Visual Working Memory Representations Research Articles

Long-term high-altitude exposure influences task-related representations in visual working memory.

Human working memory is impaired when individuals are exposed to high altitudes, however, whether the capacity of visual working memory is affected remains unclear. This study combined a lateralized change detection task and event-related potentials analysis to explore changes in visual working memory capacity among individuals who emigrated from a low-altitude environment to Tibet (a high-altitude environment). Thirty-five college students were recruited from Tibet University as the high-altitude (HA) group, and thirty-six low-altitude (LA) students were enrolled from South China Normal University (sea level) as the LA group. We measured participants' contralateral delay activity (CDA) under different memory loads. ERP component analysis showed that both the HA and LA groups reached an asymptote at memory load four. However, the contralateral and ipsilateral activity of the HA and LA groups shows different patterns. The results showed a significantly larger contralateral activity for the LA group than for the HA group at memory load one (p = 0.04, Cohen's d = 0.52) and load three (p = 0.02, Cohen's d = 0.61). Additionally, we found marginally larger contralateral activity at memory load four for the LA group (p = 0.06, Cohen's d = 0.47), but not at memory load two (p = 0.10) or load five (p = 0.12). No significant differences were observed for ipsilateral activity. In addition, we observed that the HA group performed larger ipsilateral activity than contralateral activity under each memory load, compared with the LA group. These findings demonstrated that the attentional resource of long-term HA exposure is more captured by task-irrelevant information, potentially due to impaired inhibitory control, which makes it difficult for them to exclude the interference of task-irrelevant information.

Sustained attention required for effective dimension-based retro-cue benefit in visual working memory.

In visual working memory (VWM) tasks, participants' performances can be improved through the use of dimension-based retro-cues, which direct internal attention to prioritize a particular dimension (e.g., color or orientation) of VWM representations even after the stimuli disappear. This phenomenon is known as the dimension-based retro-cue benefit (RCB). The present study investigates whether sustained attention is required for the dimension-based RCB by inserting interference or interruption between the retro-cue and the test array to distract attention. We tested the effects of perceptual interference or cognitive interruption on dimension-based RCB when the interference (Experiments 1 and 2 with masks) or interruption (Experiments 3 and 4 with an odd-even task) occurred concurrently with the stages for the maintenance of prioritized information (long cue-and-interference/interruption interstimulus interval, e.g., Experiments 1 and 3) or the deployment of attention (short cue-and-interference/interruption interstimulus interval, e.g., Experiments 2 and 4). Our results demonstrate that perceptual interference or cognitive interruption attenuates the dimension-based RCB. These findings suggest that sustained attention is necessary for the effective prioritization of a specific dimension of VWM representations.

Prioritization sharpens working memories but does not protect them from distraction.

Perceptual distraction distorts visual working memory representations. Previous research has shown that memory responses are systematically biased toward visual distractors that are similar to the memoranda. However, it remains unclear whether the prioritization of one working memory representation over another reduces the impact of perceptual distractors. In five behavioral experiments, we used different forms of retrospective cues (indicating the likelihood of testing each item and/or the reward for responding correctly to each item) to manipulate the prioritization of items in working memory before visual distraction. We examined the effects of distraction with nonparametric analyses and a novel distractor intrusion model. We found that memory responses were more precise (lower absolute response errors and stronger memory signals) for items that were prioritized. However, these prioritized items were not immune to distraction, and their memory responses were biased toward the visual distractors to the same degree as were unprioritized items. Our findings demonstrate that the benefits associated with prioritization in working memory do not include protection from distraction biases. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

White matter microstructure is associated with the precision of visual working memory

Visual working memory is critical for goal-directed behavior as it maintains continuity between previous and current visual input. Functional neuroimaging studies have shown that visual working memory relies on communication between distributed brain regions, which implies an important role for long-range white matter connections in visual working memory performance. Here, we characterized the relationship between the microstructure of white matter association tracts and the precision of visual working memory representations. To that purpose, we devised a delayed estimation task which required participants to reproduce visual features along a continuous scale. A sample of 80 healthy adults performed the task and underwent diffusion-weighted MRI. We applied mixture distribution modelling to quantify the precision of working memory representations, swap errors, and guess rates, all of which contribute to observed responses. Latent components of microstructural properties in sets of anatomical tracts were identified by principal component analysis. We found an interdependency between fibre coherence in the bilateral superior longitudinal fasciculus (SLF) I, SLF II, and SLF III, on one hand, and the bilateral inferior fronto-occipital fasciculus (IFOF), on the other, in mediating the precision of visual working memory in a functionally specific manner. We also found that individual differences in axonal density in a network comprising the bilateral inferior longitudinal fasciculus (ILF) and SLF III and right SLF II, in combination with a supporting network located elsewhere in the brain, form a common system for visual working memory to modulate response precision, swap errors, and random guess rates.

Familiarity enhances mnemonic precision but impairs mnemonic accuracy in visual working memory.

Prior stimulus familiarity has a variety of effects on visual working memory representations and processes. However, it is still unclear how familiarity interacts with the veridical correspondence between mnemonic representation and external stimuli. Here, we examined the effect of familiarity on two aspects of mnemonic correspondence, precision and accuracy, in visual working memory. Specifically, we used a hierarchical Bayesian method to model task performance in a change detection task with celebrity lookalikes (morphed faces between celebrities and noncelebrities with various ratios) as the memory stimuli. We found that familiarity improves memory precision by sharpening mnemonic representation but impairs memory accuracy by biasing mnemonic representation toward familiar faces (i.e., celebrity faces). These findings provide an integrated account of the puzzling celebrity sighting phenomena with the dissociable effects on mnemonic imprecision and bias and further highlight the importance of assessing these two aspects of memory correspondence in future research.

Exploring how visual working memory performance differs with response type

Visual working memory (VWM) holds visual information in mind to achieve task goals. Performance varies based on factors such as stimulus modality and distractor number. Several different tasks have been used to measure VWM, each resulting in differing estimates of capacity. Our goal was to examine how task demands can influence neurocognitive measures of VWM during early childhood. We administered two tasks to 4- and 5-year-olds that were identical during visual encoding and maintenance, only differing in type of response required during recall. In the change detection task (CD), a visual stimulus was compared with a VWM representation. In the cued-recall task (CR) a VWM representation was verbally labeled. Six canonical colors were used (red, orange, yellow, green, blue, purple). Neural data were collected from bilateral frontal, temporal, and parietal regions using functional near-infrared spectroscopy (fNIRS). VWM capacity was estimated to be higher in the change detection task (k4=2.48, k5=2.54) compared to the cued recall task (k4=1.13, k5=1.84) (p < .001). A network of frontal, temporal, and parietal regions was engaged across tasks. When comparing the tasks, CR showed increased activation in both the left supramarginal gyrus, F(1,35) = 11.642, p = 0.002, and the right superior parietal cortex, F(1,35) = 7.915, p = 0.008. Further, higher activation was observed for 5-year-olds during CR in right supramarginal gyrus, F(1,34) = 8.295, p = 0.007. During the CD task, right inferior frontal gyrus showed increased activation at set size two, F(2,64) = 3.643, p = 0.032, which is around capacity for this task. Thus, the CR task was observed to be more difficult than the CD task, and 5-year-olds showed increased activation in right parietal cortex during the CR task. These data suggest that children improve at engaging compensatory neural mechanisms during more challenging tasks involving the labelling of VWM representations.

EEG amplitude, not power, predicts updated memory representations in visual working memory

EEG amplitude, not power, predicts updated memory representations in visual working memory

The mechanisms of selection-for-action on visual working memory representations

The mechanisms of selection-for-action on visual working memory representations

Action intention strengthens visual working memory representations

Action intention strengthens visual working memory representations

Oculomotor rehearsal in visuospatial working memory

The neural and cognitive mechanisms of spatial working memory are tightly coupled with the systems that control eye movements, but the precise nature of this coupling is not well understood. It has been argued that the oculomotor system is selectively involved in rehearsal of spatial but not visual material in visuospatial working memory. However, few studies have directly compared the effect of saccadic interference on visual and spatial memory, and there is little consensus on how the underlying working memory representation is affected by saccadic interference. In this study we aimed to examine how working memory for visual and spatial features is affected by overt and covert attentional interference across two experiments. Participants were shown a memory array, then asked to either maintain fixation or to overtly or covertly shift attention in a detection task during the delay period. Using the continuous report task we directly examined the precision of visual and spatial working memory representations and fit psychophysical functions to investigate the sources of recall error associated with different types of interference. These data were interpreted in terms of embodied theories of attention and memory and provide new insights into the nature of the interactions between cognitive and motor systems.

Visual working memory representations bias attention more when they are the target of an action plan

Attention has frequently been regarded as an emergent property of linking sensory representations to action plans. It has recently been proposed that similar mechanisms may operate within visual working memory (VWM), such that linking an object in VWM to an action plan strengthens its sensory memory representation, which then expresses as an attentional bias. Here we directly tested this hypothesis by comparing attentional biases induced by VWM representations which were the target of a future action, to those induced by VWM representations that were equally task-relevant, but not the direct target of action. We predicted that the first condition would result in a more prioritized memory state and hence stronger attentional biases. Specifically, participants memorized a geometric shape for a subsequent memory test. At test, in case of a match, participants either had to perform a grip movement on the matching object (action condition), or perform the same movement, but on an unrelated object (control condition). To assess any attentional biases, during the delay period between memorandum and test, participants performed a visual selection task in which either the target was surrounded by the memorized shape (congruent trials) or a distractor (incongruent trials). Eye movements were measured as a proxy for attentional priority. We found a significant interaction for saccade latencies between action condition and shape congruency, reflecting more pronounced VWM-based attentional biases in the action condition. Our results are consistent with the idea that action plans prioritize sensory representations in VWM.

Perceptual comparisons modulate memory biases induced by new visual inputs.

It is well-established that stimulus-specific information in visual working memory (VWM) can be systematically biased by new perceptual inputs. These memory biases are commonly attributed to interference that arises when perceptual inputs are physically similar to VWM contents. However, recent work has suggested that explicitly comparing the similarity between VWM contents and new perceptual inputs modulates the size of memory biases above and beyond stimulus-driven effects. Here, we sought to directly investigate this modulation hypothesis by comparing the size of memory biases following explicit comparisons to those induced when new perceptual inputs are ignored (Experiment 1) or maintained in VWM alongside target information (Experiment 2). We found that VWM reports showed larger attraction biases following explicit perceptual comparisons than when new perceptual inputs were ignored or maintained in VWM. An analysis of participants' perceptual comparisons revealed that memory biases were amplified after perceptual inputs were endorsed as similar-but not dissimilar-to one's VWM representation. These patterns were found to persist even after accounting for variability in the physical similarity between the target and perceptual stimuli across trials, as well as the baseline memory precision between the distinct task demands. Together, these findings illustrate a causal role of perceptual comparisons in modulating naturally-occurring memory biases.

Attention rhythmically samples multi-feature objects in working memory

Attention allows us to selectively enhance processing of specific locations or features in our external environment while filtering out irrelevant information. It is currently hypothesized that this is achieved through boosting of relevant sensory signals which biases the competition between neural representations. Recent neurophysiological and behavioral studies revealed that attention is a fundamentally rhythmic process, tightly linked to neural oscillations in frontoparietal networks. Instead of continuously highlighting a single object or location, attention rhythmically alternates between multiple relevant representations at a frequency of 3–8 Hz. However, attention cannot only be directed towards the external world but also towards internal visual working memory (VWM) representations, e.g. when selecting one of several search templates to find corresponding objects in the external world. Two recent studies demonstrate that single-feature objects in VWM are attended in a similar rhythmic fashion as perceived objects. Here we add to the literature by showing that non-spatial retro-cues initiate comparable theta-rhythmic sampling of multi-feature objects in VWM. Our findings add to the converging body of evidence that external and internal visual representations are accessed by similar rhythmic attentional mechanisms and present a potential solution to the binding problem in working memory.

Modulation of similarity on the distraction resistance of visual working memory representation.

Controversy exists regarding the distraction resistance of priority items in visual working memory (VWM). The protection account proposes that high-priority items resist distraction more than low-priority items, while the vulnerability account proposes that distractors impair high-priority items more. We proposed another available resource threshold account: distraction will not impair items if available resources exceed their threshold needed for sufficient processing. Using a change-detection paradigm, we manipulated item priority by color similarity and inserted distractors during VWM retention. We investigated the effect of similarity on distraction resistance of relevant (color) and irrelevant (shape) feature representations (Experiments 1-2), and the neural mechanism of this effect using event-related potentials (ERPs; Experiment 3). Behavioral results showed distractors impaired the accuracy of dissimilar items when relevant features were memorized and of similar items when irrelevant features were memorized under simultaneous presentation of similar and dissimilar items. Moreover, distractors impaired the accuracy of dissimilar items when relevant features were memorized and of both similar and dissimilar items when irrelevant features were memorized under separate presentation of items. ERP results showed a smaller negative slow wave and P2 but larger N2 under the similar condition. Similarity protected relevant features of similar items against distraction by reducing memory load, decreasing attentional resources allocated to distractors, and strengthening inhibition of distractors. However, similarity did not protect irrelevant features of similar items. Our results support the available resource threshold account, suggesting that VWM is a flexible and intelligent system despite its limited capacity.

Forgetting in visual working memory: Internal noise explains decay of feature representations.

The precision of visual working memory (VWM) representations decreases as time passes. It is often assumed that VWM decay is random and caused by internal noise accumulation. However, forgetting in VWM could occur systematically, such that some features deteriorate more rapidly than others. There exist only a few studies testing these two models of forgetting, with conflicting results. Here, decay of features in VWM was thoroughly tested using signal detection theory methods: psychophysical classification images, internal noise estimation, and receiver operant characteristic (ROC). A modified same–different memory task was employed with two retention times (500 and 4000 ms). Experiment 1 investigated VWM decay using a compound grating memory task, and Experiment 2 tested shape memory using radial frequency patterns. Memory performance dropped some 15% with increasing retention time in both experiments. Interestingly, classification images showed virtually indistinguishable weighting of stimulus features at both retention times, suggesting that VWM decay is not feature specific. Instead, we found a 77% increase in stimulus-independent internal noise at the longer retention time. Finally, the slope of the ROC curve plotted as z-scores was shallower at the longer retention time, indicating that the amount of stimulus-independent internal noise increased. Together these findings provide strong support for the idea that VWM decay does not result from a systematic loss of some stimulus features but instead is caused by uniformly increasing random internal noise.

Processing symmetry between visual and auditory spatial representations in updating working memory.

Updating spatial representations in visual and auditory working memory relies on common processes, and the modalities should compete for attentional resources. If competition occurs, one type of spatial information is presumably weighted over the other, irrespective of sensory modality. This study used incompatible spatial information conveyed from two different cue modalities to examine relative dominance in memory updating. Participants mentally manoeuvred a designated target in a matrix according to visual or auditory stimuli that were presented simultaneously, to identify a terminal location. Prior to the navigation task, the relative perceptual saliences of the visual cues were manipulated to be equal, superior, or inferior to the auditory cues. The results demonstrate that visual and auditory information competed for attentional resources, such that visual/auditory guidance was impaired by incongruent cues delivered from the other modality. Although visual bias was generally observed in working-memory navigation, stimuli of relatively high salience interfered with or facilitated other stimuli regardless of modality, demonstrating the processing symmetry of spatial updating in visual and auditory spatial working memory. Furthermore, this processing symmetry can be identified during the encoding of sensory inputs into working-memory representations. The results imply that auditory spatial updating is comparable to visual spatial updating in that salient stimuli receive a high priority when selecting inputs and are used when tracking spatial representations.

Multiple representations in visual working memory can simultaneously guide attention

Multiple representations in visual working memory can simultaneously guide attention

Trial-by-trial mouse trajectory predicts variance in precision across working memory representations: A critical reanalysis of Hao et al. (2021).

Multiple representations in visual working memory (VWM) can vary in mnemonic precision. This inhomogeneity of VWM precision has received some support from recent studies with the whole-report procedure, in which all memory items are recalled in free or forced orders. Recently, Hao et al. (2021, Cognition, 214, 104739) added a novel item-selection stage before each memory recall and found smaller between-trial variance in mouse trajectory during the selection stage in free-recall condition as compared with forced recall, which was taken as evidence for less between-item interference and the resulting precision benefit under free recall. Here, we reanalyzed the original dataset with a different analytic approach and attempted independent hypothesis testing focusing on within-trial trajectory deviations. We found that the direction of trial-by-trial trajectory bias for the first to-be-recalled item was predictive of the relative mnemonic precision of the remaining items. Critically, this relationship was only present for forced recall but not for free recall. Hierarchical Bayesian modeling of recall errors further identified that this relationship was selectively driven by VWM precision. Together, our reanalysis provides evidence for the source of between-item interference and its direct association with variable precision of VWM representations, and further highlights the novel methodological benefits of probing memory decisional processes using mouse trajectory data.

Priority-based transformations of stimulus representation in visual working memory.

How does the brain prioritize among the contents of working memory (WM) to appropriately guide behavior? Previous work, employing inverted encoding modeling (IEM) of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) datasets, has shown that unprioritized memory items (UMI) are actively represented in the brain, but in a "flipped", or opposite, format compared to prioritized memory items (PMI). To acquire independent evidence for such a priority-based representational transformation, and to explore underlying mechanisms, we trained recurrent neural networks (RNNs) with a long short-term memory (LSTM) architecture to perform a 2-back WM task. Visualization of LSTM hidden layer activity using Principal Component Analysis (PCA) confirmed that stimulus representations undergo a representational transformation-consistent with a flip-while transitioning from the functional status of UMI to PMI. Demixed (d)PCA of the same data identified two representational trajectories, one each within a UMI subspace and a PMI subspace, both undergoing a reversal of stimulus coding axes. dPCA of data from an EEG dataset also provided evidence for priority-based transformations of the representational code, albeit with some differences. This type of transformation could allow for retention of unprioritized information in WM while preventing it from interfering with concurrent behavior. The results from this initial exploration suggest that the algorithmic details of how this transformation is carried out by RNNs, versus by the human brain, may differ.

Categorical bias as a crucial parameter in visual working memory: The effect of memory load and retention interval

Visual information can be stored as continuous as well as categorical representations in visual working memory (VWM) to guide subsequent behavior. Yet it is still unclear what determines whether VWM is represented as continuous or categorical information, or as a mix of both. Recent studies have shown that color VWM representations adjust flexibly depending on the number of memory items as well as the duration that these items need to be maintained for. The current study aims to extend and replicate these crucial effects. In a delayed estimation task, participants memorized one to four colored objects presented at different spatial locations, followed by a delay of 100, 500, 1000, or 2000 msec. Next, a probe indicated the location of the color that participants needed to report. We measured the extent to which responses were biased in the direction of prototypical colors. Crucially, we implemented this categorical bias in an extension to the classic mixture model (Zhang & Luck, 2008) in which the center of the error distribution is a crucial parameter that characterizes the extent to which VWM is biased by color categories. We found that VWM shows a strong categorical bias in all cases, and that this bias increases with increasing memory load; strikingly, this effect of memory load on categorical bias is stronger at longer intervals (1000 msec or longer), as compared to shorter intervals, yet it peaks for intermediate memory loads as opposed to the highest memory load. Overall, our results suggest that when visual information needs to be maintained for one second or longer, VWM becomes more reliant on categorical representations as memory load increases.