Working Memory Representations Research Articles

Computation on demand: Action-specific representations of visual task features arise during distinct movement phases.

The intention to act influences the computations of various task-relevant features. However, little is known about the time course of these computations. Furthermore, it is commonly held that these computations are governed by conjunctive neural representations of the features. But, support for this view comes from paradigms arbitrarily combining task features and affordances, thus, requiring representations in working memory. Therefore, the present study used electroencephalography and a well-rehearsed task with features that afford minimal working memory representations to investigate the temporal evolution of feature representations and their potential integration in the brain. Female and male human participants viewed and grasped objects or touched them with a knuckle. Objects had different shapes and were made of heavy or light materials with shape and weight being relevant for grasping, not for "knuckling." Using multivariate analysis showed that representations of object shape were similar for grasping and knuckling. However, only for grasping did early shape representations reactivate at later phases of grasp planning, suggesting that sensorimotor control signals feed back to early visual cortex. Grasp-specific representations of material/weight only arose during grasp execution after object contact during the load phase. A trend for integrated representations of shape and material also became grasp-specific but only briefly during Movement onset. These results suggest that the brain generates action-specific representations of relevant features as required for the different subcomponents of its action computations. Our results argue against the view that goal-directed actions inevitably join all features of a task into a sustained and unified neural representation.Significance statement The idea that all the features of a task are integrated into a joint representation or event file is widely supported but importantly based on paradigms with arbitrary stimulus-response combinations. Our study is the first to investigate grasping using electroencephalography to search for the neural basis of feature integration in such a daily-life task with overlearned stimulus-response mappings. Contrary to the notion of event files we find limited evidence for integrated representations. Instead, we find that task-relevant features form representations at specific phases of the action, suggesting that action intentions reactivate representations of relevant features. Our results show that integrated representations do not occur universally for any kind of goal-directed behaviour but in a manner of computation on demand.

Trying harder: how cognitive effort sculpts neural representations during working memory.

While the exertion of mental effort improves performance on cognitive tasks, the neural mechanisms by which motivational factors impact cognition remain unknown. Here, we used fMRI to test how changes in cognitive effort, induced by changes in task difficulty, impacts neural representations of working memory. Participants (both sexes) were precued whether working memory difficulty would be hard or easy. We hypothesized that hard trials demanded more effort as a later decision required finer mnemonic precision. Behaviorally, pupil size was larger and response times were slower on hard compared to easy trials suggesting our manipulation of effort succeeded. Neurally, we observed robust persistent activity during delay periods in prefrontal cortex, especially during hard trials. Yet, details of the memoranda could not be decoded from patterns in prefrontal activity. In the patterns of activity in visual cortex, however, we found strong decoding of memorized targets, where accuracy was higher on hard trials. To potentially link these across-region effects, we hypothesized that effort, carried by persistent activity in prefrontal cortex, impacts the quality of working memory representations encoded in visual cortex. Indeed, we found that the amplitude of delay period activity in frontal cortex predicted decoded accuracy in visual cortex on a trial-wise basis. These results indicate that effort-related feedback signals sculpt population activity in visual cortex, improving mnemonic fidelity.Significance Statement A full understanding of the neural mechanisms underlying our cognitive abilities depends on understanding their interplay with factors such as cognitive effort. Here, we relied on the simple intuition that some tasks require more effort than others and success depends on how hard we try. We show how the exertion of cognitive effort - trying harder - improves the quality of working memory representations in visual cortex mediated by feedback from prefrontal cortex. Such a mechanism describes how the limited resources that support working memory are allocated and strategically controlled. These results have implications for psychiatric disorders, like schizophrenia, where motivational deficits may masquerade as cognitive dysfunction.

Jointly looking to the past and the future in visual working memory

Working memory enables us to bridge past sensory information to upcoming future behaviour. Accordingly, by its very nature, working memory is concerned with two components: the past and the future. Yet, in conventional laboratory tasks, these two components are often conflated, such as when sensory information in working memory is encoded and tested at the same location. We developed a task in which we dissociated the past (encoded location) and future (to-be-tested location) attributes of visual contents in working memory. This enabled us to independently track the utilisation of past and future memory attributes through gaze, as observed during mnemonic selection. Our results reveal the joint consideration of past and future locations. This was prevalent even at the single-trial level of individual saccades that were jointly biased to the past and future. This uncovers the rich nature of working memory representations, whereby both past and future memory attributes are retained and can be accessed together when memory contents become relevant for behaviour.

Jointly looking to the past and the future in visual working memory.

Working memory enables us to bridge past sensory information to upcoming future behaviour. Accordingly, by its very nature, working memory is concerned with two components: the past and the future. Yet, in conventional laboratory tasks, these two components are often conflated, such as when sensory information in working memory is encoded and tested at the same location. We developed a task in which we dissociated the past (encoded location) and future (to-be-tested location) attributes of visual contents in working memory. This enabled us to independently track the utilisation of past and future memory attributes through gaze, as observed during mnemonic selection. Our results reveal the joint consideration of past and future locations. This was prevalent even at the single-trial level of individual saccades that were jointly biased to the past and future. This uncovers the rich nature of working memory representations, whereby both past and future memory attributes are retained and can be accessed together when memory contents become relevant for behaviour.

Concurrent maintenance of both veridical and transformed working memory representations within unique coding schemes

Abstract In the dynamic environment we live in, the already limited information that human working memory can maintain needs to be constantly updated to optimally guide behaviour. Indeed, previous studies showed that leading up to a response, representations maintained in working memory representations are transformed continuously. This goes hand-in-hand with the removal of task-irrelevant items. However, does such removal also include the representations of stimuli as they were originally, prior to transformation? Here we assessed the neural representation of task-relevant transformed representations, and the no-longer-relevant veridical representations they originated from. We applied multivariate pattern analysis to electroencephalographic data during maintenance of orientation gratings with and without mental rotation. During maintenance, we perturbed the representational network by means of a visual impulse stimulus, and were thus able to successfully decode veridical as well as imaginary, transformed orientation gratings from impulse-driven activity. The impulse response reflected only task-relevant (cued), but not task-irrelevant (uncued) items, suggesting that the latter were quickly discarded from working memory. By contrast, even though the original cued orientation gratings were also no longer task-relevant after mental rotation, these items continued to be represented next to the rotated ones, in different representational formats. This seemingly inefficient use of scarce working memory capacity was associated with reduced probe response times and may thus serve to increase precision and flexibility in guiding behaviour in dynamic environments.

Time course of attentional guidance by visual and verbal working memory representations

ABSTRACT Visual and verbal representations in working memory guide visual attention to a memory-matching item. It is well documented that visual cues have an advantage in target detection over verbal cues; however, little research has explored the differences in visual search processes and between attentional guidance by visual and verbal working memory. To address this issue, here we investigated the time course of attentional guidance through visual and verbal representations by comparing the inhibition of return effects. Previous research shows that both types of working memory items produce early facilitation effects and later inhibition effects, but there are lesser facilitation effects for verbal than for visual working memory guidance of attention. Results showed that in all conditions, attention was guided by memory representations, but no inhibition of return was observed. Thus, the robustness of previous findings on the time course of attentional guidance by working memory is low.

Top-down suppression of negative features applies flexibly contingent on visual search goals.

Visually searching for a frequently changing target is assumed to be guided by flexible working memory representations of specific features necessary to discriminate targets from distractors. Here, we tested if these representations allow selective suppression or always facilitate perception based on search goals. Participants searched for a target (i.e., a horizontal bar) defined by one of two different negative features (e.g., not red vs. not blue; Experiment 1) or a positive (e.g., blue) versus a negative feature (Experiments 2 and 3). A prompt informed participants about the target identity, and search tasks alternated or repeated randomly. We used different peripheral singleton cues presented at the same (valid condition) or a different (invalid condition) position as the target to examine if negative features were suppressed depending on current instructions. In all experiments, cues with negative features elicited slower search times in valid than invalid trials, indicating suppression. Additionally, suppression of negative color cues tended to be selective when participants searched for the target by different negative features but generalized to negative and non-matching cue colors when switching between positive and negative search criteria was required. Nevertheless, when the same color - red - was used in positive and negative search tasks, red cues captured attention or were suppressed depending on whether red was positive or negative (Experiment 3). Our results suggest that working memory representations flexibly trigger suppression or attentional capture contingent on a task-relevant feature's functional meaning during visual search, but top-down suppression operates at different levels of specificity depending on current task demands.

Accessibility of working memory representations in the focus of attention: Heightened or reduced?

Many researchers agree that information residing in the focus of attention in working memory benefits from a boost in memory strength and activation, as well as heightened accessibility. However, recent studies have questioned this heightened accessibility. More specifically, these recent studies found reduced accessibility for an item in the focus of attention compared to another item in working memory, which was referred to as an "inhibition-of-return-like" effect. Our study aimed to provide a detailed examination of the accessibility of information in the focus of attention. Across a series of experiments, varying task characteristics related to the time course of the effect (Experiments 2-3) and the potential role of response inhibition (Experiments 4a-4b), we repeatedly failed to find evidence for an inhibition-of-return-like effect. Instead, we mostly found heightened accessibility for an item in the focus of attention. Given that an inhibition-of-return-like effect seems to be limited to a very specific task condition, reduced accessibility of information in the focus of attention appears to be far from a general phenomenon. Therefore, based on our findings, we propose that information in the focus of attention generally benefits from heightened accessibility, although there may be factors, most likely unrelated to the functioning of the focus of attention, that could sometimes mask this and even result in data patterns that are consistent with reduced accessibility. The theoretical implications for the focus of attention and working memory are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

I remember it now, so I'll remember it later: Working memory strength guides predictions for long-term memory performance.

Judgments of learning (JOLs) are assumed to be made inferentially, based on cues. This cue-utilization approach substituted the theory that memory strength guides JOLs. The rejection of this theory ignores the existence of two memory systems: working memory (WM), which holds representations immediately accessible, and long-term memory (LTM), which is a permanent store. By manipulating and measuring WM strength, we tested a revised version of the memory-strength theory in which JOLs are guided by WM representations. In Experiment 1, participants memorized sequences of two or four colored objects, then they provided JOLs for an LTM test of these objects, and performed a WM test on the objects' colors. After learning 200 objects, the LTM test followed. Sequence-length affected WM, but not LTM performance. JOLs, however, were higher for sequences of two than for four objects and correlated higher with WM than LTM performance. We replicated these results with a simultaneous presentation of the objects (Experiment 2), in the absence of a WM test (Experiment 3), and in a word-pair task (Experiment 4). Overall, our findings are consistent with the revised memory-strength theory. WM strength should therefore be considered when examining the factors guiding JOLs.

ERPs and alpha oscillations track the encoding and maintenance of object-based representations in visual working memory.

When memorizing an integrated object such as a Kanizsa figure, the completion of parts into a coherent whole is attained by grouping processes which render a whole-object representation in visual working memory (VWM). The present study measured event-related potentials (ERPs) and oscillatory amplitudes to track these processes of encoding and representing multiple features of an object in VWM. To this end, a change detection task was performed, which required observers to memorize both the orientations and colors of six "pacman" items while inducing configurations of the pacmen that systematically varied in terms of their grouping strength. The results revealed an effect of object configuration in VWM despite physically constant visual input: change detection for both orientation and color features was more accurate with increased grouping strength. At the electrophysiological level, the lateralized ERPs and alpha activity mirrored this behavioral pattern. Perception of the orientation features gave rise to the encoding of a grouped object as reflected by the amplitudes of the Ppc. The grouped object structure, in turn, modulated attention to both orientation and color features as indicated by the enhanced N1pc and N2pc. Finally, during item retention, the representation of individual objects and the concurrent allocation of attention to these memorized objects were modulated by grouping, as reflected by variations in the CDA amplitude and a concurrent lateralized alpha suppression, respectively. These results indicate that memorizing multiple features of grouped, to-be-integrated objects involves multiple, sequential stages of processing, providing support for a hierarchical model of object representations in VWM.

Semantically congruent bimodal presentation modulates cognitive control over attentional guidance by working memory.

Although previous studies have well established that audiovisual enhancement has a promoting effect on working memory and selective attention, there remains an open question about the influence of audiovisual enhancement on attentional guidance by working memory. To address this issue, the present study adopted a dual-task paradigm that combines a working memory task and a visual search task, in which the content of working memory was presented in audiovisual or visual modalities. Given the importance of search speed in memory-driven attentional suppression, we divided participants into two groups based on their reaction time (RT) in neutral trials and examined whether audiovisual enhancement in attentional suppression was modulated by search speed. The results showed that the slow search group exhibited a robust memory-driven attentional suppression effect, and the suppression effect started earlier and its magnitude was greater in the audiovisual condition than in the visual-only condition. However, among the faster search group, the suppression effect only occurred in the trials with longer RTs in the visual-only condition, and its temporal dynamics were selectively improved in the audiovisual condition. Furthermore, audiovisual enhancement of memory-driven attention evolved over time. These findings suggest that semantically congruent bimodal presentation can progressively facilitate the strength and temporal dynamics of memory-driven attentional suppression, and that search speed plays an important role in this process. This may be due to a synergistic effect between multisensory working memory representation and top-down suppression mechanism. The present study demonstrates the flexible role of audiovisual enhancement on cognitive control over memory-driven attention.

Electrophysiological hallmarks for event relations and event roles in working memory.

The ability to maintain events (i.e., interactions between/among objects) in working memory is crucial for our everyday cognition, yet the format of this representation is poorly understood. The current ERP study was designed to answer two questions: How is maintaining events (e.g., the tiger hit the lion) neurally different from maintaining item coordinations (e.g., the tiger and the lion)? That is, how is the event relation (present in events but not coordinations) represented? And how is the agent, or initiator of the event encoded differently from the patient, or receiver of the event during maintenance? We used a novel picture-sentence match-across-delay approach in which the working memory representation was "pinged" during the delay, replicated across two ERP experiments with Chinese and English materials. We found that maintenance of events elicited a long-lasting late sustained difference in posterior-occipital electrodes relative to non-events. This effect resembled the negative slow wave reported in previous studies of working memory, suggesting that the maintenance of events in working memory may impose a higher cost compared to coordinations. Although we did not observe significant ERP differences associated with pinging the agent vs. the patient during the delay, we did find that the ping appeared to dampen the ongoing sustained difference, suggesting a shift from sustained activity to activity silent mechanisms. These results suggest a new method by which ERPs can be used to elucidate the format of neural representation for events in working memory.

The Reactivation of working memory representations affects attentional guidance.

Recent studies have suggested that the neural activity that supported working memory (WM) storage is dynamic over time and this dynamic storage decides memory performance. Does the temporal dynamic of the WM representation also affect visual search, and how does it interact with distractor suppression over time? To address these issues, we tracked the time course of the reactivation of WM representations during visual search by analyzing the electroencephalogram (EEG) and event-related optical signals (EROS) in Experiments 1 and 2, respectively, and investigated the interaction between the representation reactivation and distractor suppression in Experiment 3. Participants had to maintain a color in WM under high- or low-precision requirement and perform a subsequent search task. The reactivation of WM representations was defined by the above-chance decoding accuracy. The EEG results showed that compared with the low-precision requirement, WM-matching distractors captured more attention and the WM representation were reactivated more frequently under high-precision requirement. The EROS results showed that compared with the low-precision requirement, the increased activity in occipital cortex in the WM-matching versus WM-mismatching conditions was observed at 224 ms during visual search under high-precision requirement. Regression analysis showed that the representation reactivation during visual search directly predicted the behavioral WM-based attentional capture effect, while the representation reactivation before visual search impacted the WM-based attentional capture effect through the mediation of distractor suppression during visual search. These results suggest that the reactivation of WM representations and distractor suppression collectively determine WM-based attentional capture.

Does semantic similarity affect immediate memory for order? Usually not, but sometimes it does.

Recall performance in working memory (WM) is strongly affected by the similarity between items. When asked to encode and recall list of items in their serial order, people confuse more often the position of similar compared to dissimilar items. Models of WM explain this deleterious effect of similarity through a problem of discriminability between WM representations. In contrast, when lists of items that are all semantically similar are compared to lists of dissimilar items, semantic similarity does not negatively impact order memory, questioning the idea that semantic information is part of the WM content. This study reports four experiments in which semantic similarity was manipulated using lists composed of multiple semantic categories. These experiments revealed two main patterns. First, semantic similarity can increase, rather than decrease, order memory. Second, semantic knowledge reliably constrains the way items migrate; when migrating, items tend to do so more often toward the position of other similar items, rather than migrating toward other dissimilar items. These results challenge the way current models of WM represent similarity. The plausibility of different theoretical accounts and mechanisms is discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Cognitive mechanisms underlying the formation of offline representations in visual working memory

Cognitive mechanisms underlying the formation of offline representations in visual working memory

Точность формирования пространственных репрезентаций динамических сцен в рабочей памяти

<p>The cognitive representation of the environment is formed using cognitive systems that process data on spatial representations of two types: egocentric, encoding the position of environmental objects relative to the observer, and allocentric, encoding the position of objects relative to each other, regardless of the position of the observer. Data on spatial representations were studied mainly in problems of memorization and reconstruction of static scenes. However, the task of processing information about dynamic scenes in everyday life has a higher ecological validity. We used HMD virtual reality technologies to study the accuracy of the formation of egocentric and allocentric spatial representations of static and dynamic scenes in working memory. The subjects were presented 8 three-dimensional virtual scenes of 4 objects each for 10 seconds in static and dynamic conditions for memorization and reconstruction. Identification accuracy (number of correctly reconstructed objects) and localization accuracy (accuracy of spatial scene reconstruction) were assessed. Localization accuracy was assessed in topological units, corresponding to the accuracy of the representation of the general configuration of objects in the scene (global topological information), and in metric units, corresponding to the accuracy of the representation of the spatial coordinates of each object (local metric information). The results showed that object identification accuracy was similar in static and dynamic conditions; the processes of encoding metric local information during the formation of both types of representations of dynamic scenes worsen compared to static ones; the accuracy of encoding topological global information remains stable compared to the static condition. We can conclude that the visual and spatial systems operate independently as part of a general cognitive system that processes data on spatial representations in time-limited working memory, as well as the redistribution of its resource in dynamic condition for supporting topological data of the holistic configuration of moving objects more, than metric data. The results highlight the importance of topological spatial characteristics of spatial representations for processes of early spatial perception, decision making, and action in the environment.</p>

Working memory performance is tied to stimulus complexity

Working memory is the cognitive capability to maintain and process information over short periods. Behavioral and computational studies have shown that visual information is associated with working memory performance. However, the underlying neural correlates remain unknown. To identify how visual information affects working memory performance, we conducted behavioral experiments in pigeons (Columba livia) and single unit recordings in the avian prefrontal analog, the nidopallium caudolaterale (NCL). Complex pictures featuring luminance, spatial and color information, were associated with higher working memory performance compared to uniform gray pictures in conjunction with distinct neural coding patterns. For complex pictures, we found a multiplexed neuronal code displaying visual and value-related features that switched to a representation of the upcoming choice during a delay period. When processing gray stimuli, NCL neurons did not multiplex and exclusively represented the choice already during stimulus presentation and throughout the delay period. The prolonged representation possibly resulted in a decay of the memory trace ultimately leading to a decrease in performance. In conclusion, we found that high stimulus complexity is associated with neuronal multiplexing of the working memory representation possibly allowing a facilitated read-out of the neural code resulting in enhancement of working memory performance.

Early top-down control of internal selection induced by retrospective cues in visual working memory: advantage of peripheral over central cues.

Attention can be deployed among external sensory stimuli or internal working memory (WM) representations, and recent primate studies have revealed that these external and internal selections share a common neural basis in the prefrontal cortex (PFC). However, it remains to be elucidated how PFC implements these selections, especially in humans. The present study aimed to further investigate whether PFC responded differentially to the peripheral and central retrospective cues (retro-cues) that induced attention selection among WM representations. To achieve this, we combined magnetoencephalography (MEG, Experiment 1) and transcranial magnetic stimulation (TMS, Experiment 2) with an orientation-recall paradigm. Experiment 1 found that a peripheral retro-cue with 100% reliability had a greater benefit on WM performance than a central retro-cue, while this advantage of peripheral over central cues vanished when the cue reliability dropped to 50% (non-informative). MEG source analysis indicated that the 100% peripheral retro-cue elicited earlier (~125 ms) PFC responses than the central retro-cue (~275 ms). Meanwhile, Granger causality analysis showed that PFC had earlier (0-200 ms) top-down signals projecting to the superior parietal lobule (SPL) and the lateral occipital cortex (LOC) after the onset of peripheral retro-cues, while these top-down signals appeared later (300-500 ms) after the onset of central retro-cues. Importantly, PFC activity within this period of 300-500 ms correlated with the peripheral advantage in behavior. Moreover, Experiment 2 applied TMS at different time points to test the causal influence of brain activity on behavior and found that stimulating PFC at 100 ms abolished the behavioral benefit of the peripheral retro-cue, as well as its advantage over the central retro-cue. Taken together, our results suggested that the advantage of peripheral over central retro-cues in the mnemonic domain is realized through faster top-down control from PFC, which challenged traditional opinions that the top-down control of attention on WM required at least 300 ms to appear. The present study highlighted that in addition to the causal role of PFC in attention selection of WM representations, timing was critical as well and faster was better.

When "looking at nothing" imparts something: Retrospective gaze cues flexibly direct prioritization in visual working memory.

Previous research has shown that retrospective gaze cues direct attention to internally maintained representations in visual working memory (vWM). Here, we aimed to differentiate the dual nature of gaze and accordingly proposed two hypotheses regarding the gaze-induced prioritization in vWM. The directional cueing hypothesis claims a constant attentional shifting to the gazed-at direction. By contrast, the referential cueing hypothesis proposes that gaze cues selectively orient attention toward their referents. To test these hypotheses, we employed an adapted change-detection task wherein gaze cues were presented during the retention interval. Critically, the cue character was positioned between two barriers, which could be either opaque (the blocked condition) or transparent (the unblocked condition). Polygons previously presented at the gazed-at (vs. gazed-away) location were better memorized, but not when the visual perspective of the character was obstructed (i.e., the blocked condition, Experiment 1). Subsequent experiments demonstrated that physical motion cues (Experiment 2) and inverted face cues (Experiment 3), which disrupted the extraction of referential signals, were immune to barrier settings. In Experiment 4, we generalize this selective cueing effect to faces with fearful expressions. These consistent findings support the referential cueing hypothesis and emphasize the distinctiveness of social attention. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Supplemental Material for Accessibility of Working Memory Representations in the Focus of Attention: Heightened or Reduced?

Supplemental Material for Accessibility of Working Memory Representations in the Focus of Attention: Heightened or Reduced?