Attention is required for maintenance of feature binding in visual working memory

Working memory and attention are intimately connected. However, understanding the relationship between the two is challenging. Currently, there is an important controversy about whether objects in working memory are maintained automatically or require resources that are also deployed for visual or auditory attention. Here we investigated the effects of loading attention resources on precision of visual working memory, specifically on correct maintenance of feature-bound objects, using a dual-task paradigm. Participants were presented with a memory array and were asked to remember either direction of motion of random dot kinematograms of different colour, or orientation of coloured bars. During the maintenance period, they performed a secondary visual or auditory task, with varying levels of load. Following a retention period, they adjusted a coloured probe to match either the motion direction or orientation of stimuli with the same colour in the memory array. This allowed us to examine the effects of an attention-demanding task performed during maintenance on precision of recall on the concurrent working memory task. Systematic increase in attention load during maintenance resulted in a significant decrease in overall working memory performance. Changes in overall performance were specifically accompanied by an increase in feature misbinding errors: erroneous reporting of nontarget motion or orientation. Thus in trials where attention resources were taxed, participants were more likely to respond with nontarget values rather than simply making random responses. Our findings suggest that resources used during attention-demanding visual or auditory tasks also contribute to maintaining feature-bound representations in visual working memory—but not necessarily other aspects of working memory.     

Ageing and feature binding in visual working memory: The role of presentation time

A large body of research has clearly demonstrated that healthy ageing is accompanied by an associative memory deficit. Older adults exhibit disproportionately poor performance on memory tasks requiring the retention of associations between items (e.g., pairs of unrelated words). In contrast to this robust deficit, older adults’ ability to form and temporarily hold bound representations of an object's surface features, such as colour and shape, appears to be relatively well preserved. However, the findings of one set of experiments suggest that older adults may struggle to form temporary bound representations in visual working memory when given more time to study objects. However, these findings were based on between-participant comparisons across experimental paradigms. The present study directly assesses the role of presentation time in the ability of younger and older adults to bind shape and colour in visual working memory using a within-participant design. We report new evidence that giving older adults longer to study memory objects does not differentially affect their immediate memory for feature combinations relative to individual features. This is in line with a growing body of research suggesting that there is no age-related impairment in immediate memory for colour-shape binding.     

Location and binding in visual working memory

Visual working memory (VWM) wa sexplored separatelyfor features and for their binding. Features were better recognized when the probes retained the same binding as in the original display, but changing the locations had little effect overall. However, there were strong interactions of location with binding and with matching or new features, suggesting that, when objects are attended, features and locations are spontaneously integrated in VWM. Despite this, when the locations arechanged, features can also be accessed with little decrement, perhaps from separate feature maps. Bindings, on the other hand, are more vulnerable to location changes, suggesting that locations play a central role in the early maintenance and retrieval of bound objects as well as in their initial encoding, at least when verbal coding is prevented. The results qualify past claims about the separation of locations and objects in VWM.     

New perspectives on binding in visual working memory

How does visual working memory (WM) store the binding between different features of a visual object (like colour, orientation, and location), and does memorizing these bindings require additional resources beyond memorizing individual features? These questions have traditionally been addressed by comparing performance across different types of change detection task. More recently, experimental tasks such as analogue (cued) recall, combined with analysis methods including Bayesian hypothesis testing and formal model comparison, have shed new light on the properties of WM. A significant new perspective is that noise in neural representation limits the precision of recall, and several recent models incorporate this view to account for failures of binding in WM. We review the literature on feature binding with a focus on these new developments and discuss their implications for the interpretation of classical findings.     

Selective weighting of action-related feature dimensions in visual working memory

Planning an action primes feature dimensions that are relevant for that particular action, increasing the impact of these dimensions on perceptual processing. Here, we investigated whether action planning also affects the short-term maintenance of visual information. In a combined memory and movement task, participants were to memorize items defined by size or color while preparing either a grasping or a pointing movement. Whereas size is a relevant feature dimension for grasping, color can be used to localize the goal object and guide a pointing movement. The results showed that memory for items defined by size was better during the preparation of a grasping movement than during the preparation of a pointing movement. Conversely, memory for color tended to be better when a pointing movement rather than a grasping movement was being planned. This pattern was not only observed when the memory task was embedded within the preparation period of the movement, but also when the movement to be performed was only indicated during the retention interval of the memory task. These findings reveal that a weighting of information in visual working memory according to action relevance can even be implemented at the representational level during maintenance, demonstrating that our actions continue to influence visual processing beyond the perceptual stage.     

Rapid development of feature binding in visual short-term memory

The binding of object identity (color) and location in visual short-term memory (VSTM) was examined in 6.5- to 12.5-month-old infants (N= 144). Although we previously found that by age 6.5 months, infants can represent both color and location in VSTM, in the present study we observed that 6.5-month-old infants could not remember trivially simple color-location combinations across a 300-ms delay. However, 7.5-month-old infants could bind color and location as effectively as 12.5-month-old infants. Control conditions confirmed that the failure of 6.5-month-old infants was not a result of perceptual or attentional limitations. This rapid development of VSTM binding between 6.5 and 7.5 months occurs during a period of rapid increase in VSTM storage capacity and just after a period of dramatic neuroanatomical changes in parietal cortex. Thus, the ability to bind features and the ability to store multiple objects may both depend on a process that is mediated by posterior parietal cortex and is perhaps related to focused attention.     

Feature binding in visual working memory evaluated by type identification paradigm

Memory for feature binding comprises a key ingredient in coherent object representations. Previous studies have been equivocal about human capacity for objects in the visual working memory. To evaluate memory for feature binding, a type identification paradigm was devised and used with a multiple-object permanence tracking task. Using objects defined by shape and color, observers identified types of changes in feature combinations across an occlusion event, and the effects of object motion and number of switches were investigated. With only one switch, task performance was impaired even under stationary conditions, suggesting highly limited capacity of binding memory. Second switch improved performance only in the stationary condition, suggesting that object motion strongly disrupts feature binding. Further analyses and experiments suggest that improvement by the second switch reflects transition of binding memory by selective attention.     

Coordination in visual working memory

Coordination of mental procedures is considered in terms of control processes (Baddeley, 1989) in visual working memory and appears to be a separable aspect of the demand imposed by cascaded serial processes (Carlson & Lundy, 1992). The main task required subjects to indicate whether symbolically suggested rotations and reflections correctly describe the difference between matrix patterns of filled-in squares within a 3 x 3 grid or between line drawings. Experiments were carried out to show that coordination is a separable component in this transformation task. A marker for coordination is the difference between the time taken to execute two transformations as a whole and the sum of the component transformations in isolation. The separate coordination demand was found in an experiment with matrix patterns mentioned, in an experiment with letter-like line drawings, and also in an experiment that forced subjects to maintain whole-pattern representations. A last experiment checked whether coordination is carried out by an autonomous control unit. There was a self-paced control of serial presentation of transformation symbols instead of a simultaneous presentation of those symbols. This additional external triggering resulted in a substantial decrease in the demand for coordination. Coordination of mental procedures and temporary representations is a fundamental constraint on the use of working-memory processes.     

No evidence of binding items to spatial configuration representations in visual working memory

When detecting changes in visual features (e.g., colour or shape), object locations, represented as points within a configuration, might also be automatically represented in working memory. If the configuration of a scene is represented automatically, the locations of individual items might form part of this representation, irrespective of their relevance to the task. Participants took part in a change-detection task in which they studied displays containing different sets of items (shapes, letters, objects), which varied in their task relevance. Specifically, they were asked to remember the features of two sets, and ignore the third set. During the retention interval, an audio cue indicated which of the to-be-remembered sets would become the target set (having a 50% probability of containing a new feature). At test, they were asked to indicate whether a new feature was present amongst the target set. We measured binding of individual items to the configuration by manipulating the locations of the different sets so that their position in the test display either matched or mismatched their original location in the study display. If items are automatically bound to the configuration, location changes should disrupt performance, even if they were explicitly instructed not to remember the features of that particular set of items. There was no effect on performance of changing the locations of any of the sets between study and test displays, indicating that the configural representation did not enter their decision stage, and therefore that individual item representations are not necessarily bound to the configuration.     

No evidence for binding of items to task-irrelevant backgrounds in visual working memory

When representing visual features such as color and shape in visual working memory (VWM), participants also represent the locations of those features as a spatial configuration of the locations of those features in the display. In everyday life, we encounter objects against some background, yet it is unclear whether the configural representation in memory obligatorily constitutes the entire display, including that (often task-irrelevant) background information. In three experiments, participants completed a change detection task on color and shape; the memoranda were presented in front of uniform gray backgrounds, a textured background (Exp. 1), or a background containing location placeholders (Exps. 2 and 3). When whole-display probes were presented, changes to the objects’ locations or feature bindings impacted memory performance—implying that the spatial configuration of the probes influenced participants’ change decisions. Furthermore, when only a single item was probed, the effect of changing its location or feature bindings was either diminished or completely extinguished, implying that single probes do not necessarily elicit the entire spatial configuration. Critically, when task-irrelevant backgrounds were also presented that may have provided a spatial configuration for the single probes, the effect of location or bindings was not moderated. These findings suggest that although the spatial configuration of a display guides VWM-based recognition, this information does not necessarily always influence the decision process during change detection.     

Similarity effects in visual working memory

Perceptual similarity is an important property of multiple stimuli. Its computation supports a wide range of cognitive functions, including reasoning, categorization, and memory recognition. It is important, therefore, to determine why previous research has found conflicting effects of inter-item similarity on visual working memory. Studies reporting a similarity advantage have used simple stimuli whose similarity varied along a featural continuum. Studies reporting a similarity disadvantage have used complex stimuli from either a single or multiple categories. To elucidate stimulus conditions for similarity effects in visual working memory, we tested memory for complex stimuli (faces) whose similarity varied along a morph continuum. Participants encoded 3 morphs generated from a single face identity in the similar condition, or 3 morphs generated from different face identities in the dissimilar condition. After a brief delay, a test face appeared at one of the encoding locations for participants to make a same/different judgment. Two experiments showed that similarity enhanced memory accuracy without changing the response criterion. These findings support previous computational models that incorporate featural variance as a component of working memory load. They delineate limitations of models that emphasize cortical resources or response decisions.     

Configural encoding in visual feature binding

The role of configural encoding in feature binding was assessed using the change detection paradigm. Experiment 1 studied the relevance of location in colour–shape binding with study–test intervals ranging from 0 to 4100 ms. Location was rendered irrelevant by randomising it from study to test display or was kept unchanged from study to test. Results revealed differences between these two conditions at 0 and 200 ms, but not at 1500, 2800, and 4100 ms, suggesting that location was important for feature binding in the initial stages, but performance at longer study–test intervals was impervious to change in locations. Experiment 2 studied the effect of increasing the study-display duration by comparing performance with display durations of 200, 900, and 1500 ms, at the study test intervals of 0 and 2000 ms. Although, there was a general increase in the level of performance with increasing display duration, the interaction effect obtained in Experiment 1 was replicated. Experiments 3 and 4 studied the effect of sequential presentation of stimuli, otherwise retaining the design and procedure of Experiment 2. Different levels of performance in Experiments 2, 3, and 4 revealed the role of configural encoding in the binding process.     

Binding feature dimensions in visual short-term memory

We explored several possible influences on binding in visual short-term memory (VSTM) performance. The task was to report whether a test object was the same (“old” trials) or different (“new” trials) from any of the sample objects seen a second ago. The objects were composed of two features that varied from continuous to discrete shapes and colors. In “old” trials the test object appeared either in the same or different position. In “new” trials the test object differed along both features, requiring storage of only one feature per object; along one feature, requiring no binding but storage of all features; or it was created by recombining features from the sample, which requires binding. Existing storage hypotheses are unable to explain the similar sensitivity (d′) obtained in the two last conditions when position remained the same and may suggest that links are created between positions and features. Highest sensitivity occurred when the test object remained at the same position, required no binding, and discrete features were used. Object-type × position, and feature combination × position interactions occurred, suggesting different storage modes depending on whether objects change position during retention.     

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.     

视觉工作记忆的过滤效能

过滤效能反映了视觉工作记忆的干扰抑制功能, 研究者可基于储存容量或表征精度对其进行测量, 其神经加工过程主要分为觉察分心项目、过滤启动、实现过滤或储存, 涉及前额叶皮层和基底核、后顶叶皮层的协同作用。过滤效能的变化方向受到年龄、特殊障碍、情绪、认知特点等因素的影响。未来研究仍需解决的问题包括厘清过滤效能与工作记忆容量的关系, 辨明过滤效能的心理实现过程, 探索不同年龄、特殊障碍和职业等群体过滤效能的脑机制以及提升基础研究范式的生态学效度。     

Movement and attention in visual working memory

Three experiments that adopt an interference technique to investigate the involvement of movement in the production of a spatial code are described. Arm movements rather than the more commonly employed eye movements are used to provide initial information about the sorts of movements relevant to the code and to allow an empirical separation of the contributions of movement and attention. The results confirm the interference effects of incompatible movement on the generation of the spatial code and show that movement per se rather than attention to the movement can cause a performance decrement.     

Interactions between visual working memory representations

We investigated whether the representations of different objects are maintained independently in working memory or interact with each other. Observers were shown two sequentially presented orientations and required to reproduce each orientation after a delay. The sequential presentation minimized perceptual interactions so that we could isolate interactions between memory representations per se. We found that similar orientations were repelled from each other whereas dissimilar orientations were attracted to each other. In addition, when one of the items was given greater attentional priority by means of a cue, the representation of the high-priority item was not influenced very much by the orientation of the low-priority item, but the representation of the low-priority item was strongly influenced by the orientation of the high-priority item. This indicates that attention modulates the interactions between working memory representations. In addition, errors in the reported orientations of the two objects were positively correlated under some conditions, suggesting that representations of distinct objects may become grouped together in memory. Together, these results demonstrate that working-memory representations are not independent but instead interact with each other in a manner that depends on attentional priority.     

Auditory and visual spatial working memory

A series of experiments compared short-term memory for object locations in the auditory and visual modalities. The stimulus materials consisted of sounds and pictures presented at different locations in space. Items were presented in pure- or mixed-modality lists of increasing length. At test, participants responded to renewed presentation of the objects by indicating their original position. If two independent modality-specific and resource-limited short-term memories support the remembering of locations, memory performance should be higher in the mixed-modality than in the pure-modality condition. Yet, memory performance was the same for items in both types of list. In addition, responses to the memory load manipulation in both modalities showed very similar declines in performance. The results are interpreted in terms of object files binding object and location information in episodic working memory, independently of the input modality.     

Perceptual organization influences visual working memory

Previous studies have demonstrated that top-down factors can bias the storage of information in visual working memory. However, relatively little is known about the role that bottom-up stimulus characteristics play in visual working memory storage. In the present study, subjects performed a change detection task in which the to-be-remembered objects were organized in accordance with Gestalt grouping principles. When an attention-capturing cue was presented at the location of one object, other objects that were perceptually grouped with the cued object were more likely to be stored in working memory than were objects that were not grouped with the cued object. Thus, objects that are grouped together tend to be stored together, indicating that bottom-up perceptual organization influences the storage of information in visual working memory.