SEX AND FAMILIAL SINISTRALITY DIFFERENCES IN COGNITIVE-ABILITIES

Cognitive functioning was assessed in 69 left-handed males and females with a positive family history of left-handedness and in 77 left-hand ed and 55 right-handed males and females without familial left-handedn ess. Compared to females, males performed better on numerical reasonin g and on two visuospatial tasks involving spatial manipulations (Figur e Rotation and Surface Development). Within the group of left-handers, the multivariate effect for Familial Sinistrality was significant. Le ft-handers with familial left-handedness exhibited better scores on nu merical reasoning, on verbal reasoning, and on two visuospatial tasks involving visual closure (Hidden Figures, Picture Completion) than did left-handers without left-handed relatives. The nonfamilial left-hand ers also exhibited lower scores on both inductive reasoning tasks when they were compared to their right-handed counterparts. The outcome ru ns contrary to the prevalent conclusion that left-handers with left-ha nded relatives are more likely to exhibit lower performances on visuos patial tasks than left-handers without such relatives. (C) 1995 Academ ic Press, Inc.