Contents Of Working Memory Research Articles

Electrophysiological evidence supports the role of sustained visuospatial attention in maintaining visual WM contents

Recent empirical and theoretical work suggests that there is a close relationship between visual working memory (WM) and visuospatial attention. Here, we investigated whether visuospatial attention was involved in maintaining object representations in visual WM. To this end, the alpha lateralization and contralateral delay activity (CDA) were analyzed as neural markers for visuospatial attention and visual WM storage, respectively. In the single-task condition, participants performed a grating change-detection task. To probe the role of visuospatial attention in maintaining WM contents, two color squares were presented above and below the fixation point during the retention interval, which remained visible until the detection display was present. In the dual-task condition, participants were required to maintain lateralized gratings while staring at the center-presented color squares, to detect possible subsequent color change. With this task, sustained visuospatial attention that guided to individual memory representations was disrupted. The behavioral data showed that, the insertion of secondary task significantly deteriorated WM performance. For electrophysiological data, we divided the retention interval into two stages, the early stage and late stage, bounded by the onset of the secondary task. We found that CDA amplitude was lower under the dual-task condition than the single-task condition during the late stage, but not the early stage, and the extent to which CDA reduced tracked the impaired memory performance at the individual level. Also, alpha lateralization only could be observed in the single-task condition of the late stage, and completely disappeared in the dual-task condition, indicating the disruption of visuospatial attention directed to memory representations. Individuals who experienced greater visuospatial attention disruption, as indicated by the alpha lateralization, had lower maintenance-associated neural activity (CDA), and suffered greater impairment of memory performance. These findings confirm that sustained visuospatial attention continues improving visual WM processing after the initial encoding phase, and most likely participates in this process by supporting the maintenance of representations in an active state.

The contents of visual working memory delay the perceived offset of matching visual stimuli

Previous research suggests that the perception of stimulus onset can be accelerated by a match between the contents of visual working memory and the stimulus presented alone in the peripheral visual field. This onset acceleration effect might contribute to previously reported effects of working memory on perceived stimulus duration. However, it remains possible that the contents of visual working memory may also modulate the offset perception of matching visual stimuli, thereby contributing to the modulation of duration perception by working memory. The present study directly tested this possibility by using a simple reaction time task to assess the effect of visual working memory on perceived stimulus offset. Participants were asked to maintain a sample stimulus in working memory and subsequently had to respond to the offset of a single visual target. Across three experiments, we showed that the offset response was reliably slower when the target matched the sample held in visual working memory, as compared with when the target did not. This effect was not likely attributed to the mechanism of repetition priming from the presentation of the sample, because we failed to observe a priming effect either when the sample was only passively viewed without working memory demands or when the sample was initially encoded into memory but did not need to be actively maintained in mind by the time the offset target appeared. The findings provide direct evidence indicating that active maintenance of information in visual working memory delays the perceived offset of matching visual stimuli.

The content of visual working memory regulates the priority to access visual awareness, including bound memoranda with multiple features

The content of visual working memory regulates the priority to access visual awareness, including bound memoranda with multiple features

Tracking the content of spatial working memory during a bout of acute aerobic exercise.

Tracking the content of spatial working memory during a bout of acute aerobic exercise.

Working Memory and Attention - A Conceptual Analysis and Review.

There is broad agreement that working memory is closely related to attention. This article delineates several theoretical options for conceptualizing this link, and evaluates their viability in light of their theoretical implications and the empirical support they received. A first divide exists between the concept of attention as a limited resource, and the concept of attention as selective information processing. Theories conceptualizing attention as a resource assume that this resource is responsible for the limited capacity of working memory. Three versions of this idea have been proposed: Attention as a resource for storage and processing, a shared resource for perceptual attention and memory maintenance, and a resource for the control of attention. The first of these three is empirically well supported, but the other two are not. By contrast, when attention is understood as a selection mechanism, it is usually not invoked to explain the capacity limit of working memory – rather, researchers ask how different forms of attention interact with working memory, in two areas. The first pertains to attentional selection of the contents of working memory, controlled by mechanisms of filtering out irrelevant stimuli, and removing no-longer relevant representations from working memory. Within working memory contents, a single item is often selected into the focus of attention for processing. The second area pertains to the role of working memory in cognitive control. Working memory contributes to controlling perceptual attention – by holding templates for targets of perceptual selection – and controlling action – by holding task sets to implement our current goals.

Chimpanzees flexibly update working memory contents and show susceptibility to distraction in the self-ordered search task.

Working memory (WM) is a core executive function that allows individuals to hold, process and manipulate information. WM capacity has been repeatedly nominated as a key factor in human cognitive evolution; nevertheless, little is known about the WM abilities of our closest primate relatives. In this study, we examined signatures of WM ability in chimpanzees (Pan troglodytes). Standard WM tasks for humans (Homo sapiens) often require participants to continuously update their WM. In Experiment 1, we implemented this updating requirement in a foraging situation: zoo-housed chimpanzees (n = 13) searched for food in an array of containers. To avoid redundant searches, they needed to continuously update which containers they had already visited (similar to WM paradigms for human children) with 15 s retention intervals in between each choice. We examined chimpanzees' WM capacity and to what extent they used spatial cues and object features to memorize their previous choices. In Experiment 2, we investigated how susceptible their WM was to attentional interference, an important signature, setting WM in humans apart from long-term memory. We found large individual differences with some individuals remembering at least their last four choices. Chimpanzees used a combination of spatial cues and object features to remember which boxes they had chosen already. Moreover, their performance decreased specifically when competing memory information was introduced. Finally, we found that individual differences in task performance were highly reliable over time. Together, these findings show remarkable similarities between human and chimpanzee WM abilities despite evolutionary and life-history differences.

Selection of Visual Objects in Perception and Working Memory One at a Time

How does the content of visual working memory influence the way we process the visual environment? We addressed this question using the steady-state visual evoked potential (SSVEP), which provides a discernible measure of visuocortical activation to multiple stimuli simultaneously. Fifty-six adults were asked to remember a set of two oriented gratings. During the retention interval, two frequency-tagged oriented gratings were presented to probe the visuocortical processing of matching versus mismatching orientations relative to the memory set. Matching probes prompted an increased visuocortical response, whereas mismatching stimuli were suppressed. This suggests that the visual cortex prioritizes attentional selection of memory-relevant features at the expense of non-memory-relevant features. When two memory items were probed simultaneously, visuocortical amplification alternated between the two stimuli at a rate of 3 Hz to 4 Hz, consistent with the rate of attentional sampling of sensory events from the external world. These results suggest a serial, single-item attentional sampling of remembered features.

Can you have multiple attentional templates? Large-scale replications of Van Moorselaar, Theeuwes, and Olivers (2014) and Hollingworth and Beck (2016)

Stimuli that resemble the content of visual working memory (VWM) capture attention. However, theories disagree on how many VWM items can bias attention simultaneously. According to some theories, there is a distinction between active and passive states in VWM, such that only items held in an active state can bias attention. The single-item-template hypothesis holds that only one item can be in an active state and thus can bias attention. In contrast, the multiple-item-template hypothesis posits that multiple VWM items can be in an activate state simultaneously, and thus can bias attention. Recently, Van Moorselaar, Theeuwes, and Olivers (Journal of Experimental Psychology: Human Perception and Performance, 40(4):1450, 2014) and Hollingworth and Beck (Journal of Experimental Psychology: Human Perception and Performance, 42(7):911–917, 2016) tested these accounts, but obtained seemingly contradictory results. Van Moorselaar et al. (2014) found that a distractor in a visual-search task captured attention more when it matched the content of VWM (memory-driven capture). Crucially, memory-driven capture disappeared when more than one item was held in VWM, in line with the single-item-template hypothesis. In contrast, Hollingworth and Beck (2016) found memory-driven capture even when multiple items were kept in VWM, in line with the multiple-item-template hypothesis. Considering these mixed results, we replicated both studies with a larger sample, and found that all key results are reliable. It is unclear to what extent these divergent results are due to paradigm differences between the studies. We conclude that is crucial to our understanding of VWM to determine the boundary conditions under which memory-driven capture occurs.

Does spatial attention modulate sensory memory?

According to some theoretical models, information contained in visual short-term memory (VSTM) consists of two main memory stages/storages: sensory memory, a system wherein information is stored for a brief time with high detail and low resistance to visual interference, and visual working memory, a low-capacity system wherein information is protected from visual interference and maintained for longer delays. Previous studies have consistently shown a strong relationship between attention and visual working memory. However, evidence is contradictory on whether or not attention modulates the construction and maintenance of visual representations in sensory memory. Here, we examined whether and how spatial attention differentially affects sensory and working memory contents, by separately analysing attentional costs and attentional benefits. Results showed that both sensory memory and visual working memory were reliably affected by the distribution of spatial attention, suggesting that spatial attention modulates the VSTM content starting from very early stages of memory storage. Moreover, endogenously attending a specific location led to similar performance in sensory and working memory, and therefore to larger attentional benefits in working memory (where there was more room for improvement than in sensory memory, because of worse performance in unattended locations). On the other hand, exogenous attentional capture by peripheral unpredictive cues produced invariant attentional costs and invariant attentional benefits regardless of the memory type, with performance being higher in sensory memory than in working memory even at the attended location.

How robust and rapid can the memory-driven attentional capture be?

Previous research has indicated that visual attention can be automatically captured by sensory inputs that match the contents of visual working memory. Furthermore, the information in visual working memory can be used as a template of memory guidance for either the selection or rejection of visual attention. The current study investigated the memory-driven attentional processes in four experiments which extend and complement previous research. Participants performed a visual search task while maintaining items in visual working memory. Experiment 1 used an arrow as a pre-cue indicating which side of the screen the search target would appear on. Experiment 2 used two circles as pre-cues for the right-up/down location of the search target. Experiment 3 presented a memory-matching distractor for 300 ms followed by a blank screen. Experiment 4 presented a memory-matching distractor for 150 ms followed by the visual search task. All experiments resulted in significantly slower visual search reaction times (RTs) for the invalid condition (memory-matching distractor) compared to the neutral condition but with no significant differences in memory performance. This result suggests that the contents of working memory affect the deployment of attention in visual search. Our findings show that attentional capture occurs even within short periods of 150 ms, which demonstrates the robustness and speed of memory-driven attentional processes. Consequently, attentional capture appears to be initiated at an early phase of visual processing but can be strategically inhibited through cognitive control at later stages of analysis.

Assessing the Role of the Left Dorsal Frontal Cortex in Working Memory Guidance: Attentional or Mnemonic? A Neurostimulation Study

Perceptual selection can be guided by the contents of working memory (WM). Neuroimaging and neuropsychological data point to a role of a fronto-parietal and fronto-thalamic networks in WM guidance. Here we assessed the effect of transcranial direct current stimulation of the left dorsal frontal cortex (lDFC) in a combined WM/attention paradigm. We asked the extent to which the lDFC is implicated in mnemonic and selective attention functions during WM guidance of behavior. Observers were asked to keep information in memory while searching for a visual target, while the validity of WM contents for the search task varied. We tested the effects of lDFC-tDCS on the strength of WM guidance of search, whether any tDCS effect is dependent on the amount of WM load, and whether lDFC-tDCS primarily influences how WM contents are retained, the process of selective attention in search task, or both. Consistent with prior behavioral findings, we found that (i) selection of items that matched the contents of WM was facilitated relative to non-matching items and (ii) this WM guidance effect was reduced when the level processing/cognitive load in WM was higher. Notably, across two experiments we found that lDFC-tDCS modulated WM guidance of visual selection in the context of high processing loads in WM. No effects of tDCS were observed in WM accuracy. These findings suggest that the role of the left dorsal frontal cortex in WM guidance is associated with selective attentional control rather than mnemonic processing.

Neural Dynamics of Cognitive Control over Working Memory Capture of Attention.

The contents of working memory (WM) guide visual attention toward matching features, with visual search being faster when the target and a feature of an item held in WM spatially overlap (validly cued) than when they occur at different locations (invalidly cued). Recent behavioral studies have indicated that attentional capture by WM content can be modulated by cognitive control: When WM cues are reliably helpful to visual search (predictably valid), capture is enhanced, but when reliably detrimental (predictably invalid), capture is attenuated. The neural mechanisms underlying this effect are not well understood, however. Here, we leveraged the high temporal resolution of ERPs time-locked to the onset of the search display to determine how and at what processing stage cognitive control modulates the search process. We manipulated predictability by grouping trials into unpredictable (50% valid/invalid) and predictable (100% valid, 100% invalid) blocks. Behavioral results confirmed that predictability modulated WM-related capture. Comparison of ERPs to the search arrays showed that the N2pc, a posteriorly distributed signature of initial attentional orienting toward a lateralized target, was not impacted by target validity predictability. However, a longer latency, more anterior, lateralized effect-here, termed the "contralateral attention-related negativity"-was reduced under predictable conditions. This reduction interacted with validity, with substantially greater reduction for invalid than valid trials. These data suggest cognitive control over attentional capture by WM content does not affect the initial attentional-orienting process but can reduce the need to marshal later control mechanisms for processing relevant items in the visual world.

An age-related deficit in preserving the benefits of attention in working memory.

Deficits in the use of attention to refresh representations are argued to underlie age-related decline in working memory (WM). Retro-cues guide attention to WM contents, enabling the direct assessment of refreshing in WM. This preregistered study investigated aging deficits in refreshing via retro-cues and the preservation of refreshing boosts after distraction incurred by a secondary task. The distractor task is assumed to impede refreshing by engaging attention away from the memoranda. Any free time available before or after distractor processing, however, can be used to resume refreshing thereby ameliorating distractor-related interference. Accordingly, by varying the time available to complete the distractor task, one can vary refreshing opportunities, an effect known as cognitive load. Using an individually calibrated task that controlled for WM capacity and speed of processing, we demonstrate that focusing attention on WM representations is similarly efficient in younger and older adults. However, younger adults were able to retain this retro-cue benefit despite increasing cognitive load, whereas increasing cognitive load reduced the retro-cue benefit in older adults, suggesting that they are less able to protect focused representations from distractor-interference. This shows that aging impacts specific subcomponents of refreshing, such that the benefit of focusing attention is relatively intact in older age, but older adults struggle to preserve the refreshing benefit against distraction. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The impact of cue format and cue transparency on task switching performance.

Cues help in retrieving and implementing task-sets, that are actual representations of the to-be performed task in working memory. However, whereas previous studies revealed that the effectiveness of selecting and implementing task-sets based on cues depends on the type of cue (i.e., transparent words vs. arbitrary shapes), it is still unclear which characteristics of cues are responsible for these differences and whether the impact of the cue is bound to task-set retrieval only or also impacts task-set representations. For instance, the amount of interference during actual task performance has been reported to alter dependent on cue type as do preparation gains such as the reduction of switch cost. To investigate the effectiveness of cue characteristics (i.e., cue transparency and cue format), we manipulated those within- and between-participants in three experiments. Main dependent measures were switch costs in reaction times and error rates that occur when participants have to switch task-sets, and thus update working memory content. Our results consistently show beneficial effects of transparent cues for the reduction of switch cost. The influence of cue format was manifest in within-participants manipulation only and was mainly found in error rates. Overall, our data suggest that the amount of interference experienced in actual task performance can be significantly modulated dependent on cue type, suggesting flexible adaptation of the cognitive system to contextual information.

Prefrontal Contributions to Attention and Working Memory.

The processes of attention and working memory are conspicuously interlinked, suggesting that they may involve overlapping neural mechanisms. Working memory (WM) is the ability to maintain information in the absence of sensory input. Attention is the process by which a specific target is selected for further processing, and neural resources directed toward that target. The content of WM can be used to direct attention, and attention can in turn determine which information is encoded into WM. Here we discuss the similarities between attention and WM and the role prefrontal cortex (PFC) plays in each. First, at the theoretical level, we describe how attention and WM can both rely on models based on attractor states. Then we review the evidence for an overlap between the areas involved in both functions, especially the frontal eye field (FEF) portion of the prefrontal cortex. We also discuss similarities between the neural changes in visual areas observed during attention and WM. At the cellular level, we review the literature on the role of prefrontal DA in both attention and WM at the behavioral and neural levels. Finally, we summarize the anatomical evidence for an overlap between prefrontal mechanisms involved in attention and WM. Altogether, a summary of pharmacological, electrophysiological, behavioral, and anatomical evidence for a contribution of the FEF part of prefrontal cortex to attention and WM is provided.

Dopamine guides competition for cognitive control: Common effects of haloperidol on working memory and response conflict

Several lines of evidence suggest that dopamine modulates working memory (the ability to faithfully maintain and efficiently manipulate information over time) but its specific role has not been fully defined. Nor is it clear whether any effects of dopamine are specific to memory processes or whether they reflect more general cognitive mechanisms that extend beyond the working memory domain. Here, we examine the effect of haloperidol, principally a dopamine D2 receptor antagonist, on the ability of humans to ignore distracting information or update working memory contents. We compare these effects to performance on an independent measure of cognitive control (response conflict) which has minimal memory requirements. Haloperidol did not selectively affect the ability to ignore or update, but instead reduced the overall quality of recall. In addition, it impaired the ability to overcome response conflict. The deleterious effect of haloperidol on response conflict was selectively associated with the negative effect of the drug on ignoring – but not updating – suggesting that dopamine affects protection of working memory contents and inhibition in response conflict through a common mechanism. These findings provide new insights into the role of dopamine D2 receptors on human cognition. They suggest that D2 receptor effects on protecting the memory contents from distraction might be related to a more general process that supports inhibitory control in contexts that do not require working memory.

Frequency of prospective use modulates instructed task-set interference.

Recent studies have demonstrated that keeping an instructed task set in working memory (WM) for prospective use can interfere with behavior on an intervening task that employs shared stimuli-the prospective task-set-interference effect. One open question is whether people have strategic control over prospective task-set interference based on their expectations of whether task instructions will have to be implemented or recalled. To answer this question, we conducted two experiments that varied the likelihood with which a set of prospective task instructions would have to be implemented or recalled. Based on the hypothesis that participants are able to strategically modulate the manner in which a prospective task set is encoded in WM, we predicted that, as the frequency of implementing task instructions increased, so too would the magnitude of the prospective task-set-interference effect. We found that task instructions held in WM caused significant task-set interference, even in mostly recall conditions, but-crucially-that this interference effect scaled positively with the likelihood of having to implement the prospective set. These data suggest that task instructions are obligatorily encoded as a procedural task set, but that the degree to which this set impinges on ongoing stimulus processing is subject to some strategic control, possibly via modulation of the associations between declarative and procedural WM contents. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Hemispheric asymmetries in EEG alpha oscillations indicate active inhibition during attentional orienting within working memory

Working memory contents can be prioritized by retroactively deploying attention within memory. This is broadly interpreted as evidence of a concentration of memory resources to the attended, to-be-remembered stimulus. However, online attentional selection is known to additionally depend on distractor inhibition, raising the viable alternative that attentional deployment in working memory involves inhibitory control processes. Here, we demonstrate that active inhibition plays a central role in the deployment of attention in working memory. We do so using a retroactive cueing paradigm, where a briefly presented memory array is followed by a cue indicating a to-be-remembered target (Experiment 1) or a to-be-forgotten distractor (Experiment 2). We identify discrete indices of target selection and distractor inhibition in lateralized oscillatory activity over visual areas. When a retroactive cue identifies the location of a target, results show rapid decrease of lateral, target-elicited alpha band activity, representing attentional orienting toward the target. This is followed only later by emergence of an increase in distractor-elicited alpha activity, reflecting distractor inhibition. In contrast, when the retroactive cue identifies a distractor, evidence of distractor inhibition emerges first, only later followed by target selection. These results thus demonstrate that separate excitatory and inhibitory processes underlie the deployment of attention on the level of working memory representations.

Oculomotor capture reveals trial-by-trial neural correlates of attentional guidance by contents of visual working memory

Evidence from attentional and oculomotor capture, contingent capture, and other paradigms suggests that mechanisms supporting human visual working memory (VWM) and visual attention are intertwined. Features held in VWM bias guidance toward matching items even when those features are task irrelevant. However, the neural basis of this interaction is underspecified. Prior examinations using fMRI have primarily relied on coarse comparisons across experimental conditions that produce varying amounts of capture. To examine the neural dynamics of attentional capture on a trial-by-trial basis, we applied an oculomotor paradigm that produced discrete measures of capture. On each trial, subjects were shown a memory item, followed by a blank retention interval, then a saccade target that appeared to the left or right. On some trials, an irrelevant distractor appeared above or below fixation. Once the saccade target was fixated, subjects completed a forced-choice memory test. Critically, either the target or distractor could match the feature held in VWM. Although task irrelevant, this manipulation produced differences in behavior: participants were more likely to saccade first to an irrelevant VWM-matching distractor compared with a non-matching distractor – providing a discrete measure of capture. We replicated this finding while recording eye movements and scanning participants' brains using fMRI. To examine the neural basis of oculomotor capture, we separately modeled the retention interval for capture and non-capture trials within the distractor-match condition. We found that frontal activity, including anterior cingulate cortex and superior frontal gyrus regions, differentially predicted subsequent oculomotor capture by a memory-matching distractor. Other regions previously implicated as involved in attentional capture by VWM-matching items showed no differential activity across capture and non-capture trials, even at a liberal threshold. Our findings demonstrate the power of trial-by-trial analyses of oculomotor capture as a means to examine the underlying relationship between VWM and attentional guidance systems.

Reduced oculomotor capture by working memory contents under two- vs. one-item memory load suggests one item at a time is held in an active state

Reduced oculomotor capture by working memory contents under two- vs. one-item memory load suggests one item at a time is held in an active state