A sex difference in mental rotation in young infants.

Three- to 4-month-old female and male human infants were administered a two-dimensional mental-rotation task similar to those given to older children and adults. Infants were familiarized with the number 1 (or its mirror image) in seven different rotations between 0 degrees and 360 degrees, and then preference-tested with a novel rotation of the familiar stimulus paired with its mirror image. Male infants displayed a novelty preference for the mirror-image stimulus over the novel rotation of the familiar stimulus, whereas females divided attention between the two test stimuli. The results point toward an early emergence of a sex difference in mental rotation.