Using unitization as encoding strategy in associative recognition memory : behavioral, fMRI, and ERP evidence

Recognition memory is thought to depend on two processes. Whereas familiarity refers to a simple feeling of knowing a stimulus, recollection enables us to remember associative information such as the place of a particular episode in which the stimulus has occurred. Accordingly, recollection, which relies on the integrity of the hippocampus, is generally required to remember arbitrary associations. In contrast, a familiarity signal, presumably arising in the perirhinal cortex, is sufficient to recognize single items. However, it was shown that the integration of separate items into a single configuration (unitization) leads to reduced involvement of recollection and greater reliance on familiarity. Of special interest is the formation of novel units from previously arbitrary associations during a single encoding episode as this accomplishes the unique ability of episodic memory to remember associative information that relates to a specific event. This thesis reports four experiments in which retrieval processes for novel units were compared to those involved for arbitrary associations, pre-existing units and single items. Experiment 1 and 2 revealed behavioral and fMRI evidence that retrieval of arbitrary word pairs involves flexible recollection whereas retrieval processes relied on the exact configuration when word pairs were studied as novel conceptual units (e.g., vegetable bible = a book consulted by hobby gardeners). Hippocampal engagement during retrieval of novel units was reduced in contrast to arbitrary word pairs. Moreover, brain regions specific to the retrieval of novel units and single items were dissociated. Experiment 3 could not replicate previously reported familiarity-related ERP effects for novel conceptual units as well as pre-existing units (e.g., tea cup). Contextual factors influencing familiarity-based retrieval are discussed. The results from Experiment 4 provide preliminary evidence that arranging two unrelated objects as a scene can enhance familiarity for associations suggesting that not only contiguous entities can be perceived as units.Beim Wiedererkennensgedächtnis geht man von der Beteiligung zweier Prozesse aus. Während Vertrautheit das bloße Gefühl beschreibt, einen Stimulus zu kennen, befähigt einen Rekollektion dazu, assoziative Zusammenhänge zu erinnern, wie beispielsweise der Ort einer spezifischen Episode, in der der Stimulus vorkam. Dementsprechend ist Rekollektion, die von der Unversehrtheit des Hippokampus abhängig ist, notwendig um arbiträre Assoziationen zu erinnern. Im Gegensatz dazu ist für das Wiedererkennens eines einzelnen Items ein Vertrautheitssignal ausreichend, das vermutlich im perirhinalen Cortex entsteht. Es wurde jedoch gezeigt, dass die Integration von separaten Items in eine einzelne Konfiguration (Unitarisierung) zu einer verminderten Beteiligung von Rekollektion und einem verstärkten Zurückgreifen auf Vertrautheit führt. Von besonderer Bedeutung ist die Bildung von neuen Einheiten aus zuvor arbiträren Assoziationen während einer einzigen Lernepisode, da dies die einzigartige Fähigkeit des episodischen Gedächtnisses darstellt, assoziierte Informationen zu erinnern, die einem spezifischen Ereignis zugeordnet werden können. In dieser Dissertation werden vier Experimente berichtet, in denen Abrufprozesse für neue Einheiten mit denen für arbiträre Assoziationen, prä-existierenden Einheiten und einzelne Items verglichen wurden. Experiment 1 und 2 brachten Evidenz aus Verhaltens- und fMRT-Daten dafür, dass der Abruf von arbiträren Assoziation mithilfe flexibler Rekollektion erfolgt, während der Abruf auf der exakten Konfiguration basiert, wenn Wortpaare als neue konzeptuelle Einheiten gelernt wurden (z.B. GEMÜSE BIBEL = Ein Nachschlagewerk, das Hobbygärtner zu Rate ziehen). Hippokampale Aktivierung während des Abrufs von neuen Einheiten war reduziert im Vergleich zu arbiträren Wortpaaren. Darüberhinaus konnten Gehirnareale, die spezifisch beim Abruf von neuen Einheiten beziehungsweise einzelnen Items involviert sind, dissoziiert werden. Experiment 3 konnte zuvor berichtete vertrautheitsrelatierte EKP-Ergebnisse zu neuen konzeptuellen Einheiten und prä-experimentell unitarisierten Wortpaaren (z.B. TEE TASSE) nicht replizieren. Es werden kontextuelle Einflussfaktoren auf vertrautheitsbasiertes Wiedererkennen diskutiert. Die Ergebnisse von Experiment 4 können als vorläufige Evidenz dafür betrachtet werden, dass die Anordnung zweier unrelatierter Objekte als Szene Vertrautheit von Assoziationen verstärken kann. Dies legt nahe, dass nicht nur zusammenhängende Gebilde als Einheit verarbeitet werden können

Mulitple ways to the prior occurrence of an event: An electrophysiological dissociation of experimental and conceptually driven familiarity

Contains fulltext : 221784.pdf (publisher's version ) (Closed access)Recent research has shown that familiarity contributes to associative memory when the to-be-associated stimuli are unitized during encoding. However, the specific processes underlying familiarity-based recognition of unitized representations are still indefinite. In this study, we present electrophysiologically dissociable early old/new effects, presumably related to two different kinds of familiarity inherent in associative recognition tasks. In a study-test associative recognition memory paradigm, we employed encoding conditions that established unitized representations of two pre-experimentally unrelated words, e.g. vegetable-bible. We compared event-related potentials (ERP) during the retrieval of these unitized word pairs using different retrieval cues. Word pairs presented in the same order as during unitization at encoding elicited a parietally distributed early old/new effect which we interpret as reflecting conceptually driven familiarity for newly formed concepts. Conversely, word pairs presented in reversed order only elicited a topographically dissociable early effect, i.e. the mid-frontal old/new effect, the putative correlate of experimental familiarity. The late parietal old/new effect, the putative ERP correlate of recollection, was obtained irrespective of word order, though it was larger for words presented in same order. These results indicate that familiarity may not be a unitary process and that different task demands can promote the assessment of conceptually driven familiarity for novel unitized concepts or experimentally-induced increments of experimental familiarity, respectively.13 p

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 300–500ms 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 lifetime 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

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, thetraining 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 increasesfrom 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

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

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, thetraining 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 increasesfrom 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

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 600 ms 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