The Neural Correlates of Updating and Gating in Procedural Working Memory.

Goal-directed behavior relies on maintaining relevant goals in working memory (WM) and updating them when required. Computational modeling, behavioral, and neuroimaging work has previously identified the processes and brain regions involved in selecting, updating, and maintaining declarative information, such as letters and pictures. However, the neural substrates that underlie the analogous processes that operate on procedural information, namely, task goals, are currently unknown. Forty-three participants were therefore scanned with fMRI while performing a procedural version of the reference-back paradigm that allowed for the decomposition of WM updating processes into gate-opening, gate-closing, task switching, and task cue conflict components. Significant behavioral costs were observed for each of these components, with interactions indicating facilitation between gate-opening and task switching, and a modulation of cue conflict by gate state. In neural terms, opening the gate to procedural WM was associated with activity in medial pFC, posterior parietal cortex (PPC), the basal ganglia (BG), thalamus, and midbrain, but only when the task set needed to be updated. Closing the gate to procedural WM was associated with frontoparietal and BG activity specifically in conditions where conflicting task cues had to be ignored. Task switching was associated with activity in the medial pFC/ACC, PPC, and BG, whereas cue conflict was associated with PPC and BG activity during gate closing but was abolished when the gate was already closed. These results are discussed in relation to declarative WM and to gating models of WM.

The BTPI: An online battery for measuring susceptibility to visual illusions.

Visual illusions provide a powerful tool for probing the mechanisms that underlie perception. While most previous studies of visual illusions focused on average group-level performance, less attention has been devoted to individual differences in susceptibility to illusions. Unlike in other perceptual domains, in which there are established, validated tools to measure individual differences, such tools are not yet available in the domain of visual illusions. Here, we describe the development and validation of the BTPI (Ben-Gurion University Test for Perceptual Illusions), a new online battery designed to measure susceptibility to the influence of three prominent size illusions: the Ebbinghaus, the Ponzo, and the height-width illusions. The BTPI also measures perceptual resolution, reflected by the just noticeable difference (JND), to detect size differences in the context of each illusion. In Experiment 1 (N = 143), we examined performance in typical self-paced tasks, whereas in Experiment 2 (N = 69), we employed a fixed presentation duration paradigm. High test-retest reliability scores were found for all illusions, with little evidence for intercorrelations between different illusions. In addition, lower perceptual resolution (larger JND) was associated with a larger susceptibility to the illusory effect. The computerized task battery and analysis codes are freely available online.

Neural Substrates of Working Memory Updating.

Working memory (WM) needs to protect current content from interference and simultaneously be amenable to rapid updating with newly relevant information. An influential model suggests these opposing requirements are met via a BG-thalamus gating mechanism that allows for selective updating of PFC WM representations. A large neuroimaging literature supports the general involvement of PFC, BG, and thalamus, as well as posterior parietal cortex, in WM. However, the specific functional contributions of these regions to key subprocesses of WM updating, namely, gate opening, content substitution, and gate closing, are still unknown, as common WM tasks conflate these processes. We therefore combined fMRI with the reference-back task, specifically designed to tease apart these subprocesses. Participants compared externally presented face stimuli to a reference face held in WM, while alternating between updating and maintaining this reference, resulting in opening versus closing the gate to WM. Gate opening and substitution processes were associated with strong BG, thalamic, and frontoparietal activation, but intriguingly, the same activity profile was observed for sensory cortex supporting task stimulus processing (i.e., the fusiform face area). In contrast, gate closing was not reliably associated with any of these regions. These findings provide new support for the involvement of the BG in gate opening, as suggested by the gating model, but qualify the model's assumptions by demonstrating that gate closing does not seem to depend on the BG and that gate opening also involves task-relevant sensory cortex.

Who wrote that? Automaticity and reduced sense of agency in individuals prone to dissociative absorption.

Dissociative absorption (DA) is a tendency to become completely immersed in a stimulus while neglecting to attend to one's surroundings. Theoretically, DA implies automatic functioning in areas that are outside the focus of attention. This study examined whether high absorbers indeed act more automatically, i.e., with decreased meta-consciousness for, and therefore poor memory of, their own actions, along with reduced sense of agency (SoA). High and low absorbers (N = 63) performed three DA-promoting tasks: choice-reaction time (CRT), Tetris, and free writing. Participants were tested on memory of task details and self-reported their state SoA. As hypothesized, trait DA was correlated with impaired autobiographical memory for self-generated writing. However, DA was not related to episodic memory disruptions in externally-generated content tasks (Tetris, CRT). In most tasks, DA was associated with decreased SoA. Absorbers' specific difficulty in identifying self-generated content suggests that their memory failures stem from reduced accessibility to self-actions and intentions.

Oscillatory Correlates of Control over Working Memory Gating and Updating: An EEG Study Using the Reference-back Paradigm.

Optimal working memory (WM) functioning depends on a control mechanism that balances between maintenance and updating by closing or opening the gate to WM, respectively. Here, we examined the neural oscillation correlates of WM updating and of the control processes involved in gating. The reference-back paradigm was employed to manipulate gate opening, gate closing, and updating independently and examine how the control functions involved in these processes are mapped to oscillatory EEG activity. The results established that different oscillatory patterns were associated with the control process related to gate opening than in gate closing. During the time of gate closing, a relative increase in theta power was observed over midfrontal electrodes. This theta response is a known EEG signature of cognitive control that is proposed here to reflect reactive conflict resolution, achieved by closing the gate when facing irrelevant information. On the other hand, proactive gate opening in preparation for relevant information was associated with an increase in relative delta power over parietal-occipital electrodes. Finally, WM updating was associated with relative increase in delta power over midfrontal electrodes, suggesting a functional role of delta oscillations in WM updating.

Flow sensor based on the snap-through detection of a curved micromechanical beam.

We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecro-thermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST ). Using single crystal silicon beams, we demonstrate the snap-through voltage to flow velocity sensitivity of dV ST/du ≈ 0.13 V s m -1 with a power consumption of ≈ 360 µ W. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.

A two-level hierarchical framework of visual short-term memory.

Over the last couple of decades, a vast amount of research has been dedicated to understanding the nature and the architecture of visual short-term memory (VSTM), the mechanism by which currently relevant visual information is maintained. According to discrete-capacity models, VSTM is constrained by a limited number of discrete representations held simultaneously. In contrast, shared-resource models regard VSTM as limited in resources, which can be distributed flexibly between varying numbers of representations; and a new interference model posits that capacity is limited by interference among items. In this article, we begin by reviewing benchmark findings regarding the debate over VSTM limitations, focusing on whether VSTM storage is all-or-none and on whether object complexity affects capacity. After that, we put forward a hybrid framework of VSTM architecture, arguing that this system is composed of a two-level hierarchy of memory stores, each containing a different set of representations: (1) perceptual memory, a resourcelike level containing analog automatically formed representations of visual stimuli in varying degrees of activation, and (2) visual working memory, in which a subset of three to four items from perceptual memory are bound to conceptual representations and to their locations, thus conveying discrete (digital/symbolic) information which appears quantized. While perceptual memory has a large capacity and is relatively nonselective, visual working memory is restricted in the number of items that can be maintained simultaneously, and its content is regulated by a gating mechanism.

Working memory updating occurs independently of the need to maintain task-context: accounting for triggering updating in the AX-CPT paradigm.

Theoretical models suggest that maintenance and updating are two functional states of working memory (WM), which are controlled by a gate between perceptual information and WM representations. Opening the gate enables updating WM with input, while closing it enables keeping the maintained information shielded from interference. However, it is still unclear when gate opening takes place, and what is the external signal that triggers it. A version of the AX-CPT paradigm was used to examine a recent proposal in the literature, suggesting that updating is triggered whenever the maintenance of the context is necessary for task performance (context-dependent tasks). In four experiments using this paradigm, we show that (1) a task-switching cost takes place in both context-dependent and context-independent trials; (2) task-switching is additive to the dependency effect, and (3) unlike switching cost, the dependency effect is not affected by preparation and, therefore, does not reflect context-updating. We suggest that WM updating is likely to be triggered by a simple mechanism that occurs in each trial of the task regardless of whether maintaining the context is needed or not. The implications for WM updating and its relationship to task-switching are discussed.

Reflexive activation of newly instructed stimulus-response rules: evidence from lateralized readiness potentials in no-go trials.

Previous behavioral and electrophysiological evidence has suggested that the instructions for a new choice task are processed even when they are not currently required, indicating intention-based reflexivity. Yet these demonstrations were found in experiments in which participants were set to execute a response (go). In the present experiment, we asked whether intention-based reflexivity would also be observed under unfavorable conditions in which participants were set not to respond (no-go). In each miniblock of our paradigm, participants received instructions for a task in which two new stimuli were mapped to right/left keys. Immediately after the instructions, a no-go phase began, which was immediately followed by a go phase. We found a significant stimulus-locked lateralized readiness potential in the first no-go trial, indicating reflexive operation of the new instructions. These results show that representing instructions in working memory provides sufficient conditions for stimuli to launch task processing, proceeding all the way until motor response-specific brain activation, which takes place even under unfavorable, no-go conditions.

Updating visual working memory in the change detection paradigm.

An updating version of a visual change detection paradigm was used to investigate the behavioral outcomes and event-related potential (ERP) correlates of visual working memory updating. In each trial, participants were either presented with a memory array followed by a test probe, or with two successive memory arrays. Participants were instructed to update their working memory with the information in the second array. The second array differed from the first one in all, some, or none of the items. When a subset of the items was updated, the probe could appear in the location of a repeated item or of an updated item. Two experiments are reported, using set-sizes of six and two items, respectively. Both experiments show a benefit for probing a repeated item compared to an updated item. This result is consistent with an item-specific updating process. Experiment 2 also revealed two distinct updating-related ERP components, observed in both contralateral and ipsilateral visual hemifields. Frontal electrodes were sensitive to the number of changed items in the array. This ERP component was interpreted as reflecting the modification of information in working memory. Lateral-posterior electrodes only showed a difference between a full repetition of the array and updating, regardless of the number of updated items. This component was interpreted as reflecting attention to task-relevant information rather than the updating process per se. The finding of item-specific updating supports discrete-item architecture models of working memory.

The voluntary utilization of visual working memory.

While a vast amount of research has focused on understanding the capacity limits of visual working memory (VWM), little is known about how VWM resources are employed in unforced behavior and how they correlate with individual capacity constraints. We present a novel, openly available, and easy-to-administer paradigm enabling participants to freely utilize their VWM capacity. Participants had to reconstruct an array of colored squares. In each trial, they were allowed to alternate between the memory array and the reconstruction screen as many times as they wished, each time choosing how many items to reconstruct. This approach allowed us to estimate the number of utilized items, as well as the accuracy of the reconstruction. In addition, VWM capacity was measured using a change detection task. In two experiments, we show that participants tend to under-utilize their VWM resources, performing well below their capacity limits. Surprisingly, while the extent to which participants utilized their VWM was highly reliable, it was uncorrelated with VWM capacity, suggesting that VWM utilization is limited due to strategic considerations rather than capacity limits.

Age-related changes in the susceptibility to visual illusions of size.

As the global population ages, understanding of the effect of aging on visual perception is of growing importance. This study investigates age-related changes in adulthood along size perception through the lens of three visual illusions: the Ponzo, Ebbinghaus, and Height-width illusions. Utilizing the Bayesian conceptualization of the aging brain, which posits increased reliance on prior knowledge with age, we explored potential differences in the susceptibility to visual illusions across different age groups in adults (ages 20-85 years). To this end, we used the BTPI (Ben-Gurion University Test for Perceptual Illusions), an online validated battery of visual illusions developed in our lab. The findings revealed distinct patterns of age-related changes for each of the illusions, challenging the idea of a generalized increase in reliance on prior knowledge with age. Specifically, we observed a systematic reduction in susceptibility to the Ebbinghaus illusion with age, while susceptibility to the Height-width illusion increased with age. As for the Ponzo illusion, there were no significant changes with age. These results underscore the complexity of age-related changes in visual perception and converge with previous findings to support the idea that different visual illusions of size are mediated by distinct perceptual mechanisms.

Strategic processing in long-term repetition priming in the lexical decision task.

In a lexical decision task, faster reaction times (RTs) for old than new items is taken as evidence for an implicit memory involvement in this task. In contrast, the present study shows the involvement of both implicit and explicit memory in repetition priming. We propose a dual route model, in which lexical decisions can be made using one of two parallel processing routes: a lexical route, in which the lexical properties of the stimulus are used to determine whether it is a word or not, and a strategic route that builds on the inherent correlation between "wordness" and "oldness" in the experiment. Eliminating the strategic route by removing this correlation diminishes the priming effect at the slow end of the RT distribution, but not at the fast end. This dissociation is interpreted as evidence for the involvement of both implicit and explicit memory in repetition priming.

Task cues are quickly updated into working memory as part of their processing: The multiple-cue task-switching paradigm.

Goal-directed behavior requires maintaining the relevant goal in working memory (WM) and using it to guide behavior. The contents of WM should be regulated, so only relevant goals, but not irrelevant ones, are maintained. Computational models suggest that a gate, which is closed by default, separates WM from perceptual input. Transient opening of the gate enables WM updating. Indeed, previous studies show that updating WM with relevant information is controlled, effortful, and slow. In contrast to the above, here we show that WM updating with goal information is faster and more accurate than not updating. A multiple-cue task-switching paradigm is introduced. Participants were presented with a sequence of task cues, followed by a single probe. They needed to respond to each cue using its corresponding key. The cues were presented in red or blue. When the probe appeared, participants had to judge it using the task cued by the most recent red (but not blue) cue. Accordingly, they had to update their WM when the cue appeared in red, but not when it was blue (the color mapping was counterbalanced in Experiment 2). In two experiments, we show that performance in update trials was faster and more accurate than in no-update trials, suggesting that updating, rather than not-updating, is the default mode of operation.

Updating, Fast and Slow: Items, but Not Item-Context Bindings, are Quickly Updated Into Working Memory as Part of Response Selection.

It is commonly held that attending to items facilitates their encoding into working memory (WM). This implies that the content of WM is updated with new input as a consequence of directing attention to it. On the other hand, abundant research shows that WM updating is rather slow and effortful, suggesting that shielding WM representation against incoming input, rather than its updating, is the default. To resolve this discrepancy, we suggest that while updating item-to-context associations is costly, updating a single item is fast and is automatically carried out as part of directing attention to items, for example as part of response selection. Participants performed a choice-RT task, in which stimuli appeared within frames, and needed to update their WM with the most recent red item that appeared in each frame. The need for updating was manipulated, so that some trials required updating and others did not. Experiment 1 (N = 25) showed that updating was slower than not updating with a set-size of two items, that required item-context binding, but faster when the set-size only involved one item. Experiment 2 (N = 28) replicated this finding. Experiment 3 (N = 20) showed that the slower no-update RTs are due to the removal of erroneously updated information. In contrast to previous findings, these results suggest that updating can be effortless and obligatory.

Computational mechanisms underlying latent value updating of unchosen actions.

Current studies suggest that individuals estimate the value of their choices based on observed feedback. Here, we ask whether individuals also update the value of their unchosen actions, even when the associated feedback remains unknown. One hundred seventy-eight individuals completed a multi-armed bandit task, making choices to gain rewards. We found robust evidence suggesting latent value updating of unchosen actions based on the chosen action's outcome. Computational modeling results suggested that this effect is mainly explained by a value updating mechanism whereby individuals integrate the outcome history for choosing an option with that of rejecting the alternative. Properties of the deliberation (i.e., duration/difficulty) did not moderate the latent value updating of unchosen actions, suggesting that memory traces generated during deliberation might take a smaller role in this specific phenomenon than previously thought. We discuss the mechanisms facilitating credit assignment to unchosen actions and their implications for human decision-making.

"They don't Know Better than I do": People Prefer Seeing for Themselves Over Using the Wisdom of Crowds in Perceptual Decision Making.

Establishing the way people decide to use or avoid information when making a decision is of great theoretical and applied interest. In particular, the "big data revolution" enables decision-makers to harness the wisdom of crowds (WoC) toward reaching better decisions. The WoC is a well-documented phenomenon that highlights the potential superiority of collective wisdom over that of an individual. However, individuals may fail to utilize the power of collective wisdom as a means for optimizing decision outcomes. Using a random dot motion task, the present study examined situations in which decision-makers must choose between relying on their personal information or relying on the WoC in their decision. Although the latter was always the reward-maximizing choice, a substantial part of the participants chose to rely on their own observation and also advised others to do so. This choice tendency was associated with higher confidence, but not with better task performance, and hence reflects overconfidence. Acknowledging and understanding this decision bias may help mitigating it in applied settings.

Evidence for a single mechanism gating perceptual and long-term memory information into working memory.

An influential view of working memory (WM) holds that its contents are controlled by a selective gating mechanism that allows for relevant perceptual information to enter WM when opened, but shields WM contents from interference when closed. In support of this idea, prior studies using the reference-back paradigm have established behavioral costs for opening and closing the gate between perception and WM. WM also frequently requires input from long-term memory (LTM), but it is currently unknown whether a similar gate controls the selection of LTM representations into WM, and how WM gating of perceptual vs. LTM sources of information relate to each other. To address these key theoretical questions, we devised a novel version of the reference-back paradigm, where participants switched between gating perceptual and LTM information into WM. We observed clear evidence for gate opening and closing costs in both cases. Moreover, the pattern of costs associated with gating and input source-switching indicated that perceptual and LTM information is gated into WM via a single gate, and rely on a shared source-selection mechanism. These findings extend current models of WM gating to encompass LTM information, and outline a new functional WM architecture.

Results of an early second PCR test performed on SARS-CoV-2 positive patients may support risk assessment for severe COVID-19.

Identifying patients at increased risk for severe COVID-19 is of high priority during the pandemic as it could affect clinical management and shape public health guidelines. In this study we assessed whether a second PCR test conducted 2-7 days after a SARS-CoV-2 positive test could identify patients at risk for severe illness. Analysis of a nationwide electronic health records data of 1683 SARS-CoV-2 positive individuals indicated that a second negative PCR test result was associated with lower risk for severe illness compared to a positive result. This association was seen across different age groups and clinical settings. More importantly, it was not limited to recovering patients but also observed in patients who still had evidence of COVID-19 as determined by a subsequent positive PCR test. Our study suggests that an early second PCR test may be used as a supportive risk-assessment tool to improve disease management and patient care.

The reaction-time task-rule congruency effect is not affected by working memory load: further support for the activated long-term memory hypothesis.

Previous studies claimed that task representation is carried out by the activated long-term memory portion of working memory (WM; Meiran and Kessler in J Exp Psychol Human Percept Perform 34:137-157, 2008). The present study provides a more direct support for this hypothesis. We used the reaction-time task-rule congruency effect (RT-TRCE) in a task-switching setup, and tested the effects of loading WM with irrelevant task rules on RT-TRCE. Experiment 1 manipulated WM load in a between-subject design. WM participants performed a color/shape task switching, while having 0, 1 or 3 numerical task rules as WM load. Experiment 2 used a similar load manipulation (1 or 3 rules to load WM) in a within-subject design. Experiment 3 extended these results by loading WM with perceptual tasks that were more similar to the shape/color tasks. The results show that RT-TRCE was not affected by WM load supporting the activated long-term memory hypothesis.