This study investigated strategy and performance differences between right-handed boys and girls on a mental rotation task. Based on predictions from Casey and Brabeck's (1990) theory of sex differences, the study was also designed to identify a target group of right-handed girls with the optimal combination of genetic and environmental factors (high math/science achievers with nonright-handed immediate relatives). They were predicted to show strategies and performance more similar to those of the boys than to those of both the low math/science achieving girls and the high math/science girls with all right-handed immediate relatives (predicted to have the nonoptimal genotype). Strategy preference was measured using selective interference, whereby subjects solved mental rotation items concurrently with either verbal or visual-spatial interference tasks. Group comparisons were made on the amount of decrement in mental rotation performance as a result of the two types of interference tasks. This provided a basis for comparing the groups on the use of visual-spatial or verbal strategies on the mental rotation task. The boys: (1) did not show a significant advantage over the girls on the mental rotation items, but (2) did depend more on visual-spatial strategies than the girls, and (3) depended less on verbal strategies than the girls. The target girls: (1) outperformed the low math/science achieving girls on the mental rotation items and did not show a significant advantage over the other high math/science group, (2) depended more on visual-spatial strategies than both the other two groups of girls, and (3) depended less on verbal strategies than the low math/science girls, while showing no significant difference compared to the nonoptimal high math/science girls. Examining within-group differences, the boys preferred visual-spatial strategies, while the girls in both the nontarget groups preferred verbal ones. However, for the target girls, no within-subject strategy differences were found. The present findings support the theory that, like the boys, the target girls depend more on visual-spatial strategies than do other girls. It is possible that the target girls use a combination of visual-spatial and verbal strategies when solving mental rotation tasks. © 1991.
