Semantic processing without conscious identification: Evidence from event-related potentials

Three event-related potential (ERP) experiments examined whether semantic c ontent can be accessed From visually presented words that cannot he conscio usly identified. Category labels were shown to participants, followed by ma sked, briefly exposed words that were either exemplars of the category or n ot exemplars. The task was to verify the category, by guessing if necessary , and to identify the word naming it if possible. Exposure durations were s elected to allow identification in approximately half the trials. For ident ified words, there was a marked difference in the ERP response between in-c ategory and out-of-category words because of an N400 component. For unident ified words, there was a similar although smaller difference. Conscious ide ntification was defined using a variety of approaches: verbal report 6-alte rnative forced choice, and binary categorization (in the context of the reg ression method; A. G. Greenwald, M. R. Klinger, & E. S. Schuh, 1995). By an y definition, ERPs for unidentified words showed evidence of semantic proce ssing. In addition, there were differences in the neuronal populations recr uited to process above-threshold versus below-threshold words, suggesting q ualitative differences.