Memory Search Research Articles

Dissociations of Memory Processes: The Contribution of Research on Memory Impairment Following Traumatic Brain Injury (TBI)—A Focused Review

Objective: Deficits in memory and learning skills are frequently reported following traumatic brain injury (TBI). The goal of the present focused review is to present memory studies of moderate-to-severe TBI that found, within the same sample, that one memory component is preserved, while another is impaired, demonstrating a dissociation. By reviewing these studies, we would like to claim that the breakdown of memory processes following TBI could unmask underlying sub-processes and components that seem inseparable in intact memory. Methods: The search criterion for this focused review was studies of memory functions following TBI (mostly moderate-severe) that reported on dissociations of various memory processes within the same sample, so that one process was impaired while another was preserved. Results: We found studies that adhered to the search criterion in several domains of memory: Working memory, episodic memory, verbal learning, priming, contextual memory and visual search. Conclusions: Characterization of the memory breakdown following TBI could contribute not only to the assessment and rehabilitation of this population but also to our understanding of the composition of intact memory system. These studies, although presenting a single dissociation, can still contribute to the validation of several dissociations introduced in the memory literature.

Spatial Attention in Serial Order Working Memory: An EEG Study.

Theoretical models explaining serial order processing link order information to specified position markers. However, the precise characteristics of position marking have remained largely elusive. Recent studies have shown that space is involved in marking serial position of items in verbal working memory (WM). Furthermore, it has been suggested, but not proven, that accessing these items involves horizontal shifts of spatial attention. We used continuous electroencephalography recordings to show that memory search in serial order verbal WM involves spatial attention processes that share the same electrophysiological signatures as those operating on the visuospatial WM and external space. Accessing an item from a sequence in verbal WM induced posterior "early directing attention negativity" and "anterior directing attention negativity" contralateral to the position of the item in mental space (i.e., begin items on the left; end items on the right). In the frequency domain, we observed posterior alpha suppression contralateral to the position of the item. Our results provide clear evidence for the involvement of spatial attention in retrieving serial information from verbal WM. Implications for WM models are discussed.

Modeling Information Pooling Bias in Incident Response Teams: An Agent Based Modeling Approach

Security analysts regularly correlate disparate incidents to detect cyber-attacks. However, past research shows that team-based incident correlation analysis may be affected by information pooling bias. This article presents findings from an agent-based model used to explore the cognitive processes hypothesized to be causing this bias during information exchange within a team. The model simulated information exchange between three analysts conducting incident correlation analysis by searching for information available with them about the different incidents. Three models of memory search process were compared: Random, Local, and Memory-aided search. Results from the simulation show that agents in a local search model, compared to memory-aided search model, shared more often the information known to majority in the team. Comparing model results with data from lab experiments suggest that teams, by default, may be employing a heuristic search process during information exchange leading to sub-optimal team processes and performance.

May the source be with you! Electrophysiological correlates of retrieval orientation are associated with source memory performance

Successful source memory retrieval is assumed to rely on intact preretrieval processes, such as retrieval orientation (RO). RO is the specialized processing of retrieval cues, depending on the type of information, memory is searched for. In a previous study, a positive frontal slow wave RO ERP effect was interpreted as reflecting memory search for self-relevant information. However, such a functional interpretation is hampered by the use of retrieval strategies as a consequence of which target source information can be indirectly inferred from the correct classification of non-target source information. To overcome this limitation, the present study compared two types of source information (i.e. color or character information) by asking participants to remember details within each source type and thus enforcing the selective retrieval of target information. Consistent with previous research, a positive frontal ERP component (600–800 ms post-stimulus) differentiated between correct rejections in both tasks, probably reflecting memory search for self-relevant information. Moreover, the RO ERP effect was associated with better source memory performance, providing evidence for the beneficial effect of ROs for memory retrieval. This relationship might be covered in memory exclusion tasks due to non-target retrieval.

Some Aspects of Associative Memory Construction Based on a Hopfield Network

An implementation of associative memory based on a Hopfield network is described. In the proposed approach, memory addresses are regarded as training vectors of the artificial neural network. The efficiency of memory search is directly associated with solving the overfitting problem. A method for dividing the training and input network vectors into parts, the processing of which requires a smaller number of neurons, is proposed. Results of a series of experiments conducted on Hopfield network models with different numbers of neurons trained with different numbers of vectors and operated under different noise conditions are presented.

Direct brain recordings identify hippocampal and cortical networks that distinguish successful versus failed episodic memory retrieval

Human data collected using noninvasive imaging techniques have established the importance of parietal regions towards episodic memory retrieval, including the angular gyrus and posterior cingulate cortex. Such regions comprise part of a putative core episodic retrieval network. In free recall, comparisons between contextually appropriate and inappropriate recall events (i.e. prior list intrusions) provide the opportunity to study memory retrieval networks supporting veridical recall, and existing findings predict that differences in electrical activity in these brain regions should be identified according to the accuracy of recall. However, prior iEEG studies, utilizing principally subdural grid electrodes, have not fully characterized brain activity in parietal regions during memory retrieval and have not examined connectivity between core recollection areas and the hippocampus or prefrontal cortex. Here, we employed a data set obtained from 100 human patients implanted with stereo EEG electrodes for seizure mapping purposes as they performed a free recall task. This data set allowed us to separately analyze activity in midline versus lateral parietal brain regions, and in anterior versus posterior hippocampus, to identify areas in which retrieval-related activity predicted the recollection of a correct versus an incorrect memory. With the wide coverage afforded by the stereo EEG approach, we were also able to examine interregional connectivity. Our key findings were that differences in gamma band activity in the angular gyrus, precuneus, posterior temporal cortex, and posterior (more than anterior) hippocampus discriminated accurate versus inaccurate recall as well as active retrieval versus memory search. The left angular gyrus exhibited a significant power decrease preceding list intrusions as well as unique phase–amplitude coupling properties, whereas the prefrontal cortex was unique in exhibiting a power increase during list intrusions. Analysis of connectivity revealed significant hemispheric asymmetry, with relatively sparse left-sided functional connections compared to the right hemisphere. One exception to this finding was elevated connectivity between the prefrontal cortex and left angular gyrus. This finding is interpreted as evidence for the engagement of prefrontal cortex in memory monitoring and mnemonic decision-making.

Epistemic responsibility - Labored, loosened, and lost: Staging Alzheimer's disease

Interlocutors hold one another accountable for knowing certain information about themselves (their roles, activities, and memories) and for keeping track of information in the current conversational exchange. When speakers have trouble with this expectation, they themselves work to repair the breach, often doing a memory search, or when unsuccessful they provide an account (e.g. “I don't remember”). Memory searches (like word searches) are observable, interactional accomplishments. Speakers disengage with their interlocutors (look away), produce hesitation markers, take repeated pauses, engage in pre-positioned and post-positioned repairs, make epistemic assessments, and on finding an answer, re-engage with their interlocutors (look back). For their part, interlocutors comply with the search by not interrupting and continuing to yield the floor. At progressively severe stages of Alzheimer's disease, individuals exhibit increasingly labored memory searches that often trail off into non-answers, until at the latest stages, they eschew the search and (almost smoothly) provide either grammatically appropriate but wrong and improbable answers or give answers to previous questions on now closed topics. With data from the clinical administration of a disease staging instrument (Clinical Dementia Rating) this article examines the inexorable loss of epistemic responsibility as a key discursive dynamic in the progression of the disease.

Implementation of Data Search in Multi-Level NAND Flash Memory by Complementary Storage Scheme

We develop a novel scheme to realize data search in NAND flash memories, which is important for a wide variety of applications in data centers. In our design, the pair unit consists of double neighbor cells in the NAND string, one “data cell” and one “complementary cell”. The NAND string will be at the “Pass” state only when the searching data are completely matched with the stored data. Parameters that affect data search performance are analyzed systematically. Based on simulations in vertically stacked 3D NAND structures, it is shown that the bit-line current ratio of the fully matched case to the worst case of one mismatched data is more than ~104 in both MLC (multi-level cell) and TLC (triple-level cell) modes, and ~102 can still be obtained in QLC (quad-level cell) mode after read voltage optimizations. These results indicate that the proposed scheme is effective for data search in multi-level NAND flash memories and also friendly for peripheral circuits design.

Effective connectivity during autobiographical memory search.

IntroductionWe used dynamic causal modeling (DCM) to examine effective connectivity during cued autobiographical memory (AM) search in a left‐hemispheric network consisting of six major regions within the large network of brain regions recruited during memory retrieval processes.MethodsFunctional MRI data were acquired while participants were shown verbal cues describing common life events and requested to search for a personal memory associated with the cue. We examined directed couplings between the ventromedial (vmPFC), dorsomedial (dmPFC), and dorsolateral prefrontal cortices (dlPFC), hippocampus, angular gyrus, and the posterior midline cortex (RSC/PCC/Prec).ResultsDuring AM search, the vmPFC, dlPFC, and RSC/PCC/Prec acted as primary drivers of activity in the rest of the network. Moreover, when AM search completed successfully (Hits), the effective connectivity of the hippocampus on the vmPFC and angular gyrus was up‐modulated. Likewise, there was an increase in the influence of the RSC/PCC/Prec in the activity of the dlPFC and dmPFC. Further analysis indicated that the modulation observed during Hits is primarily a distributed phenomenon that relies on the interplay between different brain regions.ConclusionThese results suggest that prefrontal and posterior midline cortical regions together with the dlPFC largely coordinate the processes underlying AM search, setting up the conditions on which the angular gyrus and the hippocampus may act upon when the outcome of the search is successful.

Search for nonlinear memory from subsolar mass compact binary mergers

We present the first results of the search for nonlinear memory from subsolar mass binary black hole (BBH) mergers during the second observing run (O2) of the LIGO and Virgo detectors. The oscillatory chirp signal from the inspiral and merger of low mass BBHs ($M_\mathrm{Tot} \leq 0.4 M_\odot$) are at very high frequencies and fall outside the sensitivity band of the current ground-based detectors. However, the non-oscillatory memory signal during the merger saturates towards the lower frequencies and can be detected for those proposed BBHs. We show in this work that the morphology of the memory signal depends minimally upon the source parameters of the binary, thus only the overall amplitude of the signal changes and hence the result can be interpolated for extremely low mass BBH mergers. We did not find any signal which can be interpreted as a memory signal and we place upper limits on the rate of BBH mergers with $M_\mathrm{Tot} \leq 0.4 M_\odot$ for the first time.

Is Immediate Processing of Presupposition Triggers Automatic or Capacity-Limited? A Combination of the PRP Approach with a Self-Paced Reading Task

Informally speaking, presuppositions are meaning components which are part of the common ground for speakers in a conversation, that is, background information which is taken for granted by interlocutors. The current literature suggests an immediate processing of presuppositions, starting directly on the word triggering the presupposition. In the present paper, we focused on two presupposition triggers in German, the definite determiner the (German der) and the iterative particle again (German wieder). Experiment 1 replicates the immediate effects which were previously observed in a self-paced reading study. Experiment 2 then investigates whether this immediate processing of presuppositions is automatic or capacity-limited by employing the psychological refractory period approach and the locus of slack-logic, which have been successfully employed for this reason in various fields of cognitive psychology. The results argue against automatic processing, but rather suggest that the immediate processing of presuppositions is capacity-limited. This potentially helps specifying the nature of the involved processes; for example, a memory search for a potential referent.

No role for activated long-term memory in attentional control settings.

Visual spatial attentional capture is contingent on an observer's goals, or attentional control settings. Recent research has demonstrated that observers can adopt attentional control settings based on numerous visual objects represented in episodic long-term memory (LTM). But why do LTM representations that comprise an attentional control set bias attentional capture, when other LTM representations do not? In the present study, we tested the activated LTM account-that LTM representations form an attentional control set if, and only if, they are represented in activated LTM-by mixing a working memory task to test for representation in activated LTM, with a spatial blink task to test for the state of participants' attentional control settings. In Experiments 1 and 2, inducing participants to represent complex visual objects in activated LTM did not result in those objects forming an attentional control set. In Experiment 3, we found a dissociation between activated LTM and attentional control settings; objects that were represented in activated LTM produced greater intrusion effects (indicating representation in activated LTM) than objects that were part of an attentional control set, yet smaller capture effects. These results do not support the activated LTM account. We conclude that representation in activated LTM is not the factor that determines which LTM representations comprise an attentional control set, and discuss the implications of these findings for research on attentional templates and hybrid visual and memory search. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Reactivated Spatial Context Guides Episodic Recall

The medial temporal lobe (MTL) is known as the locus of spatial coding and episodic memory, but the interaction between these cognitive domains as well as the extent to which they rely on common neurophysiological mechanisms is poorly understood. Here, we use intracranial electroencephalography and a hybrid spatial-episodic memory task (29 subjects, 15 female) to determine how spatial information is dynamically reactivated in subregions of the human MTL and how this reactivation guides recall of episodic information. Our results implicate theta oscillations across the MTL as a common neurophysiological substrate for spatial coding in navigation and episodic recall. We further show that our index of retrieved spatial context is high in the hippocampus (HC) in an early time window preceding recall. Closer to recall, it decreases in the HC and increases in the parahippocampal gyrus. Finally, we demonstrate that hippocampal theta phase modulates parahippocampal gamma amplitude during retrieval of spatial context, suggesting a role for cross-frequency coupling in coding and transmitting retrieved spatial information.SIGNIFICANCE STATEMENT By recording from the human medial temporal lobe (MTL) while subjects recall items experienced in a virtual environment, we establish a direct relation between the strength of theta activity during memory search and the extent to which memories are organized by their spatial locations. We thereby pinpoint a role for theta oscillations in accessing the "cognitive map" during episodic retrieval and further highlight the dynamic interplay of hippocampus and extrahippocampal MTL in representing retrieved spatial context. Our results provide an important step toward a unified theory of MTL function encompassing its role in spatial navigation and episodic memory.

Precuneus stimulation alters the neural dynamics of autobiographical memory retrieval

Autobiographical memory (AM) unfolds over time, but little is known about the dynamics of its retrieval. Space-based models of memory implicate the hippocampus, retrosplenial cortex, and precuneus in early memory computations. Here we used transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) to investigate the causal role of the precuneus in the dynamics of AM retrieval. During early memory search and construction, precuneus stimulation compared to vertex stimulation led to delayed evoked neural activity within 1000 ​ms after cue presentation. During later memory elaboration, stimulation led to decreased sustained positivity. We further identified a parietal late positive component during memory elaboration, the amplitude of which was associated with spatial perspective during recollection. This association was disrupted following precuneus stimulation, suggesting that this region plays an important role in the neural representation of spatial perspective during AM. These findings demonstrate a causal role for the precuneus in early AM retrieval, during memory search before a specific memory is accessed, and in spatial context reinstatement during the initial stages of memory elaboration and re-experiencing. By utilizing the high temporal resolution of MEG and the causality of TMS, this study helps clarify the neural correlates of early naturalistic memory retrieval.

Distinctive encodings and the production effect: failure to retrieve distinctive encodings decreases recollection of silent items

ABSTRACTStudies have shown that when aloud and silent items are studied together, silent items are remembered more poorly than when they are studied independently. We hypothesise that this cost to silent items emerges because, at test, participants search for memories of having said items aloud and when those memory searches fail, participants become uncertain about whether silent items were studied. This effect should be exaggerated if other unique distinctive encoding conditions are also included at study (e.g., mumbling, writing, typing, etc.). To test this prediction, we examined the impact of introducing mumbled, “important” (i.e., words that participants are told are the most important to remember), and mouthed words to a study list of aloud and silent words. Introducing mumbled and “important” words further impaired the recollection of silent items. Introducing mouthed items did not further impair the memorability of silent items because mouthing and speaking aloud are so similar and hence, are not fully unique from each other. The memorability of aloud items was unaffected in all conditions. These results suggest that participants search for distinctive encoding information at test, and only for items that fail those searches (i.e., silent items) do they lose confidence.

Need something different? Here’s what’s been done: Effects of examples and task instructions on creative idea generation

Creative idea generation involves search and retrieval of memory. There is a default tendency to rely too heavily on familiar or easily accessible information during idea generation, especially in tasks such as the alternate uses task (AUT) that involve generating novel uses for common objects. Knowing which obvious ideas to avoid may be important in creating more original ideas. The present experiments tested whether instructions encouraging participants to avoid a set of common example ideas would enhance originality or cause fixation on the AUT. The results of Experiment 1 demonstrated that presenting a verbal list of common example uses along with a warning to avoid those uses enhanced originality. In contrast, when the example ideas were presented in the absence of any "avoid" instructions, there was no benefit on originality, indicating that mere example exposure did not stimulate more creative idea generation. The design of Experiment 2 was parallel to that of Experiment 1, but the verbal examples were replaced with visually depicted examples. Exposure to the visual examples led to reduced originality, suggesting fixation. Although the "avoid" instruction helped to mitigate this fixation, it did not enhance originality beyond the no-example condition. The results suggest that under some conditions presenting unoriginal examples along with an "avoid" warning can allow people to shift their focus away from easily retrieved ideas and toward more novel approaches. The results are also consistent with prior work showing a negative impact of visual presentation of examples on creativity.

VTEAM Model Based In-Memory Computation using Memristors

The recent applications in the computing field deals with huge data processing operations, which involves a lot of data transfer from the memory to processing unit and vice versa. If these data transfers between the CPU and memory are reduced, a lot of time could be saved along with advantage of getting desirable outputs at a lower latency. One of the ways to achieve this is to adopt In-memory computational techniques, where most of the computations happen inside memory itself. Memristive crossbar architecture is a memory architecture which makes use of memristors as memory cells to store data with some added computational capabilities. The need for power efficient computing in the present days motivates the search for new nonvolatile universal memories like memristors. In this paper, we present an optimal way of implementing basic ALU operations in the memristive memory block. A detailed description for simulating this is given, which includes the creation of memristor symbol, choosing a suitable memristive logic to implement basic digital logics, creation of memory crossbar and the way to realize basic ALU operations.

Ferroelectric ternary content-addressable memory for one-shot learning

Deep neural networks are efficient at learning from large sets of labelled data, but struggle to adapt to previously unseen data. In pursuit of generalized artificial intelligence, one approach is to augment neural networks with an attentional memory so that they can draw on already learnt knowledge patterns and adapt to new but similar tasks. In current implementations of such memory augmented neural networks (MANNs), the content of a network’s memory is typically transferred from the memory to the compute unit (a central processing unit or graphics processing unit) to calculate similarity or distance norms. The processing unit hardware incurs substantial energy and latency penalties associated with transferring the data from the memory and updating the data at random memory addresses. Here, we show that ternary content-addressable memories (TCAMs) can be used as attentional memories, in which the distance between a query vector and each stored entry is computed within the memory itself, thus avoiding data transfer. Our compact and energy-efficient TCAM cell is based on two ferroelectric field-effect transistors. We evaluate the performance of our ferroelectric TCAM array prototype for one- and few-shot learning applications. When compared with a MANN where cosine distance calculations are performed on a graphics processing unit, the ferroelectric TCAM approach provides a 60-fold reduction in energy and 2,700-fold reduction in latency for a single memory search operation. A compact ternary content-addressable memory cell, which is based on two ferroelectric field-effect transistors, can provide memory augmented neural networks with improved energy and latency performance compared with traditional approaches based on graphics processing units.

Searching for Semantic Knowledge: A Vector Space Semantic Analysis of the Feature Generation Task.

A recent neuropsychological study found that amnesic patients with hippocampal damage (HP) and severe declarative memory impairment produce markedly fewer responses than healthy comparison (CO) participants in a semantic feature generation task (Klooster and Duff, 2015), consistent with the idea that hippocampal damage is associated with semantic cognitive deficits. Participants were presented with a target word and asked to produce as many features of that word as possible (e.g., for target word “book,” “read words on a page”). Here, we use the response sequences collected by Klooster and Duff (2015) to develop a vector space model of semantic search. We use this model to characterize the dynamics of semantic feature generation and consider the role of the hippocampus in this search process. Both HP and CO groups tended to initiate the search process with features close in semantic space to the target word, with a gradual decline in similarity to the target word over the first several responses. Adjacent features in the response sequence showed stronger similarity to each other than to non-adjacent features, suggesting that the search process follows a local trajectory in semantic space. Overall, HP patients generated features that were closer in semantic space to the representation of the target word, as compared to the features generated by the CO group, which ranged more widely in semantic space. These results are consistent with a model in which a compound retrieval cue (containing a representation of the target word and a representation of the previous response) is used to probe semantic memory. The model suggests that the HP group's search process is restricted from ranging as far in semantic space from the target word, relative to the CO group. These results place strong constraints on the structure of models of semantic memory search, and on the role of hippocampus in probing semantic memory.

Visual search within working memory.

Attention and working memory are 2 key pillars of cognition. Despite much research, there are important aspects about the relationship between the 2 constructs that are not well understood. Here we explore the similarity in the mechanisms that select and update working memory to those that guide attention during perception, such as in visual search. We use a memory search task where participants memorize a display of objects on a grid. During memory maintenance, participants are instructed to update the spatial positions of a subset of objects. The speed of the updating process should reflect the accessibility of the to-be-updated subset. Using this task, we explored whether landmark findings in visual search would hold true for memory search. In Experiment 1, we found a search asymmetry-it was easier to access memory representations defined by a feature than defined by the lack of a feature. In Experiment 2, we found target-distractor similarity effects-updating a single target was easier when the distractors were farther away in feature space. In Experiment 3, we found a feature versus conjunction benefit-access times were much faster for instructions to move objects defined by only 1 feature (e.g., all triangles) as opposed to a conjunction of features (e.g., all red triangles). In Experiment 4, we find a set-size effect-update times increased with the number of items in memory, particularly for conjunctive stimuli. Taken together, our results suggest a common coding and selection scheme for working memory and perceptual representations. (PsycINFO Database Record (c) 2019 APA, all rights reserved).