Although people form impressions of others with ease, sometimes one's initial perceptions of individuals conflict with what one knows about them. Here, we aimed to investigate the process by which explicit knowledge about people interacts with initial perceptions on the basis of cues from facial appearance. Participants memorized the sexual orientations of men's faces wherein half of the targets were encoded with a sexual orientation opposite to their actual orientation. Subsequent categorization showed that perceivers favored appearance-based information when temporally constrained but favored explicit knowledge about group membership with increased viewing time. Additionally, real-time measures of participants' categorizations showed greater vacillation between appearance-based cues and explicit knowledge as viewing time increased. These findings suggest that explicit knowledge does not simply overrule appearance-based cues past a particular threshold but that the two may interact recurrently with top-down knowledge directing attention and perception at later processing. Copyright © 2014 John Wiley & Sons, Ltd.