Oculomotor consequences of abrupt object onsets and offsets: onsets dominate oculomotor capture

Previous research has shown that the appearance of an object (onset) and the disappearance of an object (offset) have the ability to influence the allocation of covert attention. To determine whether both onsets and offsets have the ability to influence eye movements, a series of experiments was conducted in which participants had to make goal-directed eye movements to a color singleton target in the presence of an irrelevant onset/offset. In accord with previous research, onsets had the ability to capture the eyes. The offset of an object demonstrated little or no ability to interrupt goal-directed eye movements to the target. Two experiments in which the effects of onsets and offsets on covert attention were examined suggest that offsets do not capture the eyes, because they have a lesser ability to capture covert attention than do onsets. A number of other studies that have shown strong effects of offsets on attention have used offsets that were uncorrelated with target position (i.e., nonpredictive), whereas we used onsets and offsets that never served as targets (i.e., antipredictive). The present results are consistent with a new-object theory of attentional capture in which onsets receive attentional priority over other types of changes in the visual environment.     

Attention capture by contour onsets and offsets: No special role for onsets

In five experiments, we investigated the power of targets defined by the onset or offset of one of an object’s parts (contour onsets and offsets) either to guide or to capture visual attention. In Experiment 1, search for a single contour onset target was compared with search for a single contour offset target against a static background of distractors; no difference was found between the efficiency with which each could be detected. In Experiment 2, onsets and offsets were compared for automatic attention capture, when both occurred simultaneously. Unlike in previous studies, the effects of overall luminance change, new-object creation, and number of onset and offset items were controlled. It was found that contour onset and offset items captured attention equally well. However, display size effects on both target types were also apparent. Such effects may have been due to competition for selection between multiple onset and offset stimuli. In Experiments 3 and 4, single onset and offset stimuli were presented simultaneously and pitted directly against one another among a background of static distractors. In Experiment 3, we examined “guided search,” for a target that was formed either from an onset or from an offset among static items. In Experiment 4, the onsets and offsets were uncorrelated with the target location. Similar results occurred in both experiments: target onsets and offsets were detected more efficiently than static stimuli which needed serial search; there remained effects of display size on performance; but there was still no advantage for onsets. In Experiment 5, we examined automatic attention capture by single onset and offset stimuli presented individually among static distractors. Again, there was no advantage for onset over offset targets and a display size effect was also present. These results suggest that, both in isolation and in competition, onsets that do not form new objects neither guide nor gain automatic attention more efficiently than offsets. In addition, in contrast to previous studies in which onsets formed new objects, contour onsets and offsets did not reliably capture attention automatically.     

Attentional capture by object appearance and disappearance

In two experiments we examined whether the appearance of a new object has attentional priority over disappearance. Previous failures to show differences are possibly due to onsets and offsets always being presented as a sole visual transient. Rather than presenting each alone, we presented onset and offset singletons simultaneously with a display-wide luminance transient in order to force each to compete with other visual events. Results from Experiment 1 showed that targets associated with onsets accrued a reaction time benefit whilst targets associated with offsets did not. Experiment 2 showed that onsets attracted attention even when observers were attentionally set to look for offset. By contrast, offsets needed a relevant attentional set in order to attract attention. We argue that the appearance of an object has attentional priority over disappearance.     

Offset transients modulate attentional capture by sudden onsets

Recent research with visual search tasks has suggested that stimuli which appear as sudden onsets (new objects) have attentional priority over stimuli that are created by removing segments of premasks (non-onset stimuli). Attentional capture by sudden onsets occurs despite the fact that the appearance of these new objects predicts neither the identity nor the location of the target in the visual search task. In three experiments, we examined the extent to which attentional capture by sudden onsets could be modulated by offset transients used to create non-onset objects. To that end, we systematically manipulated the ratio of non-onset to onset stimuli in the display (display ratio) as well as the ratio of offset to onset segments between the stimulus types (stimulus ratio). Increases in either the stimulus ratio or the display ratio resulted in increases in the visual search slopes for the onset targets. These results suggest that the ability of sudden onsets (new objects) to capture attention is influenced by stimulusdriven factors, such as environmental change. Interestingly, the results also indicated that goal-directed or purposeful search for sudden-onset (new-object) targets was relatively uninfluenced by the amount of change in the visual display. Therefore, it would appear that environmental change has differential effects on goal-directed and stimulus-driven search. These results are discussed in terms of their implications for our understanding of attentional capture.     

Attentional capture with various distractor and target types

Effects of nonpredictive distractors that involved changes in luminance, size, or shape were examined in three experiments. In Experiment 1, with two types of distractors (onsets and offsets), accuracy was better on trials when the distractor was near the location of either an offset or an onset target than on trials when the distractor was in a different location from that of the target, demonstrating attentional capture. Capture occurred both when the type of target (onset or offset) was blocked and therefore predictable and also when the type of target was mixed within blocks and therefore not predictable. Further experiments indicated that distractors captured attention even when the change to distractor did not create a new perceptual object. Neither a singleton-detection mode, nor a contingent involuntary orienting hypothesis, nor creation of a new object seems to explain all of these data adequately. Rather, capture may depend on a number of factors in the task.     

Attentional capture with various distractor and target types

Effects of nonpredictive distractors that involved changes in luminance, size, or shape were examined in three experiments. In Experiment 1, with two types of distractors (onsets and offsets), accuracy was better on trials when the distractor was near the location of either an offset or an onset target than on trials when the distractor was in a different location from that of the target, demonstrating attentional capture. Capture occurred both when the type of target (onset or offset) was blocked and therefore predictable and also when the type of target was mixed within blocks and therefore not predictable. Further experiments indicated that distractors captured attention even when the change to distractor did not create a new perceptual object. Neither a singleton-detection mode, nor a contingent involuntary orienting hypothesis, nor creation of a new object seems to explain all of these data adequately. Rather, capture may depend on a number of factors in the task.     

Abrupt visual onsets and selective attention: voluntary versus automatic allocation

The hypothesis that abrupt visual onsets capture attention automatically, as suggested by Yantis and Jonides (1984) was tested in four experiments. A centrally located cue directed attention to one of several stimulus positions in preparation for the identification of a target letter embedded in an array of distractor letters. In all experiments, one stimulus (either the target or one of the distractors) had an abrupt onset; the remaining letters did not. The effectiveness of the cue was manipulated (varying either its duration or its predictive validity) to test whether abrupt onsets capture attention even when subjects are in a highly focused attentional state. Results showed that onsets do not necessarily capture attention in violation of an observer's intentions. A mechanism for partially automatic attentional capture by abrupt onset is proposed, and the diagnosticity of the intentionality criterion for automaticity is discussed.     

Offsets and prioritizing the selection of new elements in search displays: More evidence for attentional capture in the preview effect

The preview effect refers to the finding that new elements in a search display are prioritized over old elements. Donk and Theeuwes (2001) suggest that this prioritization is due to bottom-up attentional capture, as new elements that abruptly appear with increases in luminance produce a preview effect whereas new elements that are equiluminant to the background do not. The present study extends this research by examining if new elements that appear from offsets, with and without luminance changes, yield similar findings to onsets. This was indeed the case, as equiluminant offsets did not produce a preview effect but offsets with corresponding increases or decreases in luminance did show the prioritization of new elements over old elements. These findings show that the prioritization of new elements is sensitive to changes in luminance but not to the direction of such changes.     

Contingent visual marking by transients

Preview search is a phenomenon in which a set of new items can be searched with seemingly no interference from items already present in the display. The preview effect has been shown to occur only when the presentation of the new items is accompanied by a luminance change (Donk & Theeuwes, 2001). In a series of experiments, we extend the type of transients that can lead to a preview benefit to offsets and motion, and confirm Donk and Theeuwes's finding that equiluminant color changes do not lead to a preview effect. Like Donk and Theeuwes, we find that preview search does not occur when only the old items undergo a transient change, suggesting that the processes responsible for preview search are triggered when the new items undergo a change detectable by the magnocellular system. In addition, we find that irrelevant transients interfere with preview search only when they match the current attentional set (e.g., luminance change or motion). Results suggest that preview search is not the automatic capture of attention by transients, but rather is contingent on top-down control settings.     

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.     

Irrelevant onsets cause inhibition of return regardless of attentional set

It is disputed whether onsets capture spatial attention either in a purely stimulus-driven fashion or only when they are contingent on one's attentional set. According to the latter assumption, interference from irrelevant onsets may result from nonspatial filtering costs. In the present study, we used inhibition of return (IOR) as a marker for spatial attention. IOR occurs mainly for locations that attention has visited before. Participants searched for a red object among white objects. An attentional set for redness was demonstrated by a spatial validity effect of red cues on response times. However, a stronger validity effect was found for irrelevant white onsets, which slowed responses when the onset contained a distractor, but speeded them when the onset contained a target. Most importantly, this onset benefit for targets turned into a deficit at longer SOAs, indicating IOR. We conclude that onset distractors capture spatial attention regardless of the observer's attentional set.     

Non-transient luminance changes do not capture attention

The processing of luminance change is a ubiquitous feature of the human visual system and provides the basis for the rapid orienting of attention to potentially important events (e.g., motion onset, object onset). However, despite its importance for attentional capture, it is not known whether a luminance change attracts attention solely because of its status as a sensory transient or can attract attention at a relatively high cognitive level. In a series of six experiments, we presented visual displays in which a single object underwent a luminance change that was either visible or obscured by a mask. A target then appeared either at the change location or elsewhere. The results showed that the luminance change attracted attention only in the visible condition. This was even observed with the largest change we could generate (> 75 cd/m(2)). These data suggest that the importance of a luminance change is only in its status as a low-level sensory transient.     

Perceptual load modulates attentional capture by abrupt onsets

The abrupt appearance of a new object captures attention, even when the object is task irrelevant. These findings suggest that abrupt onsets capture attention in a stimulus-driven manner and are not susceptible to top-down influences on attentional control. However, previous studies examining the ability of abrupt onsets to capture attention have used search displays that lacked significant complexity. Because attention is a limited capacity mechanism, it is possible that increasing the complexity, or perceptual load, of the search arrays may modulate capture by abrupt onsets. We used a flanker task to examine the effect of perceptual load on attentional capture by abruptly appearing objects. Subjects searched for a target letter through low-load (set size=1) and high-load (set size=6) displays. On each trial, irrelevant flankers also appeared, one as an onset and the other as an offset. Onset flankers affected search in low-load but not high-load displays. This modulation of attentional capture was not caused by generalized slowing when subjects searched through high-load displays; search for a single perceptually degraded target slowed response times but did not affect attentional capture. These findings demonstrate that attentional capture by an abrupt onset is attenuated when people search through high-load scenes.     

You can't stop new motion: Attentional capture despite a control set for colour

When a stationary object begins to move, visual spatial attention is reflexively deployed to the location of that object. We tested whether this capture of attention by new motion is entirely stimulus driven, or whether it is contingent on an observer's goals. Participants monitored a visual display for a colour change, inducing an attentional control set (ACS) for colour. Across the three performed experiments, irrelevant new-motion cues always captured visual spatial attention, despite the ACS for colour. This persistence of the attentional cueing effect demonstrates that ACSs, in particular an ACS for colour, cannot prevent new motion from capturing attention. Unlike other stimulus types, such as luminance changes, colour singletons, and new objects, new motion may always capture attention regardless of an observer's goals. This conclusion entails that new motion is an important determinant of when, and to where, visual spatial attention is deployed.     

Selective target processing: perceptual load or distractor salience?

Perceptual load theory (Lavie, 1995) states that participants cannot engage in focused attention when shown displays containing a low perceptual load, because attentional resources are not exhausted, whereas in high-load displays attention is always focused, because attentional resources are exhausted. An alternative "salience" hypothesis holds that the salience of distractors and not perceptual load per se determines selective attention. Three experiments were conducted to investigate the influence that target and distractor onsets and offsets have on selective processing in a standard interference task. Perceptual load theory predicts that, regardless of target or distractor presentation (onset or offset), interference from ignored distractors should occur in low-load displays only. In contrast, the salience hypothesis predicts that interference should occur when the distractor appears as an onset and would occur for distractor offsets only when the target was also an offset. Interference may even occur in highload displays if the distractor is more salient. The results supported the salience hypothesis.     

Attentional misguidance in visual search

Previous research has shown that a task-irrelevant sudden onset of an object will capture an observer’s visual attention or draw it to that object (e.g., Yantis & Jonides, 1984). However, further research has demonstrated the apparent inability of an object with a task-irrelevant but unique color or luminance to capture attention (Jonides & Yantis, 1988). In the experiments reported here, we reexplore the question of whether task-irrelevant properties other than sudden onset may capture attention. Our results suggest that uniquely colored or luminous objects, as well as salient though irrelevant boundaries, do not appear to capture attention. However, these irrelevant features do appear to serve as landmarks for a top-down search strategy which becomes increasingly likely with larger display set sizes. These findings are described in terms of stimulus-driven and goal-directed aspects of attentional control.     

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)     

Attentional capture within and between objects

The present study addressed the question whether attentional capture by abrupt onsets is affected by object-like properties of the stimulus field. Observers searched for a target circle at one of four ends of two solid rectangles. In the focused attention condition the location of the upcoming target was cued by means of a central arrowhead, whereas in the divided attention condition, the target location was not cued. Irrelevant abrupt onsets could appear either within the attended or within the non-attended object. The results showed that in the focused attention condition, onsets ceased to capture attention irrespective of whether the onset appeared within an attended object or within a non-attended object.     

Mechanisms of attentional priority

When a single abrupt onset occurs in a multielement visual display, it captures attention, possibly by generating an attentional interrupt that designates onsets as being of high priority. In 3 experiments, the mechanisms subserving attentional priority setting were investigated. Subjects searched for a prespecified target letter among multiple distractor letters, half of which had abrupt onsets and half of which did not. The target, when present, was equally often an onset element and a no-onset element. Several models for attentional priority, differing in how many onset elements have priority over no-onset elements, were assessed. The data support a model in which approximately 4 onset stimuli are processed before any no-onset stimuli are processed. Two attentional priority mechanisms are proposed: (a) queuing of a limited number of high-priority elements and (b) temporally modulated decay of attentional priority tags.     

突现对内源性选择注意的影响

本研究利用空间线索技术的实验模式,考察内源性选择注意与外源性选择注意的相互关系。实验结果表明,外周线索突现可以优先地被加工,但并不是完全高度自动化的;当注意受内源性中央线索引导集中到一个与突现刺激不一致的空间位置时,突现刺激不能引导出自动化的外源性选择注意。