Visual marking beside the mark: prioritizing selection by abrupt onsets

In a standard visual marking experiment, observers are presented with a display containing one set of elements (old elements) followed after a certain time interval by a second set of elements (new elements). The task of observers is to search for a target among the new elements. Typically, the time to find the target depends only on the number of new elements in the display and not on the number of old elements, showing that observers search only among the new elements. This effect of prioritizing new elements over old elements is explained in terms of top-down inhibition of old objects-that is, visual marking (Watson & Humphreys, 1997). The present study addressed whether this prioritizing is in fact mediated by top-down inhibition of old objects, as suggested by Watson and Humphreys (1997), or whether it is mediated by the abrupt onsets of the newly presented elements (Yantis & Jonides, 1984). In three experiments, the presentations of the old and new elements were or were not accompanied by a luminance change. The results showed that if new elements were equiluminant with the background, no visual marking occurred, suggesting that new elements must have a luminance onset in order to be prioritized over old elements. Implications for current theories on visual selection are discussed.     

Prioritization by transients in visual search

There is an ongoing debate as to whether prioritizing new objects over old objects (the so-calledpreview benefit) is the result of top-down inhibition of old objects (i.e., visual marking; Watson & Humphreys, 1997) or attentional allocation to new objects, presented with a luminance transient (Donk & Theeuwes, 2001). In the two experiments reported here, we tested whether prioritization by luminance transients alone can produce a subset-selective search similar to the preview effect. Subjects viewed multiobject displays while a subset of objects was briefly flashed. The subjects prioritized up to 14 flashed objects over at least 14 nonflashed objects. Since prioritization by luminance transients can produce a subsetselective search on its own, it may well play an important role in the preview benefit.     

Prioritizing selection of new elements: bottom-up versus top-down control

Watson and Humphreys (1997) have proposed that prioritized selection of new over old elements occurs because observers can apply top-down inhibition to the locations of the old elements by a mechanism they refer to as visual marking. However, recent evidence has suggested that the top-down mechanism is questionable (Donk & Theeuwes, 2001). In the present study, we investigated whether prioritized selection of new over old elements occurs in a bottom-up or a top-down fashion. Observers were presented with displays containing one set of elements (old elements) followed, after a certain time interval, by a second set of elements (new elements). The observers were instructed to search for the presence of a target that was presented with equal probability among the old and the new elements (Experiments 1 and 2) or twice as often among the old elements than among the new elements (Experiment 3). The results show that new elements were prioritized for selection over old ones even though the observers had no incentive to do so. The results suggest that prioritized selection of new over old elements is not mediated by a top-down inhibition process, as was proposed by Watson and Humphreys (1997). Instead, prioritization of new elements appears to be a bottom-up process. The implications of these results are discussed in terms of models of attentional control.     

Visual marking of old objects

Watson and Humphreys (1997) presented evidence that selection of new elements can be prioritized by on-line top-down attentional inhibition of old stimuli already in the visual field (visual marking). The experiments on which this evidence was based always presented old elements in green and new elements in blue. Because of this, instead of prioritizing new objects by inhibiting old objects, selection could have been based on color. The present experiment, which does not contain this confound, showed that visual marking is a strong and robust process that enables subjects to visually mark at least 15 old elements even when these elements have the same color as the new elements. The results indicate that preview of the elements is critical—not the fact that those elements contained a common feature.     

Visual marking: evidence for inhibition using a probe-dot detection paradigm

Watson and Humphreys (1997, 1998) have recently demonstrated that new objects can be prioritized for visual attentional processing by the top-down attentional inhibition of old objects already in the field, a mechanism they called visual marking. The experiments reported here show that the detection of a dim probe dot is impaired when it falls at the location of an old object (Experiments 1 and 3) but that this occurs only in conditions in which it is advantageous for subjects to mark (inhibit) old objects (Experiment 2). These results further support previous work showing that visual marking is based on the inhibition of the locations of old objects and that visual marking can be flexibly applied (or withheld), depending on the goals of current behavior.     

Aging and visual marking: selective deficits for moving stimuli

The selective processing of new visual information can be facilitated by the top-down inhibition of old stimuli already in the visual field, a capacity-limited process termed visual marking (D. G. Watson & G. W. Humphreys, 1997). Three experiments assessed the effects of aging on visual marking using stationary (Experiment 1) and moving (Experiments 2 and 3) items. For young participants, visual marking was observed in all experiments. For older participants, visual marking was observed only with stationary items. The results are not consistent with any simple account of general age-related decrements and provide further support for the deployment of different methods of visual marking depending on the properties of the old items and the current task demands.     

Determining the capacity of time-based selection

In visual search, a set of distractor items can be suppressed from future selection if they are presented (previewed) before a second set of search items arrive. This visual marking mechanism provides a top-down way of prioritizing the selection of new stimuli, at the expense of old stimuli already in the field (Watson & Humphreys, 1997). Typically, this preview benefit has been examined by measuring the efficiency of detecting a target item contained within a newly presented set. Such work has led to the suggestion that the capacity of the visual marking mechanism is extremely high. Here we present five experiments which measured performance for selecting and responding to all the new stimuli rather than a single target item within the new set. The findings illustrate that when selecting and responding to all new items intentionally trying to prioritize new stimuli has a capacity limit of approximately six to seven items and that this limit depends partly on properties of the stimuli. The findings are discussed in terms of mechanisms of time-based selection, attentional capacity limits, and the task demands of multiple item selection.     

Visual marking: a convergence of goal- and stimulus-driven processes during visual search

Watson and Humphreys (1997) proposed that visual marking is a goal-directed process that enhances visual search through the inhibition of old objects. In addition to the standard marking case with targets at new locations, included in Experiment 1 was a set of trials with targets always at old locations, as well as a set of trials with targets varying between new and old locations. The participants' performance when detecting the target at old locations was equivalent to their performance in the full-baseline condition when they knew the target would be at old locations, and was worse when the target appeared at old locations on 50% of the trials. Marking was observed when the target appeared at new locations. In Experiment 2, an offset paradigm was used to eliminate the influence of the salient abrupt-onset feature of the new objects. No significant benefits were found for targets at new locations in the absence of onsets at new locations. The results suggest that visual marking may be an attentional selection mechanism that significantly benefits visual search when (1) the observer has an appropriate search goal, (2) the goal necessitates inhibition of old objects, and (3) the new objects include a salient perceptual feature.     

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.     

Prioritizing new elements with a brief preview period: Evidence against visual marking

Watson and Humphreys (1997) have proposed that the ability to prioritize new elements over old elements involves a time-consuming process (of at least 400 msec) of active inhibition of the locations of the old elements, which they referred to asvisual marking. Recently, Donk and Theeuwes (2001) have suggested that prioritized selection of new over old elements is an instantaneous process related to the luminance change accompanying the appearance of the new elements. The aim of the present study was to test these two alternatives by investigating whether prioritized selection of new over old elements could be achieved with a very short preview of the old elements (50 msec). The results indicated that participants were able to prioritize selection of new over old elements when the new elements were presented with luminance onset whereas the old elements were not. New elements could not be prioritized if both the old and the new elements appeared with luminance onset. The results indicated that prioritization of new elements is based on an instantaneous process, rather than on a time-consuming process.     

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.     

Visual marking in moving displays: feature-based inhibition is not necessary

Visual marking is a mechanism by which new visual stimuli can gain a selection advantage by the top-down attentional inhibition of stimuli already in the field. Previous work (Olivers, Watson, & Humphreys, 1999) has shown that, for moving stimuli, there must be a unique feature difference between the old items and the new items for marking to occur. The present study shows that this constraint is not necessary if the local spatial relationships between the old moving items remain constant. It is proposed that, with a fixed configuration, the old moving items can be grouped to form a single object. An inhibitory template set up to represent the object then coordinates the application of inhibition to the individual stimuli. Implications for the theory and ecological flexibility of visual marking are discussed.     

Search of jumping items: visual marking and discrete motion

Watson and Humphreys (1997 Psychological Review 104 90-122) showed that when searching for a target, observers can ignore a previewed set of distractors (other items), effectively decreasing the number of relevant items in a difficult search display and thus speeding performance ('visual marking'). Other researchers have more recently investigated visual marking for continuously moving items, finding that shared features, and preserved inter-item spatial relationships, are helpful. Here, we tested whether visual marking occurs for a set of initial items that moves in one discrete jump (preserving shared features and inter-item spatial relationships). Marking did not occur in these displays, and we interpret this result in the context of previous research on visual marking.     

Visual marking and the perception of salience in visual search

In the present study, the gap paradigm originally developed by Watson and Humphreys (1997) was used to investigate whether the process of visual marking can influence the perceptual salience of a target in visual search. Consistent with previous studies (Watson & Humphreys, 1997), the results showed that search was not affected by the presence of the preceding distractors when the target was relatively low in salience. This finding suggests that visual marking can increase the efficiency of visual search by decreasing the size of the search set. However, more important, the results also showed that search was affected by the presence of the preceding distractors when the target was relatively high in salience. This finding suggests that visual marking may be limited in its ability to increase the perceptual salience of the target. Together, the results of the present study suggest that the effectiveness of visual marking may vary as a function of search context.     

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.     

Visual Marking of Locations and Feature Maps: Evidence from Within-dimension Defined Conjunctions

Recently, Watson and Humphreys (1997, 1998) proposed that the selection of new visual events can be aided by the top-down inhibition of old information-visual marking (VM) and that the mechanisms of marking differ for static and moving stimuli. Stationary stimuli are marked by location-based inhibition, whereas moving stimuli are marked by inhibition applied at the level of whole-feature maps. Here we provide a test of this 'two-mechanism' account. We show that static items can be marked even when old and new stimuli contain the same features and so cannot be distinguished by activation within a unique feature map. However, moving old items could not be marked unless they possessed a unique feature (colour). Manipulations of grouping strength, both within and between distractor sets, did not affect the basic findings. The results support the existence of two mechanisms for VM and counter an object-based inhibition explanation of performance.     

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 marking inhibits singleton capture

This paper is concerned with how we prioritize the selection of new objects in visual scenes. We present four experiments investigating the effects of distractor previews on visual search through new objects. Participants viewed a set of to-be-ignored nontargets, with the task being to search for a target in a second set, added to the first after 1000ms. This second set could contain a salient feature singleton, defined in terms of its color, orientation, or both color and orientation. When the singleton was a distractor, search was slowed relative to when there was no singleton. Search was facilitated when the singleton was a target. Interestingly, both the interference and facilitation effects were modulated when the preview shared features with the singleton. Follow-up experiments showed that this reduction of singleton effects was not due to: (i) low-level sensory aspects of the displays, (ii) increased heterogeneity in the search set in the preview condition, or (iii) color-based grouping of old and new items. Instead, we suggest that there is an inhibitory carry-over from the first to the second set of items based on feature similarity. We suggest the suppression stems from a process termed visual marking, which suppresses irrelevant visual objects in anticipation of more relevant new objects (Watson & Humphreys, 1997). The findings argue against alternative explanations such as the automatic capture by abrupt new onsets account.     

视觉标记：一种优先选择机制

视觉标记是与任务目标相关的自上而下的优先选择解释机制。视觉标记理论对preview效益——对后出现项目的视觉优先选择现象——提供了合理的解释：对先出现的项目自上而下的抑制提高了对后出现项目的优先选择等级。首先介绍视觉标记经典实验范式和preview效益,然后阐述研究者对视觉标记抑制机制的两种主要观点,进而介绍其他优先选择理论对preview效益的解释及其局限性,最后指出视觉标记研究中亟待解决的问题     

Prioritized selection in visual search through onset capture and color inhibition: evidence from a probe-dot detection task

Observers performed a preview search task in which, on some trials, they had to indicate the presence of a briefly presented probe-dot. Probes could be presented on locations corresponding to old or new elements and prior to or after the presentation of the new elements. After the presentation of the new elements, probes were generally detected faster on new than on old locations, indicating prioritized selection of new elements. Prior to the presentation of the new elements, probes were detected faster on new than on old locations only when old and new elements differed in color. These results suggest that prioritized selection of new elements is mediated not by visual marking but by onset capture. Additionally, observers may apply color-based inhibition.