Attentional suppression of dynamic versus static salient distractors.

Attention must be carefully controlled to avoid distraction by salient stimuli. The signal suppression hypothesis proposes that salient stimuli can be proactively suppressed to prevent distraction. Although this hypothesis has garnered much support, most previous studies have used one class of salient distractors: color singletons. It therefore remains unclear whether other kinds of salient distractors can also be suppressed. The current study directly compared suppression of a variety of salient stimuli using an attentional capture task that was adapted for eye tracking. The working hypothesis was that static salient stimuli (e.g., color singletons) would be easier to suppress than dynamic salient stimuli (e.g., motion singletons). The results showed that participants could ignore a wide variety of salient distractors. Importantly, suppression was weaker and slower to develop for dynamic salient stimuli than static salient stimuli. A final experiment revealed that adding a static salient feature to a dynamic motion distractor greatly improved suppression. Altogether, the results suggest that an underlying inhibitory process is applied to all kinds of salient distractors, but that suppression is more readily applied to static features than dynamic features.

Terms of debate: Consensus definitions to guide the scientific discourse on visual distraction.

Hypothesis-driven research rests on clearly articulated scientific theories. The building blocks for communicating these theories are scientific terms. Obviously, communication - and thus, scientific progress - is hampered if the meaning of these terms varies idiosyncratically across (sub)fields and even across individual researchers within the same subfield. We have formed an international group of experts representing various theoretical stances with the goal to homogenize the use of the terms that are most relevant to fundamental research on visual distraction in visual search. Our discussions revealed striking heterogeneity and we had to invest much time and effort to increase our mutual understanding of each other's use of central terms, which turned out to be strongly related to our respective theoretical positions. We present the outcomes of these discussions in a glossary and provide some context in several essays. Specifically, we explicate how central terms are used in the distraction literature and consensually sharpen their definitions in order to enable communication across theoretical standpoints. Where applicable, we also explain how the respective constructs can be measured. We believe that this novel type of adversarial collaboration can serve as a model for other fields of psychological research that strive to build a solid groundwork for theorizing and communicating by establishing a common language. For the field of visual distraction, the present paper should facilitate communication across theoretical standpoints and may serve as an introduction and reference text for newcomers.

The Distractor Positivity Component and the Inhibition of Distracting Stimuli.

There has been a long-lasting debate about whether salient stimuli, such as uniquely colored objects, have the ability to automatically distract us. To resolve this debate, it has been suggested that salient stimuli do attract attention but that they can be suppressed to prevent distraction. Some research supporting this viewpoint has focused on a newly discovered ERP component called the distractor positivity (PD), which is thought to measure an inhibitory attentional process. This collaborative review summarizes previous research relying on this component with a specific emphasis on how the PD has been used to understand the ability to ignore distracting stimuli. In particular, we outline how the PD component has been used to gain theoretical insights about how search strategy and learning can influence distraction. We also review alternative accounts of the cognitive processes indexed by the PD component. Ultimately, we conclude that the PD component is a useful tool for understanding inhibitory processes related to distraction and may prove to be useful in other areas of study related to cognitive control.

Is covert attention necessary for programming accurate saccades? Evidence from saccade-locked event-related potentials.

For decades, researchers have assumed that shifts of covert attention mandatorily occur prior to eye movements to improve perceptual processing of objects before they are fixated. However, recent research suggests that the N2pc component-a neural measure of covert attentional allocation-does not always precede eye movements. The current study investigated whether the N2pc component mandatorily precedes eye movements and assessed its role in the accuracy of gaze control. In three experiments, participants searched for a letter of a specific color (e.g., red) and directed gaze to it as a response. Electroencephalograms and eye movements were coregistered to determine whether neural markers of covert attention preceded the initial shift of gaze. The results showed that the presaccadic N2pc only occurred under limited conditions: when there were many potential target locations and distractors. Crucially, there was no evidence that the presence or magnitude of the presaccadic N2pc was associated with improved eye movement accuracy in any of the experiments. Interestingly, ERP decoding analyses were able to classify the target location well before the eyes started to move, which likely reflects a presaccadic cognitive process that is distinct from the attentional process measured by the N2pc. Ultimately, we conclude that the covert attentional mechanism indexed by the N2pc is not necessary for precise gaze control.

A Critique of the Attentional Window Account of Capture Failures.

There has been a lengthy debate about whether salient stimuli have the power to automatically capture attention, even when entirely task irrelevant. Theeuwes (2022) has suggested that an attentional window account could explain why capture is observed in some studies, but not others. According to this account, when search is difficult, participants narrow their attentional window, and this prevents the salient distractor from generating a saliency signal. In turn, this causes the salient distractor to fail to capture attention. In the present commentary, we describe two major problems with this account. First, the attentional window account proposes that attention must be focused so narrowly that featural information from the salient distractor will be filtered prior to saliency computations. However, many previous studies observing no capture provided evidence that featural processing was sufficiently detailed to guide attention toward the target shape. This indicates that the attentional window was sufficiently broad to allow featural processing. Second, the attentional window account proposes that capture should occur more readily in easy search tasks than difficult search tasks. We review previous studies that violate this basic prediction of the attentional window account. A more parsimonious account of the data is that control over feature processing can be exerted proactively to prevent capture, at least under certain conditions.

The role of salience in the suppression of distracting stimuli.

Researchers have long debated whether salient distractors have the power to automatically capture attention. Recent research has suggested a potential resolution, called the signal suppression hypothesis, whereby salient distractors produce a bottom-up salience signal, but can be suppressed to prevent visual distraction. This account, however, has been criticized on the grounds that previous studies may have used distractors that were only weakly salient. This claim has been difficult to empirically test because there are currently no well-established measures of salience. The current study addresses this by introducing a psychophysical technique to measure salience. First, we generated displays that aimed to manipulate the salience of two color singletons via color contrast. We then verified that this manipulation was successful using a psychophysical technique to determine the minimum exposure duration required to detect each color singleton. The key finding was that high-contrast singletons were detected at briefer exposure thresholds than low-contrast singletons, suggesting that high-contrast singletons were more salient. Next, we evaluated the participants' ability to ignore these singletons in a task in which they were task irrelevant. The results showed that, if anything, high-salience singletons were more strongly suppressed than low-salience singletons. These results generally support the signal suppression hypothesis and refute claims that highly salient singletons cannot be ignored.

A new technique for estimating the probability of attentional capture.

Latency-based metrics of attentional capture are limited: They indicate whether or not capture occurred, but they do not indicate how often capture occurred. The present study introduces a new technique for estimating the probability of capture. In a spatial cueing paradigm, participants searched for a target letter defined by color while attempting to ignore salient cues that were drawn in either a relevant or irrelevant color. The results demonstrated the typical contingent capture effect: larger cue validity effects from relevant cues than irrelevant cues. Importantly, using a novel analytical approach, we were able to estimate the probability that the salient cue captured attention. This approach revealed a surprisingly low probability of attentional capture in the spatial cuing paradigm. Relevant cues are thought to be one of the strongest attractors of attention, yet they were estimated to capture attention on only about 30% of trials. This new metric provides an index of capture strength that can be meaningfully compared across different experimental contexts, which was not possible until now.

Oculomotor suppression of abrupt onsets versus color singletons.

There is considerable evidence that salient items can be suppressed in order to prevent attentional capture. However, this evidence has relied almost exclusively on paradigms using color singletons as salient distractors. It is therefore unclear whether other kinds of salient stimuli, such as abrupt onsets, can also be suppressed. Using an additional singleton paradigm optimized for detecting oculomotor suppression, we directly compared color singletons with abrupt onsets. Participants searched for a target shape (e.g., green diamond) and attempted to ignore salient distractors that were either abrupt onsets or color singletons. First eye movements were used to assess whether salient distractors captured attention or were instead suppressed. Initial experiments using a type of abrupt onset from classic attentional capture studies (four white dots) revealed that abrupt onsets strongly captured attention whereas color singletons were suppressed. After controlling for important differences between the onsets and color singletons - such as luminance and color - abrupt-onset capture was reduced but not eliminated. We ultimately conclude that abrupt onsets are not suppressed like color singletons.

Ten simple rules to study distractor suppression.

Distractor suppression refers to the ability to filter out distracting and task-irrelevant information. Distractor suppression is essential for survival and considered a key aspect of selective attention. Despite the recent and rapidly evolving literature on distractor suppression, we still know little about how the brain suppresses distracting information. What limits progress is that we lack mutually agreed upon principles of how to study the neural basis of distractor suppression and its manifestation in behavior. Here, we offer ten simple rules that we believe are fundamental when investigating distractor suppression. We provide guidelines on how to design conclusive experiments on distractor suppression (Rules 1-3), discuss different types of distractor suppression that need to be distinguished (Rules 4-6), and provide an overview of models of distractor suppression and considerations of how to evaluate distractor suppression statistically (Rules 7-10). Together, these rules provide a concise and comprehensive synopsis of promising advances in the field of distractor suppression. Following these rules will propel research on distractor suppression in important ways, not only by highlighting prominent issues to both new and more advanced researchers in the field, but also by facilitating communication between sub-disciplines.

Covert attention is attracted to prior target locations: Evidence from the probe paradigm.

There is growing evidence that visual attention can be guided by selection history. One example of this is intertrial location priming, whereby attention is attracted to the target location from the previous trial. Most previous demonstrations of location priming have relied on manual response time effects whereby search is speeded when the target location repeats from the previous trial. However, these latency-based effects have recently been challenged as being due to response facilitation that occurs after the target has been found, rather than an attentional bias toward the previous target location. To resolve this, the current study used a probe paradigm to assess whether covert attention is biased to the previous-trial target location. On search trials, participants searched for a specific target shape amongst distractor shapes and made a speeded response to the location of a dot inside the target. On probe trials, letters briefly appeared at each search location and after a delay, participants were asked to report as many letters as possible. Probe report accuracy was used to assess the likelihood that a given location was attended. Three experiments indicated that probe report accuracy was greatly improved for letters at the previous-trial target location compared with baseline levels. Importantly, this occurred even when strong attentional guidance to the target was encouraged and even when a nontarget stimulus appeared at the primed location. Altogether, the results suggest that covert attention is strongly attracted to the previous target location during visual search.

Electrophysiological Evidence for the Suppression of Highly Salient Distractors.

There has been a longstanding debate as to whether salient stimuli have the power to involuntarily capture attention. As a potential resolution to this debate, the signal suppression hypothesis proposes that salient items generate a bottom-up signal that automatically attracts attention, but that salient items can be suppressed by top-down mechanisms to prevent attentional capture. Despite much support, the signal suppression hypothesis has been challenged on the grounds that many prior studies may have used color singletons with relatively low salience that are too weak to capture attention. The current study addressed this by using previous methods to study suppression but increased the set size to improve the relative salience of the color singletons. To assess whether salient distractors captured attention, electrophysiological markers of attentional allocation (the N2pc component) and suppression (the PD component) were measured. The results provided no evidence of attentional capture, but instead indicated suppression of the highly salient singleton distractors, as indexed by the PD component. This suppression occurred even though a computational model of saliency confirmed that the color singleton was highly salient. Altogether, this supports the signal suppression hypothesis and is inconsistent with stimulus-driven models of attentional capture.

The development of oculomotor suppression of salient distractors in children.

There is considerable evidence that adults can prevent attentional capture by physically salient stimuli via proactive inhibition. A key question is whether young children can also inhibit salient stimuli to prevent visual distraction. The current study directly compared attentional capture in children (Mage = 5.5 years) and adults (Mage = 19.3 years) by measuring overt eye movements. Participants searched for a target shape among heterogeneous distractor shapes and attempted to ignore a salient color singleton distractor. The destination of first saccades was used to assess attentional capture by the salient distractor, providing a more direct index of attentional allocation than prior developmental studies. Adults were able to suppress saccades to the singleton distractor, replicating previous studies. Children, however, demonstrated no such oculomotor suppression; first saccades were equally likely to be directed to the singleton distractor and nonsingleton distractors. Subsequent analyses indicated that children were able to suppress the distractor, but this occurred approximately 550 ms after stimulus presentation. The current results suggest that children possess some level of top-down control over visual attention, but this top-down control is delayed compared with adults. Development of this ability may be related to executive functions, which include goal-directed behavior such as organized search and impulse control as well as preparatory and inhibitory cognitive functions.

Attentional suppression of highly salient color singletons.

A longstanding debate in visual attention research has been whether physically salient objects have an automatic power to capture attention. Recent evidence has supported a hybrid model. According to the signal suppression hypothesis, salient items automatically attract attention but can be proactively suppressed via top-down control to prevent attentional capture. Although much recent evidence has suggested that salient items can be suppressed, many of these studies used color singletons with relatively low salience. It is therefore unknown whether highly salient color singletons can also be suppressed. The current study adapted the probe technique to assess capture by color singletons at large set sizes (10 or 30 items). In four experiments, we observed no evidence that highly salient color singletons captured attention and instead observed evidence that they were suppressed below baseline levels of processing. We did, however, find strong evidence of floor effects in probe report at high set sizes, which can be mitigated by limiting the number of items that are simultaneously probed. Altogether, the results support the signal suppression hypothesis. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Oculomotor inhibition and location priming in schizophrenia.

Schizophrenia is widely thought to involve elevated distractibility, which may reflect a general impairment in top-down inhibitory processes. Schizophrenia also appears to involve increased priming of previously performed actions. Here, we used a highly refined eye-tracking paradigm that makes it possible to concurrently assess distractibility, inhibition, and priming. In both healthy control subjects (HCS, N = 41) and people with schizophrenia (PSZ, N = 46), we found that initial saccades were actually less likely to be directed toward a salient "singleton" distractor than toward less salient distractors, reflecting top-down suppression of the singleton. Remarkably, this oculomotor suppression effect was as strong or stronger in PSZ than in HCS, indicating intact inhibitory control. In addition, saccades were frequently directed to the location of the previous-trial target in both groups, but this priming effect was much stronger in PSZ than in HCS. Indeed, PSZ directed gaze toward the location of the previous-trial target as often as they directed gaze to the location of the current-trial target. These results demonstrate that-at least in the context of visual search-PSZ are no more distractable than HCS and are fully capable of inhibiting salient-but-irrelevant stimuli. However, PSZ do exhibit exaggerated priming, focusing on recently attended locations even when this is not beneficial for goal attainment. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Eye movements are not mandatorily preceded by the N2pc component.

Researchers typically distinguish between two mechanisms of attentional selection in vision: overt and covert attention. A commonplace assumption is that overt eye movements are automatically preceded by shifts of covert attention during visual search. Although the N2pc component is a putative index of covert attentional orienting, little is currently known about its relationship with overt eye movements. This is because most previous studies of the N2pc component prohibit overt eye movements. The current study assessed this relationship by concurrently measuring covert attention (via the N2pc) and overt eye movements (via eye tracking). Participants searched displays for a lateralized target stimulus and were allowed to generate overt eye movements during the search. We then assessed whether overt eye movements were preceded by the N2pc component. The results indicated that saccades were preceded by an N2pc component, but only when participants were required to carefully inspect the target stimulus before initiating the eye movement. When participants were allowed to make naturalistic eye movements in service of visual search, there was no evidence of an N2pc component before eye movements. These findings suggest that the N2pc component does not always precede overt eye movements during visual search. Implications for understanding the relationship between covert and overt attention are discussed.

Progress Toward Resolving the Attentional Capture Debate.

For over 25 years, researchers have debated whether physically salient stimuli capture attention in an automatic manner, independent of the observer's goals, or whether the capture of attention depends on the match between a stimulus and the observer's task set. Recent evidence suggests an intermediate position in which salient stimuli automatically produce a priority signal, but the capture of attention can be prevented via an inhibitory mechanism that suppresses the salient stimulus. Here, proponents from multiple sides of the debate describe how their original views have changed in light of recent research, as well as remaining areas of disagreement. These perspectives highlight some emerging areas of consensus and provide new directions for future research on attentional capture.

Introspective awareness of oculomotor attentional capture.

Recent research has demonstrated that observers can learn to prevent attentional capture by physically salient stimuli. One critical question is how observers learn to avoid capture, particularly in situations where they receive no direct feedback about attentional performance. One possibility is that individuals have some level of introspective awareness of capture when it occurs. Once capture is detected, participants then adjust performance strategies to avoid subsequent attentional capture. It is currently unclear, however, if observers have any introspective awareness of attentional capture when it occurs. In the current study, participants attempted to locate a target shape and ignore a salient distractor. On half of trials, participants were then asked to classify whether their first eye movement was misdirected to the singleton distractor on that trial. The results demonstrated that participants clearly had some level of introspective awareness of attentional capture: Oculomotor capture effects were much larger on "capture" report trials than on "no capture" report trials. Interestingly, there was no evidence that awareness of oculomotor capture prevented subsequent capture by salient items. Future research is needed to definitively determine whether metacognitive awareness can be used as a training tool to prevent capture. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Progress and Remaining Issues: A Response to the Commentaries on.

Luck et al. (2021) reviewed evidence that observers can learn to suppress attentional capture by salient distractors. Several commentaries were written in response to this review paper, many of which raised important and interesting issues. Here, we respond to these commentaries. Although there has been substantial progress in the attentional capture debate, there are still remaining issues that need to be addressed before the debate is completely resolved. Specifically, we summarize the need for an independent measure of bottom-up salience and better metrics of how attentional control unfolds over time. Ultimately, the field may need a more refined theoretical model of visual attention that distinguishes between attentional priority, attentional orienting, and attentional engagement.

No identification of abrupt onsets that capture attention: evidence against a unified model of spatial attention.

Many studies have reported that spatial attention can be involuntarily captured by salient stimuli such as abrupt onsets. These involuntary shifts are often assumed to have the same effects on feature extraction as voluntary shifts: there are two different ways of moving the same attentional mechanism. According to this unified model of spatial attention, all shifts of attention should enhance the identification of attended objects. We directly tested this assumption using compatibility effects in a series of spatial cueing experiments. Participants searched a display and indicated whether the target number was greater or less than five. The salient precues were also numbers, allowing measurement of compatibility effects between the precue and the target. Precues that reliably predicted the target location produced compatibility effects (e.g., the precue "1" facilitated responding to the target "one"), indicating enhanced identification of the precue. Compatibility effects were also found for precues that were nonpredictive but had the target-finding feature (i.e., contingent capture). Critically, however, four separate experiments failed to find compatibility effects for salient abrupt onsets that were neither predictive nor task-relevant. This is surprising given that these same precues produced enormous cue validity effects (up to 186 ms), suggesting salience-based attention capture. Our findings argue against the unified model: salience-based attention capture recruits different attentional mechanisms than contingent capture or voluntary shifts in attention.