Neurophysiological correlates of face gender processing in humans

Event-related potentials (ERPs) were recorded while subjects were involved in three gender-processing tasks based on human faces and on human hands. I n one condition all stimuli were only of one gender, preventing any gender discrimination. In a second condition, faces (or hands) of men and women we re intermixed but the gender was irrelevant for the subject's task; hence g ender discrimination was assumed to be incidental. In the third condition, the task required explicit gender discrimination; gender processing was the refore assumed to be intentional. Gender processing had no effect on the oc cipito-temporal negative potential at approximate to 170 ms after stimulati on (N170 component of the ERP), suggesting that the neural mechanisms invol ved in the structural encoding of faces are different from those involved i n the extraction of gender-related facial features. In contrast, incidental and intentional processing of face (but not hand) gender affected the ERPs between 145 and 185 ms from stimulus onset at more anterior scalp location s. This effect was interpreted as evidence for the direct visual processing of faces as described in Bruce and Young's model [Bruce, V. & Young, A. (1 986) Br. J. Psychol., 77, 305-327]. Additional gender discrimination effect s were observed for both faces and hands at mid-parietal sites around 45-85 ms latency, in the incidental task only. This difference was tentatively a ssumed to reflect an early mechanism of coarse visual categorization. Final ly, intentional (but not incidental) gender processing affected the ERPs du ring a later epoch starting from approximate to 200 ms and ending at approx imate to 250 ms for faces, and approximate to 350 ms for hands. This later effect might be related to attention-based gender categorization or to a mo re general categorization activity.