Chapter 2 Design for a Working Memory

Repetitive Transcranial Magnetic Stimulation (rTMS) Treatment Reduces Variability in Brain Function in Schizophrenia: Data From a Double-Blind, Randomized, Sham-Controlled Trial

BACKGROUND/HYPOTHESIS

There is increasing awareness of interindividual variability in brain function, with potentially major implications for repetitive transcranial magnetic stimulation (rTMS) efficacy. We perform a secondary analysis using data from a double-blind randomized controlled 4-week trial of 20 Hz active versus sham rTMS to dorsolateral prefrontal cortex (DLPFC) during a working memory task in participants with schizophrenia. We hypothesized that rTMS would change local functional activity and variability in the active group compared with sham.

STUDY DESIGN

83 participants were randomized in the original trial, and offered neuroimaging pre- and post-treatment. Of those who successfully completed both scans (n = 57), rigorous quality control left n = 42 (active/sham: n = 19/23), who were included in this analysis. Working memory-evoked activity during an N-Back (3-Back vs 1-Back) task was contrasted. Changes in local brain activity were examined from an 8 mm ROI around the rTMS coordinates. Individual variability was examined as the mean correlational distance (MCD) in brain activity pattern from each participant to others within the same group.

RESULTS

We observed an increase in task-evoked left DLPFC activity in the active group compared with sham (F1,36 = 5.83, False Discovery Rate (FDR))-corrected P = .04). Although whole-brain activation patterns were similar in both groups, active rTMS reduced the MCD in activation pattern compared with sham (F1,36 = 32.57, P < .0001). Reduction in MCD was associated with improvements in attention performance (F1,16 = 14.82, P = .0014, uncorrected).

CONCLUSIONS

Active rTMS to DLPFC reduces individual variability of brain function in people with schizophrenia. Given that individual variability is typically higher in schizophrenia patients compared with controls, such reduction may "normalize" brain function during higher-order cognitive processing.

Decoding the neural impact of radical complexity in Chinese characters during working memory task

Readers of Chinese characters need to recognize how they are formed in order to identify them correctly. However, our understanding of the cognitive processing of characters in working memory is limited. In Experiment 1, using the character N-back task paradigm, electrophysiological data were recorded from 26 participants to investigate the effects of the visual feature of radicals on neural activity during the character recognition, updating and maintenance in the N-back task. Results showed that compound characters required longer response times than single-component characters. For the event-related potentials (ERPs), the compound character condition had more negative N2pc and lower P300 amplitudes than the single-component character condition. In Experiment 2, data from 26 participants were used to analyse the effect of the phonological feature of radicals on neural activity during the character recognition, updating and maintenance in the N-back task. Results showed that there was a larger P200 in the irregular character condition than in the regular character condition, but there was no difference between the regular and the irregular characters in the N2pc, P300 and slow wave (SW) components. The visual feature and the phonological feature of the radicals may have different effects on the character processing. This study reveals the neural effects of Chinese character radicals on cognitive processing in a working memory task and provides behavioural and electrophysiological evidence for a theoretical model of verbal working memory subprocesses.

A mechanism underlying improved dual-task performance after practice: Reviewing evidence for the memory hypothesis

Extensive practice can significantly reduce dual-task costs (i.e., impaired performance under dual-task conditions compared with single-task conditions) and, thus, improve dual-task performance. Among others, these practice effects are attributed to an optimization of executive function skills that are necessary for coordinating tasks that overlap in time. In detail, this optimization of dual-task coordination skills is associated with the efficient instantiation of component task information in working memory at the onset of a dual-task trial. In the present paper, we review empirical findings on three critical predictions of this memory hypothesis. These predictions concern (1) the preconditions for the acquisition and transfer of coordination skills due to practice, (2) the role of task complexity and difficulty, and (3) the impact of age-related decline in working memory capacity on dual-task optimization.

Timescales of learning in prefrontal cortex

The lateral prefrontal cortex (PFC) in humans and other primates is critical for immediate, goal-directed behaviour and working memory, which are classically considered distinct from the cognitive and neural circuits that support long-term learning and memory. Over the past few years, a reconsideration of this textbook perspective has emerged, in that different timescales of memory-guided behaviour are in constant interaction during the pursuit of immediate goals. Here, we will first detail how neural activity related to the shortest timescales of goal-directed behaviour (which requires maintenance of current states and goals in working memory) is sculpted by long-term knowledge and learning - that is, how the past informs present behaviour. Then, we will outline how learning across different timescales (from seconds to years) drives plasticity in the primate lateral PFC, from single neuron firing rates to mesoscale neuroimaging activity patterns. Finally, we will review how, over days and months of learning, dense local and long-range connectivity patterns in PFC facilitate longer-lasting changes in population activity by changing synaptic weights and recruiting additional neural resources to inform future behaviour. Our Review sheds light on how the machinery of plasticity in PFC circuits facilitates the integration of learned experiences across time to best guide adaptive behaviour.

Mechanisms of visual working memory processing task-irrelevant information retrieved from visual long-term memory

Visual working memory (VWM) can selectively filter task-irrelevant information from incoming visual stimuli. However, whether a similar filtering process applies to task-irrelevant information retrieved from visual long-term memory (VLTM) remains elusive. We assume a "resource-limited retrieval mechanism" in VWM in charge of the retrieval of irrelevant VLTM information. To make a comprehensive understanding of this mechanism, we conducted three experiments using both a VLTM learning task and a VWM task combined with pupillometry. The presence of a significant pupil light response (PLR) served as empirical evidence that VLTM information can indeed make its way into VWM. Notably, task-relevant VLTM information induced a sustained PLR, contrasting with the transient PLR observed for task-irrelevant VLTM information. Importantly, the transience of the PLR occurred under conditions of low VWM load, but this effect was absent under conditions of high load. Collectively, these results show that task-irrelevant VLTM information can enter VWM and then fade away only under conditions of low VWM load. This dynamic underscores the resource-limited retrieval mechanism within VWM, exerting control over the entry of VLTM information.

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).

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.

Modelling Working Memory Capacity: Is the Magical Number Four, Seven, or Does it Depend on What You Are Counting?

Limited attentional capacity is essential to working memory. How its limit should be assessed is a debated issue. Five experiments compare Cowan's 4-units and Pascual-Leone's 7-units models of limited working memory capacity, with presentation time and attention to operative schemes as potential explanations of this discrepancy. Experiments 1a-1c used the Compound Stimuli Visual Information (CSVI) task, with long versus brief presentation. Capacity was estimated with the Bose-Einstein model, assuming a different number of attending acts in each condition. Participants' k estimates in both conditions were highly correlated and the means were not different, indicating that the same capacity is assessed in both conditions. Experiments 2 and 3 used the 5000-msec CSVI, and the Visual Array Task (VAT) in two conditions (5000- vs. 120-msec presentation). Capacity in the VAT was estimated with Morey's Bayesian method. Participants' k estimates in both VAT conditions were correlated, but the mean was higher with long presentation, suggesting that the long condition benefits from recoding or chunking. The k estimate in the CSVI correlated with the short VAT and (to a lesser degree in Exp.2) with the long VAT. The mean estimate of k in the CSVI was one unit more than in the short VAT. We conclude that the CSVI and the short VAT tap the same capacity, one unit of which in the short VAT is allocated to an operative scheme; we discuss how Cowan's and Pascual-Leone's views on limited capacity can be reconciled.

Active maintenance in working memory reinforces bindings for future retrieval from episodic long-term memory

Many theories assume that actively maintaining information in working memory (WM) predicts its retention in episodic long-term memory (LTM), as revealed by the beneficial effects of more WM time. In four experiments, we examined whether affording more time for intentional WM maintenance does indeed drive LTM. Sequences of four words were presented during trials of simple span (short time), slow span (long time), and complex span (long time with distraction; Experiments 1-2). Long time intervals entailed a pause of equivalent duration between the words that presented a blank screen (slow span) or an arithmetic problem to read aloud and solve (complex span). In Experiments 1-3, participants either serially recalled the words (intentional encoding) or completed a no-recall task (incidental encoding). In Experiment 4, all participants were instructed to intentionally encode the words, with the trials randomly ending in the serial-recall or no-recall task. To ensure similar processing of the words between encoding groups, participants silently decided whether each word was a living or nonliving thing via key press (i.e., an animacy judgment; Experiments 1 and 3-4) or read the words aloud and then pressed the space bar (Experiment 2). A surprise delayed memory test at the end of the experiment assessed LTM. Applying Bayesian cognitive models to disambiguate binding and item memory revealed consistent benefits of free time to binding memory that were specific to intentional encoding in WM. This suggests that time spent intentionally keeping information in WM is special for LTM because WM is a system that maintains bindings.

Grouping in working memory guides chunk formation in long-term memory: Evidence from the Hebb effect

The Hebb effect refers to the improvement in immediate memory performance on a repeated list compared to unrepeated lists. That is, participants create a long-term memory representation over repetitions, on which they can draw in working memory tests. These long-term memory representations are likely formed by chunk acquisition: The whole list becomes integrated into a single unified representation. Previous research suggests that the formation of such chunks is rather inflexible and only occurs when at least the beginning of the list repeats across trials. However, recent work has shown that repetition learning strongly depends on participants recognizing the repeated information. Hence, successful chunk formation may depend on the recognizability of the repeated part of a list, and not on its position in the list. Across six experiments, we compared these two alternatives. We tested immediate serial recall of eight-letter lists, some of which partially repeated across trials. We used different partial-repetition structures, such as repeating only the first half of a list, or only every second item. We manipulated the salience of the repeating structure by spatially grouping and coloring the lists according to the repetition structure. We found that chunk formation is more flexible than previously assumed: Participants learned contiguous repeated sequences regardless of their position within the list, as long as they were able to recognize the repeated structure. Even when the repeated sequence occurred at varying positions over repetitions, learning was preserved when the repeated sequence was made salient by the spatial grouping. These findings suggest that chunk formation requires recognition of which items constitute a repeating group, and demonstrate a close link between grouping of information in working memory, and chunk formation in long-term memory.

Dynamic changes in task preparation in a multi-task environment: The task transformation paradigm

A key element of human flexible behavior concerns the ability to continuously predict and prepare for sudden changes in tasks or actions. Here, we tested whether people can dynamically modulate task preparation processes and decision-making strategies when the identity of a to-be-performed task becomes uncertain. To this end, we developed a new paradigm where participants need to prepare for one of nine tasks on each trial. Crucially, in some blocks, the task being prepared could suddenly shift to a different task after a longer cue-target interval, by changing either the stimulus category or categorization rule that defined the initial task. We found that participants were able to dynamically modulate task preparation in the face of this task uncertainty. A second experiment shows that these changes in behavior were not simply a function of decreasing task expectancy, but rather of increasing switch expectancy. Finally, in the third and fourth experiment, we demonstrate that these dynamic modulations can be applied in a compositional manner, depending on whether either only the stimulus category or categorization rule would be expected to change.

Same, Same but Different? A Multi-Method Review of the Processes Underlying Executive Control

Attention, working memory, and executive control are commonly considered distinct cognitive functions with important reciprocal interactions. Yet, longstanding evidence from lesion studies has demonstrated both overlap and dissociation in their behavioural expression and anatomical underpinnings, suggesting that a lower dimensional framework could be employed to further identify processes supporting goal-directed behaviour. Here, we describe the anatomical and functional correspondence between attention, working memory, and executive control by providing an overview of cognitive models, as well as recent data from lesion studies, invasive and non-invasive multimodal neuroimaging and brain stimulation. We emphasize the benefits of considering converging evidence from multiple methodologies centred on the identification of brain mechanisms supporting goal-driven behaviour. We propose that expanding on this approach should enable the construction of a comprehensive anatomo-functional framework with testable new hypotheses, and aid clinical neuroscience to intervene on impairments of executive functions.

When Load is Low, Working Memory is Shielded From Long-Term Memory's Influence

Previous studies found that episodic long-term memory (eLTM) enhances working memory (WM) performance when both novel and previously learnt word pairs must be retained on a short-term basis. However, there is uncertainty regarding how and when WM draws on eLTM. Three possibilities are (a) that people draw on eLTM only if WM capacity is exceeded; (b) that there is always a contribution of eLTM to WM performance, irrespective of whether prior knowledge is helpful or not; or (c) benefits of prior knowledge are specific to comparisons between conditions which are similarly ambiguous concerning whether LTM may be useful. We built on the assumption that under conditions of a contribution from LTM, these LTM traces of memoranda could benefit or hamper performance in WM tasks depending on the match between the traces stored in LTM and the ones to-be stored in WM in the current trial, yielding proactive facilitation (PF) and proactive interference (PI), respectively. Across four experiments, we familiarized participants with some items before they completed a separate WM task. In accordance with possibility (a) we show that there are indeed conditions in which only WM contributes to performance. Performance deteriorated with the addition of stimuli from eLTM when WM load was low, but not when it was high; and an exchange of information between LTM and WM occurred only when WM capacity was exceeded, with PI and PF effects affecting immediate memory performance in verbal and visual tasks only at higher set sizes.

Internal attention modulates the functional state of novel stimulus-response associations in working memory

Information in working memory (WM) is crucial for guiding behavior. However, not all WM representations are equally relevant simultaneously. Current theoretical frameworks propose a functional dissociation between 'latent' and 'active' states, in which relevant representations are prioritized into an optimal (active) state to face current demands, while relevant information that is not immediately needed is maintained in a dormant (latent) state. In this context, task demands can induce rapid and flexible prioritization of information from latent to active state. Critically, these functional states have been primarily studied using simple visual memories, with attention selecting and prioritizing relevant representations to serve as templates to guide subsequent behavior. It remains unclear whether more complex WM representations, such as novel stimulus-response associations, can also be prioritized into different functional states depending on their task relevance, and if so how these different formats relate to each other. In the present study, we investigated whether novel WM-guided actions can be brought into different functional states depending on current task demands. Our results reveal that planned actions can be flexibly prioritized when needed and show how their functional state modulates their influence on ongoing behavior. Moreover, they suggest the representations of novel actions of different functional states are maintained in WM via a non-orthogonal coding scheme, thus are prone to interference.

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.

The visual familiarity effect on attentional working memory maintenance

Attentional refreshing has been described as an attention-based, domain-general maintenance mechanism in working memory. It is thought to operate via focusing executive attention on information held in working memory, protecting it from temporal decay and interference. Although attentional refreshing has attracted a lot of research, its functioning is still debated. At least one conception of refreshing supposes that it relies on semantic long-term memory representations to reconstruct working memory traces. Although investigations in the verbal domain found evidence against this hypothesis, a different pattern could emerge in visuospatial working memory in which absence of refreshing evidence has been observed for stimuli with minimal associated long-term knowledge. In a series of four experiments, the current study investigated the hypothesis of an involvement of semantic long-term representations in the functioning of attentional refreshing in the visuospatial domain. Both cognitive and memory load effects have been proposed as indexes of attentional refreshing. Therefore, we investigated the interaction between the effects of visual familiarity (a long-term memory effect) and cognitive load on recall performance (Experiments 1A and 1B), as well as the interaction between the effects of visual familiarity and memory load on the response times in a concurrent processing task (Experiments 2A and 2B). Results were consistent across experiments and go against the hypothesis of the involvement of semantic long-term memory in the functioning of attentional refreshing in visuospatial working memory. As such, this study corroborates the results found in the verbal domain. Implications for attentional refreshing and working memory are discussed.

Self-prioritization in working memory gating

Working memory (WM) involves a dynamic interplay between temporary maintenance and updating of goal-relevant information. The balance between maintenance and updating is regulated by an input-gating mechanism that determines which information should enter WM (gate opening) and which should be kept out (gate closing). We investigated whether updating and gate opening/closing are differentially sensitive to the kind of information to be encoded and maintained in WM. Specifically, since the social salience of a stimulus is known to affect cognitive performance, we investigated if self-relevant information differentially impacts maintenance, updating, or gate opening/closing. Participants first learned to associate two neutral shapes with two social labels (i.e., "you" vs. "stranger"), respectively. Subsequently they performed the reference-back paradigm, a well-established WM task that disentangles WM updating, gate opening, and gate closing. Crucially, the shapes previously associated with the self or a stranger served as target stimuli in the reference-back task. We replicated the typical finding of a repetition benefit when consecutive trials require opening the gate to WM. In Study 1 (N = 45) this advantage disappeared when self-associated stimuli were recently gated into WM and immediately needed to be replaced by stranger-associated stimuli. However, this was not replicated in a larger sample (Study 2; N = 90), where a repetition benefit always occurred on consecutive gate-opening trials. Overall, our results do not provide evidence that the self-relevance of stimuli modulates component processes of WM. We discuss possible reasons for this null finding, including the importance of continuous reinstatement and task-relevance of the shape-label associations.

An item response theory approach to the measurement of working memory capacity

Complex span tasks are perhaps the most widely used paradigm to measure working memory capacity (WMC). Researchers assume that all types of complex span tasks assess domain-general WM. However, most research supporting this claim comes from factor analysis approaches that do not examine task performance at the item level, thus not allowing comparison of the characteristics of verbal and spatial complex span tasks. Item response theory (IRT) can help determine the extent to which different complex span tasks assess domain-general WM. In the current study, spatial and verbal complex span tasks were examined using IRT. The results revealed differences between verbal and spatial tasks in terms of item difficulty and block difficulty, and showed that most subjects with below-average ability were able to answer most items correctly across all tasks. In line with previous research, the findings suggest that examining domain-general WM by using only one task might elicit skewed scores based on task domain. Further, visuospatial complex span tasks should be prioritized as a measure of WMC if resources are limited.

Self-reported strategy use in working memory tasks

Mnemonic strategies can facilitate working memory performance, but our knowledge on strategy use as a function of task characteristics remains limited. We examined self-reported strategy use in several working memory tasks with pretest data from two large-scale online training experiments. A three-level measure of strategy sophistication (no strategy, maintenance, manipulation) was coded based on participants' open-ended strategy reports. A considerable portion of participants reported some memory strategy, and strategy sophistication was associated with objective task performance. We found a consistent effect of stimulus type: verbal stimuli (letters or digits) elicited higher strategy sophistication than nonverbal ones (colours or spatial positions). In contrast, the association between task paradigm and strategy sophistication was less consistent in the two experiments. The present results highlight the importance of self-generated strategies in understanding individual differences in working memory performance and the role of stimulus characteristics as one of the task-related determinants of strategy use.

Neural correlates of adaptive cognitive control in working memory

Conflicts in working memory (WM) can occur when retrieval cues activate competing items, which impairs the efficiency of retrieval. It has recently been shown that WM retrieval adapts similarly to these conflicts as predicted by conflict monitoring theory for selective attention tasks. Here, we utilized event-related potentials (ERPs) to investigate whether conflict and adaptive control in WM are reflected by the same neural markers that have previously been described for selective attention tasks. In our task, participants encoded two differently colored memory lists that contained four digits each (i.e., 2 5 7 1 and 4 5 9 1), and had to recognize whether a probe item from a specific list and position was correct or incorrect. Conflict during retrieval emerged when digits at corresponding positions (e.g., 2 and 5 at the first position) were different (incongruent), but not when these digits were the same (congruent). In behavioral data, we found a congruency sequence effect, that is, responses to incongruent probe items were slower, and this effect was reduced following trials with incongruent probe items. In ERPs, this behavioral marker of adaptive control was accompanied by two effects. First, congruency affected the amplitude of an N450, and this conflict effect was reduced after incongruent trials. Second, the posterior P3 amplitude varied with the congruency of the current and the previous trial. Both results resemble those found for the Stroop task and thus highlight the similarity between conflict and adaptive control in WM and selective attention tasks.

Life motion signals modulate visual working memory

Previous research has demonstrated that biological motion (BM) cues can induce a reflexive attentional orienting effect, a phenomenon referred to as social attention. However, it remains undetermined whether BM cues can further affect higher-order cognitive processes, such as visual working memory (WM). By combining a modified central pre-cueing paradigm with a traditional WM change detection task, the current study investigated whether the walking direction of BM, as a non-predictive central cue, could modulate the encoding process of WM. Results revealed a significant improvement in WM performance for the items appearing at the location cued by the walking direction of BM. The observed effect disappeared when the BM cues were shown inverted, or when the critical biological characteristics of the cues were removed. Crucially, this effect could be extended to upright feet motion cues without global configuration, reflecting the key role of local BM signals in modulating WM. More importantly, such a BM-induced modulation effect was not observed with inanimate motion cues, although these cues can also elicit attentional effects. Our findings suggest that the attentional effect induced by life motion signals can penetrate to higher-order cognitive processes, and provide compelling evidence for the existence of "life motion detector" in the human brain from a high-level cognitive function perspective.

The reactivation of task rules triggers the reactivation of task-relevant items

Working memory (WM) describes the temporary storage of task-relevant items and procedural rules to guide action. Despite its central importance for goal-directed behavior, the interplay between WM and long-term memory (LTM) remains poorly understood. Recent studies have shown that repeated use of the same task-relevant item in WM results in a hand-off of the storage of that item to LTM, and switching to a new item reactivates WM. To further elucidate the rules governing WM-LTM interactions, we here planned to probe whether a change in task rules, independent of a switch in task-relevant items, would also lead to WM reactivation of maintained items. To this end, we used scalp-recorded electroencephalogram (EEG) data, specifically the contralateral delay activity (CDA), to track WM item storage while manipulating repetitions and changes in task rules and task-relevant items across trials in a visual WM task. We tested two rival hypotheses: If changes in task rules result in a reactivation of the target item representation, then the CDA should increase when a task change is cued even when the same target has been repeated across trials. However, if the reactivation of a task-relevant item only depends on the mnemonic availability of the item itself instead of the task it is used for, then only the changes in task-relevant items should reactivate the representations. Accordingly, the CDA amplitude should decrease for repeated task-relevant items independently of a task change. We found a larger CDA on task-switch compared to task-repeat trials, suggesting that the reactivation of task rules triggers the reactivation of task-relevant items in WM. By demonstrating that WM reactivation of LTM is interdependent for task rules and task-relevant items, this study informs our understanding of visual WM and its interplay with LTM. PREREGISTERED STAGE 1 PROTOCOL: https://osf.io/zp9e8 (date of in-principle acceptance: 19/12/2021).

The Production Effect Becomes Spatial

In the verbal domain, it is well established that words read aloud are better remembered than their silently read counterparts. It has been hypothesized that this production effect stems from the addition of distinctive features, with the caveat that the processing that generates added features interferes with rehearsal. Here, we tested the idea that a similar trade-off is found in the visuospatial domain. In all experiments, a short series of single dots sequentially appeared at various locations on a screen. Participants produced the items by clicking on them at presentation, watched the items appear quietly, or produced an irrelevant click after each item to better even out rehearsal opportunities between produced and control conditions. In Experiment 1, the dots appeared within a visible grid and an order reconstruction task was used. Experiment 2 also called upon reconstruction, but with the grid removed. In Experiments 3, a recall task was used. The results show that producing items hindered performance compared to the control condition. Conversely, production improved performance compared to the control condition where rehearsal was hindered. This is the first demonstration of a visuospatial production effect. The key findings were successfully modeled by the Revised Feature Model (RFM).

Improving Cognitive Abilities in School-Age Children via Computerized Cognitive Training: Examining the Effect of Extended Training Duration

Critical neuropsychological capabilities such as working memory, cognitive flexibility, and processing speed are foundational to many daily activities. For children, such skills are essential for school success. Thus, children who demonstrate weaknesses in these abilities may experience impaired academic performance; this is especially true for students identified with learning differences who often exhibit less developed cognitive abilities. The purpose of this project was to examine the efficacy of a cognitive training program implemented during the school day to improve abilities predictive of academic achievement. Ninety-five children completed two training activities that were counterbalanced across participants. Analyses of baseline working memory, cognitive flexibility, and processing speed performance relative to those following training showed a strong treatment effect. Moreover, there is notable evidence of greater intervention efficacy with extended engagement with the training program. Implications for neuropsychological research and practice are discussed.

Cognition in Patients with Schizophrenia: Interplay between Working Memory, Disorganized Symptoms, Dissociation, and the Onset and Duration of Psychosis, as Well as Resistance to Treatment

Schizophrenia is traditionally associated with the presence of psychotic symptoms. In addition to these, cognitive symptoms precede them and are present during the entire course of the schizophrenia process. The present study aims to establish the relationship between working memory (short-term memory and attention), the features of the clinical picture, and the course of the schizophrenic process, gender distribution and resistance to treatment.

METHODS

In total, 105 patients with schizophrenia were observed. Of these, 66 were women and 39 men. Clinical status was assessed using the Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS), Dimensional Obsessive-Compulsive Symptom Scale (DOCS), scale for dissociative experiences (DES) and Hamilton Depression Rating Scale (HAM-D)-cognitive functions using the Luria 10-word test with fixation assessment, reproduction and attention analysis. The clinical evaluation of resistance to the treatment showed that 45 patients were resistant to the ongoing medical treatment and the remaining 60 had an effect from the therapy.

RESULTS

Our study showed that, in most patients, we found disorders of working memory and attention. In 69.82% of the patients, we found problems with fixation; in 38.1%, problems with reproduction; and in 62.86%, attention disorders. Conducting a regression analysis showed that memory and attention disorders were mainly related to the highly disorganized symptoms scale, the duration of the schizophrenic process and the dissociation scale. It was found that there was a weaker but significant association between the age of onset of schizophrenia and negative symptoms. In the patients with resistant schizophrenia, much greater violations of the studied parameters working memory and attention were found compared to the patients with an effect from the treatment.

CONCLUSION

Impairments in working memory and attention are severely affected in the majority of patients with schizophrenia. Their involvement is most significant in patients with resistance to therapy. Factors associated with the highest degree of memory and attention impairment were disorganized symptoms, duration of schizophrenia, dissociative symptoms and, to a lesser extent, onset of illness. This analysis gives us the right to consider that the early and systematic analysis of cognition is a reliable marker for tracking both clinical dynamics and the effect of treatment.

Time course of EEG complexity reflects attentional engagement during listening to speech in noise

Auditory distractions are recognized to considerably challenge the quality of information encoding during speech comprehension. This study explores electroencephalography (EEG) microstate dynamics in ecologically valid, noisy settings, aiming to uncover how these auditory distractions influence the process of information encoding during speech comprehension. We examined three listening scenarios: (1) speech perception with background noise (LA), (2) focused attention on the background noise (BA), and (3) intentional disregard of the background noise (BUA). Our findings showed that microstate complexity and unpredictability increased when attention was directed towards speech compared with tasks without speech (LA > BA & BUA). Notably, the time elapsed between the recurrence of microstates increased significantly in LA compared with both BA and BUA. This suggests that coping with background noise during speech comprehension demands more sustained cognitive effort. Additionally, a two-stage time course for both microstate complexity and alpha-to-theta power ratio was observed. Specifically, in the early epochs, a lower level was observed, which gradually increased and eventually reached a steady level in the later epochs. The findings suggest that the initial stage is primarily driven by sensory processes and information gathering, while the second stage involves higher level cognitive engagement, including mnemonic binding and memory encoding.

Principles of cognitive control over task focus and task switching

Adaptive behaviour requires the ability to focus on a task and protect it from distraction (cognitive stability) and to rapidly switch tasks when circumstances change (cognitive flexibility). Burgeoning research literatures have aimed to understand how people achieve task focus and task switch readiness. In this Perspective, I integrate these literatures to derive a cognitive architecture and functional rules underlying the regulation of cognitive stability and flexibility. I propose that task focus and task switch readiness are supported by independent mechanisms. However, I also suggest that the strategic regulation of both mechanisms is governed by shared learning principles: an incremental, online learner that nudges control up or down based on the recent history of task demands (a recency heuristic) and episodic reinstatement when the current context matches a past experience (a recognition heuristic). Finally, I discuss algorithmic and neural implementations of these processes, as well as clinical implications.

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.

Delayed memory for complex visual stimuli does not benefit from distraction during encoding

The covert retrieval model (McCabe, Journal of Memory and Language 58(2), 480-494, 2008) postulates that delayed memory performance is enhanced when the encoding of memoranda in working memory (WM) is interrupted by distraction. When subjects are asked to remember stimuli for an immediate memory test, they usually remember them better when the items are presented without distraction, compared to a condition in which a distraction occurs following each item. In a delayed memory test, this effect has been shown to be reversed: Memory performance is better for items followed by distraction than without. Yet, this so-called McCabe effect has not been consistently replicated in the past. In an extensive replication attempt of a previous study showing the effect for complex visual stimuli, we investigated five potential boundary conditions of the predictions of the covert retrieval model: (1) Type of Stimuli (doors vs. faces), (2) type of distractor (pictures vs. math equations), (3) expectation about task difficulty (mixed vs. blocked lists), (4) memory load in WM (small vs. large), and (5) expectation about the long-term memory (LTM) test (intentional vs. incidental encoding). Across four experiments we failed to replicate the original findings and show that delayed memory for faces and other complex visual stimuli does not benefit from covert retrieval during encoding - as suggested as being induced by distractors. Our results indicate that the transfer of information from WM to LTM does not seem to be influenced by covert retrieval processes, but rather that a fixed proportion of information is laid down as a more permanent trace.

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.

Target detection does not influence temporal memory

Target detection has been found to enhance memory for concurrently presented stimuli under dual-task conditions. This "attentional boost effect" is reminiscent of findings in the event memory literature, where conditions giving rise to event boundaries have been shown to enhance memory for boundary items. Target detection commonly requires a working memory update (e.g., adding to a covert mental target count), which is also thought to be a key contributor to creating event boundaries. However, whether target detection impacts temporal memory in similar ways as event boundaries remains unknown, because these two parallel literatures have used different types of memory tests, making direct comparisons difficult. In a preregistered experiment with sequential Bayes factor design, we examined whether target detection influences temporal binding between items by inserting target and nontarget stimuli during encoding of trial-unique object images, and then comparing subsequent temporal order and distance memory for image pairs that span a target or nontarget. We found that target detection enhanced recognition memory for target trial images but had no effect on temporal binding between items. In a follow-up experiment, we showed that when the encoding task required updating of task set rather than target count, event segmentation-related temporal memory effects were observed. These results document that target detection as such does not disrupt inter-item associations in memory, and that attention orienting in the absence of updating task sets does not create event boundaries. This suggests a key distinction between declarative and procedural working memory updates in segmenting events in memory.

Hanging on the telephone: Maintaining visuospatial bootstrapping over time in working memory

Visuospatial bootstrapping (VSB) refers to the phenomenon in which performance on a verbal working memory task can be enhanced by presenting the verbal material within a familiar visuospatial configuration. This effect is part of a broader literature concerning how working memory is influenced by use of multimodal codes and contributions from long-term memory. The present study aimed to establish whether the VSB effect extends over a brief (5-s) delay period, and to explore the possible mechanisms operating during retention. The VSB effect, as indicated by a verbal recall advantage for digit sequences presented within a familiar visuospatial configuration (modelled on the T-9 keypad) relative to a single-location display, was observed across four experiments. The presence and size of this effect changed with the type of concurrent task activity applied during the delay. Articulatory suppression (Experiment 1) increased the visuospatial display advantage, while spatial tapping (Experiment 2) and a visuospatial judgment task (Experiment 3) both removed it. Finally, manipulation of the attentional demands placed by a verbal task also reduced (but did not abolish) this effect (Experiment 4). This pattern of findings demonstrates how provision of familiar visuospatial information at encoding can continue to support verbal working memory over time, with varying demands on modality-specific and general processing resources.

Are irrelevant items actively deleted from visual working memory?: No evidence from repulsion and attraction effects in dual-retrocue tasks

Some theories propose that working memory (WM) involves the active deletion of irrelevant information, including items that were retained in WM, but are no longer relevant for ongoing cognition. Considerable evidence suggests that active-deletion occurs for categorical representations, but whether it also occurs for recall of features that are typically bound together in an object, such as line orientations, is unclear. In two experiments, with or without binding instructions, healthy young adults maintained two orientations, focused attention to recall the orientation cued first, and then switched attention to recall the orientation cued second, at which point the uncued orientation was no longer relevant on the trial. In contrast to the active-deletion hypothesis, the results showed that the no-longer-relevant items exerted the strongest bias on participants' recall, which was either repulsive or attractive depending on both the degree of difference between the target and nontarget orientations and the proximity to cardinal axes. We suggest that visual WM can bind features like line orientations into chunked representations, and an irrelevant feature of a chunked object cannot be actively deleted - it biases recall of the target feature. Models of WM need to be updated to explain this and related dynamic phenomena.

Metacognition in working memory: Confidence judgments during an n-back task

Metacognition in working memory (WM) has received less attention than episodic memory, and few studies have investigated confidence judgements while carrying out a verbal WM task. The present study investigated whether individuals are aware of their own level of performance while carrying out an ongoing verbal WM task, and whether judgments of confidence are sensitive to factors that determine WM performance. A verbal n-back task was adapted to obtain confidence judgments on a trial-by-trial basis. Memory load and lure interference were manipulated. Results showed that metacognition judgments were affected by memory load and levels of interference just as performance accuracy. Even when judgments were sensitive to memory factors, participants were overconfident and generally showed poor metacognitive accuracy at discriminating between erroneous and accurate responses. Results are discussed in terms of possible cues contributing to metacognitive judgements during an ongoing WM task and reasons for WM metacognitive accuracy.

Repetition learning is neither a continuous nor an implicit process

Learning advances through repetition. A classic paradigm for studying this process is the Hebb repetition effect: Immediate serial recall performance improves for lists presented repeatedly as compared to nonrepeated lists. Learning in the Hebb paradigm has been described as a slow but continuous accumulation of long-term memory traces over repetitions [e.g., Page & Norris, Phil. Trans. R. Soc. B 364, 3737-3753 (2009)]. Furthermore, it has been argued that Hebb repetition learning requires no awareness of the repetition, thereby being an instance of implicit learning [e.g., Guérard et al., Mem. Cogn. 39, 1012-1022 (2011); McKelvie,  J. Gen. Psychol. 114, 75-88 (1987)]. While these assumptions match the data from a group-level perspective, another picture emerges when analyzing data on the individual level. We used a Bayesian hierarchical mixture modeling approach to describe individual learning curves. In two preregistered experiments, using a visual and a verbal Hebb repetition task, we demonstrate that 1) individual learning curves show an abrupt onset followed by rapid growth, with a variable time for the onset of learning across individuals, and that 2) learning onset was preceded by, or coincided with, participants becoming aware of the repetition. These results imply that repetition learning is not implicit and that the appearance of a slow and gradual accumulation of knowledge is an artifact of averaging over individual learning curves.

Verbal working memory encodes phonological and semantic information differently

Working memory (WM) is often tested through immediate serial recall of word lists. Performance in such tasks is negatively influenced by phonological similarity: People more often get the order of words wrong when they are phonologically similar to each other (e.g., cat, fat, mat). This phonological-similarity effect shows that phonology plays an important role for the representation of serial order in these tasks. By contrast, semantic similarity usually does not impact performance negatively. To resolve and understand this discrepancy, we tested the effects of phonological and semantic similarity for the retention of positional information in WM. Across six experiments (all Ns = 60 young adults), we manipulated between-item semantic and phonological similarity in tasks requiring participants to form and maintain new item-context bindings in WM. Participants were asked to retrieve items from their context, or the contexts from their item. For both retrieval directions, phonological similarity impaired WM for item-context bindings across all experiments. Semantic similarity did not. These results demonstrate that WM encodes phonological and semantic information differently. We propose a WM model accounting for semantic-similarity effects in WM, in which semantic knowledge supports WM through activated long-term memory.

Neuropsychological Functions and Audiological Findings in Elderly Cochlear Implant Users: The Role of Attention in Postoperative Performance

Objectives: The present study aimed to investigate in a group of elderly CI users working memory and attention, conventionally considered as predictors of better CI performance and to try to disentangle the effects of these cognitive domains on speech perception, finding potential markers of cognitive decline related to audiometric findings. Methods Thirty postlingually deafened CI users aged >60 underwent an audiological evaluation followed by a cognitive assessment of attention and verbal working memory. A correlation analysis was performed to evaluate the associations between cognitive variables while a simple regression investigated the relationships between cognitive and audiological variables. Comparative analysis was performed to compare variables on the basis of subjects’ attention performance. Results: Attention was found to play a significant role in sound field and speech perception. Univariate analysis found a significant difference between poor and high attention performers, while regression analysis showed that attention significantly predicted recognition of words presented at Signal/Noise +10. Further, the high attention performers showed significantly higher scores than low attentional performers for all working memory tasks. Conclusion: Overall findings confirmed that a better cognitive performance may positively contribute to better speech perception outcomes, especially in complex listening situations. WM may play a crucial role in storage and processing of auditory-verbal stimuli and a robust attention may lead to better performance for speech perception in noise. Implementation of cognitive training in auditory rehabilitation of CI users should be investigated in order to improve cognitive and audiological performance in elderly CI users.

Repetition enhances the effects of activated long-term memory

Recent research indicates that visual long-term memory (vLTM) representations directly interface with perception and guide attention. This may be accomplished through a state known as activated LTM, however, little is known about the nature of activated LTM. Is it possible to enhance the attentional effects of these activated representations? And furthermore, is activated LTM discrete (i.e., a representation is either active or not active, but only active representations interact with perception) or continuous (i.e., there are different levels within the active state that all interact with perception)? To answer these questions, in the present study, we measured intrusion effects during a modified Sternberg task. Participants saw two lists of three complex visual objects, were cued that only one list was relevant for the current trial (the other list was, thus, irrelevant), and then their memory for the cued list was probed. Critically, half of the trials contained repeat objects (shown 10 times each), and half of the trials contained non-repeat objects (shown only once each). Results indicated that repetition enhanced activated LTM, as the intrusion effect (i.e., longer reaction times to irrelevant list objects than novel objects) was larger for repeat trials compared with non-repeat trials. These initial findings provide preliminary support that LTM activation is continuous, as the intrusion effect was not the same size for repeat and non-repeat trials. We conclude that researchers should repeat stimuli to increase the size of their effects and enhance how LTM representations interact with perception.

Attentional switching between perception and memory: Examining asymmetrical switch costs

Attention can be defined as a mechanism for the selection and prioritization of elements among many. When attention is directed to a specific piece of information, this information is assumed to be in the focus of attention. On a day-to-day basis, we need to rely on efficient switching between information we are holding in working memory (internal modality) and information presented in the world around us (external modality). A recent set of studies investigated between-modality attentional switches and found that there is an asymmetrical switch cost for switching between the internal and external focus of attention (Verschooren et al., 2020, Journal of Experimental Psychology: Human Perception and Performance, 46[9], 912-925; Verschooren, Liefooghe, et al., 2019a, Journal of Experimental Psychology: Human Perception and Performance, 45[10], 1399-1414). In particular, participants switched on a trial-by-trial basis between an internal task using stimuli retrieved from memory and an external task using on-screen presented stimuli. A larger cost was found when switching from the external modality towards the internal modality than the other way around. The authors found that this cost asymmetry could be best explained in terms of associative interference (i.e., differences in shielding efficiency against the memory traces from the competing task set). The present study aimed to replicate the asymmetrical switch cost (Experiment 1) and investigate whether an alternative explanation in terms of stimulus strength can account for the asymmetrical switch cost (Experiment 2). Overall, the results confirm the presence of a subtle, asymmetrical switch cost, but we observed little to no contribution of stimulus strength.

The relationship between working memory updating components and reading comprehension

The objective of this study was to determine the contribution of retrieval and substitution components of working memory updating to reading comprehension. Difficulties in reading comprehension have been related to the inability to update information in working memory. Updating is a complex process comprising various subprocesses, such as retrieving information into the focus of attention and substituting information that is no longer relevant. Various numerical subtasks requiring or not requiring the substitution and retrieval components of working memory updating, as well as reading comprehension and general cognitive measures, were administered to a sample (n = 148) of 4th grade children. Less-skilled comprehenders showed lower accuracy when information retrieval was required. In contrast, substitution was not related to reading comprehension. These findings suggest that reading comprehension difficulties are related to the efficacy of information retrieval during updating in working memory.

The contribution of episodic long-term memory to working memory for bindings

The present experiments support two conclusions about the capacity limit of working memory (WM). First, they provide evidence for the Binding Hypothesis, WM capacity is limited by interference between bindings but not items. Second, they show that episodic LTM contributes substantially to binding memory when the capacity of WM is stretched to the limit by larger set sizes. We tested immediate memory for sets of word-picture pairs. With increasing set size, memory for bindings declined more precipitously than memory for items, as predicted from the binding hypothesis. Yet, at higher set sizes performance was more stable than expected from a capacity limited memory, suggesting a contribution of episodic long-term memory (LTM) to circumvent the WM capacity limit. In support of that hypothesis, we show a double dissociation of contributions of WM and episodic LTM to binding memory: Performance at set sizes larger than 3 was specifically affected by proactive interference - but were immune to influences from a distractor-filled delay. In contrast, performance at set size 2 was unaffected by proactive interference but harmed by a distractor-filled delay.

Identifying and Localizing Multiple Objects Using Artificial Ventral and Dorsal Cortical Visual Pathways

In our previous study (Han & Sereno, 2022a), we found that two artificial cortical visual pathways trained for either identity or space actively retain information about both identity and space independently and differently. We also found that this independently and differently retained information about identity and space in two separate pathways may be necessary to accurately and optimally recognize and localize objects. One limitation of our previous study was that there was only one object in each visual image, whereas in reality, there may be multiple objects in a scene. In this study, we find we are able to generalize our findings to object recognition and localization tasks where multiple objects are present in each visual image. We constrain the binding problem by training the identity network pathway to report the identities of objects in a given order according to the relative spatial relationships between the objects, given that most visual cortical areas including high-level ventral steam areas retain spatial information. Under these conditions, we find that the artificial neural networks with two pathways for identity and space have better performance in multiple-objects recognition and localization tasks (higher average testing accuracy, lower testing accuracy variance, less training time) than the artificial neural networks with a single pathway. We also find that the required number of training samples and the required training time increase quickly, and potentially exponentially, when the number of objects in each image increases, and we suggest that binding information from multiple objects simultaneously within any network (cortical area) induces conflict or competition and may be part of the reason why our brain has limited attentional and visual working memory capacities.

Attention as a multi-level system of weights and balances

This opinion piece is part of a collection on the topic: "What is attention?" Despite the word's place in the common vernacular, a satisfying definition for "attention" remains elusive. Part of the challenge is there exist many different types of attention, which may or may not share common mechanisms. Here we review this literature and offer an intuitive definition that draws from aspects of prior theories and models of attention but is broad enough to recognize the various types of attention and modalities it acts upon: attention as a multi-level system of weights and balances. While the specific mechanism(s) governing the weighting/balancing may vary across levels, the fundamental role of attention is to dynamically weigh and balance all signals-both externally-generated and internally-generated-such that the highest weighted signals are selected and enhanced. Top-down, bottom-up, and experience-driven factors dynamically impact this balancing, and competition occurs both within and across multiple levels of processing. This idea of a multi-level system of weights and balances is intended to incorporate both external and internal attention and capture their myriad of constantly interacting processes. We review key findings and open questions related to external attention guidance, internal attention and working memory, and broader attentional control (e.g., ongoing competition between external stimuli and internal thoughts) within the framework of this analogy. We also speculate about the implications of failures of attention in terms of weights and balances, ranging from momentary one-off errors to clinical disorders, as well as attentional development and degradation across the lifespan. This article is categorized under: Psychology > Attention Neuroscience > Cognition.

Working memory asymmetrically modulates auditory and linguistic processing of speech

Working memory load can modulate speech perception. However, since speech perception and working memory are both complex functions, it remains elusive how each component of the working memory system interacts with each speech processing stage. To investigate this issue, we concurrently measure how the working memory load modulates neural activity tracking three levels of linguistic units, i.e., syllables, phrases, and sentences, using a multiscale frequency-tagging approach. Participants engage in a sentence comprehension task and the working memory load is manipulated by asking them to memorize either auditory verbal sequences or visual patterns. It is found that verbal and visual working memory load modulate speech processing in similar manners: Higher working memory load attenuates neural activity tracking of phrases and sentences but enhances neural activity tracking of syllables. Since verbal and visual WM load similarly influence the neural responses to speech, such influences may derive from the domain-general component of WM system. More importantly, working memory load asymmetrically modulates lower-level auditory encoding and higher-level linguistic processing of speech, possibly reflecting reallocation of attention induced by mnemonic load.

Sensory Delay Activity: More than an Electrophysiological Index of Working Memory Load

Sustained contralateral delay activity emerges in the retention period of working memory (WM) tasks and has been commonly interpreted as an electrophysiological index of the number of items held in a discrete-capacity WM resource. More recent findings indicate that these visual and tactile components are sensitive to various cognitive operations beyond the storage of discrete items in WM. In this Perspective, we present recent evidence from unisensory and multisensory visual and tactile WM tasks suggesting that, in addition to memory load, sensory delay activity may also be indicative of attentional and executive processes, as well as reflecting the flexible, rather than discrete, allocation of a continuous WM resource. Together, these findings challenge the traditional model of the functional significance of the contralateral delay activity as a pure measure of item load, and suggest that it may also reflect executive, attentional, and perceptual mechanisms operating in hierarchically organized WM systems.

Long-term learning transforms prefrontal cortex representations during working memory

The role of the lateral prefrontal cortex (lPFC) in working memory (WM) is debated. Non-human primate (NHP) electrophysiology shows that the lPFC stores WM representations, but human neuroimaging suggests that the lPFC controls WM content in sensory cortices. These accounts are confounded by differences in task training and stimulus exposure. We tested whether long-term training alters lPFC function by densely sampling WM activity using functional MRI. Over 3 months, participants trained on both a WM and serial reaction time (SRT) task, wherein fractal stimuli were embedded within sequences. WM performance improved for trained (but not novel) fractals and, neurally, delay activity increased in distributed lPFC voxels across learning. Item-level WM representations became detectable within lPFC patterns, and lPFC activity reflected sequence relationships from the SRT task. These findings demonstrate that human lPFC develops stimulus-selective responses with learning, and WM representations are shaped by long-term experience, which could reconcile competing accounts of WM functioning.

Working memory capacity estimates moderate value learning for outcome-irrelevant features

To establish accurate action-outcome associations in the environment, individuals must refrain from assigning value to outcome-irrelevant features. However, studies have largely ignored the role of attentional control processes on action value updating. In the current study, we examined the extent to which working memory-a system that can filter and block the processing of irrelevant information in one's mind-also filters outcome-irrelevant information during value-based learning. For this aim, 174 individuals completed a well-established working memory capacity measurement and a reinforcement learning task designed to estimate outcome-irrelevant learning. We replicated previous studies showing a group-level tendency to assign value to tasks' response keys, despite clear instructions and practice suggesting they are irrelevant to the prediction of monetary outcomes. Importantly, individuals with higher working memory capacity were less likely to assign value to the outcome-irrelevant response keys, thus suggesting a significant moderation effect of working memory capacity on outcome-irrelevant learning. We discuss the role of working memory processing on value-based learning through the lens of a cognitive control failure.

The role of conjunctive representations in prioritizing and selecting planned actions

For flexible goal-directed behavior, prioritizing and selecting a specific action among multiple candidates are often important. Working memory has long been assumed to play a role in prioritization and planning, while bridging cross-temporal contingencies during action selection. However, studies of working memory have mostly focused on memory for single components of an action plan, such as a rule or a stimulus, rather than management of all of these elements during planning. Therefore, it is not known how post-encoding prioritization and selection operate on the entire profile of representations for prospective actions. Here, we assessed how such control processes unfold over action representations, highlighting the role of conjunctive representations that nonlinearly integrate task-relevant features during maintenance and prioritization of action plans. For each trial, participants prepared two independent rule-based actions simultaneously, then they were retro-cued to select one as their response. Prior to the start of the trial, one rule-based action was randomly assigned to be high priority by cueing that it was more likely to be tested. We found that both full action plans were maintained as conjunctive representations during action preparation, regardless of priority. However, during output selection, the conjunctive representation of the high-priority action plan was more enhanced and readily selected as an output. Furthermore, the strength of the high-priority conjunctive representation was associated with behavioral interference when the low-priority action was tested. Thus, multiple alternate upcoming actions were maintained as integrated representations and served as the target of post-encoding attentional selection mechanisms to prioritize and select an action from within working memory.