Contents Of Working Memory Research Articles

The contents of visual working memory reduce uncertainty during visual search

Information held in visual working memory (VWM) influences the allocation of attention during visual search, with targets matching the contents of VWM receiving processing benefits over those that do not. Such an effect could arise from multiple mechanisms: First, it is possible that the contents of working memory enhance the perceptual representation of the target. Alternatively, it is possible that when a target is presented among distractor items, the contents of working memory operate postperceptually to reduce uncertainty about the location of the target. In both cases, a match between the contents of VWM and the target should lead to facilitated processing. However, each effect makes distinct predictions regarding set-size manipulations; whereas perceptual enhancement accounts predict processing benefits regardless of set size, uncertainty reduction accounts predict benefits only with set sizes larger than 1, when there is uncertainty regarding the target location. In the present study, in which briefly presented, masked targets were presented in isolation, there was a negligible effect of the information held in VWM on target discrimination. However, in displays containing multiple masked items, information held in VWM strongly affected target discrimination. These results argue that working memory representations act at a postperceptual level to reduce uncertainty during visual search.

Content-specific working memory modulation of the attentional blink.

Three experiments were conducted to investigate the effects of working memory content on temporal attention in a rapid serial visual presentation attentional blink paradigm. It was shown that categorical similarity between working memory content and the target stimuli pertaining to the attentional task (both digits) increased attentional blink magnitude compared to a condition in which this similarity was absent (colors and digits, respectively). This effect was only observed when the items in working memory were not presented as conjunctions of the involved categories (i.e., colored digits). This suggested that storage and retrieval from working memory was at least preferentially conjunctive in this case. It was furthermore shown that the content of working memory enhanced the identification rate of the second target, by means of repetition priming, when inter-target lag was short and the attentional blink was in effect. The results are incompatible with theories of temporal attention that assume working memory has no causal role in the attentional blink and support theories that do.

Task-based working memory guidance of visual attention

Previous research has established that holding a stimulus in working memory (WM) facilitates the deployment of visual attention to that stimulus relative to other stimuli. The present study examined whether maintaining a specific task in WM would also bias the allocation of attention to the stimuli associated with that task. Participants performed a speeded letter search task while simultaneously keeping in WM one of two task cues shown at the beginning of each trial. The results showed that task-based WM guidance of attention was modulated by response latencies. Whereas the participants with fast reaction times showed little influence of WM contents, the participants with slow reaction times took longer to respond when the letter target appeared in a distractor stimulus consistent with the task cue held in mind. A subsequent Stroop experiment found a larger Stroop interference effect from the participants in the slow group compared with those in the fast group, suggesting that the differential WM effect between the two groups may be associated with an individual's ability to inhibit task-irrelevant information. Taken together, these results expanded the realm of previous research and provided further evidence for a close link between attention and WM.

Control of interference during working memory updating.

The current study examined the nature of the processes underlying working memory updating. In 4 experiments using the n-back paradigm, the authors demonstrate that continuous updating of items in working memory prevents strong binding of those items to their contexts in working memory, and hence leads to an increased susceptibility to proactive interference. Results of Experiments 1 and 2 show that this interference reflects a competition between a process that reveals the degree of familiarity of an item and a context-sensitive recollection process that depends on the strength of bindings in working memory. Experiment 3 further clarifies the origins of interference during updating by demonstrating that even items that are semantically related to the updated working memory contents but that have not been maintained in working memory before cause proactive interference. Finally, the results of Experiment 4 indicate that the occurrence of interference leads to top-down behavioral adjustments that prioritize recollection over familiarity assessment. The implications of these findings for the construct validity of the n-back task, for the control processes involved in working memory updating, and for the concept of executive control more generally are discussed.

The role of the pulvinar in resolving competition between memory and visual selection: A functional connectivity study

Memory and attention interact. Information held in working memory (WM) can bias visual selection toward matching stimuli in a subsequent search display, while a search target that is different from the memory stimulus can interfere with its subsequent recognition. In recent fMRI studies, the pulvinar has been consistently shown to have an enhanced response when an item in WM matches a search target and a reduced response when the WM item matches a distracter in search. Here we used Granger causality analysis to help understand the role of the pulvinar in resolving competition between memory and selection processes. Across three experiments the results showed increased coupling between the pulvinar and the ipsilateral superior frontal gyrus, contralateral temporal–parietal junction (TPJ) and calcarine sulcus when a visual search distracter matched the item held in memory. This connection pattern suggests that the pulvinar suppresses visual responses to the target when a contralateral distracter contains information held in working memory. We propose that this suppression acts to protect the memory item from interference arising from information associated with the search target. Consistent with this proposal we showed that the strength of the thalamus-to-visual connection predicted performance on a subsequent memory test. The data therefore suggest that the thalamus modulates bottom up processing in sensory cortex to minimize interference to WM content.

Guidance of visual attention from working memory contents depends on stimulus attributes

Recent work shows that items maintained in working memory could guide the orienting of attention in visual search, demonstrating an interesting interaction between working memory and attention. For such guidance effect, some studies emphasize the importance of search task type: for fixed-target search, task-irrelevant memory items stay inside the attentional focus and guides attention; for varied-target search, these items stay outside attentional focus and do not guide attention. With two experiments, we showed that stimulus attribute of items held in working memory can play an important role in attentional guidance. The first behavioral experiment duplicated a previous fixed-target search paradigm demonstrating robust guidance effect but failed to find such effect when the stimuli was simply changed from colored shapes to complex artificial shapes. The second event-related potential experiment duplicated a previous varied-target search paradigm that used complex shapes but did not observe any guidance effect. A clear guidance effect was found when we changed the stimuli to colored shapes. The results suggest that attentional guidance from working memory depends on stimulus attributes of the items held in working memory. When effective attribute is used, task-irrelevant items that stay outside the attentional focus are still able to guide attention.

Reinforcement of inhibitory positional priming by spatial working memory contents

This study examined whether positional priming of pop-out is modulated by spatial working memory (WM). In Experiments 1A and 1B, observers were presented with a to-be-memorized item (Experiment 1A: triangle; Experiment 1B: circle) prior to performing a block of search trials, with triangular stimulus configurations (one target, two distractors) on an underlying elliptical frame. Each search block was followed by a memory test (i.e., memory conditions). In Experiment 1C, the presentation of the memory item (triangle) was immediately followed by the memory test, and the search block was performed after this test (i.e., no-memory condition). It was found that targets presented at a previous target were detected faster and targets presented at a previous distractor location slower, relative to a previous empty (‘neutral’) stimulus location, respectively. While facilitatory position priming was uninfluenced by the memory manipulation, inhibitory positional priming was larger in the memory than no-memory condition, but only when the memory stimulus (triangle) matched the (triangle) configuration formed by the three search items. This finding of larger inhibitory priming under memory conditions provides further evidence that positional priming, rather than being purely bottom-up determined, is open to top-down influences.

Attentional capture by working memory contents.

There has been controversy on whether working memory (WM) contents automatically guide attention. The present study tried to replicate the effect of WM-based attentional capture using an adaption of Downing's (2000) paradigm, in which WM and attentional capture were combined. Subjects were presented with an attention display containing two objects, one of which could be precued by a matching item being held in WM. As measured by a probe discrimination task, the memory-matching object had a privileged status to capture attention regardless of the stimulus onset asynchronies between the memory cue and the attention display, even when there was absolutely no benefit for subjects to bias attention in favour of the memory match. These results suggest that WM contents guide attention in an involuntary manner. The implications of current findings for understanding of WM effects on visual selection are discussed.

The time course of working memory effects on visual attention

Previous work has generated inconsistent results with regard to what extent working memory (WM) content guides visual attention. Some studies found effects of easy to verbalize stimuli, whereas others only found an influence of visual memory content. To resolve this, we compared the time courses of memory-based attentional guidance for different memory types. Participants first memorized a colour, which was either easy or difficult to verbalize. They then looked for an unrelated target in a visual search display and finally completed a memory test. One of the distractors in the search display could have the memorized colour. We varied the time between the to-be-remembered colour and the search display, as well as the ease with which the colours could be verbalized. We found that the influence of easy to verbalize WM content on visual search decreased with increasing time, whereas the influence of visual WM content was sustained. However, visual working memory effects on attention also decreased when the duration of visual encoding was limited by an additional task or when the memory item was presented only briefly. We propose that for working memory effects on visual attention to be sustained, a sufficiently strong visual representation is necessary.

Decoding the contents of visual working memory from activity in the human visual cortex

Decoding the contents of visual working memory from activity in the human visual cortex

Task relevance of object features modulates the content of visual working memory

Task relevance of object features modulates the content of visual working memory

Working memory enhances visual perception: Evidence from signal detection analysis.

We show that perceptual sensitivity to visual stimuli can be modulated by matches between the contents of working memory (WM) and stimuli in the visual field. Observers were presented with an object cue (to hold in WM or to merely attend) and subsequently had to identify a brief target presented within a colored shape. The cue could be re-presented in the display, where it surrounded either the target (on valid trials) or a distractor (on invalid trials). Perceptual identification of the target, as indexed by A', was enhanced on valid relative to invalid trials but only when the cue was kept in WM. There was minimal effect of the cue when it was merely attended and not kept in WM. Verbal cues were as effective as visual cues at modulating perceptual identification, and the effects were independent of the effects of target saliency. Matches to the contents of WM influenced perceptual sensitivity even under conditions that minimized competition for selecting the target. WM cues were also effective when targets were less likely to fall in a repeated WM stimulus than in other stimuli in the search display. There were no effects of WM on decisional criteria, in contrast to sensitivity. The findings suggest that reentrant feedback from WM can affect early stages of perceptual processing.

Basal ganglia contribution to cognitive and motor functions: A computational model of working memory and decision.

Event Abstract Back to Event Basal ganglia contribution to cognitive and motor functions: A computational model of working memory and decision. Henning Schroll1*, Julien Vitay1 and Fred H. Hamker1, 2 1 University of Muenster, Department of Psychology, Germany 2 Chemnitz University of Technology, Department of Information Science, Germany Basal ganglia (BG) are substantially involved in both cognitive processes and movement selection. We present a biologically plausible model of how BG contribute to working memory (WM) and motor decisions, operating within two parallel but interconnected loops. Within a prefrontal-BG-thalamic WM system, the model learns to maintain relevant stimuli while ignoring distracters. WM content then influences a motor loop of cortical area M1, BG and thalamus to learn which of a set of possible actions to perform. Based on previous work by [1], plasticity within the model relies on homeostatic Hebbian-type learning, modulated by reward-related dopamine firing of substantia nigra. Whenever the model chooses a rewarded action, the currently active synapses of BG are reinforced; an expected but omitted reward weakens active synapses by a dip in dopamine firing. Self-organizing clusters of striatal cells give rise to a direct BG pathway; globus pallidus (GP) neurons at its end develop lateral inhibition by local dopamine depletion to adjust the mapping from striatum. A cortico-subthalamic hyperdirect pathway learns to fire brief reset signals to GP to allow updating of cortical activity. The strength of our approach is to use unsupervised and reinforcement learning in real-time simulations to model interacting systems of WM and motor functions. The model succeeds in learning delayed match to sample and delayed paired associates tasks, both including distracters; by introducing context stimuli, it manages to flexibly shift between these two task sets. The model provides predictions about the progressive temporal involvement of BG structures in learning reward-guided behavior.

Functional Division Among Monkey Prefrontal Areas in Goal-Directed Behavior

Event Abstract Back to Event Functional Division Among Monkey Prefrontal Areas in Goal-Directed Behavior Keiji Tanaka1* 1 RIKEN Brain Science Institute, Japan The neural circuitries in the prefrontal cortex are thought to be critical for the flexible control of behavior in primates, but the mechanisms remain largely unknown. In the cases of sensory and motor cortices, the understanding of the functional mechanisms has advanced along with the elucidation of functional differentiation among areas. Because the prefrontal cortex is composed of multiple areas each with unique anatomical connections to other brain sites, we expected that the comparison of functional roles among the prefrontal sub-areas would help disentangle the processes of flexible behavioral control. Selection of actions based on recent experience of action-outcome contingency is one of the features of goal-directed behavior that distinguish it from habitual behavior. Therefore, we trained monkeys on a task in which the relation between visual cues, action types, and reward conditions changed regularly, such that the monkeys selected their actions based on anticipated reward conditions, and recorded neuronal activity from various subareas of the prefrontal cortex during the task performance. Neurons in the medial prefrontal cortex first showed activity, immediately after cue presentation and well before motor execution, which represented particular action-reward combinations. This activity might underlie goal-based action selection. Application of previously learned behavioral rules beyond simple stimulus-response or outcome-response associations is often necessary in goal-directed behavior, and the currently relevant rule is often not directly indicated by sensory cues. The Wisconsin Card Sorting Test (WCST) mimics such a situation. We have developed an animal version of WCST and trained monkeys with the task. The monkey selected one of the three test stimuli by matching it with the sample stimulus in color or in shape. The matching rule was constant within a block of trials, but changed between blocks without giving any notice to the monkey. There was no cue to indicate the currently relevant rule: the monkey had to determine the rule based on the reward given for correct responses. Lesioning of the principal sulcus region (PS), the orbitofrontal region (OFC) and the anterior cingulated sulcus region (ACCs) resulted in significant degradation of the overall performance of the monkeys. Further analyses of the monkeys’ performance in the task and in other probe tests showed that the reasons of the degradation were different. Only the PS lesion impaired maintenance of abstract rules in working memory; only the OFC lesion impaired rapid reward-based updating of rule value; and the ACCs lesion impaired active reference to the content of the rule working memory. These results show that the prefrontal subareas contribute to the flexible control of behavior through individually specific functions.

Electrophysiological evidence for attentional guidance by the contents of working memory

The deployment of visual attention can be strongly modulated by stimuli matching the contents of working memory (WM), even when WM contents are detrimental to performance and salient bottom-up cues define the critical target [D. Soto et al. (2006)Vision Research, 46, 1010-1018]. Here we investigated the electrophysiological correlates of this early guidance of attention by WM in humans. Observers were presented with a prime to either identify or hold in memory. Subsequently, they had to search for a target line amongst different distractor lines. Each line was embedded within one of four objects and one of the distractor objects could match the stimulus held in WM. Behavioural data showed that performance was more strongly affected by the prime when it was held in memory than when it was merely identified. An electrophysiological measure of the efficiency of target selection (the N2pc) was also affected by the match between the item in WM and the location of the target in the search task. The N2pc was enhanced when the target fell in the same visual field as the re-presented (invalid) prime, compared with when the prime did not reappear in the search display (on neutral trials) and when the prime was contralateral to the target. Merely identifying the prime produced no effect on the N2pc component. The evidence suggests that WM modulates competitive interactions between the items in the visual field to determine the efficiency of target selection.

Effects of deep brain stimulation of the peduncolopontine area on working memory tasks in patients with Parkinson's disease

The present paper was aimed at investigating the effect of low-frequency electrical stimulation (25 Hz) of the peduncolopontine (PPN) area on working memory (WM) functioning in patients with Parkinson's disease (PD). Five PD patients who underwent simultaneous PPN area- and subthalamic nucleus-deep brain stimulation (DBS) implantation participated in the study. PD patients were evaluated in the morning at least 12 h after antiparkinsonian therapy withdrawal in two conditions: i) after continuous PPN area stimulation (Off Therapy/On PPN: “On” condition); ii) at least 120 min after PPN area had been switched “Off” (Off Ther/Off PPN: “Off” condition). The experimental WM task consisted of an n-back paradigm with verbal and visual-object stimuli. PD patients showed a consistent response time decrease on both the verbal and the visual-object tasks passing from the “Off” to the “On” condition ( p < 0.05). However, the accuracy score did not significantly differ between the two experimental conditions. The present findings, although preliminary, suggest that PPN area stimulation facilitates the speed processing of information in the content of WM, possibly through the modulation of the attentional resources.

Neural Signatures of Stimulus Features in Visual Working Memory--A Spatiotemporal Approach

We examined the neural signatures of stimulus features in visual working memory (WM) by integrating functional magnetic resonance imaging (fMRI) and event-related potential data recorded during mental manipulation of colors, rotation angles, and color–angle conjunctions. The N200, negative slow wave, and P3b were modulated by the information content of WM, and an fMRI-constrained source model revealed a progression in neural activity from posterior visual areas to higher order areas in the ventral and dorsal processing streams. Color processing was associated with activity in inferior frontal gyrus during encoding and retrieval, whereas angle processing involved right parietal regions during the delay interval. WM for color–angle conjunctions did not involve any additional neural processes. The finding that different patterns of brain activity underlie WM for color and spatial information is consistent with ideas that the ventral/dorsal “what/where” segregation of perceptual processing influences WM organization. The absence of characteristic signatures of conjunction-related brain activity, which was generally intermediate between the 2 single conditions, suggests that conjunction judgments are based on the coordinated activity of these 2 streams.

Impaired selection of relevant positive information in depression

A hallmark characteristic of depression is the inability to regulate the effect of emotional material on cognition. Previous research has demonstrated that depressed individuals are less able than are nondepressed persons to expel irrelevant negative information from working memory (WM), thereby exacerbating the effects of negative content on cognition. The primary goal of this study was to examine whether depressed individuals are also impaired at selecting relevant positive content in the context of representations competing for resources in WM; such an impairment would limit depressed persons' ability to use positive material to ameliorate the cognitive effects of negative information. We administered a Recency-probes task with neutral, positive, and negative words to 20 currently depressed and 22 never-depressed participants. This task assesses the selection of relevant content in WM by inducing interference between current and prior representations of a stimulus in WM. Reaction times to interference and noninterference trials were compared across valence and group to assess how effectively depressed individuals select task-relevant emotional content to resolve interference. Compared to never-depressed controls, depressed individuals were impaired in selecting task-relevant positive stimuli; the performance of the two groups was comparable for selecting task-relevant neutral and negative stimuli. Findings indicate that a valence-specific deficit in WM may contribute to the inability of depressed individuals to regulate emotion, and provide empirical support for formulations that implicate positive insensitivity in the maintenance of depression.

Effects of dopamine‐related gene–gene interactions on working memory component processes

Dopamine modulates complex cognitive functions like working memory and cognitive control. It is widely accepted that an optimal level of prefrontal dopamine supports working memory performance. In the present study we used a molecular genetic approach to test whether the optimal activity of the dopamine system for different component processes of working memory is additionally related to the availability of dopamine D2 receptors. We sought evidence for this assumption by investigating the interaction effect (epistasis) of variations in two dopaminergic candidate genes: the catechol-O-methyltransferase (COMT) Val(158)Met polymorphism, which has been shown to influence prefrontal dopamine concentration, and the DRD2/ANKK1-Taq-Ia polymorphism, which has been related to the density of D2 receptors. Our results show that COMT effects on working memory performance are modulated by the DRD2/ANKK1-TAQ-Ia polymorphism and the specific working memory component process under investigation. Val-participants--supposedly characterized by increased prefrontal dopamine concentrations--outperformed Val+ participants in the manipulation of working memory contents, but only when D2 receptor density could be considered to be high. No such effect was present for passive maintenance of working memory contents or for maintenance in the face of distracting information. This beneficial effect of a balance between prefrontal dopamine availability and D2 receptor density reveals the importance of considering epistasis effects and different working memory subprocesses in genetic association studies.

Decoding reveals the contents of visual working memory in early visual areas

Visual working memory provides an essential link between perception and higher cognitive functions, allowing for the active maintenance of information regarding stimuli no longer in view1,2. Research suggests that sustained activity in higher-order prefrontal, parietal, inferotemporal and lateral occipital areas supports visual maintenance3-11, and may account for working memory’s limited capacity to hold up to 3-4 items9-11. Because higher-order areas lack the visual selectivity of early sensory areas, it has remained unclear how observers can remember specific visual features, such as the precise orientation of a grating, with minimal decay in performance over delays of many seconds12. One proposal is that sensory areas serve to maintain fine-tuned feature information13, but early visual areas show little to no sustained activity over prolonged delays14-16. Using fMRI decoding methods17, here we show that orientations held in working memory can be decoded from activity patterns in the human visual cortex, even when overall levels of activity are low. Activity patterns in areas V1-V4 could predict which of two oriented gratings was held in memory with mean accuracy levels upwards of 80%, even in participants exhibiting activity that fell to baseline levels after a prolonged delay. These orientation-selective activity patterns were sustained throughout the delay period, evident in individual visual areas, and similar to the responses evoked by unattended, task-irrelevant gratings. Our results demonstrate that early visual areas can retain specific information about visual features held in working memory, over periods of many seconds when no physical stimulus is present.