Schema-congruency supports the formation of unitized representations: Evidence from event-related potentials.

The main goal of the present study was to investigate whether schema-based encoding of novel word pairs (i.e., novel compound words) supports the formation of unitized representations and thus, associative familiarity-based recognition. We report two experiments that both comprise an incidental learning task, in which novel noun-noun compound words were presented in semantically congruent contexts, enabling schema-supported processing of both constituents, contrasted with a schema-neutral condition. In Experiment 1, the effects of schema congruency on memory performance were larger for associative memory performance than for item memory performance in a memory test in which intact, recombined, and new compound words had to be discriminated. This supports the view that schema congruency boosts associative memory by promoting unitization. When contrasting event-related potentials (ERPs) for hits with correct rejections or associative misses, an N400 attenuation effect (520-676 ms) indicating absolute familiarity was present in the congruent condition, but not in the neutral condition. In line with this, a direct comparison of ERPs on hits across conditions revealed more positive waveforms in the congruent than in the neutral condition. This suggests that absolute familiarity contributes to associative recognition memory when schema-supported processing is established. In Experiment 2, we tested whether schema congruency enables the formation of semantically overlapping representations. Therefore, we included semantically similar lure compound words in the test phase and compared false alarm rates to these lures across conditions. In line with our hypothesis, we found higher false alarm rates in the congruent as compared to the neutral condition. In conclusion, we provide converging evidence for the view that schema congruency enables the formation of unitized representations and supports familiarity-based memory retrieval.

Task context dissociates the FN400 and the N400.

In event-related potential studies, familiarity-based recognition has been associated with the FN400, that is, more positive-going waveforms for old items than new items 300-500 ms post-stimulus onset, maximal at frontal electrodes. We tested the proposition that the FN400 reflects the attribution of unexpected processing fluency to familiarity. This implies that the FN400 is greater when fluency is less expected, that is, for less familiar stimuli. Moreover, the FN400 should be modulated by the goal of remembering and only elicited when fluency is correctly attributed to the past, that is, by correct old responses in recognition memory tests. In the absence of a retrieval task, enhanced fluency for repeated items should be associated with an N400 attenuation as no episodic attribution takes place. In an incidental study-test design with words of low and high life-time familiarity, participants made pleasantness judgments for half of the studied words. The other half re-appeared in a recognition test. Only in the latter task, participants had the goal of remembering. As both tasks included also new words, we could compare old/new effects under conditions in which both effects are driven by increased fluency for repeated words. We did not find the expected differences in the FN400 for low vs. high life-time familiarity items. However, as expected, we found a frontally distributed FN400 in the recognition test whereas the old/new effect in the pleasantness task resembled an N400 effect. This supports the view that the FN400 occurs when fluency is attributed to familiarity during a recognition decision.

Can the elderly take the action? - The influence of unitization induced by action relationships on the associative memory deficit.

Healthy aging is associated with intact familiarity, whereas recollection, usually supporting associative memory, is attenuated. Accordingly, associative memory shows a stronger age-related decline than item memory. One approach to alleviate age-related associative memory deficits is to increase the contribution of familiarity to associative memory by creating encoding conditions that allow to integrate separate stimuli to an entity (unitization). The current study investigated whether bottom-up unitization can reduce age-related differences in associative memory. Younger (YA) and older adults (OA) studied associations between semantically unrelated objects, spatially arranged in a way that an action between these two objects is possible (unitized, e.g., emptying a bottle into a sneaker) or not (non-unitized). At test, participants distinguished intact from recombined and new object pairs. As expected, we found larger age differences for associative memory than for item memory. Additionally, the presence of action relationships supports memory performance in both age groups. In the event-related potentials (ERP) of the test phase, we observed an age-related attenuation of recollection and preserved familiarity independent of the action relationship condition. Considering comparisons including the recombined pairs, the ERP correlate of associative familiarity (i.e., intact vs. recombined) was present in OA for action-related pairs, whereas for YA, there was no evidence for enhanced familiarity for action-related pairs. In the late time window, ERP evidence for recollection for intact action-related object pairs was obtained independent of age group. In conclusion, both age groups benefited from unitization by action relationships but by different mechanisms. While YA show no associative familiarity for action-related object pairs but a general reliance on recollection for associations in action-related and -unrelated pairs, OA seem to rely more on familiarity for the specific arrangement of action-related pairs.

Effects of emotional study context on immediate and delayed recognition memory: Evidence from event-related potentials.

Whilst research has largely focused on the recognition of emotional items, emotion may be a more subtle part of our surroundings and conveyed by context rather than by items. Using ERPs, we investigated which effects an arousing context during encoding may have for item-context binding and subsequent familiarity-based and recollection-based item-memory. It has been suggested that arousal could facilitate item-context bindings and by this enhance the contribution of recollection to subsequent memory judgements. Alternatively, arousal could shift attention onto central features of a scene and by this foster unitisation during encoding. This could boost the contribution of familiarity to remembering. Participants learnt neutral objects paired with ecologically highly valid emotional faces whose names later served as neutral cues during an immediate and delayed test phase. Participants identified objects faster when they had originally been studied together with emotional context faces. Items with both neutral and emotional context elicited an early frontal ERP old/new difference (200-400 ms). Neither the neurophysiological correlate for familiarity nor recollection were specific to emotionality. For the ERP correlate of recollection, we found an interaction between stimulus type and day, suggesting that this measure decreased to a larger extend on Day 2 compared with Day 1. However, we did not find direct evidence for delayed forgetting of items encoded in emotional contexts at Day 2. Emotion at encoding might make retrieval of items with emotional context more readily accessible, but we found no significant evidence that emotional context either facilitated familiarity-based or recollection-based item-memory after a delay of 24 h.

High feature overlap and incidental encoding drive rapid semantic integration in the fast mapping paradigm.

Contrary to traditional theories, it has been shown that novel, arbitrary associations can be rapidly integrated into cortical networks through a learning paradigm called fast mapping (FM), possibly bypassing time-consuming hippocampal-neocortical consolidation processes. In the FM paradigm, an unknown item is presented next to a known item and participants answer a question referring to an unfamiliar label, presumably inferring that the label belongs to the unknown item. However, factors driving rapid cortical integration through FM are still under debate. The FM task requires the discrimination between complex objects and the binding of the unknown item to the label. Discriminating between complex and especially highly similar objects is a central function of the perirhinal cortex, a structure also involved in the binding of single elements to a unit. We suggested that triggering perirhinal processing by increasing the demands on item discrimination through increasing feature overlap between the unknown and the known item might foster the binding of the unknown item to the label and their rapid cortical integration. We found lexical integration of the labels after learning through FM, but this was not affected by feature overlap. However, semantic integration of the label immediately after FM encoding was more successful when the items shared many features than when they shared few features. Moreover, effects of rapid semantic integration through FM were reduced if encoding was intentional and if no discrimination was required. This indicates that incidental encoding and a high feature overlap are driving factors for rapid semantic integration through FM. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

High feature overlap reveals the importance of anterior and medial temporal lobe structures for learning by means of fast mapping.

Contrary to traditional theories of declarative memory, it has recently been shown that novel, arbitrary associations can rapidly and directly be integrated into cortical memory networks by means of a learning procedure called fast mapping (FM), possibly bypassing time-consuming hippocampal-neocortical consolidation processes. In the typical FM paradigm, a picture of a previously unknown item is presented next to a picture of a previously known item and participants answer a question referring to an unfamiliar label, thereby incidentally creating associations between the unknown item and the label. However, contradictory findings have been reported and factors moderating rapid cortical integration through FM yet need to be identified. Previous behavioral results showed that rapid semantic integration through FM was boosted if the unknown and the known item shared many features. In light of this, we propose that the perirhinal cortex might be especially qualified to support the rapid incorporation of these associations into cortical memory networks within the FM paradigm, due to its computational mechanisms during the processing of complex and particularly highly similar objects. We therefore expected that a high degree of feature overlap between the unknown and the known item would trigger strong engagement of the perirhinal cortex at encoding, which in turn might enhance rapid cortical integration of the novel picture-label associations. Within an fMRI experiment, we observed greater subsequent memory effects (i.e., stronger activation for subsequent hits than misses) during encoding in the perirhinal cortex and an associated anterior temporal network if the items shared many features than if they shared few features. This indicates that the perirhinal cortex indeed contributes to the acquisition of novel associations by means of FM if feature overlap is high.

The more you know: Schema-congruency supports associative encoding of novel compound words. Evidence from event-related potentials.

We aimed to investigate the neurocognitive mechanisms of event congruency with prior (schema) knowledge for the learning of novel compound words. Event-related potentials (ERPs) were recorded during an incidental learning task, in which novel noun-noun compounds were presented in a semantically congruent context, enabling schema-supported processing, or in a neutral context. As expected, associative memory performance was better for compounds preceded by a congruent context. Although the N400 was attenuated in the congruent condition, subsequent memory effects (SMEs) in the N400 time interval did not differ across conditions, suggesting that the processes reflected in the N400 cannot account for the memory advantage in the congruent condition. However, a parietal SME was obtained for compounds preceded by a congruent context, only, which we interpret as reflecting the schema-supported formation of a conceptual compound representation. A late frontal SME was obtained in both conditions, presumably reflecting the more general inter-item associative encoding of compound constituents.

The ERP correlate of episodic recollection is a neurocognitive determinant of subjective memory complaints: Implications on their predictive validity.

Objective: Subjective memory complaints (SMCs) seem to be a promising marker of cognitive decline and progressing dementia in healthy older adults. However, SMCs have not been invariably related to memory performance, probably because objective tests do not always target the specific neurocognitive processes that underlie SMCs. This study disentangles the neurocognitive basis of memory-specific SMCs by investigating their dependence on episodic recollection which relies on the hippocampal relational memory system as well as their predictive value for memory tests that target such processes. Method: In 29 healthy participants, aged 52-70 years, we assessed SMCs, using the Memory Assessment Clinics Self-Rating Scale (MAC-S), episodic recollection and associated event-related potentials (ERPs), the Verbal Learning and Memory Test (VLMT), which assesses hippocampal functions, as well as depressive symptomology, using Beck Depression Inventory II (BDI). We used correlational and regression models to estimate the association of SMCs with recollection and VLMT performance, independent of age, depressive symptomology, and the P300, an ERP correlate of attentional processes. Results: The ERP correlate of source-recollection significantly accounted for 9% unique variance in SMCs. Moreover, SMCs explained unique proportions of variance in several VLMT measures (ΔR 2 ranging from .07 to .17). Conclusions: SMCs are partially determined by malfunctioning of the hippocampal relational memory system. In line with this, SMCs predict performance in objective memory tests if they also target hippocampally dependent processes. The study emphasizes the prognostic relevance of SMCs as episodic memory decline is an important preclinical marker for the development of Alzheimer's Disease (AD). (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Usefulness of familiarity signals during recognition depends on test format: Neurocognitive evidence for a core assumption of the CLS framework.

Familiarity-based discrimination between studied items and similar foils in yes/no recognition memory tests is relatively poor. The complementary learning systems (CLS) framework explains this with the small difference in familiarity strength between targets and foils. The framework, however, also predicts that familiarity values of targets and corresponding similar foils are directly comparable - as long as they are presented side by side in a forced-choice corresponding (FCC) test. This is because in each trial, targets tend to be more familiar than their corresponding foils. In contrast, when forced-choice displays contain non-corresponding foils (FCNC) which are similar to other studied items, familiarity values are not directly comparable (as in yes/no-tasks). In a recognition memory task with pictures of objects, we found that the putative ERP correlate of familiarity, the mid-frontal old/new effect for targets vs. foils, was significantly larger in FCC compared to FCNC displays. Moreover, single-trial target-foil amplitude differences predicted the accuracy of the recognition judgment. This study supports the assumption of the CLS framework that the test format can influence the diagnostic reliability of familiarity. Moreover, it implies that the mid-frontal old/new effect does not reflect the difference in the familiarity signal between studied and non-studied items but the task-adequate assessment of this signal.

Improving episodic memory: Frontal-midline theta neurofeedback training increases source memory performance.

Cognitive and neurofeedback training (NFT) studies have demonstrated that training-induced alterations of frontal-midline (FM) theta activity (4-8 Hz) transfer to cognitive control processes. Given that FM theta oscillations are assumed to provide top-down control for episodic memory retrieval, especially for source retrieval, that is, accurate recollection of contextual details of prior episodes, the present study investigated whether FM theta NFT transfers to memory control processes. It was assessed (1) whether FM theta NFT improves source retrieval and modulates its underlying EEG characteristics and (2) whether this transfer extends over two posttests. Over seven NFT sessions, the training group who trained individual FM theta activity showed greater FM theta increase than an active control group who trained randomly chosen frequency bands. The training group showed better source retrieval in a posttraining session performed 13 days after NFT and their performance increases from pre- to both posttraining sessions were predicted by NFT theta increases. Thus, training-induced enhancement of memory control processes seems to protect newly formed memories from proactive interference of previously learned information. EEG analyses revealed that during pretest both groups showed source memory specific theta activity at frontal and parietal sites. Surprisingly, training-induced improvements in source retrieval tended to be accompanied by less prestimulus FM theta activity, which was predicted by NFT theta change for the training but not the control group, suggesting a more efficient use of memory control processes after training. The present findings provide unique evidence for the enhancement of memory control processes by FM theta NFT.

From fluency to recognition decisions: A broader view of familiarity-based remembering.

The goal of this article is to critically examine current claims and assumptions about the FN400, an event-related potential (ERP) component which has been related to familiarity memory though some uncertainty exists regarding the cognitive processes captured by the FN400. It is proposed that familiarity can be multiply determined and that an important distinction has to be made between a recent-exposure, relative familiarity mechanism indexed by the FN400 and an absolute/baseline familiarity mechanism being reflected by a coincidental but topographically distinct ERP effect. We suggest a broader conceptualization of the memory processes reflected by the FN400 and propose an unexpected fluency-attribution account of familiarity according to which familiarity results from a fast assessment of ongoing processing fluency relative to previous events or current expectations. The computations underlying fluency attribution may be closely related to those characterizing the relative familiarity mechanism underlying the FN400. We also argue that concerted activation of the perirhinal cortex (PrC) and the lateral prefrontal cortex (PFC) plays a pivotal role for fluency attributions and the generation of the FN400.

Evidence for fast mapping in adults - Moderating factors yet need to be identified.

Cooper, Greve, and Henson (this issue) discuss if fast mapping (FM) is dissociable from other learning procedures in adults. We strongly agree that drawing conclusions on cortical integration from recognition accuracy is questionable in healthy young adults. Additionally, we advise against interpreting explicit measures in patient studies if residual hippocampal functioning cannot be excluded or extra-hippocampal structures are also affected. Due to promising fMRI data patterns and confounds in studies reporting no evidence for implicitly measured semantic integration, we suggest that factors moderating FM learning success need to be systematically identified rather than doubting rapid cortical integration through FM.

Unitization of word pairs in young and older adults: Encoding mechanisms and retrieval outcomes.

We investigated whether healthy older adults are able to use an episodic encoding strategy known as unitization, which allows for subsequent associative retrieval based on familiarity, to overcome their associative memory deficit. Young and healthy older participants were presented with word pairs either together with a definition that allowed to combine the word pairs to a new concept (high unitization condition), or together with a sentence frame (low unitization condition). In Experiment 1, an age-related reduction in performance on a standard associative recognition test was observed in both conditions. This deficit was unexpectedly not reduced, but tended to be larger in the high than the low unitization condition. According to receiver-operating characteristics, this difference was due to a reduction of recollection, but not familiarity, in the high unitization condition. Instead of a standard recognition test, Experiment 2 used a 2 alternative forced choice (2AFC) test designed to maximize the contribution of familiarity to associative recognition. Although the disadvantage of older adults in the high versus the low unitization condition was abolished, there was still no performance advantage for the high unitization condition. Event-related potentials (ERPs) recorded during the encoding phase of Experiment 1 suggest that, while young adults engage in predictive processing during unitization, older adults do not engage in such predictive processing, which may prevent them from using unitization to their advantage in the subsequent associative memory test. We discuss the task characteristics that have an impact on the effect of unitization conditions on associative memory in older adults. (PsycINFO Database Record

Topographical differences of frontal-midline theta activity reflect functional differences in cognitive control abilities.

Electrophysiological oscillations are assumed to be the core mechanism for large-scale network communication. The specific role of frontal-midline theta oscillations as cognitive control mechanism is under debate. According to the dual mechanisms of control framework, cognitive control processes can be divided into proactive and reactive control. The present study aimed at investigating the role of frontal-midline theta activity by assessing oscillations in two tasks varying in the type of cognitive control needed. More specifically, a delayed match to sample (DMTS) task requiring proactive control and a color Stroop task recruiting reactive control processes were conducted within the same group of participants. Moreover, both tasks contained conditions with low and high need for cognitive control. As expected larger frontal-midline theta activity was found in conditions with high need for cognitive control. However, theta activity was focally activated at frontal sites in the DMTS task whereas it had a broader topographical distribution in the Stroop task, indicating that both proactive and reactive control are reflected in frontal-midline theta activity but reactive control is additionally characterized by a broader theta activation. These findings support the conclusion that frontal-midline theta acts functionally different depending on task requirements.

Age effects on associative memory for novel picture pairings.

Normal aging is usually accompanied by greater memory decline for associations than for single items. Though associative memory is generally supported by recollection, it has been suggested that familiarity can also contribute to associative memory when stimuli can be unitized and encoded as a single entity. Given that familiarity remains intact during healthy aging, this may be one route to reducing age-related associative deficits. The current study investigated age-related differences in associative memory under conditions that were expected to differentially promote unitization, in this case by manipulating the spatial arrangement of two semantically unrelated objects positioned relative to each other in either spatially implausible or plausible orientations. Event-related potential (ERP) correlates of item and associative memory were recorded whilst younger and older adults were required to discriminate between old, recombined and new pairs of objects. These ERP correlates of item and associative memory did not vary with plausibility, whereas behavioral measures revealed that both associative and item memory were greater for spatially plausible than implausible pair arrangements. Contrary to predictions, older adults were less able to take advantage of this memory benefit than younger participants. Potential reasons for this are considered, and these are informed by those lines of evidence which indicate older participants were less sensitive to the bottom-up spatial manipulation employed here. It is recommended that future strategies for redressing age-related associative deficits should take account of the aging brain's increasing reliance on pre-existing semantic associations.

Separating Event-related Potential Effects for Conceptual Fluency and Episodic Familiarity.

ERP old/new effects have been associated with different subprocesses of episodic recognition memory. The notion that recollection is reflected in the left parietal old/new effect seems to be uncontested. However, an association between episodic familiarity and the mid-frontal old/new effect is not uncontroversial. It has been argued that the mid-frontal old/new effect is functionally equivalent to the N400 and hence merely reflects differences in conceptual fluency between old and new items. Therefore, it is related to episodic familiarity only in situations in which conceptual fluency covaries with familiarity. Alternatively, the old/new effect in this time window reflects an interaction of episodic familiarity and conceptual processing with each making a unique functional contribution. To test this latter account, we manipulated conceptual fluency and episodic familiarity orthogonally in an incidental recognition test: Visually presented old and new words were preceded by either conceptually related or unrelated auditory prime words. If the mid-frontal old/new effect is functionally distinguishable from conceptual priming effects, an ERP contrast reflecting pure priming (correct rejections in the related vs. unrelated condition) and a contrast reflecting priming plus familiarity (hits in the related vs. correct rejections in the unrelated condition) should differ in scalp distribution. As predicted, the pure priming contrast had a right-parietal distribution, as typically observed for the N400 effect, whereas the priming plus familiarity contrast was significantly more frontally accentuated. These findings implicate that old/new effects in this time window are driven by unique functional contributions of episodic familiarity and conceptual processing.

ERP Subsequent Memory Effects Differ between Inter-Item and Unitization Encoding Tasks.

The "subsequent memory paradigm" is an analysis tool to identify brain activity elicited during episodic encoding that is associated with successful subsequent retrieval. Two commonly observed event-related potential "subsequent memory effects" (SMEs) are the parietal SME in the P300 time window and the frontal slow wave SME, but to date a clear characterization of the circumstances under which each SME is observed is missing. To test the hypothesis that the parietal SME occurs when aspects of an experience are unitized into a single item representation, while inter-item associative encoding is reflected in the frontal slow wave effect, participants were assigned to one of two conditions that emphasized one of the encoding types under otherwise matched study phases of a recognition memory experiment. Word pairs were presented either in the context of a definition that allowed to combine the word pairs into a new concept (unitization or item encoding) or together with a sentence frame (inter-item encoding). Performance on the recognition test did not differ between the groups. The parietal SME was only found in the definition group, supporting the idea that this SME occurs when the components of an association are integrated in a unitized item representation. An early prefrontal negativity also exhibited an SME only in this group, suggesting that the formation of novel units occurs through interactions of multiple brain areas. The frontal slow wave SME was pronounced in both groups and may thus reflect processes generally involved in encoding of associations. Our results provide evidence for a partial dissociation of the eliciting conditions of the two types of SMEs and therefore provide a tool for future studies to characterize the different types of episodic encoding.

The Effect of Unitizing Word Pairs on Recollection Versus Familiarity-Based Retrieval- Further Evidence From ERPs.

We investigated the contribution of familiarity and recollection to associative retrieval of word pairs depending on the extent to which the pairs have been unitized through task instructions in the encoding phase. Participants in the unitization condition encoded word pairs in the context of a definition that tied them together such that they were treated as a coherent new item, while in the control condition word pairs were inserted into a sentence frame in which each word remained an individual unit. Contrasting event-related potentials (ERERPs) elicited in a subsequent recognition test by old (intact) and recombined (a new combination of two words from different study pairs) word pairs, an early frontal effect, the putative ER P correlate of familiarity-based retrieval, was apparent in the unitization condition. The left parietal old/new effect, reflecting recollection-based retrieval, was elicited only in the control condition. This suggests that in the unitization condition only, familiarity was sufficiently diagnostic to distinguish old from recombined pairs, while in the control condition, recollection contributed to associative recognition. Our findings add to a body of literature suggesting that unitization of associations increases the relative contribution of familiarity to subsequent associative retrieval.

Is a novel conceptual unit more than the sum of its parts?: FMRI evidence from an associative recognition memory study.

Recollection, an effortful process relying on the integrity of a brain network including the hippocampus, is generally required to remember arbitrary associations whereas a simple familiarity signal arising in the perirhinal cortex is sufficient to recognize single items. However, the integration of separate items into a single configuration (unitization) leads to reduced involvement of recollection and greater reliance on familiarity. This seems to imply that unitized associations are processed similar to single items. Here, using functional magnetic resonance imaging, we investigated the effects of unitization as encoding strategy on retrieval processes in a between-group-design. A definition was provided that allows combining two unrelated words into a novel conceptual unit (e.g., milk taxi = a delivery service, which is directly dispatched from a farm). We compared this to an encoding strategy in which the words were studied as parts of a sentence. We included pairs in reversed order at test because reversing a unitized word pair is assumed to disrupt the unit while leaving item familiarity for the single constituents intact. This enabled us to compare recognition memory for novel units and single items. Sentence encoding led to a flexible recruitment of brain areas previously associated with recollection, irrespective of the order of the test pair. Unitization encoding reduced the involvement of the recollection network and specifically engaged regions within the parahippocampal cortex and the medial prefrontal cortex for novel units. In contrast, recognition of reversed pairs involved activation of BA 45 in the left inferior frontal gyrus. This possibly suggests that familiarity for novel units and single items are associated with different brain networks.

More ways than one: ERPs reveal multiple familiarity signals in the word frequency mirror effect.

Recent dual-process models of the word frequency mirror effect place absolute familiarity, an item׳s baseline familiarity at a given time point, as responsible for false alarm differences and recollection for hit rate differences between high and low frequency items. One of the earliest dual-process propositions, however, posits an additional relative familiarity mechanism which is sensitive to recent presentation but relative to the absolute familiarity of a particular item (Mandler, 1980). In this study, it was possible to map these three mechanisms onto known event-related potential (ERP) effects in an old/new recognition task with high and low frequency words. Contrasts between ERPs elicited by high and low frequency new items were assumed to index absolute familiarity, and the distribution of this effect from 300 to 600ms was topographically distinct from a temporally-overlapping midfrontally-distributed old/new effect which was larger for low than high frequency words, as would be expected from a relative familiarity mechanism. A later left parietal old/new effect, strongly linked to recollection, was only present for low frequency items. These frequency-sensitive amplitude differences for both old/new effects disappeared in a second recognition task in which old/new decisions were made under a time constraint, although the posterior absolute familiarity effect remained unaffected by the speeding of responses. The data support the assertion that three distinct recognition processes are affected by word frequency in recognition memory tasks, and the qualitatively distinct distributions associated with the two familiarity contrasts support the presence of two cognitively distinct familiarity mechanisms.