Executive processes in visual and spatial working memory tasks

Three experiments are reported, which have investigated the nature of the cognitive mechanisms that underlie performance on specific visuo-spatial working memory tasks, with the emphasis on exploring the extent of central executive involvement. Experiments 1 and 2 employed oral random digit generation as an executive task within a dual-task paradigm. The results of both experiments indicated that visuo-spatial tasks that involve sequential processing of information show more interference with random digit generation than do visuo-spatial tasks that involve simultaneous processing. The third experiment substituted oral random digit generation for executive tasks that did not involve memory for serial order (vigilance tasks adapted from Vandierendonck, De Vooght, & Van der Goten, 1998b). The results indicated significant interference between the vigilance tasks and the sequential visuo-spatial task, but not with the simultaneous visuo-spatial task. Overall the results of the three experiments are interpreted as indicating that serial sequential visuo-spatial tasks involve executive resources to a significantly greater extent than do simultaneous visuo-spatial tasks, and that this can have implications for studies that attempt to make use of such tasks to fractionate separable visual and spatial components within working memory.     

Executive processes in visual and spatial working memory tasks

Three experiments are reported, which have investigated the nature of the cognitive mechanisms that underlie performance on specific visuo-spatial working memory tasks, with the emphasis on exploring the extent of central executive involvement. Experiments 1 and 2 employed oral random digit generation as an executive task within a dual-task paradigm. The results of both experiments indicated that visuo-spatial tasks that involve sequential processing of information show more interference with random digit generation than do visuo-spatial tasks that involve simultaneous processing. The third experiment substituted oral random digit generation for executive tasks that did not involve memory for serial order (vigilance tasks adapted from Vandierendonck, De Vooght, & Van der Goten, 1998b). The results indicated significant interference between the vigilance tasks and the sequential visuo-spatial task, but not with the simultaneous visuo-spatial task. Overall the results of the three experiments are interpreted as indicating that serial sequential visuo-spatial tasks involve executive resources to a significantly greater extent than do simultaneous visuo-spatial tasks, and that this can have implications for studies that attempt to make use of such tasks to fractionate separable visual and spatial components within working memory.     

工作记忆与知觉负载对工作记忆表征引导注意的调节

本研究采用4个眼动实验探讨不同知觉负载条件下的视觉搜索任务中工作记忆负载对基于工作记忆表征的注意引导效应的影响。实验1和实验3采用低知觉负载的视觉搜索任务,结果在视觉工作记忆负载为1和2时观察到了显著的注意引导效应,但当负载增加到4时注意引导效应消失了;实验2和实验4采用高知觉负载的视觉搜索任务,结果发现注意引导效应在工作记忆负载增加到2时就已经消失了。上述结果表明:工作记忆负载和知觉负载都能够通过调控认知资源的方式来影响工作记忆表征对注意的引导,当认知资源充足时,工作记忆能够同时保持多个记忆表征对视觉注意的引导。     

Neuroimaging studies of working memory:

We performed meta-analyses on 60 neuroimaging (PET and fMRI) studies of working memory (WM), considering three types of storage material (spatial, verbal, and object), three types of executive function (continuous updating of WM, memory for temporal order, and manipulation of information in WM), and interactions between material and executive function. Analyses of material type showed the expected dorsal-ventral dissociation between spatial and nonspatial storage in the posterior cortex, but not in the frontal cortex. Some support was found for left frontal dominance in verbal WM, but only for tasks with low executive demand. Executive demand increased right lateralization in the frontal cortex for spatial WM. Tasks requiring executive processing generally produce more dorsal frontal activations than do storage-only tasks, but not all executive processes show this pattern. Brodmann’s areas (BAs) 6, 8, and 9, in the superior frontal cortex, respond most when WM must be continuously updated and when memory for temporal order must be maintained. Right BAs 10 and 47, in the ventral frontal cortex, respond more frequently with demand for manipulation (including dual-task requirements or mental operations). BA 7, in the posterior parietal cortex, is involved in all types of executive function. Finally, we consider a potential fourth executive function: selective attention to features of a stimulus to be stored in WM, which leads to increased probability of activating the medial prefrontal cortex (BA 32) in storage tasks.     

The contributions of visual and central attention to visual working memory

We investigated the role of two kinds of attention—visual and central attention—for the maintenance of visual representations in working memory (WM). In Experiment 1 we directed attention to individual items in WM by presenting cues during the retention interval of a continuous delayed-estimation task, and instructing participants to think of the cued items. Attending to items improved recall commensurate with the frequency with which items were attended (0, 1, or 2 times). Experiments 1 and 3 further tested which kind of attention—visual or central—was involved in WM maintenance. We assessed the dual-task costs of two types of distractor tasks, one tapping sustained visual attention and one tapping central attention. Only the central attention task yielded substantial dual-task costs, implying that central attention substantially contributes to maintenance of visual information in WM. Experiment 2 confirmed that the visual-attention distractor task was demanding enough to disrupt performance in a task relying on visual attention. We combined the visual-attention and the central-attention distractor tasks with a multiple object tracking (MOT) task. Distracting visual attention, but not central attention, impaired MOT performance. Jointly, the three experiments provide a double dissociation between visual and central attention, and between visual WM and visual object tracking: Whereas tracking multiple targets across the visual filed depends on visual attention, visual WM depends mostly on central attention.     

视觉工作记忆对前注意阶段注意定向的调节

在注意阶段,视觉工作记忆与注意共享某些特征时,视觉工作记忆内容会引导注意定向。在前注意阶段的影响又是如何？对此问题的研究却很少见,本研究采用工作记忆与基于特征的视觉搜索相结合的任务深入探讨了此问题。研究结果发现：即使在前注意阶段,注意定向也会受到视觉工作记忆自上而下的调节。然而与注意阶段不同的是：当视觉工作记忆内容与随后视觉搜索任务的目标相关时,与记忆内容匹配的搜索项目会引导注意定向到该项目所在的位置,但只有此项目作为分心物时,才会明显地延迟对靶子的加工,而此项目作为靶子时,这种影响并不明显;当视觉工作记忆中保持的项目与随后视觉搜索任务的目标无关时,注意会忽略视觉工作记忆中保持的项目,有效地检测靶子     

Executive working memory load does not compromise perceptual processing during visual search: Evidence from additive factors analysis

Executive working memory (WM) load reduces the efficiency of visual search, but the mechanisms by which this occurs are not fully known. In the present study, we assessed the effect of executive load on perceptual processing during search. Participants performed a serial oculomotor search task, looking for a circle target among gapped-circle distractors. The participants performed the task under high and low executive WM load, and the visual quality (Experiment 1) or discriminability of targets and distractors (Experiment 2) was manipulated across trials. By the logic of the additive factors method (Sternberg, 1969, 1998), if WM load compromises the quality of perceptual processing during visual search, manipulations of WM load and perceptual processing difficulty should produce nonadditive effects. Contrary to this prediction, the effects of WM load and perceptual difficulty were additive. The results imply that executive WM load does not degrade perceptual analysis during visual search.     

Age-related differences in executive control of working memory

In two experiments, we used dual-task methodology to assess the effect of aging on executive control of working memory. We hypothesized that (1) age-related dual-task costs would be observed even when individual tasks represent different perceptual modalities; (2) age would modulate the effect of increased temporal overlap on dual-task performance; and (3) the vulnerability of specific memory mechanisms to interference would be age related. We found that aging was associated with disproportionate dual-task costs that increased when extending the overlap between individual tasks. The effect of interference with encoding, and arguably output, was disproportionately larger in old than in young individuals. Ensuring that individual tasks represent different perceptual modalities is important but insufficient when using dual-task methodology to assess the effect of aging on executive function. The degree of temporal overlap between individual tasks and the sensitivity of specific memory operations to interference should be considered, as well.     

The extent of working memory deficits associated with Williams syndrome: exploration of verbal and spatial domains and executively controlled processes

The present study investigated verbal and spatial working memory (WM) functioning in individuals with the neuro-developmental disorder Williams syndrome (WS) using WM component tasks. While there is strong evidence of WM impairments in WS, previous research has focused on short-term memory and has neglected assessment of executive components of WM. There is a particular lack of consensus concerning the profile of verbal WM functioning in WS. Here, WS participants were compared to typically developing participants matched for (1) verbal ability and (2) spatial ability (N = 14 in each of the 3 groups). Individuals with WS were impaired on verbal WM tasks, both those involving short-term maintenance of information and executive manipulation, in comparison to verbal-matched controls. Surprisingly, individuals with WS were not impaired on a spatial task assessing short-term maintenance of information in memory (remembering spatial locations) compared to spatial-matched controls. They were, however, impaired on a spatial executive WM task requiring the manipulation of spatial information in memory. The present study suggests that individuals with WS show WM impairments that extend to both verbal and spatial domains, although spatial deficits are selective to executive aspects of WM function.     

Concurrent performance of two memory tasks: evidence for domain-specific working memory systems

Previous studies of dual-task coordination in working memory have shown a lack of dual-task interference when a verbal memory task is combined with concurrent perceptuomotor tracking. Two experiments are reported in which participants were required to perform pairwise combinations of (1) a verbal memory task, a visual memory task, and perceptuomotor tracking (Experiment 1), and (2) pairwise combinations of the two memory tasks and articulatory suppression (Experiment 2). Tracking resulted in no disruption of the verbal memory preload over and above the impact of a delay in recall and showed only minimal disruption of the retention of the visual memory load. Performing an ongoing verbal memory task had virtually no impact on retention of a visual memory preload or vice versa, indicating that performing two demanding memory tasks results in little mutual interference. Experiment 2 also showed minimal disruption when the two memory tasks were combined, although verbal memory (but not visual memory) was clearly disrupted by articulatory suppression interpolated between presentation and recall. These data suggest that a multiple-component working memory model provides a better account for performance in concurrent immediate memory tasks than do theories that assume a single processing and storage system or a limited-capacity attentional system coupled with activated memory traces.     

Automatic guidance of visual attention from verbal working memory

Previous studies have shown that visual attention can be captured by stimuli matching the contents of working memory (WM). Here, the authors assessed the nature of the representation that mediates the guidance of visual attention from WM. Observers were presented with either verbal or visual primes (to hold in memory, Experiment 1; to verbalize, Experiment 2; or merely to attend, Experiment 3) and subsequently were required to search for a target among different distractors, each embedded within a colored shape. In half of the trials, an object in the search array matched the prime, but this object never contained the target. Despite this, search was impaired relative to a neutral baseline in which the prime and search displays did not match. An interesting finding is that verbal primes were effective in generating the effects, and verbalization of visual primes elicited similar effects to those elicited when primes were held in WM. However, the effects were absent when primes were only attended. The data suggest that there is automatic encoding into WM when items are verbalized and that verbal as well as visual WM can guide visual attention.     

Spatial and nonspatial working memory and visual search

It has been indicated that visual search is interfered with in spatial working memory (WM), although not in nonspatial WM. In this study, the effects on visual search of individual differences in spatial and nonspatial WM were examined. Two visual search conditions were used: a conjunction search condition comprising two features (color and shape) and a disjunction condition comprising only one feature (color or shape). 96 participants (42 men, 54 women, M age = 20.9 yr., SD = 3.5) participated in this study. The participants were divided into high and low WM groups based on their spatial and nonspatial WM test scores. As a result, statistically significant group differences in the conjunction search rate were observed in spatial WM but not in nonspatial WM. These results suggest there is a relationship between visual search and the individual spatial WM ability, but this does not hold for nonspatial WM.     

Dual-task interference in visual working memory: A limitation in storage capacity but not in encoding or retrieval

The concurrent maintenance of two visual working memory (VWM) arrays can lead to profound interference. It is unclear, however, whether these costs arise from limitations in VWM storage capacity (Fougnie & Maro is, 2006) or from interference between the storage of one visual array and encoding or retrieval of another visual array (Cowan & Morey, 2007). Here, we show that encoding a VWM array does not interfere with maintenance of another VWM array unless the two displays exceed maintenance capacity (Experiments 1 and 2). Moreover, manipulating the extent to which encoding and maintenance can interfere with one another had no discernable effect on dual-task performance (Experiment 2). Finally, maintenance of a VWM array was not affected by retrieval of information from another VWM array (Experiment 3). Taken together, these findings demonstrate that dual-task interference between two concurrent VWM tasks is due to a capacity-limited store that is independent from encoding and retrieval processes.     

Item strength affects working memory capacity

Do the processing and online manipulation of stimuli that are less familiar require more working memory (WM) resources? Is it more difficult to solve demanding problems when the symbols involved are less rather than more familiar? We explored these questions with a dual-task paradigm in which subjects had to solve algebra problems of different complexities while simultaneously holding novel symbol–digit associations in WM. The symbols were previously unknown Chinese characters, whose familiarity was manipulated by differential training frequency with a visual search task for nine hour-long sessions over 3 weeks. Subsequently, subjects solved equations that required one or two transformations. Before each trial, two different integers were assigned to two different Chinese characters of the same training frequency. Half of the time, those characters were present as variables in the equation and had to be substituted for the corresponding digits. After attempting to solve the equation, subjects had to recognize which two characters were shown immediately before that trial and to recall the integer associated with each. Solution accuracy and response times were better when the problems required one transformation only; variable substitution was not required; or the Chinese characters were high frequency. The effects of stimulus familiarity increased as the WM demands of the equation increased. Character–digit associations were also recalled less well with low-frequency characters. These results provide strong support that WM capacity depends not only on the number of chunks of information one is attempting to process but also on their strength or familiarity.     

Cognitive control over working memory biases of selection

Across many studies, researchers have found that representations in working memory (WM) can guide visual attention toward items that match the features of the WM contents. While some researchers have contended that this occurs involuntarily, others have suggested that the impact of WM contents on attention can be strategically controlled. Here, we varied the probability that WM items would coincide with either targets or distractors in a visual search task to examine (1) whether participants could intentionally enhance or inhibit the influence of WM items on attention and (2) whether cognitive control over WM biases would also affect access to the memory contents in a surprise recognition test. We found visual search to be faster when the WM item coincided with the search target, and this effect was enhanced when the memory item reliably predicted the location of the target. Conversely, visual search was slowed when the memory item coincided with a search distractor, and this effect was diminished, but not abolished, when the memory item was reliably associated with distractors. This strategic dampening of the influence of WM items on attention came at a price to memory, however, as participants were slowest to perform WM recognition tests on blocks in which the WM contents were consistently invalid. These results document that attentional capture by WM contents is partly, but not fully, malleable by top-down control, which appears to adjust the state of the WM contents to optimize search behavior. These data illustrate the role of cognitive control in modulating the strength of WM biases of selection, and they support a tight coupling between WM and attention.     

Escaping capture: bilingualism modulates distraction from working memory

We ask whether bilingualism aids cognitive control over the inadvertent guidance of visual attention from working memory and from bottom-up cueing. We compare highly-proficient Catalan-Spanish bilinguals with Spanish monolinguals in three visual search conditions. In the working memory (WM) condition, attention was driven in a top-down fashion by irrelevant objects held in WM. In the Identify condition, attention was driven in a bottom-up fashion by visual priming. In the Singleton condition, attention was driven in a bottom-up fashion by including a unique distracting object in the search array. The results showed that bilinguals were overall faster than monolinguals in the three conditions, replicating previous findings that bilinguals can be more efficient than monolinguals in the deployment of attention. Interestingly, bilinguals were less captured by irrelevant information held in WM but were equally affected by visual priming and unique singletons in the search displays. These observations suggest that bilingualism aids top-down WM-mediated guidance of attention, facilitating processes that keep separate representations in WM from representations that guide visual attention. In contrast, bottom-up attentional capture by salient yet unrelated input operates similarly in bilinguals and monolinguals.     

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.     

Effect of articulatory suppression on task-switching performance: implications for models of working memory

In a series of experiments, we examine some effects of articulatory suppression in task switching. The results from Experiments 1a and 2a showed that switch costs in the articulatory suppression condition were larger than those in the control and tapping conditions when the switching cues were not provided. On the other hand, articulatory suppression did not have any effect on switch costs in Experiments 1b and 2b, where the switching cues were provided. In Experiment 3, using a computer-assisted experimentation, this pattern of data was replicated in a two-factor design with articulatory suppression and switching cues factors. The results indicate that a specific component in working memory, the phonological loop, might contribute to the performance in task switching, at least in situations where the external task cues were not available. The data reported here suggest that the phonological loop plays an important role in one of the executive control processes, and challenge the traditional idea that the slave systems are simply governed by the central executive in the working memory.     

颜色和形状工作记忆对非空间返回抑制效应的影响

为进一步考察非空间返回抑制效应是否受工作记忆内容的影响,分别采用颜色和形状工作记忆内容,通过两个实验考察了工作记忆对非空间返回抑制效应的影响。实验结果表明,在颜色和形状工作记忆条件下,均产生了颜色或形状返回抑制效应,并且颜色或形状返回抑制效应量之间均无显著差异,颜色和形状工作记忆内容只增加了判断靶刺激的反应时。研究结论对进一步认识工作记忆内容与非空间返回抑制效应之间的关系有重要参考价值。     

工作记忆表征精度加工需求对注意引导的影响

采用注意捕获范式, 通过行为和事件相关脑电位(ERP)实验, 探讨工作记忆表征精度加工需求对注意引导的影响, 行为结果发现, 在低精度加工需求条件下, 只有一个工作记忆表征引导注意, 且处于高激活状态的工作记忆表征产生的注意捕获大于低激活状态; 而在高精度加工需求条件下, 有两个工作记忆表征引导注意, 且处于高、低激活状态的工作记忆表征产生的注意捕获没有差异。ERP结果显示, 高精度加工需求条件下诱发的NSW和LPC大于低精度加工需求条件; 在高精度加工需求条件下, 干扰项与记忆项匹配比不匹配时, 诱发更大的N2和更小的N2pc, 而在低精度加工需求条件下, 干扰项与记忆项匹配和不匹配时诱发的N2、N2pc没有差异。研究表明, 工作记忆表征精度加工需求影响注意引导的机制可能是高精度加工需求下, 工作记忆表征消耗的认知资源增加, 搜索目标获得的资源减少, 干扰项捕获的注意增加。