ. There were also genetic factors specific to 8-choice RT, working memory, and IQ. The results confirmed a strong relationship between choice RT and IQ (phenotypic correlations: -0.31 to -0.53 in females, -0.32 to -0.56 in males; genotypic correlations: -0.45 to -0.70) and a weaker but significant association between working memory and IQ (phenotypic: 0.26 in females, 0.13 in males; genotypic: 0.34). A significant part of the genetic variance (43%) in IQ was not related to either choice RT or delayed response performance, and may represent higher order cognitive processes.
authors.affiliation: Genetic Epidemiology Laboratory, Queensland Institute of Medical Research, Brisbane, Australia. michelLu@qimr.edu.au
authors.forename: M
authors.initials: M
authors.lastname: Luciano
authors.forename: M
authors.initials: M
authors.lastname: Wright
authors.forename: G A
authors.initials: GA
authors.lastname: Smith
authors.forename: G M
authors.initials: GM
authors.lastname: Geffen
authors.forename: L B
authors.initials: LB
authors.lastname: Geffen
authors.forename: N G
authors.initials: NG
authors.lastname: Martin
mesh_terms: D000293:Adolescent; D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D007360:Intelligence / Q000235:genetics*; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D008957:Models, Genetic; D015999:Multivariate Analysis; D010641:Phenotype; D011930:Reaction Time / Q000235:genetics*; D014427:Twins / Q000235:genetics*