Working memory capacity and visual attention: top-down and bottom-up guidance

Previous studies have indicated that working memory capacity (WMC) is related to visual attention when selection of critical information must be made in the face of distraction. The present study examines whether WMC-related differences in flanker task performance might be decreased by displays that are designed to support bottom-up guidance of attention. Participants were required to respond to a centrally located target while ignoring a peripheral flanker. In one condition, bottom-up support was provided by embedding the target in a row of zeros. In another condition, the zeros were removed, thus emphasizing the role of top-down attention in selecting spatially defined information. It was found that the inclusion of zeros led to the elimination of WMC-related flanker effects. We conclude that bottom-up attentional guidance can attenuate the role of WMC in selective attention.     

Working memory capacity and visual attention: Top-down and bottom-up guidance

Previous studies have indicated that working memory capacity (WMC) is related to visual attention when selection of critical information must be made in the face of distraction. The present study examines whether WMC-related differences in flanker task performance might be decreased by displays that are designed to support bottom-up guidance of attention. Participants were required to respond to a centrally located target while ignoring a peripheral flanker. In one condition, bottom-up support was provided by embedding the target in a row of zeros. In another condition, the zeros were removed, thus emphasizing the role of top-down attention in selecting spatially defined information. It was found that the inclusion of zeros led to the elimination of WMC-related flanker effects. We conclude that bottom-up attentional guidance can attenuate the role of WMC in selective attention.     

Task-based working memory guidance of visual attention

Previous research has established that holding a stimulus in working memory (WM) facilitates the deployment of visual attention to that stimulus relative to other stimuli. The present study examined whether maintaining a specific task in WM would also bias the allocation of attention to the stimuli associated with that task. Participants performed a speeded letter search task while simultaneously keeping in WM one of two task cues shown at the beginning of each trial. The results showed that task-based WM guidance of attention was modulated by response latencies. Whereas the participants with fast reaction times showed little influence of WM contents, the participants with slow reaction times took longer to respond when the letter target appeared in a distractor stimulus consistent with the task cue held in mind. A subsequent Stroop experiment found a larger Stroop interference effect from the participants in the slow group compared with those in the fast group, suggesting that the differential WM effect between the two groups may be associated with an individual's ability to inhibit task-irrelevant information. Taken together, these results expanded the realm of previous research and provided further evidence for a close link between attention and WM.     

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.     

Object-based visual attention with endogenous orienting

In a series of experiments, we examined covert orienting using endogenous cuing, in which attention is voluntarily directed toward a peripheral location. In one experiment, subjects were cued to attend to one end of an oblong object. They then detected targets on the cued object or elsewhere. In another experiment, subjects provided judgments of the relative temporal order of two flashes after their attention had moved endogenously. In a third experiment, subjects were directed to attend to an empty spatial location and subsequently discriminated features of objects that appeared at or near the locus of attention. In each of these situations, attentional orienting was object based, in the sense that nonattended locations that were on the cued object had an advantage over nonattended locations that were not on the object. The results are discussed in terms of their implications for object-based representations and the differences between exogenous and endogenous orienting of attention.     

Endogenous-like orienting of visual attention in rats

This study investigated the orienting of visual attention in rats using a 3-hole nose-poke task analogous to Posner, Information processing in cognition: the Loyola Symposium, Erlbaum, Hillsdale, (1980) covert attention task for humans. The effects of non-predictive (50% valid and 50% invalid) and predictive (80% valid and 20% invalid) peripheral visual cues on reaction times and response accuracy to a target stimulus, using Stimuli-Onset Asynchronies (SOAs) varying between 200 and 1,200 ms, were investigated. The results showed shorter reaction times in valid trials relative to invalid trials for both subjects trained in the non-predictive and predictive conditions, particularly when the SOAs were 200 and 400 ms. However, the magnitude of this validity effect was significantly greater for subjects exposed to predictive cues, when the SOA was 800 ms. Subjects exposed to invalid predictive cues exhibited an increase in omission errors relative to subjects exposed to invalid non-predictive cues. In contrast, valid cues reduced the proportion of omission errors for subjects trained in the predictive condition relative to subjects trained in the non-predictive condition. These results are congruent with those usually reported for humans and indicate that, in addition to the exogenous capture of attention promoted by both predictive and non-predictive peripheral cues, rats exposed to predictive cues engaged an additional slower process equivalent to human's endogenous orienting of attention. To our knowledge, this is the first demonstration of an endogenous-like process of covert orienting of visual attention in rats.     

Alerting and orienting of attention without visual awareness

Two types of the attentional network, alerting and orienting, help organisms respond to environmental events for survival in the temporal and spatial dimensions, respectively. Here, we applied chromatic flicker beyond the critical fusion frequency to address whether awareness was necessary for activation of the two attentional networks. We found that high-frequency chromatic flicker, despite its failure to reach awareness, produced the alerting and orienting effects, supporting the dissociation between attention and awareness. Furthermore, as the flicker frequency increased, the orienting effect attenuated whereas the alerting effect remained unchanged. According to the systematic decline in temporal frequency sensitivity across the visual hierarchy, this finding suggests that unconscious alerting might be associated with activity in earlier visual areas than unconscious orienting. Since high-frequency flicker has been demonstrated to only activate early visual cortex, we suppose that neural activation in early visual areas might be sufficient to activate the two attentional networks.     

Working memory and focal attention

Measures of retrieval speed indicated that only a small subset of representations in working memory falls within the focus of attention. An n-back task, which required tracking an item 1, 2, or 3 back in a sequentially presented list, was used to examine the representation and retrieval of recent events and how control processes can be used to maintain an item in focal attention while concurrently processing new information. A speed-accuracy trade-off procedure was used to derive measures of the availability and the speed with which recent events can be accessed. Results converge with other time course studies in demonstrating that attention can be concurrently allocated only to a small number of memory representations, perhaps just 1 item. Measures of retrieval speed further demonstrate that order information is retrieved by a slow search process when an item is not maintained within focal attention.     

Competition between endogenous and exogenous orienting of visual attention

The relation between reflexive and voluntary orienting of visual attention was investigated with 4 experiments: a simple detection task, a localization task, a saccade toward the target task, and a target identification task in which discrimination difficulty was manipulated. Endogenous and exogenous orienting cues were presented in each trial and their validity was manipulated orthogonally to examine whether attention mechanisms are mediated by separate systems and whether they have additive and independent effects on visual detection and discrimination. The results showed that each orienting mechanism developed its typical and independent effect in every case except for the difficult identification task. A theoretical framework for understanding the relationship between endogenous and exogenous orienting of attention is proposed, tested, and confirmed.     

Emotional attention: effects of emotion and gaze direction on overt orienting of visual attention

In the present study we considered the two factors that have been advocated for playing a role in emotional attention: perception of gaze direction and facial expression of emotions. Participants performed an oculomotor task in which they had to make a saccade towards one of the two lateral targets, depending on the colour of the fixation dot which appeared at the centre of the computer screen. At different time intervals (stimulus onset asynchronies, SOAs: 50,100,150 ms) following the onset of the dot, a picture of a human face (gazing either to the right or to the left) was presented at the centre of the screen. The gaze direction of the face could be congruent or incongruent with respect to the location of the target, and the expression could be neutral or angry. In Experiment 1 the facial expressions were presented randomly in a single block, whereas in Experiment 2 they were shown in separate blocks. Latencies for correct saccades and percentage of errors (saccade direction errors) were considered in the analyses. Results showed that incongruent trials determined a significantly higher percentage of saccade direction errors with respect to congruent trials, thus confirming that gaze direction, even when task-irrelevant, interferes with the accuracy of the observer’s oculomotor behaviour. The angry expression was found to hold attention for a longer time with respect to the neutral one, producing delayed saccade latencies. This was particularly evident at 100 ms SOA and for incongruent trials. Emotional faces may then exert a modulatory effect on overt attention mechanisms.     

Attention to memory: orienting attention to sound object representations

Despite a growing acceptance that attention and memory interact, and that attention can be focused on an active internal mental representation (i.e., reflective attention), there has been a paucity of work focusing on reflective attention to ‘sound objects’ (i.e., mental representations of actual sound sources in the environment). Further research on the dynamic interactions between auditory attention and memory, as well as its degree of neuroplasticity, is important for understanding how sound objects are represented, maintained, and accessed in the brain. This knowledge can then guide the development of training programs to help individuals with attention and memory problems. This review article focuses on attention to memory with an emphasis on behavioral and neuroimaging studies that have begun to explore the mechanisms that mediate reflective attentional orienting in vision and more recently, in audition. Reflective attention refers to situations in which attention is oriented toward internal representations rather than focused on external stimuli. We propose four general principles underlying attention to short-term memory. Furthermore, we suggest that mechanisms involved in orienting attention to visual object representations may also apply for orienting attention to sound object representations.     

The spatial distribution of attention during covert visual orienting

Many studies of covert orienting of visual attention in response to informative pre-cues have focused on the spatial distribution of improved or impaired performance. One can find at least four different models in the literature, each describing a different distribution: the fixed gradient spotlight; the zoom lens spotlight; the hemifield activation hypothesis; and the flexible allocation of resources model. In previous work examining procedural details that might have led to the formulation of the hemifield activation hypothesis, it was postulated (Klein and McCormick 1989) that under conditions of uncertainty about which of two locations to attend, an observer may focus attention on a visual channel (i.e., midlocation placement of a fixed gradient spotlight) that is spatially intermediate. The present experiment was designed to distinguish among the four models of attentional distribution, and to test the midlocation placement strategy. Our findings show support for midlocation placement, demonstrate evidence against flexible allocation and hemifield activation, but could not differentiate between fixed gradient and zoom lens variants of the spotlight model.     

Dynamic states in working memory modulate guidance of visual attention: Evidence from an n-back paradigm

Items held in working memory (WM) can automatically bias attention when they reappear in visual displays. Recent evidence, however, suggests that WM biases of attention may be reduced under certain conditions, for example with increasing memory load. We employed a dual task paradigm to investigate how WM biases are affected by dynamic updating of memory contents. 1-back and 2-back versions of a memory task with colour stimuli were interrupted at intervals by an unrelated visual search task. Reappearance in the search display of the item that was currently active in WM guided attention, while suppressed or inactive items did not. We conclude that the rapid updating of memory contents facilitates the shifting of memory representations into different activity states on a moment-to-moment basis. The finding is consistent with models that propose that only one item can be “active” in WM at any one time to guide attention.     

Relations between covert orienting and filtering in the development of visual attention

This study examined a widely held assumption concerning the development of visual attention, namely, that different aspects of visual selectivity depend on common processing resources. Observers aged 5, 7, 9, and 24 years participated in a speeded classification task designed to examine the relations between covert shifts of attention and filtering. There were three important findings: (1) covert orienting and filtering share processing resources, (2) the ability to orient covertly to a target location and to filter competing information on the same trial became more efficient with age, and (3) 5 year olds were able to filter as efficiently as adults when target location was precued. The implications of these results for theories of attentional development are discussed.     

Working memory capacity and the top-down control of visual search: Exploring the boundaries of "executive attention"

The executive attention theory of working memory capacity (WMC) proposes that measures of WMC broadly predict higher order cognitive abilities because they tap important and general attention capabilities (R. W. Engle & M. J. Kane, 2004). Previous research demonstrated WMC-related differences in attention tasks that required restraint of habitual responses or constraint of conscious focus. To further specify the executive attention construct, the present experiments sought boundary conditions of the WMC-attention relation. Three experiments correlated individual differences in WMC, as measured by complex span tasks, and executive control of visual search. In feature-absence search, conjunction search, and spatial configuration search, WMC was unrelated to search slopes, although they were large and reliably measured. Even in a search task designed to require the volitional movement of attention (J. M. Wolfe, G. A. Alvarez, & T. S. Horowitz, 2000), WMC was irrelevant to performance. Thus, WMC is not associated with all demanding or controlled attention processes, which poses problems for some general theories of WMC.     

Automatic guidance of attention from working memory

Recent research has shown interactions between the process of keeping information 'online' in working memory, and the processes that select relevant information for a response. In particular, our ability to select stimuli in the environment can be modulated by whether the stimuli match the current contents of working memory. Guidance of selection from working memory occurs automatically, even when it is detrimental to performance. Neurophysiological data, from functional brain imaging, indicate that the interaction between working memory and attention is based on neuronal mechanisms distinct from the processes mediating 'bottom-up' priming effects from implicit memory. We discuss the importance of 'top-down' influences from working memory on the 'early' deployment of attention and on the processes that gate visual information into awareness.     

Social attention orienting integrates visual information from head and body orientation

Subjects were asked to detect visual, laterally presented reaction signals preceded by head-body cue stimuli in a spatial cueing task. A head rotated towards the reaction signal combined with a front view of a body resulted in shorter reaction times in comparison to the front view of a head and body. In contrast, a cue showing the head and body rotated towards the reaction signal did not result in such a facilitation in reaction times. The results suggest that the brain mechanisms involved in social attention orienting integrate ventrally processed visual information from the head and body orientation. A cue signaling that the other person, in his or her frame of reference, has an averted attention direction shifts the observer's own attention in the same direction.     

Control of goal-directed movements: the contribution of orienting of visual attention and motor preparation.

Three experiments investigated the role of attention and motor preparation for the control of goal-directed movements. In Experiment 1 (double step paradigm), a movement correction was required on 25% of the trials towards the left or right of the initial target. Within these 25% of trials, the probability of location of the second target was manipulated. The efficiency of movement control increased when increasing the probability of correcting the movement in a given direction. In Experiment 2, attentional processes were isolated by asking the subjects to verbally detect the more or less probable target displacement, without correcting their movement. Subjects were able to orient visual attention during movement execution, thus improving the processing of visual feedbacks from target displacement. In Experiment 3, motor preparation processes were isolated by asking the subjects to correct their movement towards a fixed target in response to a more or less probable mechanical perturbation. It was shown that motor preparation not only specifies the initial movement parameters but may also include some parameters of the most probable movement modulations. Overall, these results highlight the role of both attentional and motor preparation processes in the control of goal-directed movements and suggest that the feedback-based corrections of the movement are modulated by a feedforward control.     

Movement and attention in visual working memory

Three experiments that adopt an interference technique to investigate the involvement of movement in the production of a spatial code are described. Arm movements rather than the more commonly employed eye movements are used to provide initial information about the sorts of movements relevant to the code and to allow an empirical separation of the contributions of movement and attention. The results confirm the interference effects of incompatible movement on the generation of the spatial code and show that movement per se rather than attention to the movement can cause a performance decrement.