Visual Working Memory Storage Research Articles

Electroencephalogram Decoding Reveals Distinct Processes for Directing Spatial Attention and Encoding Into Working Memory

Past work reveals a tight relationship between spatial attention and storage in visual working memory. But is spatially attending an item tantamount to working memory encoding? Here, we tracked electroencephalography (EEG) signatures of spatial attention and working memory encoding while independently manipulating the number of memory items and the spatial extent of attention in two studies of adults (N = 39; N = 33). Neural measures of spatial attention tracked the position and size of the attended area independent of the number of individuated items encoded into working memory. At the same time, multivariate decoding of the number of items stored in working memory was insensitive to variations in the breadth and position of spatial attention. Finally, representational similarity analyses provided converging evidence for a pure load signal that is insensitive to the spatial extent of the stored items. Thus, although spatial attention is a persistent partner of visual working memory, it is functionally dissociable from the selection and maintenance of individuated representations in working memory.

A negative emotional state impairs individuals' ability to filter distractors from working memory: an ERP study.

Capacity-limited visual working memory (VWM) requires that individuals have sufficient memory space and the ability to filter distractors. Negative emotional states are known to impact VWM storage, yet their influence on distractor filtering within VWM remains underexplored. We conducted direct neural measurement of participants (n = 56) who conducted a lateralized change detection task with distractors, while manipulating the emotional state by presenting neutral or negative images before each trial. We found a detrimental effect of distractors on memory accuracy under both neutral and negative emotional states. Usingtheevent-related potential (ERP) component, contralateral delay activity (CDA; sensitive to VWM load), to observe the VWM load in each condition, we found that in the neutral state, the participants showed significantly higher late CDA amplitudes when remembering 4 targets compared with 2 targets and 2 targets with 2 distractors but no significant difference when remembering 2 targets compared with 2 targets with 2 distractors. In the negative state, no significant CDA amplitude differences were evident when remembering 4 targets and 2 targets, but CDA was significantly higher when remembering 2 targets with 2 distractors compared with 2 targets. These results suggest that the maximum number of items participants could store in VWM was lower under negative emotional states than under neutral emotional states. Importantly, the participants could filter out distractors when in a neutral emotional state but not in a negative emotional state, indicating that negative emotional states impair their ability to filter out distractors in VWM.

Object-based encoding constrains storage in visual working memory.

The fundamental unit of visual working memory (WM) has been debated for decades. WM could be object-based, such that capacity is set by the number of individuated objects, or feature-based, such that capacity is determined by the total number of feature values stored. The present work examined whether object- or feature-based models would best explain how multifeature objects (i.e., color/orientation or color/shape) are encoded into visual WM. If maximum capacity is limited by the number of individuated objects, then above-chance performance should be restricted to the same number of items as in a single-feature condition. By contrast, if the capacity is determined by independent storage resources for distinct features-without respect to the objects that contain those features-then successful storage of feature values could be distributed across a larger number of objects than when only a single feature is relevant. We conducted four experiments using a whole-report task in which subjects reported both features from every item in a six-item array. The crucial finding was that above-chance recall-for both single- and multifeatured objects-was restricted to the first three or four responses, while the later responses were best modeled as guesses. Thus, whole-report with multifeature objects reveals a distribution of recalled features that indicates an object-based limit on WM capacity. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Tracing the emergence of the memorability benefit

Some visual stimuli are consistently better remembered than others across individuals, due to variations in memorability (the stimulus-intrinsic property that determines ease of encoding into visual long-term memory (VLTM)). However, it remains unclear what cognitive processes give rise to this mnemonic benefit. One possibility is that this benefit is imbued within the capacity-limited bottleneck of VLTM encoding, namely visual working memory (VWM). More precisely, memorable stimuli may be preferentially encoded into VLTM because fewer cognitive resources are required to store them in VWM (efficiency hypothesis). Alternatively, memorable stimuli may be more competitive in obtaining cognitive resources than forgettable stimuli, leading to more successful storage in VWM (competitiveness hypothesis). Additionally, the memorability benefit might emerge post-VWM, specifically, if memorable stimuli are less prone to be forgotten (i.e., are “stickier”) than forgettable stimuli after they pass through the encoding bottleneck (stickiness hypothesis). To test this, we conducted two experiments to examine how memorability benefits emerge by manipulating the stimulus memorability, set size, and degree of competition among stimuli as participants encoded them in the context of a working memory task. Subsequently, their memory for the encoded stimuli was tested in a VLTM task. In the VWM task, performance was better for memorable stimuli compared to forgettable stimuli, supporting the efficiency hypothesis. In addition, we found that when in direct competition, memorable stimuli were also better at attracting limited VWM resources than forgettable stimuli, supporting the competitiveness hypothesis. However, only the efficiency advantage translated to a performance benefit in VLTM. Lastly, we found that memorable stimuli were less likely to be forgotten after they passed through the encoding bottleneck imposed by VWM, supporting the “stickiness” hypothesis. Thus, our results demonstrate that the memorability benefit develops across multiple cognitive processes.

Visual-cortical enhancement by acoustic distractors: The effects of endogenous spatial attention and visual working memory load

Past work has shown that when a peripheral sound captures our attention, it activates the contralateral visual cortex as revealed by an event-related potential component labelled the auditory-evoked contralateral occipital positivity (ACOP). This cross-modal activation of the visual cortex has been observed even when the sounds were not relevant to the ongoing task (visual or auditory), suggesting that peripheral sounds automatically activate the visual cortex. However, it is unclear whether top-down factors such as visual working memory (VWM) load and endogenous attention, which modulate the impact of task-irrelevant information, may modulate this spatially-specific component. Here, we asked participants to perform a lateralized VWM task (change detection), whose performance is supported by both endogenous spatial attention and VWM storage. A peripheral sound that was unrelated to the ongoing task was delivered during the retention interval. The amplitude of sound-elicited ACOP was analyzed as a function of the spatial correspondence with the cued hemifield, and of the memory array set-size. The typical ACOP modulation was observed over parieto-occipital sites in the 280–500 ms time window after sound onset. Its amplitude was not affected by VWM load but was modulated when the location of the sound did not correspond to the hemifield (right or left) that was cued for the change detection task. Our results suggest that sound-elicited activation of visual cortices, as reflected in the ACOP modulation, is unaffected by visual working memory load. However, endogenous spatial attention affects the ACOP, challenging the hypothesis that it reflects an automatic process.

Alterations in working memory maintenance of fearful face distractors in depressed participants: An ERP study.

Task-irrelevant threatening faces (e.g., fearful) are difficult to filter from visual working memory (VWM), but the difficulty in filtering non-threatening negative faces (e.g., sad) is not known. Depressive symptoms could also potentially affect the ability to filter different emotional faces. We tested the filtering of task-irrelevant sad and fearful faces by depressed and control participants performing a color-change detection task. The VWM storage of distractors was indicated by contralateral delay activity, a specific event-related potential index for the number of objects stored in VWM during the maintenance phase. The control group did not store sad face distractors, but they automatically stored fearful face distractors, suggesting that threatening faces are specifically difficult to filter from VWM in non-depressed individuals. By contrast, depressed participants showed no additional consumption of VWM resources for either the distractor condition or the non-distractor condition, possibly suggesting that neither fearful nor sad face distractors were maintained in VWM. Our control group results confirm previous findings of a threat-related filtering difficulty in the normal population while also suggesting that task-irrelevant non-threatening negative faces do not automatically load into VWM. The novel finding of the lack of negative distractors within VWM storage in participants with depressive symptoms may reflect a decreased overall responsiveness to negative facial stimuli. Future studies should investigate the mechanisms underlying distractor filtering in depressed populations.

Executivo Central e Seleção de Alvos na Memória de Trabalho Visual

Abstract The goal of this study was to investigate if the selection of external information for storage in visual working memory requires control by the central executive when the categorization of targets is guided by instructions. The design was experimental 3 (concurrent task) x 2 (instruction). Forty-eight university students saw eight colored shapes, four of them surrounded by square outlines. Memory was assessed using a recognition task. Targets varied with instructions: targets were presented within squares in the first block and outside squares in the second block. There were three concurrent tasks: no task, articulatory suppression, and backward counting. Performance was measured by hits, false alarms, corrected recognition, and sensitivity (A’), compared using within-subject ANOVAs. Results showed a main effect only for concurrent task, with lower performance in the backward counting condition for all measures. These results suggest that the central executive does not control the perceptual filter, corroborating earlier results.

Object-based encoding in visual working memory: A critical revisit.

Visual working memory (VWM) is responsible for the temporal retention and manipulation of visual information. It has been suggested that VWM employs an object-based encoding (OBE) manner to extract highly discriminable information from visual perception: Whenever one feature dimension of the objects is selected for entry into VWM, the other task-irrelevant highly discriminable dimension is also extracted into VWM involuntarily. However, the task-irrelevant feature in OBE studies might reflect a high capacity fragile VWM (FVWM) trace that stores maskable sensory representations. To directly compare the VWM storage hypothesis and the FVWM storage hypothesis, we used a unique characteristic of FVWM that the representations in FVWM could be erased by backward masks presented at the original locations of the memory array. We required participants to memorise the orientations of three coloured bars while ignoring their colours, and presented backward masks during the VWM maintenance interval. In four experiments, we consistently observed that the OBE occurs regardless of the presentation of the backward masks, except when even the task-relevant features in VWM were significantly interrupted by immediate backward masks, suggesting that the task-irrelevant features of objects are stored in VWM rather than in FVWM.

Reliability of Visual Access: Modeling the trade-off between internal storage in visual working memory and external sampling

Reliability of Visual Access: Modeling the trade-off between internal storage in visual working memory and external sampling

Understanding how analysis choices are essential for the meaningful interpretation of visual working memory data

Visual working memory (VWM) relies on a distributed cortical network. Yet, the role of individual cortical areas, like early visual cortex (EVC) and intraparietal sulcus (IPS), remains debated. Criteria have been suggested to determine if an area is essential for storage, such as resiliency against visual distraction, and correlations with behavior. Here, we reanalyzed existing data from two independent labs, and caution that adherence to simple criteria could limit our comprehension of the VWM system. Instead, we encourage close consideration of analysis choices for a more complete perspective. When participants remembered an orientation while simultaneously viewing different visual distractors (Rademaker et al., 2019) fMRI activity patterns in EVC and IPS did not distinguish between distractor conditions. While such resiliency implies that both areas are critical for VWM storage, the analysis used (leave-one-out cross-validation) capitalizes on any signal differentiating memory representations during the delay. Instead, an analysis using sensory driven responses for model-training captures only representations that are sensory-like, and can yield different conclusions. That analysis choices matter is further illustrated by a task with two memory items - one attended, one unattended (Christophel et al., 2018). Originally, delay-period representations of unattended items were not found in EVC. Our reanalysis reveals that with a model trained on stronger signals (the attended instead of the unattended items) EVC does represent unattended memory items. Finally, both datasets reveal a brain-behavior relationship in EVC, but not IPS. Before declaring EVC essential to storage, a careful examination of analysis choices (like the quantification and read-out of neural error) should be performed to guide interpretation. In sum, a thorough understanding of analyses and the specific principles they test is crucial for unraveling the mechanisms of VWM.

Prefrontal Lesions Disrupt Posterior Alpha-Gamma Coordination of Visual Working Memory Representations.

How does the human brain prioritize different visual representations in working memory (WM)? Here, we define the oscillatory mechanisms supporting selection of "where" and "when" features from visual WM storage and investigate the role of pFC in feature selection. Fourteen individuals with lateral pFC damage and 20 healthy controls performed a visuospatial WM task while EEG was recorded. On each trial, two shapes were presented sequentially in a top/bottom spatial orientation. A retro-cue presented mid-delay prompted which of the two shapes had been in either the top/bottom spatial position or first/second temporal position. We found that cross-frequency coupling between parieto-occipital alpha (α; 8-12 Hz) oscillations and topographically distributed gamma (γ; 30-50 Hz) activity tracked selection of the distinct cued feature in controls. This signature of feature selection was disrupted in patients with pFC lesions, despite intact α-γ coupling independent of feature selection. These findings reveal a pFC-dependent parieto-occipital α-γ mechanism for the rapid selection of visual WM representations.

Towards a better understanding of information storage in visual working memory

ABSTRACT Chota, S., & Van der Stigchel, S. (2021). Dynamic and flexible transformation and reallocation of visual working memory representations (this issue); Iamshchinina, P., Christophel, T. B., Gayet, S., & Rademaker, R. L. (2021). Essential considerations for exploring visual working memory storage in the human brain (this issue); Lorenc, E. S., & Sreenivasa, K. K. (2021). Reframing the debate: the distributed systems view of working memory (this issue); and Teng, C., & Postle, B. R. (2021). Understanding occipital and parietal contributions to visual working memory: Commentary to Xu (2020) (this issue) each present a commentary regarding Xu, Y. (2020). Revisit once more the sensory storage account of visual working memory. Visual Cognition, 28(5-8), 433–446. https://doi.org/10.1080/13506285.2020.1818659 where I conclude that sensory regions are nonessential for the storage of information in visual working memory (VWM). They argue instead that sensory regions are critical to VWM storage. Here I briefly reiterate some of the key evidence against this account, some of which has not been accounted by the four commentaries. I also provide a detailed reanalysis of why the main evidence supporting this account may be problematic. Collectively, existence evidence from human neuroimaging and TMS studies and that from monkey neurophysiology studies does not provide strong support for the sensory storage account of VWM. To form an accurate understanding of the distinctive role each brain region may play in perception and VWM as well as how they may interact to collectively support a VWM task, it is important that we properly survey and evaluate all the available evidence.

Essential considerations for exploring visual working memory storage in the human brain

ABSTRACT Visual working memory (VWM) relies on a distributed cortical network. Yet, the extent to which individual cortical areas, like early visual cortex and intraparietal sulcus, are essential to VWM storage remains debated. Here, we reanalyze key datasets from two independent labs to address three topics at the forefront of current-day VWM research: Resiliency of mnemonic representations against visual distraction, the role of attentional priority in memory, and brain–behavior relationships. By utilizing different analysis approaches, each designed to test different aspects of mnemonic coding, our results provide a comprehensive perspective on the role of early visual and intraparietal areas. We emphasize the importance of analysis choices, and how a thorough understanding of the principles they test is crucial for unraveling the distributed mechanisms of VWM. Consequently, we caution against the idea of a singular essential storage area, which could limit our comprehension of the VWM system.

Greater Visual Working Memory Capacity for Visually Matched Stimuli When They Are Perceived as Meaningful.

Almost all models of visual working memory-the cognitive system that holds visual information in an active state-assume it has a fixed capacity: Some models propose a limit of three to four objects, where others propose there is a fixed pool of resources for each basic visual feature. Recent findings, however, suggest that memory performance is improved for real-world objects. What supports these increases in capacity? Here, we test whether the meaningfulness of a stimulus alone influences working memory capacity while controlling for visual complexity and directly assessing the active component of working memory using EEG. Participants remembered ambiguous stimuli that could either be perceived as a face or as meaningless shapes. Participants had higher performance and increased neural delay activity when the memory display consisted of more meaningful stimuli. Critically, by asking participants whether they perceived the stimuli as a face or not, we also show that these increases in visual working memory capacity and recruitment of additional neural resources are because of the subjective perception of the stimulus and thus cannot be driven by physical properties of the stimulus. Broadly, this suggests that the capacity for active storage in visual working memory is not fixed but that more meaningful stimuli recruit additional working memory resources, allowing them to be better remembered.

Bias in confidence: A critical test for discrete-state models of change detection.

Ongoing discussions on the nature of storage in visual working memory have mostly focused on 2 theoretical accounts: On one hand we have a discrete-state account, postulating that information in working memory is supported with high fidelity for a limited number of discrete items by a given number of "slots," with no information being retained beyond these. In contrast with this all-or-nothing view, we have a continuous account arguing that information can be degraded in a continuous manner, reflecting the amount of resources dedicated to each item. It turns out that the core tenets of this discrete-state account constrain the way individuals can express confidence in their judgments, excluding the possibility of biased confidence judgments. Importantly, these biased judgments are expected when assuming a continuous degradation of information. We report 2 studies showing that biased confidence judgments can be reliably observed, a behavioral signature that rejects a large number of discrete-state models. Finally, complementary modeling analyses support the notion of a mixture account, according to which memory-based confidence judgments (in contrast with guesses) are based on a comparison between graded, fallible representations, and response criteria. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Multivariate EEG evidence for feature-independent storage in visual working memory

Multivariate EEG evidence for feature-independent storage in visual working memory

Stimulus-induced Alpha Suppression Tracks the Difficulty of Attentional Selection, Not Visual Working Memory Storage.

Human alpha-band activity (8-12 Hz) has been proposed to index a variety of mechanisms during visual processing. Here, we distinguished between an account in which alpha suppression indexes selective attention versus an account in which it indexes subsequent working memory storage. We manipulated two aspects of the visual stimuli that perceptual attention is believed to mitigate before working memory storage: the potential interference from distractors and the size of the focus of attention. We found that the magnitude of alpha-band suppression tracked both of these aspects of the visual arrays. Thus, alpha-band activity after stimulus onset is clearly related to how the visual system deploys perceptual attention and appears to be distinct from mechanisms that store target representations in working memory.

Revisit once more the sensory storage account of visual working memory

ABSTRACT Recent work has highlighted the role of early visual areas in visual working memory (VWM) storage and put forward a sensory storage account of VWM. Using a distractor interference paradigm, however, we previoulsy showed that the contribution of early visual areas to VWM storage may not be essential. Instead, higher cortical regions such as the posterior parietal cortex may play a more significant role in VWM storage. This is consistent with reviews of other available behavioural, neuroimaging and neurophysiology evidence. Recently, a number of studies brought forward new evidence regarding this debate. Here I review these new pieces of evidence in detail and show that there is still no strong and definitive evidence supporting an essential role of the early visual areas in VWM storage. Instead, converging evidence suggests that early visual areas may contribute to the decision stage of a VWM task by facilitating target and probe comparison. Apart from further clarifying this debate, it is also important to emphasize that whether or not VWM storage uses a sensory code depends on how it is defined, and that behavioural interactions between VWM and perception tasks do not necessarily support the involvement of sensory regions in VWM storage.

Limitations of concurrently representing objects within view and in visual working memory

Representing visibly present stimuli is as limited in capacity as representing invisible stimuli in visual working memory (WM). In this study, we explored whether concurrently representing stimuli within view affects representing objects in visual WM, and if so, whether this effect is modulated by the storage states (active and silent state) of memory contents? In experiment 1, participants were asked to perform the change-detect task in a simultaneous-representing condition in which WM content and the continuously-visible stimuli in view were simultaneously represented, as well as a baseline condition in which only the representations of visual WM content were maintained. The results showed that the representations in visual WM would be impaired when the continuously-visible stimuli in view were concurrently represented, revealed by the reduced CDA amplitude and the lower behavior performance. In experiment 2, a dual-serial retro-cue paradigm was adopted to guide participants to maintain memory items in two different storage states, and the results revealed that simultaneously representing the continuously-visible stimuli and the WM content would only impair the WM representations in the active state. These evidences demonstrated that only the visual WM representations that were maintained in the active state would definitely share the limited resources with the representations of continuously-visible information, and further supported the dissociation between the active state and silent state of visual WM storage.

Visual working memory capacity in Korsakoff’s amnesia

ABSTRACTIntroduction: Despite the interest in memory functioning in Korsakoff’s syndrome (KS), visual working memory capacity in KS is still poorly understood. Results from the last decades on working memory limitations in KS appear to be mixed, clearly calling for further investigations.Method: We investigated visual working memory storage capacity of patients diagnosed with KS using a change detection paradigm. Nine patients diagnosed with KS and thirty age- and education- matched healthy controls were presented twice with 2, 3, 4, or 6 bars with different orientations and had to detect whether the orientation of the target bar had changed.Results: As a group, KS patients performed significantly worse than controls on all set sizes, with an average capacity of 1.13 items, compared to 1.75 items in the control participants. In case study analysis, 4 out of 9 patients performed significantly worse than control participants, while 5 had relatively intact visual working memory capacity. In patients, deficits in visual working memory could not be explained by other cognitive deficits.Conclusion: Based on these results, we conclude that visual working memory deficits are a prominent characteristic in some, but not all KS patients. Training visual working memory capacity could possibly optimize other cognitive difficulties in this population.