Familiarity and recollection are qualitatively different explicit-memory phenomena evident during recognition testing. Investigations of the neurocognitive substrates of familiarity and recollection, however, have typically disregarded implicit-memory processes likely to be engaged during recognition tests. We reasoned that differential neural responses to old and new items in a recognition test may reflect either explicit or implicit memory. Putative neural correlates of familiarity in prior experiments, for example, may actually reflect contamination by implicit memory. In two experiments, we used obscure words that subjects could not formally define to tease apart electrophysiological correlates of familiarity and one form of implicit memory, conceptual priming. In Experiment 1, conceptual priming was observed for words only if they elicited meaningful associations. In Experiment 2, two distinct neural signals were observed in conjunction with familiarity-based recognition: late posterior potentials for words that both did and did not elicit meaningful associations and FN400 potentials only for the former. Given that symbolic meaning is a prerequisite for conceptual priming, the combined results specifically link late posterior potentials and FN400 potentials with familiarity and conceptual priming, respectively. These findings contradict previous interpretations of FN400 potentials as generic signals of familiarity and show that repeated stimuli in recognition tests can engender facilitated processing of conceptual information in addition to retrieval processing that leads to the awareness of memory retrieval. The different characteristics of the electrical markers of these two types of process further underscore the biological validity of the distinction between implicit memory and explicit memory.
Familiarity and conceptual implicit memory: Individual differences and neural correlates
