Information In Visual Working Memory Research Articles

Brain oscillatory correlates of working memory constraints

It has been claimed that the coordination of neuronal oscillations differing in frequency is relevant for cognition. However, the validity of this claim has scarcely been investigated. Recent studies revealed that cross-frequency phase coupling and modulations of alpha-power dissociate between retention of relevant and suppression of irrelevant information in visual working memory (WM). We summarize these important results, and discuss possible implications for understanding the neural mechanisms of WM constraints.

Storing fine detailed information in visual working memory--Evidence from event-related potentials

Visual working memory (VWM) maintains and manipulates a limited set of visual objects being actively used in visual processing. To explore whether and how the fine detailed information is stored in VWM, four experiments have been conducted while recording the contralateral delay activity (CDA), an event-related potential difference wave that reflects the information maintenance in VWM. The type of the remembered information was manipulated by adopting simple objects and complex objects as materials. We found the amplitude of CDA was modulated by object complexity: as the set size of memory array rose from 2 to 4, the amplitude of CDA stopped increasing for maintaining complex objects with detailed information, while continued increasing for storing highly discriminable simple objects. These results suggest that VWM can store the fine detailed information; however it can not store all the fine detailed information from 4 complex objects. It implies that the capacity of VWM is not only characterized by a fixed number of objects, there is at least one stage influenced by the detailed information contained in the objects. These results are further discussed within a two-stage storing model of VWM: different types of perceptual information (highly discriminable features and fine detailed features) are maintained in VWM via two distinctive mechanisms.

Overwriting and rebinding: Why feature-switch detection tasks underestimate the binding capacity of visual working memory

In these two experiments, we explored the ability to store bound representations of colour and location information in visual working memory using three different tasks. In the location-cue task, we probed how well colour information could be recalled when observers are given a location cue. In the feature-cue task, we probed how well location information could be recalled when observers are given a colour cue. Finally, in the feature-switch detection task, we tested how well observers could detect a recombination of features (e.g., switching the locations of the red and green items). We hypothesized that these tasks might reveal differences in binding capacity limits between switching and nonswitching tests of visual working memory. We also hoped the tasks could provide an explanation for those differences in terms of the component processes of working memory—do failures occur in the encoding, maintenance, or retrieval stages of the task? Experiment 1 showed that performance in the two cued-recall tasks was equally high, and was significantly better than performance in the feature-switch detection task. Thus, the feature-switch detection task underestimates the number of colour–location bindings that can be remembered, but is a useful task for examining the fragile nature of feature binding in working memory. Experiment 2 explored why feature-switch detection underestimates the binding capacity of visual working memory by examining whether the feature switch errors occur at the level of encoding, maintaining, or retrieving binding information from visual working memory. The results suggest that feature switch errors reflect failures to maintain bound objects in working memory, perhaps due to the automatic rewriting and rebinding of information in the face of new perceptual input.

Proactive interference from items previously stored in visual working memory

This study investigates the fate of information that was previously stored in visual working memory but that is no longer needed. Previous research has found inconsistent results, with some showing effective release of irrelevant information and others showing proactive interference. Using change detection tasks of colors or shapes, we show that participants tend to falsely classify a changed item as "no change" if it matches one of the memory items on the preceding trial. The interference is spatially specific: Memory for the preceding trial interferes more if it matches the feature value and the location of a test item than if it does not. Interference results from retaining information in visual working memory, since it is absent when items on the preceding trials are passively viewed, or are attended but not memorized. We conclude that people cannot fully eliminate unwanted visual information from current working memory tasks.

Visual search is slowed when visuospatial working memory is occupied.

Visual working memory plays a central role in most models of visual search. However, a recent study showed that search efficiency was not impaired when working memory was filled to capacity by a concurrent object memory task (Woodman, Vogel, & Luck, 2001). Objects and locations may be stored in separate working memory subsystems, and it is plausible that visual search relies on the spatial subsystem, but not on the object subsystem. In the present study, we sought to determine whether maintaining spatial information in visual working memory impairs the efficiency of a concurrent visual search task. Visual search efficiency and spatial memory accuracy were both impaired when the search and the memory tasks were performed concurrently, as compared with when the tasks were performed separately. These findings suggest that common mechanisms are used to process information during difficult visual search tasks and to maintain spatial information in working memory.

Perceptual organization influences visual working memory.

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

Aging effects on intra- and inter-attribute spatial frequency information for luminance, color, and working memory

Visual working memory (VWM) for spatial frequency information was assessed in both young and older observers. In the first experiment we assessed the effect of a memory mask on a VWM task. We found no effect of mask on retention for either the young or older groups. This argues against the `inhibition' hypothesis of aging in regards to visual processing, which suggests that the elderly should have difficulty to inhibit irrelevant information. We conclude that the suggestion of an inefficient inhibition process in aging derived from evidence obtained for higher-level WM tasks cannot be generalized to the discrimination of basic patterns in VWM. The second experiment focused on processing resources within VWM by assessing VWM for intra-attribute (color or luminance), and inter-attribute (color and luminance)-defined spatial frequency information. Results show that retention of spatial frequency information in VWM is robust for both the younger and older group regardless of the defining attribute. Thresholds were significantly higher in the inter-attribute condition, indicating increased processing demands for this task and suggesting that these attributes are initially processed in parallel. Older observers showed higher discrimination thresholds than young observers for all conditions indicating a deficit in perceptual abilities rather than in VWM for basic stimuli. The difference in thresholds for the older group was highest in the inter-attribute condition suggesting that older observers show more deficits on visual tasks with increased processing demands.

Visual search remains efficient when visual working memory is full.

Many theories of attention have proposed that visual working memory plays an important role in visual search tasks. The present study examined the involvement of visual working memory in search using a dual-task paradigm in which participants performed a visual search task while maintaining no, two, or four objects in visual working memory. The presence of a working memory load added a constant delay to the visual search reaction times, irrespective of the number of items in the visual search array. That is, there was no change in the slope of the function relating reaction time to the number of items in the search array, indicating that the search process itself was not slowed by the memory load. Moreover, the search task did not substantially impair the maintenance of information in visual working memory. These results suggest that visual search requires minimal visual working memory resources, a conclusion that is inconsistent with theories that propose a close link between attention and working memory.

On the nature of the span of apprehension

Summary. Typically, people can only report about four or five items from a briefly presented array of alphanumeric items. A new span task was used to explore the basis of this limitation. In Experiment 1, performance suffered when very brief display durations were combined with a verbalload task, but no significant effects of display duration were found when there was no verbal load. In Experiment 2, a similar interaction was observed between verbal load and the presence of a visual suffix; performance was worse in the verbal-load condition with a visual suffix, but no such effect was observed without verbal load. In both experiments, poorer performance was associated with enhanced serial-position effects. The results can be explained on the assumption that the verbal-load task required some processing resources, and that the quality of information in visual working memory depends on available resources. Thus, both brief-array presentation and the visual suffix degrade the information in visual working memory, but span performance is impaired only when processing resources are relatively scarce.