Items In Visual Working Memory Research Articles

Induced and Evoked Human Electrophysiological Correlates of Visual Working Memory Set-Size Effects at Encoding.

The ability to encode, store, and retrieve visually presented objects is referred to as visual working memory (VWM). Although crucial for many cognitive processes, previous research reveals that VWM strictly capacity limited. This capacity limitation is behaviorally observable in the set size effect: the ability to successfully report items in VWM asymptotes at a small number of items. Research into the neural correlates of set size effects and VWM capacity limits in general largely focus on the maintenance period of VWM. However, we previously reported that neural resources allocated to individual items during VWM encoding correspond to successful VWM performance. Here we expand on those findings by investigating neural correlates of set size during VWM encoding. We hypothesized that neural signatures of encoding-related VWM capacity limitations should be differentiable as a function of set size. We tested our hypothesis using High Density Electroencephalography (HD-EEG) to analyze frequency components evoked by flickering target items in VWM displays of set size 2 or 4. We found that set size modulated the amplitude of the 1st and 2nd harmonic frequencies evoked during successful VWM encoding across frontal and occipital-parietal electrodes. Frontal sites exhibited the most robust effects for the 2nd harmonic (set size 2 > set size 4). Additionally, we found a set-size effect on the induced power of delta-band (1–4 Hz) activity (set size 2 > set size 4). These results are consistent with a capacity limited VWM resource at encoding that is distributed across to-be-remembered items in a VWM display. This resource may work in conjunction with a task-specific selection process that determines which items are to be encoded and which are to be ignored. These neural set size effects support the view that VWM capacity limitations begin with encoding related processes.

Contralateral delay activity predicts the affective consequences of ignoring items in visual working memory

Contralateral delay activity predicts the affective consequences of ignoring items in visual working memory

Memory-based attention capture when multiple items are maintained in visual working memory.

Efficient visual search requires that attention is guided strategically to relevant objects, and most theories of visual search implement this function by means of a target template maintained in visual working memory (VWM). However, there is currently debate over the architecture of VWM-based attentional guidance. We contrasted a single-item-template hypothesis with a multiple-item-template hypothesis, which differ in their claims about structural limits on the interaction between VWM representations and perceptual selection. Recent evidence from van Moorselaar, Theeuwes, and Olivers (2014) indicated that memory-based capture during search, an index of VWM guidance, is not observed when memory set size is increased beyond a single item, suggesting that multiple items in VWM do not guide attention. In the present study, we maximized the overlap between multiple colors held in VWM and the colors of distractors in a search array. Reliable capture was observed when 2 colors were held in VWM and both colors were present as distractors, using both the original van Moorselaar et al. singleton-shape search task and a search task that required focal attention to array elements (gap location in outline square stimuli). In the latter task, memory-based capture was consistent with the simultaneous guidance of attention by multiple VWM representations. (PsycINFO Database Record

Invalid retro-cues can eliminate the retro-cue benefit: Evidence for a hybridized account.

The contents of visual working memory (VWM) are capacity limited and require frequent updating. The retrospective cueing (retro-cueing) paradigm clarifies how directing internal attention among VWM items boosts VWM performance. In this paradigm a cue appears prior to retrieval, but after encoding and maintenance. The retro-cue effect (RCE) refers to superior VWM after valid versus neutral retro-cues. Here we investigated the effect of the invalid retro-cues' inclusion on VWM performance. We conducted 2 pairs of experiments, changing both probe type (recognition and recall) as well as presence and absence of invalid retro-cue trials. Furthermore, to fully characterize these effects over time, we used extended post-retro-cue delay durations. In the first set of experiments, probing VWM using recognition indicated that the RCE remained consistent in magnitude with or without invalid retro-cue trials. In the second set of experiments, VWM was probed with recall. Here, the RCE was eliminated when invalid retro-cues were included. This finer-grained measure of VWM fidelity showed that all items were subject to decay over time. We conclude that the invalid retro-cues impaired the protection of validly cues items, but they remain accessible, suggesting greater concordance with a prioritization account.

In competition for the attentional template: Only a single item in visual working memory can guide attention

In competition for the attentional template: Only a single item in visual working memory can guide attention

The binding pool: A model of shared neural resources for distinct items in visual working memory

Visual working memory (VWM) refers to the ability to encode, store, and retrieve visual information. The two prevailing theories that describe VWM assume that information is stored either in discrete slots or within a shared pool of resources. However, there is not yet a good understanding of the neural mechanisms that would underlie such theories. To address this gap, we provide a computationally realized neural account that uses a pool of shared neurons to store information about one or more distinct stimuli. The binding pool model is a neural network that is essentially a hybrid of the slot and resource theories. It describes how information can be stored and retrieved from a pool of shared resources using a type/token architecture (Bowman & Wyble in Psychological Review 114(1), 38-70, 2007; Kanwisher in Cognition 27, 117-143, 1987; Mozer in Journal of Experimental Psychology: Human Perception and Performance 15(2), 287-303, 1989). The model can store multiple distinct objects, each containing binding links to one or more features. The binding links are stored in a pool of shared resources and, thus, produce mutual interference as memory load increases. Given a cue, the model retrieves a specific object and then reconstructs other features bound to that object, along with a confidence metric. The model can simulate data from continuous report and change detection paradigms and generates testable predictions about the interaction of report accuracy, confidence, and stimulus similarity. The testing of such predictions will help to identify the boundaries of shared resource theories, thereby providing insight into the roles of ensembles and context in explaining our ability to remember visual information.

Understanding age-related reductions in visual working memory capacity: Examining the stages of change detection

Visual working memory (VWM) capacity is reduced in older adults. Research has shown age-related impairments to VWM encoding, but aging is likely to affect multiple stages of VWM. In the present study, we recorded the event-related potentials (ERPs) of younger and older adults during VWM maintenance and retrieval. We measured encoding-stage processing with the P1 component, maintenance-stage processing with the contralateral delay activity (CDA), and retrieval-stage processing by comparing the activity for old and new items (old-new effect). Older adults showed lower behavioral capacity estimates (K) than did younger adults, but surprisingly, their P1 components and CDAs were comparable to those of younger adults. This remarkable dissociation between neural activity and behavior in the older adults indicated that the P1 and CDA did not accurately assess their VWM capacity. However, the neural activity evoked during VWM retrieval yielded results that helped clarify the age-related differences. During retrieval, younger adults showed early old-new effects in frontal and occipital areas and a late central-parietal old-new effect, whereas older adults showed a late right-lateralized parietal old-new effect. The younger adults' early old-new effects strongly resembled an index of perceptual fluency, suggesting that perceptual implicit memory was activated. The activation of implicit memory could have facilitated the younger adults' behavior, and the lack of these early effects in older adults may suggest that they have much lower-resolution memory than do younger adults. From these data, we speculated that younger and older adults store the same number of items in VWM, but that younger adults store a higher-resolution representation than do older adults.

Selective visual processing across competition episodes: a theory of task-driven visual attention and working memory

The goal of this review is to introduce a theory of task-driven visual attention and working memory (TRAM). Based on a specific biased competition model, the ‘theory of visual attention’ (TVA) and its neural interpretation (NTVA), TRAM introduces the following assumption. First, selective visual processing over time is structured in competition episodes. Within an episode, that is, during its first two phases, a limited number of proto-objects are competitively encoded—modulated by the current task—in activation-based visual working memory (VWM). In processing phase 3, relevant VWM objects are transferred via a short-term consolidation into passive VWM. Second, each time attentional priorities change (e.g. after an eye movement), a new competition episode is initiated. Third, if a phase 3 VWM process (e.g. short-term consolidation) is not finished, whereas a new episode is called, a protective maintenance process allows its completion. After a VWM object change, its protective maintenance process is followed by an encapsulation of the VWM object causing attentional resource costs in trailing competition episodes. Viewed from this perspective, a new explanation of key findings of the attentional blink will be offered. Finally, a new suggestion will be made as to how VWM items might interact with visual search processes.

Infants use statistical regularities to chunk items in visual working memory.

Introduction. Infants’ visual working memory (VWM) has a 3-item limit (Feigenson & Carey, 2003), but infants can "chunk" items using perceptually available properties, such as common features or spatial proximity, thereby overcoming that limit (Feigenson & Halberda, 2004; 2008). When such chunking cues are not available, adults can extract statistical regularities between visual arrays presented over time, and use these regularities to more efficiently group items in VWM (Brady, et al, 2009). Here we asked whether 13-month-old infants could also use statistical regularities between objects to increase VWM. Participants & Method. During 10 Familiarization trials, infants (N=21) saw 4 objects (red disk, blue cross, green pentagon, yellow squiggle) placed sequentially on a stage 2 at a time. In the No-Regularity condition, the objects were paired randomly on each Familiarization trial. In the Regularity condition, object identity was yoked such that, across Familiarization trials, the identity of one shape perfectly predicted the identity of the other. Next, infants saw 6 Test Trials in which all 4 objects were sequentially hidden behind an occluder, which was then removed to reveal either all 4 objects (Expected Outcome) or only 3 (Unexpected Outcome), on alternating trials. Results. As predicted by previous findings, infants in the No Regularity condition failed to look longer at the Unexpected Outcome when four objects were hidden and just three were revealed, F(1,10)=0.005, p=n.s.). This finding replicates earlier work demonstrating an upper limit on infants’ VWM. In contrast, infants in the Regularity condition increased their looking to the Unexpected Outcome, F(1,28)=6.37, p=0.024 (see Figure 1). This suggests that seeing statistical regularities between individual objects allowed infants to group or chunk the objects in VWM, and hence to remember more total information about the scene. Conclusions. Infants can chunk items in VWM based on the statistical regularities present as events unfold. Meeting abstract presented at VSS 2013

The contralateral delay activity is insensitive to microsaccades induced by increasing number of items in visual working memory

The contralateral delay activity is insensitive to microsaccades induced by increasing number of items in visual working memory

Retrospective attention enhances visual working memory in the young but not the old: An ERP study

Behavioral evidence from the young suggests spatial cues that orient attention toward task-relevant items in visual working memory (VWM) enhance memory capacity. Whether older adults can also use retrospective cues ("retro-cues") to enhance VWM capacity is unknown. In the current event-related potential (ERP) study, young and old adults performed a VWM task in which spatially informative retro-cues were presented during maintenance. Young but not older adults' VWM capacity benefited from retro-cueing. The contralateral delay activity (CDA) ERP index of VWM maintenance was attenuated after the retro-cue, which effectively reduced the impact of memory load. CDA amplitudes were reduced prior to retro-cue onset in the old only. Despite a preserved ability to delete items from VWM, older adults may be less able to use retrospective attention to enhance memory capacity when expectancy of impending spatial cues disrupts effective VWM maintenance.

A probabilistic model of visual working memory: Incorporating higher order regularities into working memory capacity estimates.

When remembering a real-world scene, people encode both detailed information about specific objects and higher order information like the overall gist of the scene. However, formal models of change detection, like those used to estimate visual working memory capacity, assume observers encode only a simple memory representation that includes no higher order structure and treats items independently from one another. We present a probabilistic model of change detection that attempts to bridge this gap by formalizing the role of perceptual organization and allowing for richer, more structured memory representations. Using either standard visual working memory displays or displays in which the items are purposefully arranged in patterns, we find that models that take into account perceptual grouping between items and the encoding of higher order summary information are necessary to account for human change detection performance. Considering the higher order structure of items in visual working memory will be critical for models to make useful predictions about observers' memory capacity and change detection abilities in simple displays as well as in more natural scenes.

Strategic and automatic effects of visual working memory on attention in visual search

Previous research indicates that visual attention can be automatically captured by sensory inputs that match the contents of visual working memory. However, Woodman and Luck (2007) showed that information in working memory can be used flexibly as a template for either selection or rejection according to task demands. We report two experiments that extend their work. Participants performed a visual search task while maintaining items in visual working memory. Memory items were presented for either a short or long exposure duration immediately prior to the search task. Memory was tested by a change-detection task immediately afterwards. On a random half of trials items in memory matched either one distractor in the search task (Experiment 1) or three (Experiment 2). The main result was that matching distractors speeded or slowed target detection depending on whether memory items were presented for a long or short duration. These effects were more in evidence with three matching distractors than one. We conclude that the influence of visual working memory on visual search is indeed flexible but is not solely a function of task demands. Our results suggest that attentional capture by perceptual inputs matching information in visual working memory involves a fast automatic process that can be overridden by a slower top-down process of attentional avoidance.

Consolidation of multifeature items in visual working memory: Central capacity requirements for visual consolidation

In the present study, we examined whether greater attentional resources are required for consolidating two features (e.g., color and orientation) than for consolidating one feature (e.g., color) in visual working memory (WM). We used a dual-task procedure: Subjects performed a WM task and a secondary probe task, sometimes concurrently. In the WM task, subjects decided whether two displays (containing one to four objects composed of one or two features) were the same or different. In the probe task, subjects made a speeded discrimination response to a tone. Performance in both tasks was impaired when they were performed concurrently; however, performance costs in the tone task were not greater for multi- than for single-feature conditions (when the orientation and conjunction conditions were considered). Results suggested that equivalent attentional resources were necessary for consolidation of single-orientation or multifeature items.

Ensemble statistics influence the representation of items in visual working memory

Ensemble statistics influence the representation of items in visual working memory

Are visual working memory and multiple object tracking limited by a common attention capacity?

About 4 objects can be kept in visual working memory (VWM) and about 4 objects can be visually tracked simultaneously in the Multiple Object Tracking (MOT) task. This resemblance was caught by Cowan (2001) as evidence for a common attention limit underlying both VWM and MOT. Consistent with Cowan's argument, fMRI studies showed that the activation of the posterior parietal cortex increases with the number of items in VWM or MOT. However, it should be noted that MOT is closely associated with location information whereas many VWM tasks demand a comparison of visual properties at the same location in sample and probe displays. So it might be the processing of spatial information that leads to the similarity between VWM and MOT. We tested this possibility in two experiments by examining the dual-task interference of MOT and VWM. In Experiment 1, we found that there was interference between VWM for color-location combination and MOT but no interference between VWM for color-shape combination and MOT. In Experiment 2, we further tested whether tracking more targets would lead to more impairment on location-relevant VWM and found that it depended on speed of objects in MOT. Only under low speed did more targets lead to more impairment. In summary, our results suggest that VWM and MOT might share some capacity-limited resource related to spatial processing, but not a common attention resource.

Effects of familiarity on visual working memory of upright and inverted faces

Aim: Can we hold more familiar items than novel items in visual working memory (VWM)? Previous studies suggest not: familiar polygons are not remembered more efficiently than novel ones and upright letters are not remembered better than inverted letters. In this study we report an exception to this rule when faces of different familiarity were tested. Methods: Our study was revised from Buttle & Raymond (2003) who tested perception of briefly presented and masked faces. To study VWM rather than perception, we presented faces for a long duration (500ms or several seconds) and inserted a long retention interval (1000ms) in a change detection task. VWM for three types of faces was tested: superfamiliar faces of celebrities or one's friends, moderately familiar faces that had been viewed 160 times before, and novel faces. Subjects held 4 faces in VWM while performing an articulatory suppression task. Results: VWM for superfamiliar upright faces (celebrities or friends) was significantly better than that for novel upright faces, but this enhancement was not observed for recently trained upright faces and was eliminated by the inversion of faces. These results extend the superfamiliarity effect observed by Buttle & Raymond (2003) from a perceptual task to a VWM task. Conclusion: Our study suggests VWM can be influenced by long-term visual memory, but only if the set of items that must be distinguished in VWM are subtly different and that subjects have achieved superfamiliarity with the stimuli.

Object perception is selectively slowed by a visually similar working memory load

The capacity of visual working memory has been extensively characterized, but little work has investigated how occupying visual memory influences other aspects of cognition and perception. Here we show a novel effect: maintaining an item in visual working memory slows processing of similar visual stimuli during the maintenance period. Subjects judged the gender of computer rendered faces or the naturalness of body postures while maintaining different visual memory loads. We found that when stimuli of the same class (faces or bodies) were maintained in memory, perceptual judgments were slowed. Interestingly, this is the opposite of what would be predicted from traditional priming. Our results suggest there is interference between visual working memory and perception, caused by visual similarity between new perceptual input and items already encoded in memory.

Familiarity enhances visual working memory for faces.

Although it is intuitive that familiarity with complex visual objects should aid their preservation in visual working memory (WM), empirical evidence for this is lacking. This study used a conventional change-detection procedure to assess visual WM for unfamiliar and famous faces in healthy adults. Across experiments, faces were upright or inverted and a low- or high-load concurrent verbal WM task was administered to suppress contribution from verbal WM. Even with a high verbal memory load, visual WM performance was significantly better and capacity estimated as significantly greater for famous versus unfamiliar faces. Face inversion abolished this effect. Thus, neither strategic, explicit support from verbal WM nor low-level feature processing easily accounts for the observed benefit of high familiarity for visual WM. These results demonstrate that storage of items in visual WM can be enhanced if robust visual representations of them already exist in long-term memory.

Event-Related Potential Measures of Visual Working Memory

Visual working memory is a limited capacity system that temporarily maintains information about objects in the immediate visual environment. Psychophysical experiments have shown that most people are able to actively maintain 3 or 4 items in visual working memory at any point in time. To better understand how this process works and why our working memory capacity is so limited, a variety of neurophysiological approaches have been employed. In recent years, there has been a surge of interest in understanding how visual information is maintained in working memory at the neural level. Single-cell research with nonhuman primates has shown that neuronal firing during the retention period reflects the information that is currently held in working memory. In humans, event-related potentials (ERPs) have been used to examine the maintenance of information in working memory. An event-related potential component, known as the negative slow wave (NSW), has been used to measure the maintenance of information in working memory "online" during a given trial. More recently, another ERP component, the contralateral delay activity (CDA) has been shown to be a fairly specific correlate of the current contents of working memory. This component is sensitive to an individual's working memory capacity and may provide a window into the operations of this central cognitive construct.