Feature binding and attention in working memory: a resolution of previous contradictory findings

The role of attention and verbal rehearsal in remembering more valuable item-colour binding

Selectively remembering more valuable information can improve memory efficiency. Such value effects have been observed on long-term memory for item-colour binding, but the possible contributory factors are unclear. The current study explored contributions from attention (Experiment 1) and verbal rehearsal (Experiment 2). Across two experiments, memory was superior for item-colour bindings that were associated with high (relative to low) point values at encoding, both in an immediate test and a delayed re-test. When availability of attentional resources was reduced during encoding, value only influenced immediate and not delayed memory (Experiment 1). This indicates that a transient value effect can be obtained with little attentional resources, but attentional resources are involved in creating a longer lasting effect. When articulatory suppression was implemented during encoding (Experiment 2), value effects were somewhat reduced in the immediate test and abolished in the delayed re-test, suggesting a role for verbal rehearsal in value effects on item-colour binding memory. These patterns of value effects did not interact with encoding presentation format (i.e., sequential vs. simultaneous presentation of objects). Together, these results suggest that attentional resources and verbal rehearsal both contribute to value effects on item-colour binding memory, with varying impacts on the durability of these effects.

The Relation Between Attention and Memory

The relation between attention and memory has long been deemed important for understanding cognition, and it was heavily researched even in the first experimental psychology laboratory by Wilhelm Wundt and his colleagues. Since then, the importance of the relation between attention and memory has been explored in myriad subdisciplines of psychology, and we incorporate a wide range of these diverse fields. Here, we examine some of the practical consequences of this relation and summarize work with various methodologies relating attention to memory in the fields of working memory, long-term memory, individual differences, life-span development, typical brain function, and neuropsychological conditions. We point out strengths and unanswered questions for our own embedded processes view of information processing, which is used to organize a large body of evidence. Last, we briefly consider the relation of the evidence to a range of other theoretical views before drawing conclusions about the state of the field.

Examining the role of attention during feature binding in visuospatial working memory

The current experiments address the enduring debate regarding the role of attention in feature binding in visuospatial working memory by considering the nature of the to-be-bound features, i.e., whether they are intrinsic (integrated within the object, such as its color and shape) or extrinsic (not part of the object, such as its spatial location). Specifically, arrays of different-colored shapes in different locations were followed by probed recall: One feature of the probed object prompted recall of one of its remaining two features (e.g., a shape probe prompts recall of color, with the probe displayed at the center of the screen (i.e., without spatial information)) to test the retention of intrinsic (shape, color) and extrinsic (location) features. During the retention interval, we manipulated attention via disruption (Experiment 1) and retro-cues (Experiment 2) to determine their impacts on binding errors, as estimated from a three-parameter mixture model fit to recall error (i.e., the distance between the target and response). Disrupting central versus peripheral attention in Experiment 1 did not respectively increase extrinsic and intrinsic binding errors as predicted, but disrupting central attention reduced target memory of the extrinsic feature relative to a no-disruption baseline. Guiding attention via extrinsic and intrinsic retro-cues in Experiment 2 did not respectively reduce extrinsic and intrinsic binding errors as predicted, but we observed retro-cue benefits to target memory that did not distinguish between extrinsic and intrinsic features. Thus, this work highlights that attentional resources aid target memory, with no consistent distinction between intrinsic and extrinsic features.

Effects of cholinesterase inhibition on attention and working memory in Lewy body dementias

Cholinesterase inhibitors are frequently used to treat cognitive symptoms in Lewy body dementias (Parkinson's disease dementia and dementia with Lewy bodies). However, the selectivity of their effects remains unclear. In a novel rivastigmine withdrawal design, Parkinson's disease dementia and dementia with Lewy bodies patients were tested twice: once when taking rivastigmine as usual and once when they had missed one dose. In each session, they performed a suite of tasks (sustained attention, simple short-term recall, distractor resistance and manipulating the focus of attention) that allowed us to investigate the cognitive mechanisms through which rivastigmine affects attentional control. Consistent with previous literature, rivastigmine withdrawal significantly impaired attentional efficacy (quicker response latencies without a change in accuracy). However, it had no effects on cognitive control as assessed by the ability to withhold a response (inhibitory control). Worse short-term memory performance was also observed when patients were OFF rivastigmine, but these effects were delay and load independent, likely due to impaired visual attention. In contrast to previous studies that have examined the effects of dopamine withdrawal, cognitively complex tasks requiring control over the contents of working memory (ignoring, updating or shifting the focus of attention) were not significantly impaired by rivastigmine withdrawal. Cumulatively, these data support that the conclusion that cholinesterase inhibition has relatively specific and circumscribed-rather than global-effects on attention that may also affect performance on simple short-term memory tasks, but not when cognitive control over working memory is required. The results also indicate that the withdrawal of a single dose of rivastigmine is sufficient to reveal these impairments, demonstrating that cholinergic withdrawal can be an informative clinical as well as an investigative tool.

Hanging on the telephone: Maintaining visuospatial bootstrapping over time in working memory

Visuospatial bootstrapping (VSB) refers to the phenomenon in which performance on a verbal working memory task can be enhanced by presenting the verbal material within a familiar visuospatial configuration. This effect is part of a broader literature concerning how working memory is influenced by use of multimodal codes and contributions from long-term memory. The present study aimed to establish whether the VSB effect extends over a brief (5-s) delay period, and to explore the possible mechanisms operating during retention. The VSB effect, as indicated by a verbal recall advantage for digit sequences presented within a familiar visuospatial configuration (modelled on the T-9 keypad) relative to a single-location display, was observed across four experiments. The presence and size of this effect changed with the type of concurrent task activity applied during the delay. Articulatory suppression (Experiment 1) increased the visuospatial display advantage, while spatial tapping (Experiment 2) and a visuospatial judgment task (Experiment 3) both removed it. Finally, manipulation of the attentional demands placed by a verbal task also reduced (but did not abolish) this effect (Experiment 4). This pattern of findings demonstrates how provision of familiar visuospatial information at encoding can continue to support verbal working memory over time, with varying demands on modality-specific and general processing resources.

Intentional and incidental odour-colour binding in working memory

The question of how features are bound together in working memory has become a topic of much research in recent years. However, this is typically focused on visual and/or auditory stimuli. The purpose of this study is to apply established feature binding procedures to investigate odour binding in working memory. Across three experiments, memory for intentionally and incidentally formed odour-colour pairings was tested. Experiment 1 showed that following explicit instruction to remember the odour-colour combinations, young adults can recall lists of 3-pairings at levels above that of chance and exhibit a recency advantage for the last pairing. In Experiment 2 participants were asked to prioritise the first pairing in the list or treat all pairings equally. We observed only limited evidence of prioritisation affecting the serial position function. Experiment 3 explored incidental odour-colour binding. Using a yes/no recognition procedure, accuracy did not differ for positive test probes presented in the same (bound) or different (unbound) colour to encoding. This study is one of the first to examine odour-colour binding in working memory and, taking the evidence together, suggests that odour-colour bindings can be formed in working memory; however, functionality may be limited compared to that of visual feature binding.

Chunking in Visual Working Memory: Are Visual Features of Real-World Objects Stored in Chunks?

Are visual features of real-world objects stored as bound units? Previous research has shown that simple visual features (e.g., colored squares or geometric shapes) can be effectively bound together when forming predictable pairs in memory tasks. Through a "memory compression" process, observers can take advantage of these features to compress them into a chunk. However, a recent study found that visual features in real-world objects are stored independently. In the present study, we explored this issue by using drawings of fruits as memory stimuli, presenting four pictures of fruit in separate test trials in which we required observers to remember eight total features (i.e., four colors and four shapes). In the congruent trials, the color of the fruit matched its natural appearance (e.g., a red apple), while in incongruent trials, the color of the fruit mismatched its natural appearance (e.g., a red banana). We paired the shape of the fruits randomly with a color (without replacement). According to chunking theory, if visual features of real-world objects are stored in a chunk, the highest memory capacity should be accompanied by the longest response time in congruent trials due to an extra decoding process required from the chunk. We did find that participants had the highest memory capacity in the congruent condition, but their response times in the congruent condition were significantly faster than in the incongruent condition. Thus, observers did not undergo a decoding process in the congruent condition, and we concluded that visual features in real-world objects are not stored in a chunk.

Central Executive and Target Selection in Visual Working Memory

Abstract The goal of this study was to investigate if the selection of external information for storage in visual working memory requires control by the central executive when the categorization of targets is guided by instructions. The design was experimental 3 (concurrent task) x 2 (instruction). Forty-eight university students saw eight colored shapes, four of them surrounded by square outlines. Memory was assessed using a recognition task. Targets varied with instructions: targets were presented within squares in the first block and outside squares in the second block. There were three concurrent tasks: no task, articulatory suppression, and backward counting. Performance was measured by hits, false alarms, corrected recognition, and sensitivity (A’), compared using within-subject ANOVAs. Results showed a main effect only for concurrent task, with lower performance in the backward counting condition for all measures. These results suggest that the central executive does not control the perceptual filter, corroborating earlier results.

Feature Binding and Working Memory in Children with ADHD: Evidence of Episodic Buffer Impairment

Previous examinations of working memory impairments in children with attention-deficit/hyperactivity disorder (ADHD) have predominantly focused on discreet visuospatial and phonological subsystem processes, as well as the domain-general central executive. The episodic buffer component of working memory, a neurocognitive process that allows for temporary storage and maintenance of bound episodes/features of information, is understudied in ADHD and initial findings have been equivocal. Heterogeneity in previous findings may reflect between-study methodological variability, floor effects unrelated to episodic buffer processes (i.e., excessive central executive demands), and limitations associated with previous investigations' use of novel paradigms. This study examined ADHD-related episodic buffer processing via an established paradigm (Allen et al., 2006) in well-defined groups of children with attention-deficit/hyperactivity disorder (ADHD) and typically developing peers (TD). Seventy-one children (ADHD n = 34, TD n = 37) aged 8-12 years (M = 9.81, SD = 1.50; 32% female) completed two conditions of a computerized working memory task that presented single feature stimuli (color and shape), and a third condition that presented dual-feature stimuli (color/shape binding). Overall, the ADHD group exhibited a large-magnitude deficit during the color/shape binding condition (d = .77), and both groups evinced worse performance accuracy in the color/shape binding condition compared to the single feature color and shape conditions. Collectively, these findings appear to provide evidence that children with ADHD exhibit large magnitude episodic buffer deficits that are not attributable to visuospatial subsystem or domain-general central executive processes.

Cognitive Dimensions of Learning in Children With Problems in Attention, Learning, and Memory

A data-driven, transdiagnostic approach was used to identify the cognitive dimensions linked with learning in a mixed group of 805 children aged 5 to 18 years recognised as having problems in attention, learning and memory by a health or education practitioner. Assessments included phonological processing, information processing speed, short-term and working memory, and executive functions, and attainments in word reading, spelling, and maths. Data reduction methods identified three dimensions of phonological processing, processing speed and executive function for the sample as a whole. This model was comparable for children with and without ADHD. The severity of learning difficulties in literacy was linked with phonological processing skills, and in maths with executive control. Associations between cognition and learning were similar across younger and older children and individuals with and without ADHD, although stronger links between learning-related problems and both executive skills and processing speed were observed in children with ADHD. The results establish clear domain-specific cognitive pathways to learning that distinguish individuals in the heterogeneous population of children struggling to learn.

Fractionating the episodic buffer

The episodic buffer is a putative component of working memory proposed to account for several short-term memory functions, including unexpectedly preserved immediate prose recall by amnesic patients. Over the course of time, this component has increasingly become associated with binding functions. Considering recent findings regarding the performance of both memory-impaired and healthy individuals on the range of tasks purported to require the contribution of the episodic buffer, we suggest that it should be fractionated into two functional systems. One is a schematic store instantiated in brain areas responsible for conceptual and schema representations, which is likely to be hippocampus-independent, and preserved in the face of amnesia. In contrast, short-term maintenance of novel associative binding is likely to require the contribution of the hippocampus and may therefore not be functionally dissociable from long-term memory.

The Association between the Binding Processes of Working Memory and Vascular Risk Profile in Adults

Episodic buffer (EB), a key component of working memory, seems to have a rather complicated function as part of binding processes. Recent papers on the field claim that binding processes of working memory (WM) are assisted by attention and executive functions. On the same page, vascular pathology is gaining more ground as the main underlying cause for many brain pathologies. Hypercholesterolemia, hypertension, obesity, diabetes, lack of exercise and smoking are the most common risk factors that people of all ages suffer from and constitute the main vascular risk factors responsible for a possible decline in executive functions and attention. Thus, this research is an attempt to examine the relation between the binding functions of WM and the existence of vascular risk factors via a computerized test focusing on feature binding. The study comprised adults (n = 229) with and without vascular risk factors. The main tools used were a biomarker questionnaire and a feature binding test (FBT). The results showed that participants who report suffering from one or more vascular risk factors had significantly lower performance on specific subtasks of the FBT in comparison to the participants who were healthy. This allows us to assume that there might be a positive association between feature binding and a vascular risk profile in adults, and such a test could be a useful diagnostic tool for early cognitive impairment due to incipient vascular pathology.

The Influence of Cognitive Load on Distractor-Response Bindings

Binding theories postulate an integration of stimulus and response features into temporary episodic traces or event files. In general, in the visual binding literature, attention is considered to be necessary to feature binding, and a higher cognitive load can lead to worse performance. On the other hand, in stimulus-response binding theories, central attention is not regarded as necessary in binding effects. A possible discrepancy between the visual feature binding findings and the findings in stimulus-response binding studies could lie in the amount of central load implemented, whereas another discrepancy was related to a specific type of process that was manipulated. In the present study, load was manipulated in three levels, such as no load, low load, and high load, and the binding effects were tested under each condition. Load was manipulated by using a secondary task, which was to be carried out simultaneously with the primary task. Additionally, the influence of targeting different working memory processes (maintenance and updating) was examined by varying the time point of the presentation of the secondary task. The results indicate that, under high load, binding effects are observed if memory contents are merely maintained, but not observed when memory contents are actively updated.

Does the presence of more features in a bound representation in working memory require extra object-based attention?

Recent studies have examined the role of attention in retaining bound representations in working memory (WM) and found that object-based attention plays a pivotal role. However, no study has investigated whether maintaining bound representations with more features in WM requires extra object-based attention. We investigated this by examining whether a secondary task consuming object-based attention was more disruptive to the maintenance of bindings in WM when more features were stored per object. We instructed participants to memorize three bound representations in a WM task while manipulating the number of features (two vs. three features) contained in each representation. Moreover, we manipulated whether a secondary task consuming object-based attention was interpolated into the maintenance phase of WM. If extra object-based attention was required after the addition of an extra feature in the bound representation, the secondary task would result in a greater disruption of the three- rather than two-featured binding. In two experiments, we found that the added secondary task significantly impaired the binding performance, but the performance of the two- and three-featured bindings was disrupted to the same extent. These results suggest that the presence of more features in a bound representation in WM does not require extra object-based attention.

Target familiarity and visual working memory do not influence familiarity effect in visual search

Familiarity effect refers to the phenomenon that searching for a novel target among familiar distractors is more efficient than that searching for a familiar target among novel distractors. While the familiarity of distractors is considered as a key role on familiarity effect, the familiarity of targets contribute to this asymmetric visual search is unclear. The present study investigated how target familiarity influences visual search efficiency from the perspective of perceptual load. Experiment 1 using two similar Chinese characters (“甲” and “由”) suggested that searching for a familiar target from familiar distractors is an inefficient search process in Chinese context. Experiment 2 adopted a dual-task paradigm with a visual working memory task to increase the perceptual load and attempt to affect the efficiency of searching a novel target (mirrored “舌”) from familiar distractors (“舌”). Results demonstrated no difference in the search efficiency between single and dual-task conditions. The present study suggests that the familiarity of target does not influence the search efficiency with familiar distractors when involving semantic processing of Chinese characters. Additionally, the interference of extra working memory load would not impair the efficiency of searching target among familiar distractors, supporting the critical effect of distractor familiarity on the efficiency of visual search.

Aging and binding in short-term memory: processes involved in conjunctive and relational binding

In visual short-term binding memory tasks, some studies suggested that aging disrupts relational binding more than conjunctive binding, whereas others report equivalent age-related differences in both types of binding. Yet, demands in controlled resources are potentially the greatest for relational short-term binding. In order to test the hypothesis that aging would affect preferentially tasks demanding in controlled processes, we assessed the contribution of controlled and automatic memory processes to relational and conjunctive short-term binding. Groups of young and older adults studied shape-colour (Exp.1 and 3) or object-colour (Exp.2) pairs in a relational condition in which items were linked to colour patches and a conjunctive condition where colour was integrated into the items. Memory for bindings was tested with a reconstruction task (Exp. 1 and 2) or with a recognition memory task (Exp. 3) under inclusion and exclusion instructions (Process Dissociation Procedure). The three experiments showed that the retrieval of both relational and conjunctive bindings relied primarily on controlled memory processes, the use of which was diminished in older participants. This study brings additional evidence that age-related differences in top-down control processes explain at least partly decreased short-term binding capacities.

Constancy bias: When we "fill in the blanks" of unattended or forgotten stimuli

Our ability to form predictions about the behavior of objects outside our focus of attention and to recognize when those expectations have been violated is critical to our survival. One principle that greatly influences our beliefs about unattended stimuli is that of constancy, or the tendency to assume objects outside our attention have remained constant, and the next time we attend to them they will be unchanged. Although this phenomenon is familiar from research on inattentional blindness, it is currently unclear when constancy is assumed and what conditions are adequate to convince us that unattended stimuli have likely undergone a change while outside of our attentional spotlight. Using a simple change-detection task, we sought to show that unattended stimuli are strongly predisposed to be perceived as unchanging when presented on constant, unchanging backgrounds; however, when stimuli were presented with significant incidental visual activity, participants were no longer biased towards change rejection. We found that participants were far more likely to report that a change had occurred if target presentation was accompanied by salient, incidental visual activity. We take these results to indicate that when an object is not represented in working memory, we use environmental conditions to judge whether or not these items are likely to have undergone a change or remained constant.

Impacts of trait anxiety on visual working memory, as a function of task demand and situational stress

Higher trait anxiety can impair cognitive functioning via attention, but relatively little is known about the impacts on visual working memory. These were investigated using previously validated visual feature binding tasks. In Study 1, participants' memory for visual features (shapes) and feature bindings (coloured shapes) was assessed. Stimulus presentation was simultaneous or sequential, varying attentional demand, and participants were grouped according to trait cognitive anxiety (low, moderate, high). No reliable effect of trait anxiety, either cognitive or somatic, was found on memory accuracy, but moderate trait cognitive anxiety was associated with faster correct response times (i.e. increased efficiency) when stimuli were sequentially presented. In Study 2, the role of situational stress was explored during a simultaneously presented task. Higher trait cognitive and somatic anxiety were both associated with poorer efficiency during both shape and binding memory tasks. Trait somatic anxiety also predicted poorer binding effectiveness (i.e. accuracy), in those reporting higher state cognitive anxiety. Situational stress predicted binding effectiveness, but never interacted with trait anxiety, and was therefore not necessary to observe these trait anxiety-visual working memory relationships. Trait cognitive and somatic anxiety, and situational stress, therefore each influence visual working memory performance.

The attentional boost effect enhances the recognition of bound features in short-term memory

In the Attentional Boost Effect (ABE), images or words encoded with unrelated to-be-responded targets are later remembered better than images or words encoded with to-be-ignored distractors. In the realm of short-term memory, the ABE has been previously shown to enhance the short-term recognition of single-feature stimuli. The present study replicated this finding and extended it to a condition requiring the encoding and retention of colour-shape associations. Across four experiments, participants studied arrays of four coloured squares (the colour-only condition), four gray shapes (the shape-only condition) or four coloured shapes (the binding condition), paired with either a target letter (to which participants had to respond by pressing the spacebar) or a distractor letter (for which no response was required). After a short delay, they were presented with a probe array and asked to decide whether it matched or not the encoded array. Results showed that, in all conditions, the recognition of target-paired arrays was significantly better than the recognition of distractor-paired arrays. These findings suggest that the ABE can enhance feature binding.

The role of attention in retaining the binding of integral features in working memory

Previous studies have suggested that retaining bindings in working memory (WM) requires more object-based attention than retaining constituent features. However, we still need to address the object-based attention hypothesis to determine both the generality (Does the object-based attention hypothesis of binding apply to feature bindings other than those tested?) and the reality (Was the observed effect in previous studies an artifact of the testing process?). We addressed these two issues by focusing on the binding of integral features, which was ignored in previous studies. Integral features can be manipulated independently but cannot be attended to or processed independently of each other, and they are primarily perceived in a more unitary fashion. Consequently, integral-feature bindings should be processed as integrated units without the help of extra object-based attention. We examined whether or not the object-based attention hypothesis applied to integral-feature bindings (generality), and these results enabled us to check the reality of the hypothesis. In line with our prediction, we found that a secondary task consuming object-based attention did not selectively impair the binding performance (Experiments 1, 2, 3, 5, and 7). The absence of selective binding impairment was not attributable to the use of an invalid secondary task (Experiment 4), failure to memorize the binding between length and width (Experiment 6), tapping the incorrect type of attention (Experiment 6), the feasibility of feature categorization (Experiment 7), or poor task performance (Experiment 7). Overall, these results suggest that the object-based attention hypothesis does not fit for the integral-feature bindings, and that the pivotal role of object-based attention reported by previous studies was reliable.

Object-based attention in retaining binding in working memory: Influence of activation states of working memory

It has been suggested that retaining bindings in working memory (WM) requires more object-based attention than retaining constituent features. Recent studies have found that when memorized stimuli are presented sequentially, the most recent stimulus is in a highly accessible privileged state such that it is retained in a relatively automatic and resource-free manner, whereas the other stimuli are in a non-privileged state. The current study investigated whether the activation states of WM modulate the role of object-based attention in retaining bindings in WM. To address this question, we presented three colored shapes sequentially and added a transparent-motion task (Experiment 1) or a mental rotation task (Experiment 2) into the WM maintenance phase to consume object-based attention. We consistently found that consuming object-based attention led to a larger impairment to bindings relative to constituent features, which is independent of the WM activation states, suggesting that object-based attention is critical in retaining bindings in WM across activation states of WM.

Attention and binding in visual working memory: Two forms of attention and two kinds of buffer storage

We review our research on the episodic buffer in the multicomponent model of working memory (Baddeley, 2000), making explicit the influence of Anne Treisman's work on the way our research has developed. The crucial linking theme concerns binding, whereby the individual features of an episode are combined as integrated representations. We summarize a series of experiments on visual working memory that investigated the retention of feature bindings and individual features. The effects of cognitive load, perceptual distraction, prioritization, serial position, and their interactions form a coherent pattern. We interpret our findings as demonstrating contrasting roles of externally driven and internally driven attentional processes, as well as a distinction between visual buffer storage and the focus of attention. Our account has strong links with Treisman's concept of focused attention and aligns with a number of contemporary approaches to visual working memory.

Retaining event files in working memory requires extra object-based attention than the constituent elements

Retaining events containing action-related information in working memory (WM) is vital to daily activities such as action planning and social interaction. During processing of such events, action-related information is bound with other visual elements (e.g., colours) as event files. In this study, we explored whether retaining event files in WM consumes more attention than retaining the constituent elements. Considering that object-based attention underlies the rehearsal of static feature bindings in WM, we hypothesised that object-based attention played a key role in retaining event files in WM. As biological motion (BM) is one of the most frequently observed events in daily life, we employed BM-related event files as the tested stimuli. In separate blocks, we required participants to memorise BM, colours (or locations), or the binding between these elements (i.e., event files). Critically, we added an object-feature report task, which consumed object-based attention, during the WM maintenance phase. We predicted that the added secondary task would lead to larger impairment for BM event files than for the constituent elements. In line with this prediction, Experiments 1 and 2 consistently revealed a selective impairment to BM event files, which could not be attributed to an unbalanced number of elements between memory conditions (Experiment 3), or to the visual processing of a secondary task (Experiment 4). Taken together, these results suggest that object-based attention plays a pivotal role in maintaining event files in WM.

Does maintaining bindings in visual working memory require more attention than maintaining features?

Whether more attention is required for maintaining bindings than maintaining features in visual working memory (VWM) remains an open question. If maintaining bindings in VWM does not require more attention than maintaining features, is it related to the stability of binding representations? In this study, we explored whether maintaining bindings requires more attention than maintaining features for similar and dissimilar objects by inserting a feature report task into the maintenance phase of VWM in Experiments 1 and 2. We also investigated whether the effect of similarity on the attentional requirement for maintaining bindings and features is due to the stability of VWM representations by inserting a suffix during the maintenance phase of VWM in Experiment 3. The results showed that when object-based attention was consumed, bindings were more impaired than features for dissimilar objects but not for similar objects. We also found that the bindings of similar objects were less interfered by the suffix than those of dissimilar objects. Our findings suggest that maintaining bindings does not require more attention than maintaining features when the binding representations are stable in VWM and similarity improves the stability of binding representations.

The role of attention in remembering important item-location associations

When encountering an excess of information, people are able to selectively remember high-value information by strategically allocating attention during the encoding period, termed value-directed remembering. This has been demonstrated in both the episodic verbal and visuospatial memory domains. Importantly, the allocation of attention also plays a crucial role in the binding of identity and location information in visuospatial memory. We examined how taxing attentional resources to various degrees during encoding might affect visuospatial memory and selectivity. Participants studied items paired with point values indicating their value in a grid display and were asked to maximize their point score (a summation of the points associated with correctly remembered information). Participants viewed items under either a sequential or simultaneous presentation format and in either the presence or absence of a secondary tone discrimination task. While participants in the divided attention conditions recalled fewer item-location associations overall, participants in all encoding conditions prioritized high-value information in memory, providing further evidence that selectivity can be maintained even when attentional resources are taxed. However, differences between presentation formats emerged when conducting spatial resolution analyses examining errors. Errors in the simultaneous conditions were only influenced by item value when attention was full during encoding, while errors in the sequential conditions were not influenced by item value, regardless of available attentional resources. The results suggest participants can strategically allocate attention during encoding even under cognitively-demanding conditions and that gist-based visuospatial memory may only be influenced by information importance when adequate attentional resources are available.

Visuospatial bootstrapping: Binding useful visuospatial information during verbal working memory encoding does not require set-shifting executive resources

Immediate serial recall of digits is better when the digits are shown by highlighting them in a familiar array, such as a phone keypad, compared with presenting them serially in a single location, a pattern referred to as "visuospatial bootstrapping." This pattern implies the establishment of temporary links between verbal and spatial working memory, alongside access to information in long-term memory. However, the role of working memory control processes like those implied by the "Central Executive" in bootstrapping has not been directly investigated. Here, we report a study addressing this issue, focusing on executive processes of attentional shifting. Tasks in which information has to be sequenced are thought to be heavily dependent on shifting. Memory for digits presented in keypads versus single locations was assessed under two secondary task load conditions, one with and one without a sequencing requirement, and hence differing in the degree to which they invoke shifting. Results provided clear evidence that multimodal binding (visuospatial bootstrapping) can operate independently of this form of executive control process.

Perceptual Processing is Not Spared During the Attentional Blink

Identification of the second of two targets is impaired when these appear within 500 ms of each other. This phenomenon, known as the attentional blink (AB) is thought to reflect disrupted post-perceptual processing. Yet, decisive empirical support for this claim is lacking. We measured the depth of the AB, while manipulating the second target’s reporting feature. We reasoned that if perceptual processing is unaffected by the blink, all the features of the blinked target should have equal access to working memory. In contrast with this prediction, we found identity and semantic-category reports to be more severely impaired by the blink than color reports, although baseline performance was similar in the two report conditions. These findings suggest that high-level features are more poorly represented in working memory than low-level features during the blink. We conclude that the attentional blink disrupts perceptual processing. Implications for contemporary models of the attentional blink are discussed.

Differential age-related effects on conjunctive and relational visual short-term memory binding

An age-related associative deficit has been described in visual short-term binding memory tasks. However, separate studies have suggested that ageing disrupts relational binding (to associate distinct items or item and context) more than conjunctive binding (to integrate features within an object). The current study directly compared relational and conjunctive binding with a short-term memory task for object-colour associations in 30 young and 30 older adults. Participants studied a number of object-colour associations corresponding to their individual object span level in a relational task in which objects were associated to colour patches and a conjunctive task where colour was integrated into the object. Memory for individual items and for associations was tested with a recognition memory test. Evidence for an age-related associative deficit was observed in the relational binding task, but not in the conjunctive binding task. This differential impact of ageing on relational and conjunctive short-term binding is discussed by reference to two underlying age-related cognitive difficulties: diminished hippocampally dependent binding and attentional resources.

Semantic congruent audiovisual integration during the encoding stage of working memory: an ERP and sLORETA study

Although multisensory integration is an inherent component of functional brain organization, multisensory integration during working memory (WM) has attracted little attention. The present study investigated the neural properties underlying the multisensory integration of WM by comparing semantically related bimodal stimulus presentations with unimodal stimulus presentations and analysing the results using the standardized low-resolution brain electromagnetic tomography (sLORETA) source location approach. The results showed that the memory retrieval reaction times during congruent audiovisual conditions were faster than those during unisensory conditions. Moreover, our findings indicated that the event-related potential (ERP) for simultaneous audiovisual stimuli differed from the ERP for the sum of unisensory constituents during the encoding stage and occurred within a 236-530 ms timeframe over the frontal and parietal-occipital electrodes. The sLORETA images revealed a distributed network of brain areas that participate in the multisensory integration of WM. These results suggested that information inputs from different WM subsystems yielded nonlinear multisensory interactions and became integrated during the encoding stage. The multicomponent model of WM indicates that the central executive could play a critical role in the integration of information from different slave systems.

Executive and perceptual distraction in visual working memory

The contents of visual working memory are likely to reflect the influence of both executive control resources and information present in the environment. We investigated whether executive attention is critical in the ability to exclude unwanted stimuli by introducing concurrent potentially distracting irrelevant items to a visual working memory paradigm, and manipulating executive load using simple or more demanding secondary verbal tasks. Across 7 experiments varying in presentation format, timing, stimulus set, and distractor number, we observed clear disruptive effects of executive load and visual distraction, but relatively minimal evidence supporting an interactive relationship between these factors. These findings are in line with recent evidence using delay-based interference, and suggest that different forms of attentional selection operate relatively independently in visual working memory.

This study demonstrates that the ability to encode and temporarily hold visual information depends both on how active (executive) attentional control is allocated, and whether there are (perceptual) distracting stimuli present in the visual environment. Across seven experiments, memory accuracy was always reduced when participants performed a more demanding task at the same time, and when to-be-remembered targets were accompanied by additional irrelevant items. These two forms of attentional interference appear to have relatively distinct impacts, indicating that we do not necessarily become more vulnerable to perceptual distraction when our executive attention is preoccupied by other tasks. This work provides new insights for the current debate on how working memory and attention might interact.

Retrieval from long-term memory reduces working memory representations for visual features and their bindings

The ability to remember feature bindings is an important measure of the ability to maintain objects in working memory (WM). In this study, we investigated whether both object- and feature-based representations are maintained in WM. Specifically, we tested the hypotheses that retaining a greater number of feature representations (i.e., both as individual features and bound representations) results in a more robust representation of individual features than of feature bindings, and that retrieving information from long-term memory (LTM) into WM would cause a greater disruption to feature bindings. In four experiments, we examined the effects of retrieving a word from LTM on shape and color-shape binding change detection performance. We found that binding changes were more difficult to detect than individual-feature changes overall, but that the cost of retrieving a word from LTM was the same for both individual-feature and binding changes.

Feature binding and the processing of global-local shapes in bilingual and monolingual children

In the present study, we examined the effects of bilingualism and age on a color-shape binding task (assessing visual working memory) and a global-local task (assessing inhibitory processes) in a sample of 55 bilingual and 49 monolingual children 8 and 10 years old. In the color-shape binding task, corrected recognition scores increased in older children; bilingual children performed better than monolinguals in the shape-only condition, but the two groups were equally accurate in the color-only and combination conditions. In the global-local task, accuracy was higher in bilingual than in monolingual children, particularly on incongruent trials; monolingual children showed a strong global precedence effect (higher accuracy in the global than in the local conditions and greater global-to-local interference), whereas bilingual children exhibited a small, but significant, local precedence effect (higher accuracy in the local than in the global conditions and greater local-to-global interference). These findings confirm and extend previous evidence indicating that the bilingualism advantage is more pronounced in working memory tasks involving inhibitory processes.

Feature Binding Deficits in Subjective Cognitive Decline and in Mild Cognitive Impairment

BACKGROUND

Feature binding is a sensitive and specific cognitive marker for Alzheimer's disease (AD). Subjective cognitive decline (SCD) and mild cognitive impairment (MCI) are clinical categories associated with an increased risk for AD.

OBJECTIVE

To investigate whether the SCD and MCI group are impaired with regard to feature binding.

METHODS

The feature binding test was administered to memory clinic patients with either SCD (n = 19, mean MMSE: 29.2) or with MCI (n = 23, mean MMSE: 26.5), and to a group of healthy controls (HC, n = 23, mean MMSE: 29.0). Participants were assessed with the CERAD Plus neuropsychological test battery. Cognitive performance of the three groups was compared by ANCOVA with age, gender and education as covariates and planned contrasts.

RESULTS

Groups differed in the binding condition. Planned contrasts showed significant differences in adjusted means between HC and SCD (p = 0.003), as well as between HC and MCI (p <  0.0001).

DISCUSSION

The feature binding task detects subtle cognitive impairments in participants with SCD, who are unimpaired in traditional neuropsychological testing. This corroborates the use of feature binding tests in preclinical AD studies and suggests that specific cognitive deficits can be found in SCD. Future studies incorporating AD biomarkers and longitudinal follow-up are needed to further establish the clinical utility of feature binding.

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.

A Working Memory System With Distributed Executive Control

Working memory consists of domain-specific storage facilities and domain-general executive control processes. In some working memory theories, these control processes are accounted for via a homunculus, the central executive. In the present article, the author defends a mechanistic view of executive control by adopting the position that executive control is situated in the context of goal-directed behavior to maintain and protect the goal and to select an action to attain the goal. On the basis of findings in task switching and dual tasking, he proposes an adapted multicomponent working memory model in which the central executive is replaced by three interacting components: an executive memory that maintains the task set, a collection of acquired procedural rules, and an engine that executes the procedural rules that match the ensemble of working memory contents. The strongest among the rules that match the ensemble of working memory contents is applied, resulting in changes of the working memory contents or in motor actions. According to this model, goals are attained when the route to the goals is known or can be searched when the route is unknown (problem solving). Empirical evidence for this proposal and new predictions are discussed.

Modality independence of order coding in working memory: Evidence from cross-modal order interference at recall

Working memory researchers do not agree on whether order in serial recall is encoded by dedicated modality-specific systems or by a more general modality-independent system. Although previous research supports the existence of autonomous modality-specific systems, it has been shown that serial recognition memory is prone to cross-modal order interference by concurrent tasks. The present study used a serial recall task, which was performed in a single-task condition and in a dual-task condition with an embedded memory task in the retention interval. The modality of the serial task was either verbal or visuospatial, and the embedded tasks were in the other modality and required either serial or item recall. Care was taken to avoid modality overlaps during presentation and recall. In Experiment 1, visuospatial but not verbal serial recall was more impaired when the embedded task was an order than when it was an item task. Using a more difficult verbal serial recall task, verbal serial recall was also more impaired by another order recall task in Experiment 2. These findings are consistent with the hypothesis of modality-independent order coding. The implications for views on short-term recall and the multicomponent view of working memory are discussed.

Glucose improves object-location binding in visual-spatial working memory

RATIONALE

There is evidence that glucose temporarily enhances cognition and that processes dependent on the hippocampus may be particularly sensitive. As the hippocampus plays a key role in binding processes, we examined the influence of glucose on memory for object-location bindings.

OBJECTIVE

This study aims to study how glucose modifies performance on an object-location memory task, a task that draws heavily on hippocampal function.

METHODS

Thirty-one participants received 30 g glucose or placebo in a single 1-h session. After seeing between 3 and 10 objects (words or shapes) at different locations in a 9 × 9 matrix, participants attempted to immediately reproduce the display on a blank 9 × 9 matrix. Blood glucose was measured before drink ingestion, mid-way through the session, and at the end of the session.

RESULTS

Glucose significantly improves object-location binding (d = 1.08) and location memory (d = 0.83), but not object memory (d = 0.51). Increasing working memory load impairs object memory and object-location binding, and word-location binding is more successful than shape-location binding, but the glucose improvement is robust across all difficulty manipulations. Within the glucose group, higher levels of circulating glucose are correlated with better binding memory and remembering the locations of successfully recalled objects.

CONCLUSIONS

The glucose improvements identified are consistent with a facilitative impact on hippocampal function. The findings are discussed in the context of the relationship between cognitive processes, hippocampal function, and the implications for glucose's mode of action.

The role of working memory and verbal fluency in autobiographical memory in early Alzheimer's disease and matched controls

Retrieval of autobiographical memories (AMs) is important for "sense of self". Previous research and theoretical accounts suggest that working memory (WM) and semantic and phonemic fluency abilities facilitate the hierarchical search for, and reliving of past, personal events in the mind's eye. However, there remains a lack of consensus as to the nature of the relationships between these cognitive functions and the truly episodic aspects of AM. The present study therefore aimed to explore the associations between these variables in a sample with a wide range of cognitive abilities. The study incorporated a between-groups component, and a correlational component with multiple regression. Participants with Alzheimer's disease (n=10) and matched healthy controls (n=10) were assessed on measures of semantic and episodic AM search and retrieval, auditory and spatial WM, and semantic and phonemic fluency. The AD group produced less episodic AM content compared to controls. Semantic fluency predicted episodic AM retrieval independent of age effects but there were no significant relationships between measures of phonemic fluency, WM and episodic AM. The results suggest that the ability to maintain hierarchical search of the semantic knowledge-base is important for truly episodic reliving, and interventions for people with AM impairment might therefore benefit from incorporating structured, individualised external memory-aids to facilitate AM search and retrieval.