Configural representations in spatial working memory

Two studies investigate the nature of representations in spatial working memory, directly addressing the question of whether people represent the configuration information above and beyond independent positional information when representing multiple sequentially presented locations. In Experiment 1, participants performed a location memory task in which they recalled the location of objects that were presented sequentially on a screen. Comparison of participants' data with simulated data modelled to represent independent positional representation of spatial locations revealed that participants represented the configural properties of shorter sequences (3 and 4 locations) but not of longer ones (5 and 7 locations). Experiment 2 employed a sequential recognition task in which participants were asked to judge whether two consequently presented spatial sequences were identical. These experiments confirmed sensitivity to configural properties of spatial sequences.     

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。     

Simultaneous control of attention by multiple working memory representations

Working memory representations play a key role in controlling attention by making it possible to shift attention to task-relevant objects. Visual working memory has a capacity of three to four objects, but recent studies suggest that only one representation can guide attention at a given moment. We directly tested this proposal by monitoring eye movements while observers performed a visual search task in which they attempted to limit attention to objects drawn in two colors. When the observers were motivated to attend to one color at a time, they searched many consecutive items of one color (long run lengths) and exhibited a delay prior to switching gaze from one color to the other (switch cost). In contrast, when they were motivated to attend to both colors simultaneously, observers' gaze switched back and forth between the two colors frequently (short run lengths), with no switch cost. Thus, multiple working memory representations can concurrently guide attention.     

Top-down modulation: bridging selective attention and working memory

Selective attention, the ability to focus our cognitive resources on information relevant to our goals, influences working memory (WM) performance. Indeed, attention and working memory are increasingly viewed as overlapping constructs. Here, we review recent evidence from human neurophysiological studies demonstrating that top-down modulation serves as a common neural mechanism underlying these two cognitive operations. The core features include activity modulation in stimulus-selective sensory cortices with concurrent engagement of prefrontal and parietal control regions that function as sources of top-down signals. Notably, top-down modulation is engaged during both stimulus-present and stimulus-absent stages of WM tasks; that is, expectation of an ensuing stimulus to be remembered, selection and encoding of stimuli, maintenance of relevant information in mind and memory retrieval.     

Automatic and strategic effects in the guidance of attention by working memory representations

Theories of visual attention suggest that working memory representations automatically guide attention toward memory-matching objects. Some empirical tests of this prediction have produced results consistent with working memory automatically guiding attention. However, others have shown that individuals can strategically control whether working memory representations guide visual attention. Previous studies have not independently measured automatic and strategic contributions to the interactions between working memory and attention. In this study, we used a classic manipulation of the probability of valid, neutral, and invalid cues to tease apart the nature of such interactions. This framework utilizes measures of reaction time (RT) to quantify the costs and benefits of attending to memory-matching items and infer the relative magnitudes of automatic and strategic effects. We found both costs and benefits even when the memory-matching item was no more likely to be the target than other items, indicating an automatic component of attentional guidance. However, the costs and benefits essentially doubled as the probability of a trial with a valid cue increased from 20% to 80%, demonstrating a potent strategic effect. We also show that the instructions given to participants led to a significant change in guidance distinct from the actual probability of events during the experiment. Together, these findings demonstrate that the influence of working memory representations on attention is driven by both automatic and strategic interactions.     

Overlapping mechanisms of attention and spatial working memory

Spatial selective attention and spatial working memory have largely been studied in isolation. Studies of spatial attention have provided clear evidence that observers can bias visual processing towards specific locations, enabling faster and better processing of information at those locations than at unattended locations. We present evidence supporting the view that this process of visual selection is a key component of rehearsal in spatial working memory. Thus, although working memory has sometimes been depicted as a storage system that emerges 'downstream' of early sensory processing, current evidence suggests that spatial rehearsal recruits top-down processes that modulate the earliest stages of visual analysis.     

Exogenous and endogenous spatial attention effects on visuospatial working memory

In this study, we investigate how exogenous and endogenous orienting of spatial attention affect visuospatial working memory (VSWM). Specifically, we focused on two attentional effects and their consequences on storage in VSWM, when exogenous (Experiment 1) or endogenous (Experiment 2) orienting cues were used. The first effect, known as the meridian effect, is given by a decrement in behavioural performance when spatial cues and targets are presented in locations separated by vertical and/or horizontal meridians. The second effect, known as the distance effect, is given by a decrement in the orienting effects as a function of the spatial distance between cues and targets. Our results revealed a dissociation between exogenous and endogenous orienting mechanisms in terms of both meridian and distance effects. We found that meridian crossing affects performance only when endogenous cues were used. Specifically, VSWM performance with endogenous cueing depended more on the number of meridian crossings than on distance between cue and target. By contrast, a U-shaped distance dependency was observed using exogenous cues. Our findings therefore suggest that exogenous and endogenous orienting mechanisms lead to different forms of attentional bias for storage in VSWM.     

Spatial attention and feature-based attention are differentially sensitive to individual working memory capacity and perceptual load

ABSTRACT

A central and long-standing topic of interest to both psychologists and neuroscientists has been the capacity limited nature of perception, cognition and action. Most often, attention is the term invoked to label the mechanism by which a limited cognitive system can prioritize and select a subset of task-relevant sensory inputs and actions amongst a seemingly unbounded set of possible representations and behaviour. This selective mechanism is often modelled as a unitary and domain-general capacity-limited resource that is dynamically shifted to meet the processing demands invoked by the context. The present work offers a test of the unitary attention hypothesis using a variant of a classic validity manipulation [(Posner, M. I. (1980). Orienting of attention. Quarterly Journal of Experimental Psychology, 32, 3–25)] and the inferential logic of Sternberg (2001. Separate modifiability, mental modules, and the use of pure and composite measures to reveal them. Acta Psychologica, 106, 147–246). The results stand as evidence for at least two modular visual attention systems split according to a spatial and feature-based reference.     

Binding serial order to representations in working memory: a spatial/verbal dissociation

Verbal information is coded naturally as ordered representations in working memory (WM). However, this may not be true for spatial information. Accordingly, we used memory span tasks to test the hypothesis that serial order is more readily bound to verbal than to spatial representations. Removing serial-order requirements improved performance more for spatial locations than for digits. Furthermore, serial order was freely reproduced twice as frequently for digits as for locations. When participants reordered spatial sequences, they minimized the mean distance between items. Participants also failed to detect changes in serial order more frequently for spatial than for verbal sequences. These results provide converging evidence for a dissociation in the binding of serial order to spatial versus verbal representations. There may be separable domain-specific control processes responsible for this binding. Alternatively, there may be fundamental differences in how effectively temporal information can be bound to different types of stimulus features in WM.     

Shifting attention among working memory representations: testing cue type, awareness, and strategic control

It is well known that visual working memory (VWM) performance is modulated by attentional cues presented during encoding. Interestingly, retrospective cues presented after encoding, but prior to the test phase also improve performance. This improvement in performance is termed the retro-cue benefit. We investigated whether the retro-cue benefit is sensitive to cue type, whether participants were aware of their improvement in performance due to the retro-cue, and whether the effect was under strategic control. Experiment 1 compared the potential cueing benefits of abrupt onset retro-cues relying on bottom-up attention, number retro-cues relying on top-down attention, and arrow retro-cues, relying on a mixture of both. We found a significant retro-cue effect only for arrow retro-cues. In Experiment 2, we tested participants' awareness of their use of the informative retro-cue and found that they were aware of their improved performance. In Experiment 3, we asked whether participants have strategic control over the retro-cue. The retro-cue was difficult to ignore, suggesting that strategic control is low. The retro-cue effect appears to be within conscious awareness but not under full strategic control.     

Attention on our mind: The role of spatial attention in visual working memory

The current study shows that spatial visual attention is used to retrieve information from visual working memory. Participants had to keep four colored circles in visual working memory. While keeping this information in memory we asked whether one of the colors was present in the array. While retrieving this information, on some trials a probe dot was presented. When this probe dot was presented at the location of the color that had to be retrieved, participants responded faster than when it was presented at another location. Our findings further elaborate the role of visual attention in working memory: not only is attention the mechanism by which information is stored into working memory, it is also the mechanism by which information is retrieved from visual working memory.     

No evidence of binding items to spatial configuration representations in visual working memory

When detecting changes in visual features (e.g., colour or shape), object locations, represented as points within a configuration, might also be automatically represented in working memory. If the configuration of a scene is represented automatically, the locations of individual items might form part of this representation, irrespective of their relevance to the task. Participants took part in a change-detection task in which they studied displays containing different sets of items (shapes, letters, objects), which varied in their task relevance. Specifically, they were asked to remember the features of two sets, and ignore the third set. During the retention interval, an audio cue indicated which of the to-be-remembered sets would become the target set (having a 50% probability of containing a new feature). At test, they were asked to indicate whether a new feature was present amongst the target set. We measured binding of individual items to the configuration by manipulating the locations of the different sets so that their position in the test display either matched or mismatched their original location in the study display. If items are automatically bound to the configuration, location changes should disrupt performance, even if they were explicitly instructed not to remember the features of that particular set of items. There was no effect on performance of changing the locations of any of the sets between study and test displays, indicating that the configural representation did not enter their decision stage, and therefore that individual item representations are not necessarily bound to the configuration.     

No functional role of attention-based rehearsal in maintenance of spatial working memory representations

The present study systematically examined the role of attention in maintenance of spatial representations in working memory as proposed by the attention-based rehearsal hypothesis [Awh, E., Jonides, J., & Reuter-Lorenz, P. A. (1998). Rehearsal in spatial working memory. Journal of Experimental Psychology - Human Perception and Performance, 24(3), 780-790]. Three main issues were examined. First, Experiments 1-3 demonstrated that inhibition and not facilitation of visual processing is often observed at the memorized location during the retention interval. This inhibition was caused by keeping a location in memory and not by the exogenous nature of the memory cue. Second, Experiment 4 showed that inhibition of the memorized location does not lead to any significant impairment in memory accuracy. Finally, Experiment 5 connected current results to the previous findings and demonstrated facilitation of processing at the memorized location. Importantly, facilitation of processing did not lead to more accurate memory performance. The present results challenge the functional role of attention in maintenance of spatial working memory representations.     

The modulation of the flash-lag effect by voluntary attention

In the flash-lag effect (FLE), a flashing object appears to lag behind a moving object when both happen to be physically aligned to each other. According to an earlier account of the FLE (Baldo and Klein 1995 Nature 378 565-566), this perceptual phenomenon would result from differential delays in the perceptual processing of moving and flashing stimuli, presumably involving attentional mechanisms. Here, we have attempted to demonstrate in a more convincing way the participation of voluntary attention as a major component of the FLE. In experiment 1 the observer's attentional set was induced by the spatial probability structure of the visual stimulus. A flashing dot (relative to which the location of a moving dot should be judged) was presented, in separate blocks, at fixed, alternating, or randomly chosen locations. The two former conditions, providing a higher spatial predictability, yielded a smaller FLE than the latter condition, which provided a lower spatial predictability of the flashing dot. In experiment 2 we employed a standard cueing procedure, in which a participant was instructed to shift covertly his/her attentional focus according to a symbolic cue. The cue indicated, with a validity of 80%, the visual hemifield at which the flashing dot would be presented. As predicted by our conceptual model, the mean magnitude of the FLE in the valid trials was significantly smaller than that found in the invalid ones. Therefore, both experiments provided strong evidence supporting the participation of voluntary attention in the FLE. Attentional mechanisms should be seen not as the primary cause of the FLE, but rather as an important modulatory component of a broader process whose spatiotemporal dynamics engenders the FLE and possibly other related phenomena. Even though we elected an account based on the influence of attention on perceptual latencies, our empirical findings are compatible with other theoretical models embraced by the current flash-lag controversy and should be accommodated by every attempt to explain this perceptual phenomenon.     

Enhancement of perceptual representations by endogenous attention biases competition in response selection

Perception and response selection are core processes in the generation of overt behavior. Selective attention is known to facilitate behavioral performance by altering perceptual processes. It remains unclear, however, whether selective attention can aid the resolution of response conflict, and if so, at what stage of processing this takes place. In two experiments, an endogenous cuing task was combined with a flanker task to assess the interaction of selective attention with response selection. The results of Experiment 1 show that cuing reduces the flanker-congruency effect when the cue and flanker are presented in close temporal proximity to each other. The results of Experiment 2 demonstrate that pre- but not post-cuing the target reduced the congruency effect, showing that selective attention can affect performance, but is ineffective once stimulus processing has proceeded to response selection. Our results provide evidence that selective attention can aid the resolution of response conflict by altering early perceptual processing stages.     

Visual and proprioceptive representations in spatial memory

It has been shown that spatial information can be acquired from both visual and nonvisual modalities. The present study explored how spatial information from vision and proprioception was represented in memory, investigating orientation dependence of spatial memories acquired through visual and proprioceptive spatial learning. Experiment 1 examined whether visual learning alone and proprioceptive learning alone yielded orientation-dependent spatial memory. Results showed that spatial memories from both types of learning were orientation dependent. Experiment 2 explored how different orientations of the same environment were represented when they were learned visually and proprioceptively. Results showed that both visually and proprioceptively learned orientations were represented in spatial memory, suggesting that participants established two different reference systems based on each type of learning experience and interpreted the environment in terms of these two reference systems. The results provide some initial clues to how different modalities make unique contributions to spatial representations.     

Neural representations in human spatial memory

Ekstrom et al. report the responses of single neurons recorded from the brains of human subjects performing a spatial navigation task in virtual reality. They found cells encoding the subject's current location, view and destination. These data, and related findings in animals, directly reveal some of the representations underlying spatial cognition. They highlight the potential for cognitive psychology and systems neuroscience to combine to provide a neuronal-level understanding of human behaviour.     

Individual working memory capacity is uniquely correlated with feature-based attention when combined with spatial attention

A growing literature suggests that working memory and attention are closely related constructs. Both involve the selection of task-relevant information, and both are characterized by capacity limits. Furthermore, studies using a variety of methodological approaches have demonstrated convergent working memory and attention-related processing at the individual, neural and behavioral level. Given the varieties of both constructs, the specific kinds of attention and WM must be considered. We find that individuals' working memory capacity (WMC) uniquely interacts with feature-based attention when combined with spatial attention in a cuing paradigm (Posner, 1980). Our findings suggest a positive correlation between WM and feature-based attention only within the spotlight of spatial attention. This finding lends support to the controlled attention view of working memory by demonstrating that integrated feature-based expectancies are uniquely correlated with individual performance on a working memory task.     

Attention and spatial selection: electrophysiological evidence for modulation by perceptual load

Behavioral data have suggested that perceptual load can modulate spatial selection by influencing the allocation of attentional resources at perceptual-level processing stages (Lavie & Tsal, 1994). To directly test this hypothesis, event-related potentials (ERPs) were recorded for both low- and high-perceptual-load targets in a probabilistic spatial cuing paradigm. The results from three experiments showed that, as measured by the lateral occipital P1 and N1 ERP components, the magnitude of spatially selective processing in extrastriate visual cortex increased with perceptual load. Furthermore, these effects on spatial selection were found in the P1 at lower levels of perceptual load than in the N1. The ERP data thus provide direct electrophysiological support for proposals that link perceptual load to early spatial selection in visual processing. However, our findings suggest a relatively broader model--where perceptual load is but one of many factors mediating early selection.