Stimulus-driven capture and contingent capture

Isolating the impact of a visual search template's color and form information on search guidance and verification times

Visual search can be guided by biasing one's attention towards features associated with a target. Prior work has shown that high-fidelity, picture-based cues are more beneficial to search than text-based cues. However, typically picture cues provide both detailed form information and color information that is absent from text-based cues. Given that visual resolution deteriorates with eccentricity, it is not clear that high-fidelity form information would benefit guidance to peripheral objects - much of the picture benefit could be due to color information alone. To address this, we conducted a search task with eye-tracking that had four types of cues that comprised a 2 (text/pictorial cue) × 2 (no color/color) design. We hypothesized that color information would be important for efficient search guidance while high-fidelity form information would be important for efficient verification times. In Experiment 1 cues were a colored picture of the target, a gray-scaled picture of the target, a text-based cue that included color (e.g., "blue shoe"), or a text-based cue without color (e.g., "shoe"). Experiment 2 was a replication of Experiment 1, except that the color word in the text-based cue was presented in the precise color that was the dominant color in the target. Our results show that high-fidelity form information is important for efficient verifications times (with color playing less of a role) and color is important for efficient guidance, but form information also benefits guidance. These results suggest that different features of the cue independently contribute to different aspects of the search process.

More than a feeling: The emotional attentional blink relies on non-emotional "pop out," but is weak compared to the attentional blink

The attentional blink (AB) reveals temporal limits of goal-driven attention: the second of two proximate targets presented in a rapid stream of non-targets is often missed. In the emotional AB (EAB, also termed emotion-induced blindness), an emotionally valenced distractor replacing the first target yields a similar blink. However, the AB and EAB have not been adequately compared, and thus the extent of their mechanistic similarity remains unclear. The current study interleaved AB and EAB trials using identical stimuli in the same participants and observed that the AB is consistently larger than the EAB. Moreover, the four main experiments varied in both target-defining features (semantic vs. perceptual) and EAB distractor salience (emotion alone vs. emotion plus physical distinctiveness); an EAB was observed only when distractors were physically distinct. Even when a large EAB was observed, the AB was still larger using a task with identical targets and fillers in the same individuals. These results suggest that: (1) goal-driven attentional control (measured by the AB) has a greater influence than stimulus-driven attentional control (measured by the EAB: emotion valence and physical distinctiveness) on selection from a dynamic series of stimuli, and (2) emotional valence is insufficient on its own to trigger an EAB. However, these results are consistent with the account that when attention has already been captured by a physically salient distractor, emotional content can interfere with disengagement from the already-attended stimulus.

Priming effects in inefficient visual search: Real, but transient

In visual search tasks, responses to targets on one trial can influence responses on the next trial. Most typically, target repetition speeds response while switching to a different target slows response. Such “priming” effects have sometimes been given very significant roles in theories of search (e.g., Theeuwes, Philosophical Transactions of the Royal Society B: Biological Sciences, 368, 1628, 2013). Most work on priming has involved “singleton” or “popout” tasks. In non-popout priming tasks, observers must often perform a task-switching operation because the guiding template for one target (e.g., a red vertical target in a conjunction task) is incompatible with efficient search for the other target (green horizontal, in this example). We examined priming in inefficient search where the priming feature (Color: Experiments 1–3, Shape: Experiments 4–5) was irrelevant to the task of finding a T among Ls. We wished to determine if finding a red T on one trial helped observers to be more efficient if the next T was also red. In all experiments, we found additive priming effects. The reaction time (RT) for the second trial was shorter if the color of the T was repeated. However, there was no interaction with set size. The slope of the RT × Set Size function was not shallower for runs of the same target color, compared to trials where the target color switched. We propose that priming might produce transient guidance of the earliest deployments of attention on the next trial or it might speed decisions about a selected target. Priming does not appear to guide attention over the entire search.

Interactions among endogenous, exogenous, and agency-driven attentional selection mechanisms in interactive displays

Attentional selection is driven, in part, by a complex interplay between endogenous and exogenous cues. Recently, one's interactions with the physical world have also been shown to bias attention. Specifically, the sense of agency that arises when our actions cause predictable outcomes biases our attention toward those things which we control. We investigated how this agency-driven attentional bias interacts with simultaneously presented endogenous (words) and exogenous (color singletons) environmental cues. Participants controlled the movement of one object while others moved independently. In a subsequent search task, targets were either the previously controlled objects or not. Targets were also validly or invalidly cued. Both cue types influenced attention allocation. Endogenous cues and agency-driven attentional selection were independent and additive, indicating they are separable mechanisms of selection. In contrast, exogenous cues eliminated the effects of agency, indicating that perceptually salient environmental cues can override internally derived effects of agency. This is the first demonstration of a boundary condition on agency-driven selection.

The Ecological View of Selective Attention

Accumulating evidence is supporting the hypothesis that our selective attention is a manifestation of mechanisms that evolved early in evolution and are shared by many organisms from different taxa. This surge of new data calls for the re-examination of our notions about attention, which have been dominated mostly by human psychology. Here, we present an hypothesis that challenges, based on evolutionary grounds, a common view of attention as a means to manage limited brain resources. We begin by arguing that evolutionary considerations do not favor the basic proposition of the limited brain resources view of attention, namely, that the capacity of the sensory organs to provide information exceeds the capacity of the brain to process this information. Moreover, physiological studies in animals and humans show that mechanisms of selective attention are highly demanding of brain resources, making it paradoxical to see attention as a means to release brain resources. Next, we build on the above arguments to address the question why attention evolved in evolution. We hypothesize that, to a certain extent, limiting sensory processing is adaptive irrespective of brain capacity. We call this hypothesis the ecological view of attention (EVA) because it is centered on interactions of an animal with its environment rather than on internal brain resources. In its essence is the notion that inherently noisy and degraded sensory inputs serve the animal’s adaptive, dynamic interactions with its environment. Attention primarily functions to resolve behavioral conflicts and false distractions. Hence, we evolved to focus on a particular target at the expense of others, not because of internal limitations, but to ensure that behavior is properly oriented and committed to its goals. Here, we expand on this notion and review evidence supporting it. We show how common results in human psychophysics and physiology can be reconciled with an EVA and discuss possible implications of the notion for interpreting current results and guiding future research.

Psychometric Curves Reveal Three Mechanisms of Vigilance Decrement

The vigilance decrement is a decline in signal detection rate that occurs over time on a sustained-attention task. The effect has typically been ascribed to conservative shifts of response bias and losses of perceptual sensitivity. Recent work, though, has suggested that sensitivity losses in vigilance tasks are spurious, and other findings have implied that attentional lapses contribute to vigilance failures. To test these possibilities, we used Bayesian hierarchical modeling to compare psychometric curves for the first and last blocks of a visual vigilance task. Participants were a convenience sample of 99 young adults. Data showed evidence for all three postulated mechanisms of vigilance loss: a conservative shift of response bias, a decrease in perceptual sensitivity, and a tendency toward more frequent attentional lapses. Results confirm that sensitivity losses are possible in a sustained-attention task but indicate that mental lapses can also contribute to the vigilance decrement.

Guided Search 6.0: An updated model of visual search

This paper describes Guided Search 6.0 (GS6), a revised model of visual search. When we encounter a scene, we can see something everywhere. However, we cannot recognize more than a few items at a time. Attention is used to select items so that their features can be "bound" into recognizable objects. Attention is "guided" so that items can be processed in an intelligent order. In GS6, this guidance comes from five sources of preattentive information: (1) top-down and (2) bottom-up feature guidance, (3) prior history (e.g., priming), (4) reward, and (5) scene syntax and semantics. These sources are combined into a spatial "priority map," a dynamic attentional landscape that evolves over the course of search. Selective attention is guided to the most active location in the priority map approximately 20 times per second. Guidance will not be uniform across the visual field. It will favor items near the point of fixation. Three types of functional visual field (FVFs) describe the nature of these foveal biases. There is a resolution FVF, an FVF governing exploratory eye movements, and an FVF governing covert deployments of attention. To be identified as targets or rejected as distractors, items must be compared to target templates held in memory. The binding and recognition of an attended object is modeled as a diffusion process taking > 150 ms/item. Since selection occurs more frequently than that, it follows that multiple items are undergoing recognition at the same time, though asynchronously, making GS6 a hybrid of serial and parallel processes. In GS6, if a target is not found, search terminates when an accumulating quitting signal reaches a threshold. Setting of that threshold is adaptive, allowing feedback about performance to shape subsequent searches. Simulation shows that the combination of asynchronous diffusion and a quitting signal can produce the basic patterns of response time and error data from a range of search experiments.

Numerosity adaptation partly depends on the allocation of implicit numerosity-contingent visuo-spatial attention

Like other perceptual attributes, numerosity is susceptible to adaptation. Nevertheless, it has never been fully investigated whether adaptation to numerosity is fully perceptual in nature or if it stems from the mixed influence of perception and attention. In the present work, we addressed this point throughout three separate experiments aiming at investigating the potential role played by visuo-spatial attentional mechanisms in shaping numerosity perception and adaptation. In Experiments 1 and 2, we showed that the magnitude of numerosity adaptation can be strongly influenced by the distribution of numerosity-contingent visuo-spatial attentional resources during the adaptation period. Results from Experiment 1 revealed a robust reduction of adaptation magnitude whenever a second numerical stimulus was presented in a diametrically opposite location from that of the adaptor, despite this second adapter being neutral as matched in numerosity with the following stimulus displayed in that location. In Experiment 2, we showed that this reduction in adaptation did not occur in cases where the second stimulus was not numerical, suggesting that attentional resources specifically related to numerosity information accounts for the results of Experiment 1. Finally, in Experiment 3, we showed that uninformative visuo-spatial cues shape numerosity discrimination judgments both at baseline and during adaptation. Taken together, our results seem to indicate that visuo-spatial attention plays a relevant role in numerosity perception and that adaptation to numerosity is actively influenced by this cognitive process.

Value Associations Modulate Visual Attention and Response Selection

Every day, we are confronted with a vast amount of information that all competes for our attention. Some of this information might be associated with rewards (e.g., gambling) or losses (e.g., insurances). To what extent such information, even if irrelevant for our current task, not only attracts attention but also affects our actions is still a topic under examination. To address this issue, we applied a new experimental paradigm that combines visual search and a spatial compatibility task. Although colored stimuli did not modulate the spatial compatibility effect more than gray stimuli, we found clear evidence that reward and loss associations attenuated this effect, presumably by affecting attention and response selection. Moreover, there are hints that differences in these associations are also reflected in a modulation of the spatial compatibility effect. We discuss theoretical implications of our results with respect to the influences of color, reward, and loss association on selective attention and response selection.

Which search are you on? Adapting to color while searching for shape

Human observers adjust their attentional control settings when searching for a target in the presence of predictable changes in the target-defining feature dimension. We investigated whether observers also adapt to changes in a nondefining target dimension. According to feature integration theory, stimuli that are unique in their environment in a single feature dimension can be detected with little effort. In two experiments, we studied how observers searching for such singletons adapt their attentional control settings to a dynamical change in a nondefining target dimension. Participants searched for a shape singleton and freely chose between two targets in each trial. The two targets differed in color, and the ratio of distractors colored like each target varied dynamically across trials. A model-based analysis with a Bayesian estimation approach showed that participants adapted their target choices to the color ratio: They tended to select the target from the smaller color subset, and switched their preference both when the color ratio changed between gray and heterogeneous colors (Exp. 1) and when it changed between red and blue (Exp. 2). Participants thus tuned their attentional control settings toward color, although the target was defined by shape. We concluded that observers spontaneously adapted their behavior to changing regularities in the environment. Because adaptation was more pronounced when color homogeneity allowed for element grouping, we suggest that observers adapt to regularities that can be registered without attentional resources. They do so even if the changes are not relevant for accomplishing the task-a process presumably based on statistical learning.

Behavioral and neuronal study of inhibition of return in barn owls

Inhibition of return (IOR) is the reduction of detection speed and/or detection accuracy of a target in a recently attended location. This phenomenon, which has been discovered and studied thoroughly in humans, is believed to reflect a brain mechanism for controlling the allocation of spatial attention in a manner that enhances efficient search. Findings showing that IOR is robust, apparent at a very early age and seemingly dependent on midbrain activity suggest that IOR is a universal attentional mechanism in vertebrates. However, studies in non-mammalian species are scarce. To explore this hypothesis comparatively, we tested for IOR in barn owls (Tyto alba) using the classical Posner cueing paradigm. Two barn owls were trained to initiate a trial by fixating on the center of a computer screen and then turning their gaze to the location of a target. A short, non-informative cue appeared before the target, either at a location predicting the target (valid) or a location not predicting the target (invalid). In one barn owl, the response times (RT) to the valid targets compared to the invalid targets shifted from facilitation (lower RTs) to inhibition (higher RTs) when increasing the time lag between the cue and the target. The second owl mostly failed to maintain fixation and responded to the cue before the target onset. However, when including in the analysis only the trials in which the owl maintained fixation, an inhibition in the valid trials could be detected. To search for the neural correlates of IOR, we recorded multiunit responses in the optic tectum (OT) of four head-fixed owls passively viewing a cueing paradigm as in the behavioral experiments. At short cue to target lags (<100 ms), neural responses to the target in the receptive field (RF) were usually enhanced if the cue appeared earlier inside the RF (valid) and were suppressed if the cue appeared earlier outside the RF (invalid). This was reversed at longer lags: neural responses were suppressed in the valid conditions and were unaffected in the invalid conditions. The findings support the notion that IOR is a basic mechanism in the evolution of vertebrate behavior and suggest that the effect appears as a result of the interaction between lateral and forward inhibition in the tectal circuitry.

Top-Down Prioritization of Salient Items May Produce the So-Called Stimulus-Driven Capture

The current study proposes that top-down attentional prioritization of salient items may produce the so-called stimulus-driven capture. To test this proposal, the “expectation-based paradigm” was designed on the basis of a visual search task. In Experiment 1, a task-irrelevant singleton frame was presented at the same location in 70% of the trials. The target was either presented at chance level within the singleton location, or away from it. In line with the singleton capture phenomenon, participants were faster in identifying the target when it appeared in the singleton location compared to non-singleton locations. However, leaving out the singleton frame in 30% of the trials led to a similar effect; participants were faster in identifying the target when it appeared in the expected singleton location compared to expected non-singletons locations (a “quasi-capture” effect). These results suggest that the participants allocated their attention to the expected singleton location, rather than that the singleton itself captured attention. In Experiment 2, the same task-irrelevant color singleton was presented in a random position in 70% of the trials. This color frame was shown as a non-singleton in all of the 30% singleton-absent multicolored trials. A similar facilitation effect was obtained when the target appeared in the expected singleton color frame compared to other frames, in singleton-absent trials as in singleton-present trials. These results further support the idea that instances of singleton capture can be explained by top-down attentional shifts toward singleton items. Theoretical implications of these results are discussed. Mostly, the study calls to consider the possibility that all sources of attentional control may be represented by a continuous variable of top-down control, including the category of “physical salience.”

Interactions between top-down and bottom-up attention in barn owls (Tyto alba)

Selective attention, the prioritization of behaviorally relevant stimuli for behavioral control, is commonly divided into two processes: bottom-up, stimulus-driven selection and top-down, task-driven selection. Here, we tested two barn owls in a visual search task that examines attentional capture of the top-down task by bottom-up mechanisms. We trained barn owls to search for a vertical Gabor patch embedded in a circular array of differently oriented Gabor distractors (top-down guided search). To track the point of gaze, a lightweight wireless video camera was mounted on the owl's head. Three experiments were conducted in which the owls were tested in the following conditions: (1) five distractors; (2) nine distractors; (3) five distractors with one distractor surrounded by a red circle; or (4) five distractors with a brief sound at the initiation of the stimulus. Search times and number of head saccades to reach the target were measured and compared between the different conditions. It was found that search time and number of saccades to the target increased when the number of distractors was larger (condition 2) and when an additional irrelevant salient stimulus, auditory or visual, was added to the scene (conditions 3 and 4). These results demonstrate that in barn owls, bottom-up attention interacts with top-down attention to shape behavior in ways similar to human attentional capture. The findings suggest similar attentional principles in taxa that have been evolutionarily separated for 300 million years.

Distractors associated with reward break through the focus of attention

In the present study, we investigated the conditions in which rewarded distractors have the ability to capture attention, even when attention is directed toward the target location. Experiment 1 showed that when the probability of obtaining reward was high, all salient distractors captured attention, even when they were not associated with reward. This effect may have been caused by participants suboptimally using the 100%-valid endogenous location cue. Experiment 2 confirmed this result by showing that salient distractors did not capture attention in a block in which no reward was expected. In Experiment 3, the probability of the presence of a distractor was high, but it only signaled reward availability on a low number of trials. The results showed that those very infrequent distractors that signaled reward captured attention, whereas the distractors (both frequent and infrequent ones) not associated with reward were simply ignored. The latter experiment indicates that even when attention is directed to a location in space, stimuli associated with reward break through the focus of attention, but equally salient stimuli not associated with reward do not.

Temporally evolving gain mechanisms of attention in macaque area V4

Cognitive attention and perceptual saliency jointly govern our interaction with the environment. Yet, we still lack a universally accepted account of the interplay between attention and luminance contrast, a fundamental dimension of saliency. We measured the attentional modulation of V4 neurons' contrast response functions (CRFs) in awake, behaving macaque monkeys and applied a new approach that emphasizes the temporal dynamics of cell responses. We found that attention modulates CRFs via different gain mechanisms during subsequent epochs of visually driven activity: an early contrast-gain, strongly dependent on prestimulus activity changes (baseline shift); a time-limited stimulus-dependent multiplicative modulation, reaching its maximal expression around 150 ms after stimulus onset; and a late resurgence of contrast-gain modulation. Attention produced comparable time-dependent attentional gain changes on cells heterogeneously coding contrast, supporting the notion that the same circuits mediate attention mechanisms in V4 regardless of the form of contrast selectivity expressed by the given neuron. Surprisingly, attention was also sometimes capable of inducing radical transformations in the shape of CRFs. These findings offer important insights into the mechanisms that underlie contrast coding and attention in primate visual cortex and a new perspective on their interplay, one in which time becomes a fundamental factor.NEW & NOTEWORTHY We offer an innovative perspective on the interplay between attention and luminance contrast in macaque area V4, one in which time becomes a fundamental factor. We place emphasis on the temporal dynamics of attentional effects, pioneering the notion that attention modulates contrast response functions of V4 neurons via the sequential engagement of distinct gain mechanisms. These findings advance understanding of attentional influences on visual processing and help reconcile divergent results in the literature.

Peripheral Visual Cues: Their Fate in Processing and Effects on Attention and Temporal-Order Perception

Peripheral visual cues lead to large shifts in psychometric distributions of temporal-order judgments. In one view, such shifts are attributed to attention speeding up processing of the cued stimulus, so-called prior entry. However, sometimes these shifts are so large that it is unlikely that they are caused by attention alone. Here we tested the prevalent alternative explanation that the cue is sometimes confused with the target on a perceptual level, bolstering the shift of the psychometric function. We applied a novel model of cued temporal-order judgments, derived from Bundesen's Theory of Visual Attention. We found that cue-target confusions indeed contribute to shifting psychometric functions. However, cue-induced changes in the processing rates of the target stimuli play an important role, too. At smaller cueing intervals, the cue increased the processing speed of the target. At larger intervals, inhibition of return was predominant. Earlier studies of cued TOJs were insensitive to these effects because in psychometric distributions they are concealed by the conjoint effects of cue-target confusions and processing rate changes.

The time course of attentional bias to cues of threat and safety

It is well known that relative to neutral stimuli, attention is biased towards processing stimuli that convey threat. In a previous study in which a particular stimulus (e.g. a blue diamond) was associated with the delivery of an electrical shock, the presence of the fear-conditioned stimulus interfered with the execution of voluntary eye movements to other locations. Here, we show that this effect not only occurs early in time, but remains present long after the fear-conditioned stimulus was removed from the screen. In a subsequent experiment, we associated the presence of a particular stimulus with safety, that is, when this stimulus was present it was certain that no electrical shock would be delivered. The presence of the safety signalling stimulus also interfered with the execution of voluntary saccades, but only when the time between stimulus and cue presentation was relatively long. The results indicate that both signals of threat and signals of safety interfere with execution of a saccade long after the source of threat or safety has been removed. However, only threatening stimuli affect saccade execution early in time, suggesting that threatening stimuli drive selection exogenously.

The role of context in volitional control of feature-based attention

Visual selection can be biased toward nonspatial feature values such as color, but there is continued debate about whether this bias is subject to volitional control or whether it is an automatic bias toward recently seen target features (selection history). Although some studies have tried to separate these 2 sources of selection bias, mixed findings have not offered a clear resolution. The present work offers a possible explanation of conflicting findings by showing that the context in which a trial is presented can determine whether volitional control is observed. We used a cueing task that enabled independent assessments of the effects of color repetitions and current selection goals. When the target was presented among distractors with multiple colors (heterogeneous blocks), Experiment 1 revealed clear goal-driven selection effects, but these effects were eliminated when the target was a color singleton (pop-out blocks). When heterogeneous and pop-out displays were mixed within a block (Experiment 2), however, goal-driven selection was observed with both types of displays. In Experiment 3, this pattern was replicated using an encoding-limited task that included brief displays and an A' measure of performance. Thus, goal-driven selection of nonspatial features is potentiated in contexts where there is strong competition with distractors. Selection history has powerful effects, but we find clear evidence that observers can exert volitional control over feature-based attention. (PsycINFO Database Record

The attentional effects of single cues and color singletons on visual sensitivity

Sudden changes in the visual periphery can automatically draw attention to their locations. For example, the brief flash of a single object (a "cue") rapidly enhances contrast sensitivity for subsequent stimuli in its vicinity. Feature singletons (e.g., a red circle among green circles) can also capture attention in a variety of tasks. Here, we evaluate whether a peripheral cue that enhances contrast sensitivity when it appears alone has a similar effect when it appears as a color singleton, with the same stimuli and task. In four experiments we asked observers to report the orientation of a target Gabor stimulus, which was preceded by an uninformative cue array consisting either of a single disk or of 16 disks containing a color or luminance singleton. Accuracy was higher and contrast thresholds lower when the single cue appeared at or near the target's location, compared with farther away. The color singleton also modulated performance but to a lesser degree and only when it appeared exactly at the target's location. Thus, this is the first study to demonstrate that cueing by color singletons, like single cues, can enhance sensory signals at an early stage of processing.

Visual search

Visual search is the act of looking for a predefined target among other objects. This task has been widely used as an experimental paradigm to study visual attention, and because of its influence has also become a subject of research itself. When used as a paradigm, visual search studies address questions including the nature, function, and limits of preattentive processing and focused attention. As a subject of research, visual search studies address the role of memory in search, the procedures involved in search, and factors that affect search performance. In this article, we review major theories of visual search, the ways in which preattentive information is used to guide attentional allocation, the role of memory, and the processes and decisions involved in its successful completion. We conclude by summarizing the current state of knowledge about visual search and highlight some unresolved issues. WIREs Cogn Sci 2013, 4:415-429. doi: 10.1002/wcs.1235 The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

The influence of onsets and offsets on saccade programming

When making a saccadic eye movement to a peripheral target, a simultaneous stimulus onset at central fixation generally increases saccadic latency, while offsets reduce latency ('gap effect'). Visual onsets remote from fixation also increase latency ('remote distractor effect'); however, the influence of remote visual offsets is less clear. Previous studies, which used a search task, found that remote offsets either facilitated, inhibited, or did nothing to saccade latencies towards a peripheral target. It cannot be excluded, however, that the target selection process in such search tasks influenced the results. We therefore simplified the task and asked participants to make eye movements to a predictable target. Simultaneously with target onset, either one or multiple remote stimulus onsets and offsets were presented. It was found that peripheral onsets increased saccade latencies, but offsets did not influence the initiation of a saccade to the target. Moreover, the number of onsets and offsets did not affect the results. These results suggest that earlier effects of remote stimulus offsets and of the number of remote distractor onsets reside in the target identification process of the visual search task rather than the competition between possible saccade goals. The results are discussed in the context of models of saccade target selection.

Unconscious attentional orienting to exogenous cues: A review of the literature

The present paper reviews research that focuses on the dissociation between bottom-up attention and consciousness. In particular, we focus on studies investigating spatial exogenous orienting in the absence of awareness. We discuss studies that use peripheral masked onset cues and studies that use gaze cueing. The results from these studies show that the classic biphasic pattern of facilitation and inhibition, which is characteristic of conscious exogenous cueing can also be obtained with subliminal spatial cues. It is hypothesized that unconscious attentional orienting is mediated by the subcortical retinotectal pathway. Moreover, a possible neural network including superior colliculus, pulvinar and amygdala is suggested as the underlying mechanism.