Distractor ignoring: strategies, learning, and passive filtering

How does color distribution learning affect goal-directed visuomotor behavior?

While the visual world is rich and complex, importantly, it nevertheless contains many statistical regularities. For example, environmental feature distributions tend to remain relatively stable from one moment to the next. Recent findings have shown how observers can learn surprising details of environmental color distributions, even when the colors belong to actively ignored stimuli such as distractors in visual search. Our aim was to determine whether such learning influences orienting in the visual environment, measured with saccadic eye movements. In two visual search experiments, observers had to find an odd-one-out target. Firstly, we tested cases where observers selected targets by fixating them. Secondly, we measured saccadic eye movements when observers made judgments on the target and responded manually. Trials were structured in blocks, containing learning trials where distractors came from the same color distribution (uniform or Gaussian) while on subsequent test trials, the target was at different distances from the mean of the learning distractor distribution. For both manual and saccadic measures, performance improved throughout the learning trials and was better when the distractor colors came from a Gaussian distribution. Moreover, saccade latencies during test trials depended on the distance between the color of the current target and the distractors on learning trials, replicating results obtained with manual responses. Latencies were slowed when the target color was within the learning distractor color distribution and also revealed that observers learned the difference between uniform and Gaussian distributions. The importance of several variables in predicting saccadic and manual reaction times was studied using random forests, revealing similar rankings for both modalities, although previous distractor color had a higher impact on free eye movements. Overall, our results demonstrate learning of detailed characteristics of environmental color distributions that affects early attentional selection rather than later decisional processes.

The rise and fall of durable color-induced attentional bias

Target and distractor templates play a pivotal role in guiding attentional control during visual search, with the former template facilitating target search and the latter template leading distractor suppression. We first investigated whether task-irrelevant colors could earn their value through color-target contingency in the training phase and bias attention when they became a distractor in search for a singleton shape during the test phase. Colors provided useful information for target selection, with high- and low-informational values, respectively, in Experiments 1 and 2. Experience-based attentional biases were observed in the first half of the former experiment, and null results were observed in the latter. Experiment 3 verified whether the null results were elicited because the response-relevant feature inside of the singleton shape was also a singleton. Colors were task defined in the training phase, and the test display was the same as that used in Experiment 2. Experience-based attentional biases were observed in the first half of the test phase. In Experiment 4, we tested whether decreasing the consistency of distractor processing can lengthen the duration of experience-based attentional biases by increasing the number of possible response-relevant features inside of the colored distractor. The results showed experience-based attentional biases throughout the test phase. The results highlight the ideas that the informational value provided by a feature dimension for facilitating target selection can modify a target template and that the consistency of rejecting a distractor feature can play a role in the formation of a distractor template.

Why are some individuals better at using negative attentional templates to suppress distractors? Exploration of interindividual differences in cognitive control efficiency

Negative templates are based on foreknowledge of distractor features and can lead to more efficient visual search at the group level. However, large individual differences exist in the size of benefits induced by negative cues. The cognitive factors underlying these interindividual differences remain unknown. Previous research has suggested higher engagement of proactive control for negative templates compared to positive templates. We thus hypothesized that interindividual differences in proactive control efficiency may explain the large variability in negative cue benefits. A large data set made up of data from two previously published studies was reanalyzed (N = 139), with eye movements recorded in 36 participants. Individual proactive control efficiency was measured through reaction time (RT) variability. Participants with higher proactive control efficiency exhibited larger benefits after negative cues across two critical measures: Individuals with higher proactive control showed larger RT benefits following negative compared to neutral cues; similarly, individuals with higher proactive control exhibited lower first saccades to cued distractor items. No such relationship was observed for positive cues. Our results confirmed the existence of large interindividual differences in the benefits induced by negative attentional templates. Critically, we show that proactive control drives these interindividual differences in negative template use. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

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.

Object-based suppression in target search but not in distractor inhibition

The present study investigated the effect of object representation on attentional priority regarding distractor inhibition and target search processes while the statistical regularities of singleton distractor location were biased. A color singleton distractor appeared more frequently at one of six stimulus locations, called the 'high-probability location,' to induce location-based suppression. Critically, three objects were presented, each of which paired two adjacent stimuli in a target display by adding background contours (Experiment 1) or using perceptual grouping (Experiments 2 and 3). The results revealed that attention capture by singleton distractors was hardly modulated by objects. In contrast, target selection was impeded at the location in the object containing the high-probability location compared to an equidistant location in a different object. This object-based suppression in target selection was evident when object-related features were parts of task-relevant features. These findings suggest that task-irrelevant objects modulate attentional suppression. Moreover, different features are engaged in determining attentional priority for distractor inhibition and target search processes.

Individual differences in emotion-induced blindness: Are they reliable and what do they measure?

The emotion-induced-blindness (EIB) paradigm has been extensively used to investigate attentional biases to emotionally salient stimuli. However, the low reliability of EIB scores (the difference in performance between the neutral and emotionally salient condition) limits the effectiveness of the paradigm for investigating individual differences. Here, across two studies, we investigated whether we could improve the reliability of EIB scores. In Experiment 1, we introduced a mid-intensity emotionally salient stimuli condition, with the goal of obtaining a wider range of EIB magnitudes to promote reliability. In Experiment 2, we sought to reduce the attentional oddball effect, so we created a modified EIB paradigm by removing the filler images. Neither of these approaches improved the reliability of the EIB scores. Reliability for the high- and mid-intensity EIB difference scores were low, while reliability of the scores for absolute performance (neutral, high-, and mid-intensity) were high and the scores were also highly correlated, even though overall performance in the emotionally salient conditions were significantly worse than in the neutral conditions. Given these results, we can conclude that while emotionally salient stimuli impair performance in the EIB task compared with the neutral condition, the strong correlation between the emotionally salient and neutral conditions means that while EIB can be used to investigate individual differences in attentional control, it is not selective to individual differences in attentional biases to emotionally salient stimuli.

Separate Cue- and Alpha-Related Mechanisms for Distractor Suppression

Research on selective attention has largely focused on the enhancement of behaviorally important information, with less focus on the suppression of distracting information. Enhancement and suppression can operate through a push-pull relationship attributable to competitive interactions among neural populations. There has been considerable debate, however, regarding (1) whether suppression can be voluntarily deployed, independent of enhancement, and (2) whether voluntary deployment of suppression is associated with neural processes occurring prior to the distractor onset. Here, we investigated the interplay between pre- and post-distractor neural processes, while male and female human subjects performed a visual search task with a cue that indicated the location of an upcoming distractor. We utilized two established EEG markers of suppression: the distractor positivity (PD) and alpha power (∼8-15 Hz). The PD-a component of event-related potentials-has been linked with successful distractor suppression, and increased alpha power has been linked with attenuated sensory processing. Cueing the location of an upcoming distractor speeded responses and led to an earlier PD, consistent with earlier suppression due to strategic use of a spatial cue. In comparison, higher predistractor alpha power contralateral to distractors led to a later PD, consistent with later suppression. Lower alpha power contralateral to distractors instead led to distractor-related attentional capture. Lateralization of alpha power was not linked to the spatial cue. This observation, combined with differences in the timing of suppression-as indexed by earlier and later PD components-demonstrates that cue-related, voluntary suppression can occur separate from alpha-related gating of sensory processing.

Multifaceted consequences of visual distraction during natural behaviour

Visual distraction is a ubiquitous aspect of everyday life. Studying the consequences of distraction during temporally extended tasks, however, is not tractable with traditional methods. Here we developed a virtual reality approach that segments complex behaviour into cognitive subcomponents, including encoding, visual search, working memory usage, and decision-making. Participants copied a model display by selecting objects from a resource pool and placing them into a workspace. By manipulating the distractibility of objects in the resource pool, we discovered interfering effects of distraction across the different cognitive subcomponents. We successfully traced the consequences of distraction all the way from overall task performance to the decision-making processes that gate memory usage. Distraction slowed down behaviour and increased costly body movements. Critically, distraction increased encoding demands, slowed visual search, and decreased reliance on working memory. Our findings illustrate that the effects of visual distraction during natural behaviour can be rather focal but nevertheless have cascading consequences.

Distinct mechanisms of attentional suppression: exploration of trait factors underlying cued- and learned-suppression

Attention allows us to focus on relevant information while ignoring distractions. Effective suppression of distracting information is crucial for efficient visual search. Recent studies have developed two paradigms to investigate attentional suppression: cued-suppression which is based on top-down control, and learned-suppression which is based on selection history. While both types of suppression reportedly engage proactive control, it remains unclear whether they rely on shared mechanisms. This study aimed to determine the relationship between cued- and learned-suppression. In a within-subjects design, 54 participants performed a cued-suppression task where pre-cues indicated upcoming target or distractor colors, and a learned-suppression task where a salient color distractor was present or absent. No significant correlation emerged between performance in the two tasks, suggesting distinct suppression mechanisms. Cued-suppression correlated with visual working memory capacity, indicating reliance on explicit control. In contrast, learned-suppression correlated with everyday distractibility, suggesting implicit control based on regularities. These results provide evidence for heterogeneous proactive control mechanisms underlying cued- and learned-suppression. While both engage inhibition, cued-suppression relies on deliberate top-down control modulated by working memory, whereas learned-suppression involves implicit suppression shaped by selection history and distractibility traits.

Attentional focusing and filtering in multisensory categorization

Selective attention refers to the ability to focus on goal-relevant information while filtering out irrelevant information. In a multisensory context, how do people selectively attend to multiple inputs when making categorical decisions? Here, we examined the role of selective attention in cross-modal categorization in two experiments. In a speed categorization task, participants were asked to attend to visual or auditory targets and categorize them while ignoring other irrelevant stimuli. A response-time extended multinomial processing tree (RT-MPT) model was implemented to estimate the contribution of attentional focusing on task-relevant information and attentional filtering of distractors. The results indicated that the role of selective attention was modality-specific, with differences found in attentional focusing and filtering between visual and auditory modalities. Visual information could be focused on or filtered out more effectively, whereas auditory information was more difficult to filter out, causing greater interference with task-relevant performance. The findings suggest that selective attention plays a critical and differential role across modalities, which provides a novel and promising approach to understanding multisensory processing and attentional focusing and filtering mechanisms of categorical decision-making.

Fundamental units of numerosity estimation

Humans can approximately enumerate a large number of objects at a single glance. While several mechanisms have been proposed to account for this ability, the fundamental units over which they operate remain unclear. Previous studies have argued that estimation mechanisms act only on topologically distinct units or on units formed by spatial grouping cues such as proximity and connectivity, but not on units grouped by similarity. Over four experiments, we tested this claim by systematically assessing and demonstrating that similarity grouping leads to underestimation, just as spatial grouping does. Ungrouped objects with the same low-level properties as grouped objects did not cause underestimation. Further, the underestimation caused by spatial and similarity grouping was additive, suggesting that these grouping processes operate independently. These findings argue against the proposal that estimation mechanisms operate solely on topological units. Instead, we conclude that estimation processes act on representations constructed after Gestalt grouping principles, whether similarity based or spatial, have organised incoming visual input.

Distractor suppression does and does not depend on pre-distractor alpha-band activity

Selective attention enhances behaviorally important information and suppresses distracting information. Research on the neural basis of selective attention has largely focused on sensory enhancement, with less focus on sensory suppression. Enhancement and suppression can operate through a push-pull relationship that arises from competitive interactions among neural populations. There has been considerable debate, however, regarding (i) whether suppression can also operate independent of enhancement and (ii) whether neural processes associated with the voluntary deployment of suppression can occur prior to distractor onset. We provide further behavioral and electrophysiological evidence of independent suppression at cued distractor locations while humans performed a visual search task. We specifically utilize two established EEG markers of suppression: alpha power (∼8-15 Hz) and the distractor positivity (P D ). Increased alpha power has been linked with attenuated sensory processing, while the P D -a component of event-related potentials-has been linked with successful distractor suppression. The present results demonstrate that cueing the location of an upcoming distractor speeded responding and led to an earlier onset P D , consistent with earlier suppression due to strategic use of a spatial cue. We further demonstrate that higher pre-distractor alpha power contralateral to distractors was generally associated with successful suppression on both cued and non-cued trials. However, there was no consistent change in alpha power associated with the spatial cue, meaning cueing effects on behavioral and neural measures occurred independent of alpha-related gating of sensory processing. These findings reveal the importance of pre-distractor neural processes for subsequent distractor suppression.

Significance Statement

Selective suppression of distracting information is important for survival, contributing to preferential processing of behaviorally important information. Does foreknowledge of an upcoming distractor's location help with suppression? Here, we recorded EEG while subjects performed a target detection task with cues that indicated the location of upcoming distractors. Behavioral and electrophysiological results revealed that foreknowledge of a distractor's location speeded suppression, thereby facilitating target detection. The results further revealed a significant relationship between pre-stimulus alpha-band activity and successful suppression; however, pre-stimulus alpha-band activity was not consistently lateralized relative to the spatially informative cues. The present findings therefore demonstrate that target detection can benefit from foreknowledge of distractor location in a process that is independent of alpha-related gating of sensory processing.

No evidence for spatial suppression due to across-trial distractor learning in visual search

Previous studies have shown that during visual search, participants are able to implicitly learn across-trial regularities regarding target locations and use these to improve search performance. The present study asks whether such across-trial visual statistical learning also extends to the location of salient distractors. In Experiments 1 and 2, distractor regularities were paired so that a specific distractor location was 100% predictive of another specific distractor location on the next trial. Unlike previous findings that employed target regularities, the current results show no difference in search times between predictable and unpredictable trials. In Experiments 3-5 the distractor location was presented in a structured order (a sequence) for one group of participants, while it was presented randomly for the other group. Again, there was no learning effect of the across-trial regularities regarding the salient distractor locations. Across five experiments, we demonstrated that participants were unable to exploit across-trial spatial regularities regarding the salient distractors. These findings point to important boundary conditions for the modulation of visual attention by statistical regularities and they highlight the need to differentiate between different types of statistical regularities.

Age-related differences in frontoparietal activation for target and distractor singletons during visual search

Age-related decline in visual search performance has been associated with different patterns of activation in frontoparietal regions using functional magnetic resonance imaging (fMRI), but whether these age-related effects represent specific influences of target and distractor processing is unclear. Therefore, we acquired event-related fMRI data from 68 healthy, community-dwelling adults ages 18-78 years, during both conjunction (T/F target among rotated Ts and Fs) and feature (T/F target among Os) search. Some displays contained a color singleton that could correspond to either the target or a distractor. A diffusion decision analysis indicated age-related increases in sensorimotor response time across all task conditions, but an age-related decrease in the rate of evidence accumulation (drift rate) was specific to conjunction search. Moreover, the color singleton facilitated search performance when occurring as a target and disrupted performance when occurring as a distractor, but only during conjunction search, and these effects were independent of age. The fMRI data indicated that decreased search efficiency for conjunction relative to feature search was evident as widespread frontoparietal activation. Activation within the left insula mediated the age-related decrease in drift rate for conjunction search, whereas this relation in the FEF and parietal cortex was significant only for individuals younger than 30 or 44 years, respectively. Finally, distractor singletons were associated with significant parietal activation, whereas target singletons were associated with significant frontoparietal deactivation, and this latter effect increased with adult age. Age-related differences in frontoparietal activation therefore reflect both the overall efficiency of search and the enhancement from salient targets.

Assessing recoding accounts of negative attentional templates using behavior and eye tracking

Can we use attentional control to ignore known distractor features? Providing cues before a visual search trial about an upcoming distractor color (negative cue) can lead to reaction time benefits compared with no cue trials. This suggests top-down control may use negative templates to actively suppress distractor features, a notion that challenges the mechanisms of top-down control provided in many theories of attention. However, there is currently mixed support for this mechanism in the literature. Alternative explanations have been proposed, which do not require suppression within top-down control but instead involve recoding the negative cue into a positive template based on color or spatial layouts. In three experiments, we contrasted the predictions of active suppression and the recoding strategies. Across experiments, we found consistent evidence against a color recoding account. We also found evidence of accuracy, reaction time, and eye movement benefits when location recoding was not possible. These results suggest that prior benefits from negative cues cannot be explained exclusively by spatial or color recoding. The results indicate that active suppression likely plays a role in the attentional benefits following negative cues. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Individual differences in executive attention and inhibitory control are related to spatial memory biases in adults

Executive attention is involved in working memory; however, the role of executive attention in the maintenance of information in spatial working memory is debated. This study examined whether inhibitory control was related to spatial working memory biases in adults in a simple spatial memory task where participants had to remember one location on an otherwise blank computer screen. On some trials, a distractor was presented during the maintenance period. Eighty-four participants completed the spatial working memory task and a battery of cognitive control measures. When a distractor was presented during the maintenance period of the spatial memory task, performance on two of the cognitive control measures, a measure of overall attention and a measure of inhibitory control was related to memory errors. When a distractor was not presented during the spatial memory task, memory errors were not related to performance on the cognitive control tasks. Overall, these effects demonstrated that attention is related to maintaining locations in spatial working memory in adults, and inhibitory control may also be related such that those with more efficient inhibitory control were less influenced by distractors presented during the maintenance period.

Priming of probabilistic attentional templates

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

Directing memory content to attentional templates: The finiteness effect of predictive information

Visual search can be accelerated according to the properties of information stored in memory and prior knowledge of the upcoming work. This helps the searcher direct their attention to (or avoid) items that match these properties. Meanwhile, different functional areas where these properties exist become attentional templates. Compared with neutral conditions, the use of attentional templates significantly benefits reaction time (RT). However, previous studies might have confounded the memory-driven and cue-driven effects. Thus, it is less clear which factor influences the template benefits. Modeled on previous research, this study employed a new design to explore the independent effects of textual cues, thus finding an inverse effect. More specifically, positively cueing an item retained in memory did not improve behavioral performance, whereas negatively cueing an item did achieve such an enhancement. Moreover, positive cueing even resulted in some damage to attentional searching under some conditions, thus indicating that the advantages of positive cueing reported in previous studies may be driven by working memory, while the effects of negative cueing are driven by prior knowledge.

Serial dependence in visual perception: A review

How does the visual system represent continuity in the constantly changing visual input? A recent proposal is that vision is serially dependent: Stimuli seen a moment ago influence what we perceive in the present. In line with this, recent frameworks suggest that the visual system anticipates whether an object seen at one moment is the same as the one seen a moment ago, binding visual representations across consecutive perceptual episodes. A growing body of work supports this view, revealing signatures of serial dependence in many diverse visual tasks. Yet, the variety of disparate findings and interpretations calls for a more general picture. Here, we survey the main paradigms and results over the past decade. We also focus on the challenge of finding a relationship between serial dependence and the concept of "object identity," taking centuries-long history of research into account. Among the seemingly contrasting findings on serial dependence, we highlight common patterns that may elucidate the nature of this phenomenon and attempt to identify questions that are unanswered.

Negative and positive templates: Two forms of cued attentional control

Our ability to control our attention to focus on goal-relevant information is critical for functioning in daily life. In addition to the typical attentional control driven by target enhancement described in most theories of attention, recent research has focused on our ability to use information about distractions maintained in working memory to direct our attention away from known distractors. Using these negative templates can improve the efficiency of attention, much in the same way as enhancing information matching search targets. However, these effects only occur for specific tasks or in specific circumstances. In this review, I will focus on our emerging understanding of the relationship between distractor ignoring from negative templates and target enhancement from positive templates. I will also highlight key remaining questions for further study.

Distractor ignoring is as effective as target enhancement when incidentally learned but not when explicitly cued

Explicit knowledge about upcoming target or distractor features can increase performance in tasks like visual search. However, explicit distractor cues generally result in smaller performance benefits than target cues, suggesting that suppressing irrelevant information is less effective than enhancing relevant information. Is this asymmetry a general principle of feature-based attention? Across four experiments (N = 75 each) we compared the efficiency of target selection and distractor ignoring through either incidental experience or explicit instructions. Participants searched for an orientation-defined target amidst seven distractors-three in the target color and four in another color. In Experiment 1, either targets (Exp. 1a) or distractors (Exp. 1b) were presented more often in a specific color than other possible search colors. Response times showed comparable benefits of learned attention towards (Exp. 1a) and away from (Exp. 1b) the frequent color, suggesting that learned target selection and distractor ignoring can be equally effective. In Experiment 2, participants completed a nearly identical task, only with explicit cues to the target (Exp. 2a) or distractor color (Exp. 2b), inducing voluntary attention. Both target and distractor cues were beneficial for search performance, but distractor cues much less so than target cues, consistent with previous results. Cross-experiment analyses verified that the relative inefficiency of distractor ignoring versus target selection is a unique characteristic of voluntary attention that is not shared by incidentally learned attention, pointing to dissociable mechanisms of voluntary and learned attention to support distractor ignoring.

Learned low priority of attention after training to suppress color singleton distractor

Allocating attention to significant events, such as a salient object, is effortless. Our brain is effective on this type of processing because doing so is generally beneficial for survival. However, a salient object could also be distracting and ignoring it costs a large amount of cognitive resource. In the present study, we conducted two behavioral experiments to investigate the effect of learned suppression of a salient color. Particularly, we were interested in the effect of learning in a new task context in which the previously suppressed color was task irrelevant. In Experiment 1, we trained the participants for five days with explicit instruction to suppress a color singleton distractor in a visual search task. We measured the effect of training with a dot probe task before and after the training. Colors in the dot probe task only served as the background and were not associated with the position of the target dot. However, we found that attention was involuntarily biased away from the previously suppressed color. In Experiment 2, the color singleton could either be the target or distractor in the visual search task, making the suppression of the color singleton inefficient for task performance. The results showed no training effect in the dot probe task after this manipulation. These findings provided direct evidence for the learned low priority of attention after training to suppress the color singleton distractor.

Can enhancement and suppression concurrently guide attention? An assessment at the individual level

Background: Although people can pay attention to targets while ignoring distractors, previous research suggests that target enhancement and distractor suppression work separately and independently. Here, we sought to replicate previous findings and re-establish their independence. Methods: We employed an internet-based psychological experiment. We presented participants with a visual search task in which they searched for a specified shape with or without a singleton. We replicated the singleton-presence benefit in search performance, but this effect was limited to cases where the target color was fixed across all trials. In a randomly intermixed probe task (30% of all trials), the participants searched for a letter among colored probes; we used this task to assess how far attention was separately allocated toward the target or distractor dimensions. Results: We found a negative correlation between target enhancement and distractor suppression, indicating that the participants who paid closer attention to target features ignored distractor features less effectively and vice versa. Averaged data showed no benefit from target color or cost from distractor color, possibly because of the substantial differences in strategy across participants. Conclusions: These results suggest that target enhancement and distractor suppression guide attention in mutually dependent ways and that the relative contribution of these components depends on the participants’ search strategy.

Attenuating the 'attentional white bear' effect enhances suppressive attention

Trying to ignore an object can bias attention towards it – a phenomenon referred to as the ‘attentional white bear’ (AWB) effect. The mechanisms behind this effect remain unclear. On one hand, the AWB may reflect reactive, ‘search and destroy’ distractor suppression, which directs attention toward irrelevant objects in order to suppress further attention to them. However, another possibility is that the AWB results from failed proactive distractor suppression – attempting to suppress attention to an irrelevant object from the outset may inadvertently result in an attentional shift towards it. To distinguish these two possibilities, we developed a categorical visual search task that addresses limitations present in prior studies. In five experiments (N_total = 96), participants searched displays of naturalistic stimuli cued only with distractor categories (targets were unknown and unpredictable). We observed an AWB and later attenuated it by presenting a pre-search stimulus, likely disrupting guidance from distractor templates in working memory. We conclude that the AWB resulted from a failure of proactive suppression rather than a search and destroy process.

Temporal integration of feature probability distributions

Humans are surprisingly good at learning the statistical characteristics of their visual environment. Recent studies have revealed that not only can the visual system learn repeated features of visual search distractors, but also their actual probability distributions. Search times were determined by the frequency of distractor features over consecutive search trials. The search displays applied in these studies involved many exemplars of distractors on each trial and while there is clear evidence that feature distributions can be learned from large distractor sets, it is less clear if distributions are well learned for single targets presented on each trial. Here, we investigated potential learning of probability distributions of single targets during visual search. Over blocks of trials, observers searched for an oddly colored target that was drawn from either a Gaussian or a uniform distribution. Search times for the different target colors were clearly influenced by the probability of that feature within trial blocks. The same search targets, coming from the extremes of the two distributions were found significantly slower during the blocks where the targets were drawn from a Gaussian distribution than from a uniform distribution indicating that observers were sensitive to the target probability determined by the distribution shape. In Experiment 2, we replicated the effect using binned distributions and revealed the limitations of encoding complex target distributions. Our results demonstrate detailed internal representations of target feature distributions and that the visual system integrates probability distributions of target colors over surprisingly long trial sequences.

Selection history and task predictability determine the precision expectations in attentional control

Predictive processing frameworks have demonstrated the central role that prediction plays in a range of cognitive processes including bottom-up and top-down mechanisms of attention control. However, relatively little is understood about how predictive processes interact with the third main determinant of attentional priority - selection history. In this experiment, participants developed a history of either color or shape selection while we observed the impact of these histories in an additional singleton search task using behavioral measures and ERP measures of attentional control. Throughout the experiment, participants were encouraged to predict the upcoming display, but prediction errors were either high or low depending on session. Persistent group differences in our results showed that selection history contributes to the precision weighting of a stimulus, and that this is mediated by overall prediction error. Color-singleton distractors captured attention and required greater suppression when participants had a history of color selection; however, these participants gained large benefits when the upcoming stimuli were highly predictable. We suggest that selection history modulates the precision expectations for a feature in a persistent and implicit way, producing an attentional bias that predictability can help to counteract, but cannot prevent or eliminate entirely.

Habituation to abrupt-onset distractors with different spatial occurrence probability

Previous studies have shown that abrupt onsets randomly appearing at different locations can be ignored with practice, a result that was interpreted as an instance of habituation. Here we addressed whether habituation of capture can be spatially selective and determined by the rate of onset occurrence at different locations, and whether habituation is achieved via spatial suppression applied at the distractor location. In agreement with the habituation hypothesis, we found that capture attenuation was larger where the onset distractor occurred more frequently, similarly to what has been documented for feature-singleton distractors (the “distractor-location effect”), and that onset interference decreased across trials at both the high- and low-probability distractor locations. By contrast, evidence was inconclusive as to whether distractor filtering was also accompanied by a larger impairment in target processing when it appeared at the more likely distractor location (the “target-location effect”), as instead previously reported for feature-singleton distractors. Finally, here we discuss how and to what extent distractor rejection based on statistical learning and habituation of capture are different, and conclude that the two notions are intimately related, as the Sokolov model of habituation operates by comparing the upcoming sensory input with expectation based on the statistics of previous stimulation.

What to expect where and when: how statistical learning drives visual selection

While the visual environment contains massive amounts of information, we should not and cannot pay attention to all events. Instead, we need to direct attention to those events that have proven to be important in the past and suppress those that were distracting and irrelevant. Experiences molded through a learning process enable us to extract and adapt to the statistical regularities in the world. While previous studies have shown that visual statistical learning (VSL) is critical for representing higher order units of perception, here we review the role of VSL in attentional selection. Evidence suggests that through VSL, attentional priority settings are optimally adjusted to regularities in the environment, without intention and without conscious awareness.

Tracking Neural Markers of Template Formation and Implementation in Attentional Inhibition under Different Distractor Consistency

Performing visual search tasks requires optimal attention deployment to promote targets and inhibit distractors. Rejection templates based on the feature of the distractor can be built to constrain the search process. We measured electroencephalography (EEG) of human participants of both sexes when they performed a visual search task in conditions where the distractor cues were constant within a block (fixed cueing) or changed on a trial-by-trial basis (varied cueing). In the fixed-cueing condition, sustained decoding of the cued colors could be achieved during the retention interval, and participants with higher decoding accuracy showed larger suppression benefits of the distractor cueing in the search period. In the varied-cueing condition, the cued color could only be transiently decoded after its onset, and higher decoding accuracy was observed from the participants who demonstrated lower suppression benefit. The differential neural representations of the to-be-ignored color in the two cueing conditions as well as their reverse associations with behavioral performance implied that rejection templates were formed in the fixed-cueing condition but not in the varied-cueing condition. Additionally, we observed stronger posterior alpha lateralization and midfrontal theta/beta power during the retention interval of the varied-cueing condition, indicating the cognitive costs in template formation caused by the trialwise change of distractor colors. Together, our findings revealed the neural markers associated with the critical roles of distractor consistency in linking template formation to successful inhibition.SIGNIFICANCE STATEMENT How do we strategically build a rejection template based on distractor features to filter out matched items when performing visual search tasks? Previous studies have suggested that the consistency of the to-be-ignored feature may play a significant role in this process. We recorded scalp EEGs when human participants searched for a target among distractors. Capitalized on multivariate decoding technique and time-frequency analysis, we revealed the neural markers of the rejection template under different distractor consistencies. Being able to track these processes in visual search could help us to understand the connection between template formation and successful distractor inhibition. Our findings may also benefit future EEG-based interventions on individuals with deficits in attentional control.

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.

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.

•

Distractor suppression is the ability to filter out irrelevant information.

•

At present, we know little about how the brain suppresses distraction.

•

We offer ten rules that are fundamental when investigating distractor suppression.

•

Following the rules will propel research and foster interaction between disciplines.

No evidence for proactive suppression of explicitly cued distractor features

Visual search benefits from advance knowledge of nontarget features. However, it is unknown whether these negatively cued features are suppressed in advance (proactively) or during search (reactively). To test this, we presented color cues varying from trial-to-trial that predicted target or nontarget colors. Experiment 1 (N = 96) showed that both target and nontarget cues speeded search. To test whether attention proactively modified cued feature representations, in Experiment 2 (N = 200), we interleaved color probe and search trials and had participants detect the color of a briefly presented ring that could either match the cued color or not. People detected positively cued colors better than other colors, whereas negatively cued colors were detected no better or worse than other colors. These results demonstrate that nontarget features are not suppressed proactively, and instead suggest that anticipated nontarget features are ignored via reactive mechanisms.

Inhibition continues to guide search under concurrent visual working memory load

It is well known that attention can be automatically attracted to salient items. However, recent studies show that it is possible to avoid distraction by a salient item (with a known feature), leading to facilitated search. This article tests a proposed mechanism for distractor inhibition: that a mental representation of the distractor feature held in visual working memory (VWM) allows attention to be guided away from the distractor. We tested this explanation by examining color-based inhibition in visual search for a shape target with and without VWM load. In Experiment 1 the presence of a distractor facilitated visual search under low and high VWM loads, as reflected in faster response times when the distractor was present (compared to absent), and in fewer eye movements to the salient distractor than the non-target items. However, the eye movement inhibition effect was noticeably weakened in the load conditions. Experiment 2 explored further, to distinguish between inhibition of the distractor color and activation of the (irrelevant) target color. Intermittently presenting single-color search trials that contained only either a target, distractor or a neutral-colored singleton revealed that the distractor color attracted attention less than the neutral color with and without VWM load. The target color, however, only attracted attention more than neutral colors under no load, whereas a VWM load completely eliminated this effect. This suggests that although VWM plays a role in guiding attention to the (irrelevant) target color, distractor-feature inhibition can operate independently.

Memory precision for salient distractors decreases with learned suppression

Attention operates as a cognitive gate that selects sensory information for entry into memory and awareness (Driver, 2001, British Journal of Psychology, 92, 53-78). Under many circumstances, the selected information is task-relevant and important to remember, but sometimes perceptually salient nontarget objects will capture attention and enter into awareness despite their irrelevance (Adams & Gaspelin, 2020, Attention, Perception, & Psychophysics, 82[4], 1586-1598). Recent studies have shown that repeated exposures with salient distractor will diminish their ability to capture attention, but the relationship between suppression and later cognitive processes such as memory and awareness remains unclear. If learned attentional suppression (indicated by reduced capture costs) occurs at the sensory level and prevents readout to other cognitive processes, one would expect memory and awareness to dimmish commensurate with improved suppression. Here, we test this hypothesis by measuring memory precision and awareness of salient nontargets over repeated exposures as capture costs decreased. Our results show that stronger learned suppression is accompanied by reductions in memory precision and confidence in having seen a color singleton at all, suggesting that such suppression operates at the sensory level to prevent further processing of the distractor object.

Is Statistical Learning of a Salient Distractor's Color Implicit, Inflexible and Distinct From Inter-Trial Priming?

Being able to overcome distraction by salient distractors is critical in order to allocate our attention efficiently. Previous research showed that observers can learn to ignore salient distractors endowed with some regularity, such as a high-probability location or feature - a phenomenon known as distractor statistical learning. Unlike goal-directed attentional guidance, the bias induced by statistical learning is thought to be implicit, long-lasting and inflexible. We tested these claims with regard to statistical learning of distractor color in a high-power (N = 160) pre-registered experiment. Participants searched for a known-shape singleton target and a color singleton distractor, when present, appeared most often in one color during the learning phase, but equally often in all possible colors during the extinction phase. We used a sensitive measure of participants' awareness of the probability manipulation. The awareness test was administered after the extinction phase for one group, and after the leaning phase for another group - which was informed that the probability imbalance would be discontinued in the upcoming extinction phase. Participants learned to suppress the high-probability distractor color very fast, an effect partly due to intertrial priming. Crucially, there was only little evidence that the bias survived during extinction. Awareness of the manipulation was associated with reduced color suppression, suggesting that the bias was implicit. Finally, results showed that the awareness test was more sensitive when administered early vs. late. We conclude that learnt color suppression is an implicit bias that emerges and decays rapidly, and discuss the methodological implications of our findings.

Shielding working-memory representations from temporally predictable external interference

Protecting working-memory content from distracting external sensory inputs and intervening tasks is an ubiquitous demand in daily life. Here, we ask whether and how temporal expectations about external events can help mitigate effects of such interference during working-memory retention. We manipulated the temporal predictability of interfering items that occurred during the retention period of a visual working-memory task and report that temporal expectations reduce the detrimental influence of external interference on subsequent memory performance. Moreover, to determine if the protective effects of temporal expectations rely on distractor suppression or involve shielding of internal representations, we compared effects after irrelevant distractors that could be ignored vs. interrupters that required a response. Whereas distractor suppression may be sufficient to confer protection from predictable distractors, any benefits after interruption are likely to involve memory shielding. We found similar benefits of temporal expectations after both types of interference. We conclude that temporal expectations may play an important role in safeguarding behaviour based on working memory - acting through mechanisms that include the shielding of internal content from external interference.

Impaired selection of a previously ignored singleton: Evidence for salience map plastic changes

Spatial suppression of a salient colour distractor is achievable via statistical learning. Distractor suppression attenuates unwanted capture, but at the same time target selection at the most likely distractor location is impaired. This result corroborates the idea that the distractor salience is attenuated via inhibitory signals applied to the corresponding location in the priority map. What is less clear, however, is whether lingering impairment in target selection when the distractor is removed are due to the proactive strategic maintenance of the suppressive signal at the previous most likely distractor location or result from the fact that suppression has induced plastic changes in the priority map, probably changing input weights. Here, we provide evidence that supports the latter possibility, as we found that impairment in target selection persisted even when the singleton distractor in the training phase became the target of search in a subsequent test phase. This manipulation rules out the possibility that the observed impairments at the previous most likely distractor location were caused by a signal suppression maintained at this location. Rather, the results reveal that the inhibitory signals cause long-lasting changes in the priority map, which affect future computation of the target salience at the same location, and therefore the efficiency of attentional selection.

What kind of empirical evidence is needed for probabilistic mental representations? An example from visual perception

Recent accounts of perception and cognition propose that the brain represents information probabilistically. While this assumption is common, empirical support for such probabilistic representations in perception has recently been criticized. Here, we evaluate these criticisms and present an account based on a recently developed psychophysical methodology, Feature Distribution Learning (FDL), which provides promising evidence for probabilistic representations by avoiding these criticisms. The method uses priming and role-reversal effects in visual search. Observers' search times reveal the structure of perceptual representations, in which the probability distribution of distractor features is encoded. We explain how FDL results provide evidence for a stronger notion of representation that relies on structural correspondence between stimulus uncertainty and perceptual representations, rather than a mere co-variation between the two. Moreover, such an account allows us to demonstrate what kind of empirical evidence is needed to support probabilistic representations as posited in current probabilistic Bayesian theories of perception.

You see what you look for: Targets and distractors in visual search can cause opposing serial dependencies

Visual perception is, at any given moment, strongly influenced by its temporal context-what stimuli have recently been perceived and in what surroundings. We have previously shown that to-be-ignored items produce a bias upon subsequent perceptual decisions that acts in parallel with other biases induced by attended items. However, our previous investigations were confined to biases upon the perceived orientation of a visual search target, and it is unclear whether these biases influence perceptual decisions in a more general sense. Here, we test whether the biases from visual search targets and distractors affect the perceived orientation of a neutral test line, one that is neither a target nor a distractor. To do so, we asked participants to search for an oddly oriented line among distractors and report its location for a few trials and next presented a test line irrelevant to the search task. Participants were asked to report the orientation of the test line. Our results indicate that in tasks involving visual search, targets induce a positive bias upon a neutral test line if their orientations are similar, whereas distractors produce an attractive bias for similar test lines and a repulsive bias if the orientations of the test line and the average orientation of the distractors are far apart in feature space. In sum, our results show that both attentional role and proximity in feature space between previous and current stimuli determine the direction of biases in perceptual decisions.

Classic Visual Search Effects in an Additional Singleton Task: An Open Dataset

Visual search refers to our ability to find what we are looking for among many competing visual inputs. Here, we report the availability of a rich dataset that replicates key visual search effects and shows that these effects are robust to several changes to the experimental design. Experiment 1 replicates classic findings from an additional singleton visual search task. First, participants are captured by a salient but irrelevant color singleton, as indexed by slower response times when a color singleton distractor is present versus absent. Second, attentional capture by a color singleton is reduced when the visual search array contains heterogeneous shapes rather than homogenous shapes. Finally, attentional capture by a color singleton is reduced when the display colors are repeated rather than switched unpredictably from trial to trial. Experiment 2 demonstrates that these classic visual search effects are robust to small procedural changes such as task timing (i.e., a 2-8 second rather than ~1 second inter-trial interval). Experiment 3 demonstrates that these classic effects are likewise robust to changes to the distractor frequency (75% rather than 50%) and to fully blocking versus interleaving blocks of two task conditions. All told, this dataset includes 8 sub-experiments, 190 participants and >210,000 trials, and it will serve as a useful resource for power analyses and exploratory analyses of visual search behaviors.

Statistical learning of target selection and distractor suppression shape attentional priority according to different timeframes

Recent findings suggest that attentional and oculomotor control is heavily affected by past experience, giving rise to selection and suppression history effects, so that target selection is facilitated if they appear at frequently attended locations, and distractor filtering is facilitated at frequently ignored locations. While selection history effects once instantiated seem to be long-lasting, whether suppression history is similarly durable is still debated. We assessed the permanence of these effects in a unique experimental setting investigating eye-movements, where the locations associated with statistical unbalances were exclusively linked with either target selection or distractor suppression. Experiment 1 and 2 explored the survival of suppression history in the long and in the short term, respectively, revealing that its lingering traces are relatively short lived. Experiment 3 showed that in the very same experimental context, selection history effects were long lasting. These results seem to suggest that different mechanisms support the learning-induced plasticity triggered by selection and suppression history. Specifically, while selection history may depend on lasting changes within stored representations of the visual space, suppression history effects hinge instead on a functional plasticity which is transient in nature, and involves spatial representations which are constantly updated and adaptively sustain ongoing oculomotor control.

Across-trial spatial suppression in visual search

In order to focus on objects of interest, humans must be able to avoid distraction by salient stimuli that are not relevant to the task at hand. Many recent studies have shown that through statistical learning we are able to suppress the location that is most likely to contain a salient distractor. Here we demonstrate a remarkable flexibility in attentional suppression. Participants had to search for a shape singleton while a color distractor singleton was present. Unbeknown to the participant, the color distractor was presented according to a consistent pattern across trials. Our findings show that participants learn this distractor sequence as they proactively suppressed the anticipated location of the distractor on the next trial. Critically, none of the participants were aware of these hidden sequences. We conclude that the spatial priority map is highly flexible, operating at a subconscious level preparing the attentional system for what will happen next.

Distractor filtering is affected by local and global distractor probability, emerges very rapidly but is resistant to extinction

Effects of statistical learning (SL) of distractor location have been shown to persist when the probabilities of distractor occurrence are equalized across different locations in a so-called extinction phase. Here, we asked whether lingering effects of SL are still observed when a true extinction phase, during which the distractor is completely omitted, is implemented. The results showed that, once established, the effects of SL of distractor location do survive the true extinction phase, indicating that the pattern of suppression in the saliency map is encoded in a form of long-lasting memory. Quite unexpectedly, we also found that the amount of filtering implemented at a given location is not only dictated by the specific rate of distractor occurrence at that location, as previously found, but also by the global distractor probability. We therefore suggest that the visual attention system could be more or less (implicitly) prone to suppression as a function of how often the distractor is encountered overall, and that this suppressive bias affects the degree of suppression at the specific distractor-probability location. Finally, our results showed that the effects of SL of distractor location can appear much more rapidly than has been previously documented, requiring a few trials to become manifest. Hence, SL of distractor location appears to have an asymmetrical rate of learning during acquisition and extinction, while the amount of suppression exerted at a specific distractor location is modulated by distractor contextual probabilistic information.

Gaze dynamics of feature-based distractor inhibition under prior-knowledge and expectations

Prior information about distractor facilitates selective attention to task-relevant items and helps the optimization of oculomotor planning. In the present study, we capitalized on gaze-position decoding to examine the dynamics of attentional deployment in a feature-based attentional task that involved two groups of dots (target/distractor dots) moving toward different directions. In Experiment 1, participants were provided with target cues indicating the moving direction of target dots. The results showed that participants were biased toward the cued direction and tracked the target dots throughout the task period. In Experiment 2 and Experiment 3, participants were provided with cues that informed the moving direction of distractor dots. When the distractor cue varied on a trial-by-trial basis (Experiment 2), participants continuously monitored the distractor's direction. However, when the to-be-ignored distractor direction remained constant (Experiment 3), participants would strategically bias their attention to the distractor's direction before the cue onset to reduce the cost of redeployment of attention between trials and reactively suppress further attraction evoked by distractors during the stimulus-on stage. This functional dissociation reflected the distinct influence that expectation produced on ocular control. Taken together, these results suggest that monitoring the distractor's feature is a prerequisite for feature-based attentional inhibition, and this process is facilitated by the predictability of the distractor's feature.

Optimizing perception: Attended and ignored stimuli create opposing perceptual biases

Humans have remarkable abilities to construct a stable visual world from continuously changing input. There is increasing evidence that momentary visual input blends with previous input to preserve perceptual continuity. Most studies have shown that such influences can be traced to characteristics of the attended object at a given moment. Little is known about the role of ignored stimuli in creating this continuity. This is important since while some input is selected for processing, other input must be actively ignored for efficient selection of the task-relevant stimuli. We asked whether attended targets and actively ignored distractor stimuli in an odd-one-out search task would bias observers' perception differently. Our observers searched for an oddly oriented line among distractors and were occasionally asked to report the orientation of the last visual search target they saw in an adjustment task. Our results show that at least two opposite biases from past stimuli influence current perception: A positive bias caused by serial dependence pulls perception of the target toward the previous target features, while a negative bias induced by the to-be-ignored distractor features pushes perception of the target away from the distractor distribution. Our results suggest that to-be-ignored items produce a perceptual bias that acts in parallel with other biases induced by attended items to optimize perception. Our results are the first to demonstrate how actively ignored information facilitates continuity in visual perception.

Steady-State Visually Evoked Potentials and Feature-based Attention: Preregistered Null Results and a Focused Review of Methodological Considerations

Feature-based attention is the ability to selectively attend to a particular feature (e.g., attend to red but not green items while looking for the ketchup bottle in your refrigerator), and steady-state visually evoked potentials (SSVEPs) measured from the human EEG signal have been used to track the neural deployment of feature-based attention. Although many published studies suggest that we can use trial-by-trial cues to enhance relevant feature information (i.e., greater SSVEP response to the cued color), there is ongoing debate about whether participants may likewise use trial-by-trial cues to voluntarily ignore a particular feature. Here, we report the results of a preregistered study in which participants either were cued to attend or to ignore a color. Counter to prior work, we found no attention-related modulation of the SSVEP response in either cue condition. However, positive control analyses revealed that participants paid some degree of attention to the cued color (i.e., we observed a greater P300 component to targets in the attended vs. the unattended color). In light of these unexpected null results, we conducted a focused review of methodological considerations for studies of feature-based attention using SSVEPs. In the review, we quantify potentially important stimulus parameters that have been used in the past (e.g., stimulation frequency, trial counts) and we discuss the potential importance of these and other task factors (e.g., feature-based priming) for SSVEP studies.

Dissociating implicit and explicit ensemble representations reveals the limits of visual perception and the richness of behavior

Our senses provide us with a rich experience of a detailed visual world, yet the empirical results seem to suggest severe limitations on our ability to perceive and remember. In recent attempts to reconcile the contradiction between what is experienced and what can be reported, it has been argued that the visual world is condensed to a set of summary statistics, explaining both the rich experience and the sparse reports. Here, we show that explicit reports of summary statistics underestimate the richness of ensemble perception. Our observers searched for an odd-one-out target among heterogeneous distractors and their representation of distractor characteristics was tested explicitly or implicitly. Observers could explicitly distinguish distractor sets with different mean and variance, but not differently-shaped probability distributions. In contrast, the implicit assessment revealed that the visual system encodes the mean, the variance, and even the shape of feature distributions. Furthermore, explicit measures had common noise sources that distinguished them from implicit measures. This suggests that explicit judgments of stimulus ensembles underestimate the richness of visual representations. We conclude that feature distributions are encoded in rich detail and can guide behavior implicitly, even when the information available for explicit summary judgments is coarse and limited.

Preparing for the Worst: Attention is Enhanced Prior to Any Upcoming Emotional or Neutral Stimulus

Do people allocate more or fewer attentional resources when preparing for negative emotional visual stimuli to appear? In three experiments (total N = 150), participants performed a change-detection task while expecting a neutral, threatening, disgusting, or joyful stimulus or no stimulus to appear at a fixed moment. Responses to an infrequent dot probe were faster when participants were expecting a distracting stimulus. Importantly, although only negative stimuli impaired change-detection performance, there was no difference between the preparation effect for threatening and neutral stimuli (Experiment 1) or disgusting and joyful stimuli (Experiment 3). The preparation effects were also unaffected by the participant's anxiety level. Experiment 2 confirmed that the threatening images affected performance when the dot probe appeared after the image. These results suggest that the visual system increases alertness in response to any upcoming stimulus and further imply that the effects of emotional stimuli largely occur after, but not before, the stimuli appear.