Short-term memory based on activated long-term memory: A review in response to Norris (2017)

Subjective-Objective Sleep Discrepancy in a Predominately White and Educated Older Adult Population: Examining the Associations With Cognition and Insomnia

OBJECTIVES

This study examined associations between various cognitive domains and sleep discrepancy (self-reported vs objectively measured sleep), and evaluated interactive associations with insomnia status (non-insomnia vs insomnia).

METHODS

Older adults (N = 65, Mage = 68.72, SD = 5.06, 43 insomnia/22 non-insomnia) aged 60+ reported subjective sleep (7 days of sleep diaries), objective sleep assessment (one-night polysomnography, PSG, via Sleep Profiler during the 7-day period), and completed cognitive tasks (National Institutes of Health Toolbox-Cognition Battery) measuring attention and processing speed, working memory, inhibitory control, cognitive flexibility, and episodic memory. The sleep diary variable corresponding to the same one night of PSG was used to calculate the sleep discrepancy (diary minus PSG parameter) variables for total sleep time (TST), sleep onset latency, wake after sleep onset, and sleep efficiency. Regression analyses determined independent and interactive (with insomnia status) associations between cognition and sleep discrepancy, controlling for age, sex, apnea-hypopnea index, and sleep medication usage.

RESULTS

Working memory interacted with insomnia status in associations with sleep discrepancy related to TST and sleep efficiency. In those with insomnia, worse working memory was associated with shorter self-reported TST (p = .008) and lower sleep efficiency (p = .04) than PSG measured.

DISCUSSION

In older adults with insomnia, worse working memory may be a contributing factor to sleep discrepancy. Future investigations of underlying neurophysiological factors and consideration of other objective sleep measures (actigraphy) are warranted. Prospective findings may help determine whether sleep discrepancy is a potential marker of future cognitive decline.

Working memory limitations constrain visual episodic long-term memory at both specific and gist levels of representation

Limitations in one's capacity to encode information in working memory (WM) constrain later access to that information in long-term memory (LTM). The present study examined whether these WM constraints on episodic LTM are limited to specific representations of past episodes or also extend to gist representations. Across three experiments, young adult participants (n = 40 per experiment) studied objects in set sizes of two or six items, either sequentially (Experiments 1a and 1b) or simultaneously (Experiment 2). They then completed old/new recognition tests immediately after each sequence (WM tests). After a long study phase, participants completed LTM conjoint recognition tests, featuring old but untested items from the WM phase, lures that were similar to studied items at gist but not specific levels of representation, and new items unrelated to studied items at both specific and gist levels of representation. Results showed that LTM estimates of specific and gist memory representations from a multinomial-processing-tree model were reduced for items encoded under supra-capacity set sizes (six items) relative to within-capacity set sizes (two items). These results suggest that WM encoding capacity limitations constrain episodic LTM at both specific and gist levels of representation, at least for visual objects. The ability to retrieve from LTM each type of representation for a visual item is contingent on the degree to which the item could be encoded in WM.

What you don't know can't hurt you: Retro-cues benefit working memory regardless of prior knowledge in long-term memory

Knowledge stored in long-term memory (LTM) impacts working memory (WM) overall, but it is unclear whether LTM facilitates focusing or switching attention in WM. We addressed this question using the retro-cue paradigm: Briefly presented arrays of individually calibrated numbers of shapes (concrete or abstract) were followed by a blank retention interval (no-cue) or a retro-cue to focus participants' attention to the to-be-probed shape. Experiment 3 included double retro-cue trials that required participants to switch their attention to a different shape. Participants recalled the color (Experiments 1) or location (Experiment 2) of the probed shape, or recognized the target shape among two other options (Experiment 3). Confirming the overall LTM effect on WM, fewer abstract shapes were needed to match the performance of concrete shapes during the calibration phase. Most importantly, retro-cues benefitted performance regardless of the nature of the shape, suggesting that LTM impacts WM overall without moderating attention.

Working memory forgetting: Bridging gaps between human and animal studies

The causes of forgetting in working memory (WM) remain a source of debate in cognitive psychology, partly because it has always been challenging to probe the complex neural mechanisms that govern rapid cognitive processes in humans. In this review, we argue that neural, and more precisely animal models, provide valuable tools for exploring the precise mechanisms of WM forgetting. First, we discuss theoretical perspectives concerning WM forgetting in humans. Then, we present neuronal correlates of WM in animals, starting from the initial evidence of delay activity observed in the prefrontal cortex to the later synaptic theory of WM. In the third part, specific theories of WM are discussed, including the notion that silent versus non-silent activity is more consistent with the processes of refreshing and decay proposed in human cognitive models. The review concludes with an exploration of the relationship between long-term memory and WM, revealing connections between these two forms of memory through the long-term synaptic hypothesis, which suggests that long-term storage of interference can potentially disrupt WM.

Encoding-related Brain Activity Predicts Subsequent Trial-level Control of Proactive Interference in Working Memory

Proactive interference (PI) appears when familiar information interferes with newly acquired information and is a major cause of forgetting in working memory. It has been proposed that encoding of item-context associations might help mitigate familiarity-based PI. Here, we investigate whether encoding-related brain activation could predict subsequent level of PI at retrieval using trial-specific parametric modulation. Participants were scanned with event-related fMRI while performing a 2-back working memory task with embedded 3-back lures designed to induce PI. We found that the ability to control interference in working memory was modulated by level of activation in the left inferior frontal gyrus, left hippocampus, and bilateral caudate nucleus during encoding. These results provide insight to the processes underlying control of PI in working memory and suggest that encoding of temporal context details support subsequent interference control.

Activated long-term memory and visual working memory during hybrid visual search: Effects on target memory search and distractor memory

In hybrid visual search, observers must maintain multiple target templates and subsequently search for any one of those targets. If the number of potential target templates exceeds visual working memory (VWM) capacity, then the target templates are assumed to be maintained in activated long-term memory (aLTM). Observers must search the array for potential targets (visual search), as well as search through memory (target memory search). Increasing the target memory set size reduces accuracy, increases search response times (RT), and increases dwell time on distractors. However, the extent of observers' memory for distractors during hybrid search is largely unknown. In the current study, the impact of hybrid search on target memory search (measured by dwell time on distractors, false alarms, and misses) and distractor memory (measured by distractor revisits and recognition memory of recently viewed distractors) was measured. Specifically, we aimed to better understand how changes in behavior during hybrid search impacts distractor memory. Increased target memory set size led to an increase in search RTs, distractor dwell times, false alarms, and target identification misses. Increasing target memory set size increased revisits to distractors, suggesting impaired distractor location memory, but had no effect on a two-alternative forced-choice (2AFC) distractor recognition memory test presented during the search trial. The results from the current study suggest a lack of interference between memory stores maintaining target template representations (aLTM) and distractor information (VWM). Loading aLTM with more target templates does not impact VWM for distracting information.

Short-term retention of words as a function of encoding depth

The traditional short- and long-term storage view of information processing and the levels-of-processing view both discuss the forgetting of information over time. In the traditional stage view, there is loss of at least poorly encoded information across several seconds when the information cannot be rehearsed (e.g., Ricker et al., 2020, Learning, Memory, and Cognition, 46, 60-76). In the levels-of-processing approach, information that is encoded in a shallow manner is lost more quickly over time than deeply-encoded information (Craik & Lockhart, 1972, Journal of Verbal Learning and Verbal Behavior, 11, 671-684.). Previous studies of the depth of encoding, however, have mostly been conducted using delayed tests, so there are few studies directly comparing the rate of forgetting over time for information as a function of different depths of encoding. We manipulated the level of processing with immediate recall in a modified Brown-Peterson task. An effect of the level of processing was robust, but evidence of forgetting across retention intervals was not always observed. When encoding time was curtailed (in Experiments 3 and 4), we found main effects of both the level of processing and the retention interval, but no interaction between the two variables. The results suggest that the depth-of-encoding effect may occur during the initial encoding of items, but without differential forgetting within the range of retention intervals that we examined (0-18 s), in contrast to the suggestion by Craik and Lockhart. Further work is needed to determine whether the depth-of-processing effect would grow over longer intervals.

Does value-based prioritization at working memory enhance long-term memory?

Research has demonstrated that individuals can direct their attention to valuable information in both working memory and long-term memory tasks with observable effects on performance. However, it is currently unclear whether prioritising an item for a working memory task automatically translates into a boost at long-term memory. This was examined in two experiments using relatively short (250 ms per item; Experiment 1) and longer (500 ms per item; Experiment 2) encoding times. Participants first completed a visual working memory task, in which they were presented with series of photographs of everyday objects. Following a brief delay (1,000 ms), they completed a four-alternative forced-choice test. Prior to encoding, participants were informed of the point values associated with each item. In some trials, the first item in the sequence was worth more points than the rest. In other trials, all items were equally valuable. After a filled delay, participants completed a surprise long-term memory task. At working memory, a value effect was reliably observed on recognition accuracy, along with some evidence of faster response times for high-value items. However, there was little consistent evidence of this effect automatically persisting into long-term memory. Thus, the benefits of attentional prioritization in working memory do not always translate into longer-term performance. More broadly, this provides further evidence that manipulations that enhance working memory performance do not necessarily enhance long-term memory.

Comparison of semantic and phonological false memories in short- and long-term tests

The Deese-Roediger-McDermott (DRM) paradigm has been at the centre of false memory research. Whereas most work with this paradigm has examined memory at the long term and with semantically associated lists, the present study examines phonological and semantic false memories at both short- and long-term delays. In two experiments, participants studied short lists containing six (Experiment 1) or four (Experiment 2) items, either semantically or phonologically related to the same non-studied critical items (CI). Following each list, participants completed 36 trials of an immediate recognition task (short-term memory [STM]-only condition) only or they also completed a surprise recognition test after a 1-min delay after all 36 STM trials (STM + long-term memory [LTM] condition). In STM, false alarms were higher in phonological lists, whereas after the delay, false alarms were higher in semantic lists, reflecting differential sensitivity to the type of association as a function of delay. A third experiment examined LTM performance after controlling for prior testing and yielded highly similar results. Both the activation-monitoring framework (AMF) and fuzzy-trace theory (FTT) can explain the majority of the findings, with some remaining issues. These results confirm that information from the knowledge base (LTM) does influence accuracy in an STM task, albeit less so than perceptual level similarity.

The Relation Between Attention and Memory

The relation between attention and memory has long been deemed important for understanding cognition, and it was heavily researched even in the first experimental psychology laboratory by Wilhelm Wundt and his colleagues. Since then, the importance of the relation between attention and memory has been explored in myriad subdisciplines of psychology, and we incorporate a wide range of these diverse fields. Here, we examine some of the practical consequences of this relation and summarize work with various methodologies relating attention to memory in the fields of working memory, long-term memory, individual differences, life-span development, typical brain function, and neuropsychological conditions. We point out strengths and unanswered questions for our own embedded processes view of information processing, which is used to organize a large body of evidence. Last, we briefly consider the relation of the evidence to a range of other theoretical views before drawing conclusions about the state of the field.

Are latent working memory items retrieved from long-term memory?

Switching one's focus of attention between to-be-remembered items in working memory (WM) is critical for cognition, but the mechanisms by which this is accomplished are unclear. A long-term memory (LTM) account suggests that switching attention away from an item, and passively retaining and reactivating such "latent" items back into the focus of attention involves episodic LTM retrieval processes, even for delays of only a few seconds. We tested this hypothesis using a two-item, double-retrocue WM task that requires participants to switch attention away from and reactivate items followed by subsequent LTM tests for reactivated items from the initial WM task (vs. continuously retained or untested control items). We compared performance on these tests between older adults (a population with LTM deficits) and young adults with either full (Experiment 1) or divided (Experiment 2) attention during the WM delay periods. The effects of reactivating latent items, as well as ageing and divided attention, had significant effects on WM performance, but did not interact with or systematically affect subsequent LTM for reactivated versus control items on item-, location-, or associative-recognition memory judgements made with either high or low confidence. Experiment 3 confirmed that these effects did not depend on whether or not young participants were warned about the subsequent LTM tests before performing the WM task. These dissociations between WM and LTM are inconsistent with the LTM account of latent WM; they are more consistent with the dynamic processing model of WM (Current Directions in Psychological Science).

Separate orexigenic hippocampal ensembles shape dietary choice by enhancing contextual memory and motivation

The hippocampus (HPC), traditionally known for its role in learning and memory, has emerged as a controller of food intake. While prior studies primarily associated the HPC with food intake inhibition, recent research suggests a critical role in appetitive processes. We hypothesized that orexigenic HPC neurons differentially respond to fats and/or sugars, potent natural reinforcers that contribute to obesity development. Results uncover previously-unrecognized, spatially-distinct neuronal ensembles within the dorsal HPC (dHPC) that are responsive to separate nutrient signals originating from the gut. Using activity-dependent genetic capture of nutrient-responsive HPC neurons, we demonstrate a causal role of both populations in promoting nutrient-specific preference through different mechanisms. Sugar-responsive neurons encode an appetitive spatial memory engram for meal location, whereas fat-responsive neurons selectively enhance the preference and motivation for fat intake. Collectively, these findings uncover a neural basis for the exquisite specificity in processing macronutrient signals from a meal that shape dietary choices.

When the mind's eye prevails: The Internal Dominance over External Attention (IDEA) hypothesis

Throughout the 20th century, the psychological literature has considered attention as being primarily directed at the outside world. More recent theories conceive attention as also operating on internal information, and mounting evidence suggests a single, shared attentional focus between external and internal information. Such sharing implies a cognitive architecture where attention needs to be continuously shifted between prioritizing either external or internal information, but the fundamental principles underlying this attentional balancing act are currently unknown. Here, we propose and evaluate one such principle in the shape of the Internal Dominance over External Attention (IDEA) hypothesis: Contrary to the traditional view of attention as being primarily externally oriented, IDEA asserts that attention is inherently biased toward internal information. We provide a theoretical account for why such an internal attention bias may have evolved and examine findings from a wide range of literatures speaking to the balancing of external versus internal attention, including research on working memory, attention switching, visual search, mind wandering, sustained attention, and meditation. We argue that major findings in these disparate research lines can be coherently understood under IDEA. Finally, we consider tentative neurocognitive mechanisms contributing to IDEA and examine the practical implications of more deliberate control over this bias in the context of psychopathology. It is hoped that this novel hypothesis motivates cross-talk between the reviewed research lines and future empirical studies directly examining the mechanisms that steer attention either inward or outward on a moment-by-moment basis.

Disentangling Processing and Storage Accounts of Working Memory Development in Childhood

Researchers have been asking the question of what drives the development of working memory (WM) during childhood for decades. This question is particularly challenging because so many aspects of cognition develop with age that it is difficult to disentangle them and find out which factors are causal or fundamental. In this review, we first prepare to discuss this issue by inquiring whether increases in storage, processing, or both are the fundamental driving factor(s) of the age-related increase in WM capability in childhood. We contend that by experimentally manipulating either factor and observing changes in the other, it is possible to learn about causal roles in WM development. We discuss research on school-aged children that seems to suggest, by means of such an approach, that the growth of storage is causal for some phases or steps in WM tasks, but that the growth of processing is causal for other steps. In our theoretical proposal, storage capacity of the focus of attention determines earlier steps of information processing by constraining the selective encoding of information into WM, whereas processing dependent on the focus of attention determines later steps, like the detection of patterns that can simplify the effective memory load and adoption of a proactive stance of maintenance in dual-task settings. Future directions for research are discussed.

When Does Episodic Memory Contribute to Performance in Tests of Working Memory?

Both the experimental and the psychometric investigation of the WM capacity limit depend critically on the assumption that performance in our tests of WM reflects that capacity limit to a good approximation. Most tasks to measure WM rely on testing memory after a short time during which participants are asked to maintain information in WM. In these tests, episodic long-term memory is likely to also lay down a trace of the memory set. Therefore, participants can draw on two sources of information when memory is tested, making it difficult to separate the contributions of WM and episodic LTM to the performance on immediate-memory tests. Here we use proactive interference to distinguish between these two sources of remembered information, building on the fact that episodic memory is vulnerable to proactive interference, whereas WM is protected against it. We use a release-from-PI paradigm to determine the extent to which commonly used WM tasks reflect contributions from episodic LTM. We focus on memory for serial order of verbal lists, but also include visual and spatial WM tasks. The results of five experiments demonstrate that although some tasks used to investigate WM are heavily contaminated by episodic LTM, other popular paradigms such as serial and probed recall, and the standard version of the continuous color-reproduction task, are not. Measuring proactive interference can help researchers determine the extent to which WM and episodic LTM contribute to performance in immediate-memory tasks.

Social memory in female mice is rapidly modulated by 17β-estradiol through ERK and Akt modulation of synapse formation

Social memory is essential to the functioning of a social animal within a group. Estrogens can affect social memory too quickly for classical genomic mechanisms. Previously, 17β-estradiol (E2) rapidly facilitated short-term social memory and increased nascent synapse formation, these synapses being potentiated following neuronal activity. However, what mechanisms underlie and coordinate the rapid facilitation of social memory and synaptogenesis are unclear. Here, the necessity of extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K) signaling for rapid facilitation of short-term social memory and synaptogenesis was tested. Mice performed a short-term social memory task or were used as task-naïve controls. ERK and PI3K pathway inhibitors were infused intradorsal hippocampally 5 min before E2 infusion. Forty minutes following intrahippocampal E2 or vehicle administration, tissues were collected for quantification of glutamatergic synapse number in the CA1. Dorsal hippocampal E2 rapid facilitation of short-term social memory depended upon ERK and PI3K pathways. E2 increased glutamatergic synapse number (bassoon puncta positive for GluA1) in task-performing mice but decreased synapse number in task-naïve mice. Critically, ERK signaling was required for synapse formation/elimination in task-performing and task-naïve mice, whereas PI3K inhibition blocked synapse formation only in task-performing mice. While ERK and PI3K are both required for E2 facilitation of short-term social memory and synapse formation, only ERK is required for synapse elimination. This demonstrates previously unknown, bidirectional, rapid actions of E2 on brain and behavior and underscores the importance of estrogen signaling in the brain to social behavior.

Adaptive Memory of a Neuromorphic Transistor with Multi-Sensory Signal Fusion

One of the ultimate goals of artificial intelligence is to achieve the capability of memory evolution and adaptability to changing environments, which is termed adaptive memory. To realize adaptive memory in artificial neuromorphic devices, artificial synapses with multi-sensing capability are required to collect and analyze various sensory cues from the external changing environments. However, due to the lack of platforms for mediating multiple sensory signals, most artificial synapses have been mainly limited to unimodal or bimodal sensory devices. Herein, we present a multi-modal artificial sensory synapse (MASS) based on an organic synapse to realize sensory fusion and adaptive memory. The MASS receives optical, electrical, and pressure information and in turn generates typical synaptic behaviors, mimicking the multi-sensory neurons in the brain. Sophisticated synaptic behaviors, such as Pavlovian dogs, writing/erasing, signal accumulation, and offset, were emulated to demonstrate the joint efforts of bimodal sensory cues. Moreover, associative memory can be formed in the device and be subsequently reshaped by signals from a third perception, mimicking modification of the memory and cognition when encountering a new environment. Our MASS provides a step toward next-generation artificial neural networks with an adaptive memory capability.

Instructional load induces functional connectivity changes linked to task automaticity and mnemonic preference

Learning new rules rapidly and effectively via instructions is ubiquitous in our daily lives, yet the underlying cognitive and neural mechanisms are complex. Using functional magnetic resonance imaging we examined the effects of different instructional load conditions (4 vs. 10 stimulus-response rules) on functional couplings during rule implementation (always 4 rules). Focusing on connections of lateral prefrontal cortex (LPFC) regions, the results emphasized an opposing trend of load-related changes in LPFC-seeded couplings. On the one hand, during the low-load condition LPFC regions were more strongly coupled with cortical areas mostly assigned to networks such as the fronto-parietal network and the dorsal attention network. On the other hand, during the high-load condition, the same LPFC areas were more strongly coupled with default mode network areas. These results suggest differences in automated processing evoked by features of the instruction and an enduring response conflict mediated by lingering episodic long-term memory traces when instructional load exceeds working memory capacity limits. The ventrolateral prefrontal cortex (VLPFC) exhibited hemispherical differences regarding whole-brain coupling and practice-related dynamics. Left VLPFC connections showed a persistent load-related effect independent of practice and were associated with 'objective' learning success in overt behavioral performance, consistent with a role in mediating the enduring influence of the initially instructed task rules. Right VLPFC's connections, in turn, were more susceptible to practice-related effects, suggesting a more flexible role possibly related to ongoing rule updating processes throughout rule implementation.

Working Memory Constrains Long-Term Memory in Children and Adults: Memory of Objects and Bindings

We explored how individual and age-related differences in working memory (WM) capacity affected subsequent long-term memory (LTM) retrieval. Unlike past studies, we tested WM and LTM not only for items, but also for item-color bindings. Our sample included 82 elementary school children and 42 young adults. The participants performed a WM task with images of unique everyday items presented sequentially at varying set sizes in different colors. Later, we tested LTM for items and item-color bindings from the WM task. The WM load during encoding constrained LTM, and participants with a higher WM capacity retrieved more items in the LTM test. Even when accounting for young children's poor item memory by considering only the items that they did remember, they exhibited an exacerbated difficulty with remembering item-color bindings in WM. Their LTM binding performance, however, as a proportion of remembered objects, was comparable to that of older children and adults. The WM binding performance was better during sub-span encoding loads, but with no clear transfer of this benefit to LTM. Overall, LTM item memory performance was constrained by individual and age-related WM limitations, but with mixed consequences for binding. We discuss the theoretical, practical, and developmental implications of this WM-to-LTM bottleneck.

Effects of bilingualism on autobiographical memory: variation in idea density and retrieval speed

Prior work on bilingual memory has largely focused on working memory and less on autobiographical memory. In the present study, we tested the effect of bilingualism on autobiographical memory and examined whether an effect would be moderated or mediated by working memory. Spanish-English bilingual and English-only monolingual adults completed an autobiographical cued-recall task, as well as a working memory measure. Memories were coded for retrieval speed and propositional idea density. Bilingual status was associated with faster memory retrieval but did not affect propositional idea density. Better working memory was associated with slower memory retrieval but did not affect propositional idea density, nor did working memory moderate or mediate the effect of bilingualism. Together, these results indicate an effect of bilingualism on the speed of autobiographical memory retrieval that does not extend to autobiographical memory content and suggest that the effect of bilingualism is independent of the effect of working memory.

Gradistics: An underappreciated dimension in evolutionary space

The growth of complexity is an unsolved and underappreciated problem. We consider possible causes of this growth, hypotheses testing, molecular mechanisms, complexity measures, cases of simplification, and significance for biomedicine. We focus on a general ability of regulation, which is based on the growing information storage and processing capacities, as the main proxy of complexity. Natural selection is indifferent to complexity. However, complexification can be inferred from the same first principle, on which natural selection is founded. Natural selection depends on potentially unlimited reproduction under limited environmental conditions. Because of the demographic pressure, the simple ecological niches become fulfilled and diversified (due to species splitting and divergence). Diversification increases complexity of biocenoses. After the filling and diversification of simple niches, the more complex niches can arise. This is the 'atomic orbitals' (AO) model. Complexity has many shortcomings but it has an advantage. This advantage is ability to regulatory adaptation, including behavioral, formed in the evolution by means of genetic adaptation. Regulatory adaptation is much faster than genetic one because it is based on the information previously accumulated via genetic adaptation and learning. Regulatory adaptation further increases complexity of biocenoses. This is the 'regulatory advantage' (RA) model. The comparison of both models allows testable predictions. We focus on the animal evolution because of the appearance of higher regulatory level (nervous system), which is absent in other lineages, and relevance to humans (including biomedical aspects).

The tradeoff between item and order information in short-term memory does not depend on encoding time

Participants can optimize encoding of an immediate verbal memory test for item or for order information, or they can try to be ready for either type of test. Dividing encoding between both kinds of information, however, comes at a cost. Recently, it has been shown that the cost is more severe for order information compared to item information (Guitard et al., 2022). Here, for the first time, we evaluated which factor can better account for this asymmetry by contrasting two hypotheses. According to a rate hypothesis, divided attention affects the rate of encoding more for order than for items. According to an alternative, asymptote hypothesis, divided attention does not affect the rates but diminishes the endpoint, or asymptotic level, of order encoding more than item encoding. In three experiments to distinguish these hypotheses, participants prepared for an item fragment completion test, an order reconstruction test, or both types of tests, in trials with different durations of presentation. Overall, our results were better accounted for by a model which assumes that dividing attention between preparation for item and order testing affects the asymptote of encoding more for order than for items, with no effects on the rates of order or item encoding compared to preparation for a single test. The findings not only replicate our prior results, but also demonstrate that the allocation of attention to item or order processing can be disentangled from the time on task. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Attentional Refreshing in the Absence of Long-Term Memory Content: Role of Short-Term and Long-Term Consolidation

Contradictory results in the literature suggest that attentional refreshing can seemingly not operate efficiently in the absence of semantic representations, while at the same time it does not rely directly on retrieval from semantic memory. The objective of the present study was a better understanding of the bidirectional links between working memory (WM) and long-term memory (LTM), by assessing on the one hand the role of WM mechanisms in long-term recall and on the other hand how their functioning is modulated by the prior LTM content. Through two experiments, we investigated a new hypothesis: attentional refreshing requires stable WM representations independently of the presence or the absence of associated LTM traces. We manipulated this stability through short-term consolidation (Experiment 1) and multiple presentations of memoranda (Experiment 2) to evaluate how it would affect maintenance of words and pseudowords. While we found that lexicality, short-term consolidation and multiple presentations affected short-term and long-term recall, both experiments converged on the conclusion that none of these factors modulated the effect of the cognitive load of the concurrent processing task, suggesting that refreshing does not depend on LTM content nor WM representations' stability. Additionally, we found that delayed recall performance was not affected by the cognitive load, in contradiction with previous literature. These results provide new insight into the functioning of refreshing and the links between WM and LTM.

Constraints of attention, stimulus modality, and feature similarity in working memory

Two of the most important concepts in working memory that differentiate many theories are the role of attention and similarity between items. Investigators have debated whether there is a central, general resource of attention, and whether interference between items depends mostly on their modality and type of code (i.e., verbal/acoustic versus visual/spatial coding) or upon multiple dimensions of feature similarity even within a modality. Here, we examine results from three experiments in which the features of items to be remembered differed for visual objects in color or orientation, or for acoustic objects in noise duration or tone pitch. There were one or two of these sets on a trial and, when there were two sets, the similarity between their features varied: there were sets in different modalities, sets with different feature types within a modality, or sets of the same feature type. One-set trials consistently produced superior performance. For two-set trials, dissimilarity of the sets mattered only when both sets had to be attended, compared with attention to only one set. Feature differences within a modality mattered at least as much as between-modality differences. The findings conflict with what would be expected if modality were the sole organizing principle and support a working memory model in which a capacity-limited attention is constrained by the feature similarity of task-relevant items.

Rhythms of human attention and memory: An embedded process perspective

It remains a dogma in cognitive neuroscience to separate human attention and memory into distinct modules and processes. Here we propose that brain rhythms reflect the embedded nature of these processes in the human brain, as evident from their shared neural signatures: gamma oscillations (30–90 Hz) reflect sensory information processing and activated neural representations (memory items). The theta rhythm (3–8 Hz) is a pacemaker of explicit control processes (central executive), structuring neural information processing, bit by bit, as reflected in the theta-gamma code. By representing memory items in a sequential and time-compressed manner the theta-gamma code is hypothesized to solve key problems of neural computation: (1) attentional sampling (integrating and segregating information processing), (2) mnemonic updating (implementing Hebbian learning), and (3) predictive coding (advancing information processing ahead of the real time to guide behavior). In this framework, reduced alpha oscillations (8–14 Hz) reflect activated semantic networks, involved in both explicit and implicit mnemonic processes. Linking recent theoretical accounts and empirical insights on neural rhythms to the embedded-process model advances our understanding of the integrated nature of attention and memory – as the bedrock of human cognition.

Unconsciously registered items reduce working memory capacity

The assumption that the contents of consciousness correspond to those of working memory (WM) is challenged by evidence that stimuli masked from awareness can be retained for several seconds (Soto et al., 2011; Bergström & Eriksson, 2015). To assess whether conscious and unconscious items compete in a unitary WM store we conducted an experiment in which some of the memory items in an array were masked from conscious sight using continuous flash suppression (CFS) while others remained visible. After a retention interval, participants decided whether the probed item (either masked or visible) had changed its orientation. Behavioral results indicated that change detection for visible items was significantly impaired when masked items were present, suggesting that masked items either displaced or reduced the precision of visible items in WM. However, change detection for masked items was at chance levels, indicating that these items were not stored. The unsuccessful attempt to encode them may have drawn upon a common pool of attentional resources needed to retain or retrieve visible items. Contralateral Delay Activity, an EEG index of net WM load, failed to temporally localize this interference.

Deconfounding serial recall: Response timing and the overarching role of grouping

We used the timing of serial recall in several situations to reveal important aspects of recall groupings that participants construct and the reasons those groupings occur. We examined the timing of responses in the recall of digit strings within two published experiments. Cowan, Saults, Elliott, and Moreno (2002) examined memory for nine-item lists in a way that deconfounded the presentation modality, input versus output serial position (using a varied starting point of recall), memory load from items not yet recalled (using whole vs. partial recall), and the presence or absence of the temporal grouping of the lists into triads. Accuracy was strikingly different in the two modalities, with grouping drastically changing recall of acoustic lists but with little difference between grouped versus ungrouped visual lists. Despite the modality difference in recall, the present timing results show that participants imposed a similar grouped structure in recall for both modalities. When errors were made, the original grouping structure still was maintained in the output timing. Cowan et al. (2005, Experiment 1) presented ungrouped acoustic lists of varying lengths in a span task. In this case, there was never a grouping structure presented to the participant and the accuracy data did not reveal evidence of grouping, but we show clear grouping in the timing structure. This grouping structure varied with both the list length and an individual's span. Timing in both experiments shows that a grouping structure is imposed on responses in a manner that is dependent on several factors not present in the stimuli. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Attention allocation between item and order information in short-term memory

In immediate memory for verbal lists, recently it has been shown that participants can choose to carry out encoding that prioritises readiness for an item test at some cost to order information or, conversely, that prioritises readiness for an order test at a cost to item information. Here, we ask whether participants can control attention to items and order in a graded fashion. We examined this issue by manipulating the percentage of order or item test trials participants would receive in a block (for each type of test, 25%, 50%, 75%, or 100% of the trials in a block). Overall, the results revealed that participants were able to allocate their attention in a fine-grained manner that took into account the trial distribution within the block. However, there was a difference between the effects of allocating attention to item versus order. Divided attention, compared with full attention to one attribute, had an asymmetry, such that divided attention impaired order performance more than item performance. The exact point at which this asymmetry could be seen differed between two experiments, which included different item tests (fragment completion vs. free recall). The results suggest a common resource for item and order encoding and/or retention in working memory, which can be voluntarily allocated to different mixtures of these two attributes.

Working Memory Predicts New Word Learning Over and Above Existing Vocabulary and Nonverbal IQ

PURPOSE

The purpose of this study was to use an established model of working memory in children to predict an established model of word learning to determine whether working memory explained word learning variance over and above the contributions of expressive vocabulary and nonverbal IQ.

METHOD

One hundred sixty-seven English-speaking second graders (7- to 8-year-olds) with typical development from two states participated. They completed a comprehensive battery of working memory assessments and six word learning tasks that assessed the creation, storage, retrieval, and production of phonological and semantic representations of novel nouns and verbs and the ability to link those representations.

RESULTS

A structural equation model with expressive vocabulary, nonverbal IQ, and three working memory factors predicting two word learning factors fit the data well. When working memory factors were entered as predictors after expressive vocabulary and nonverbal IQ, they explained 45% of the variance in the phonological word learning factor and 17% of the variance in the semantic word learning factor. Thus, working memory explained a significant amount of word learning variance over and above expressive vocabulary and nonverbal IQ.

CONCLUSION

Results show that working memory is a significant predictor of dynamic word learning over and above the contributions of expressive vocabulary and nonverbal IQ, suggesting that a comprehensive working memory assessment has the potential to identify sources of word learning difficulties and to tailor word learning interventions to a child's working memory strengths and weaknesses.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.19125911.

Working memory development: A 50-year assessment of research and underlying theories

The author has thought about working memory, not always by that name, since 1969 and has conducted research on its infant and child development since the same year that the seminal work of Baddeley and Hitch (1974) was published. The present article assesses how the field of working memory development has been influenced since those years by major theoretical perspectives: empiricism (along with behaviorism), nativism (along with modularity), cognitivism (along with constructivism), and dynamic systems theory. The field has not fully discussed the point that these theoretical perspectives have helped to shape different kinds of proposed working memory systems, which in turn have deeply influenced what is researched and how it is researched. Here I discuss that mapping of theoretical viewpoints onto assumptions about working memory and trace the influence of this mapping on the field of working memory development. I illustrate where these influences have led in my own developmental research program over the years.

A model of working memory for latent representations

We propose a mechanistic explanation of how working memories are built and reconstructed from the latent representations of visual knowledge. The proposed model features a variational autoencoder with an architecture that corresponds broadly to the human visual system and an activation-based binding pool of neurons that links latent space activities to tokenized representations. The simulation results revealed that new pictures of familiar types of items can be encoded and retrieved efficiently from higher levels of the visual hierarchy, whereas truly novel patterns are better stored using only early layers. Moreover, a given stimulus in working memory can have multiple codes, which allows representation of visual detail in addition to categorical information. Finally, we validated our model's assumptions by testing a series of predictions against behavioural results obtained from working memory tasks. The model provides a demonstration of how visual knowledge yields compact visual representation for efficient memory encoding.

EXPRESS: The Company a Word Keeps: The Role of Neighbourhood Density in Verbal Short-Term Memory

Psycholinguistic information plays an important role in verbal memory over the short-term (vSTM). One such linguistic feature is neighbourhood density (ND)-the number of words that can be derived from a given word by changing a single phoneme or single letter-so that vSTM performance is better when word sequences are from dense rather than sparse neighbourhoods, an effect attributed to higher levels of supportive activation among neighbouring words. Generally, it has been assumed that lexical variables influence item memory but not order memory, and we show that the typical vSTM advantage for dense neighbourhood words in serial recall is eliminated when using serial recognition. However, we also show that the usual effect of ND is reversed-for both serial recall and serial recognition-when using a subset of those same words. The findings call into question the way in which ND has been incorporated into accounts of vSTM that invoke mutual support from long-term representations on either encoding or retrieval.

Tradeoffs between Item and Order Information in Short-Term Memory

Recently, Guitard et al. (2021) used a two-list procedure and varied the kind of encoding carried out for each list (item or order encoding). They found dual-list impairment on an order test was consistently greater when the other list was also encoded for an order test, compared to when it was in the presence of another list encoded for an item test. They also found a dual-list cost relative to one list for both order and item information. Here we address the bases of the interference costs with a novel task in which, prior to each list presentation, participants are instructed to expect an item fragment completion test, an order reconstruction test, or either type of test. In five experiments, we contrast two competing accounts of item and order processing, the conflicting representation hypothesis and the common resource hypothesis. An asymmetry with larger dual-attention costs on order compared to item tests was found, with the effect magnitude changing with task conditions. Our results support a version of the common resource hypothesis in which both item and order processing occur no matter which test is expected, but in which additional processing is divided between item and order codes in a manner that depends on task demands.

The domain-specificity of serial order working memory

Making a turn while driving is simple: turn on the indicator, check for cars, then turn. Two types of information are required to perform this sequence of events: information about the items (e.g., the correct indicator), and the serial order of those items (e.g., checking before turning rather than vice-versa). Previous research has found distinct working memory capacities (WMCs) for item and serial order information in both verbal and nonverbal domains. The current study investigates whether the serial order WMC is shared for sequences from different content domains. One hundred and fifty-three participants performed sequence matching tasks with verbal (letters and words) and nonverbal (locations and arrows) stimuli. The accuracy of detecting mismatched item-identity and serial order information in sequences was used to operationalize item and order WMC. Using structural equation modeling analyses, we directly compared models that included either domain-specific or domain-general serial order WMC latent variables, finding that models with domain-specific serial order WMC latent variables for verbal and nonverbal materials fit the data better than models with domain-general latent variables. The findings support the hypothesis that there are separate capacities for serial order working memory depending on the type of material being ordered.

Is long-term memory used in a visuo-spatial change-detection paradigm?

In tests of working memory with verbal or spatial materials, repeating the same memory sets across trials leads to improved memory performance. This well-established "Hebb repetition effect" could not be shown for visual materials in previous research. The absence of the Hebb effect can be explained in two ways: Either persons fail to acquire a long-term memory representation of the repeated memory sets, or they acquire such long-term memory representations, but fail to use them during the working memory task. In two experiments (N1 = 18 and N2 = 30), we aimed to decide between these two possibilities by manipulating the long-term memory knowledge of some of the memory sets used in a change-detection task. Before the change-detection test, participants learned three arrays of colors to criterion. The subsequent change-detection test contained both previously learned and new color arrays. Change detection performance was better on previously learned compared with new arrays, showing that long-term memory is used in change detection.

Fractionating the episodic buffer

The episodic buffer is a putative component of working memory proposed to account for several short-term memory functions, including unexpectedly preserved immediate prose recall by amnesic patients. Over the course of time, this component has increasingly become associated with binding functions. Considering recent findings regarding the performance of both memory-impaired and healthy individuals on the range of tasks purported to require the contribution of the episodic buffer, we suggest that it should be fractionated into two functional systems. One is a schematic store instantiated in brain areas responsible for conceptual and schema representations, which is likely to be hippocampus-independent, and preserved in the face of amnesia. In contrast, short-term maintenance of novel associative binding is likely to require the contribution of the hippocampus and may therefore not be functionally dissociable from long-term memory.

Latching dynamics as a basis for short-term recall

We discuss simple models for the transient storage in short-term memory of cortical patterns of activity, all based on the notion that their recall exploits the natural tendency of the cortex to hop from state to state—latching dynamics. We show that in one such model, and in simple spatial memory tasks we have given to human subjects, short-term memory can be limited to similar low capacity by interference effects, in tasks terminated by errors, and can exhibit similar sublinear scaling, when errors are overlooked. The same mechanism can drive serial recall if combined with weak order-encoding plasticity. Finally, even when storing randomly correlated patterns of activity the network demonstrates correlation-driven latching waves, which are reflected at the outer extremes of pattern space.

What makes short-term memory so poor, that over a minute we tend to forget even phone numbers, if we cannot rehearse or record them electronically? In comparison, long-term memory can be amazingly rich and accurate. Was it so difficult to equip our brain with a short-term memory device of reasonable capacity?

We discuss the hypothesis that instead of an ad hoc device, short-term memory relies on long-term representations, and that the short-term recall of multiple items exploits the natural tendency of the cortex to jump from state to state, by only adding imprecisely determined “kicks” that spur cortical dynamics towards the states representing those items. We show that a plausible neural model for such kicks performs similarly to human subjects we have tested, both in conditions when short-term recall is terminated by errors, and when errors are overlooked and subjects are asked to keep trying. The same mechanism can drive serial recall, if combined with equally imprecise kicks encoding item order. Our analysis suggests that a proper short-term memory device may have never evolved in our brain, which had, therefore, to make do with tweaking its superb long-term memory capabilities.

The development of metacognitive accuracy in working memory across childhood

Growth in working memory capacity, the number of items kept active in mind, is thought to be an important aspect of childhood cognitive development. Here, we focused on participants' awareness of the contents of their working memory, or meta-working memory, which seems important because people can put cognitive abilities to best use only if they are aware of their limitations. In two experiments on the development of meta-working memory in children between 6 and 13 years old and adults, participants were to remember arrays of colored squares and to indicate if a probe item was in the array. On many trials, before the probe recognition test, they reported a metajudgment, how many items they thought they remembered. We compared meta-working memory judgments to actual performance and looked for associations between these measures on individual and trial-by-trial levels. Despite much lower working memory capacity in younger children there was little change in meta-working memory judgments across age groups. Consequently, younger participants were much less realistic in their metajudgments concerning their working memory capability. Higher cognitive capacity was associated with more accurate meta-working memory judgments within an age group. Trial-by-trial tuning of metajudgments was evident only in young adults and then only for small array set sizes. In sum, meta-working memory ability is a sophisticated skill that develops with age and may be an integral aspect of the development of working memory across the school years. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Children's long-term retention is directly constrained by their working memory capacity limitations

We explored the causal role of individual and age-related differences in working memory (WM) capacity in long-term memory (LTM) retrieval. Our sample of 160 participants included 120 children (6-13-years old) and 40 young adults (18-24 years). Participants performed a WM task with images of unique everyday items, presented at varying set sizes. Subsequently, we tested participants' LTM for items from the WM task. Using these measures, we estimated the ratio at which items successfully held in WM were recognized in LTM. While WM and LTM generally improved with age, the ability to transfer information from WM to LTM appeared consistent between age groups. Moreover, individual differences in WM capacity appeared to predict LTM encoding. Overall, these results suggested that LTM performance was constrained by experimental, individual, and age-related WM limitations. We discuss the theoretical and practical implications of this WM-to-LTM bottleneck.

Immediate recall of serial numbers with or without multiple item repetitions

Immediate recall of lists of items in random serial order has been examined in thousands of studies throughout the history of experimental psychology. In most studies, though, there have been no repetitions of items within a list, or occasionally a single repetition. These stimuli differ from the common uses of item series, which often include multiple repetitions (e.g., identification numbers; orders of people at a restaurant table). To begin to understand such cases we presented lists that, in some trial blocks, were constructed with no restrictions on repetitions. Specifically, we examined immediate serial recall of visually-presented, nine-digit lists, either spatially separated into three separate groups of three digits (Experiment 1) or undivided (Experiment 2). Many of the lists included single or multiple repetitions of digits, with repeated digits either adjacent or non-adjacent in an unpredictable manner. We assessed theoretical expectations derived from prior research. Effects of repetition were often helpful but, when repetitions favoured a grouping that conflicted with the presented grouping into threes in Experiment 1, repetition was disadvantageous. We suggest a theoretical analysis in which participants can use presented grouping cues or, when those cues are absent, create their own groupings to exploit repetitions among the stimuli.

Role of verbal working memory in rapid procedural acquisition of a choice response task

How quickly are instructions for a task translated into an effective task-set? If declarative working memory (dWM) is used to maintain a task's S-R rules until practice compiles them adequately into procedural memory, variables that affect retrieval from dWM should influence task performance while it is still dependent on dWM. Participants were trained on a series of 6-choice RT tasks, with a 1:1 mapping from object pictures to keys. In Experiments 1 and 2, an instruction phase - presentation of the S-R rules one by one -was followed by test trials. The phonological similarity of the objects' names significantly affected performance only during the first few encounters with the stimuli. Serial position effects were also consistent with retrieval from verbal dWM during those early trials. In Experiment 3, instruction onon the S-R rules was omitted, so participants had to learn the S-R mappings by trial and error alone; the effect of phonological similarity lasted longer, but still disappeared after a dozen encounters with each stimulus. Experiment 4 showed that instructions and just four trials of practice per S-R rule were sufficient to form a persisting representation of the S-R rules robust enough to interfere with later acquisition of a competing S-R rule after several minutes spent acquiring other task-sets. An effective and lasting task-set is rapidly compiled into procedural memory through instruction and early feedback; verbal dWM plays little role thereafter.

Are visual working memory and episodic memory distinct processes? Insight from stroke patients by lesion-symptom mapping

Working memory and episodic memory are two different processes, although the nature of their interrelationship is debated. As these processes are predominantly studied in isolation, it is unclear whether they crucially rely on different neural substrates. To obtain more insight in this, 81 adults with sub-acute ischemic stroke and 29 elderly controls were assessed on a visual working memory task, followed by a surprise subsequent memory test for the same stimuli. Multivariate, atlas- and track-based lesion-symptom mapping (LSM) analyses were performed to identify anatomical correlates of visual memory. Behavioral results gave moderate evidence for independence between discriminability in working memory and subsequent memory, and strong evidence for a correlation in response bias on the two tasks in stroke patients. LSM analyses suggested there might be independent regions associated with working memory and episodic memory. Lesions in the right arcuate fasciculus were more strongly associated with discriminability in working memory than in subsequent memory, while lesions in the frontal operculum in the right hemisphere were more strongly associated with criterion setting in subsequent memory. These findings support the view that some processes involved in working memory and episodic memory rely on separate mechanisms, while acknowledging that there might also be shared processes.

What affects the magnitude of age-related dual-task costs in working memory? The role of stimulus domain and access to semantic representations

Although there is evidence that the effect of including a concurrent processing demand on the storage of information in working memory is disproportionately larger for older than younger adults, not all studies show this age-related impairment, and the critical factors responsible for any such impairment remain elusive. Here we assess whether domain overlap between storage and processing activities, and access to semantic representations, are important determinants of performance in a sample of younger and older adults (N = 119). We developed four versions of a processing task by manipulating the type of stimuli involved (either verbal or non-verbal) and the decision that participants had to make about the stimuli presented on the screen. Participants either had to perform a spatial judgement, in deciding whether the verbal or non-verbal item was presented above or below the centre of the screen, or a semantic judgement, in deciding whether the stimulus refers to something living or not living. The memory task was serial-ordered recall of visually presented letters. The study revealed a large increase in age-related memory differences when concurrent processing was required. These differences were smaller when storage and processing activities both used verbal materials. Dual-task effects on processing were also disproportionate for older adults. Age differences in processing performance appeared larger for tasks requiring spatial decisions rather than semantic decisions. We discuss these findings in relation to three competing frameworks of working memory and the extant literature on cognitive ageing.

Attention effects in working memory that are asymmetric across sensory modalities

A key unanswered question about working memory is the nature of interference between items. At one extreme of existing theories, interference occurs between any two items because of a general capacity limit. At another extreme, interference depends on the similarity between particular features of different items. We examine this question in three experiments by presenting two sets of items on each trial, comprising tones or colors, with three levels of similarity between the two sets: cross-modal, unimodal with different marking features (two different musical instruments or shapes), and unimodal with the same marking feature. Another question is the extent to which the entry of presented items into working memory is obligatory or optional, which we examined by requiring retention of the first, the second, or both sets of stimuli for a recognition test shortly after the presentation of the two sets. The combination of the set similarity and attention manipulations allows us to draw conclusions about the nature of working-memory storage. The findings were not entirely in accord with any pre-existing theory. The effects of feature similarity were present in both modalities but more pronounced for sounds, whereas the detrimental effects of attention to both sets for retention occurred only for visual stimuli. Based on the findings we suggest a new, hybrid conception of working memory storage.

Sentence Recall in Latent and Anomic Aphasia: An Exploratory Study of Semantics and Syntax

We investigated whether semantic plausibility and syntactic complexity affect immediate sentence recall in people with latent and anomic aphasia. To date, these factors have not been explored in these types of aphasia. As with previous studies of sentence recall, we measured accuracy of verbatim recall and uniquely real-time speech measures. The results showed that accuracy did not distinguish performance between latent aphasia and neurotypical controls. However, some of the real-time speech measures distinguished performance between people with latent aphasia and neurotypical controls. There was some evidence, though not pervasive, that semantic plausibility and syntactic complexity influenced recall performance. There were no interactions between semantic plausibility and syntactic complexity. The speed of preparation of responses was slower in latent aphasia than controls; it was also slower in anomic aphasia than both latent and control groups. It appears that processing speed as indexed by temporal speech measures may be differentially compromised in latent and anomic aphasia. However, semantic plausibility and syntactic complexity did not show clear patterns of performance among the groups. Notwithstanding the absence of interactions, we advance an explanation based on conceptual short-term memory as to why semantically implausible sentences are typically more erroneous and possibly also slower in recall.

Working memory limits severely constrain long-term retention

There has been considerable controversy in recent years as to whether information held in working memory (WM) is rapidly forgotten or automatically transferred to long-term memory (LTM). Although visual WM capacity is very limited, we appear able to store a virtually infinite amount of information in visual LTM. Still, LTM retrieval often fails. Some view visual WM as a mental sketchpad that is wiped clean when new information enters, but not a consistent precursor of LTM. Others view the WM and LTM systems as inherently linked. Distinguishing between these possibilities has been difficult, as attempts to directly manipulate the active holding of information in visual WM has typically introduced various confounds. Here, we capitalized on the WM system's capacity limitation to control the likelihood that visual information was actively held in WM. Our young-adult participants (N = 103) performed a WM task with unique everyday items, presented in groups of two, four, six, or eight items. Presentation time was adjusted according to the number of items. Subsequently, we tested participants' LTM for items from the WM task. LTM was better for items presented originally within smaller WM set sizes, indicating that WM limitations contribute to subsequent LTM failures, and that holding items in WM enhances LTM encoding. Our results suggest that a limit in WM capacity contributes to an LTM encoding bottleneck for trial-unique familiar objects, with a relatively large effect size.

Short-term memory capacity and sensitivity to language statistics in dyslexia and among musicians

Poor short-term memory (STM) capacity in individuals with dyslexia (IDDs) and enhanced STM capacity in musicians are well documented, yet their causes are disputed. Previous studies also found poor use of stimuli statistics by IDDs and enhanced use by musicians. We hypothesized that these observations are functionally related, as follows: Enhanced sensitivity to statistics facilitates musicians' benefit from each exposure, and reduced sensitivity to statistics hinders IDDs' benefit. Thus, larger group differences are expected for larger exposure: STM capacity, which is sensitive to item familiarity, will thus be larger among musicians, and smaller among IDDS, particularly for high-frequency items. Testing this hypothesis using syllable span, we found that musicians' advantage and IDDs' difficulty were indeed larger for high-frequency syllables than for low-frequency ones. By contrast, benefits from sequence repetition did not differ between musicians, controls and IDDs, suggesting that online sequence learning is based on a different mechanism. To test this dissociation we recruited, in addition to native Hebrew speakers, native English speakers, matched to the Hebrew-speaking controls. Their spans for high-frequency syllables in Hebrew, which do not have high frequency in English, were small - as expected from reduced exposure to these syllables. Yet, their benefit from sequence repetition was similar to that of the three Hebrew-speaking groups. Taken together, these experiments suggest that different sensitivities to item frequency explain some of the population-related variability in STM tasks. By contrast, benefits from sequence repetition do not depend on item familiarity, and do not differ between groups.