Three event-related potential (ERP) experiments examined whether semantic content can be accessed from visually presented words that cannot be consciously identified. Category labels were shown to participants, followed by masked, briefly exposed words that were either exemplars of the category or not exemplars. The task was to verify the category, by guessing if necessary, and to identify the word, naming it if possible. Exposure durations were selected to allow identification in approximately half the trials. For identified words, there was a marked difference in the ERP response between in-category and out-ofcategory words because of an N400 component. For unidentified words, there was a similar although smaller difference. Conscious identification was defined using a variety of approaches: verbal report, 6-altemative forced choice, and binary categorization (in the context of the regression method; A. G. Greenwald, M. R. Klinger, & E. S. Schuh, 1995). By any definition, ERPs for unidentified words showed evidence of semantic processing. In addition, there were differences in the neuronal populations recruited to process above-threshold versus below-threshold words, suggesting qualitative differences.Perception of stimuli under severely data-limited conditions has been studied throughout the history of experimental psychology, and a number of early studies (reviewed by Adams, 1957) showed that participants performed at levels exceeding chance while expressing very low subjective confidence in their perceptions. The dissociation between a direct measure of aware perception, such as a verbal report, and a different measure, such as a forced guess (which is purportedly sensitive to unconscious processing), has remained a focus of research interest. Whereas the early studies often focused on sensory judgments about nonsymbolic stimuli such as weights and lines, Marcel and others (