Evidence against the low-salience account of attentional suppression.

Do salient distractors have the power to automatically capture attention? This question has led to a heated debate concerning the role of salience in attentional control. A potential resolution, called the signal suppression hypothesis, has proposed that salient items produce a bottom-up signal that vies for attention, but that salient stimuli can be suppressed via top-down control to prevent the capture of attention. This hypothesis, however, has been criticized on the grounds that the distractors used in initial studies of support were weakly salient. It has been difficult to know how seriously to take this low-salience criticism because assertions about high and low salience were made in the absence of a common (or any) measure of salience. The current study used a recently developed psychophysical technique to compare the salience of distractors from two previous studies at the center of this debate. Surprisingly, we found that the original stimuli criticized as having low salience were, if anything, more salient than stimuli from the later studies that purported to increase salience. Follow-up experiments determined exactly why the original stimuli were more salient and tested whether further improving salience could cause attentional capture as predicted by the low-salience account. Ultimately, these findings challenge purely stimulus-driven accounts of attentional control. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

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.

A Critique of the Attentional Window Account of Capture Failures.

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

The role of salience in the suppression of distracting stimuli.

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

Standing out in a small crowd: The role of display size in attracting attention.

Strong evidence supporting the top-down modulation of attention has come from studies in which participants learned to suppress a singleton in a heterogeneous four-item display. These studies have been criticized on the grounds that the displays are so sparse that the singleton is not actually salient. We argue that similar evidence of suppression has been found with substantially larger displays where salience is not in question. Additionally, we examine the results of applying salience models to four-item displays, and find prominent markers of salience at the location of the singleton. We conclude that small heterogeneous displays do not preclude strong salience signals. Beyond that, we reflect on how further basic research on salience may speed resolution of the attentional capture debate.

Can salient stimuli really be suppressed?

Although it is often assumed that a physically salient stimulus automatically captures attention even when it is irrelevant to a current task, the signal-suppression hypothesis proposes that observers can actively suppress a salient-but-irrelevant distractor. However, it is still unknown whether suppression alone (i.e., without target enhancement) is potent enough to override attentional capture by a salient singleton in an otherwise-homogeneous background. The current study addressed this issue. On search trials (70% of trials), participants searched for a shape target on trials that either did or did not contain an irrelevant color singleton. The effects of learning to suppress the color of the singleton were examined on interleaved probe trials (30% of trials). On these trials, participants searched for a probe target letter; those letters were presented on four ovals (one colored oval and three gray ovals). Each colored oval was a singleton that was one of three types: the color of the distractor on search trials, the color of the target on search trials, or a neutral color that had not appeared on search trials. Responses were faster for the probe target on a neutral-colored or target-colored item than on a gray-colored item; however, responses were slower for the probe target on a distractor-colored item than on a gray-colored item. The results demonstrate a powerful suppression mechanism overriding attentional capture by a singleton item.

Enhancement and Suppression Flexibly Guide Attention.

Previous research suggests that observers can suppress salient-but-irrelevant stimuli in a top-down manner. However, one question left unresolved is whether such suppression is, in fact, solely due to distractor-feature suppression or whether it instead also reflects some degree of target-feature enhancement. The present study (N = 60) addressed this issue. On search trials (70% of trials), participants searched for a shape target when an irrelevant color singleton was either present or absent; performance was better when a color singleton was present. On interleaved probe trials (30% of trials), participants searched for a letter target. Responses were faster for the letter on a target-colored item than on a neutral-colored item, whereas responses were slower for the letter on a distractor-colored item than on a neutral-colored item. The results demonstrate that target-feature enhancement and distractor-feature suppression contribute to attentional guidance independently; enhancement and suppression flexibly guide attention as the occasion demands.

The capture of attention by entirely irrelevant pictures of calorie-dense foods.

Inborn preference for palatable energy-dense food is thought to be an evolutionary adaptation. One way this preference manifests itself is through the control of visual attention. In the present study, we investigated how attentional capture is influenced by changes in naturally occurring goal-states, in this case desire for energy-dense foods (typically high fat and/or high sugar). We demonstrate that even when distractors are entirely irrelevant, participants were significantly more distracted by energy-dense foods compared with non-food objects and even low-energy foods. Additionally, we show the lability of these goal-states by having a separate set of participants consume a small amount of calorie-dense food prior to the task. The amount of distraction by the energy-dense food images in this case was significantly reduced and no different than distraction by images of low-energy foods and images of non-food objects. While naturally occurring goal-states can be difficult to ignore, they also are highly flexible.

Taming the White Bear: Initial Costs and Eventual Benefits of Distractor Inhibition.

Previous research indicates that prior information about a target feature, such as its color, can speed search. Can search also be speeded by knowing what a target willnotlook like? In the two experiments reported here, participants searched for target letters. Prior to viewing search displays, participants were prompted either with the color in which one or more nontarget letters would appear (ignore trials) or with no information about the search display (neutral trials). Critically, when participants were given one consistent color to ignore for the duration of the experiment, compared with when they were given no information, there was a cost in reaction time (RT) early in the experiment. However, after extended practice, RTs on ignore trials were significantly faster than RTs on neutral trials, which provides a novel demonstration that knowledge about nontargets can improve search performance for targets. When the to-be-ignored color changed from trial to trial, no RT benefit was observed.

Massive memory revisited: Limitations on storage capacity for object details in visual long-term memory.

Previous work suggests that visual long-term memory (VLTM) is highly detailed and has a massive capacity. However, memory performance is subject to the effects of the type of testing procedure used. The current study examines detail memory performance by probing the same memories within the same subjects, but using divergent probing methods. The results reveal that while VLTM representations are typically sufficient to support performance when the procedure probes gist-based information, they are not sufficient in circumstances when the procedure requires more detail. We show that VLTM capacity, albeit large, is heavily reliant on gist as well as detail. Thus, the nature of the mnemonic representations stored in VLTM is important in understanding its capacity limitations.

When Does Feature Search Fail to Protect Against Attentional Capture?

When participants search for a shape (e.g., a circle) among a set of homogenous shapes (e.g., triangles) they are subject to distraction by color singletons that are more salient than the target. However, when participants search for a shape among heterogeneous shapes, the presence of a non-target color singleton does not slow responses to the target. Attempts have been made to explain these results from both bottom-up and top-down perspectives. What both accounts have in common is that they do not predict the occurrence of attentional capture on typical feature search displays. Here, we present a case where manipulating selection history, rather than the displays themselves, leads to attentional capture on feature search trials. The ability to map specific colors to the target and distractor appears to be what enables resistance to capture during feature search.

Inhibition drives early feature-based attention.

Attention can modulate processing of visual input according to task-relevant features, even as early as approximately 100 ms after stimulus presentation. In the present study, event-related potential and behavioral data revealed that inhibition of distractor features, rather than activation of target features, is the primary driver of early feature-based selection in human observers. This discovery of inhibition consistent with task goals during early visual processing suggests that inhibition plays a much larger role at an earlier stage of target selection than previously recognized. It also highlights the importance of understanding the role of inhibition (in addition to activation) in attention.

Detection is unaffected by the deployment of focal attention.

There has been much debate regarding how much information humans can extract from their environment without the use of limited attentional resources. In a recent study, Theeuwes et al. (2008) argued that even detection of simple feature targets is not possible without selection by focal attention. Supporting this claim, they found response time (RT) benefits in a simple feature (color) detection task when a target letter's identity was repeated on consecutive trials, suggesting that the letter was selected by focal attention and identified prior to detection. This intertrial repetition benefit remained even when observers were required to simultaneously identify a central digit. However, we found that intertrial repetition benefits disappeared when a simple color target was presented among a heterogeneously (rather than homogeneously) colored set of distractors, thus reducing its bottom-up salience. Still, detection performance remained high. Thus, detection performance was unaffected by whether a letter was focally attended and identified prior to detection or not. Intertrial identity repetition benefits also disappeared when observers were required to perform a simultaneous, attention-demanding central task (Experiment 2), or when unfamiliar Chinese characters were used (Experiment 3). Together, these results suggest that while shifts of focal attention can be affected by target salience, by the availability of excess cognitive resources, and by target familiarity, detection performance itself is unaffected by these manipulations and is thus unaffected by the deployment of focal attention.

The ignoring paradox: cueing distractor features leads first to selection, then to inhibition of to-be-ignored items.

Observers find a target item more quickly when they have foreknowledge of target-defining attributes, such as identity, color, or location. However, it is less clear whether foreknowledge of nontarget attributes can also speed search. Munneke, Van der Stigchel, and Theeuwes Acta Psychologica 129:101-107, (2008) found that observers found the target more quickly when they were cued to ignore a region of space where a target would not appear. Using a similar paradigm, we explored the effects of cueing nontarget features on search. We found that when we cued observers to ignore nontarget features, search was slowed. The results from a probe-dot detection task revealed that this slowing occurred because, paradoxically, observers initially selected an item appearing in the to-be-ignored color. Finally, we found that cueing nontarget features sped search when placeholders matching the location of the to-be-ignored color preceded presentation of the search display by at least 800 ms; thus, it appears that some limited inhibition of to-be-ignored items occurs following selection. Taken together, these results suggest that observers are unable to explicitly avoid selection of items matching known nontarget features. Instead, when nontarget features are cued, observers select the to-be-ignored feature or the locations of objects matching that feature early in search, and only inhibit them after this selection process.

Trial-by-trial adjustments of top-down set modulate oculomotor capture.

The role of top-down control in visual search has been a subject of much debate. Recent research has focused on whether attentional and oculomotor capture by irrelevant salient distractors can be modulated through top-down control, and if so, whether top-down control can be rapidly initiated based on current task goals. In the present study, participants searched for a unique shape in an array containing otherwise homogeneous shapes. A cue prior to each trial indicated the probability that an irrelevant color singleton distractor would appear on that trial. Initial saccades were less likely to land on the target and participants took longer to initiate a saccade to the target when a color distractor was present than when it was absent; this cost was greatly reduced on trials in which the probability that a distractor would appear was high, as compared to when the probability was low. These results suggest that top-down control can modulate oculomotor capture in visual search, even in a singleton search task in which distractors are known to readily capture both attention and the eyes. Furthermore, the results show that top-down distractor suppression mechanisms can be initiated quickly in anticipation of irrelevant salient distractors and can be adjusted on a trial-by-trial basis.

The role of within-dimension singleton priming in visual search.

The authors report a newly identified intertrial priming phenomenon, within-dimension singleton priming, by which search for a target that happens to be a singleton on the current trial is faster when the target on the previous trial had also been a singleton on the same dimension rather than a nonsingleton. This effect was replicated in 6 experiments with different procedures, with singletons on various dimensions, when the featural contrast defining the singleton remained the same or changed within a dimension from one trial to the next, and when the target was a singleton on a target-defining dimension or on an irrelevant dimension. These findings cannot be explained by previously demonstrated intertrial repetition effects such as dimension-specific priming or priming of pop-out. Theoretical implications of the within-dimension singleton priming phenomenon are discussed relative to the dimension-weighting hypothesis, the role of stimulus-driven salience in feature-guided search, and the roles of intertrial priming and goal-directed factors in visual search.

Biased competition and visual search: the role of luminance and size contrast.

The biased-competition theory of attention proposes that objects compete for cortical representation in a mutually inhibitory network; competition is biased in favor of the attended item. Here we test two predictions derived from the biased-competition theory. First we assessed whether increasing an object's relative brightness (luminance contrast) biased competition in favor of (i.e., prioritized) the brighter object. Second we assessed whether increasing an object's size biased competition in favor of the larger object. In fulfillment of these aims we used an attentional capture paradigm to test whether a featural singleton (an item unique with respect to a feature such as size or brightness) can impact attentional priority even when those features are irrelevant to finding the target. The results support the prediction that a singleton with respect to luminance contrast receives attentional prioritization and extend the biased-competition account to include size contrast, because a large singleton also receives attentional prioritization.

Effects of search mode and intertrial priming on singleton search.

There is no consensus as to what information guides search for a singleton target. Does the most salient display element capture attention, regardless of the observer's attentional set? Do observers adopt a default salience-based search mode? Does knowledge of the target's defining featural property (when available) affect search? Finally, can intertrial contingencies account for the disparate results in the literature? We investigated search for a shape singleton when (1) the target and nontarget shapes switched unpredictably from trial to trial, (2) the target feature remained fixed, and (3) the target was a singleton on only one third of the trials. We examined overall reaction times, search slopes, errors, and the magnitude of the slowing caused by a cross-dimensional singleton distractor. Our results argue against the idea that search is guided solely by stimulus-driven factors or that subjects adopt a singleton detection mode that is blind to feature information. They show also that intertrial contingencies, although potent, cannot account for the variety of results in the literature.

Target-nontarget similarity modulates stimulus-driven control in visual search.

The literature contains conflicting results concerning whether an irrelevant featural singleton (an item unique with respect to a feature such as color or brightness) can control attention in a stimulus-driven manner. The present study explores whether target-nontarget similarity influences stimulus-driven shifts of attention to a distractor. An experiment evaluated whether manipulating target-nontarget similarity by varying orientation would modulate distraction by an irrelevant feature (a bright singleton). We found that increasing target-nontarget similarity resulted in a decreased impact of a uniquely bright object on visual search. This method of manipulating the target-nontarget similarity independent of the salience of a distracting feature suggests that the extent to which visual attention is stimulus-driven depends on the target-nontarget similarity.