A study of cognitive sex differences as related to brain laterality

Abstract

Subjects were given a short form of the WAIS plus two group tests, one verbal and one spatial. Hand preference was assessed by responses to the Annett Handedness questionnaire. Verbal and perceptual-spatial abilities were compared for firm right, firm left and mixed left males and females. It was predicted that left-handed females would be most impaired, relative to dextral males, on the spatial measures, while left-handed males and right-handed females would be intermediate in spatial competence between right-handed males and left-handed females, but not different from them in verbal competence. Mode of writing in sinistrals was also examined. -- The group tests proved more sensitive to the phenomena under study. Predictions were confirmed on the verbal group test, and on the spatial test all differences were in the expected directions but were statistically significant only for firm left subjects. Firm left, mixed left and right-handed females were not different from their opposite-sex groups on either the verbal or spatial measure; thus on these tests handedness proved to be a better predictor of cognitive abilities than sex. -- The WAIS measures found no significant differences, and several possible explanations for this are discussed. -- Results for normal- and inverted-writing left handers were not different for males, but female inverted writers were impaired both verbally and spatially relative to normal-writing females. -- These results lend partial support to Levy's hypothesis that poorer spatial ability reflects weaker functional lateralization. However, a careful definition of handedness is needed, as well as a clear description of "spatial" and "verbal" abilities. It is also necessary to determine which tests can best detect various aspects of cognitive function.