Electrophysiological correlates of exemplar-specific processes in implicit and explicit memory

The present ERP study investigated the retrieval of task-irrelevant exemplar-specific information under implicit and explicit
memory conditions. Subjects completed either an indirect memory test (a natural/artificial judgment) or a direct recognition
memory test. Both test groups were presented with new items, identical repetitions, and perceptually different but conceptually
similar exemplars of previously seen study objects. Implicit and explicit memory retrieval elicited clearly dissociable ERP
components that were differentially affected by exemplar changes from study to test. In the indirect test, identical repetitions,
but not different exemplars, elicited a significant ERP repetition priming effect. In contrast, both types of repeated objects
gave rise to a reliable old/new effect in the direct test. The results corroborate that implicit and explicit memory fall
back on distinct cognitive representation and, more importantly, indicate that these representations differ in the type of
stimulus information stored. Implicit retrieval entailed obligatory access to exemplar-specific perceptual information, despite
its being task irrelevant. In contrast, explicit retrieval proved to be more flexible with conceptual and perceptual information
accessed according to task demands.