Rapid, object-based learning in the deployment of transient attention

Priming of probabilistic attentional templates

Attentional priming has a dominating influence on vision, speeding visual search, releasing items from crowding, reducing masking effects, and during free-choice, primed targets are chosen over unprimed ones. Many accounts postulate that templates stored in working memory control what we attend to and mediate the priming. But what is the nature of these templates (or representations)? Analyses of real-world visual scenes suggest that tuning templates to exact color or luminance values would be impractical since those can vary greatly because of changes in environmental circumstances and perceptual interpretation. Tuning templates to a range of the most probable values would be more efficient. Recent evidence does indeed suggest that the visual system represents such probability, gradually encoding statistical variation in the environment through repeated exposure to input statistics. This is consistent with evidence from neurophysiology and theoretical neuroscience as well as computational evidence of probabilistic representations in visual perception. I argue that such probabilistic representations are the unit of attentional priming and that priming of, say, a repeated single-color value simply involves priming of a distribution with no variance. This "priming of probability" view can be modelled within a Bayesian framework where priming provides contextual priors. Priming can therefore be thought of as learning of the underlying probability density function of the target or distractor sets in a given continuous task.

Target detection and discrimination in pop-out visual search with two targets

To successfully interact with objects in complex and crowded environments, we often perform visual search to detect or identify a relevant target (or targets) among distractors. Previous studies have reported a redundancy gain when two targets instead of one are presented in a simple target detection task. However, research is scant about the role of multiple targets in target discrimination tasks, especially in the context of visual search. Here, we address this question and investigate its underlying mechanisms in a pop-out search paradigm. In Experiment 1, we directly compared visual search performance for one or two targets for detection or discrimination tasks. We found that two targets led to a redundancy gain for detection, whereas it led to a redundancy cost for discrimination. To understand the basis for the redundancy cost observed in discrimination tasks for multiple targets, we further investigated the role of perceptual grouping (Experiment 2) and stimulus-response feature compatibility (Experiment 3). We determined that the strength of perceptual grouping among homogenous distractors was attenuated when two targets were present compared with one. We also found that response compatibility between two targets contributed more to the redundancy cost compared with perceptual compatibility. Taken together, our results show how pop-out search involving two targets is modulated by the level of feature processing, perceptual grouping, and compatibility of perceptual and response features.

Eating disorder symptoms and foraging for food related items

BACKGROUND

Foraging tasks have recently been increasingly used to investigate visual attention. Visual attention can be biased when certain stimuli capture our attention, especially threatening or anxiety-provoking stimuli, but such effects have not been addressed in foraging studies.

METHODS

We measured potential attentional bias associated with eating disorder symptoms to food related stimuli with our previously developed iPad foraging task. Forty-four participants performed a foraging task where they were instructed to tap predesignated food related targets (healthy and unhealthy) and other non-food objects and completed four self-report questionnaires measuring symptoms of eating disorders. Participants were split into two groups based on their questionnaire scores, a symptom group and no symptom group.

RESULTS

The foraging results suggest that there are differences between the groups on switch costs and target selection times (intertarget times) but they were only statistically significant when extreme-group analyses (EGA) were used. There were also notable food versus non-food category effects in the foraging patterns.

CONCLUSIONS

The results suggest that foraging tasks of this sort can be used to assess attentional biases and we also speculate that they may eventually be used to treat them through attention bias modification. Additionally, the category effects that we see between food items and other items are highly interesting and encouraging. At the same time, task sensitivity will need to be improved. Finally, future tests of clinical samples could provide a clearer picture of the effects of eating disorder symptoms on foraging for food.

Measuring Biases of Visual Attention: A Comparison of Four Tasks

Attention biases to stimuli with emotional content may play a role in the development and maintenance of anxiety disorders. The most commonly used tasks in measuring and treating such biases, the dot-probe and spatial cueing tasks, have yielded mixed results, however. We assessed the sensitivity of four visual attention tasks (dot-probe, spatial cueing, visual search with irrelevant distractor and attentional blink tasks) to differences in attentional processing between threatening and neutral faces in 33 outpatients with a primary diagnosis of social anxiety disorder (SAD) and 26 healthy controls. The dot-probe and cueing tasks revealed no differential processing of neutral and threatening faces between the SAD and control groups. The irrelevant distractor task showed some sensitivity to differential processing for the SAD group, but the attentional blink task was uniquely sensitive to such differences in both groups, and revealed processing differences between the SAD and control groups. The attentional blink task also revealed interesting temporal dynamics of attentional processing of emotional stimuli and may provide a uniquely nuanced picture of attentional response to emotional stimuli. Our results therefore suggest that the attentional blink task is more suitable for measuring preferential attending to emotional stimuli and treating dysfunctional attention patterns than the more commonly used dot-probe and cueing tasks.

Associative cueing of attention through implicit feature-location binding

In order to assess associative learning between two task-irrelevant features in cueing spatial attention, we devised a task in which participants have to make an identity comparison between two sequential visual stimuli. Unbeknownst to them, location of the second stimulus could be predicted by the colour of the first or a concurrent sound. Albeit unnecessary to perform the identity-matching judgment the predictive features thus provided an arbitrary association favouring the spatial anticipation of the second stimulus. A significant advantage was found with faster responses at predicted compared to non-predicted locations. Results clearly demonstrated an associative cueing of attention via a second-order arbitrary feature/location association but with a substantial discrepancy depending on the sensory modality of the predictive feature. With colour as predictive feature, significant advantages emerged only after the completion of three blocks of trials. On the contrary, sound affected responses from the first block of trials and significant advantages were manifest from the beginning of the second. The possible mechanisms underlying the associative cueing of attention in both conditions are discussed.

The effect of object-centered instructions in Cartesian and polar coordinates on saccade vector

Express saccades (ES) are the most reflexive saccadic eye movements, with very short reaction times of 70-110 ms. It is likely that ES have the shortest saccade reaction times (SRTs) possible given the known physiological and anatomical delays present in sensory and motor systems. Nevertheless, it has been demonstrated that a vector displacement of ES to spatially extended stimuli can be influenced by spatial cognition. Edelman, Kristjansson, and Nakayama (2007) found that when two horizontally separated visual stimuli appear at a random location, the spatial vector, but not the reaction time, of human ES is strongly influenced by an instruction to make a saccade to one side (either left or right) of a visual stimulus array. Presently, we attempt to extend these findings of cognitive effects on saccades in three ways: (a) determining whether ES could be affected by other types of spatial instructions: vertical, polar amplitude, and polar direction; (b) determining whether these spatial effects increased with practice; and (c) determining how these effects depended on SRTs. The results demonstrate that both types of Cartesian as well as polar amplitude instructions strongly affect ES vector, but only modestly affect SRTs. Polar direction instructions had sizable effects only on nonreflexive saccades where the visual stimuli could be viewed for several hundred milliseconds prior to saccade execution. Short- (trial order within a block) and long-term (experience across several sessions) practice had little effect, though the effect of instruction increased with SRT. Such findings suggest a generalized, innate ability of cognition to affect the most reflexive saccadic eye movements.

Surface Assignment Modulates Object Formation for Visual Short-Term Memory

Recent results have suggested that the operational units of visual short-term memory (VSTM) are whole objects, rather than features or the total amount of information to be remembered. Here, for the first time, the influence of surface assignment on object formation for VSTM was investigated. The observers had to memorize the features of four briefly presented (300 ms) two-part objects, followed by a mask and a cue indicating which object to report on. The experiments contrasted whether there were any apparent depth differences between the two parts of each object, and whether observers had to report on only one or both features of the post-cued target object. Depth differences induced with stereoscopic disparity, and with a pictorial depth cue (simple interposition of object features), interfered strongly with performance when both features of an object needed to be memorized, but aided performance when only a single feature needed to be remembered. Furthermore, there was considerable within-feature interference consistent with some previous findings, but contradicting others. The potential implications for conceptions of VSTM are discussed in the light of two hypothesized stages: an early feature-based stage, as well as a higher-level object-based stage where the depth manipulations exert their effects. The results argue for a strong modulatory influence of surface assignment on object formation for a VSTM task.

Do New Objects Capture Attention?

The visual system relies on several heuristics to direct attention to important locations and objects. One of these mechanisms directs attention to sudden changes in the environment. Although a substantial body of research suggests that this capture of attention occurs only for the abrupt appearance of a new perceptual object, more recent evidence shows that some luminance-based transients (e.g., motion and looming) and some types of brightness change also capture attention. These findings show that new objects are not necessary for attention capture. The present study tested whether they are even sufficient. That is, does a new object attract attention because the visual system is sensitive to new objects or because it is sensitive to the transients that new objects create? In two experiments using a visual search task, new objects did not capture attention unless they created a strong local luminance transient.

Barking up the wrong tree in attentional bias modification? Comparing the sensitivity of four tasks to attentional biases

BACKGROUND AND OBJECTIVES

Attentional bias modification (ABM) is a potentially exciting new development in the treatment of anxiety disorders. However, reported therapeutic benefits have not always been replicated. To gauge the sensitivity of tasks used in ABM treatment and assessment, we used a counterbalanced within-subject design to measure their discriminant sensitivity to neutral and threatening facial expressions, comparing them with other well-known tasks that measure visual attention.

METHODS

We compared two tasks often used in the assessment and treatment of attention bias (the dot-probe and the spatial cueing paradigms) with two well-known visual attention tasks (the irrelevant singleton and attentional blink paradigms), measuring their sensitivity to processing differences between threatening and neutral expressions for non-clinical observers.

RESULTS

The dot-probe, spatial cueing and irrelevant singleton paradigms showed little or no sensitivity to processing differences between facial expressions while the attentional blink task proved very sensitive to such differences. Furthermore, the attentional blink task provided an intriguing picture of the temporal dynamics of attentional biases that the other paradigms cannot do.

LIMITATIONS

These results need to be replicated with larger samples, including a comparison of a group of individuals diagnosed with social anxiety disorder and normal controls.

CONCLUSIONS

Our results indicate that the sensitivity of putative attentional bias measures should be assessed experimentally for more powerful assessment and treatment of such biases. If the attentional blink task is indeed particularly sensitive to attentional biases, as our findings indicate, it is not unreasonable to expect that interventions based on this task may be more effective than those based on the tasks that are currently used.

Positional priming of visual pop-out search is supported by multiple spatial reference frames

The present study investigates the representations(s) underlying positional priming of visual ‘pop-out’ search (Maljkovic and Nakayama, 1996). Three search items (one target and two distractors) were presented at different locations, in invariant (Experiment 1) or random (Experiment 2) cross-trial sequences. By these manipulations it was possible to disentangle retinotopic, spatiotopic, and object-centered priming representations. Two forms of priming were tested: target location facilitation (i.e., faster reaction times – RTs– when the trial n target is presented at a trial n-1 target relative to n-1 blank location) and distractor location inhibition (i.e., slower RTs for n targets presented at n-1 distractor compared to n-1 blank locations). It was found that target locations were coded in positional short-term memory with reference to both spatiotopic and object-centered representations (Experiment 1 vs. 2). In contrast, distractor locations were maintained in an object-centered reference frame (Experiments 1 and 2). We put forward the idea that the uncertainty induced by the experiment manipulation (predictable versus random cross-trial item displacements) modulates the transition from object- to space-based representations in cross-trial memory for target positions.

Exogenous attention to unseen objects?

Attention and awareness are closely related phenomena, but recent evidence has shown that not all attended stimuli give rise to awareness. Controversy still remains over whether, and the extent to which, a dissociation between attention and awareness encompasses all forms of attention. For example, it has been suggested that attention without awareness is more readily demonstrated for voluntary, endogenous attention than its reflexive, exogenous counterpart. Here we examine whether exogenous attentional cueing can have selective behavioural effects on stimuli that nevertheless remain unseen. Using a task in which object-based attention has been shown in the absence of awareness, we remove all possible contingencies between cues and target stimuli to ensure that any cueing effects must be under purely exogenous control, and find evidence of exogenous object-based attention without awareness. In a second experiment we address whether this dissociation crucially depends on the method used to establish that the objects indeed remain unseen. Specifically, to confirm that objects are unseen we adopt appropriate signal detection task procedures, including those that retain parity with the primary attentional task (by requiring participants to discriminate the two types of trial that are used to measure an effect of attention). We show a significant object-based attention effect is apparent under conditions where the selected object indeed remains undetectable.

Nonspecific competition underlies transient attention

Cueing a target by abrupt visual stimuli enhances its perception in a rapid but short-lived fashion, an effect known as transient attention. Our recent study showed that when targets are cued at a constant, central location, the emergence of the transient performance pattern was dependent on the presence of competing distractors, whereas targets presented in isolation were enhanced in a sustained manner (Wilschut et al., PLoS ONE, 6:e27661, 2011). The current study examined in more detail whether the transience depends on the specific nature of the competition. We first replicated and extended the competition-dependent transient pattern for peripheral and variable target locations. We then investigated the role of feature similarity, compatibility, and proximity. Both competition by feature similarity and compatibility between the target and distractors were found to impair performance, but effects were additive with the effects of the cueing interval and did not change the transient performance function. Varying the spatial distance between target and distractors yielded mixed evidence, but here too a transient pattern could be observed for targets flanked by both close and far distractors. The results thus show that the presence or absence of competition determines whether attention appears transient or sustained, while the specific nature of the competition (in terms of location or feature) affects selection independent of time.

Spatial distribution of attentional bias in visuo-spatial working memory following multiple cues

When attention is focused on one location, its spatial distribution depends on many factors, such as the distance between the attended location and the target location, the presence of visual meridians in between them, and the way, endogenous or exogenous, by which attention is oriented. However, it is not well known how attention distributes when more than one location is endogenously or exogenously cued, which was the focus of the current study. Furthermore, the distribution of attention has been manly investigated in perception. In the present study we faced this issue from a different perspective, by examining the spatial distribution of the attentional bias in visuo-spatial working memory (VSWM), when attention is oriented either exogenously or endogenously, i.e., after two peripheral vs. central symbolic cues (also manipulating cue-target predictability). Results indicated a systematic difference between endogenous and exogenous attention regarding the distribution of the attentional bias over VSWM. In fact, attentional bias following endogenous cues was affected by the presence of visual meridians and by the split of the attentional focus, converging in a unipolar attentional distribution, independently of cue-target predictability. On the other hand, when pulled by exogenous cues, attention distributed uni-modally or multi-modally depending on the distance between the cued locations, with larger effects for highly predictive cues. Results are discussed in terms of space-based, object-based and perceptual grouping mechanisms.

Modeling the effect of selection history on pop-out visual search

While attentional effects in visual selection tasks have traditionally been assigned “top-down” or “bottom-up” origins, more recently it has been proposed that there are three major factors affecting visual selection: (1) physical salience, (2) current goals and (3) selection history. Here, we look further into selection history by investigating Priming of Pop-out (POP) and the Distractor Preview Effect (DPE), two inter-trial effects that demonstrate the influence of recent history on visual search performance. Using the Ratcliff diffusion model, we model observed saccadic selections from an oddball search experiment that included a mix of both POP and DPE conditions. We find that the Ratcliff diffusion model can effectively model the manner in which selection history affects current attentional control in visual inter-trial effects. The model evidence shows that bias regarding the current trial's most likely target color is the most critical parameter underlying the effect of selection history. Our results are consistent with the view that the 3-item color-oddball task used for POP and DPE experiments is best understood as an attentional decision making task.

Matching Cue Size and Task Properties in Exogenous Attention

Exogenous attention is an involuntary, reflexive orienting response that results in enhanced processing at the attended location. The standard view is that this enhancement generalizes across visual properties of a stimulus. We test whether the size of an exogenous cue sets the attentional field and whether this leads to different effects on stimuli with different visual properties. In a dual task with a random-dot kinematogram (RDK) in each quadrant of the screen, participants discriminated the direction of moving dots in one RDK and localized one red dot. Precues were uninformative and consisted of either a large or a small luminance-change frame. The motion discrimination task showed attentional effects following both large and small exogenous cues. The red dot probe localization task showed attentional effects following a small cue, but not a large cue. Two additional experiments showed that the different effects on localization were not due to reduced spatial uncertainty or suppression of RDK dots in the surround. These results indicate that the effects of exogenous attention depend on the size of the cue and the properties of the task, suggesting the involvement of receptive fields with different sizes in different tasks. These attentional effects are likely to be driven by bottom-up mechanisms in early visual areas.

Simultaneous attentional guidance by working-memory and selection history reveals two distinct sources of attention

Recent theories of attention have proposed that selection history is a separate, dissociable source of information that influences attention. The current study sought to investigate the simultaneous involvement of selection history and working-memory on attention during visual search. Experiments 1 and 2 used target feature probability to manipulate selection history and found significant effects of both working-memory and selection history, although working-memory dominated selection history when they cued different locations. Experiment 3 eliminated the contribution of voluntary refreshing of working-memory and replicated the main effects, although selection history became dominant. Using the same methodology, but with reduced probability cue validity, both effects were present in Experiment 4 and did not significantly differ in their contribution to attention. Effects of selection history and working-memory never interacted. These results suggest that selection history and working-memory are separate influences on attention and have little impact on each other. Theoretical implications for models of attention are discussed.

Early perceptual interactions shape the time course of cueing

Performance in spatial cueing tasks is characterized by a rapid attentional enhancement with increasing cue-target SOA. We recently found that this enhancement function also applies when the cue and the target are presented invariably at a single central location, suggesting a universal cueing time course [Wilschut et al., 2011, PLoS ONE, 6, e27661]. However, using a very similar cueing task, Nieuwenstein et al. [2009, JoV, 9, 1-14] have found a rather different pattern, namely a U-shaped deficit in performance after a cue-like stimulus. The present study varied the properties of the cue and the target in order to investigate the mechanisms underlying the different time functions. In four experiments, cueing was found to either improve or decrease performance with increasing SOA, depending on the type of target that was used. In addition, the level of performance at the shortest cue-target intervals (33-83ms) was dependent on the relative strength of the cue and the target, akin to what has been found in visual masking studies. The results suggest that cueing shapes performance via two mechanisms, one sensory-related and one attention-related, the combination of which results in either U-shaped or monotonic patterns.

Object-centered representations support flexible exogenous visual attention across translation and reflection

Visual attention can be deployed to stimuli based on our willful, top-down goal (endogenous attention) or on their intrinsic saliency against the background (exogenous attention). Flexibility is thought to be a hallmark of endogenous attention, whereas decades of research show that exogenous attention is attracted to the retinotopic locations of the salient stimuli. However, to the extent that salient stimuli in the natural environment usually form specific spatial relations with the surrounding context and are dynamic, exogenous attention, to be adaptive, should embrace these structural regularities. Here we test a non-retinotopic, object-centered mechanism in exogenous attention, in which exogenous attention is dynamically attracted to a relative, object-centered location. Using a moving frame configuration, we presented two frames in succession, forming either apparent translational motion or in mirror reflection, with a completely uninformative, transient cue presented at one of the item locations in the first frame. Despite that the cue is presented in a spatially separate frame, in both translation and mirror reflection, behavioralperformance in visual search is enhanced when the target in the second frame appears at the same relative location as the cue location than at other locations. These results provide unambiguous evidence for non-retinotopic exogenous attention and further reveal an object-centered mechanism supporting flexible exogenous attention. Moreover, attentional generalization across mirror reflection may constitute an attentional correlate of perceptual generalization across lateral mirror images, supporting an adaptive, functional account of mirror images confusion.

Rewards teach visual selective attention

Visual selective attention is the brain function that modulates ongoing processing of retinal input in order for selected representations to gain privileged access to perceptual awareness and guide behavior. Enhanced analysis of currently relevant or otherwise salient information is often accompanied by suppressed processing of the less relevant or salient input. Recent findings indicate that rewards exert a powerful influence on the deployment of visual selective attention. Such influence takes different forms depending on the specific protocol adopted in the given study. In some cases, the prospect of earning a larger reward in relation to a specific stimulus or location biases attention accordingly in order to maximize overall gain. This is mediated by an effect of reward acting as a type of incentive motivation for the strategic control of attention. In contrast, reward delivery can directly alter the processing of specific stimuli by increasing their attentional priority, and this can be measured even when rewards are no longer involved, reflecting a form of reward-mediated attentional learning. As a further development, recent work demonstrates that rewards can affect attentional learning in dissociable ways depending on whether rewards are perceived as feedback on performance or instead are registered as random-like events occurring during task performance. Specifically, it appears that visual selective attention is shaped by two distinct reward-related learning mechanisms: one requiring active monitoring of performance and outcome, and a second one detecting the sheer association between objects in the environment (whether attended or ignored) and the more-or-less rewarding events that accompany them. Overall this emerging literature demonstrates unequivocally that rewards "teach" visual selective attention so that processing resources will be allocated to objects, features and locations which are likely to optimize the organism's interaction with the surrounding environment and maximize positive outcome.

Cueing effects of target location probability and repetition

The search performance for targets is improved when the targets appear in a specific location more frequently than in other locations. Although this phenomenon, called the "probability cueing effect," has been reported in past studies, it is unclear whether probability cueing is driven by statistical learning and/or intertrial facilitation of the target location. We investigated the underlying mechanisms for probability cueing effects by manipulating probabilities and repetitions of the target appearance at each target location. The first experiment demonstrated that the reaction time benefits of both statistical learning and intertrial facilitation contributed to the probability cueing effect. In contrast, the second and third experiments demonstrated that the probability cueing effect did not occur when target location repetitions on consecutive trials were fully or partially restricted. Also, any intertrial facilitation effects disappeared if there were more than one intervening trials. These results suggest that consecutive target location repetitions throughout the experiment facilitate learning of the target location probability.

Dynamic coding of temporal luminance variation

The range of variation in environmental stimuli is much larger than the visual system can represent. It is therefore sensible for the system to adjust its responses to the momentary input statistics of the environment, such as when our pupils contract to limit the light entering the eye. Previous evidence indicates that the visual system increasingly centers responses on the mean of the visual input and scales responses to its variation during adaptation. To what degree does adaptation to a stimulus varying in luminance over time result in such adjustment of responses? The first two experiments were designed to test whether sensitivity to changes in the amplitude and the mean of a 9.6° central patch varying sinusoidally in luminance at 0.6 Hz would increase or decrease with adaptation. This was also tested for a dynamic peripheral stimulus (random patches rotating on the screen) to test to what extent the effects uncovered in the first two experiments reflect retinotopic mechanisms. Sensitivity to changes in mean and amplitude of the temporal luminance variation increased sharply the longer the adaptation to the variation, both for the large patch and the peripheral patches. Adaptation to luminance variation leads to increased sensitivity to temporal luminance variation for both central and peripheral presentation, the latter result ruling retinotopic mechanisms out as sole explanations for the adaptation effects.

Changes in search rate but not in the dynamics of exogenous attention in action videogame players

Many previous studies have shown that the speed of processing in attentionally demanding tasks seems enhanced following habitual action videogame play. However, using one of the diagnostic tasks for efficiency of attentional processing, a visual search task, Castel and collaborators (Castel, Pratt, & Drummond, Acta Psychologica 119:217-230, 2005) reported no difference in visual search rates, instead proposing that action gaming may change response execution time rather than the efficiency of visual selective attention per se. Here we used two hard visual search tasks, one measuring reaction time and the other accuracy, to test whether visual search rate may be changed by action videogame play. We found greater search rates in the gamer group than in the nongamer controls, consistent with increased efficiency in visual selective attention. We then asked how general the change in attentional throughput noted so far in gamers might be by testing whether exogenous attentional cues would lead to a disproportional enhancement in throughput in gamers as compared to nongamers. Interestingly, exogenous cues were found to enhance throughput equivalently between gamers and nongamers, suggesting that not all mechanisms known to enhance throughput are similarly enhanced in action videogamers.

Context-gated statistical learning and its role in visual-saccadic decisions

Adaptive behavior in a nonstationary world requires humans to learn and track the statistics of the environment. We examined the mechanisms of adaptation in a nonstationary environment in the context of visual-saccadic inhibition of return (IOR). IOR is adapted to the likelihood that return locations will be refixated in the near future. We examined 2 potential learning mechanisms underlying adaptation: (a) a local tracking or priming mechanism that facilitates behavior that is consistent with recent experience and (b) a mechanism that supports retrieval of knowledge of the environmental statistics based on the contextual features of the environment. Participants generated sequences of 2 saccadic eye movements in conditions where the probability that the 2nd saccade was directed back to the previously fixated location varied from low (.17) to high (.50). In some conditions, the contingency was signaled by a contextual cue (the shape of the movement cue). Adaptation occurred in the absence of contextual signals but was more pronounced in the presence of contextual cues. Adaptation even occurred when different contingencies were randomly intermixed, showing the parallel formation of multiple associations between context and statistics. These findings are accounted for by an evidence accumulation framework in which the resting baseline of decision alternatives is adjusted on a trial-by-trial basis. This baseline tracks the subjective prior beliefs about the behavioral relevance of the different alternatives and is updated on the basis of the history of recent events and the contextual features of the current environment.

The time course of attention: selection is transient

The time course of attention has often been investigated using a spatial cuing task. However, attention likely consists of multiple components, such as selectivity (resolving competition) and orienting (spatial shifting). Here we sought to investigate the time course of the selective aspect of attention, using a cuing task that did not require spatial shifting. In several experiments, targets were always presented at central fixation, and were preceded by a cue at different cue-target intervals. The selection component of attention was investigated by manipulating the presence of distractors. Regardless of the presence of distractors, an initial rapid performance enhancement was found that reached its maximum at around 100 ms post cue onset. Subsequently, when the target was the only item in the display, performance was sustained, but when the target was accompanied by irrelevant distractor items, performance declined. This temporal pattern matches closely with the transient attention response that has been found in spatial cuing studies, and shows that the selectivity aspect of attention is transient.

Individual differences and metacognitive knowledge of visual search strategy

A crucial ability for an organism is to orient toward important objects and to ignore temporarily irrelevant objects. Attention provides the perceptual selectivity necessary to filter an overwhelming input of sensory information to allow for efficient object detection. Although much research has examined visual search and the ‘template’ of attentional set that allows for target detection, the behavior of individual subjects often reveals the limits of experimental control of attention. Few studies have examined important aspects such as individual differences and metacognitive strategies. The present study analyzes the data from two visual search experiments for a conjunctively defined target (Proulx, 2007). The data revealed attentional capture blindness, individual differences in search strategies, and a significant rate of metacognitive errors for the assessment of the strategies employed. These results highlight a challenge for visual attention studies to account for individual differences in search behavior and distractibility, and participants that do not (or are unable to) follow instructions.

Temporal consistency is currency in shifts of transient visual attention

Background

Observers respond more accurately to targets in visual search tasks that share properties with previously presented items, and transient attention can learn featural consistencies on a precue, irrespective of its absolute location.

Methodology/Principal Findings

We investigated whether such attentional benefits also apply to temporal consistencies. Would performance on a precued Vernier acuity discrimination task, followed by a mask, improve if the cue-lead times (CLTs; 50, 100, 150 or 200 ms) remained constant between trials compared to when they changed? The results showed that if CLTs remained constant for a few trials in a row, Vernier acuity performance gradually improved while changes in CLT from one trial to the next led to worse than average discrimination performance. The results show that transient attention can quickly adjust to temporal regularities, similarly to spatial and featural regularities. Further experiments show that this form of learning is not under voluntary control.

Conclusions/Significance

The results add to a growing literature showing how consistency in visual presentation improves visual performance, in this case temporal consistency.

Strength in numbers: combining neck vibration and prism adaptation produces additive therapeutic effects in unilateral neglect

Unilateral neglect is a multifaceted disorder. Many authors have, for this reason, speculated that the best treatment for neglect will involve combinations of different therapeutic techniques. Two well-known interventions, neck vibration (NV) and prism adaptation (PA), have often been considered to be among the most effective treatments for neglect. Here, two experiments were performed to explore possible additive benefits when these interventions are used in combination to treat chronic neglect. Both experimental groups received NV for 20 minutes, while the second group received simultaneous PA. The effects of treatment were measured with a time-restricted and feedback-based visual search task, which has previously been found to abolish the beneficial effects of PA, and with standard neglect tests. Baseline and intervention measures were performed on separate days. Findings for both groups indicated improved visual search following intervention, but the patients that underwent the combined intervention (NVPA) showed clear improvements on visual search paper and pencil neglect tests unlike the NV-only group. Overall, our results suggest that PA strengthens the effects of NV and that feedback-based tasks do not abolish the beneficial effects of PA, when NV is applied simultaneously. The results support the view that the most effective treatment for neglect will involve the combination of different treatments.

The prioritization of perceptual processing in categorization

In three experiments, the effects of selective attention on perceptual processes in a complex multidimensional object categorization task were investigated. In each experiment, participants completed a perceptual-matching task to gain estimates of the perceptual salience of each stimulus dimension, then a categorization task using the same stimuli. In Experiments 1 and 2, the perceptual processing of stimulus dimensions was faster when dimensions were more diagnostic of category membership, regardless of their perceptual salience. Experiment 3 demonstrated that this prioritization of perceptual processing was evident even when stimuli were presented in unpredictable locations during categorization, indicating that the physical characteristics of the stimulus guide selective attention to diagnostic stimulus dimensions.

Subliminally presented and stored objects capture spatial attention

When objects disappear from view, we can still bring them to mind, at least for brief periods of time, because we can represent those objects in visual short-term memory (VSTM) (Sperling, 1960; Cowan, 2001). A defining characteristic of this representation is that it is topographic, that is, it preserves a spatial organization based on the original visual percept (Vogel and Machizawa, 2004; Astle et al., 2009; Kuo et al., 2009). Recent research has also shown that features or locations of visual items that match those being maintained in conscious VSTM automatically capture our attention (Awh and Jonides, 2001; Olivers et al., 2006; Soto et al., 2008). But do objects leave some trace that can guide spatial attention, even without participants intentionally remembering them? Furthermore, could subliminally presented objects leave a topographically arranged representation that can capture attention? We presented objects either supraliminally or subliminally and then 1 s later re-presented one of those objects in a new location, as a "probe" shape. As participants made an arbitrary perceptual judgment on the probe shape, their covert spatial attention was drawn to the original location of that shape, regardless of whether its initial presentation had been supraliminal or subliminal. We demonstrate this with neural and behavioral measures of memory-driven attentional capture. These findings reveal the existence of a topographically arranged store of "visual" objects, the content of which is beyond our explicit awareness but which nonetheless guides spatial attention.

BOLD signal in intraparietal sulcus covaries with magnitude of implicitly driven attention shifts

A lot is known about the neural basis of directing attention based on explicit cues. In real life however, attention shifts are rarely directed by explicit cues but rather generated implicitly, for example on the basis of previous experience with a given situation. Here, we aimed at studying attention shifts dependent on recent trial history. While explicitly cued attention shifts involve activity in cortex of the intraparietal sulcus, whether this region is also involved in shifting attention according to recent history is still unknown. We asked observers to detect targets in a stream of visual stimuli with three feature dimensions: color, shape and motion. Critically, target occurrence probability was always higher in one stimulus dimension than in the others, and probabilities switched between dimensions over blocks of trials. After each probability switch, target detection times decreased exponentially for high-probability targets and increased for low-probability targets, compatible with gradual shifts in attention dependent on trial history since the switch. BOLD signal in left prefrontal and intraparietal sulcus regions was higher in the early phase after the switch, while anterior cingulate, cuneus, precuneus, temporal and more anterior frontal regions showed more activation later after the switch. These findings are compatible with the engagement of regions involved in the establishment and maintenance of attentional sets. BOLD signal in left intraparietal sulcus correlated with the size of the performance changes consecutive to the detected targets, suggesting that it reflects the size of attention shifts induced by updating target probabilities over recent trial history.

Prism adaptation improves visual search in hemispatial neglect

Visuomotor prism adaptation has been found to induce a lateral bias of spatial attention in chronic hemispatial neglect patients. Here, two experiments were conducted to explore the effects of 10 degrees prism adaptation on visual search tasks and standard visual inattention tests. Baselines and intervention effects were measured on separate days for all patients. The first experiment explored whether prism adaptation affects performance on a time restricted visual search task (maximum 3500ms presentation followed by visual and auditory feedback). No positive effects of prism adaptation were found on accuracy in visual search nor on traditional neglect tests. These results accord well with previous studies showing that increased cognitive load can lead to prism de-adaptation or unchanged performance following prism adaptation. Response times in visual search became faster following intervention but this was not the case for the standard neglect tests. In the second experiment, the same single-featured search task was used, but the participants had unlimited search time and received no feedback on their response. This time, the patients showed accuracy improvements in visual search and all four on regular neglect tests. Therapeutic effects lasted for at least 90-120min. Response times on all tasks became faster after prism adaptation. The results are consistent with studies showing effects of prism adaptation on neuropsychological neglect tests and other attentional tasks that are not speeded or time restricted, where feedback is not provided, or are performed following non-feedback-based tasks. The current findings show that prism adaptation improves visual search in neglect and that these beneficial effects can disappear with feedback.

Repetition streaks increase perceptual sensitivity in visual search of brief displays

Studies examining possible priming effects on visual search have generally shown that repeating the same type of search facilitates or speeds performance. But such studies typically assess any priming via measuring response latency, in tasks where accuracy is at or near ceiling. This leaves open the possibility that criterion shifts alone might produce the apparent improvements, and such shifts could plausibly arise when, say, a particular type of repeated search display becomes predictable. Here we assessed criterion free perceptual sensitivity (d') for visual search, in two experiments that used brief masked displays to bring performance off ceiling. In experiment 1, sensitivity for conjunction search improved with successive repetitions of the same type of search, with sensitivity enhanced for both target-present and target-absent trials. In experiment 2, sensitivity for a search task requiring discrimination on a color-singleton target likewise showed enhancement with repetition. We conclude that priming in visual search, arising due to repetition streaks, is characterized by genuine improvements in perceptual sensitivity, not just criterion shifts.

On the Benefits of Transient Attention across the Visual Field

There are well-known differences in resolution and performance across the visual field with performance generally better for the lower than the upper visual hemifield. Here we attempted to assess how transient attention summoned by a peripheral precue affects performance across the visual field. Four different attentional precueing tasks were used, varying in difficulty and attentional load. When a single discrimination target was presented (experiments 1 and 2), precues that summon transient attention had very little, if any, effect upon performance. However, when the target was presented among distractors (experiments 3 and 4), the precue had a substantial effect upon discrimination performance. The results showed that asymmetries in visual resolution between the upper and lower hemifields become more pronounced with increasing eccentricity. Furthermore, when the observers performed a precued acuity task with distractors, involving the judgment of the relative position of a small disk within a larger one, there was an asymmetry in the transient attentional effect on discrimination performance; the benefits of transient attention were larger in the upper than in the lower hemifield. Areas in the visual field where visual performance is generally worse thus appear to receive the largest attentional boost when needed. Possible ecological explanations for this are discussed.

Saccade landing point selection and the competition account of pro- and antisaccade generation: The involvement of visual attention ? A review

This paper presents a review and summary of experimental findings on the role of attention in the preparation of saccadic eye movements. The focus is on experiments where performance of prosaccades (saccades towards a suddenly appearing item) and antisaccades (saccades of equal amplitude in the direction opposite to where the target moved) is compared. Evidence suggests that these two opposite responses to the same stimulus event entail competition between neural pathways that generate reflexive movements to the target and neural mechanisms involved in inhibiting the reflex and generating a voluntary gaze shift in the opposite direction to the target appearance. Evidence for such a competition account is discussed in light of a large amount of experimental findings and the overall picture clearly indicates that this competition account has great explanatory power when data on saccadic reaction times and error rates are compared for the two types of saccade. The role of attention is also discussed in particular in light of the finding that the withdrawal of attention by a secondary task 200 to 500 ms before the saccade target appears, leads to speeded antisaccades (without a similar increase in error rates), showing that the results do not simply reflect a speed-accuracy trade-off. This result indicates that the tendency for "reflexive" prosaccades is diminished when attention is engaged in a different task. Furthermore, experiments are discussed that show that as the tendency for a reflexive prosaccade is weakened, antisaccades are speeded up, further supporting the competition account of pro- and antisaccade generation. In the light of evidence from neurophysiology of monkeys and humans, a tentative model of pro- and antisaccade generation is proposed.

The simultaneous type, serial token model of temporal attention and working memory

A detailed description of the simultaneous type, serial token (ST2) model is presented. ST2 is a model of temporal attention and working memory that encapsulates 5 principles: (a) M. M. Chun and M. C. Potter's (1995) 2-stage model, (b) a Stage 1 salience filter, (c) N. G. Kanwisher's (1987, 1991) types-tokens distinction, (d) a transient attentional enhancement, and (e) a mechanism for associating types with tokens called the binding pool. The authors instantiate this theoretical position in a connectionist implementation, called neural-ST2, which they illustrate by modeling temporal attention results focused on the attentional blink (AB). They demonstrate that the ST2 model explains a spectrum of AB findings. Furthermore, they highlight a number of new temporal attention predictions arising from the ST2 theory, which are tested in a series of behavioral experiments. Finally, the authors review major AB models and theories and compare them with ST2.

Neural basis for priming of pop-out during visual search revealed with fMRI

Maljkovic and Nakayama first showed that visual search efficiency can be influenced by priming effects. Even "pop-out" targets (defined by unique color) are judged quicker if they appear at the same location and/or in the same color as on the preceding trial, in an unpredictable sequence. Here, we studied the potential neural correlates of such priming in human visual search using functional magnetic resonance imaging (fMRI). We found that repeating either the location or the color of a singleton target led to repetition suppression of blood oxygen level-dependent (BOLD) activity in brain regions traditionally linked with attentional control, including bilateral intraparietal sulci. This indicates that the attention system of the human brain can be "primed," in apparent analogy to repetition-suppression effects on activity in other neural systems. For repetition of target color but not location, we also found repetition suppression in inferior temporal areas that may be associated with color processing, whereas repetition of target location led to greater reduction of activation in contralateral inferior parietal and frontal areas, relative to color repetition. The frontal eye fields were also implicated, notably when both target properties (color and location) were repeated together, which also led to further BOLD decreases in anterior fusiform cortex not seen when either property was repeated alone. These findings reveal the neural correlates for priming of pop-out search, including commonalities, differences, and interactions between location and color repetition. fMRI repetition-suppression effects may arise in components of the attention network because these settle into a stable "attractor state" more readily when the same target property is repeated than when a different attentional state is required.

Effect of colour pop-out on the recognition of letters in crowding conditions

The crowding effect of adjacent objects on the recognition of a target can be reduced when target and flankers differ in some feature, that is irrelevant to the recognition task. In this study, the mechanisms of this effect were explored using targets and flankers of the same and different colours. It was found that facilitation nearly equal to that of differently coloured targets and flankers can be observed with a differently coloured background blob in the location of the target. The different-colour effect does not require advance knowledge of the target and flanker colours, but the effect increases in the course of three trials with constant mapping of colours. The results are consistent with the notion of exogenous attention that facilitates the processing at the most salient locations in the visual field.

Simultaneous priming along multiple feature dimensions in a visual search task

What we have recently seen generally has a large effect on how we consequently perceive our visual environment. Such priming effects play a surprisingly large role in visual search tasks, for example. It is unclear, however, whether different features of an object show independent but simultaneous priming. For example, if the color and orientation of a target item are the same as on a previous trial, is performance better than if only one of those features is repeated? In other words this paper presents an attempt at assessing the capacity of priming for different feature dimensions. Observers searched for a three featured object (a gabor patch that was either redscale or greenscale, oriented either to the left or right of vertical and of high or low spatial frequency) among distractors with different values along these feature dimensions. Which feature was the target defining feature; which was the response defining feature and which was the irrelevant feature, was varied between the different experiments. Task relevant features (target defining, or response defining) always resulted in priming effects, while when spatial frequency or orientation were task irrelevant neither resulted in priming, but color always did, even when task irrelevant. Further experiments showed that priming from spatial frequency and orientation could occur when they were task irrelevant but only when the other feature of the two was kept constant across all display items. The results show that simultaneous priming for different features can occur simultaneously, but also that task relevance has a strong modulatory effect on the priming.

Brain representation of object-centered space in monkeys and humans

Visuospatial cognition requires taking into account where things are relative to each other and not just relative to the viewer. Consequently it would make sense for the brain to form an explicit representation of object-centered and not just of ego-centered space. Evidence bearing on the presence and nature of neural maps of object-centered space has come from two sources: single-neuron recording in behaving monkeys and assessment of the visual abilities of human patients with hemispatial neglect. Studies of the supplementary eye field of the monkey have revealed that it contains neurons with object-centered spatial selectivity. These neurons fire when the monkey has selected, as target for an eye movement or attention, a particular location defined relative to a reference object. Studies of neglect have revealed that in some patients the condition is expressed with respect to an object-centered and object-aligned reference frame. These patients neglect one side of an object, as defined relative to its intrinsic midline, regardless of its location and orientation relative to the viewer. The two sets of observations are complementary in the sense that the loss of neurons, such as observed in the monkey, could explain the spatial distribution of neglect in these patients.

A primitive memory system for the deployment of transient attention

When transient attention is summoned by the sudden appearance of a large cue, it can be deployed to a small portion of the cue where a target appeared on previous trials (Kristjánsson, Mackeben, & Nakayama, 2001). This result runs counter to the view that transient, or exogenous, attention is summoned automatically and indiscriminately to abruptly appearing stimuli. To further characterize the short-term learning mediating this phenomenon, we report the following results. (1) When there was a consistent relationship between a small identifying portion of the cue and the target, learning occurred rapidly. Thus, transient attention can be summoned to a distinctively colored or distinctively shaped portion of the cue as a consequence of repeated pairing (Experiments 1 and 2). (2) When there was a consistent relation between a given position on the object and its overall color or shape, no learning occurred (Experiments 3 and 4). Thus, transient attention cannot learn a complex relation between target position and shape or color. (3) We confirmed the fast object-centered learning of position shown in Kristjánsson et al. (2001). (4) Explicit knowledge of the cue-target relationship had no effect on the performance of the task. The results provide evidence for the existence of a primitive object-centered learning mechanism beneficial for the rapid deployment of transient attention. The possible role of such a mechanism in the maintenance of representations of the visual environment is discussed.

Test of the effect of attention on judged length of a line

Studies to assess experimentally whether attention affects the judged length of a line have produced discordant results. This paper reports the results of a test designed to avoid factors that were not controlled in previous studies. Stimuli were either two vertical lines or two horizontal lines of equal physical length presented briefly on opposite sides of a fixation cross. Subjects were asked to direct their attention to one line when the arm of the cross pointing to the line changed in luminance. This arm was used either as a precue or as a postcue. Subjects judged lines to be longer when a precue preceded the line than when a postcue followed the line.