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

Abstract

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.

ERP evidence for hemispheric asymmetries in exemplar-specific explicit memory access

“…It has been hypothesized that a perceptual processing focus during encoding is necessary for exemplar-changes to affect FN400 old/new effects (Küper et al, 2012). The present data are in line with this idea as we observed exemplar-specific FN400 effects with a size estimation study task that put high demands on perceptual processing and imagery (cf., Kosslyn, 1975).…”

“…The same result pattern has emerged in retrieval tasks with three response alternatives requiring participants to distinguish between identical repetitions of studied items, modified study items and new unstudied items (e.g., Haese & Czernochowski, 2015). In contrast, memory inclusion tasks in which both types of old items have to be accepted as 'old' have given rise to comparable LPC old/new effects for both types of old items (see the discussion in Küper et al, 2012). The present results extend these findings and indicate that exemplar-specificity in LPC modulations can similarly be contingent on top-down processes associated with the cerebral hemisphere governing initial stimulus processing at retrieval.…”

“…in memory exclusion but not inclusion tasks (cf., Küper et al, 2012). As such we would expect to see equivalent LPC old/new effects for both different exemplars and identical repetitions of study items, at the very least with RVF/LH presentation.…”

“…Yet, presenting perceptually changed versions or different exemplars of study items at test has reduced the FN400 old/new effect, at least when stimulus encoding was perceptually focused (Ecker et al, 2007a;2007b;Groh-Bordin et al, 2005;2006;Schloerscheidt & Rugg, 2004;Grove & Wilding, 2009). When perceptual information was not prioritized, however, equivalent FN400 old/new effects have emerged for studied and modified items (Curran, 2000;Curran & Cleary, 2003;Curran & Dien, 2003;Küper et al, 2012). This illustrates that accessing perceptual feature information in the course of familiarity-based retrieval is a relatively flexible process that can be contingent on memory encoding or retrieval task demands.…”

“…Since we used a perceptually focused encoding task, we would expect to find increased familiarity as indexed by more pronounced FN400 old/new effects for identical repetitions as opposed to different exemplars of study items (cf., the discussion in Küper et al, 2012). In the context of a memory inclusion task which renders exemplar-specific information task-irrelevant, exemplar-specific FN400 effects in both hemispheres would indicate that both are capable of addressing specific perceptual information in a relatively automatic fashion.…”