Sex differences in infants' visual interest in toys

Evidence indicating that sex-linked toy preferences exist in two nonhuman primate species support the hypothesis that developmental sex differences such as those observed in children's object preferences are shaped in part by inborn factors. If so, then preferences for sex-linked toys may emerge in children before any self-awareness of gender identity and gender-congruent behavior. In order to test this hypothesis, interest in a doll and a toy truck was measured in 30 infants ranging in age from 3 to 8 months using eye-tracking technology that provides precise indicators of visual attention. Consistent with primary hypothesis, sex differences in visual interest in sex-linked toys were found, such that girls showed a visual preference (d > 1.0) for the doll over the toy truck and boys compared to girls showed a greater number of visual fixations on the truck (d = .78). Our findings suggest that the conceptual categories of "masculine" and "feminine" toys are preceded by sex differences in the preferences for perceptual features associated with such objects. The existence of these innate preferences for object features coupled with well-documented social influences may explain why toy preferences are one of the earliest known manifestations of sex-linked social behavior.