Retrieval Dynamics Research Articles

Symmetry breaking and non-ergodicity in a driven-dissipative ensemble of multilevel atoms in a cavity

Dissipative light-matter systems can display emergent collective behavior. Here, we report a Z2-symmetry-breaking phase transition in a system of multilevel Rb87 atoms strongly coupled to a weakly driven two-mode optical cavity. In the symmetry-broken phase, nonergodic dynamics manifests in the emergence of multiple stationary states with disjoint basins of attraction. This feature enables the amplification of a small atomic population imbalance into a characteristic macroscopic cavity transmission signal. Our experiment does not only showcase strongly dissipative atom-cavity systems as platforms for probing nontrivial collective many-body phenomena, but also highlights their potential for hosting technological applications in the context of sensing, density classification, and pattern retrieval dynamics within associative memories. Published by the American Physical Society 2024

Neuroscientist's Behavioral Toolbox for Studying Episodic-Like Memory.

Episodic memory, the ability to recall specific events and experiences, is a cornerstone of human cognition with profound clinical implications. While animal studies have provided valuable insights into the neuronal underpinnings of episodic memory, research has largely relied on a limited subset of tasks that model only some aspects of episodic memory. In this narrative review, we provide an overview of rodent episodic-like memory tasks that expand the methodological repertoire and diversify the approaches used in episodic-like memory research. These tasks assess various aspects of human episodic memory, such as integrated what-where-when or what-where memory, source memory, free recall, temporal binding, and threshold retrieval dynamics. We review each task's general principle and consider whether alternative non-episodic mechanisms can account for the observed behavior. While our list of tasks is not exhaustive, we hope it will guide researchers in selecting models that align with their specific research objectives, leading to novel advancements and a more comprehensive understanding of mechanisms underlying specific aspects of episodic memory.

How retrieval processes change with age: Exploring age differences in semantic network and retrieval dynamics.

This study investigated the impact of age on semantic memory networks and retrieval dynamics using a single-list free recall paradigm, involving 318 participants. The younger group, with 175 participants aged 25-55 years (M = 46.68 years; SD = 10.69), and the older group, consisting of 143 participants aged 61-88 years (M = 68.71 years; SD = 6.09), completed a word recall test to assess delayed recall performance. Semantic memory networks were constructed from recall data by analyzing the co-occurrence and sequence of recalled words. We observed significant differences in network structure, where the older group displayed higher average shortest path length and modularity values, indicative of less integrated networks, while the younger group exhibited a higher clustering coefficient, suggesting a more interconnected network. In terms of retrieval dynamics, both groups showed a temporal contiguity effect with forward asymmetry. However, this effect was less pronounced in older adults. The study also identified participants that diverted from the average dynamic curves: one subgroup relied on nontemporal mechanisms, and the other employed a backward direction in memory search. Participants utilizing forward temporal associations demonstrated the highest recall performance. Overall, our findings suggest that lower free recall performance in older adults may be related to a diminished capacity to reinstate temporal context for retrieval and distinct differences in their semantic memory network structure. Specifically, older adults appear to exhibit networks with a less flexible, small-world-like structure. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Dynamic analysis of the tethered satellite system considering uncertain but bounded parameters

Dynamic analysis of the tethered satellite system (TSS) can provide a fundamental guideline to the evaluation of performance and robust design of the system examined. Uncertainties inherited with the parameters would induce unexpected variation of the response and deteriorate the reliability of the system. In this work, the effect of uncertain mass of the satellites on the deployment and retrieval dynamics of the TSS is investigated. First the interval mode is employed to take the variation of mass of satellite into account in the processes of deployment and retrieval. Then, the Chebyshev interval method is used to obtain the lower and upper response bounds of the TSS. To achieve a smooth and reliable implementation of deployment and retrieval, the nonlinear programming based on the Gauss pseudo-spectral method is adopted to obtain optimal trajectory of tether velocity. Numerical results show that the uncertainties of mass of the satellites have a distinct influence on the response of tether tension in the processes of deployment and retrieval.

Memory modeling of counterfactual generation.

We use a computational model of memory search to study how people generate counterfactual outcomes in response to an established target outcome. Hierarchical Bayesian model fitting to data from six experiments reveals that counterfactual outcomes that are perceived as more desirable and more likely to occur are also more likely to come to mind and are generated earlier than other outcomes. Additionally, core memory mechanisms such as semantic clustering and word frequency biases have a strong influence on retrieval dynamics in counterfactual thinking. Finally, we find that the set of counterfactuals that come to mind can be manipulated by modifying the total number of counterfactuals that participants are prompted to generate, and our model can predict these effects. Overall, our findings demonstrate how computational memory search models can be integrated with current theories of counterfactual thinking to provide novel insights into the process of generating counterfactual thoughts. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Value-directed retrieval: The effects of divided attention at encoding and retrieval on memory selectivity and retrieval dynamics.

Value-directed remembering refers to the tendency to best remember important information at the expense of less valuable information, and this ability may draw on strategic attentional processes. In six experiments, we investigated the role of attention in value-directed remembering by examining memory for important information under conditions of divided attention during encoding and retrieval. We presented participants with lists of words of varying objective or subjective value and compared participants completing the study phase under full or divided attention, in addition to participants completing the testing phase under full or divided attention. Results revealed that certain forms of selectivity were impaired when attention was divided during encoding but not when attention was divided during retrieval. Participants initiated recall (i.e., probability of first recall [PFR]) with high-value words as well as with words they subjectively deemed important; these value-mediated PFR retrieval dynamics resisted influence from reduced attentional resources during encoding and retrieval. Thus, while value-directed remembering involves both strategic encoding and retrieval operations, attentional resources during encoding appear crucial for subsequent recollection of valuable and important information; however, attentional resources during retrieval may be less influential in strategic selective memory. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Acetylcholine-sensitive control of long-term synaptic potentiation in hippocampal CA3 neurons.

A Hebbian form of long-term potentiation (LTP) is believed to be the basis of memory storage at CA3 recurrent synapses. Abnormalities in CA3 intrinsic connectivity have been related to memory deficits in a variety of neurological disorders. Despite the promise of computational modeling for illuminating the pathogenic implication of connectivity changes, common Hebbian-based models with preset structural topologies fall short in this regard. Here, I introduce a structure-independent approach to modeling CA3 network focusing on how LTP shapes CA3 functional connectivity. Network simulations demonstrate that only a small fraction of the active synapses should be potentiated onto engram-bearing cells for reaching CA3 optimal performance, and that this fraction should be actively regulated at the single-cell level to maintain precise control over excitatory inputs to and from overlapping engram cells. In light of these findings, I develop a theory suggesting that synaptic potentiation is regulated through extrinsic and intrinsic cellular mechanisms involving the cholinergic modulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The theory posits that the progressive increase of acetylcholine release during learning is commensurate with the rate of AMPA receptor trafficking during LTP development and that this dynamics is intended to conceal AMPA receptor potentiation and thereby to propel LTP progression until a target level of potentiation is attained at a restricted number of the active synapses. Functionally, this form of regulation allows encoding and retrieval dynamics to be dictated at the single-cell level and thereby acts at the cell-population level as a secondary mechanism complementing dentate gyrus-mediated pattern separation or compensating for possible deficiencies. Conversely, when this regulation fails, the strength of AMPA receptors and their variability across synapses change over time and lead to pathological states.

Retrieval dynamics in resolving relational inconsistency during verbal analogical reasoning.

Reasoning about verbal analogies requires selective retrieval of relevant relational information. A consequence of this may be that inhibitory processes in memory cause reduced recall of information associated with analogy-irrelevant relations. The current experiments apply the retrieval-induced forgetting framework to investigate the potential role of such inhibitory processes in analogical reasoning. Participants studied verbal analogies in A-B :: C-D form. Then, half of the A-B pairs from the study phase appeared in verbal analogy problems but with a new C term (A-B :: C-?), and half the items did not appear in verbal analogy problems. A final recall test was then administered for all the original analogies. When the new C term in the analogical reasoning phase conveyed a new relation that was inconsistent with the original relation, reduced recall for items appearing in analogies was observed (Experiment 1). However, when the new C term conveyed a relation that was consistent with the original relation, no forgetting effect was observed (Experiment 1). This forgetting effect occurred even when a hint of the original relation was provided at final recall (Experiment 2). These results indicate that reasoning about analogies may involve inhibitory processes that help reduce competition among competing relations. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Retrieval dynamics and control for approach of tethered on-orbit service satellite

Approach and docking with space tether system has the advantages of less system complexity and lower cost compared with conventional rendezvous and docking which are usually essential operations in on-orbit service of spacecraft. This paper deals with the relative dynamics and control of the tethered on-orbit service satellite for the process of approach and docking by retrieving tether. Considering the system safety, it is necessary to keep the pitch angle constant or it varying in a small range during the approach. Therefore, we propose a control law for tether retrieval. Specifically, the relative dynamics equations are established to analyze the effects of orbit eccentricity, orbit altitude, and tether length rate on the system dynamics as well as investigate the property of pitch motion. Then the retrieval control law with constant pitch angle constraint is proposed using the dynamic inverse method based on the dynamics analyses. We further discuss the feasible region of orbit eccentricity and constant pitch angle for the control law to retrieve the tether. The numerical simulation experiments show that the proposed law can realize stable retrieval while maintaining a constant pitch angle.

Forgetting Leads to Chaos in Attractor Networks

Attractor networks are an influential theory for memory storage in brain systems. This theory has recently been challenged by the observation of strong temporal variability in neuronal recordings during memory tasks. In this work, we study a sparsely connected attractor network where memories are learned according to a Hebbian synaptic plasticity rule. After recapitulating known results for the continuous, sparsely connected Hopfield model, we investigate a model in which new memories are learned continuously and old memories are forgotten, using an online synaptic plasticity rule. We show that for a forgetting timescale that optimizes storage capacity, the qualitative features of the network’s memory retrieval dynamics are age dependent: most recent memories are retrieved as fixed-point attractors while older memories are retrieved as chaotic attractors characterized by strong heterogeneity and temporal fluctuations. Therefore, fixed-point and chaotic attractors coexist in the network phase space. The network presents a continuum of statistically distinguishable memory states, where chaotic fluctuations appear abruptly above a critical age and then increase gradually until the memory disappears. We develop a dynamical mean field theory to analyze the age-dependent dynamics and compare the theory with simulations of large networks. We compute the optimal forgetting timescale for which the number of stored memories is maximized. We found that the maximum age at which memories can be retrieved is given by an instability at which old memories destabilize and the network converges instead to a more recent one. Our numerical simulations show that a high degree of sparsity is necessary for the dynamical mean field theory to accurately predict the network capacity. To test the robustness and biological plausibility of our results, we study numerically the dynamics of a network with learning rules and transfer function inferred from in vivo data in the online learning scenario. We found that all aspects of the network’s dynamics characterized analytically in the simpler model also hold in this model. These results are highly robust to noise. Finally, our theory provides specific predictions for delay response tasks with aging memoranda. In particular, it predicts a higher degree of temporal fluctuations in retrieval states associated with older memories, and it also predicts fluctuations should be faster in older memories. Overall, our theory of attractor networks that continuously learn new information at the price of forgetting old memories can account for the observed diversity of retrieval states in the cortex, and in particular, the strong temporal fluctuations of cortical activity.1 MoreReceived 3 December 2021Revised 31 August 2022Accepted 6 December 2022DOI:https://doi.org/10.1103/PhysRevX.13.011009Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLearningMemoryNeuronal networksPhysical SystemsArtificial neural networksTechniquesDynamical mean field theoryInterdisciplinary PhysicsNetworksStatistical PhysicsNonlinear DynamicsBiological Physics

Taxonomic and thematic semantic relationships in picture naming as revealed by Laplacian-transformed event-related potentials.

Semantically related concepts co-activate when we speak. Prior research reported both behavioral interference and facilitation due to co-activation during picture naming. Different word relationships may account for some of this discrepancy. Taxonomically related words (e.g., WOLF-DOG) have been associated with semantic interference; thematically related words (e.g., BONE-DOG) have been associated with facilitation. Although these different semantic relationships have been associated with opposite behavioral outcomes, electrophysiological studies have found inconsistent effects on event-related potentials. We conducted a picture-word interference electroencephalography experiment to examine word retrieval dynamics in these different semantic relationships. Importantly, we used traditional monopolar analysis as well as Laplacian transformation allowing us to examine spatially deblurred event-related components. Both analyses revealed greater negativity (150-250 ms) for unrelated than related taxonomic pairs, though more restricted in space for thematic pairs. Critically, Laplacian analyses revealed a larger negative-going component in the 300 to 500 ms time window in taxonomically related versus unrelated pairs which were restricted to a left frontal recording site. In parallel, an opposite effect was found in the same time window but localized to a left parietal site. Finding these opposite effects in the same time window was feasible thanks to the use of the Laplacian transformation and suggests that frontal control processes are concurrently engaged with cascading effects of the spread of activation through semantically related representations.

Set Size of Information in Long-Term Memory Similarly Modulates Retrieval Dynamics in Young and Older Adults.

Our ability to rapidly distinguish new from already stored (old) information is important for behavior and decision making, but the underlying processes remain unclear. Here, we tested the hypothesis that contextual cues lead to a preselection of information and, therefore, faster recognition. Specifically, on the basis of previous modeling work, we hypothesized that recognition time depends on the amount of relevant content stored in long-term memory, i.e., set size, and we explored possible age-related changes of this relationship in older humans. In our paradigm, subjects learned by heart four different word lists (24, 48, 72, and 96 words) written in different colors (green, red, orange, and blue). On the day of testing, a color cue (e.g., green) indicated with a probability of 50% that a subsequent word might be from the corresponding list or from a list of new words. The old/new status of the word had to be distinguished via button press. As a main finding, we can show in a sample of n = 49 subjects, including 26 younger and 23 older humans, that response times increased linearly and logarithmically as a function of set size in both age groups. Conversely, corrected hit rates decreased as a function of set size with no statistically significant differences between both age groups. As such, our findings provide empirical evidence that contextual information can lead to a preselection of relevant information stored in long-term memory to promote efficient recognition, possibly by cyclical top-down and bottom-up processing.

Effect of Lexical-Semantic Cues during Real-Time Sentence Processing in Aphasia.

Using a visual world eye-tracking paradigm, we investigated the real-time auditory sentence processing of neurologically unimpaired listeners and individuals with aphasia. We examined whether lexical-semantic cues provided as adjectives of a target noun modulate the encoding and retrieval dynamics of a noun phrase during the processing of complex, non-canonical sentences. We hypothesized that the real-time processing pattern of sentences containing a semantically biased lexical cue (e.g., the venomous snake) would be different than sentences containing unbiased adjectives (e.g., the voracious snake). More specifically, we predicted that the presence of a biased lexical cue would facilitate (1) lexical encoding (i.e., boosted lexical access) of the target noun, snake, and (2) on-time syntactic retrieval or dependency linking (i.e., increasing the probability of on-time lexical retrieval at post-verb gap site) for both groups. For unimpaired listeners, results revealed a difference in the time course of gaze trajectories to the target noun (snake) during lexical encoding and syntactic retrieval in the biased compared to the unbiased condition. In contrast, for the aphasia group, the presence of biased adjectives did not affect the time course of processing the target noun. Yet, at the post-verb gap site, the presence of a semantically biased adjective influenced syntactic re-activation. Our results extend the cue-based parsing model by offering new and valuable insights into the processes underlying sentence comprehension of individuals with aphasia.

Memory retrieval dynamics and storage capacity of a modular network model of association cortex with featural decomposition

The primate heteromodal cortex presents an evident functional modularity at a mesoscopic level, with physiological and anatomical evidence pointing to it as likely substrate of long-term memory. In order to investigate some of its properties, a model of multimodular autoassociator is studied. Each of the many modules represents a neocortical functional ensemble of recurrently connected neurons and operates as a Hebbian autoassociator, storing a number of local features which it can recall upon cue. The global memory patterns are made of combinations of features sparsely distributed across the modules. Intermodular connections are modelled as a finite-connectivity random graph. Any pair of features in any respective pair of modules is allowed to be involved in several memory patterns; the coarse-grained modular network dynamics is defined in such a way as to overcome the consequent ambiguity of associations. Effects of long-range homeostatic synaptic scaling on network performance are also assessed.The dynamical process of cued retrieval almost saturates a natural upper bound while producing negligible spurious activation. The extent of finite-size effects on storage capacity is quantitatively evaluated. In the limit of infinite size, the functional relationship between storage capacity and number of features per module reduces to that which other authors found by methods from equilibrium statistical mechanics, which suggests that the origin of the functional form is of a combinatorial nature. In contrast with its apparent inevitability at intramodular level, long-range synaptic scaling results to be of minor relevance to both retrieval and storage capacity, casting doubt on its existence in the neocortex. A conjecture is also posited about how statistical fluctuation of connectivity across the network may underpin spontaneous emergence of semantic hierarchies through learning.

The role of attention and ageing in the retrieval dynamics of value-directed remembering.

For memory to be efficient, people need to remember important information. This involves selective encoding and retrieval operations to maximise the recall of valuable information at the expense of less important information. While past research has examined this in terms of strategic encoding operations, we investigated differences in the dynamics of retrieval in value-directed remembering tasks with younger adults under full and divided attention during encoding as well as in older adults. Participants typically initiated recall with the first presented, last presented, or highest valued words and also strategically organised retrieval according to information value such that high-value words tended to be recalled before low-value words. However, the average value of older adults' first recalled word was greater than that of younger adults, likely contributing to their enhanced selectivity. In addition, there were no differences in lag-conditional-response probabilities in younger adults under full or divided attention, but older adults showed impairments in the retrieval of items sharing contextual features with nearby items, while younger adults relied more on temporal-contextual cues to recall words. Together, this study suggests that both strategic encoding and strategic retrieval operations contribute to selectivity for valuable information and older adults may be able to maximise retrieval operations despite displaying impairments in temporal binding during encoding and an overall recall deficit.

Semantic Congruence Drives Long-Term Memory and Similarly Affects Neural Retrieval Dynamics in Young and Older Adults.

Learning novel information can be promoted if it is congruent with already stored knowledge. This so-called semantic congruence effect has been broadly studied in healthy young adults with a focus on neural encoding mechanisms. However, the impacts on retrieval, and possible impairments during healthy aging, which is typically associated with changes in declarative long-term memory, remain unclear. To investigate these issues, we used a previously established paradigm in healthy young and older humans with a focus on the neural activity at a final retrieval stage as measured with electroencephalography (EEG). In both age groups, semantic congruence at encoding enhanced subsequent long-term recognition memory of words. Compatible with this observation, semantic congruence led to differences in event-related potentials (ERPs) at retrieval, and this effect was not modulated by age. Specifically, congruence modulated old/new ERPs at a fronto-central (Fz) and left parietal (P3) electrode in a late (400–600 ms) time window, which has previously been associated with recognition memory processes. Importantly, ERPs to old items also correlated with the positive effect of semantic congruence on long-term memory independent of age. Together, our findings suggest that semantic congruence drives subsequent recognition memory across the lifespan through changes in neural retrieval processes.

Towards a Cognitive Theory of Cyber Deception.

This work is an initial step toward developing a cognitive theory of cyber deception. While widely studied, the psychology of deception has largely focused on physical cues of deception. Given that present-day communication among humans is largely electronic, we focus on the cyber domain where physical cues are unavailable and for which there is less psychological research. To improve cyber defense, researchers have used signaling theory to extended algorithms developed for the optimal allocation of limited defense resources by using deceptive signals to trick the human mind. However, the algorithms are designed to protect against adversaries that make perfectly rational decisions. In behavioral experiments using an abstract cybersecurity game (i.e., Insider Attack Game), we examined human decision-making when paired against the defense algorithm. We developed an instance-based learning (IBL) model of an attacker using the Adaptive Control of Thought-Rational (ACT-R) cognitive architecture to investigate how humans make decisions under deception in cyber-attack scenarios. Our results show that the defense algorithm is more effective at reducing the probability of attack and protecting assets when using deceptive signaling, compared to no signaling, but is less effective than predicted against a perfectly rational adversary. Also, the IBL model replicates human attack decisions accurately. The IBL model shows how human decisions arise from experience, and how memory retrieval dynamics can give rise to cognitive biases, such as confirmation bias. The implications of these findings are discussed in the perspective of informing theories of deception and designing more effective signaling schemes that consider human bounded rationality.

Exactness of Mean-Field Equations for Open Dicke Models with an Application to Pattern Retrieval Dynamics.

Open quantum Dicke models are paradigmatic systems for the investigation of light-matter interaction in out-of-equilibrium quantum settings. Albeit being structurally simple, these models can show intriguing physics. However, obtaining exact results on their dynamical behavior is challenging, since it requires the solution of a many-body quantum system with several interacting continuous and discrete degrees of freedom. Here, we make a step forward in this direction by proving the validity of the mean-field semiclassical equations for open multimode Dicke models, which, to the best of our knowledge, so far has not been rigorously established. We exploit this result to show that open quantum multimode Dicke models can behave as associative memories, displaying a nonequilibrium phase transition toward a pattern-recognition phase.

Animate and Inanimate Words Demonstrate Equivalent Retrieval Dynamics Despite the Occurrence of the Animacy Advantage.

People demonstrate a memory advantage for animate (living) concepts over inanimate (nonliving) concepts in a variety of memory tasks, including free recall, but we do not know the mechanism(s) that produces this effect. We compared the retrieval dynamics (serial-position effects, probability of first recall, output order, categorical clustering, and recall contiguity) of animate and inanimate words in a typical free recall task to help elucidate this effect. Participants were more likely to recall animate than inanimate words, but we found few, if any, differences in retrieval dynamics by word type. The animacy advantage was obtained across serial position, including occurring in both the primacy and recency regions of the lists. Participants were equally likely to recall an animate or inanimate word first on the tests and did not prioritize recalling words of one type earlier in retrieval or demonstrate strong clustering by animacy at recall. Participants showed some greater contiguity of recall for inanimate words, but this outcome ran counter to the animacy effect. Together, the results suggest that the animacy advantage stems from increased item-specific memory strength for animate over inanimate words and is unlikely to stem from intentional or strategic differences in encoding or retrieval by word type, categorical strategies, or differences in temporal organization. Although the present results do not directly support or refute any current explanations for the animacy advantage, we suggest that measures of retrieval dynamics can help to inspire or constrain future accounts for this effect and can be incorporated into relevant hypothesis testing.

Contributions of Arousal, Attention, Distinctiveness, and Semantic Relatedness to Enhanced Emotional Memory: An Event-Related Potential and Electrocardiogram Study.

Enhanced emotional memory (EEM) describes memory benefits for emotional items, traditionally attributed to impacts of arousal at encoding; however, attention, semantic relatedness, and distinctiveness likely also contribute in various ways. The current study manipulated arousal, semantic relatedness, and distinctiveness while recording changes in event-related potentials and heart rate during memory encoding. Trials were classified as remembered or forgotten by immediate recall performance. Negative images were remembered significantly better than neutral, and related neutral images were remembered significantly better than unrelated neutral images. Higher P300 and late positive potential (LPP) amplitudes were associated with memory for negative images as compared with related neutral images, suggesting that negative images received additional attentional processing at encoding, and that this cannot be accounted for only by the inherent relatedness of negative stimuli. No encoding benefits were found for related neutral images though they were better remembered than unrelated neutral images, indicating retrieval dynamics impacted memory. When image types were intermixed, greater heart rate changes occurred, and negative and unrelated neutral images received increased elaborative processing as compared with related neutral images, perhaps due to the prioritization of encoding resources. These results suggest encoding and retrieval processes contribute to EEM, with emotional items benefiting additively.