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

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.

Cochlear implantation is a well-established method for restoring hearing sensation in individuals with severe to profound hearing loss. It significantly improves verbal communication for many users, despite substantial variability in patients' reports and performance on speech perception tests and quality-of-life outcome measures. Such variability in outcome measures remains several years after implantation and could reflect difficulties in attentional regulation. The current study assessed the ability to use a cue to guide attention internally toward visual or auditory working memory (i.e., reflective attention) in cochlear implant (CI) users. Participants completed a cognitive task called the delayed match-to-sample task in which a visual gradient was presented on a computer screen and a piano tone was presented through speakers simultaneously. A visual cue (i.e., letter A or V) instructed participants to focus attention on the item held in auditory or visual working memory. After a delay following the cue presentation, participants were presented with a probe item and indicated by pressing a button whether it matched the cued item in working memory. CI users and age-matched normal hearing adults showed comparable benefit from having an informative cue relative to an uninformative cue (i.e., letter X). Although CI users have had a history of severe deafness and experience coarse sound information, they were able to retrospectively orient their attention to an item in auditory or visual working memory. These findings suggest that CI users with at least one year of CI experience can successfully regulate attention to a level that is comparable to that of normal hearing individuals.

Visual working memory (VWM) maintains a subset of visual representations that are relevant to ongoing tasks. Visual attention selects a subset of currently visible stimuli for further perceptual processing, memory consolidation, and action. Interactions between VWM and visual attention are central to theories of attention and visual search, with VWM maintaining template properties for the guidance of attention. Here, I discuss three lines of research probing the architecture of this interaction. First, I review work suggesting that the attentional guidance provided by VWM is inherently positive: VWM can enhance the salience of matching stimuli, but it cannot be configured to reduce the salience of matching stimuli. Second, I review evidence regarding representational states in VWM that do and do not interact with attention, concluding that guidance can be flexibly limited to a subset of items in VWM and that this "template" state can encompass multiple objects. Finally, I review recent work indicating that although VWM is structured by objects and locations, these structural properties do not appear to manifest in the guidance of attention, suggesting an architectural division between object coding in VWM and mechanisms of attention guidance.

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.

It is widely accepted that features and locations are represented independently in an initial stage of visual processing. But to what degree are they represented separately at a later stage, after objects enter visual working memory (VWM)? In one of her last studies on VWM, Treisman raised an open question about how people represent locations in VWM, suggesting that locations may be remembered independently of what occupies them. Using photographs of real-world objects, we tested the independence of location memory from object identity in a location change detection task. We introduced changes to object identities between the encoding and test arrays, but instructed participants to treat the objects as placeholders. Three experiments showed that location memory was disrupted when the placeholders changed shape or orientation. The disruption was more noticeable for elongated than for round placeholders and was comparable between real-world objects and rectangles of similar aspect ratio. These findings suggest that location representation is sensitive to the placeholders' geometric properties. Though they contradict the idea that objects are just placeholders in location working memory (WM), the findings support Treisman's proposal that the items in VWM are bound to the global configuration of the memory array.

Although it is well accepted that the formation of visual working memory (VWM) representations from simple static features is a rapid and effortless process that completes within several hundred milliseconds, the storage of motion information in VWM within that time scale can be challenging due to the limited processing capacity of the visual system. Memory formation can also be demanding especially when motion stimuli are visually complex. Here, we investigated whether the formation of VWM representations of motion direction is more gradual than that of static orientation and examined the effects of stimulus complexity on that process. To address these issues, we examined how the number and the precision of stored items in VWM develop over time by using a continuous report procedure. Results showed that while a viewing duration of several seconds was required for the successful storage of multiple motion directions in VWM regardless of motion complexity, the accumulation of memory precision was much slower when the motion stimulus was visually complex (Experiments 1 & 2). Additional experiments showed that the difference in memory performance for simple and complex motion stimuli cannot be explained by differences in signal-to-noise levels of the stimulus (Experiment 3). These results demonstrate remarkable temporal limitations in the formation of VWM representations for dynamic objects, and further show how this process is affected by stimulus properties such as visual complexity and signal-to-noise levels.

The serial and spatially extended nature of many real-world visual tasks suggests the need for control over the content of visual working memory (VWM). We examined the management of VWM in a task that required participants to prioritize individual objects for retention during scene viewing. There were 5 principal findings: (a) Strategic retention of task-relevant objects was effective and was dissociable from the current locus of visual attention; (b) strategic retention was implemented by protection from interference rather than by preferential encoding; (c) this prioritization was flexibly transferred to a new object as task demands changed; (d) no-longer-relevant items were efficiently eliminated from VWM; and (e) despite this level of control, attended and fixated objects were consolidated into VWM regardless of task relevance. These results are consistent with a model of VWM control in which each fixated object is automatically encoded into VWM, replacing a portion of the content in VWM. However, task-relevant objects can be selectively protected from replacement.

A rapidly growing body of work suggests that visual working memory (VWM) is fundamentally action oriented. Consistent with this, we recently showed that attention is more strongly biased by VWM representations of objects when we plan to act on those objects in the future. Using EEG and eye tracking, here, we investigated neurophysiological correlates of the interactions between VWM and action. Participants (n = 36) memorized a shape for a subsequent VWM test. At test, a probe was presented along with a secondary object. In the action condition, participants gripped the actual probe if it matched the memorized shape, whereas in the control condition, they gripped the secondary object. Crucially, during the VWM delay, participants engaged in a visual selection task, in which they located a target as fast as possible. The memorized shape could either encircle the target (congruent trials) or a distractor (incongruent trials). Replicating previous findings, we found that eye gaze was biased toward the VWM-matching shape and, importantly, more so when the shape was directly associated with an action plan. Moreover, the ERP results revealed that during the selection task, future action-relevant VWM-matching shapes elicited (1) a stronger Ppc (posterior positivity contralateral), signaling greater attentional saliency; (2) an earlier PD (distractor positivity) component, suggesting faster suppression; (3) a larger inverse (i.e., positive) sustained posterior contralateral negativity in incongruent trials, consistent with stronger suppression of action-associated distractors; and (4) an enhanced response-locked positivity over left motor regions, possibly indicating enhanced inhibition of the response associated with the memorized item during the interim task. Overall, these results suggest that action planning renders objects in VWM more attentionally salient, supporting the notion of selection-for-action in working memory.

Visual working memory temporarily represents a continuous stream of task-relevant objects as we move through our environment performing tasks. Previous work has identified candidate neural mechanisms of visual working memory storage; however, we do not know which of these mechanisms enable the storage of objects as we sequentially encounter them in our environment. Here, we measured the contralateral delay activity (CDA) and lateralized alpha oscillations as human subjects were shown a series of objects that they needed to remember. The amplitude of CDA increased following the presentation of each to-be-remembered object, reaching asymptote at about three to four objects. In contrast, the concurrently measured lateralized alpha power remained constant with each additional object. Our results suggest that the CDA indexes the storage of objects in visual working memory, whereas lateralized alpha suppression indexes the focusing of attention on the to-be-remembered objects.

How do verbal descriptions affect visual memory over the short and long term? Here we show for the first time that verbal labeling can boost visual memories, but the source of this benefit depends on whether representations are maintained over the short term in visual working memory or over the long term in visual long-term memory. Across three experiments, we contrasted color memory of randomly colored objects when participants labeled (a) the color, (b) the object, or (c) the color-object binding, to memory under an articulatory suppression condition inhibiting labeling. Memory was tested at two time points: after three objects (visual working memory) and at the end of the experiment (visual long-term memory). In Experiment 1, color labeling improved, whereas object labeling impaired, visual working memory in comparison to suppression. Visual long-term memory remained unchanged across conditions. Experiment 2 tested whether this was attributable to poor overall long-term learning by repeating the colored objects over three successive working memory trials. This increased performance over the short and long term, yet labeling did not change learning rate over repetitions or delayed memory performance, showing no long-term memory benefit. In Experiment 3, a labeling benefit was observed when the color-object binding was labeled both over the short and long term. Mixture modeling indicated that color-labeling benefits in visual working memory resulted from an increase of detailed visual memory, whereas long-term memory benefits accrued from categorical representations. Our findings point to dissociations on the role of language in visual working memory and visual long-term memory. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

In daily life, people frequently need to observe dynamic objects and temporarily maintain their representations in visual working memory (VWM). The present study explored the mechanism underlying the binding between perceptual features and locations of dynamic objects in VWM. In three experiments, we measured and compared the memory performance for feature-location binding of multiple dynamic and static objects. The results showed that the feature-location binding was impaired for the dynamic objects compared with the static objects. The impairment persisted when the global spatial configuration of the objects remained intact during the motion, as well as when the binding task was relatively easy, such as binding between single-feature objects and coarse locations. The results indicate that object features and locations are not maintained in VWM as well-integrated object files; rather, the formation of feature-location binding may require additional processes, which are disrupted by the constant change of locations in dynamic circumstances. We propose a consolidation process as possible underlying mechanism, and discuss factors that may influence the strength of feature-location binding in dynamic circumstances.

During scene viewing, visual working memory (VWM) is used to retain information from recently attended and fixated objects. In the present study, I examined whether and how people can strategically control the content of VWM during scene viewing, prioritizing task-relevant objects for retention even as the eyes are directed to subsequent objects. Participants viewed a set of real-world objects presented serially within a 3-D rendered scene. One object in the sequence was cued by a tone as to-beremembered. At the end of the sequence, memory for the visual form of one object was tested. Participants exhibited tight control over the content of VWM, implementing prioritization after the encoding of an object into VWM, protecting that item from subsequent interference. Participants also successfully reallocated protection to subsequent objects, regardless of the duration of prioritization of the original item. Such strategic maintenance of objects in VWM is likely to play an important role in real-world visual behavior, especially when object information must be maintained across shifts of attention and the eyes to other objects (such as when comparing two spatially separated objects). Abstract Approved:________________________________________________________ Thesis Supervisor ________________________________________________________ Title and Department ________________________________________________________ DateApproved:________________________________________________________ Thesis Supervisor ________________________________________________________ Title and Department ________________________________________________________ Date STRATEGIC CONTROL OF VISUAL WORKING MEMORY DURING SCENE VIEWING by Ashleigh Monette Richard A thesis submitted in partial fulfillment of the requirements for the Doctor of Philosophy degree in Psychology in the Graduate College of The University of Iowa

Occipital, parietal, and frontal cortices selectively maintain task-relevant features of multi-feature objects in visual working memory

Human brains are finite, and thus have bounded capacity. An efficient strategy for a capacity-limited agent is to continuously adapt by dynamically reallocating capacity in a task-dependent manner. Here we study this strategy in the context of visual working memory (VWM). People use their VWM stores to remember visual information over seconds or minutes. However, their memory performances are often error-prone, presumably due to VWM capacity limits. We hypothesize that people attempt to be flexible and robust by strategically reallocating their limited VWM capacity based on two factors: (a) the statistical regularities (e.g., stimulus feature means and variances) of the to-be-remembered items, and (b) the requirements of the task that they are attempting to perform. The latter specifies, for example, which types of errors are costly versus irrelevant for task performance. These hypotheses are formalized within a normative computational modeling framework based on rate-distortion theory, an extension of conventional Bayesian approaches that uses information theory to study rate-limited (or capacity-limited) processes. Using images of plants that are naturalistic and precisely controlled, we carried out two sets of experiments. Experiment 1 found that when a stimulus dimension (the widths of plants' leaves) was assigned a distribution, subjects adapted their VWM performances based on this distribution. Experiment 2 found that when one stimulus dimension (e.g., leaf width) was relevant for distinguishing plant categories but another dimension (leaf angle) was irrelevant, subjects' responses in a memory task became relatively more sensitive to the relevant stimulus dimension. Together, these results illustrate the task-dependent robustness of VWM, thereby highlighting the dependence of memory on learning.

Humans process single objects in relation to other simultaneously maintained objects in visual working memory. This interdependence is called spatial configuration. Humans are able to reorganize global spatial configurations into relevant partial configurations. We conducted three experiments investigating the process underlying reorganization by manipulating memory set size and the presence of configurations at retrieval. Participants performed a location change detection task for a single object probed at retrieval. At the beginning of each trial, participants memorized the locations of all objects (set size: 4, 8, 12, or 16). During maintenance, a valid retro cue highlighted the side containing the object probed at retrieval, thus enabling participants to reorganize the memorized global spatial configuration to the partial cued configuration. At retrieval, the object probed was shown together with either all objects (complete configuration; Experiment 1a), the cued objects only (congruent configuration; all Experiments), the non-cued objects only (incongruent configuration, all Experiments) or alone (no configuration; Experiment 1b). We observed reorganization of spatial configurations as indicated by a superior location change detection performance with a congruent partial configuration than an incongruent partial configuration across all three experiments. We also observed an overall decrease in accuracy with increasing set size. Most importantly, however, we did not find evidence for a reliable impairment of reorganization with increasing set size. We discuss these findings with regard to the memory representation underlying spatial configurations.