An electrophysiological study of attention capture by salience: Does rarity enable capture?

Several behavioural studies have suggested that rarity is critical for enabling irrelevant, salient objects to capture attention. We tested this hypothesis using the N2pc thought to reflect attentional allocation. A cue display was followed by a target display in which participants identified the letter in a specific colour. Experiment 1 pitted rare, irrelevant abrupt onset cues (appearing on only 20% of trials) against target-relevant colour cues. The relevant colour cue produced large N2pc and cue validity effects even when competing with a rare, salient, simultaneous abrupt onset. Similar results occurred even when abrupt onset frequency was reduced to only 10% of trials (Experiment 2). Experiment 3 examined rare, irrelevant colour singleton cues (20% of trials). Despite being rare and salient, these singleton cues produced no N2pc or cue validity effect indicating little attentional capture. Experiment 4 greatly increased colour cue salience by adding four background boxes, increasing colour contrast and tripling the cue display duration (from 50 to 150 ms). Small cue validity and N2pc effects were obtained, but did not strongly depend on degree of rarity (20% vs. 100%). We argue that rarity by itself is neither necessary nor sufficient to produce attention capture.     

Contingent attentional capture by top-down control settings: converging evidence from event-related potentials

Theories of attentional control are divided over whether the capture of spatial attention depends primarily on stimulus salience or is contingent on attentional control settings induced by task demands. The authors addressed this issue using the N2-posterior- contralateral (N2pc) effect, a component of the event-related brain potential thought to reflect attentional allocation. They presented a cue display followed by a target display of 4 letters. Each display contained a green item and a red item. Some participants responded to the red letter and others to the green letter. Converging lines of evidence indicated that attention was captured by the cues with the same color as the target. First, these target-color cues produced a cuing validity effect on behavioral measures. Second, distractors appearing in the cued location produced larger compatibility effects. Third, the target-color cue produced a robust N2pc effect, similar in magnitude to the N2pc effect to the target itself. Furthermore, the target-color cue elicited a similar N2pc effect regardless of whether it competed with a simultaneous abrupt onset. The findings provide converging evidence for attentional capture contingent on top-down control settings.     

Aging and involuntary attention capture: electrophysiological evidence for preserved attentional control with advanced age

The present study examined whether people become more susceptible to capture by salient objects as they age. Participants searched a target display for a letter in a specific color and indicated its identity. In Experiment 1, this target display was preceded by a non-informative cue display containing one target-color box, one ignored-color box, and two white boxes. On half of the trials, this cue display also contained a salient-but-irrelevant abrupt onset. To assess capture by the target-color cue, we used the N2pc component of the event-related potential, thought to reflect attentional allocation to the left or right visual field. The target-color box in the cue display produced a substantial N2pc effect for younger adults and, most importantly, this effect was not diminished by the presence of an abrupt onset. Therefore, the abrupt onset was unable to capture attention away from the target-color cue. Critically, older adults demonstrated the same resistance to capture by the abrupt onset. Experiment 2 extended these findings to irrelevant color singleton cues. Thus, we argue that the ability to attend to relevant stimuli and resist capture by salient-but-irrelevant stimuli is preserved with advancing age.     

Top-down control settings and the attentional blink: Evidence for nonspatial contingent capture

Previous studies have shown that spatial attention can be “captured” by irrelevant events, but only if the eliciting stimulus matches top-down attentional control settings. Here we explore whether similar principles hold for nonspatial attentional selection. Subjects searched for a coloured target letter embedded in an RSVP stream of letters inside a box centred on fixation. On critical trials, a distractor, consisting of a brief change in the colour of the box, occurred at various temporal lags prior to the target. In Experiment 1, the distractor produced a decrement in target detection, but only when it matched the target colour. Experiments 2 and 3 provide evidence that this effect does not reflect masking or the dispersion of spatial attention. The results establish that (1) nonspatial selection is subject to “capture”, (2) such capture is contingent on top-down attentional control settings, and (3) control settings for nonspatial capture can vary in specificity.     

注意控制定势和线索类型在注意捕获中的作用

采用前线索范式, 通过3个实验考察了注意控制定势和线索类型在注意捕获中的作用。实验1要求被试搜索颜色奇异项目标或突现目标, 涉及较弱的注意控制定势, 结果表明, 突现线索在作为匹配线索和不匹配线索时都能捕获注意, 而颜色奇异项线索只有在作为匹配线索时才能捕获注意。实验2要求被试搜索具体特征的红色或白色目标, 使被试建立较强的特征搜索定势, 结果表明, 颜色奇异项线索和突现线索在作为匹配线索时都能捕获注意, 但是在不匹配条件下, 颜色奇异项线索被抑制了, 而突现线索不能捕获注意; 实验3采取go/no-go范式, 要求被试对红色目标进行反应, 对白色目标进行抑制, 并通过设置不同的线索-目标时间间隔来进一步考察注意捕获的机制, 结果表明, 在600 ms间隔下, no-go突现线索被抑制, 而对于go颜色奇异项线索来说, 随着时间间隔的增加, 注意捕获效应减少。结果与相倚捕获假说和抑制独立捕获假说不符, 支持注意转移假说：自上而下的注意控制定势通过把注意从和目标不匹配的特征位置转移发挥作用; 颜色奇异项线索和突现线索的注意捕获机制相同, 但是突现线索相对于颜色奇异项线索来说, 在与目标不匹配的条件下, 更容易捕获注意, 更难被抑制。     

On the generality of the displaywide contingent orienting hypothesis: Can a visual onset capture attention without top-down control settings for displaywide onset?

The contingent orienting hypothesis (Folk, Remington, & Johnston, 1992) states that attentional capture is contingent on top-down control settings induced by task demands. Past studies supporting this hypothesis have identified three kinds of top-down control settings: for target-specific features, for the strategy to search for a singleton, and for visual features in the target display as a whole. Previously, we have found stimulus-driven capture by onset that was not contingent on the first two kinds of settings (Yeh & Liao, 2008). The current study aims to test the third kind: the displaywide contingent orienting hypothesis (Gibson & Kelsey, 1998). Specifically, we ask whether an onset stimulus can still capture attention in the spatial cueing paradigm when attentional control settings for the displaywide onset of the target are excluded by making all letters in the target display emerge from placeholders. Results show that a preceding uninformative onset cue still captured attention to its location in a stimulus-driven fashion, whereas a color cue captured attention only when it was contingent on the setting for displaywide color. These results raise doubts as to the generality of the displaywide contingent orienting hypothesis and help delineate the boundary conditions on this hypothesis.     

Attention capture while switching search strategies: Evidence for a breakdown in top-down attentional control

Whereas capture experiments typically repeat a single task many times, real world cognition is characterized by frequent switching. Lien, Ruthruff, and Johnston (2010) reported that the attentional control system can rapidly and fully switch between different search settings (e.g., red to green), with no carryover and no intertrial priming. The present study examined whether this impressive flexibility is possible even when the switch is not between different features along the same dimension, but between mutually incompatible search modes. On each trial, participants were prompted to find and identify the letter that was in a specific colour (feature search mode) or was uniquely coloured (singleton search mode). Within each block, search mode was either pure or mixed; the mixed blocks contained a fixed AABB search sequence (singleton-singleton-feature-feature) in Experiment 1 and a random sequence in Experiment 2. The target display was preceded by a noninformative cue display containing a nontarget colour singleton. In pure feature search blocks, these irrelevant singleton cues were generally unable to capture attention, replicating previous findings of “contingent capture”. In mixed blocks, however, irrelevant colour singletons captured attention on feature search trials. This breakdown indicates a limitation in the sharpness of attentional control following mode switches, which might be common in the real world.     

Top-down task sets for combined features: Behavioral and electrophysiological evidence for two stages in attentional object selection

We studied whether visual search for targets defined by a combination of features from different dimensions is guided by separately represented target features or by an integrated representation of the target objects. In Experiment 1, participants searched for target singleton bars that were defined by a specific combination of color (red or blue) and size (small or large). The target arrays were preceded by cue arrays that contained a spatially uninformative color/size singleton. Behavioral spatial-cueing effects indicative of attentional capture were triggered only by cues that matched both target-defining features, but not by partially target-matching cues, suggesting that attention was guided by integrated object representations. However, the presence of reliable N2pc components for partially matching cues demonstrated that these cues did capture attention, in line with independent feature-based guidance of attention. This dissociation between the electrophysiological and behavioral markers of attentional capture was confirmed in Experiment 2, in which targets were defined by a color/size disjunction. Our results suggest that the attentional selection of targets that are defined by a combination of features is a two-stage process: Attention is initially captured by all target-matching features, but is then rapidly withdrawn from nontarget objects that share some but not all features with the current target.     

Capturing attention is not that simple: Different mechanisms for stimulus-driven and contingent capture

Attentional orienting can be involuntarily directed to task-irrelevant stimuli, but it remains unsolved whether such attentional capture is contingent on top-down settings or could be purely stimulus-driven. We propose that attentional capture depends on the stimulus property because transient and static features are processed differently; thus, they might be modulated differently by top-down controls. To test this hybrid account, we adopted a spatial cuing paradigm in which a noninformative onset or color cue preceded an onset or color target with various stimulus onset asynchronies (SOAs). Results showed that the onset cue captured attention regardless of target type at short—but not long—SOAs. In contrast, the color cue captured attention at short and long SOAs, but only with a color target. The overall pattern of results corroborates our hypothesis, suggesting that different mechanisms are at work for stimulus-driven capture (by onset) and contingent capture (by color). Stimulus-driven capture elicits reflexive involuntary orienting, and contingent capture elicits voluntary feature-based enhancement.     

An effective attentional set for a specific colour does not prevent capture by infrequently presented motion distractors

An organism's survival depends on the ability to rapidly orient attention to unanticipated events in the world. Yet, the conditions needed to elicit such involuntary capture remain in doubt. Especially puzzling are spatial cueing experiments, which have consistently shown that involuntary shifts of attention to highly salient distractors are not determined by stimulus properties, but instead are contingent on attentional control settings induced by task demands. Do we always need to be set for an event to be captured by it, or is there a class of events that draw attention involuntarily even when unconnected to task goals? Recent results suggest that a task-irrelevant event will capture attention on first presentation, suggesting that salient stimuli that violate contextual expectations might automatically capture attention. Here, we investigated the role of contextual expectation by examining whether an irrelevant motion cue that was presented only rarely (～3–6% of trials) would capture attention when observers had an active set for a specific target colour. The motion cue had no effect when presented frequently, but when rare produced a pattern of interference consistent with attentional capture. The critical dependence on the frequency with which the irrelevant motion singleton was presented is consistent with early theories of involuntary orienting to novel stimuli. We suggest that attention will be captured by salient stimuli that violate expectations, whereas top-down goals appear to modulate capture by stimuli that broadly conform to contextual expectations.     

Attentional capture is contingent on the interaction between task demand and stimulus salience

The aim of this research was to investigate the potential impacts of task demand and stimulus salience on the stimulus-driven attentional capture effect. The participants performed an inefficient visual search task while an irrelevant luminance singleton was present. In Experiment 1, the task demand was manipulated while the stimulus salience of the irrelevant singleton was fixed. With the same salient singleton, the attentional capture effect was observed in the low-difficulty condition but disappeared in the high-difficulty condition. In Experiment 2, the stimulus salience was manipulated while the task demand was fixed. With the same task, the highly salient singleton captured attention, whereas the relatively lowly salient singleton could not. In Experiment 3, both task demand and stimulus salience were manipulated simultaneously. The stimulus-driven attentional capture effect by the irrelevant singleton increased not only as the task demand decreased but also as the stimulus salience increased. The present study might provide a way to reconcile conflicting findings in the attentional capture literature; the underlying neural mechanism is discussed. 2009 The Psychonomic Society, Inc.     

Contingent attentional capture occurs by activated target congruence

Contingent attentional capture occurs when a stimulus property captures an observer's attention, usually related to the observer's top-down attentional set for target-defining properties. In this study, we examined whether contingent attentional capture occurs for a distractor that does not share the target-defining property at a physical level, but does share that property at an abstract level of representation. In a rapid serial visual presentation stream, we defined the target by color (e.g., a green-colored Japanese kanji character). Before the target onset, we presented a distractor that referred to the target-defining color (e.g., a white-colored character meaning "green"). We observed contingent attentional capture by the distractor, which was reflected by a deficit in identifying the subsequent target. This result suggests that because of the attentional set, stimuli were scanned on the basis of the target-defining property at an abstract semantic level of representation.     

The initial stage of visual selection is controlled by top-down task set: new ERP evidence

Salient visual singleton stimuli produce spatial cueing effects indicative of attentional capture only when they match current task sets, suggesting that capture is subject to top-down control. However, such task-set contingent capture effects could be associated with the top-down controlled disengagement of attention from non-matching stimuli that follows their initial bottom-up salience-driven selection. Using the N2pc component as an event-related potential marker of attentional capture, we demonstrate that top-down task set already controls the initial rapid selection of salient visual singleton stimuli prior to any subsequent attentional disengagement. These findings provide new evidence for the primacy of top-down control over bottom-up salience in attentional capture.     

The role of relational information in contingent capture

On the contingent capture account, top-down attentional control settings restrict involuntary attentional capture to items that match the features of the search target. Attention capture is involuntary, but contingent on goals and intentions. The observation that only target-similar items can capture attention has usually been taken to show that the content of the attentional control settings consists of specific feature values. In contrast, the present study demonstrates that the top-down target template can include information about the relationship between the target and nontarget features (e.g., redder, darker, larger). Several spatial cuing experiments show that a singleton cue that is less similar to the target but that shares the same relational property that distinguishes targets from nontargets can capture attention to the same extent as cues that are similar to the target. Moreover, less similar cues can even capture attention more than cues that are identical to the target when they are relationally better than identical cues. The implications for current theories of attentional capture and attentional guidance are discussed.     

Made you blink! Contingent attentional capture produces a spatial blink

Previous studies have shown that the capture of attention by an irrelevant stimulus can be eliminated by fore knowledge of the spatial location of the relevant target stimulus. To explore whether spatial certainty is sufficient to eliminate capture, four experiments are reported in which the spatial location of the target is certain but the temporal position is uncertain. Subjects viewed a central rapid serial visual presentation stream in which a target letter was defined by a particular color (e.g., red). On critical trials, irrelevant color singletons appeared in the periphery. In Experiments 1 and 2, peripheral singletons produced a decrement in central target identification that was contingent on the match between the singleton color and the target color. Experiments 3 and 4 provided evidence that this decrement reflected a shift of spatial attention to the location of the distractor. The results suggest that spatial certainty is not sufficient to eliminate attentional capture and that attentional capture can result in a spatial "blink" that is conditional on top-down attentional control settings.     

The time course of intended and unintended allocation of attention

According to the contingent involuntary orienting hypothesis, only stimuli that match the attentional control settings based on intentions capture attention. In contrast, the surprise-capture hypothesis states that expectancy-discrepant stimuli can capture attention even if they do not match the control settings, implying unintended capture. The purpose of this study is to investigate whether unintended and intended attentional shifts are characterized by different time courses, indicating different underlying mechanisms. An unintended attentional shift was tested by the first, unannounced presentation of a color singleton at the location of a visual search target, and intended shifts by the following repeated presentations of a predictive singleton. Differences in time course were revealed by varying the stimulus onset asynchrony (SOA) between singleton and target. Results showed that accuracy with expected singletons was barely affected by SOA, whereas SOA strongly affected accuracy with the unexpected singleton. The results are interpreted as supporting the surprise-capture hypothesis. It is furthermore argued that a division of labor between contingent capture and surprise in the control of attention supports adaptive behavior.     

The visual hemifield asymmetry in the spatial blink during singleton search and feature search

The present study examined a visual field asymmetry in the contingent capture of attention that was previously observed by Du and Abrams (2010). In our first experiment, color singleton distractors that matched the color of a to-be-detected target produced a stronger capture of attention when they appeared in the left visual hemifield than in the right visual hemifield. This replicated Du and Abrams and also revealed a difference between hemifields in the time course of this effect. Our second experiment suggested that this asymmetry is moderated by the tuning of attentional control settings: when the target was easier to detect the asymmetry was attenuated. Our third experiment showed that this asymmetry is also present during singleton detection: a color singleton distractor produced a larger capture effect in the left hemifield than in the right hemifield. Finally, our fourth experiment suggested that this asymmetry is moderated by the salience of the attention-capturing distractor: when the distractor was not salient, the asymmetry was attenuated. These results suggest that there are boundary conditions in the observed hemifield asymmetry in the contingent capture of attention and several underlying brain systems might be involved.     

Goal-driven attentional capture by invisible colors: Evidence from event-related potentials

We combined event-related brain potentials (ERPs) and behavioral measures to test whether subliminal visual stimuli can capture attention in a goal-dependent manner. Participants searched for visual targets defined by a specific color. Search displays served as metacontrast masks for preceding cue displays that contained one cue in the target color. Although this target-color cue was spatially uninformative, it produced behavioral spatial cuing effects and triggered an ERP correlate of attentional selection (i.e., the N2pc component). These results demonstrate that target-color cues captured attention, in spite of the fact that cue localization performance assessed in separate blocks was at chance level. We conclude that task-set contingent attentional capture is not restricted to supraliminal stimuli, but is also elicited by visual events that are not consciously perceived.     

Attentional capture by abrupt onsets and feature singletons produces inhibitory surrounds

Two experiments found that form discriminations to a target item were inhibited when the target appeared adjacent to an attentionally salient item. Experiment 1 manipulated the attentional salience of an irrelevant color singleton through the attentional set adopted by the subjects. Color singletons captured attention when the target was itself a feature singleton, but not when the target was defined as a conjunction of features. Attentional capture was accompanied by an inhibitory region (i.e., slowed target reaction times), which dissipated with distance from the color singleton. In Experiment 2, the attentional salience of abrupt onsets and color singletons was compared. Irrelevant abrupt onsets captured attention, whereas irrelevant color singletons failed to capture attention. Again, an inhibitory region surrounded the attentionally salient abrupt onsets, but not the color singletons. The results are discussed in the context of current models of visual spatial attention and suggest a distinction between attentional preparation and attentional selection.     

不同搜索情境下老化对自上而下注意加工的影响

在视觉搜索过程中,老年人是否可以在不同情境下调节自上而下和自下而上的加工水平尚不明确。为了探讨老化对认知灵活性的影响,研究采用空间线索范式,通过比较有效线索和无效线索来考察对线索的注意加工水平（注意捕获、注意抑制）,通过比较目标相关和目标无关线索的注意加工水平来考察自上而下和自下而上的作用,通过改变分心物一致性来调控不同的目标凸显情境。结果发现,年轻组在目标非凸显时的空间线索效应高于目标凸显时,表明年轻人会依据目标凸显性调整自上而下的加工水平;但老年组却没有产生这种差异,其更依赖自上而下的加工,注意系统会对目标相关的线索进行注意捕获,对目标无关的线索进行注意抑制。结果表明,随着年龄的增长,认知控制的灵活性下降,表现出对自上而下加工较多的依赖;此外,老年人依然保留着注意捕获和注意抑制的能力,这对认知老化中抑制能力受损的观点提出了挑战。