Investigating the relationship between implicit and explicit memory: Evidence that masked repetition priming speeds the onset of recollection

Evolving Engrams Demand Changes in Effective Cues

A longstanding principle in episodic memory research, known as the encoding specificity hypothesis, holds that an effective retrieval cue should closely match the original encoding conditions. This principle assumes that a successful retrieval cue remains static over time. Despite the broad acceptance of this idea, it conflicts with one of the most well-established findings in memory research: The dynamic and ever-changing nature of episodic memories. In this article, we propose that the most effective retrieval cue should engage with the current state of the memory, which may have shifted significantly since encoding. By redefining the criteria for successful recall, we challenge a core principle of the field and open new avenues for exploring memory accessibility, offering fresh insights into both theoretical, and applied domains.

Separating the FN400 and N400 event-related potential components in masked word priming

Masked word repetition (priming) increases "old" responses on an episodic recognition test, which has been attributed to more fluent target processing. Such results hinge on comparisons to a control prime that is "fluency-neutral". A common practice is to use unrelated word primes for this purpose when some evidence suggests that they actually decrease target word processing fluency (disfluency). ERP and behavioral measures were collected in three experiments that used non-letter symbols as a fluency-neutral control and match primes to increase processing fluency. Experiment 1 compared unrelated word primes and orthographically dissimilar nonword primes to determine whether these primes cause disfluency. Experiment 2 contrasted orthographically dissimilar and similar nonword primes. Experiment 3 examined semantically related primes to test theoretical predictions derived from Experiments 1 and 2. All three experiments provide evidence that the FN400 and N400 are distinct ERP components because many primes altered only one of the components. Relative to the control condition, match (Exps 1 & 2) and semantic primes selectively affected N400 amplitudes, whereas unrelated word primes and orthographically dissimilar nonword primes selectively affected FN400 amplitudes. The Unexpected Fluency Attribution model (Mecklinger & Bader, 2020) provides a framework for understanding the cognitive processes associated with each ERP component.

Multiple sources of unconscious-information processing affect a single response: independent unconscious priming effects

At present there is little knowledge on whether and how multiple pieces of unconscious information can simultaneously affect a single conscious response. In the present study, we manipulated the congruency relation between a masked prime arrow and the target arrow, as well as that between masked flankers and the target arrow. The results demonstrated that the masked prime and flankers produced independent unconscious priming effects on the response to the target. In the process of studying the above phenomenon, two secondary findings were made. First, although the prime congruency effect was obtained, the flanker congruency effect was smaller when the flankers were displayed simultaneously with the target than when they were displayed sequentially before the target. This suggested that priming stimulation required enough time to be processed to a sufficient extent to produce an unconscious priming effect. Second, when the prime stimulus was removed, leaving only the flankers, the flanker priming effect increased, suggesting that the attention attracted to the prime and its conscious mask could also reduce the flanker congruency effect. These results observed across several experiments were replicated in one within-subjects experiment. We proposed an "independent unconscious influence hypothesis" for the phenomenon. This hypothesis was further integrated into a more comprehensive unconscious information processing model. The possible causes of the observed phenomena were discussed.

Separating the role of perceptual and conceptual fluency on masked word priming using event-related potentials

Masked word repetition increases "old" responses on an episodic recognition test (Jacoby & Whitehouse, 1989). This effect is commonly attributed to perceptual fluency; that is, unconscious perception of the prime speeds reading of the target and this fluency leads to elevated familiarity. Two experiments directly tested the claim that perceptual fluency is responsible for word priming effects. Experiment 1 held prime-target meaning constant and altered the physical characteristics of match primes (e.g., "RIGHT" primes "RIGHT") by including both lowercase (e.g, "right") and mixed case primes (e.g., "rIgHt"). If word priming effects are due to perceptual fluency, then lowering the perceptual overlap between the prime and target should decrease or eliminate word priming effects. Instead, all three conditions showed robust priming effects in the behavioral and ERP (i.e., N400) measures. Experiment 2 equated the prime-target perceptual features and lowered the conceptual overlap by using orthographically similar nonwords as primes (e.g., "JIGHT" primes "RIGHT"). Removing prime-target conceptual overlap eliminated behavioral evidence of priming and N400 ERP differences correlated with priming. The evidence suggests that word priming effects on episodic recognition memory are more likely a product of conceptual fluency than perceptual fluency.

Event-Related Potential (ERP) evidence for fluency and disfluency effects on recognition memory

Masked priming is used in recognition memory studies to alter fluency and create familiarity. Primes are flashed briefly before target words that are considered for a recognition judgment. Matching primes are hypothesized to produce greater familiarity by increasing the perceptual fluency of the target word. Experiment 1 tested this claim by contrasting match primes (i.e., "RIGHT" primes "RIGHT"), semantic primes (e.g., "LEFT" primes "RIGHT"), and orthographically similar (OS) primes (e.g., "SIGHT" primes "RIGHT") while recording event-related potentials (ERPs). Relative to match primes, OS primes elicited fewer "old" responses and more negative ERPs during the interval associated with familiarity (300-500 ms). This result was replicated when control primes consisting of unrelated words (Experiment 2) or symbols (Experiment 3) were inserted into the sequence. The behavioral and ERP evidence suggest that word primes are perceived as a unit and the prime word activation will affect target fluency and recognition judgments. When the prime matches the target, fluency is increased and more familiarity experiences are created. When the primes are words that do not match the target, fluency is decreased (disfluency) and fewer familiarity experiences result. This evidence suggests that the effects of disfluency on recognition should be carefully considered.

The impact of learning new meaning on the previously learned meaning of L2 ambiguous words: The role of semantic similarity

Previous study has found that previously learned meaning affects the learning of new meaning for known second language (L2) words. However, it is not clear whether learning a new meaning also affects the previously learned meaning and whether this effect is modulated by the semantic similarity between them. The current study aimed to explore this issue using event-related potential technique. A word learning task was used, in which Chinese-English bilinguals were required to learn a new meaning that was semantically related or unrelated to the previously learned meaning of familiar L2 words and judge the semantic relatedness between the trained word and a probe word in the same trial. The results showed that both the N400 and late-positive component (LPC) amplitudes for probe words in the unrelated new meaning condition were significantly different from the unlearned condition, which suggests learning new meaning interferes with accessing the previously learned meaning. Moreover, significantly less positive LPC was found in the unrelated new meaning condition relative to the related new meaning condition, showing a mediation of semantic similarity in the perturbation effect. We conclude that learning L2 new meaning has a backward interference effect on accessing the previously learned meaning and this effect is modulated by semantic similarity. These findings provide supporting evidence for the interaction mechanism of learning the multiple meanings of L2 ambiguous words.

How Processing Fluency Contributes to the Old/New Effects of Familiarity and Recollection: Evidence From the Remember/Know Paradigm

Previous investigations have demonstrated FN400 and LPC, 2 event-related potential old/new effects that respectively reflect familiarity- and recollection-based processes in memory. However, it is unclear whether these effects are susceptible to processing fluency, particularly different types of processing fluency. To address this issue, applying a masked priming paradigm, we conducted an event-related potential experiment by manipulating semantic relations between the prime and the target as identical (reflecting perceptual fluency), thematically and taxonomically related (referring to conceptual fluency), and unrelated. A remember/know (R/K) judgment task in the test phase was used to distinguish familiarity- and recollection-based processes. Behaviorally, both task performance and response speed were modulated by the variables of priming condition, item type, and response type. All 4 priming conditions elicited significant FN400 and LPC. Compared with the K response, the R response was more relevant to the recollection-based processes reflected by LPC. Both FN400 and LPC were modulated by whether there was a response of R, K, or new. The former was susceptible only to conceptual fluency, and the latter was sensitive to both perceptual fluency and conceptual fluency, which offered telling evidence for the dual process model. Considerations for future investigations are proposed. See supplemental materials here: https://www.press.uillinois.edu/journals/ajp/media/evidence_in_remember_know_paradigm/

Left lateral parietal rTMS improves cognition and modulates resting brain connectivity in patients with Alzheimer's disease: Possible role of BDNF and oxidative stress

Repetitive Transcranial Magnetic Stimulation (rTMS) is a non-invasive neuromodulation technique which is increasingly used for cognitive impairment in Alzheimer's Disease (AD). Although rTMS has been shown to modify Brain-Derived Neurotrophic Factor (BDNF) and oxidative stress levels in many neurological and psychiatric diseases, there is still no study evaluating the relationship between memory performance, BDNF, oxidative stress, and resting brain connectivity following rTMS in Alzheimer's patients. Furthermore, there are increasing clinical data showing that the stimulation of strategic brain regions may lead to more robust improvements in memory functions compared to conventional rTMS. In this study, we aimed to evaluate the possible disease-modifying effects of rTMS on the lateral parietal cortex in AD patients who have the highest connectivity with the hippocampus. To fill the mentioned research gaps, we have evaluated the relationships between resting-state Functional Magnetic Resonance Imaging (fMRI), cognitive scores, blood BDNF levels, and total oxidative/antioxidant status to explain the therapeutic and potential disease-modifying effects of rTMS which has been applied at 20 Hz frequencies for two weeks. Our results showed significantly increased visual recognition memory functions and clock drawing test scores which were associated with elevated peripheral BDNF levels, and decreased oxidant status after two weeks of left lateral parietal TMS stimulation. Clinically our findings suggest that the left parietal region targeted rTMS application leads to significant improvement in familiarity-based cognition associated with the network connections between the left parietal region and the hippocampus.

The effect of repetition priming on implicit recognition memory as measured by Fast Periodic Visual Stimulation and EEG

INTRODUCTION

The development of rapid and reliable neural measures of memory is an important goal of cognitive neuroscience research and clinical practice. Fast Periodic Visual Stimulation (FPVS) is a recently developed electroencephalography (EEG) method that involves presenting a mix of novel and previously-learnt stimuli at a fast rate. Recent work has shown that implicit recognition memory can be measured using FPVS, however the role of repetition priming remains unclear. Here, we attempted to separate out the effects of recognition memory and repetition priming by manipulating the degree of repetition of the stimuli to be remembered.

METHOD

Twenty-two participants with a mean age of 20.8 (±4.3) yrs. completed an FPVS-oddball paradigm with a varying number of repetitions of the oddball stimuli, ranging from very high repetition to no repetition. In addition to the EEG task, participants completed a behavioural recognition task and visual memory subtests from the Wechsler Memory Scale - 4th edition (WMS-IV).

RESULTS

An oddball memory response was observed in all four experimental conditions (very high repetition to no repetition) compared to the control condition (no oddball stimuli). The oddball memory response was largest in the very high repetition condition and smaller, but still significant, in conditions with less/no oddball repetition. Behavioural recognition performance was at ceiling, suggesting that all images were encoded successfully. There was no correlation with either behavioural memory performance or WMS-IV scores, suggesting the FPVS-oddball paradigm captures different memory processes than behavioural measures.

CONCLUSION

Repetition priming significantly modulates the FPVS recognition memory response, however recognition is still detectable even in the total absence of repetition priming. The FPVS-oddball paradigm could potentially be developed into an objective and easy-to-administer memory assessment tool.

Electrophysiological correlates of the perceptual fluency effect on recognition memory in different fluency contexts

The present study used event-related potentials (ERPs) to investigate the contribution of perceptual fluency to recognition memory in different fluency contexts. In a recognition memory test with a modified remember-know paradigm, we employed conceptually impoverished items (kaleidoscope images) as stimuli and manipulated the perceptual fluency of recognition test cues through masked repetition priming. There were two fluency context conditions. In the random fluency context (RC) condition, primed and unprimed trials were randomly inter-mixed. In the blocked fluency context (BC) condition, primed and unprimed trials were grouped into blocks. Behavioral results showed that priming elevated the incidence of remember hits and the accuracy of remember judgements in the RC condition; no such effects were evident in the BC condition. In addition, priming effects on reaction times were found only for remember hit responses in the RC condition. The ERP results revealed an early100-200 ms effect related to masked repetition priming, which took the form of greater positivity for primed than unprimed trials. This effect was modulated neither by fluency context or response type. The present findings suggest that perceptual fluency induced by masked repetition priming affects recollection-related memory judgments in a specific fluency context and indicate that relative, rather absolute, fluency plays a critical role in influencing recognition memory judgments.

Repetition attenuates the influence of recency on recognition memory: Behavioral and electrophysiological evidence

Studies of recognition memory often demonstrate a recency effect on behavioral performance, whereby response times (RTs) are faster for stimuli that were previously presented recently as opposed to more remotely in the past. One account of this relationship between performance and presentation lag posits that memories are accessed by serially searching backward in time, such that RT indicates the self-terminating moment of such a process. Here, we investigated the conditions under which this serial search gives way to more efficient means of retrieving memories. Event-related potentials (ERPs) were recorded during a continuous recognition task, in which subjects made binary old/new judgments to stimuli that were each presented up to four times across a range of lags. Stimulus repetition and shorter presentation lag both gave rise to speeded RTs, consistent with previous findings, and we novelly extend these effects to a robust latency measure of the left parietal ERP correlate of retrieval success. Importantly, the relationship between repetition and recency was further elucidated, such that repetition attenuated lag-related differences that were initially present in both the behavioral and neural latency data. These findings are consistent with the idea that an effortful search through recent memory can quickly be abandoned in favor of relying on more efficient "time-independent" cognitive processes or neural signals.

Reminiscence in the Care of People with Mild Dementia: A Concept Analysis

AIM

To clarify the concept of reminiscence in the care of people with mild dementia, highlight its uses as a nursing intervention in dementia care, and propose an operational definition of the concept.

BACKGROUND

Reminiscence is one of the leading nonpharmacological interventions in dementia care. The existing literature lacks a unified definition of reminiscence as it applies to the care of patients with mild dementia and a precise understanding of the concept's applications in nursing care.

DATA SOURCES

We derived data from literature searches in CINAHL, PsycINFO, PubMed, Google Scholar, Scopus, and Cochrane Library databases.

DESIGN

Concept Analysis.

REVIEW METHODS

The review method used was the Walker and Avant's (2019) eight-step method.

RESULTS

Identification of the key attributes, antecedents, consequences, and empirical referents of the concept resulted in an operational definition of the concept. The proposed operational definition identifies reminiscence in the care of patients with mild dementia as a cognitive, functional process of recalling and reconstructing distant memories using memory stimuli through mutual interaction with a trained facilitator.

CONCLUSION

Clarifying the concept will add validity to the current and future literature, help to develop new research instruments that accurately measure this concept, and function as a framework for holistic nursing interventions.

Paired walkers with better first impression synchronize better

This study measured automatic walking synchronization and how it associates with social impression. Previous studies discovered positive social consequence of motor synchrony with ecological paradigms (e.g. body movement synchrony between therapists and patients in clinical sessions, and the synchrony of side-by-side walkers). However, most studies of joint movement with high ecological validity face the same challenge, namely that conversations between participants might be the main or a partial contributor to the observed social benefits, as conversation is well documented to promote understanding and motor synchronization. We addressed this issue by using a novel paradigm to remove the conversation component and examined how synchrony per se interacted with social impression. Participants were paired to walk side by side in silence (i.e. without conversation) and their social impression toward each other was rated before/after the paired walk. Our results showed that walkers' first impression was positively associated with their step synchronization rate in the silent paired walk. Together with past findings, the bi-directional relation between body entrainment and social functions suggests that implicit nonverbal communication plays a significant role in providing a basis for interpersonal interaction.

Perceptual identification task points to continuity between implicit memory and recall

Adopting a continuous identification task (CID-R) with embedded questions about prior occurrence, recent research has proposed that implicit and explicit memory are underpinned by a single memory system, since there is a systematic relationship between implicit memory (measured by identification) and explicit memory (measured by subjective report of recognition; for an example, see Berry, Shanks, & Henson, 2008). We were interested in whether this pattern would extend to recall of information from a study phase (Experiment 1) or recall from semantic memory (Experiment 2). We developed a degraded face identification version of the CID-R task using Gaussian blur. We reproduced previous results regarding the relationship between explicit responses on the recognition task (old/new) and stimuli identification, pointing to a continuity between explicit and implicit memory. Critically, we also found that the strength of the implicit effect (i.e., stimuli identification) was predicted by the accuracy in recall (retrieval of context in Experiment 1 and correct responses to general knowledge questions about the face in Experiment 2). Our results support the idea that memory is unidimensional and related to memory trace strength; both for recall and recognition, and interestingly, for semantic and episodic recall.

The neural mechanism of fluency-based memory illusions: the role of fluency context

Recognition memory judgments can be influenced by a variety of signals including fluency. Here, we investigated whether the neural correlates of memory illusions (i.e., misattribution of fluency to prior study) can be modulated by fluency context. Using a masked priming/recognition memory paradigm, we found memory illusions for low confidence decisions. When fluency varied randomly across trials, we found reductions in perirhinal cortex (PrC) activity for primed trials, as well as a (pre)cuneus-PrC (BA 35) connectivity. When the fluency context was unchanging, there was increased PrC activity for primed trials, with the (pre)cuneus showing greater connectivity with PrC (BA 36). Thus, our results tentatively suggest two neural mechanisms via which fluency can lead to memory illusions.

The temporal dynamics of perceptual and conceptual fluency on recognition memory

Recognition memory can be driven by both perceptual and conceptual fluency, but when and to what extent they contribute to recognition memory remains an open question. The present study used event-related potentials (ERPs) to investigate the neural correlates of perceptual and conceptual fluency, when they gave rise to recognition. We manipulated the perceptual and conceptual fluency of retrieval cues in the recognition test independently to obtain the effects of different types of fluency. Behavioral results showed that perceptual fluency selectively affected K hits, while conceptual fluency affected R hits and K false alarms. In addition, conceptual fluency facilitated the response times of R hits. The ERP results showed that perceptual fluency effect appeared at 100-200 ms and conceptual fluency effect appeared at 300-500 ms. The parietal LPC peaked earlier for conceptually primed trials compared to unprimed trials. These results suggest that perceptual and conceptual fluency had different effects on recognition judgments, and these two types of fluency can be delineated by distinct ERP correlates. The current finding indicates that unconscious memory processes can support recognition and have provided insights into the underlying mechanism involved in recognition memory.

Electrophysiological signals associated with fluency of different levels of processing reveal multiple contributions to recognition memory

Processing fluency appears to influence recognition memory judgements, and the manipulation of fluency, if misattributed to an effect of prior exposure, can result in illusory memory. Although it is well established that fluency induced by masked repetition priming leads to increased familiarity, manipulations of conceptual fluency have produced conflicting results, variously affecting familiarity or recollection. Some recent studies have found that masked conceptual priming increases correct recollection (Taylor & Henson, 2012), and the magnitude of this behavioural effect correlates with analogous fMRI BOLD priming effects in brain regions associated with recollection (Taylor, Buratto, & Henson, 2013). However, the neural correlates and time-courses of masked repetition and conceptual priming were not compared directly in previous studies. The present study used event-related potentials (ERPs) to identify and compare the electrophysiological correlates of masked repetition and conceptual priming and investigate how they contribute to recognition memory. Behavioural results were consistent with previous studies: Repetition primes increased familiarity, whereas conceptual primes increased correct recollection. Masked repetition and conceptual priming also decreased the latency of late parietal component (LPC). Masked repetition priming was associated with an early P200 effect and a later parietal maximum N400 effect, whereas masked conceptual priming was only associated with a central-parietal maximum N400 effect. In addition, the topographic distributions of the N400 repetition priming and conceptual priming effects were different. These results suggest that fluency at different levels of processing is associated with different ERP components, and contributes differentially to subjective recognition memory experiences.