Objects In Visual Working Memory Research Articles

Similarity-based clustering of multifeature objects in visual working memory.

This study investigated the similarity-based clustering mechanism of multifeature stimuli, wherein items are separated or grouped based on their similarity in visual working memory (VWM). In particular, we investigated whether clustering occurred at an individual feature level or at an integrated object level when participants encoded objects with multiple features for VWM. To test this, we conducted two experiments in which participants remembered and reconstructed a randomly chosen feature (either color or orientation) from one of five presented stimuli. As a key manipulation, we kept the distributions of the two feature dimensions constant while controlling the conjunction between the two dimensions in two different conditions: congruent conjunction (CC) and incongruent conjunction (IC). With this manipulation, we expected to observe the same number of clusters regardless of the conjunction condition when clustering occurred at the feature level. However, we expected a different number of clusters for CC and IC conditions when clustering occurred at the object level. Across two experiments, we consistently observed evidence that favored feature-level clustering. Nevertheless, we found that the swap error rates increased in the IC condition only when two features had to be encoded in VWM. These results suggest that clustering occurs at the feature level in VWM and that feature-level clustering influences item-level feature binding. Therefore, our study demonstrated the flexibility of representational units in VWM.

The facilitating effect of identical objects in visual working memory.

According to the associative network of memory representations proposed by embedded processes models, the links between related memory representations were automatically established, which rendered these representations more easily activated. The present study adopted color recall tasks to explore whether the memory performance of identical objects was enhanced via the strengthening links between them, producing facilitating effect of identical objects. In Experiment 1, the number of identical items was manipulated. The results evidenced the facilitating effect, which was positively related to the number of identical objects. Experiment 2 modulated the spatial location of identical objects, which suggested that the facilitating effect was absent when two pairs of identical objects were located diagonally. Furthermore, Experiment 3 suggested that the facilitating effect was observed for the identical items which were presented in the second and fourth quadrants, rather than the first and third quadrants. Together, these results evidenced the facilitating effect of identical objects, which, however, was affected by spatial bias.

Perceptual redundancy and semantic grouping effects among real-world objects in visual working memory come from different processes

Perceptual redundancy and semantic grouping effects among real-world objects in visual working memory come from different processes

Attention rhythmically samples multi-feature objects in working memory

Attention allows us to selectively enhance processing of specific locations or features in our external environment while filtering out irrelevant information. It is currently hypothesized that this is achieved through boosting of relevant sensory signals which biases the competition between neural representations. Recent neurophysiological and behavioral studies revealed that attention is a fundamentally rhythmic process, tightly linked to neural oscillations in frontoparietal networks. Instead of continuously highlighting a single object or location, attention rhythmically alternates between multiple relevant representations at a frequency of 3–8 Hz. However, attention cannot only be directed towards the external world but also towards internal visual working memory (VWM) representations, e.g. when selecting one of several search templates to find corresponding objects in the external world. Two recent studies demonstrate that single-feature objects in VWM are attended in a similar rhythmic fashion as perceived objects. Here we add to the literature by showing that non-spatial retro-cues initiate comparable theta-rhythmic sampling of multi-feature objects in VWM. Our findings add to the converging body of evidence that external and internal visual representations are accessed by similar rhythmic attentional mechanisms and present a potential solution to the binding problem in working memory.

I can look for it! Modulation of a concurrent Visual Working Memory task in Visual Search in development.

Daily classroom activities that require children to perform visual search (VS) tasks are common across all educational levels: from searching for a missing piece of a puzzle in kindergarten to solving equations in college. However, VS tasks are often not performed in isolation, but rather students are maintaining information related to an ongoing task that loads working memory (WM). Unfortunately, it is still unclear how these processes interact and evolve in development. The present work aims to study how a concurrent visual WM (VWM) load can modulate VS performance based on the Developmental Model of Endogenous Mental Attention (Pascual-Leone and Johnson, 1999, 2005, 2021). A sample of kindergarten, elementary (2nd and 4th grades), middle school (6th grade), and college students looked for real-world photorealistic targets while maintaining similar objects in VWM in a dual-task paradigm. VWM load was manipulated using high and low memory load conditions. Additionally, looking for potential modulations related to individual differences, we studied the relationship between IQ, VWM span, and executive functions with VS efficiency. Finally, we also registered reported measures of potential strategies employed during the VS task. The results from a large sample of 147 participants between 5 and 25 years old revealed that even the youngest children could efficiently perform a VS task with a concurrent VWM load, replicating previous results found in adulthood. However, we found a slight increase in false alarms and commission errors when memory was highly loaded for all the participants regardless of age. As expected, we found positive correlations between VS efficiency and IQ and VWM span measures. Interestingly, the proportion of participants who used tracking organization strategies increased with age in all cases. However, although cognitive strategies to remember the target became more complex as age increased, it was only significant under the low VWM load conditions. The results seem relevant to understanding the development of VS based on the Model of Endogenous Mental Attention and the design of training programs to improve attention. The implications in educational contexts are discussed and are especially relevant for students with learning disabilities or attention problems.

Meaningful stimuli inflate the role of proactive interference in visual working memory.

The use of meaningful daily objects in visual working memory (VWM) tasks revealed two uncharacteristic findings: enlarged memory capacity, and strong proactive interference (PI), which was previously believed to play only a modest role in VWM. To disassociate the roles of meaning and visual complexity in these effects, a set of stimuli composed of meaningful daily objects was compared to visually similar meaningless sets. These sets were included in a Repeated (PI-prone) condition in which stimuli were repeatedly drawn from a limited set of items, and in a Unique (PI-free) condition in which each stimulus appeared only once. In line with past findings, the results consistently showed superior memory for meaningful stimuli. Importantly, they also showed a stronger PI-effect for meaningful stimuli as the difference between the Repeated and Unique conditions was greatly reduced (Experiment 1) or eliminated (Experiment 2) for meaningless stimuli. Together, these results strongly imply that meaning, and not visual complexity, plays a key role not only in boosting memory capacity but also in inflating the role of PI in VWM.

Automatically binding relevant and irrelevant features in visual working memory.

It is generally assumed that, to save storage space, features are stored as integrated objects in visual working memory (VWM). Although such an object-based account does not always hold because features can be processed in parallel, a previous study has shown that different features can be automatically bound with their locations (task-irrelevant feature) into an integrated unit, resulting in improved memory performance. The present study was designed to further explore this phenomenon by investigating whether other features, which are not spatial in origin, can act as the binding cue to form such automatic binding. To test this, we used three different features as binding cues (i.e., colour, spatial frequency, and shape) over multiple separate experiments. The results consistently showed that when two features shared the same binding cue, memory performance was better relative to when each of those features had their own binding cue. We conclude that any task-irrelevant feature can act as a binding cue to automatically bind with task-relevant features even across different objects, resulting in memory enhancement.

Disjunctive strategies for tracking occluded objects in visual working memory in children and adults

Disjunctive strategies for tracking occluded objects in visual working memory in children and adults

Real-world objects are not stored in holistic representations in visual working memory.

When storing multiple objects in visual working memory, observers sometimes misattribute perceived features to incorrect locations or objects. These misattributions are called binding errors (or swaps) and have been previously demonstrated mostly in simple objects whose features are easy to encode independently and arbitrarily chosen, like colors and orientations. Here, we tested whether similar swaps can occur with real-world objects, where the connection between features is meaningful rather than arbitrary. In Experiments 1 and 2, observers were simultaneously shown four items from two object categories. Within a category, the two exemplars could be presented in either the same or different states (e.g., open/closed; full/empty). After a delay, both exemplars from one of the categories were probed, and participants had to recognize which exemplar went with which state. We found good memory for state information and exemplar information on their own, but a significant memory decrement for exemplar–state combinations, suggesting that binding was difficult for observers and swap errors occurred even for meaningful real-world objects. In Experiment 3, we used the same task, but in one-half of the trials, the locations of the exemplars were swapped at test. We found that there are more errors in general when the locations of exemplars were swapped. We concluded that the internal features of real-world objects are not perfectly bound in working memory, and location updates impair object and feature representations. Overall, we provide evidence that even real-world objects are not stored in an entirely unitized format in working memory.

Limitations of concurrently representing objects within view and in visual working memory

Representing visibly present stimuli is as limited in capacity as representing invisible stimuli in visual working memory (WM). In this study, we explored whether concurrently representing stimuli within view affects representing objects in visual WM, and if so, whether this effect is modulated by the storage states (active and silent state) of memory contents? In experiment 1, participants were asked to perform the change-detect task in a simultaneous-representing condition in which WM content and the continuously-visible stimuli in view were simultaneously represented, as well as a baseline condition in which only the representations of visual WM content were maintained. The results showed that the representations in visual WM would be impaired when the continuously-visible stimuli in view were concurrently represented, revealed by the reduced CDA amplitude and the lower behavior performance. In experiment 2, a dual-serial retro-cue paradigm was adopted to guide participants to maintain memory items in two different storage states, and the results revealed that simultaneously representing the continuously-visible stimuli and the WM content would only impair the WM representations in the active state. These evidences demonstrated that only the visual WM representations that were maintained in the active state would definitely share the limited resources with the representations of continuously-visible information, and further supported the dissociation between the active state and silent state of visual WM storage.

Reorganization of spatial configurations in visual working memory: A matter of set size?

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.

The Contralateral Delay Activity Tracks the Sequential Loading of Objects into Visual Working Memory, Unlike Lateralized Alpha Oscillations.

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.

Reorganization of spatial configurations in visual working memory.

Human beings have to constantly process multiple objects in visual working memory (VWM). Positional relations to other objects known as spatial configurations contribute significantly to the organization of information in VWM. The aim of our study was to clarify whether spatial configurations can be reorganized to a subset of objects during maintenance. Participants were shown an array of objects, and afterwards the objects disappeared. A valid cue was shown either during encoding or maintenance to highlight the side of the following probed object. Afterwards, the objects reappeared and participants were instructed to detect whether or not a particular object changed its location. We manipulated the configurations at retrieval regarding the number of objects, ranging from all objects to a single object. Our first and second experiment investigated reorganization for a number of six and 12 objects, respectively. In the third experiment, we used a retro cue only and manipulated eye movements (free view vs. enforced fixation). While showing that reorganization of spatial configurations during maintenance is possible in principle, we found some boundary conditions. There was no spatial configuration effect when participants had to fixate. Thus, eye movements are required for a configuration effect to occur.

Robust color-shape binding representations for multiple objects in visual working memory.

The nature of feature-bound object representations in visual working memory (VWM) remains unclear. Many studies claim that they are held by a resource-limited system and are fragile. Using a novel paradigm called the redundant feature reviewing task, the current study showed that color-shape binding representations for multiple objects are maintained and matched with perceptual representation in a robust fashion in VWM. A set of features was presented in a two-object memory display, followed by a linking display in which placeholders either moved or stayed. Then participants judged if a single object probe contained any features of the memory display, regardless of object correspondence. The advantage of color-shape conjunction relative to single features, as indexed by feature coactivation, was retained in the memory matching within the same object and between different objects, regardless of object motion. In contrast, the object-specific preview benefit (OSPB), an index of accessibility to memory representations, was reduced when objects moved, suggesting that motion disrupts the spatiotemporal continuity of memory representations. A meta-analysis of the magnitude of the OSPB in the moving condition across the experiments showed a significant OSPB, suggesting that object file representations bound to spatiotemporal locations are responsible for feature coactivation. Taken together, these findings suggest that the nonspatial features of multiple objects are bound and maintained in VWM, in a robust fashion, regardless of the objects' motion. The cost of object motion in the memory matching performance likely reflects the correspondence between identity and spatiotemporal location, rather than the binding of nonspatial features. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Real-world objects are not stored in bound representations in visual working memory

When storing multiple objects in visual working memory, observers sometimes misattribute perceived features to incorrect locations or objects. These misattributions are called binding errors (or swaps) and have been previously demonstrated mostly in simple objects whose features are easy to encode independently and arbitrarily chosen, like colors and orientations. Here, we tested whether similar swaps can occur with real-world objects, where the connection between features is meaningful rather than arbitrary. In Experiments 1 and 2, observers were simultaneously shown four items from two object categories. Within a category, the two exemplars could be presented in either the same or different states (e.g., open/closed; full/empty). After a delay, both exemplars from one of the categories were probed, and participants had to recognize which exemplar went with which state. We found good memory for state information and exemplar information on their own, but a significant memory decrement for exemplar-state combinations, suggesting that binding was difficult for observers and swap errors occurred even for meaningful real-world objects. In Experiment 3, we used the same task, but in one-half of the trials, the locations of the exemplars were swapped at test. We found that there are more errors in general when the locations of exemplars were swapped. We concluded that the internal features of real-world objects are not perfectly bound in working memory, and location updates impair object and feature representations. Overall, we provide evidence that even real-world objects are not stored in an entirely unitized format in working memory.

Evidence of gradual loss of precision for simple features and complex objects in visual working memory.

Previous studies have suggested that people can maintain prioritized items in visual working memory for many seconds, with negligible loss of information over time. Such findings imply that working memory representations are robust to the potential contaminating effects of internal noise. However, once visual information is encoded into working memory, one might expect it to inevitably begin degrading over time, as this actively maintained information is no longer tethered to the original perceptual input. Here, we examined this issue by evaluating working memory for single central presentations of an oriented grating, color patch, or face stimulus, across a range of delay periods (1, 3, 6, or 12 s). We applied a mixture-model analysis to distinguish changes in memory precision over time from changes in the frequency of outlier responses that resemble random guesses. For all 3 types of stimuli, participants exhibited a clear and consistent decline in the precision of working memory as a function of temporal delay, as well as a modest increase in guessing-related responses for colored patches and face stimuli. We observed a similar loss of precision over time while controlling for temporal distinctiveness. Our results demonstrate that visual working memory is far from lossless: while basic visual features and complex objects can be maintained in a quite stable manner over time, these representations are still subject to noise accumulation and complete termination. (PsycINFO Database Record

Formation and maintenance of mean orientation of sequentially presented objects in visual working memory

Formation and maintenance of mean orientation of sequentially presented objects in visual working memory

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

Previous studies have shown that information held in visual working memory is represented in the occipital, parietal, and frontal cortices. However, less is known about whether the mnemonic information of multi-feature objects is modulated by task demand in the parietal and frontal regions. To address this question, we asked participants to remember either color or orientation of one of the two colored gratings for a delay. Using fMRI and an inverted encoding model, we reconstructed population-level, feature-selective responses in the occipital, parietal and frontal cortices during memory maintenance. We found that not only orientation but also color information can be maintained in higher-order parietal and frontal cortices as well as the early visual cortex when it was cued to be remembered. Conversely, neither the task-irrelevant feature of the cued object, nor any feature of the uncued object was maintained in the occipital, parietal, or frontal cortices. These results suggest a highly selective mechanism of visual working memory that maintains task-relevant features only.

Feature-based attentional weighting and spreading in visual working memory

Attention can be directed at features and feature dimensions to facilitate perception. Here, we investigated whether feature-based-attention (FBA) can also dynamically weight feature-specific representations within multi-feature objects held in visual working memory (VWM). Across three experiments, participants retained coloured arrows in working memory and, during the delay, were cued to either the colour or the orientation dimension. We show that directing attention towards a feature dimension (1) improves the performance in the cued feature dimension at the expense of the uncued dimension, (2) is more efficient if directed to the same rather than to different dimensions for different objects, and (3) at least for colour, automatically spreads to the colour representation of non-attended objects in VWM. We conclude that FBA also continues to operate on VWM representations (with similar principles that govern FBA in the perceptual domain) and challenge the classical view that VWM representations are stored solely as integrated objects.

What are the effects of attentional prioritization on multifeature objects in WM?

Event Abstract Back to Event What are the effects of attentional prioritization on multifeature objects in WM? Muhammet Ikbal Sahan1, 2*, Andrew D. Sheldon3, 4 and Bradley Postle2, 5 1 Ghent University, Experimental Psychology, Belgium 2 University of Wisconsin-Madison, Psychiatry, United States 3 University of Wisconsin-Madison, Neuroscience Training Program, United States 4 University of Wisconsin-Madison, Medical Scientist Training Program, United States 5 University of Wisconsin-Madison, Psychology, United States Attentional prioritization is a dynamic mechanism for selecting objects in visual working memory (VWM). It has been shown that the content of VWM representations that are in the attentional focus can be flexibly decoded from multivariate pattern activity (Lewis-Peacock, Drysdale, Oberauer & Postle, 2012). However, what is unknown is how this attentional prioritization works for features that are bound to an object themselves. To address this question, two multidimensional objects (colored dots drifting coherently in one direction) were presented as memoranda, followed by retrospective cues instructing the subject to retain either one of the two features that are bound into an object (color and motion direction), or one of the two features across objects (i.e., the color or the motion direction of each object). The aim was to obtain fMRI-based pattern activation reconstructions of the cued and uncued feature representations that were bound into an object. Despite elevated BOLD activity in frontoparietal network during delay, no representational content could be decoded from these regions. To the contrary, we could reconstruct high-fidelity representations in the sensory regions that did not show elevated BOLD activation during delay. While the cued visual feature reconstruction remained robust throughout the whole delay, the uncued feature representation could also be reconstructed though with a decrease in robustness by time. Importantly, this effect was only observed when the features were bound into an object. These results have implications for competing theories about the prioritization of object and feature representations in VWM. References Lewis-Peacock, J. A., Drysdale, A. T., Oberauer, K., & Postle, B. R. (2012). Neural evidence for a distinction between short-term memory and the focus of attention. Keywords: fMRI, inverted encoding model, working memory, short term memory, Attention Conference: 12th National Congress of the Belgian Society for Neuroscience, Gent, Belgium, 22 May - 22 May, 2017. Presentation Type: Poster Presentation Topic: Cognition and Behavior Citation: Sahan M, Sheldon AD and Postle B (2019). What are the effects of attentional prioritization on multifeature objects in WM?. Front. Neurosci. Conference Abstract: 12th National Congress of the Belgian Society for Neuroscience. doi: 10.3389/conf.fnins.2017.94.00062 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Apr 2017; Published Online: 25 Jan 2019. * Correspondence: Mr. Muhammet Ikbal Sahan, Ghent University, Experimental Psychology, Ghent, Belgium, muhammet.sahan@ugent.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Muhammet Ikbal Sahan Andrew D Sheldon Bradley Postle Google Muhammet Ikbal Sahan Andrew D Sheldon Bradley Postle Google Scholar Muhammet Ikbal Sahan Andrew D Sheldon Bradley Postle PubMed Muhammet Ikbal Sahan Andrew D Sheldon Bradley Postle Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.