Priority of spontaneous gender categorization of same-sex faces in young adults.

To cluster others into male and female groups during face perception is pivotal for appropriate social behaviours. What remains unclear is whether gender categorization of faces is mediated by the same pattern of cognitive and neural processes in women and men. The perception bias hypothesis predicts earlier gender categorization of female (vs. male) faces regardless of an observer's gender. In contrast, the social task demand hypothesis predicts earlier gender categorization of faces that are of the same (vs. different) sex of an observer. We tested these predictions by recording electroencephalography signals to faces of one gender presented in a repetition condition and to both female and male faces in an alternating condition. The neural processes underlying gender categorization were assessed by quantifying repetition suppression of brain activities to faces in the repetition relative to alternating conditions. We found significant repetition suppression of a positive frontal-central activity at 170-210 ms after face onset (the P2 component) to female (but not to male) faces in women. However, repetition suppression of the P2 amplitude occurred to male (but not to female) faces in men. Our findings suggest that observers' genders are pivotal for prioritization of gender categorization of male or female faces in young adults.