Implicit memory within a word recognition task: an event-related potentialstudy in human subjects

First, we recorded brain potentials from 15 healthy young subjects during t he performance of a word/non-word discrimination task. During continuous vi sual presentation, some of the meaningful words were repeated after 86-94 s . We found a significant decrease of response time associated with the clas sification of repeated words which is an index for priming, an unconscious brain process. However, event-related potentials (ERPs) did not differ sign ificantly between first and second presentations. Second, we recorded brain potentials during a following recognition test. Some of the meaningful wor ds which were presented only once during the semantic discrimination task w ere repeated and had to be discriminated from randomly interspersed new wor ds. We compared ERPs produced by incorrectly classified repeated words (mis ses) with ERPs produced by correctly classified new words (correct rejectio ns). We found early ERP differences between 250 and 400 ms and later differ ences starting at about 500 ms after the stimulus onset. The early effect o ccurred over parietal scalp locations and the later effect over frontal, pa rietal and occipital scalp locations. This is evidence for unconscious brai n activity related to the processing of missed repeated words. We suggest t hat the later frontal effect we found is due to an enhanced effort of the r etrieval of item representations during word recognition and that the earli er parietal effect reflects partial recognition. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.