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.

The PD Reflects Selection of Nontarget Locations, Not Distractor Suppression.

In visual search tasks, negative features provide information about stimuli that can be excluded from search. It has been shown that these negative features help participants to locate the target, possibly by attentional suppression of stimuli sharing the negative feature. Attentional suppression is assumed to be reflected in an event-related potential, the PD component. To provide a further test of these assumptions, we presented the color of the distractor at the start of a trial and asked participants to find the other colored stimulus in the subsequent search display. Consistent with attentional suppression, we observed a PD to a lateral distractor shown with a vertical target. However, the PD occurred in this condition only when target and distractor could also be on opposite sides of fixation. The effect of trial context on the PD suggests that the PD reflects a search strategy whereby participants select stimuli opposite to the distractor when trials with opposite placements occur during the experiment. Therefore, the PD to the distractor may in fact be an N2pc to the opposite stimulus, indicating that the distractor is not suppressed, but avoided by redirecting attentional selection to the opposite side.

Does attentional suppression occur at the level of perception or decision-making? Evidence from Gaspelin et al.'s (2015) probe letter task.

Visual attention is often inadvertently captured by salient stimuli. It was suggested that it is possible to prevent attentional capture in some search tasks by suppressing salient stimuli below baseline. Evidence for attentional suppression comes from a probe task that was interleaved with the main search task. In the probe task of Gaspelin et al. (Psychol Sci 26(11):1740-1750, 2015. https://doi.org/10.1177/0956797615597913 ), letters were shown on the stimuli of the search display and participants had to identify as many letters as possible. Performance was found to be worse for letters shown on the distractor compared to non-salient non-target stimuli, suggesting that distractor processing was suppressed below baseline. However, it is unclear whether suppression occurred at the level of perception or decision-making because participants may have reported letters on the distractor less frequently than letters on nontargets. This decision-level bias may have degraded performance for letters on distractor compared to nontarget stimuli without changing perception. After replicating the original findings, we conducted two experiments where we avoided report bias by cueing only a single letter for report. We found that the difference between distractor and nontarget stimuli was strongly reduced, suggesting that decision-level processes contribute to attentional suppression. In contrast, the difference between target and non-target stimuli was unchanged, suggesting that it reflected perceptual-level enhancement of the target stimuli.

Search mode, not the attentional window, determines the magnitude of attentional capture.

A salient color distractor is known to capture attention during search for a less salient shape target, but the mechanisms underlying attentional capture are debated. Theeuwes (2004, Psychonomic Bulletin & Review, 11(1), 65-70) argued that attentional capture depends on the size of the attentional window. If the attentional window is large, search is efficient and attentional capture should be stronger because the distractor is more likely to be inside the window. Consistently, we found higher search efficiency and more attentional capture in singleton than in feature search. However, differences in attentional capture only occurred when singleton and feature search were performed by different groups of participants, but not when singleton and feature search occurred unpredictably in the same group of participants. This result contradicts the attentional window account because search efficiency was always higher in singleton than in feature search. Rather, the results support search mode theory, which claims that participants looked for the most salient stimulus in singleton search ("singleton detection mode"), which resulted in more capture by the salient color distractor. When search types varied unpredictably, it was impossible to apply a consistent search strategy, which eliminated the differences between singleton and feature search. Further, we manipulated search efficiency by target-nontarget similarity. With dissimilar nontargets, the target was salient and search efficiency was high. Therefore, the attentional window account predicts more capture. However, we found the opposite result in singleton search and no difference in feature search. Taken together, these observations are inconsistent with the attentional window account but support search mode theory.

The allocation of working memory resources determines the efficiency of attentional templates in single- and dual-target search.

Attentional templates are representations of target features in working memory (WM). Although two attentional templates can guide visual search in dual-target search, search efficiency is reduced compared with one attentional template in single-target search. Here, we investigated whether the allocation of WM resources contributes to these differences. Participants always memorized two colors, but the use of the corresponding WM representations varied. In the blocked conditions, the two colors were either maintained as attentional templates for dual-target search or as simple WM representations for recall only. In the mixed condition, one color was maintained as an attentional template for single-target search and the other as a simple WM representation for recall only. Reaction times (RTs) were delayed and recall precision reduced with two attentional templates in the blocked condition compared with one attentional template in the mixed condition, indicating that search efficiency and WM resources decreased in dual- compared with single-target search. Moreover, the attentional template was always recalled more precisely than the simple WM representation in the mixed condition, despite lowered visual search frequency (Experiment 2) and retro-cueing (Experiment 3). Consistent with the existence of an "active" WM state, resources were strongly biased toward the attentional template in single-target search. In dual-target search, however, resources were balanced between two attentional templates and flexibly adjusted with retro-cues, as with two simple WM representations. Therefore, the allocation of WM resources goes beyond the traditional dichotomy between "active" and "accessory" WM states and explains how attentional templates guide visual search with variable efficiency. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Biased Competition between Targets and Distractors Reduces Attentional Suppression: Evidence from the Positivity Posterior Contralateral and Distractor Positivity.

The biased competition account claims that competition between two stimuli increases when they are close together compared with when they are far apart. The reason is that nearby stimuli are more likely to be represented in the same receptive fields, requiring top-down or bottom-up biases to resolve the ambiguity. Consistent with biased competition, previous research showed that an index of attentional enhancement, the N2pc component, was attenuated when two targets were close together. In contrast, it is unclear whether distractor processing would also be attenuated when the distractor is close to the target. To answer this question, we used the additional singleton paradigm where a target is sometimes accompanied by a more salient, but entirely irrelevant, distractor. In the conditions of interest, the distance between the target and the distractor was systematically manipulated whereas the eccentricity to central fixation was always the same. The results showed that two indices of attentional suppression, the positivity posterior contralateral and distractor positivity components, were attenuated when the distractor was close to the target. Consistent with biased competition, attentional suppression of distractors was inhibited when the distance between target and distractor was short. The reduced attentional suppression of distractors with nearby targets may contribute to the increased behavioral interference with close distractors.

Statistical learning in visual search reflects distractor rarity, not only attentional suppression.

In visual search tasks, salient distractors may capture attention involuntarily, but interference can be reduced when the salient distractor appears more frequently on one out of several possible positions. The reduction was attributed to attentional suppression of the high-probability position. However, all previous studies on this topic compared performance on the high-probability position to the remaining positions, which had a low probability of containing the distractor. Therefore, it is not clear whether the difference resulted from reduced interference on the high-probability position or from increased interference on the low-probability positions. To decide between these alternatives, we compared high-probability and low-probability with equal-probability positions. Consistent with attentional suppression, interference was reduced on the high-probability position compared with equal-probability positions. However, there was also an increase in interference on low-probability positions compared with equal-probability positions. The increase is in line with previous reports of boosted interference when distractors are rare. Our results show that the experimental design used in previous research is insufficient to separate effects of attentional suppression and those of distractor rarity.

Guidance of visual search by negative attentional templates depends on task demands.

Visual search for a target is faster when its features are known before the search display appears, but there is an ongoing discussion about whether knowledge of nontarget features has a similar effect. Stored target or nontarget features used to guide visual search are referred to as positive or negative attentional templates, respectively. We suggest that the inconsistent findings concerning negative attentional templates may arise from 2 methodological choices in past research. The activation of negative attentional templates was never directly assessed and the use of negative attentional templates by the participant was optional. We addressed these issues in the contingent capture paradigm, which provides a marker for the activation of attentional templates in conditions where attentional templates are optional or mandatory. If an attentional template for a color is activated, cuing effects are larger for spatial cues in a matching color than for spatial cues in a nonmatching color. The question is whether the activation of negative attentional templates results in a similar difference between matching and nonmatching colors. We found that negative attentional templates were not activated when the target could be located based on its saliency (singleton search) and the use of the negative attentional template was optional. In contrast, when the negative attentional template was necessary to locate the target (feature search), we found the expected difference between matching and nonmatching spatial cues. Thus, the activation of negative attentional templates depends on task demands. In contrast, positive attentional templates were activated irrespective of task demands. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Capacity limitations in template-guided multiple color search.

Visual selection of target objects relies on representations of their known features in visual working memory. These representations are referred to as attentional templates. We asked how the capacity of visual working memory relates to the maximal number of attentional templates that can simultaneously guide visual selection. To measure the number of active attentional templates, we used the contingent capture paradigm where cues matching the attentional template have larger effects than cues in a non-matching color. We found larger cueing effects for matching than non-matching cues in one-, two-, and also three-color searches, suggesting that participants can establish up to three attentional templates. However, scrutiny of matching cue trials showed that with three attentional templates, larger cueing effects only occurred when the matching cue had the same color as the actual target. When the matching cue had a possible target color that was different from the actual target color, cueing effects were similar to non-matching cue colors. We assume that processing of a matching cue activates one of the three templates, which inhibits the remaining templates to the level of non-matching colors. With two colors, the inhibition from the activated template is less complete because the initial template activation is higher. Overall, only a maximum of two attentional templates can operate successfully in the contingent capture paradigm. The capacity of template-guided search is therefore far below the capacity of visual working memory.

Do we need attentional suppression?

Gaspelin and Luck describe the signal suppression hypothesis, which proposes that attentional suppression prevents the capture of visual attention by salient distractors. We will discuss several problems with this proposal. On a theoretical level, we will argue that attentional suppression is a dispensable mechanism. Most effects of attentional suppression can be easily explained by reduced target expectancy at the distractor location. On an empirical level, we will argue that electrophysiological evidence for attentional suppression is spurious because, in key conditions, the PD most likely reflects idiosyncratic scan paths.

Attentional guidance by irrelevant features depends on their successful encoding into working memory.

Attentional selection is guided by templates of the target in working memory. It has been proposed that attentional templates integrate target features (e.g., purple chair) to guide attention in an object-based fashion. Alternatively, it may be that attentional templates are established for each target feature individually (e.g., purple and chair). To provide support for the latter account, we used a task where participants memorized a target shape while ignoring an irrelevant color. In the combined condition, the shape was shown in the irrelevant color. In the separate condition, the irrelevant color was spatially separate from the shape. After the initial presentation and a blank retention interval, participants were asked to make a saccade to the initially viewed shape, which was shown together with a distractor. Attentional guidance by the irrelevant color was strongly reduced with separate presentation, suggesting that guidance is object-based. However, it may be that irrelevant color was less reliably encoded with separate presentation. Therefore, we asked participants to store the irrelevant color for later recall. With the additional memory task, guidance by irrelevant color occurred regardless of whether it was presented as part of an object or separately. Thus, effects of irrelevant features are easier to observe with combined presentation because all features of an object are automatically encoded into working memory, where they form integrated feature templates. Nonetheless, guidance by separate features is possible, but the poor encoding of irrelevant features with separate presentation makes it more difficult to observe. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Attentional templates are protected from retroactive interference during visual search: Converging evidence from event-related potentials.

Attentional templates are stored representations of target features that guide visual search. Target features may remain fixed or change on every trial, requiring sustained or transient templates, respectively. In separate blocks of trials, two sustained templates guide visual search as efficiently as two transient templates. In mixed blocks, however, the transient template interferes with the sustained template, impairing its efficiency in guiding visual search. Here, we hypothesized that the priority of the sustained template would increase when threatened by interference, eventually restoring efficient guidance of visual search. Participants memorized two possible target colors before the onset of the search display. At encoding, we assessed attentional selection of the two possible target colors with the N2pc. During subsequent maintenance, we measured the CDA as an index of resource allocation in working memory. In Experiment 1, the CDA was smaller with sustained than transient templates in separate blocks, but similar in mixed blocks. Thus, the sustained template received more working memory resources when maintained concurrently with an interfering transient template, suggesting that it was prioritized. In Experiment 2, the priority of the sustained template was further increased as it guided visual search in 80% of cases. The N2pc to possible target colors matching the sustained template was enhanced both at encoding and during visual search, thus eliminating interference from the transient template. Therefore, sustained templates are not necessarily less efficient than transient templates. Rather, prioritization through attentional selection at encoding and resource allocation during maintenance may restore efficient guidance of visual search.

Meeting another's gaze shortens subjective time by capturing attention.

Gaze directed at the observer (direct gaze) is an important and highly salient social signal with multiple effects on cognitive processes and behavior. It is disputed whether the effect of direct gaze is caused by attentional capture or increased arousal. Time estimation may provide an answer because attentional capture predicts an underestimation of time whereas arousal predicts an overestimation. In a temporal bisection task, observers were required to classify the duration of a stimulus as short or long. Stimulus duration was selected randomly between 988 and 1479 ms. When gaze was directed at the observer, participants underestimated stimulus duration, suggesting that effects of direct gaze are caused by attentional capture, not increased arousal. Critically, this effect was limited to dynamic stimuli where gaze appeared to move toward the participant. The underestimation was present with stimuli showing a full face, but also with stimuli showing only the eye region, inverted faces and high-contrast eye-like stimuli. However, it was absent with static pictures of full faces and dynamic nonfigurative stimuli. Because the effect of direct gaze depended on motion, which is common in naturalistic scenes, more consideration needs to be given to the ecological validity of stimuli in the study of social attention.

Visual selective attention and the control of tracking eye movements: a critical review.

People's eyes are directed at objects of interest with the aim of acquiring visual information. However, processing this information is constrained in capacity, requiring task-driven and salience-driven attentional mechanisms to select few among the many available objects. A wealth of behavioral and neurophysiological evidence has demonstrated that visual selection and the motor selection of saccade targets rely on shared mechanisms. This coupling supports the premotor theory of visual attention put forth more than 30 years ago, postulating visual selection as a necessary stage in motor selection. In this review, we examine to which extent the coupling of visual and motor selection observed with saccades is replicated during ocular tracking. Ocular tracking combines catch-up saccades and smooth pursuit to foveate a moving object. We find evidence that ocular tracking requires visual selection of the speed and direction of the moving target, but the position of the motion signal may not coincide with the position of the pursuit target. Further, visual and motor selection can be spatially decoupled when pursuit is initiated (open-loop pursuit). We propose that a main function of coupled visual and motor selection is to serve the coordination of catch-up saccades and pursuit eye movements. A simple race-to-threshold model is proposed to explain the variable coupling of visual selection during pursuit, catch-up and regular saccades, while generating testable predictions. We discuss pending issues, such as disentangling visual selection from preattentive visual processing and response selection, and the pinpointing of visual selection mechanisms, which have begun to be addressed in the neurophysiological literature.

Allocation of resources in working memory: Theoretical and empirical implications for visual search.

Recently, working memory (WM) has been conceptualized as a limited resource, distributed flexibly and strategically between an unlimited number of representations. In addition to improving the precision of representations in WM, the allocation of resources may also shape how these representations act as attentional templates to guide visual search. Here, we reviewed recent evidence in favor of this assumption and proposed three main principles that govern the relationship between WM resources and template-guided visual search. First, the allocation of resources to an attentional template has an effect on visual search, as it may improve the guidance of visual attention, facilitate target recognition, and/or protect the attentional template against interference. Second, the allocation of the largest amount of resources to a representation in WM is not sufficient to give this representation the status of attentional template and thus, the ability to guide visual search. Third, the representation obtaining the status of attentional template, whether at encoding or during maintenance, receives an amount of WM resources proportional to its relevance for visual search. Thus defined, the resource hypothesis of visual search constitutes a parsimonious and powerful framework, which provides new perspectives on previous debates and complements existing models of template-guided visual search.

Attentional Templates Are Sharpened through Differential Signal Enhancement, Not Differential Allocation of Attention.

In visual search, the internal representation of the target feature is referred to as the attentional template. The attentional template can be broad or precise depending on the task requirements. In singleton search, the attentional template is broad because the target is the only colored element in the display. In feature search, a precise attentional template is required because the target is in a specific color in an array of varied colors. To measure the precision of the attentional template, we used a cue-target paradigm where cueing benefits decrease when the cue color differs from the target color. Consistent with broad and precise attentional templates, the decrease of cueing effects was stronger in feature than in singleton search. Measurements of ERPs showed that the N2pc elicited by the cue decreased with increasing color difference, suggesting that attention was more strongly captured by cues that were similar to the target. However, the cue-elicited N2pc did not differ between feature and singleton search, making it unlikely to reflect the mechanism underlying attentional template precision. Furthermore, there was no evidence for attentional suppression as there was no cue-elicited PD, even in conditions where the cueing benefit turned into a same-location cost. However, an index of signal enhancement, the contralateral positivity, reflected attention template precision. In general, there was sensory enhancement of the stimulus appearing at the cued location in the search display. With broad attentional templates, any stimulus at the cued location was enhanced, whereas enhancement was restricted to target-matching colors with precise attentional templates.

Statistical regularities cause attentional suppression with target-matching distractors.

Visual search may be disrupted by the presentation of salient, but irrelevant stimuli. To reduce the impact of salient distractors, attention may suppress their processing below baseline level. While there are many studies on the attentional suppression of distractors with features distinct from the target (e.g., a color distractor with a shape target), there is little and inconsistent evidence for attentional suppression with distractors sharing the target feature. In this study, distractor and target were temporally separated in a cue-target paradigm, where the cue was shown briefly before the target display. With target-matching cues, RTs were shorter when the cue appeared at the target location (valid cues) compared with when it appeared at a nontarget location (invalid cues). To induce attentional suppression, we presented the cue more frequently at one out of four possible target positions. We found that invalid cues appearing at the high-frequency cue position produced less interference than invalid cues appearing at a low-frequency cue position. Crucially, target processing was also impaired at the high-frequency cue position, providing strong evidence for attentional suppression of the cued location. Overall, attentional suppression of the frequent distractor location could be established through feature-based attention, suggesting that feature-based attention may guide attentional suppression just as it guides attentional enhancement.

New templates interfere with existing templates depending on their respective priority in visual working memory.

Attentional templates are stored representations of target features that guide visual search. While transiently active templates are as efficient as templates held in a sustained fashion, their simultaneous activation generates costs for the sustained template. Here, we investigated whether the quality of the memory representation determines these costs. Two possible target colors were cued before search display onset. In blocked conditions, the 2 colors either changed on every trial or were fixed throughout. In the mixed condition, 1 color was fixed, while the other varied from trial to trial. In Experiment 1, participants also reproduced 1 of the 2 target colors on a memory wheel after each search episode. The analysis of search performance replicated longer reaction times (RTs) to sustained than transient targets when template types were mixed, but no difference when they were blocked. Critically, analysis of memory judgments showed that random guesses for sustained templates increased from the blocked to the mixed condition, mirroring RTs. This suggests that newly activated transient templates retroactively interfered with already activated sustained templates, impairing their efficiency to guide attention and their stability in memory. Increasing the priority of sustained templates through maintenance constraints (Experiments 1 vs. 2) or retro-cueing (Experiment 3) reduced the associated costs. Finally, these costs were unaffected by different retention intervals (Experiment 4). We argue that retroactive interference affects the control of visual search and memory maintenance alike, but critically depends on the respective priority of representations in visual working memory. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Direct evidence for the optimal tuning of attention.

In search arrays where the target is presented with similar nontarget stimuli, it is advantageous to shift the internal representation of the target features away from the nontarget features. According to optimal tuning theory (Navalpakkam & Itti, 2007), the shift of the attentional template increases the signal-to-noise ratio because the overlap of neural populations representing the target and nontarget features is reduced. While previous research has shown that the internal representation of the target is indeed shifted, there is little evidence in favor of a shift in attentional selectivity. To fill this gap, we used a cue-target paradigm where shorter reaction times (RTs) at cued than at uncued locations indicate attentional capture by the cue. Consistent with previous research, we found that attentional capture decreased with decreasing similarity between cue and target color. Importantly, target-similar cue colors closer to the nontarget colors captured attention less than target-similar cue colors further away from the nontarget colors, suggesting that attentional selectivity was biased away from the nontarget colors. The shift of attentional selectivity matched the shift of the memory representation of the target. Further, the bias in attentional capture was reduced when the nontarget colors were more distinct from the target. We discuss alternative accounts of the data, such as saliency-driven capture and the relational account of attentional capture (Becker, 2010), but conclude that optimal tuning theory provides the best explanation. (PsycInfo Database Record (c) 2020 APA, all rights reserved).