Category expectations: a differential modulation of the N170 potential for faces and words.

The goal of the present study was to explore whether endogenous attention can be oriented to different perceptual categories and to examine how these expectations modulate visual stimulus processing. We designed a cueing paradigm that prepared participants, on a trial-by-trial basis, for the most likely stimulus category of the target, which could be either a face or a word. Participants were asked to discriminate the gender of the stimuli, regardless of their category. We measured participants' brain activity by means of a high-density electroencephalographic recording system to investigate the neural correlates of orienting attention to faces and words. As expected, we observed a behavioural facilitation for valid compared to invalid trials. In addition, target expectations influenced stimulus processing at several points in time. Most importantly, attention modulated the lateralized N170 component in a category-specific fashion. These results show that, at least under certain circumstances, orienting endogenous attention to different categories can influence the perceptual stages of face and word visual processing.