Twin-family studies of perceptual speed ability

Perceptual speed tests exhibit consistent sex differences, and an X-linked dominant gene has been hypothesized to explain female superiority in the aptitude. To evaluate that hypothesis, two tests from the ETS battery were administered to like-sex twins of college age, adult monozygotic twins, and their spouses and children. Offspring of MZ twins are genetic half-siblings reared as cousins in separate households; comparisons of the half-fraternities and half-sororities of male and female twin parents provide a direct test of X linkage. Test scores were transformed within age bands, and the age-sex standardized scores were evaluated for genetic variance and X-linked transmission. The analysis documents substantial heritability in perceptual speed that is inconsistent with X linkage. Gender differences in the ability may reflect polygenic transmission, with differing thresholds arising from cultural stereotypy in sex-role training.This is publication No. 78-42 from the Department of Medical Genetics and was supported by a USPHS Training Grant (GM 1056) and by the Indiana University Human Genetics Center (GM 21054).