旧客体抑制和新客体捕获视角下预览效应的机制

预览效应是一种在已经存在的多个旧客体中优先选择多个新客体, 对新客体表现出优先加工的现象。文章综述了预览效应认知神经机制的两种主要观点：(1)旧客体抑制观点, 认为预览效应是由于对旧客体的抑制; (2)新客体突现捕获注意观点, 认为预览效应是由于新客体出现伴随着亮度突然增加捕获注意。这两种观点之间的主要争论在于：预览效应与新旧客体亮度变化的关系; 新旧客体的颜色关系是否影响对目标的搜索; 在一些因素的作用下, 旧客体形状变化是否还会破坏预览效应。文章指出, 预览效应是旧客体抑制机制与新客体突现捕获注意机制共同作用的结果。     

Resisting change: The influence of luminance changes on visual marking and the preview benefit

Visual search can benefit when one set of distractors is presented as a preview, prior to the appearance the second set of distractors plus the target (Watson & Humphreys, 1997). It has been shown that changing the shape of the old, previewed stimuli when the new items appear causes the old stimuli to recompete for selection with the new ones. In contrast, changing the luminance or color of the old stimuli has no detrimental effects. Here, we present five experiments that reassessed the effect of luminance changes in preview search. We show (1) that preview search is remarkably resistant to large changes in the absolute luminance of the old stimuli, even when those changes would ordinarily be sufficient to signal the appearance of a new object and draw attention (Experiments 1 and 2), and (2) that resistance to luminance changes can be bolstered by feature-based inhibitory processes (Experiments 3–5). These findings are discussed in terms of the possible ecological properties of time-based visual selection and possible mechanisms underlying the preview benefit.     

Is it impossible to inhibit isoluminant items, or does it simply take longer? Evidence from preview search

Visual search can be facilitated when participants receive a preview of half the distractors (the preview benefit in search; Watson & Humphreys, 1997). Donk and Theeuwes (2001) have argued that preview-based benefits are abolished if the display items are isoluminant to a background. This is consistent with the preview benefit being due to onset capture by the new stimuli. In contrast, the present experiments challenge this suggestion and show that preview benefits can occur under isoluminant conditions, providing that they are given enough time to occur. In Experiment 1, we showed that a preview benefit can occur even with isoluminant stimuli, provided that the old items are previewed for a sufficient time. In Experiment 2, we tested and rejected the idea that this advantage is due to low-level sensory fatigue for the preview stimuli. These findings indicate that the preview effect is not caused solely by onset capture.     

Object-based inhibitory priming in preview search: Evidence from the “top-up” procedure

Visual search in a conjunction task can be facilitated if half the distractor items are previewed prior to the other half of the distractors and the target item. Here, we investigate the nature of this preview by using a top-up procedure, which presents an initial preview followed by a secondary preview after a period of time (the offset period). In Experiment 1, we demonstrate that increasing the time of the offset period decreases search efficiency. If the offset period is increased to 2 sec, the previewed items are searched to a greater extent than when the offset period is 450 msec. This holds even when the old items remain in the same positions across presentations and when they differ in color from new search stimuli. However, when the offset intervals are reduced, the preview can be discounted from search even when the old items change locations between exposures (Experiment 2) and when they are not distinguished from search displays by their color (Experiment 3). The last result occurs only as long as the preview items can be grouped in terms of form. When the preview stimuli are heterogeneous, they are no longer discounted from search if their locations change across the offset period (Experiment 4). We interpret the data in terms of object-based priming, which enables the repeated form of the old distractors to be filtered more easily from search.     

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.     

Spatiotemporal segregation in visual search: evidence from parietal lesions

The mechanisms underlying segmentation and selection of visual stimuli over time were investigated in patients with posterior parietal damage. In a modified visual search task, a preview of old objects preceded search of a new set for a target while the old items remained. In Experiment 1, control participants ignored old and prioritized new items, but patients had severe difficulties finding the target (especially on the contralesional side). In Experiment 2, simplified displays yielded analogous results, ruling out search ease as a crucial factor in poor preview search. In Experiment 3, outlines around distractor groups (to aid segmentation) improved conjunction but not preview search, suggesting a specific deficit in spatiotemporal segmentation. Experiment 4 ruled out spatial disengagement problems as a factor. The data emphasize the role of spatiotemporal segmentation cues in preview search and the parietal lobe in the role of these cues to prioritize search of new stimuli.     

Visual marking: dissociating effects of new and old set size

Visual marking makes it possible to ignore old items during search. In a typical study, old items are previewed 1 s before adding an equal number of new items, one of which is the target. Previewing half of the items reduces the search slope relating response time (RT) to overall set size by half. However, this manipulation sometimes only reduces overall RT but not search slope (Experiment 1). By orthogonally varying the numbers of old and new items, Experiment 2 shows that old and new set sizes interactively affect visual marking. Given a constant new set size, the size of the old set has negligible effect on RT. However, increasing the new set size reduces the preview benefit in overall RT. Experiment 3 shows that this reduction may be restricted to paradigms that use temporal segregation cues. Studies should vary old and new set size orthogonally to avoid missing a visual marking effect where one may be present.     

Preview search and contextual cuing

We investigated the effect of contextual cuing (M. M. Chun & Y. Jiang, 1998) within the preview paradigm (D. G. Watson & G. W. Humphreys, 1997). Contextual cuing was shown with a 10-item letter search but not with more crowded 20-item displays. However, contextual learning did occur in a preview procedure in which 10 preview items were followed by 10 new items. Repeating the new items alone did not generate contextual learning, but repeating the preview items alone did, as long as they had a consistent spatial relation with the target. This was not merely due to the onset of the preview items being associated with the target location. No learning effect took place with a preview of homogeneous items that competed less for selection with new stimuli. The results provide evidence for old items being processed in preview search and providing a context for subsequent search of new items.     

Top-up search and the attentional blink: A two-stage account of the preview effect in search

An inefficient visual search task can be facilitated if half the distractor items are presented as a preview prior to the presentation of the remaining distractor items and target. This benefit in search is termed the preview effect. Recent research has found that a preview effect can still occur if the previewed items disappear before reappearing again just before the search items (the “top-up” procedure). In this paper we investigate the attentional demands of processing during the preview and the top-up periods. Experiment 1 found that if attention is withdrawn from the top-up stage then no preview effect occurs. Likewise if attention is withdrawn from the initial preview period then the preview effect is reduced (Experiment 2). The data suggest that the preview effect is dependent on attention being paid both to the initial display and also to the re-presentation of the old display before the search display appears. The data counter accounts of preview search in terms of automatic attention capture by new items or by inhibition of return. We discuss alternative accounts of the results, and in particular suggest an amalgamation of a temporal grouping and a visual marking account of preview search.     

What is "marked" in visual marking? Evidence for effects of configuration in preview search

Visual search for a conjunction target is facilitated when distractor sets are segmented over time: the preview benefit Watson and Humphreys (1997) suggested that this benefit involved inhibition of old items (visual marking, VM). We investigated whether the preview benefit is sensitive to the configuration of the old distractors. Old distractors changed their location prior to the occurrence of the new items, while also either changing or maintaining their configuration. Configuration changes disrupted search. The results are consistent with object-based VM, which is sensitive to the configuration of old stimuli.     

Fast color grouping and slow color inhibition: evidence for distinct temporal windows for separate processes in preview search

The authors report 4 experiments that examined color grouping and negative carryover effects in preview search via a probe detection task (J. J. Braithwaite, G. W. Humphreys, & J. Hodsoll, 2003). In Experiment 1, there was evidence of a negative color carryover from the preview to new items, using both search and probe detection measures. There was also a negative bias against probes on old items that carried the majority color in the preview. With a short preview duration (150 ms) carryover effects to new items were greatly reduced, but probe detection remained biased against the majority color in the old items. Experiments 2 and 4 showed that the color bias effects on old items could be reduced when these items had to be prioritized relative to being ignored. Experiment 3 tested and rejected the idea that variations in the probability of whether minority or majority colors were probed were crucial. These results show that the time course of color carryover effects can be separated from effects of early color grouping in the preview display: Color grouping is fast, and inhibitory color carryover effects are slow.     

Parieto-occipital areas involved in efficient filtering in search: A time course analysis of visual marking using behavioural and functional imaging procedures

Search for a colour-form conjunction target can be facilitated by presenting one set of distractors prior to the second set of distractors and the target: the preview benefit (Watson & Humphreys, 1997). The early presentation of one set of distractors enables them to be efficiently filtered from search. We report two studies investigating the time course of the preview benefit. In Experiment 1 we use a standard reaction time analysis to show that the benefit has a relatively slow time course; old items need to precede the new set by 600 ms or more in order to be fully filtered from search. Furthermore, the reductions in reaction time across time in the preview condition varied nonlinearly with the display size, suggesting that old items were discounted from search in parallel. In Experiment 2 we examined the neural locus of this filtering effect over time, using positron emission tomography (PET). We show that regions of parieto-occipital cortex are selectively activated in a preview search condition relative to a detection baseline. These regions also increase in activation as the preview interval increases (and search then becomes easier), consistent with them modulating the parallel filtering of distractors from targets in spatial search. Interestingly, the same areas as those activated in preview search were also active in conjunction search relative to its own detection baseline. Thus these regions either modulate parallel filtering in conjunction search too, or they modulate different behavioural functions according to task constraints.     

Visual marking: the effects of irrelevant changes on preview search

Visual search is facilitated when participants receive a preview of half of the distractors before presentation of the second distractor set (Watson & Humphreys, 1997). In seven experiments, we examined the effects of irrelevant change on this preview benefit. Experiments 1-4 showed that the benefit was not disrupted by the abrupt appearance of irrelevant distractors during the preview period unless they were the same color as the new items. However, blinking off-and-on irrelevant distractors that were present at the start of the preview period disrupted the preview benefit irrespective of their feature overlap with other items (Experiments 5-7). The data are consistent with the inhibition of old stimuli (visual marking) via a location-based template along with an anticipatory feature-based set for new stimuli.     

Visual change with moving displays: more evidence for color feature map inhibition during preview search

Preview search with moving stimuli was investigated. The stimuli moved in multiple directions, and preview items could change either their color or their shape before onset of the new (search) displays. In Experiments 1 and 2, the authors found that (a) a preview benefit occurred even when more than 5 moving items had to be ignored, and (b) color change, but not shape change, disrupted preview search in moving stimuli. In contrast, shape change, but not color change, disrupted preview search in static stimuli (Experiments 3 and 4). Results suggest that preview search with moving displays is influenced by inhibition of a color map, whereas preview search with static displays is influenced by inhibition of locations of old distractors.     

What is “marked” in visual marking? evidence for effects of configuration in preview search

Visual search for a conjunction target is facilitated when distractor sets are segmented over time: the preview benefit. Watson and Humphreys (1997) suggested that this benefit involved inhibition of old items (visual marking, VM). We investigated whether the preview benefit is sensitive to the configuration of the old distractors. Old distractors changed their location prior to the occurrence of the new items, while also either changing or maintaining their configuration. Configuration changes disrupted search. The results are consistent with object-based VM, which is sensitive to the configuration of old stimuli.     

Revisiting preview search at isoluminance: new onsets are not necessary for the preview advantage

It has been argued that search performance under preview conditions relies on automatic capture by luminance onsets (Donk & Theeuwes, 2001). We present three experiments in which preview search was examined with both isoluminant and nonisoluminant items (e.g., as defined by luminance onsets). Experiment 1 provided evidence against the automatic capture of attention by onsets. Search benefited when onset previews were followed by new onset stimuli, as compared with a full-set baseline matched for the number of new onsets but in which half the distractors appeared simultaneously at isoluminance. Furthermore, both Experiments 1 and 2 established a preview advantage when isoluminant targets followed onset previews, when compared with appropriate full-set baselines. Experiment 3 replicated this result, while showing that the preview benefit was disrupted by dual-task interference. The data indicate that new onsets are not necessary to generate a preview advantage in search. We discuss the data in terms of search's benefiting from active inhibition of old onset-defined stimuli.     

An analysis of the time course of attention in preview search

We used a probe dot procedure to examine the time course of attention in preview search (Watson & Humphreys, 1997). Participants searched for an outline red vertical bar among other new red horizontal bars and old green vertical bars, superimposed on a blue background grid. Following the reaction time response for search, the participants had to decide whether a probe dot had briefly been presented. Previews appeared for 1,000 msec and were immediately followed by search displays. In Experiment 1, we demonstrated a standard preview benefit relative to a conjunction search baseline. In Experiment 2, search was combined with the probe task. Probes were more difficult to detect when they were presented 1,200 msec, relative to 800 msec, after the preview, but at both intervals detection of probes at the locations of old distractors was harder than detection on new distractors or at neutral locations. Experiment 3A demonstrated that there was no difference in the detection of probes at old, neutral, and new locations when probe detection was the primary task and there was also no difference when all of the shapes appeared simultaneously in conjunction search (Experiment 3B). In a final experiment (Experiment 4), we demonstrated that detection on old items was facilitated (relative to neutral locations and probes at the locations of new distractors) when the probes appeared 200 msec after previews, whereas there was worse detection on old items when the probes followed 800 msec after previews. We discuss the results in terms of visual marking and attention capture processes in visual search.     

When a reappearance is old news: visual marking survives occlusion

Performance in a visual search task becomes more efficient if half of the distractors are presented before the rest of the stimuli. This "preview benefit" may partly be due to inhibition of the old (previewed) items. The preview effect is abolished, however, if the old items offset briefly before reappearing (D. G. Watson & G. W. Humphreys, 1997). The authors examined whether this offset effect still occurred if the old items undergo occlusion. Results show that a preview benefit was found when the old items were occluded but not otherwise, consistent with the idea of top-down attentional inhibition being applied to the old items. The preview benefit is attenuated, however, by movement of the irrelevant stimuli in the displays.     

History matters: the preview benefit in search is not onset capture

Visual search for a conjunction target is made easier when distractor items are temporally segregated over time to produce two separate old and new groups (the new group containing the target item). The benefit of presenting half the distractors first is known as the preview effect. Recently, some researchers have argued that the preview effect occurs because new stimuli capture attention. This account was tested in the present study by using a novel "top-up" condition that exploits the fact that when previews appear only briefly before the search display, there is minimal preview benefit. We show that effects of a brief preview can be "topped up" by an earlier exposure of the same items, even when the preview disappears between its first and second presentations.This top-up effect demonstrates that the history of the old stimuli is important for the preview benefit, contrary to the account favoring onset capture. We discuss alternative accounts of how the preview benefit arises.     

Eye movements and time-based selection: Where do the eyes go in preview search?

In visual search tasks, presenting one set of distractors (previewing them) before a second set which contains the target, improves search efficiency compared to when all items appear simultaneously. It has been proposed that this preview benefit reflects an attentional bias against old information and toward new information. Here we tested directly whether there was such a bias by measuring eye movement behavior. The main findings were that fixations were biased against, and overall dwell times were shorter on, old stimuli during search in the preview condition. In addition, the initial onset of search was delayed in the preview condition and saccades made during the preview period did not disrupt the ability to prioritize new items. The data demonstrate directly that preview search results in an attentional bias toward new items and against old items.