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 role of salience in the suppression of distracting stimuli.

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

A new technique for estimating the probability of attentional capture.

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

Learned distractor rejection persists across target search in a different dimension.

Attention is guided by several factors, including task-relevant target features, which attract attention, but also statistical regularities associated distractors, which repel attention away from themselves. However, whether feature-based distractor regularities (e.g., color) are extracted automatically from a feature dimension orthogonal to the target-guiding dimension (e.g., shape) remains to be tested. In two experiments, we tested if learned distractor rejection by color operated when color was not part of the attentional control settings, specifically, while attention was guided by a shape-based target template. Participants performed a visual search task for a task-relevant shape in displays containing two unsegregated colors. These displays allowed us to manipulate target guidance (based on shape) independently from distractor-based regularities (based on color). In both experiments we found clear evidence for learned distractor rejection: faster mean response times to locate the target when a consistent distractor color was present than when it was absent. Critically, these task-irrelevant learned distractor rejection effects were robust despite strong target guidance by an orthogonal search dimension. These findings corroborate recent demonstrations of learned distractor rejection during strong target guidance, indicating that learned distractor rejection and target guidance can operate on separate feature dimensions.

Testing the underlying processes leading to learned distractor rejection: Learned oculomotor avoidance.

Target templates stored in visual memory guide visual attention toward behaviorally relevant target objects. Visual attention also is guided away from nontarget distractors by longer-term learning, a phenomenon termed "learned distractor rejection." Template guidance and learned distractor rejection can occur simultaneously to further increase search efficiency. However, the underlying processes guiding learned distractor rejection are unknown. In two visual search experiments employing eye-tracking, we tested between two plausible processes: proactive versus reactive attentional control. Participants searched through two-color, spatially unsegregated displays. Participants could guide attention by both target templates and consistent nontarget distractors. We observed fewer distractor fixations (including the first eye movement) and shorter distractor dwell times. The data supported a single mechanism of learned distractor rejection, whereby observers adopted a learned, proactive attentional control setting to avoid distraction whenever possible. Further, when distraction occurred, observers rapidly recovered. We term this proactive mechanism "learned oculomotor avoidance." The current study informs theories of visual attention by demonstrating the underlying processes leading to learned distractor suppression during strong target guidance.

Electrophysiological Evidence for the Suppression of Highly Salient Distractors.

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

Attentional suppression of highly salient color singletons.

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

Learned distractor rejection in the face of strong target guidance.

Visual attention is guided toward behaviorally relevant objects by target "templates" stored in visual memory. Visual attention also is guided away from nontarget distractors by learned distractor rejection. In a series of 5 visual search experiments, we asked if learned distractor rejection operated while attention was simultaneously guided by a target template. Participants performed a visual search in 2-color, spatially unsegregated displays where we manipulated attentional guidance by both target templates and consistent nontarget distractors. We observed faster mean response times to the target when a consistent nontarget distractor was present than when it was absent-the hallmark of learned distractor rejection-despite the use of strong target guidance. Learned distractor rejection indeed operates alongside guidance from a target template, indicating that theories of visual attention should incorporate guidance by both target templates and learned nontargets. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Feature-based statistical regularities of distractors modulate attentional capture.

Ignoring salient distracting information is paramount to efficiently guiding attention during visual search. Learning to reject or suppress these strong sources of distraction leads to more effective visual search for targets. Participants can learn to overcome salient distractors if given reliable search regularities. If salient distractors appear in 1 location more frequently than any other, the visual system can use this environmental regularity to reduce attentional capture at the more frequent location (Wang & Theeuwes, 2018). We asked if reduced attentional capture is limited to location-based regularities, or, if the visual attentional system is configured to use feature-based regularities in reducing attentional capture as well. In 4 experiments examining attentional capture by task-irrelevant color singletons, participants searched for a shape singleton target among homogenously colored distractors. Critically, on a proportion of trials, a salient, color singleton distractor was presented. Color singleton distractors that appeared at a frequent location captured attention less than color singleton distractors that appeared at infrequent locations, replicating previous findings. In subsequent experiments we manipulated the frequency of the colors of the color singleton distractors and observed robust increases in capture based on color feature regularities. Despite strong location information, we observed reliable attentional capture attenuation by frequently presented distractor colors. Our results suggest that attentional capture is attenuated by both location and feature information. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Learned and cued distractor rejection for multiple features in visual search.

Ignoring distracting information is critical for effective visual search. When individuals are cued to ignore a stimulus, they first attend the to-be-ignored stimulus before learning to reject it. Individuals can learn to overcome the initial distraction produced by the explicit cues, although this cued distractor rejection appears for only one distractor feature. Multiple distractor colors cannot be rejected effectively, even with extensive experience. We asked if this apparent limit on distractor rejection was caused by a restriction on the number of different features (i.e., colors) that could be learned and rejected as distractors. To explore this potential capacity limitation, we asked if attention can learn to reject the smallest possible number of multiple distractors, namely, two. In four experiments examining cued distractor rejection, individuals searched through heterogeneously colored arrays containing reliable, non-target color information. In Experiments 1 and 2, we explicitly cued individuals with which of two colors (both colors in Experiment 1 or one color in Experiment 2) could be safely ignored. Cued distractors were not reliably rejected, replicating previous findings. Additionally, in Experiment 2, we presented a to-be-ignored color without explicit cues and we found that these "uncued" distractors were reliably rejected. In Experiments 3 and 4, we presented the to-be-ignored color information without explicit cues; individuals learned to reliably ignore multiple distractor colors without explicit cueing. These results suggest that learned distractor rejection is better suited to experience-driven learning than explicitly cued distractor learning: Explicit cueing reliably interferes with learned distractor rejection.