Mapping visual working memory models to a theoretical framework

The body of research on visual working memory (VWM)-the system often described as a limited memory store of visual information in service of ongoing tasks-is growing rapidly. The discovery of numerous related phenomena, and the many subtly different definitions of working memory, signify a challenge to maintain a coherent theoretical framework to discuss concepts, compare models and design studies. A lack of robust theory development has been a noteworthy concern in the psychological sciences, thought to be a precursor to the reproducibility crisis (Oberauer & Lewandowsky, Psychonomic Bulletin & Review, 26, 1596-1618, 2019). I review the theoretical landscape of the VWM field by examining two prominent debates-whether VWM is object-based or feature-based, and whether discrete-slots or variable-precision best describe VWM limits. I share my concerns about the dualistic nature of these debates and the lack of clear model specification that prevents fully determined empirical tests. In hopes of promoting theory development, I provide a working theory map by using the broadly encompassing memory for latent representations model (Hedayati et al., Nature Human Behaviour, 6, 5, 2022) as a scaffold for relevant phenomena and current theories. I illustrate how opposing viewpoints can be brought into accordance, situating leading models of VWM to better identify their differences and improve their comparison. The hope is that the theory map will help VWM researchers get on the same page-clarifying hidden intuitions and aligning varying definitions-and become a useful device for meaningful discussions, development of models, and definitive empirical tests of theories.

Comparing memory capacity across stimuli requires maximally dissimilar foils: Using deep convolutional neural networks to understand visual working memory capacity for real-world objects

The capacity of visual working and visual long-term memory plays a critical role in theories of cognitive architecture and the relationship between memory and other cognitive systems. Here, we argue that before asking the question of how capacity varies across different stimuli or what the upper bound of capacity is for a given memory system, it is necessary to establish a methodology that allows a fair comparison between distinct stimulus sets and conditions. One of the most important factors determining performance in a memory task is target/foil dissimilarity. We argue that only by maximizing the dissimilarity of the target and foil in each stimulus set can we provide a fair basis for memory comparisons between stimuli. In the current work we focus on a way to pick such foils objectively for complex, meaningful real-world objects by using deep convolutional neural networks, and we validate this using both memory tests and similarity metrics. Using this method, we then provide evidence that there is a greater capacity for real-world objects relative to simple colors in visual working memory; critically, we also show that this difference can be reduced or eliminated when non-comparable foils are used, potentially explaining why previous work has not always found such a difference. Our study thus demonstrates that working memory capacity depends on the type of information that is remembered and that assessing capacity depends critically on foil dissimilarity, especially when comparing memory performance and other cognitive systems across different stimulus sets.

The influence of depth on object selection and manipulation in visual working memory within a 3D context

Recent studies have examined whether the internal selection mechanism functions similarly for perception and visual working memory (VWM). However, the process of how we access and manipulate object representations distributed in a 3D space remains unclear. In this study, we utilized a memory search task to investigate the effect of depth on object selection and manipulation within VWM. The memory display consisted of colored items half positioned at the near depth plane and the other half at the far plane. During memory maintenance, the participants were instructed to search for a target representation and update its color. The results showed that under object-based attention (Experiments 1, 3, and 5), the update time was faster for targets at the near plane than for those at the far plane. This effect was absent in VWM when deploying spatial attention (Experiment 2) and in visual search regardless of the type of attention deployed (Experiment 4). The differential effects of depth on spatial and object-based attention in VWM suggest that spatial attention primarily relied on 2D location information irrespective of depth, whereas object-based attention seemed to prioritize memory representations at the front plane before shifting to the back. Our findings shed light on the interaction between depth perception and the selection mechanisms within VWM in a 3D context, emphasizing the importance of ordinal, rather than metric, spatial information in guiding object-based attention in VWM.

The impact of caregiver inhibitory control on infant visual working memory

Visual working memory (VWM) emerges in the first year of life and has far-reaching implications for academic and later life outcomes. Given that caregivers play a significant role in shaping cognitive function in children, it is important to understand how they might impact VWM development as early as infancy. The current study investigated whether caregivers' efficiency of regulating inhibitory control was associated with VWM function in their infants. Eighty-eight caregivers were presented with a Go-NoGo task to assess inhibitory control. An efficiency score was calculated using their behavioural responses. Eighty-six 6-to-10-month-old infants were presented with a preferential looking task to assess VWM function. VWM load was manipulated across one (low load), two (medium load) and three (high load) items. Functional near-infrared spectroscopy was used to record brain activation from caregivers and their infants. We found no direct association between caregiver efficiency and infant VWM behaviour. However, we found an indirect association - caregiver efficiency was linked to infant VWM through left-lateralized fronto-parietal engagement. Specifically, infants with low efficiency caregivers showed decreasing left-lateralized parietal engagement with increasing VWM performance at the medium and high loads compared to infants with high efficiency caregivers, who did not show any load- or performance-dependent modulation. Our findings contribute to a growing body of literature examining the role that caregivers play in early neurocognitive development.

Investigating the effects of perceptual complexity versus conceptual meaning on the object benefit in visual working memory

Previous research has demonstrated greater visual working memory (VWM) performance for real-world objects compared with simple features. Greater amplitudes of the contralateral delay activity (CDA)-a sustained event-related potential measured during the delay period of a VWM task-have also been noted for meaningful stimuli, despite being thought of as a neural marker of a fixed working memory capacity. The current study aimed to elucidate the factors underlying improved memory performance for real-world objects by isolating the relative contributions of perceptual complexity (i.e., number of visual features) and conceptual meaning (i.e., availability of semantic, meaningful features). Participants (N = 22) performed a lateralized VWM task to test their memory of intact real-world objects, scrambled real-world objects and colours. The CDA was measured during both encoding and WM retention intervals (600-1000 ms and 1300-1700 ms poststimulus onset, respectively), and behavioural performance was estimated by using d' (memory strength in a two-alternative forced choice task). Behavioural results revealed significantly better performance within-subjects for real-world objects relative to scrambled objects and colours, with no difference between colours and scrambled objects. The amplitude of the CDA was also largest for intact real-world objects, with no difference in magnitude for scrambled objects and colours, during working memory maintenance. However, during memory encoding, both the colours and intact real-world objects had significantly greater amplitudes than scrambled objects and were comparable in magnitude. Overall, findings suggest that conceptual meaning (semantics) supports the memory benefit for real-world objects.

The role of visual working memory in capacity-limited cross-modal ensemble coding

Ensemble coding refers to the brain's ability to rapidly extract summary statistics, such as average size and average cost, from a large set of visual stimuli. Although ensemble coding is thought to circumvent a capacity limit of visual working memory, we recently observed a VWM-like capacity limit in an ensemble task where observers extracted the average sweetness of groups of food pictures (i.e., they could only integrate information from four out of six available items), thus suggesting the involvement of VWM in this novel form of cross-modal ensemble coding. Therefore, across two experiments we investigated if this cross-modal ensemble capacity limit could be explained by individual differences in VWM processing. To test this, observers performed both an ensemble task and a VWM task, and we determined 1) how much information they integrated into their ensemble percepts, and 2) how much information they remembered from those displays. Interestingly, we found that individual differences in VWM capacity did not explain differences in performance on the ensemble coding task (i.e., high-capacity individuals did not have significantly higher "ensemble abilities" than low-capacity individuals). While our data cannot definitively state whether or not VWM is necessary to perform the ensemble task, we conclude that it is certainly not sufficient to support this cognitive process. We speculate that the capacity limit may be explained by 1) a bottleneck at the perceptual stage (i.e., a failure to process multiple visual features across multiple items, as there are no singular features that convey taste), or 2) the interaction of multiple cognitive systems (e.g., VWM, gustatory working memory, long term memory). Our results highlight the importance of examining ensemble perception across multiple sensory and cognitive domains to provide a clearer picture of the mechanisms underlying everyday behavior.

The Intensity of Internal and External Attention Assessed with Pupillometry

Not only is visual attention shifted to objects in the external world, attention can also be directed to objects in memory. We have recently shown that pupil size indexes how strongly items are attended externally, which was reflected in more precise encoding into visual working memory. Using a retro-cuing paradigm, we here replicated this finding by showing that stronger pupil constrictions during encoding were reflective of the depth of encoding. Importantly, we extend this previous work by showing that pupil size also revealed the intensity of internal attention toward content stored in visual working memory. Specifically, pupil dilation during the prioritization of one among multiple internally stored representations predicted the precision of the prioritized item. Furthermore, the dynamics of the pupillary responses revealed that the intensity of internal and external attention independently determined the precision of internalized visual representations. Our results show that both internal and external attention are not all-or-none processes, but should rather be thought of as continuous resources that can be deployed at varying intensities. The employed pupillometric approach allows to unravel the intricate interplay between internal and external attention and their effects on visual working memory.

Association of white matter microstructural alteration with non-suicidal self-injury behavior and visual working memory in adolescents with borderline personality disorder

BACKGROUND

Non-suicidal self-injurious behavior (NSSI) is the core characteristic of adolescent borderline personality disorder (BPD) and visual working memory is involved in the pathological processes of BPD. This study aimed to investigate alterations in white matter microstructure and their association with NSSI and visual working memory in adolescents with BPD.

METHODS

53 adolescents diagnosed with BPD and 39 healthy controls (HCs) were enrolled. White matter microstructure was assessed with the fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging (DTI). Correlation analysis was performed to assess the association between FA/MD and core features of BPD. A mediation analysis was performed to test whether the effects of white matter alterations on NSSI could be mediated by visual working memory.

RESULTS

Adolescents with BPD showed a reduced FA and an increased MD in the cortical-limbic and cortical-thalamus circuit when compared to the HCs (p < 0.05). Increased MD was positively correlated with NSSI, impulse control and identity disturbance (p < 0.05), and was negatively correlated with the score of visual reproduction. Reserved visual working memory masked the effects of white matter microstructural alterations on NSSI behavior.

CONCLUSIONS

White matter microstructural deficits in the cortical-limbic and cortical-thalamus circuits may be associated with NSSI and visual working memory in adolescents with BPD. Reserved visual working memory may protect against NSSI.

Limitations on flexible allocation of visual short-term memory resources with multiple levels of goal-directed attentional prioritization

Studies suggest that visual short-term memory (VSTM) is a continuous resource that can be flexibly allocated using probabilistic cues that indicate test likelihood (i.e., goal-directed attentional priority to those items). Previous studies using simultaneous cues have not examined this flexible allocation beyond two distinct levels of priority. Moreover, previous studies have not examined whether there are individual differences in the ability to flexibly allocate VSTM resources, as well as whether this ability benefits from practice. The current study used a continuous report procedure to examine whether participants can use up to three levels of attentional priority to allocate VSTM resources via simultaneous probabilistic spatial cues. Three experiments were performed with differing priority levels, cues, and cue presentation times. Group level analysis demonstrated flexible allocation of VSTM resources; however, there was limited evidence that participants could use three goal-directed priority levels. A temporal analysis suggested that task fatigue, rather than practice effects, may interact with item priority. A Bayesian individual-differences analysis revealed that a minority of participants were using three levels of attentional priority, demonstrating that, while possible, it is not the predominant pattern of behaviour. Thus, we provided evidence that flexible allocation to three attention levels is possible under simultaneous cuing conditions for a minority of participants. Flexible allocation to three categories may be interpreted as a skill of high-performing participants akin to high memory capacity.

Learned associations serve as target proxies during difficult but not easy visual search

The target template contains information in memory that is used to guide attention during visual search and is typically thought of as containing features of the actual target object. However, when targets are hard to find, it is advantageous to use other information in the visual environment that is predictive of the target's location to help guide attention. The purpose of these studies was to test if newly learned associations between face and scene category images lead observers to use scene information as a proxy for the face target. Our results showed that scene information was used as a proxy for the target to guide attention but only when the target face was difficult to discriminate from the distractor face; when the faces were easy to distinguish, attention was no longer guided by the scene unless the scene was presented earlier. The results suggest that attention is flexibly guided by both target features as well as features of objects that are predictive of the target location. The degree to which each contributes to guiding attention depends on the efficiency with which that information can be used to decode the location of the target in the current moment. The results contribute to the view that attentional guidance is highly flexible in its use of information to rapidly locate the target.

Sequential encoding aids working memory for meaningful objects' identities but not for their colors

Previous studies have found that real-world objects' identities are better remembered than simple features like colored circles, and this effect is particularly pronounced when these stimuli are encoded one by one in a serial, item-based way. Recent work has also demonstrated that memory for simple features like color is improved if these colors are part of real-world objects, suggesting that meaningful objects can serve as a robust memory scaffold for their associated low-level features. However, it is unclear whether the improved color memory that arises from the colors appearing on real-world objects is affected by encoding format, in particular whether items are encoded sequentially or simultaneously. We test this using randomly colored silhouettes of recognizable versus unrecognizable scrambled objects that offer a uniquely controlled set of stimuli to test color working memory of meaningful versus non-meaningful objects. Participants were presented with four stimuli (silhouettes of objects or scrambled shapes) simultaneously or sequentially. After a short delay, they reported either which colors or which shapes they saw in a two-alternative forced-choice task. We replicated previous findings that meaningful stimuli boost working memory performance for colors (Exp. 1). We found that when participants remembered the colors (Exp. 2) there was no difference in performance across the two encoding formats. However, when participants remembered the shapes and thus identity of the objects (Exp. 3), sequential presentation resulted in better performance than simultaneous presentation. Overall, these results show that different encoding formats can flexibly impact visual working memory depending on what the memory-relevant feature is.

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.

Similarity-based clustering of multifeature objects in visual working memory

This study investigated the similarity-based clustering mechanism of multifeature stimuli, wherein items are separated or grouped based on their similarity in visual working memory (VWM). In particular, we investigated whether clustering occurred at an individual feature level or at an integrated object level when participants encoded objects with multiple features for VWM. To test this, we conducted two experiments in which participants remembered and reconstructed a randomly chosen feature (either color or orientation) from one of five presented stimuli. As a key manipulation, we kept the distributions of the two feature dimensions constant while controlling the conjunction between the two dimensions in two different conditions: congruent conjunction (CC) and incongruent conjunction (IC). With this manipulation, we expected to observe the same number of clusters regardless of the conjunction condition when clustering occurred at the feature level. However, we expected a different number of clusters for CC and IC conditions when clustering occurred at the object level. Across two experiments, we consistently observed evidence that favored feature-level clustering. Nevertheless, we found that the swap error rates increased in the IC condition only when two features had to be encoded in VWM. These results suggest that clustering occurs at the feature level in VWM and that feature-level clustering influences item-level feature binding. Therefore, our study demonstrated the flexibility of representational units in VWM.

VWM-based bias in conscious access can be extended to a new sandwich masking task and real-life stimuli

Previous studies using breaking continuous flash suppression observed that the content of visual working memory (VWM) influences the priority for accessing visual awareness. However, most studies have used simple stimuli, whereas real-life objects are typically more meaningful and contain more perceptual information than simple objects. In this study, we intermixed a delayed match-to-sample task to manipulate the content of VWM, and a breaking repeated masking suppression (b-RMS) task to investigate whether this memory-based effect in conscious access can be extended to a new sandwich masking task and real-life stimuli. The results revealed that memory-congruent objects broke RMS faster than incongruent objects for both simple and real-life objects. Specifically, for simple objects, color-matching targets broke RMS faster than color-mismatching targets, whereas state-matching targets broke RMS faster than state-mismatching targets for real-life objects. These results suggest that the faster detection of VWM-matching over VWM mismatching stimuli-which has been mostly studied using only one type of task (b-CFS) and stimulus (colored shapes)-extends to (1) yet another masking technique (b-RMS) and to (2) a novel stimulus type (real-life objects), providing evidence that memory-based biases in conscious access are a ubiquitous phenomenon.

Serial dependence in facial identity perception and visual working memory

Serial dependence (SD) refers to the effect in which a person's current perceptual judgment is attracted toward recent stimulus history. Perceptual and memory processes, as well as response and decisional biases, are thought to contribute to SD effects. The current study examined the processing stages of SD facial identity effects in the context of task-related decision processes and how such effects may differ from visual working memory (VWM) interactions. In two experiments, participants were shown a series of two sequentially presented face images. In Experiment 1, the two faces were separated by an interstimulus interval (ISI) of 1, 3, 6, or 10 s, and participants were instructed to reproduce the second face after a varying response delay of 0, 1, 3, 6, or 10 s. Results showed that SD effects occurred most consistently at ISI of 1 s and response delays of 1 and 6 s consistent with early and late stages of processing. In Experiment 2, the ISI was held constant at 1 s, and to separate SD from VWM interactions participants were post-cued to reproduce either the first or the second face. When the second face was the target, SD effects again occurred at response delays of 1 and 6 s, but not when the first face was the target. Together, the results demonstrates that SD facial identity effects occur independently of task-related processes in a distinct temporal fashion and suggest that SD and VWM interactions may rely on separate underlying mechanisms.

Assessing the interaction between working memory and perception through time

Content maintained in visual working memory changes concurrent visual processing, suggesting that visual working memory may recruit an overlapping neural representation with visual perception. However, it remains unclear whether visual working memory representations persist as a sensory code through time, or are recoded later into an abstract code. Here, we directly contrasted a temporal decay + visual code account and a temporal decay + abstract code account within the temporal dynamics of the interaction between working memory and perception. By manipulating the ISI (inter-stimulus interval) between working memory encoding and a perceptual discrimination task, we found that task-relevant and therefore actively maintained perceptual information parametrically altered participants' ability to discriminate perceptual stimuli even 4 s after encoding, whereas task-irrelevant information caused only an acutely transient effect. While continuously present, the size of this shift in discrimination thresholds gradually decreased over time. Concomitantly, the size of the bias in working memory reports increased over time. The opposing directions of threshold and bias effects are consistent with the local maintenance of information in perceptual areas, explained by a temporal decay + visual code account. As the maintained representation decays over time, its ability to alter incoming perceptual signals decreases (reduced threshold effects) while its likelihood of being impacted by those same signals increases (increased bias effects). Altogether, these results suggest that the readout of working memory relies on a sensory representation at a cost of increased interference by ongoing perception.

A spatially continuous diffusion model of visual working memory

We present results from five visual working memory (VWM) experiments in which participants were briefly shown between 2 and 6 colored squares. They were then cued to recall the color of one of the squares and they responded by choosing the color on a continuous color wheel. The experiments provided response proportions and response time (RT) measures as a function of angle for the choices. Current VWM models for this task include discrete models that assume an item is either within working memory or not and resource models that assume that memory strength varies as a function of the number of items. Because these models do not include processes that allow them to account for RT data, we implemented them within the spatially continuous diffusion model (SCDM, Ratcliff, 2018) and use the experimental data to evaluate these combined models. In the SCDM, evidence retrieved from memory is represented as a spatially continuous normal distribution and this drives the decision process until a criterion (represented as a 1-D line) is reached, which produces a decision. Noise in the accumulation process is represented by continuous Gaussian process noise over spatial position. The models that fit best from the discrete and resource-based classes converged on a common model that had a guessing component and that allowed the height of the normal memory-strength distribution to vary with number of items. The guessing component was implemented as a regular decision process driven by a flat evidence distribution, a zero-drift process. The combination of choice and RT data allows models that were not identifiable based on choice data alone to be discriminated.

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.

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.

Distinguishing guesses from fuzzy memories: Further evidence for item limits in visual working memory

There is consistent debate over whether capacity in working memory (WM) is subject to an item limit, or whether an unlimited number of items can be held in this online memory system. The item limit hypothesis clearly predicts guessing responses when capacity is exceeded, and proponents of this view have highlighted evidence for guessing in visual working memory tasks. Nevertheless, various models that deny item limits can explain the same empirical patterns by asserting extremely low fidelity representations that cannot be distinguished from guesses. To address this ambiguity, we employed a task for which guess responses elicited a qualitatively distinct pattern from low fidelity memories. Inspired by work from Rouder et al. (2014), we employed an orientation WM task that required subjects to recall the precise orientation of each of six memoranda presented 1 s earlier. The orientation stimuli were created by rotating the position of a "clock hand" inside a circular region that was demarcated by four colored quadrants. Critically, when observers guess with these stimuli, the distribution of responses is biased towards the center of these quadrants, creating a "banded" pattern that cannot be explained by a low precision memory. We confirmed the presence of this guessing pattern using formal model comparisons, and we show that the prevalence of this pattern matches observers' own reports of when they thought they were guessing. Thus, these findings provide further evidence for guessing behaviors predicted by item limit models of WM capacity.

Change localization: A highly reliable and sensitive measure of capacity in visual working memory

The change detection paradigm has been a widely used approach for measuring capacity in visual working memory (WM). In this task, subjects see an array of visual items, followed by a short blank delay and a single test item. Their task is to indicate whether that test item changed relative to the item in the sample array. This task provides reliable measurements of WM capacity that exhibit robust correlations with many outcome variables of interest. Here, we offer a new variant of this task that we call "change localization." This task is closely modeled after the change detection task described above, except that the test array contains the same number of items as the sample array, and one item has always changed in each trial. The subject's task is to select the changed item in the test array. Using both color and shape stimuli, scores in the change localization task were highly correlated with those in the change detection task, suggesting that change localization taps into the same variance in WM ability. Moreover, the change localization task was far more reliable than change detection, such that only half the number of trials were required to achieve robust reliability. To further validate the approach, we replicated known effects from the literature, demonstrating that they could be detected with far fewer trials than with change detection. Thus, change localization provides a highly reliable and sensitive approach for measuring visual working memory capacity.

Control of bottom-up attention in scene cognition contributes to visual working memory performance

Several studies have investigated the relationship between working memory and attention. However, most of the relevant studies so far investigated top-down attention; only a few have examined possible interactions between bottom-up attention and visual working memory. In the present study, we focused on the visual saliency of different parts of pictures as an index of the degree to which one's bottom-up attention can be drawn towards each of them. We administered the Picture Span Test (PST) to investigate whether salient parts of pictures can influence the performance of visual working memory. The task required participants to judge the semantic congruency of objects in pictures and remember specific parts of pictures. In Experiment 1, we calculated a saliency map for the PST stimuli and found that salient but task-irrelevant parts of pictures could evoke intrusion errors. In Experiment 2, we demonstrated that longer gazing time at target areas results in a higher probability of making correct recognition. In addition, frequent gaze fixation and high normalized scan-path saliency values in task-irrelevant areas were associated with intrusion errors. These results suggest that visual information processed by bottom-up attention may affect working memory.

There Is no Theory-Free Measure of "Swaps" in Visual Working Memory Experiments

Visual working memory is highly limited, and its capacity is tied to many indices of cognitive function. For this reason, there is much interest in understanding its architecture and the sources of its limited capacity. As part of this research effort, researchers often attempt to decompose visual working memory errors into different kinds of errors, with different origins. One of the most common kinds of memory error is referred to as a "swap," where people report a value that closely resembles an item that was not probed (e.g., an incorrect, non-target item). This is typically assumed to reflect confusions, like location binding errors, which result in the wrong item being reported. Capturing swap rates reliably and validly is of great importance because it permits researchers to accurately decompose different sources of memory errors and elucidate the processes that give rise to them. Here, we ask whether different visual working memory models yield robust and consistent estimates of swap rates. This is a major gap in the literature because in both empirical and modeling work, researchers measure swaps without motivating their choice of swap model. Therefore, we use extensive parameter recovery simulations with three mainstream swap models to demonstrate how the choice of measurement model can result in very large differences in estimated swap rates. We find that these choices can have major implications for how swap rates are estimated to change across conditions. In particular, each of the three models we consider can lead to differential quantitative and qualitative interpretations of the data. Our work serves as a cautionary note to researchers as well as a guide for model-based measurement of visual working memory processes.

Cerebellar Transcranial Magnetic Stimulation (TMS) Impairs Visual Working Memory

An increasing body of evidence points to the involvement of the cerebellum in cognition. Specifically, previous studies have shown that the superior and inferior portions of the cerebellum are involved in different verbal working memory (WM) mechanisms as part of two separate cerebro-cerebellar loops for articulatory rehearsal and phonological storage mechanisms. In comparison, our understanding of the involvement of the cerebellum in visual WM remains limited. We have previously shown that performance in verbal WM is disrupted by single-pulse transcranial magnetic stimulation (TMS) of the right superior cerebellum. The present study aimed to expand on this notion by exploring whether the inferior cerebellum is similarly involved in visual WM. Here, we used fMRI-guided, double-pulse TMS to probe the necessity of left superior and left inferior cerebellum in visual WM. We first conducted an fMRI localizer using the Sternberg visual WM task, which yielded targets in left superior and inferior cerebellum. Subsequently, TMS stimulation of these regions at the end of the encoding phase resulted in decreased accuracy in the visual WM task. Differences in the visual WM deficits caused by stimulation of superior and inferior left cerebellum raise the possibility that these regions are involved in different stages of visual WM.

Mountains of memory in a sea of uncertainty: Sampling the external world despite useful information in visual working memory

A large part of research on visual working memory (VWM) has traditionally focused on estimating its maximum capacity. Yet, humans rarely need to load up their VWM maximally during natural behavior, since visual information often remains accessible in the external world. Recent work, using paradigms that take into account the accessibility of information in the outside world, has indeed shown that observers utilize only one or two items in VWM before sampling from the external world again. One straightforward interpretation of this finding is that, in daily behavior, much fewer items are memorized than the typically reported capacity limits. Here, we first investigate whether this lower reliance on VWM when information is externally accessible might instead reflect resampling before VWM is actually depleted. To this aim we devised an online task, in which participants copied a model (six items in a 4x4 grid; always accessible) in an adjacent empty 4x4 grid. A key aspect of our paradigm is that we (unpredictably) interrupted participants just before inspection of the model with a 2-alternative-forced-choice (2-AFC) question, probing their VWM content. Critically, we observed above-chance performance on probes appearing just before model inspection. This finding shows that the external world was resampled, despite VWM still containing relevant information. We then asked whether increasing the cost of sampling causes participants to load up more information in VWM or, alternatively, to squeeze out more information from VWM (at the cost of making more errors). To manipulate the cost of resampling, we made it more difficult (specifically, more time-consuming) to access the model. We show that with increased cost of accessing the model (which lead to fewer, but longer model inspections), participants could place more items correctly immediately after sampling, and they kept attempting to place items for longer after their first error. These findings demonstrate that participants both encoded more information in VWM and made attempts to squeeze out more information from VWM when sampling became more costly. We argue that human observers constantly evaluate how certain they are of their VWM contents, and only use that VWM content of which their certainty exceeds a context-dependent "action threshold". This threshold, in turn, depends on the trade-off between the cost of resampling and the benefits of making an action. We argue that considering the interplay between the available VWM contents and a context-dependent action threshold, is key for reconciling the traditional VWM literature with VWM use in our day-to-day behavior.