Visual short-term memory is not improved by training

A critical question in visual working or short-term memory (VSTM) research is whether the ability to remember briefly presented visual stimuli can be increased. Here we test whether VSTM for locations and shapes is improved by training that allows one to utilize another memory system, visual longterm memory (VLTM). Training was done by repeatedly presenting a subset of memory displays, creating long-term memory traces for these displays. Surprisingly, VSTM performance for repeated displays was not higher than for nonrepeated ones, even though participants recognized repeated displays on a forced-choice test given at the end of the experiment. We suggest that the fidelity of information held by VLTM is inferior to that of information held by VSTM and thus provides no additional benefit over what is extracted on the fly by VSTM.     

Dual-task interference in visual working memory: A limitation in storage capacity but not in encoding or retrieval

The concurrent maintenance of two visual working memory (VWM) arrays can lead to profound interference. It is unclear, however, whether these costs arise from limitations in VWM storage capacity (Fougnie & Maro is, 2006) or from interference between the storage of one visual array and encoding or retrieval of another visual array (Cowan & Morey, 2007). Here, we show that encoding a VWM array does not interfere with maintenance of another VWM array unless the two displays exceed maintenance capacity (Experiments 1 and 2). Moreover, manipulating the extent to which encoding and maintenance can interfere with one another had no discernable effect on dual-task performance (Experiment 2). Finally, maintenance of a VWM array was not affected by retrieval of information from another VWM array (Experiment 3). Taken together, these findings demonstrate that dual-task interference between two concurrent VWM tasks is due to a capacity-limited store that is independent from encoding and retrieval processes.     

Searching while loaded: Visual working memory does not interfere with hybrid search efficiency but hybrid search uses working memory capacity

In “hybrid search” tasks, such as finding items on a grocery list, one must search the scene for targets while also searching the list in memory. How is the representation of a visual item compared with the representations of items in the memory set? Predominant theories would propose a role for visual working memory (VWM) either as the site of the comparison or as a conduit between visual and memory systems. In seven experiments, we loaded VWM in different ways and found little or no effect on hybrid search performance. However, the presence of a hybrid search task did reduce the measured capacity of VWM by a constant amount regardless of the size of the memory or visual sets. These data are broadly consistent with an account in which VWM must dedicate a fixed amount of its capacity to passing visual representations to long-term memory for comparison to the items in the memory set. The data cast doubt on models in which the search template resides in VWM or where memory set item representations are moved from LTM through VWM to earlier areas for comparison to visual items.     

Orienting attention in visual working memory reduces interference from memory probes

Given a changing visual environment, and the limited capacity of visual working memory (VWM), the contents of VWM must be in constant flux. Using a change detection task, the authors show that VWM is subject to obligatory updating in the face of new information. Change detection performance is enhanced when the item that may change is retrospectively cued 1 s after memory encoding and 0.5 s before testing. The retro-cue benefit cannot be explained by memory decay or by a reduction in interference from other items held in VWM. Rather, orienting attention to a single memory item makes VWM more resistant to interference from the test probe. The authors conclude that the content of VWM is volatile unless it receives focused attention, and that the standard change detection task underestimates VWM capacity.     

A core knowledge architecture of visual working memory

Visual working memory (VWM) is widely thought to contain specialized buffers for retaining spatial and object information: a 'spatial-object architecture.' However, studies of adults, infants, and nonhuman animals show that visual cognition builds on core knowledge systems that retain more specialized representations: (1) spatiotemporal representations for object tracking, (2) object identity representations for object recognition, and (3) view-dependent snapshots for place recognition. In principle, these core knowledge systems may retain information separately from one another. Consistent with this hypothesis, this study provides evidence that these three types of information are subject to independent working memory storage limits. These results, combined with those from previous studies, indicate that VWM contains three specialized buffers for retaining spatiotemporal information, object identity information, and snapshot information. Thus, VWM buffers parallel core knowledge systems. This 'core knowledge architecture' links the study of visual working memory to the study of the biological foundations of visual cognition.     

Spatiotemporal configuration of memory arrays as a component of VWM representations

Visual working memory (VWM) has been found to support a very limited representation of visual information and yet relatively little is known about the mechanisms that underlie this important cognitive construct. Prior investigations have revealed that VWM performance can be affected by relatively minor changes in the test method as well as the method of encoding. In the present two experiments, we separately investigated these two factors. The results suggest that sequential object displays can improve VWM performance significantly but that a lack of context relatedness between encoding and retrieval impairs performance. This impairment seems to be caused by a mismatch in the spatiotemporal configuration of the memory and test displays, and, importantly, cannot be compensated by selective attention. These findings suggest that spatiotemporal configuration information may be a fundamental component of the information that is stored in VWM as suggested by a number of influential theories.     

Indirect assessment of visual working memory for simple and complex objects

Previous research has shown that visual search performance is modulated by the current contents in visual working memory (VWM), even when the contents of VWM are irrelevant to the search task. For example, visual search is faster when the target--rather than a distractor--is surrounded by a shape currently held in VWM. This study uses the modulation of visual search by VWM to investigate properties of VWM. Participants wereasked to remember the color or the shape of novel polygons whose "goodness" of figure varied according to Garner's (1962) rotation and reflection transformation principle. During the memory retention interval, participants searched for a tilted line among vertical lines embedded inside colored polygons. Search was faster when the target--rather than a distractor--was enclosed by the remembered polygons. The congruity effect diminished with increasing memory load and decreasing figure goodness. We conclude that congruity effects in visual search can indirectly assess VWM representation strength.     

Investigating the other-race effect in working memory

People have difficulties in remembering other-race faces; this so-called other-race effect (ORE) has been frequently observed in long-term recognition memory (LTM). Several theories argue that the ORE in LTM is caused by differences in earlier processing stages, such as encoding of ingroup and outgroup faces. We test this hypothesis by exploring whether the ORE can already be observed in visual working memory (VWM)—an intermediate system located between encoding processes and LTM storage. In four independent experiments, we observed decreased performance for outgroup faces compared to ingroup faces using three different VWM tasks: an adaptive N-back task, a self-ordered pointing task, and a change detection task. Also, we found that the number of items stored in VWM is smaller for outgroup faces than for ingroup faces. Further, we explored whether performance differences in the change detection task are related to the classic ORE in recognition memory. Our results provide further evidence that the ORE originates during earlier stages of cognitive processing. We discuss that (how) future ORE research may benefit from considering theories and evidence from the VWM literature.     

Distinct capacity limits for attention and working memory: Evidence from attentive tracking and visual working memory paradigms

A hallmark of both visual attention and working memory is their severe capacity limit: People can attentively track only about four objects in a multiple object tracking (MOT) task and can hold only up to four objects in visual working memory (VWM). It has been proposed that attention underlies the capacity limit of VWM. We tested this hypothesis by determining the effect of varying the load of a MOT task performed during the retention interval of a VWM task and comparing the resulting dual-task costs with those observed when a VWM task was performed concurrently with another VWM task or with a verbal working memory task. Instead of supporting the view that the capacity limit of VWM is solely attention based, the results indicate that VWM capacity is set by the interaction of visuospatial attentional, central amodal, and local task-specific sources of processing.     

Task-relevant perceptual features can define categories in visual memory too

Although Konkle, Brady, Alvarez, and Oliva (2010, Journal of Experimental Psychology: General, 139(3), 558) claim that visual long-term memory (VLTM) is organized on underlying conceptual, not perceptual, information, visual memory results from visual search tasks are not well explained by this theory. We hypothesized that when viewing an object, any task-relevant visual information is critical to the organizational structure of VLTM. In two experiments, we examined the organization of VLTM by measuring the amount of retroactive interference created by objects possessing different combinations of task-relevant features. Based on task instructions, only the conceptual category was task relevant or both the conceptual category and a perceptual object feature were task relevant. Findings indicated that when made task relevant, perceptual object feature information, along with conceptual category information, could affect memory organization for objects in VLTM. However, when perceptual object feature information was task irrelevant, it did not contribute to memory organization; instead, memory defaulted to being organized around conceptual category information. These findings support the theory that a task-defined organizational structure is created in VLTM based on the relevance of particular object features and information.     

Internal attention to features in visual short-term memory guides object learning

Attending to objects in the world affects how we perceive and remember them. What are the consequences of attending to an object in mind? In particular, how does reporting the features of a recently seen object guide visual learning? In three experiments, observers were presented with abstract shapes in a particular color, orientation, and location. After viewing each object, observers were cued to report one feature from visual short-term memory (VSTM). In a subsequent test, observers were cued to report features of the same objects from visual long-term memory (VLTM). We tested whether reporting a feature from VSTM: (1) enhances VLTM for just that feature (practice-benefit hypothesis), (2) enhances VLTM for all features (object-based hypothesis), or (3) simultaneously enhances VLTM for that feature and suppresses VLTM for unreported features (feature-competition hypothesis). The results provided support for the feature-competition hypothesis, whereby the representation of an object in VLTM was biased towards features reported from VSTM and away from unreported features (Experiment 1). This bias could not be explained by the amount of sensory exposure or response learning (Experiment 2) and was amplified by the reporting of multiple features (Experiment 3). Taken together, these results suggest that selective internal attention induces competitive dynamics among features during visual learning, flexibly tuning object representations to align with prior mnemonic goals.     

Associative learning improves visual working memory performance

The ability to remember visual stimuli over a short delay period is limited by the small capacity of visual working memory (VWM). Here the authors investigate the role of learning in enhancing VWM. Participants saw 2 spatial arrays separated by a 1-s interval. The 2 arrays were identical except for 1 location. Participants had to detect the difference. Unknown to the participants, some spatial arrays would repeat once every dozen trials or so for up to 32 repetitions. Spatial VWM performance increased significantly when the same location changed across display repetitions, but not at all when different locations changed from one display repetition to another. The authors suggest that a major role of learning in VWM is to mediate which information gets retained, rather than to directly increase VWM capacity.     

The perceptual root of object-based storage: an interactive model of perception and visual working memory

Mainstream theories of visual perception assume that visual working memory (VWM) is critical for integrating online perceptual information and constructing coherent visual experiences in changing environments. Given the dynamic interaction between online perception and VWM, we propose that how visual information is processed during visual perception can directly determine how the information is going to be selected, consolidated, and maintained in VWM. We demonstrate the validity of this hypothesis by investigating what kinds of perceptual information can be stored as integrated objects in VWM. Three criteria for object-based storage are introduced: (a) automatic selection of task-irrelevant features, (b) synchronous consolidation of multiple features, and (c) stable maintenance of feature conjunctions. The results show that the outputs of parallel perception meet all three criteria, as opposed to the outputs of serial attentive processing, which fail all three criteria. These results indicate that (a) perception and VWM are not two sequential processes, but are dynamically intertwined; (b) there are dissociated mechanisms in VWM for storing information identified at different stages of perception; and (c) the integrated object representations in VWM originate from the "preattentive" or "proto" objects created by parallel perception. These results suggest how visual perception, attention, and VWM can be explained by a unified framework.     

Memory-based attentional capture by colour and shape contents in visual working memory

Current theories assume that there is substantial overlap between visual working memory (VWM) and visual attention functioning, such that active representations in VWM automatically act as an attentional set, resulting in attentional biases towards objects that match the mnemonic content. Most evidence for this comes from visual search tasks in which a distractor similar to the memory interferes with the detection of a simultaneous target. Here we provide additional evidence using one of the most popular paradigms in the literature for demonstrating an active attentional set: The contingent spatial orienting paradigm of Folk and colleagues. This paradigm allows memory-based attentional biases to be more directly attributed to spatial orienting. Experiment 1 demonstrated a memory-contingent spatial attention effect for colour but not for shape contents of VWM. Experiment 2 tested the hypothesis that the placeholders used for spatial cueing interfered with the shape processing, and showed that memory-based attentional capture for shape returned when placeholders were removed. The results of the present study are consistent with earlier findings from distractor interference paradigms, and provide additional evidence that biases in spatial orienting contribute to memory-based influences on attention.     

Flexible representations in visual working memory and interactions with long‐term learning: Commentary on the special issue

This special issue of the British Journal of Psychology brings together cutting edge research on a range of topics in visual working memory (VWM). In this commentary, we attempt to summarize common themes in current VWM research exemplified in this issue. The articles include several reviews of important topics as well as empirical papers covering three main themes. The first concerns the nature of mental representations of memoranda in the commonly used delayed estimation task, where both fine‐grained and broad categorical details appear to be represented, and their susceptibility to interference. The second concerns interactions between VWM representations, both those that produce individuation of representations and those that create an overarching ensemble structure. Finally, the third main topic concerns the use of VWM during visual search and in the learning of repeated configurations in search displays. The work presented here, and other work in the field, points to a rich interplay between representations in VWM but also between VWM and information in long‐term memory. Opportunities for further investigation are highlighted throughout.     

视觉工作记忆负载类型对注意选择的影响

通过操纵Flanker任务相对于视觉工作记忆任务的呈现位置, 探讨在视觉工作记忆编码和保持阶段, 精度负载和容量负载对注意选择的影响。行为结果发现, Flanker任务呈现位置和视觉工作记忆负载类型影响注意选择; ERP结果发现, 在保持阶段, 当搜索目标和干扰项不一致时, 负载类型影响N2成分。研究表明, 在编码阶段, 视觉工作记忆负载主要通过占用更多知觉资源降低干扰效应, 支持知觉负载理论; 而在保持阶段, 当Flanker任务位于记忆项内部时, 两类负载在工作记忆表征过程中不同的神经活动导致投入到注意选择的认知控制资源不同, 可能是两类负载影响保持阶段注意选择的机制。     

Tuning perception: Visual working memory biases the quality of visual awareness

Studies of consciousness reveal that it is possible to manipulate subjective awareness of a visual stimulus. For example, items held in visual working memory (VWM) that match target features increase the speed with which the target reaches visual awareness. To examine the effect of VWM on perception, previous studies have mainly used coarse measures of awareness, such as present/absent or forced-choice judgments. These methods can reveal whether or not an individual has seen an item, but they do not provide information about the quality with which the item was seen. Using continuous report methods it has been shown that the fidelity of a perceived item can be affected by whether or not that item is masked. In the present study, we used an object-substitution masking task to examine whether items held in VWM would influence the quality with which a masked target reached awareness, or whether the threshold for awareness was instead affected by stimuli held in memory. We observed that targets matching the contents of VWM were recalled with greater precision compared to items that did not match the contents of VWM. Importantly, this effect occurred without affecting the likelihood of the target being perceived. These results suggest that VWM plays a greater role in modulating the fidelity of perceived representations than in lowering the overall threshold of awareness.     

The aftermath of memory retrieval for recycling visual working memory representations

We examined the aftermath of accessing and retrieving a subset of information stored in visual working memory (VWM)—namely, whether detection of a mismatch between memory and perception can impair the original memory of an item while triggering recognition-induced forgetting for the remaining, untested items. For this purpose, we devised a consecutive-change detection task wherein two successive testing probes were displayed after a single set of memory items. Across two experiments utilizing different memory-testing methods (whole vs. single probe), we observed a reliable pattern of poor performance in change detection for the second test when the first test had exhibited a color change. The impairment after a color change was evident even when the same memory item was repeatedly probed; this suggests that an attention-driven, salient visual change made it difficult to reinstate the previously remembered item. The second change detection, for memory items untested during the first change detection, was also found to be inaccurate, indicating that recognition-induced forgetting had occurred for the unprobed items in VWM. In a third experiment, we conducted a task that involved change detection plus continuous recall, wherein a memory recall task was presented after the change detection task. The analyses of the distributions of recall errors with a probabilistic mixture model revealed that the memory impairments from both visual changes and recognition-induced forgetting are explained better by the stochastic loss of memory items than by their degraded resolution. These results indicate that attention-driven visual change and recognition-induced forgetting jointly influence the “recycling” of VWM representations.     

Encoding strategies in self-initiated visual working memory

During a typical day, visual working memory (VWM) is recruited to temporarily maintain visual information. Although individuals often memorize external visual information provided to them, on many other occasions they memorize information they have constructed themselves. The latter aspect of memory, which we term self-initiated WM, is prevalent in everyday behavior but has largely been overlooked in the research literature. In the present study we employed a modified change detection task in which participants constructed the displays they memorized, by selecting three or four abstract shapes or real-world objects and placing them at three or four locations in a circular display of eight locations. Half of the trials included identical targets that participants could select. The results demonstrated consistent strategies across participants. To enhance memory performance, participants reported selecting abstract shapes they could verbalize, but they preferred real-world objects with distinct visual features. Furthermore, participants constructed structured memory displays, most frequently based on the Gestalt organization cue of symmetry, and to a lesser extent on cues of proximity and similarity. When identical items were selected, participants mostly placed them in close proximity, demonstrating the construction of configurations based on the interaction between several Gestalt cues. The present results are consistent with recent findings in VWM, showing that memory for visual displays based on Gestalt organization cues can benefit VWM, suggesting that individuals have access to metacognitive knowledge on the benefit of structure in VWM. More generally, this study demonstrates how individuals interact with the world by actively structuring their surroundings to enhance performance.     

Action relevance induces an attentional weighting of representations in visual working memory

Information maintained in visual working memory (VWM) can be strategically weighted according to its task-relevance. This is typically studied by presenting cues during the maintenance interval, but under natural conditions, the importance of certain aspects of our visual environment is mostly determined by intended actions. We investigated whether representations in VWM are also weighted with respect to their potential action relevance. In a combined memory and movement task, participants memorized a number of items and performed a pointing movement during the maintenance interval. The test item in the memory task was subsequently presented either at the movement goal or at another location. We found that performance was better for test items presented at a location that corresponded to the movement goal than for test items presented at action-irrelevant locations. This effect was sensitive to the number of maintained items, suggesting that preferential maintenance of action relevant information becomes particularly important when the demand on VWM is high. We argue that weighting according to action relevance is mediated by the deployment of spatial attention to action goals, with representations spatially corresponding to the action goal benefitting from this attentional engagement. Performance was also better at locations next to the action goal than at locations farther away, indicating an attentional gradient spreading out from the action goal. We conclude that our actions continue to influence visual processing at the mnemonic level, ensuring preferential maintenance of information that is relevant for current behavioral goals.