Handedness is modulated by sex and self-perception

Abstract

The distribution of handedness is different for men and women. Less pronounced right- or left-handedness in men is well established and often attributed to direct effects of genetic factors. Many studies observing this sex difference assessed handedness via questionnaire. It may therefore be influenced by a sex-specific bias in self-perception. Permanent inadequate self-perceptions are key characteristics of hypochondriasis. The study therefore tested 1017 participants (614 females) on two standard questionnaires to assess handedness and hypochondriasis: the Edinburgh Inventory and the Whiteley Index. Effects of sex, hypochondriac traits and the direction of handedness (left-handers; right-handers) on the degree of handedness (DH; the strength of lateralisation) were tested with multivariate linear regression. In confirmation of previous results, the DH is lower (less pronounced) in right-handed males than right-handed females, but is similar across sexes in left-handers. Regression analyses showed that for right-handers, male sex and higher hypochondriac traits are independent predictors of lower DH. For left-handers, main effects of sex and hypochondriac traits are not significant whereas a significant interaction of these two factors indicates that in left-handed men higher hypochondriac traits are associated with a differentially stronger shift towards lower DH compared to left-handed women. In conclusion, the DH is modulated by sex-specific effects of self-perception for left-handers but not right-handers. The implications of this finding on current theories of the inheritance of handedness are discussed. The assessment of hypochondriac traits might be useful to control response bias in questionnaire-based studies of human handedness.