Contingent capture in cueing: the role of color search templates and cue-target color relations

Visual search studies have shown that attention can be top-down biased to a specific target color, so that only items with this color or a similar color can capture attention. According to some theories of attention, colors from different categories (i.e., red, green, blue, yellow) are represented independently. However, other accounts have proposed that these are related—either because color is filtered through broad overlapping channels (4-channel view), or because colors are represented in one continuous feature space (e.g., CIE space) and search is governed by specific principles (e.g., linear separability between colors, or top-down tuning to relative colors). The present study tested these different views using a cueing experiment in which observers had to select one target color (e.g., red) and ignore two or four differently colored distractors that were presented prior to the target (cues). The results showed clear evidence for top-down contingent capture by colors, as a target-colored cue captured attention more strongly than differently colored cues. However, the results failed to support any of the proposed views that different color categories are related to one another by overlapping channels, linear separability, or relational guidance (N = 96).     

Part—whole information is useful in visual search for size × size but not orientation × orientation conjunctions

In visual search tasks, subjects look for a target among a variable number of distractor items. If the target is defined by a conjunction of two different features (e.g., color × orientation), efficient search is possible when parallel processing of information about color and about orientation is used to “guid” the deployment of attention to the target. Another type of conjunction search has targets defined by two instances of one type of feature (e.g., a conjunction of two colors). In this case, search is inefficient when the target is an item defined by parts of two different colors but much more efficient if the target can be described as a whole item of one color with a part of another color (Wolfe, Friedman-Hill, & Bilsky, 1994). In this paper, we show that the same distinction holds for size. “Part— whole” size × size conjunction searches are efficient; “part-part” searches are not (Experiments 1–3). In contrast, all orientation × orientation searches are inefficient (Experiments 4–6). This difference between preattentive processing of color and size, on the one hand, and orientation, on the other, may reflect structural relationships between features in real-world objects.     

Measuring the time course of selection during visual search

In visual search tasks, observers can guide their attention towards items in the visual field that share features with the target item. In this series of studies, we examined the time course of guidance toward a subset of items that have the same color as the target item. Landolt Cs were placed on 16 colored disks. Fifteen distractor Cs had gaps facing up or down while one target C had a gap facing left or right. Observers searched for the target C and reported which side contained the gap as quickly as possible. In the absence of other information, observers must search at random through the Cs. However, during the trial, the disks changed colors. Twelve disks were now of one color and four disks were of another color. Observers knew that the target C would always be in the smaller color set. The experimental question was how quickly observers could guide their attention to the smaller color set. Results indicate that observers could not make instantaneous use of color information to guide the search, even when they knew which two colors would be appearing on every trial. In each study, it took participants 200–300 ms to fully utilize the color information once presented. Control studies replicated the finding with more saturated colors and with colored C stimuli (rather than Cs on colored disks). We conclude that segregation of a display by color for the purposes of guidance takes 200–300 ms to fully develop.     

Mapping the color space of saccadic selectivity in visual search

Color coding is used to guide attention in computer displays for such critical tasks as baggage screening or air traffic control. It has been shown that a display object attracts more attention if its color is more similar to the color for which one is searching. However, what does similar precisely mean? Can we predict the amount of attention that a display color will receive during a search for a given target color? To tackle this question, two color‐search experiments measuring the selectivity of saccadic eye movements and mapping out its underlying color space were conducted. A variety of mathematical models, predicting saccadic selectivity for given target and display colors, were devised and evaluated. The results suggest that applying a Gaussian function to a weighted Euclidean distance in a slightly modified HSI color space is the best predictor of saccadic selectivity in the chosen paradigm. Hue and intensity information by itself provides a basis for useful predictors, spanning a possibly spherical color space of saccadic selectivity. Although the current models cannot predict saccadic selectivity values for a wide variety of visual search tasks, they reveal some characteristics of color search that are of both theoretical and applied interest, such as for the design of human–computer interfaces.     

Parallel processing of park-whole information in visual search tasks

Combination of information from the parallel processing of different basic features (color, size, etc.) can be used to guide attention to targets defined by conjunctions of those features. Wolfe et al. (1990) argued that, although it was possible to guide attention to the conjunction of, for instance, color and orientation, it was not possible to guide attention to targets defined by conjunctions of two colors or two orientations. The present experiments demonstrate an exception to this rule. Although it is true that attention cannot be guided to a target that hasred and green parts, attention can be guided to an item that can be described as awhole red target with agreen part. In Experiments 1 and 2, we illustrate this point. In Experiments 3 and 4, we rule out some simple size-based accounts of this finding- In Experiments 5 and 6, we begin to explore the nature of these first steps toward dividing the visual scene into parts and wholes.     

Guided search for triple conjunctions

A key tenet of feature integration theory and of related theories such as guided search (GS) is that the binding of basic features requires attention. This would seem to predict that conjunctions of features of objects that have not been attended should not influence search. However, Found (1998) reported that an irrelevant feature (size) improved the efficiency of search for a Color × Orientation conjunction if it was correlated with the other two features across the display, as compared to the case in which size was not correlated with color and orientation features. We examined this issue with somewhat different stimuli. We used triple conjunctions of color, orientation, and shape (e.g., search for a red, vertical, oval-shaped item). This allowed us to manipulate the number of features that each distractor shared with the target (sharing) and it allowed us to vary the total number of distractor types (and, thus, the number of groups of identical items: grouping). We found that these triple conjunction searches were generally very efficient—producing very shallow Reaction Time × Set Size slopes, consistent with strong guidance by basic features. Nevertheless, both of the variables, sharing and grouping, modulated performance. These influences were not predicted by previous accounts of GS; however, both can be accommodated in a GS framework. Alternatively, it is possible, though not necessary, to see these effects as evidence for “preattentive binding” of conjunctions.     

Visual search performance on an lcd monitor: effects of color combination of figure and icon background, shape of icon, and line width of icon border

This study investigated the effects of color combinations for the figure/icon background, icon shape, and line width of the icon border on visual search performance on a liquid crystal display screen. In a circular stimulus array, subjects had to search for a target item which had a diameter of 20 cm and included one target and 19 distractors. Analysis showed that the icon shape significantly affected search performance. The correct response time was significantly shorter for circular icons than for triangular icons, for icon borders with a line width of 3 pixels than for 1 or 2 pixels, and for 2 pixels than for 1 pixel. The color combination also significantly affected the visual search performance: white/yellow, white/blue, black-red, and black/ yellow color combinations for the figure/icon background had shorter correct response times compared to yellow/blue, red/green, yellow/green, and blue/red. However, no effects were found for the line width of the icon border or the icon shape on the error rate. Results have implications for graphics-based design of interfaces, such as for mobile phones, Web sites, and PDAs, as well as complex industrial processes.     

Reward Priority of Visual Target Singletons Modulates Event-Related Potential Signatures of Attentional Selection

ABSTRACT— We examined visual search for color singleton targets, whose shape was discriminated. Critically, we varied the reward priority of singleton colors (correct fast performance was worth more bonus points for red singletons than for green singletons, or vice versa) to test whether event-related potential signatures of visual selection can be affected by distinct reward priorities for different target types, even when every target has to be selected for report. The N2pc component was earlier and larger for high- than for low-reward targets. This influence of reward on the N2pc correlated with the subject-by-subject impact of reward level on efficiency of behavioral performance. Later postselection processing was also affected by reward level. These results demonstrate that visual selection of task-relevant items is rapidly modulated by reward-related priorities, even when every target has to be selected for response.     

Searching through synaesthetic colors

Synaesthesia can be characterized by illusory colors being elicited automatically when one reads an alphanumeric symbol. These colors can affect attention; synaesthetes can show advantages in visual search of achromatic symbols that normally cause slow searches. However, some studies have failed to find these advantages, challenging the conclusion that synaesthetic colors influence attention in a manner similar to the influence of perceptual colors. In the present study, we investigated 2 synaesthetes who reported colors localized in space over alphanumeric symbols’ shapes. The Euclidian distance in CIE xyY color space between two synaesthetic colors was computed for each specific visual search, so that the relationship between color distance (CD) and efficiency of search could be explored with simple regression analyses. Target-to-distractors color salience systematically predicted the speed of search, but the CD between a target or distractors and the physically presented achromatic color did not. When the synaesthetic colors of a target and distractors were nearly complementary, searches resembled popout performance with real colors. Control participants who performed searches for the same symbols (which were colored according to the synaesthetic colors) showed search functions very similar to those shown by the synaesthetes for the physically achromatic symbols.     

Guided search: an alternative to the feature integration model for visual search

Subjects searched sets of items for targets defined by conjunctions of color and form, color and orientation, or color and size. Set size was varied and reaction times (RT) were measured. For many unpracticed subjects, the slopes of the resulting RT X Set Size functions are too shallow to be consistent with Treisman's feature integration model, which proposes serial, self-terminating search for conjunctions. Searches for triple conjunctions (Color X Size X Form) are easier than searches for standard conjunctions and can be independent of set size. A guided search model similar to Hoffman's (1979) two-stage model can account for these data. In the model, parallel processes use information about simple features to guide attention in the search for conjunctions. Triple conjunctions are found more efficiently than standard conjunctions because three parallel processes can guide attention more effectively than two.     

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.     

A feature-weighting account of priming in conjunction search

Previous research on the priming effect in conjunction search has shown that repeating the target and distractor features across displays speeds mean response times but does not improve search efficiency: Repetitions do not reduce the set size effect—that is, the effect of the number of distractor items—but only modulate the intercept of the search function. In the present study, we investigated whether priming modulates search efficiency when a conjunctively defined target randomly changes between red and green. The results from an eyetracking experiment show that repeating the target across trials reduced the set size effect and, thus, did enhance search efficiency. Moreover, the probability of selecting the target as the first item in the display was higher when the target—distractor displays were repeated across trials than when they changed. Finally, red distractors were selected more frequently than green distractors when the previous target had been red (and vice versa). Taken together, these results indicate that priming in conjunction search modulates processes concerned with guiding attention to the target, by assigning more attentional weight to features sharing the previous target’s color.     

Perceptual selectivity for color and form

Three visual-search experiments tested whether the preattentive parallel stage can-selectively guide the attentive stage to a particular known-to-be-relevant target feature. Subjects searched multielement displays for a salient green circle that had a unique form when surrounded by green nontarget squares or had a unique color when surrounded by red nontarget circles. In the distractor conditions, a salient item in the other dimension was present as well. As an extension of earlier findings (Theeuwes, 1991), the results showed that complete top-down selectivity toward a particular feature was not possible, not even after extended and consistent practice. The results reveal that selectivity depends on the relative discriminability of the stimulus dimensions: the presence of an irrelevant item with a unique color interferes with parallel search for a unique form, and vice versa.     

Top-down search for color prevents voluntary directing of attention to informative singleton cues

Visuo-spatial attention can be directed in a top-down controlled way to search for color targets and it can be captured by color contrasts, regardless of color identity. Here we tested whether participants can both search for a particular color target (e.g., red) and make use of a color-contrast cue that predicted the target's most likely position to direct their attention voluntarily. Our results show that this was impossible for the participants. Results support that top-down search for particular colors is incommensurate with directing attention to just any color contrast. The results are discussed in light of the current debates concerning the roles of color and color contrast for visuo-spatial attention.     

Perceptual selectivity for color and form.

Three visual-search experiments tested whether the preattentive parallel stage can selectively guide the attentive stage to a particular known-to-be-relevant target feature. Subjects searched multielement displays for a salient green circle that had a unique form when surrounded by green nontarget squares or had a unique color when surrounded by red nontarget circles. In the distractor conditions, a salient item in the other dimension was present as well. As an extension of earlier findings (Theeuwes, 1991), the results showed that complete top-down selectivity toward a particular feature was not possible, not even after extended and consistent practice. The results reveal that selectivity depends on the relative discriminability of the stimulus dimensions: the presence of an irrelevant item with a unique color interferes with parallel search for a unique form, and vice versa.     

How do we select multiple features? Transient costs for selecting two colors rather than one,persistent costs for color–location conjunctions

In a previous study Lo, Howard, & Holcombe (Vision Research 63:20–33, 2012), selecting two colors did not induce a performance cost, relative to selecting one color. For example, requiring possible report of both a green and a red target did not yield a worse performance than when both targets were green. Yet a cost of selecting multiple colors was observed when selection needed be contingent on both color and location. When selecting a red target to the left and a green target to the right, superimposing a green distractor to the left and a red distractor to the right impeded performance. Possibly, participants cannot confine attention to a color at a particular location. As a result, distractors that share the target colors disrupt attentional selection of the targets. The attempt to select the targets must then be repeated, which increases the likelihood that the trial terminates when selection is not effective, even for long trials. Consistent with this, here we find a persistent cost of selecting two colors when the conjunction of color and location is needed, but the cost is confined to short exposure durations when the observer just has to monitor red and green stimuli without the need to use the location information. These results suggest that selecting two colors is time-consuming but effective, whereas selection of simultaneous conjunctions is never entirely successful.     

Attentional capture by irrelevant color singletons

Four experiments investigated attentional capture by a color singleton in visual search for a nonsingleton target. B. S. Gibson and E. M. Kelsey (1998) found that a color singleton in a precuing array facilitated target discrimination at that location if the same color also signaled the target array onset. The authors found similar cuing effects regardless of whether the singleton color matched the target array and regardless of whether subjects could anticipate the singleton or target-array color. In Experiment 4, a color singleton captured attention when it appeared in the precuing array but not when it appeared in the target array. The results indicate that attentional control settings for displaywide attributes are imprecise: Although subjects may anticipate a specific color, they cannot avoid attentional capture by other irrelevant colors. In addition, the effect of irrelevant singletons depends on whether a target is simultaneously present in the array.     

The structure of color experience and the existence of surface colors

Color experience is structured. Some “unique” colors (red, green, yellow, and blue) appear as “pure,” or containing no trace of any other color. Others can be considered as a mixture of these colors, or as “binary colors.” According to a widespread assumption, this unique/binary structure of color experience is to be explained in terms of neurophysiological structuring (e.g., by opponent processes) and has no genuine explanatory basis in the physical stimulus. The argument from structure builds on these assumptions to argue that colors are not properties of surfaces and that color experiences are neural processes without environmental counterparts. We reconsider the argument both in terms of its logic and in the light of recent models in vision science which point at environment-involving patterns that may be at the basis of the unique/binary structure of color experience. We conclude that, in the light of internal and external problems which arise for it, the argument from structure fails.     

Stimulus-determined discrimination mechanisms for color search.

Visual attention can be goal driven, stimulus driven, or a combination of the two. Here we report evidence for an unexpectedly stimulus-driven component of visual search for a target defined by color. Observers demonstrated a surprisingly cost-free ability to incorporate multiple classifiers in search for a target of one color from among distractors of other colors. A target color was presented among distractors that could change from trial to trial (intermixed presentation) or that remained constant across all trials in a block (blocked presentation). For blocked presentation, a single search classifier (a mechanism that segregates the target from distractors in color space) could be adopted, whereas for intermixed presentation different classifiers had to be used when the distractor colors changed. The benefit of blocked presentation was very small, suggesting that the appropriate classifier was determined very quickly in trials for which the classifier changed. The results suggest that the stimulus-driven activation of an appropriate stimulus classifier can be very efficient.