Target uncertainty does not lead to more distraction by singletons: intertrial priming does

In two experiments, we examined why a singleton distractor has a stronger interfering effect in visual search when the target identity is uncertain. When participants searched for a shape, a color singleton distractor had a larger slowing effect in a mixed block, in which the target shape could change from trial to trial, than in a pure block, in which the target shape remained the same. Importantly, this increased singleton distractor effect could be traced back entirely to intertrial priming, since the increased costs occurred only on trials in which the target and the singleton distractor swapped identity (Experiment 1, allowing for priming between targets and singleton distractors) or on trials in which the target alone changed identity while the singleton distractor remained constant (Experiment 2, allowing for priming between targets only). This suggests that target uncertainty itself does not lead to strategic changes in the attentional selection of singletons. Instead, selection is affected by relatively automatic priming mechanisms that may be enhanced by competition for attention.     

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.     

Role of frontal cortex in attentional capture by singleton distractors

The role of frontal cortex in selective attention to visual distractors was examined in an attentional capture task in which participants searched for a unique shape in the presence or absence of an additional colour singleton distractor. The presence of the additional singleton was associated with slower behavioural responses to the shape target, and a greater neural signal in inferior frontal gyrus. To investigate the involvement of cognitive control functions of the frontal lobes in the capture of attention by the additional singletons, we measured the effect of the additional singleton in a context of either low or high working memory load. Whereas behavioural capture was unaffected by the level of load on working memory, greater activity associated with the presence of the additional singleton was observed in inferior frontal gyrus, but only under high load. This effect was greater in participants who experienced greater capture. We argue that the role of inferior frontal gyrus in selective attention is to detect potential sources of distraction.     

Attentional capture by singletons is contingent on top-down control settings: Evidence from electrophysiological measures

The present study examined whether the capture of spatial attention is driven by stimulus salience (e.g., object uniqueness) or by a match to current attentional control settings (contingent capture). We measured the N2pc effect, a component of the event-related brain potential thought to reflect lateralized attentional allocation. On every trial, a noninformative cue display containing a colour singleton box was followed by a target display of letters. Participants searched for a target letter in a specified colour (in Experiments 1–3) or within a specified shape (in Experiment 4) while ignoring other stimuli. The key manipulation was whether the singleton cue contained the target-defining feature (e.g., a specific colour). Experiment 1 revealed signs of attention capture—a cue validity effect and an N2pc effect—only for singleton cues that contained the target-defining feature. This pattern persisted even when we increased the salience of the singleton box (Experiments 2 and 3). Irrelevant colour singletons also failed to produce a significant N2pc effect when the target was defined based on shape rather than colour (Experiment 4). We conclude that attention capture is strongly contingent on top-down attentional control settings, not bottom-up stimulus salience.     

Evidence for attentional capture by a surprising color singleton in visual search

Three experiments were conducted to investigate whether surprising color singletons capture attention. Participants performed a visual search task in which a target letter had to be detected among distractor letters. Experiments 1 and 2 assessed accuracy as the dependent variable. In Experiment 1, the unannounced presentation of a color singleton 500 ms prior to the letters (and in the same position as the target letter) resulted in better performance than in the preceding conjunction search segment, in which no singleton was presented, and performance was as good in this surprise–singleton trial as in the following feature search segment, in which the singleton always coincided with the target. In contrast, no improvement was observed when the color singleton was presented simultaneously with the letters in Experiment 2, indicating that attentional capture occurred later in the surprise trial than in the feature search segment. In Experiment 3, set size was varied, and reaction time was the dependent variable. Reaction time depended on set size in the conjunction search segment, but not in the surprise trial nor in the feature search segment. The results of the three experiments support the view that surprising color singletons capture attention independently of a corresponding attentional set.     

Do locally defined feature discontinuities capture attention?

Results from previous visual search studies have suggested that abrupt onsets produce involuntary shifts of attention (i.e., attentional capture), but discontinuities in simple features such as color and brightness do not (Jonides & Yantis, 1988). In the present study we tested whether feature discontinuities (i.e., “singletons”) can produce attentional capture in a visual search task if defined “locally” or over a small spatial range. On each trial, a variable number of letters appeared, one of which differed from the others in color or intensity. The location of this singleton was uncorrelated with target location. Local discontinuities were created by embedding the letters in a dot texture. In Experiment 1, display size effects for singleton targets were not reduced with the addition of a background dot texture. Similar results were obtained in Experiment 2, regardless of variations in texture density. Experiment 3 confirmed that when targets are defined by a color or intensity singleton, they are detected preattentively, and that increasing texture density yields faster detection. We conclude that the spatial range over which feature discontinuities are defined may influence the guidance of spatial attention, but it has no influence on their ability to capture attention.     

Stimulus-driven attentional capture by equiluminant color change

The aim of this research was to investigate the mechanisms underlying stimulus-driven attentional capture by feature changes in basic dimensions, and we chose color for the present investigation. In Experiment 1, participants searched for a target letter among colored disks containing distractor letters while a disk underwent color change. Although color change was irrelevant to the task and uninformative about the target position, we found a strong form of stimulus-driven attentional capture. Experiment 2 demonstrated that salient color discontinuity per se could not capture attention, ruling out the possibility that the capture effect we observed might be due to color discontinuity. In Experiment 3, we observed the capture effect by color change again in a more optimized experimental design. The present findings show that color change captures attention, supporting our view that dynamic feature changes can capture attention in a stimulus-driven manner.     

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。     

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.     

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.     

Attentional capture in serial audiovisual search tasks

The phenomenon of attentional capture has typically been studied in spatial search tasks. Dalton and Lavie recently demonstrated that auditory attention can also be captured by a singleton item in a rapidly presented tone sequence. In the experiments reported here, we investigated whether these findings extend cross-modally to sequential search tasks using audiovisual stimuli. Participants searched a stream of centrally presented audiovisual stimuli for targets defined on a particular dimension (e.g., duration) in a particular modality. Task performance was compared in the presence versus absence of a unique singleton distractor. Irrelevant auditory singletons captured attention during visual search tasks, leading to interference when they coincided with distractors but to facilitation when they coincided with targets. These results demonstrate attentional capture by auditory singletons during nonspatial visual search.     

Temporal attentional capture: Effects of irrelevant singletons on rapid serial visual search

The presence of a unique yet irrelevantsingleton in visual search or spatial-cuing tasks is typically associated with performance costs, suggesting that singletons tend to capture attention. However, since singletons have always been spatially separated from targets in previous experiments, it remains unclear whether an irrelevant visual singleton that occurs at the same spatial location as the target but at a different point in time can produce temporal capture of attention. Here, we asked participants to search visual sequences at fixation for targets defined by size (larger or smaller than the nontargets). The presence (vs. absence) of a color singleton lengthened response times on the size discrimination task, suggesting that irrelevant singletons can lead to a temporal attentional capture.     

Masked singleton effects

In the present study, we tested whether visual singletons remaining outside awareness are processed. Singletons differ by at least one feature from their more homogeneous neighbors. Here, we used backward masking to prevent awareness of shape singleton primes (Experiments 1-4) or color singleton primes (Experiment 5). Masked singleton primes nonetheless produced a congruence effect: Congruent singletons indicating the location of subsequent visible targets facilitated responses, in comparison with incongruent singletons at positions away from the targets. This congruence effect was found with singletons defined by feature presence or feature absence. It was at least partly due to attentional capture by singletons remaining outside of the participants' awareness. Results are discussed in light of theories pertaining to singleton effects and masked-priming effects.     

Attentional capture in singleton-detection and feature-search modes

Six experiments were conducted to determine the circumstances under which an irrelevant singleton captures attention. Subjects searched for a target while ignoring a salient distractor that appeared at different stimulus onset asynchronies (SOAs) prior to each search display. Spatial congruency and interference effects were measured. The strategies available to find the target were controlled (only singleton-detection mode, only feature-search mode, or both search strategies available). An irrelevant abrupt onset captured attention in search for a color target, across SOAs, whatever strategies were available. In contrast, in search for a shape target, an irrelevant color singleton captured attention in the singleton-detection condition but delayed response at its location in the feature-search condition, across SOAs. When both strategies were available, capture was short lived (50- to 100-msec SOAs). The theoretical implications of these findings in relation to current views on attentional capture are discussed. ((c) 2003 APA, all rights reserved)     

Characteristics of covert and overt visual orienting: Evidence from attentional and oculomotor capture

Five visual search experiments found oculomotor and attentional capture consistent with predictions of contingent orienting, contrary to claims that oculomotor capture is purely stimulus driven. Separate saccade and attend-only conditions contained a color target appearing either singly, with an onset or color distractor, or both. In singleton mode, onsets produced oculomotor and attentional capture. In feature mode, capture was absent or greatly reduced, providing evidence for top-down modulation of both types of capture. Although attentional capture by color abstractors was present throughout, oculomotor capture by color occurred only when accompanied by transient change, providing evidence for a dissociation between oculomotor and attentional capture. Oculomotor and attentional capture appear to be mediated by top-down attentional control settings, but transient change may be necessary for oculomotor capture. ((c) 2003 APA, all rights reserved)     

Statistical regularities modulate attentional capture independent of search strategy

An earlier study using the additional singleton task showed that statistical regularities regarding the distractor location can cause an attentional bias that affects the amount of attentional capture by distractors and the efficiency of selection of targets. The distractor singleton was systematically present more often in one location than in all other locations. The present study investigated whether this bias also occurs when observers adopt a feature search mode, i.e., when they search for a specific feature (circle) between elements with different shapes, while ignoring a colored distractor singleton. It is assumed that in feature search, observers can ignore distractors in a top-down way and as such one expects that statistical regularities about the distractor location should not play a role. Contrary to this prediction, we found that even in feature search, both attentional capture by the distractors and the efficiency of selecting the target were impacted by these statistical regularities. Moreover, statistical regularities regarding the feature value of the distractor (its color) had no effect on the amount of capture or the efficiency of selection. We claim that statistical regularities cause passive lingering biases of attention such that on the priority map, the location containing a high probability distractor competes less for attention than locations that are less likely to contain distractors.     

Overriding auditory attentional capture

Attentional capture by color singletons during shape search can be eliminated when the target is not a feature singleton (Bacon & Egeth, 1994). This suggests that a "singleton detection" search strategy must be adopted for attentional capture to occur. Here we find similar effects on auditory attentional capture. Irrelevant high-intensity singletons interfered with an auditory search task when the target itself was also a feature singleton. However, singleton interference was eliminated when the target was not a singleton (i.e., when nontargets were made heterogeneous, or when more than one target sound was presented). These results suggest that auditory attentional capture depends on the observer's attentional set, as does visual attentional capture. The suggestion that hearing might act as an early warning system that would always be tuned to unexpected unique stimuli must therefore be modified to accommodate these strategy-dependent capture effects.     

Attentional shifts to rare singletons

Five experiments examined whether extremely rare featural singletons (e.g., presented in 4% of all trials) capture attention, and whether this effect could be explained by top-down contingent capture or stimulus-driven singleton capture. To this end, performance (accuracy in Experiments 1–4, reaction time in Experiment 5) in a demanding letter search task was measured in singleton trials that were presented within rare-singleton blocks consisting mainly of no-singleton trials, and in singleton trials that occurred in all-singleton blocks. In separate blocks, either target singletons (i.e., a singleton at target position), or distractor singletons (i.e., a singleton at a distractor position) were presented in each trial. Results are consistent with the contingent-capture view. When the letters were presented briefly and accuracy was the dependent variable, a large performance benefit was obtained, revealing that attention was shifted very fast to the singleton. An examination of search efficiency with a variation of set size and reaction time as the dependent variable revealed a strong gain in search efficiency with a rare target singleton. The large benefit was not accompanied by proportionally large costs for distractor singletons relative to the no-distractor trials. Moreover, a comparison of singleton trials from the all-singleton and from the rare-singleton blocks revealed nonspatial costs for the rare singletons that were of about the same size for target and distractor singletons. In summary, results show that an attentional control setting can remain “dormant” for many trials where it is not applicable, but is then applied nearly as efficiently as when the control setting has been used just recently.     

Contingent orienting or contingent capture: A size singleton matching the target–distractor size relation cannot capture attention

In the present study, we examined whether a peripheral size-singleton distractor that matches the target–distractor size relation can capture attention and disrupt central target identification. Three experiments consistently showed that a size singleton that matches the target–distractor size relation cannot capture attention when it appears outside of the attentional window, even though the same size singleton produces a cuing effect. In addition, a color singleton that matches the target color, instead of a size singleton that matches the target–distractor size relation, captures attention when it is outside of the attentional window. Thus, a size-relation-matched distractor is much weaker than a color-matched distractor in capturing attention and cannot capture attention when the distractor appears outside of the attentional window.     

Capture versus suppression of attention by salient singletons: Electrophysiological evidence for an automatic attend-to-me signal

There is considerable controversy about whether salient singletons capture attention in a bottom-up fashion, irrespective of top-down control settings. One possibility is that salient singletons always generate an attention capture signal, but this signal can be actively suppressed to avoid capture. In the present study, we investigated this issue by using event-related potential recordings, focusing on N2pc (N2-posterior-contralateral; a measure of attentional deployment) and Pd (distractor positivity; a measure of attentional suppression). Participants searched for a specific letter within one of two regions, and irrelevant color singletons were sometimes present. We found that the irrelevant singletons did not elicit N2pc but instead elicited Pd; this occurred equally within the attended and unattended regions. These findings suggest that salient singletons may automatically produce an attend-to-me signal, irrespective of top-down control settings, but this signal can be overridden by an active suppression process to prevent the actual capture of attention.