Browsing by Author "Vuoksimaa, Eero"

Studies concerning cognitive sex differences have indicated that, on average, females outperform males in some verbal abilities, whereas males outperform females in some visual-spatial abilities. Prenatal hormones play important role in sexual differentiation. Presence of androgens is believed to cause male brain differentiation. According to animal studies prenatal exposure to testosterone in females can result in masculinized behaviour or physiological traits. Human studies of possible masculinization of females from opposite-sex twin pairs are controversial. Some studies have indicated that female members of opposite-sex twins may be masculinized in some traits, while other studies show no evidence of masculinization. Hence the aim of the present study is to investigate sex differences and possible masculinization of cognitive functions in young adult twins. Subjects (N=336) were recruited from the ongoing longitudinal FinnTwin16 study of Finnish twins born in 1974-1979. Results indicate female superiority in verbal and executive functions and male superiority in visual and working memory functions. Further, in female members of opposite-sex twin pairs the visual abilities were enhanced to the male level. However, they still outperformed males in verbal and executive functions. In male members of opposite-sex twin pairs there were no signs of better performance in functions that favored females. Nor there were evidence of reduced performance in functions that favored males. This study suggests that there occurs masculinization of cognitive functions in females who have a male co-twin. In contrast, males with female co-twins are not feminized in their cognitive functions. These results indicate some benefits of twinship in female members of opposite-sex twin pairs in cognitive abilities. Whether the masculinization is a result of organizational effects of prenatal testosterone or postnatal environmental influences could not be resolved. Future research, with control over environmental influences, is needed to determine the origin of masculinization of cognitive abilities.