Remembering and knowing: electrophysiological distinctions at encoding but not retrieval.

Contemporary memory theories often distinguish between contextual recollection and acontextual familiarity as two fundamentally different types of recognition memory. It is currently unclear whether recollection and familiarity are supported by two correspondingly distinct retrieval mechanisms, or whether the same type of retrieval processing supports both phenomena. Electrophysiological findings in humans have widely been cited as support for the former, two-process position, in that late-onset parietal "LPC" potentials have been linked to recollection and earlier frontal "FN400" potentials to familiarity. However, recognition memory is generally studied using conceptually rich stimuli such as words, which leaves open an alternative interpretation that one or both of these electrophysiological signals reflect conceptual processing distinct from recollection and familiarity per se. We tested this hypothesis using conceptually impoverished kaleidoscope images, such that opportunities for conceptual processing were minimized. Recollection-based and familiarity-based recognition in a remember/know paradigm were both indexed by LPC potentials. Old/new amplitude differences were greater for recollection compared to familiarity. Despite ample familiarity-based recognition, FN400 old/new effects were not observed, consistent with the contention that these potentials index conceptual processing rather than familiarity. These results cast doubt on interpretations of prior electrophysiological evidence obtained using conceptually rich stimuli as dissociating neural mechanisms of recollection and familiarity. We also found that neural events during encoding differentially predicted later recollection versus later familiarity. Collectively, these findings suggest that the engagement of distinct encoding processes can preferentially lead to recollection or to familiarity even if one type of retrieval process is responsible for both memory expressions.