Illuminating sex differences in mental rotation using pupillometry

We use pupillometry to measure sex differences in mental rotation (MR) and to investigate the contentious claim that it is a unique spatial ability marked by male advantage in performance. Across two MR tasks – using Shepard-Metzler style cube figures and images of human hands – we measure reaction time (RT) and sensitivity, d’ and supplement these behavioural data with a physiological metric of ‘cognitive effort’ pupil diameter. Differences in RT and in d’ between the sexes are slight for the cubes task, while females are consistently faster than males on the hands task. In contrast, pupillometry reveals striking a sex difference, with males showing significantly lower pupil dilation during the cubes task, suggesting less cognitive effort for comparable behavioural performance. This difference is attenuated during the MR of hands, in line with recent findings that sex differences in spatial abilities dissipate when elements of social perspective taking are introduced.