Binding in short-term visual memory.

The integration of complex information in working memory, and its effect on capacity, shape the limits of conscious cognition. The literature conflicts on whether short-term visual memory represents information as integrated objects. A change-detection paradigm using objects defined by color with location or shape was used to investigate binding in short-term visual memory. Results showed that features from the same dimension compete for capacity, whereas features from different dimensions can be stored in parallel. Binding between these features can occur, but focused attention is required to create and maintain the binding over time, and this integrated format is vulnerable to interference. In the proposed model, working memory capacity is limited both by the independent capacity of simple feature stores and by demands on attention networks that integrate this distributed information into complex but unified thought objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age effects in coding tasks: Componential analysis and test of the sensory deficit hypothesis.

Multiple forms of a symbol-digit substitution task were used to provide a componential analysis of age differences in coding task performance. The results demonstrated age differences in feature encoding, memory, and visual search. A 2nd experiment was conducted with young adults to investigate a sensory deficit as a locus of age differences. The spatial contrast sensitivity deficit of older adults was simulated on forms by applying a digital filter. Persons in the age-simulated contrast condition performed worse than those in the normal contrast condition. The stimulus degradation effect was linked to visual search speed. The study illustrates the utility of componential analysis and offers direct support for the hypothesis that sensory deficits affect performance on tasks used to assess intelligence (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What's in a location? Comparing object-based and space-based models of feature integration in visual search.

What is the unit of selection for feature integration in visual search: location or perceptual object? Feature integration theory (A. Treisman, 1988) asserts that it is location. Two alternative models are put forward and tested in a series of 4 experiments using a special conjunctive search task In this task, each stimulus item consists of 2 overlapping forms (perceptual objects). In general, the search was more efficient when the search features were linked to the same perceptual object than when they were linked to different perceptual objects at the same stimulus location. This same-object advantage, however, was shown to depend on stimulus discriminability and density, grouping strength, and hierarchical object structure. The results support a hierarchical object-based model, with important implications for feature integration, visual search, late versus early selection, and object-based versus space-based views of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature-based memory-driven attentional capture: Visual working memory content affects visual attention.

In 7 experiments, the authors explored whether visual attention (the ability to select relevant visual information) and visual working memory (the ability to retain relevant visual information) share the same content representations. The presence of singleton distractors interfered more strongly with a visual search task when it was accompanied by an additional memory task. Singleton distractors interfered even more when they were identical or related to the object held in memory, but only when it was difficult to verbalize the memory content. Furthermore, this content-specific interaction occurred for features that were relevant to the memory task but not for irrelevant features of the same object or for once-remembered objects that could be forgotten. Finally, memory-related distractors attracted more eye movements but did not result in longer fixations. The results demonstrate memory-driven attentional capture on the basis of content-specific representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal limitations in the effective binding of attended target attributes in the mutual masking of visual objects.

The problem of feature binding has been examined under conditions of distributed attention or with spatially dispersed stimuli. We studied binding by asking whether selective attention to a feature of a masked object enables perceptual access to the other features of that object using conditions in which spatial attention was directed at a single location where all objects appeared. In an identification condition, the task required reporting the same property of each object. High rates of identification showed good perceptual availability. In a search condition, the task required reporting the property (e.g., shape) that was associated with a specific value of the searched property (e.g., surface texture) of the same object. Focusing of attention on a target’s searched property value did not result in a high rate of identifying the target’s other property, and strong object masking was found. Backward masking between spatially superimposed visual objects appears to be primarily due to a difficulty in feature binding of a target object rather than to a substitution of an integrated object by the following stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The time course of consolidation in visual working memory.

How long does it take to form a durable representation in visual working memory? Several theorists have proposed that this consolidation process is very slow. Here, we measured the time course of consolidation. Observers performed a change-detection task for colored squares, and shortly after the presentation of the first array, pattern masks were presented at the locations of each of the colored squares to disrupt representations that had not yet been consolidated. Performance on the memory task was impaired when the delay between the colored squares and the masks was short, and this effect became larger when the number of colored squares was increased. The rate of consolidation was approximately 50 ms per item, which is considerably faster than previous proposals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual task performance after diazepam intake: can resource depletion explain the benzodiazepine-induced amnesia?

It was tested whether a depletion in resources can account for the benzodiazepine-induced memory impairment. In two experiments, it was examined whether dividing attention had a disproportionately detrimental effect on learning semantically related and unrelated word pairs after diazepam intake. Word pairs had to be learned in both a single task condition and while performing a visual discrimination task concurrently (dual task condition). Moreover, the complexity of the visual discrimination task was manipulated systematically. Diazepam (15 mg, orally) or placebo was administered in a double-blind, between-subjects design. Subjects after diazepam intake were clearly impaired in learning unrelated word pairs, but not in learning related word pairs. Dividing attention in the dual task condition was associated with a reduction in learning unrelated word pairs, but this was not disproportionately reduced after diazepam intake. Moreover, the magnitude of resource depletion did not correlate with the severity of the diazepam-induced memory impairment. In general, the pattern of results does not support the hypothesis that a depletion of resources can explain the benzodiazepine-induced memory impairment.     

Organization of visual short-term memory.

The authors examined the organization of visual short-term memory (VSTM). Using a change-detection task, they reported that VSTM stores relational information between individual items. This relational processing is mediated by the organization of items into spatial configurations. The spatial configuration of visual objects is important for VSTM of spatial locations, colors, and shapes. When color VSTM is compared with location VSTM, spatial configuration plays an integral role because configuration is important for color VSTM, whereas color is not important for location VSTM. The authors also examined the role of attention and found that the formation of configuration is modulated by both top-down and bottom-up attentional factors. In summary, the authors proposed that VSTM stores the relational information of individual visual items on the basis of global spatial configuration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual-task assessment of age differences in automatic process development.

The present experiment assessed dual-task performance in 20 young (mean age 21) and 20 old (mean age 72) adults. Ss first received extensive single-task practice on consistent and varied search tasks. Next, they received dual-task practice in 2 conditions: (1) varied visual search plus varied memory search and (2) consistent visual search plus varied memory search. In the varied-varied condition, young and old adults showed similar dual-task decrements. These results, along with the current data in the literature, suggest that practice may play an important role in determining age-related dual-task differences (or lack thereof). In the consistent-varied condition, young adults attained single-task performance levels, because they had automatized the consistent task. Old adults were unable to match their single-task performance levels, indicating that they were unable to automatize the consistent task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search performance among persons with schizophrenia as a function of target eccentricity.

The current study investigated one possible mechanism of impaired visual attention among patients with schizophrenia: a reduced visual span. Visual span is the region of the visual field from which one can extract information during a single eye fixation. This study hypothesized that schizophrenia-related visual search impairment is mediated, in part, by a smaller visual span. To test this hypothesis, 23 patients with schizophrenia and 22 healthy controls completed a visual search task where the target was pseudorandomly presented at different distances from the center of the display. Response times were analyzed as a function of search condition (feature vs. conjunctive), display size, and target eccentricity. Consistent with previous reports, patient search times were more adversely affected as the number of search items increased in the conjunctive search condition. It was important however, that patients’ conjunctive search times were also impacted to a greater degree by target eccentricity. Moreover, a significant impairment in patients’ visual search performance was only evident when targets were more eccentric and their performance was more similar to healthy controls when the target was located closer to the center of the search display. These results support the hypothesis that a narrower visual span may underlie impaired visual search performance among patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When Do Visual and Verbal Memories Conflict? The Importance of Working-Memory Load and Retrieval.

Examinations of interference between verbal and visual materials in working memory have produced mixed results. If there is a central form of storage (e.g., the focus of attention; N. Cowan, 2001), then cross-domain interference should be obtained. The authors examined this question with a visual-array comparison task (S. J. Luck & E. K. Vogel, 1997) combined with various verbal memory load conditions. Interference between tasks occurred if there was explicit retrieval of the verbal load during maintenance of a visual array. The effect was localized in the maintenance period of the visual task and was not the result of articulation per se. Interference also occurred when especially large silent verbal and visual loads were held concurrently. These results suggest central storage along with code-specific passive storage. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Spectra of spontaneous frameshift mutations at the hisD3052 allele of Salmonella typhimurium in four DNA repair backgrounds

In the model of Baddeley (Working Memory, Oxford University Press, Oxford, 1986), one function of the visuospatial sketchpad (VSSP) component of working memory is to allow the processing of mental images. Properties of the VSSP were investigated by means of the usual dual-task paradigm (to search for interference from the other components of working memory, i.e., the articulatory loop and the central executive), applied to three distinct subprocesses of mental imagery (Kosslyn, 1994 Image and Brain. MIT Press, Cambridge, MA): image generation (Experiment 1), image maintenance (Experiment 2), and image rotation (Experiment 3). First, in the control condition (no interference task) of each experiment, we replicated the effects of stimulus or task complexity already reported. Second, no interference from the articulatory loop was observed. Third, maintenance of images appeared free from any interference. And fourth, generation and rotation tasks were interfered to a greater extent by the central executive than by the involvement of the VSSP in a secondary task. These observations (a) support the dissociation between the articulatory loop and the VSSP, (b) suggest an important use of central attentional resources in the generation and rotation of mental images, (c) would support the distinction between visual and spatial components in the structure of working memory, and (d) suggest the dissociation of the VSSP into two subcomponents: a passive visuospatial store and an active device for recapitulating visuospatial information.     

Task Demands Control Acquisition and Storage of Visual Information.

Attention and working memory limitations set strict limits on visual representations, yet researchers have little appreciation of how these limits constrain the acquisition of information in ongoing visually guided behavior. Subjects performed a brick sorting task in a virtual environment. A change was made to 1 of the features of the brick being held on about 10% of trials. Rates of change detection for feature changes were generally low and depended on the pick-up and put-down relevance of the feature to the sorting task. Subjects' sorting decision suggests that changes may be missed because of a failure to update the changed feature. The authors also explore how hand and eye behavior are coordinated for strategic acquisition and storage of visual information throughout the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preattentive and attentive visual search in individuals with hemispatial neglect.

Preattentive and attentive visual processing was examined in patients with hemispatial neglect, hemispatial neglect with hemianopia, and control participants. In the preattentive search task, targets possessed a unique feature that was not shared by distractors. In the attentive search task, targets lacked a feature that was present in the distractors. Preattentive search was normal in 3 neglect patients with cortical lesions but not in 2 neglect patients with hemianopia. A 4th neglect patient without hemianopia with a subcortical infarct abnormally used serial search mechanisms in the preattentive task. Neglect patients were characteristically impaired in the contralesional field in the attentive search task. This study demonstrates preserved explicit detection of visual features in cases of hemispatial neglect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the speed of pop-out in feature search.

When something unique is present in a scene, this element may become immediately visible and one has the impression that it pops out from the scene. This phenomenon, known as pop-out in the visual search literature, is thought to produce the fastest search possible, and response times for the detection of the pop-out target do not vary as a function of the number of nontargets. In this study, we challenge this notion and show that the detection of a given visual feature is faster for multiple targets than for a single pop-out target. However, when the task requires a detailed target analysis, the pop-out condition can be faster than the multiple-target condition. Current models of visual search are discussed in light of the findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The contribution of covert attention to the set-size and eccentricity effects in visual search.

To reexamine the role of covert attention in visual search, the authors directly manipulated attention by peripherally cueing the target location and analyzed its effects on the set-size and the eccentricity effects. Observers participated in feature and conjunction tasks. Experiment 1 used precues, and Experiment 2 used postcues in a yes–no task under valid-, invalid-, and neutral-cueing conditions. Experiments 3 and 4 used a 2-interval alternative forced-choice visual-search task under cued and neutral conditions. Precueing the target location improved performance in feature and conjunction searches; postcueing did not. For the cued targets, the eccentricity effect for features and conjunctions was diminished, suggesting that the attentional mechanism improves the quality of the sensory representation of the attended location. The conjunction set-size effect was reduced but not eliminated. This questions serial-search models that attribute a major role to covert attention in visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of divided attention on encoding and retrieval processes in human memory.

The authors examined the effects of divided attention (DA) at encoding and retrieval in free recall, cued recall, and recognition memory in 4 experiments. Lists of words or word pairs were presented auditorily and recalled orally; the secondary task was a visual continuous reaction-time (RT) task with manual responses. At encoding, DA was associated with large reductions in memory performance, but small increases in RT; trade-offs between memory and RT were under conscious control. In contrast, DA at retrieval resulted in small or no reductions in memory, but in comparatively larger increases in RT, especially in free recall. Memory performance was sensitive to changes in task emphasis at encoding but not at retrieval. The results are discussed in terms of controlled and automatic processes and speculatively linked to underlying neuropsychological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rehearsal in spatial working memory

This article reports 3 experiments that tested a hypothesis regarding the nature of rehearsal in spatial working memory, one in which discrete shifts of spatial selective attention mediate the maintenance of location-specific representations. Experiment 1 demonstrated increases in visual processing efficiency for locations held in working memory, which suggested that attention was oriented toward these locations. Experiment 2 eliminated key alternative explanations for Experiment 1 by using an identical stimulus display with a nonspatial memory task, and little or no facilitation of processing at memorized locations was found under these conditions. Finally, Experiment 3 showed that spatial working memory was impaired when participants were hindered in their ability to attend to memorized locations. It is argued that these results implicate selective spatial attention as a rehearsal mechanism for spatial working memory.     

The comparison of visual working memory representations with perceptual inputs.

The human visual system can notice differences between memories of previous visual inputs and perceptions of new visual inputs, but the comparison process that detects these differences has not been well characterized. In this study, the authors tested the hypothesis that differences between the memory of a stimulus array and the perception of a new array are detected in a manner that is analogous to the detection of simple features in visual search tasks. That is, just as the presence of a task-relevant feature in visual search can be detected in parallel, triggering a rapid shift of attention to the object containing the feature, the presence of a memory–percept difference along a task-relevant dimension can be detected in parallel, triggering a rapid shift of attention to the changed object. Supporting evidence was obtained in a series of experiments in which manual reaction times, saccadic reaction times, and event-related potential latencies were examined. However, these experiments also showed that a slow, limited-capacity process must occur before the observer can make a manual change detection response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)