Bottom-up guidance in visual search for conjunctions.

Understanding the relative role of top-down and bottom-up guidance is crucial for models of visual search. Previous studies have addressed the role of top-down and bottom-up processes in search for a conjunction of features but with inconsistent results. Here, the author used an attentional capture method to address the role of top-down and bottom-up processes in conjunction search. The role of bottom-up processing was assayed by inclusion of an irrelevant-size singleton in a search for a conjunction of color and orientation. One object was uniquely larger on each trial, with chance probability of coinciding with the target; thus, the irrelevant feature of size was not predictive of the target's location. Participants searched more efficiently for the target when it was also the size singleton, and they searched less efficiently for the target when a nontarget was the size singleton. Although a conjunction target cannot be detected on the basis of bottom-up processing alone, participants used search strategies that relied significantly on bottom-up guidance in finding the target, resulting in interference from the irrelevant-size singleton. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Roles of salience and strategy in conjunction search.

In some cases, the search for a conjunction target proceeds through the smaller group of elements in a display, whereas in others, search is limited to those elements that share a particular feature with the target. In 6 experiments, participants searched for a conjunction target among displays consisting of various proportions of 2 distractor types. Smaller-group search was more prevalent than target-feature search with denser displays and with features that were highly discriminable. Explicit instructions to limit search to a specific feature affected performance only when the discriminability of the guiding feature was much greater than the other target feature. Together, these experiments show that bottom-up factors have more influence in guiding conjunction searches than previously thought. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions between search mechanisms in conjuction search.

We report the results of a technique designed to measure interactions between different visual search processes. We interrupted pop-out search before it produced a detection response, by adding extra distractors to the display so that a target initially defined by a single feature difference could then only be found on the basis of the conjunction of two features. This technique has been used to measure the duration of the perceptual components of pop-out search, independent of overall response time, for targets presented among different sets of distractors. In addition, when pop-out failed because it was interrupted, past work has shown that it nevertheless provided useful information to the processes responsible for difficult search. That is, partial pop-out assisted difficult search, when extra distractors made search difficult because the target was between the two types of distractors in the relevant feature space (E. Olds, W. Cowan, & P. Jolicoeur, 2000a,b,c). The present results demonstrate that partial pop-out also assists difficult search when difficult search is a conjunction search, and therefore these interactions may occur at a stage where information from different feature dimensions is combined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modifying guided search: Preattentive object files.

Many models of visual search behaviour consist of a first stage in which basic features are processed "in parallel" at all locations across the visual field and a second, limited-capacity stage in which processing is restricted to a single item or location. Perhaps the best known of these models is Feature Integration Theory (FIT) (e.g. Treisman, 1993). The original FIT was the starting point for our Guided Search (Wolfe, 1994). The heart of Guided Search is the proposal that the parallel first stage can guide the spatial deployment of the limited resources of the second stage. For example, consider a conjunction search for a red vertical line among green vertical lines and red horizontal lines. There is good reason to believe that no first stage mechanism is specifically designed to be sensitive to conjunctions of colour and orientation. Nevertheless, searches for conjunctions of this sort are quite efficient; more efficient than they ought to be if second stage resources were deployed from item to item in a random, serial search. This efficiency can be obtained if information is combined from two first stage feature processors. If a colour processor guides attention toward all red items while an orientation processor guides all attention toward the vertical items, attention would be guided most strongly toward the red vertical items. Even if we assume that guidance is not perfect, the combination of these two sources of information will make the search for a conjunction more efficient that it would have been in the absence of guidance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measuring search efficiency in complex visual search tasks: Global and local clutter.

[Correction Notice: An erratum for this article was reported in Vol 17(2) of Journal of Experimental Psychology: Applied (see record 2011-11863-002). The copyright for the article was incorrectly listed. The copyright is in the correction.] Set size and crowding affect search efficiency by limiting attention for recognition and attention against competition; however, these factors can be difficult to quantify in complex search tasks. The current experiments use a quantitative measure of the amount and variability of visual information (i.e., clutter) in highly complex stimuli (i.e., digital aeronautical charts) to examine limits of attention in visual search. Undergraduates at a large southern university searched for a target among 4, 8, or 16 distractors in charts with high, medium, or low global clutter. The target was in a high or low local-clutter region of the chart. In Experiment 1, reaction time increased as global clutter increased, particularly when the target was in a high local-clutter region. However, there was no effect of distractor set size, supporting the notion that global clutter is a better measure of attention against competition in complex visual search tasks. As a control, Experiment 2 demonstrated that increasing the number of distractors leads to a typical set size effect when there is no additional clutter (i.e., no chart). In Experiment 3, the effects of global and local clutter were minimized when the target was highly salient. When the target was nonsalient, more fixations were observed in high global clutter charts, indicating that the number of elements competing with the target for attention was also high. The results suggest design techniques that could improve pilots' search performance in aeronautical charts. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Feature integration theory revisited: Dissociating feature detection and attentional guidance in visual search.

In feature integration theory (FIT; A. Treisman & S. Sato, 1990), feature detection is driven by independent dimensional modules, and other searches are driven by a master map of locations that integrates dimensional information into salience signals. Although recent theoretical models have largely abandoned this distinction, some observed results are difficult to explain in its absence. The present study measured dimension-specific performance during detection and localization, tasks that require operation of dimensional modules and the master map, respectively. Results showed a dissociation between tasks in terms of both dimension-switching costs and cross-dimension attentional capture, reflecting a dimension-specific nature for detection tasks and a dimension-general nature for localization tasks. In a feature-discrimination task, results precluded an explanation based on response mode. These results are interpreted to support FIT's postulation that different mechanisms are involved in parallel and focal attention searches. This indicates that the FIT architecture should be adopted to explain the current results and that a variety of visual attention findings can be addressed within this framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The magnitude of binocular disparity modulates search time for targets defined by a conjunction of depth and colour.

Nakayama and Silverman (1986) proposed that, when searching for a target defined by a conjunction of color and stereoscopic depth, observers partition 3D space into separate depth planes and then rapidly search each such plane in turn, thereby turning a conjunctive search into a "feature" search. In their study, they found, consistent with their hypothesis, shallow search slopes when searching depth planes separated by large binocular disparities. Here, the authors investigated whether the search slope depends upon the extent of the stereoscopically induced separation between the planes to be searched (i.e., upon the magnitude of the binocular disparity. The obtained slope shows that (1) a rapid search only occurs with disparities greater than 6 min of arc, a value that vastly exceeds the stereo threshold, and that (2) the steepness of this slope increases in a major way at lower disparities. The ability to implement the search mode envisaged by Nakayama and Silverman is thus clearly limited to large disparities; less efficient search strategies are mandated by lower disparity values, as under such conditions items from one depth plane may be more likely to "intrude" upon the other. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the speed of pop-out in feature search.

When something unique is present in a scene, this element may become immediately visible and one has the impression that it pops out from the scene. This phenomenon, known as pop-out in the visual search literature, is thought to produce the fastest search possible, and response times for the detection of the pop-out target do not vary as a function of the number of nontargets. In this study, we challenge this notion and show that the detection of a given visual feature is faster for multiple targets than for a single pop-out target. However, when the task requires a detailed target analysis, the pop-out condition can be faster than the multiple-target condition. Current models of visual search are discussed in light of the findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The serial process in visual search.

The conditions for serial search are described. A multiple target search methodology (Thornton & Gilden, 2007) is used to home in on the simplest target/distractor contrast that effectively mandates a serial scheduling of attentional resources. It is found that serial search is required when (a) targets and distractors are mirror twins, and (b) when the search elements lack the Gestalt property of intrinsic orientation. The finding is put into the context of Feature Integration Theory (Treisman & Gelade, 1980) that first identified the occasions of serial search to be important to object perception and understanding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

More than just finding color: Strategy in global visual search is shaped by learned target probabilities.

In 2 experiments, eye movements were examined during searches in which elements were grouped into four 9-item clusters. The target (a red or blue T) was known in advance, and each cluster contained different numbers of target-color elements. Rather than color composition of a cluster invariantly guiding the order of search though clusters, the use of color was determined by the probability that the target would appear in a cluster of a certain color type: When the target was equally likely to be in any cluster containing the target color, fixations were directed to those clusters approximately equally, but when targets were more likely to appear in clusters with more target-color items, those clusters were likely to be fixated sooner. (The target probabilities guided search without explicit instruction.) Once fixated, the time spent within a cluster depended on the number of target-color elements, consistent with a search of only those elements. Thus, between-cluster search was influenced by global target probabilities signaled by amount of color or color ratios, whereas within-cluster search was directly driven by presence of the target color. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Measuring search efficiency in complex visual search tasks: Global and local clutter": Correction to Beck et al. (2010).

Reports an error in "Measuring search efficiency in complex visual search tasks: Global and local clutter" by Melissa R. Beck, Maura C. Lohrenz and J. Gregory Trafton (Journal of Experimental Psychology: Applied, 2010[Sep], Vol 16[3], 238-250). The copyright for the article was incorrectly listed. The correct copyright information is provided in the erratum. (The following abstract of the original article appeared in record 2010-19027-002.) Set size and crowding affect search efficiency by limiting attention for recognition and attention against competition; however, these factors can be difficult to quantify in complex search tasks. The current experiments use a quantitative measure of the amount and variability of visual information (i.e., clutter) in highly complex stimuli (i.e., digital aeronautical charts) to examine limits of attention in visual search. Undergraduates at a large southern university searched for a target among 4, 8, or 16 distractors in charts with high, medium, or low global clutter. The target was in a high or low local-clutter region of the chart. In Experiment 1, reaction time increased as global clutter increased, particularly when the target was in a high local-clutter region. However, there was no effect of distractor set size, supporting the notion that global clutter is a better measure of attention against competition in complex visual search tasks. As a control, Experiment 2 demonstrated that increasing the number of distractors leads to a typical set size effect when there is no additional clutter (i.e., no chart). In Experiment 3, the effects of global and local clutter were minimized when the target was highly salient. When the target was nonsalient, more fixations were observed in high global clutter charts, indicating that the number of elements competing with the target for attention was also high. The results suggest design techniques that could improve pilots' search performance in aeronautical charts. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Contextual cueing in naturalistic scenes: Global and local contexts.

In contextual cueing, the position of a target within a group of distractors is learned over repeated exposure to a display with reference to a few nearby items rather than to the global pattern created by the elements. The authors contrasted the role of global and local contexts for contextual cueing in naturalistic scenes. Experiment 1 showed that learned target positions transfer when local information is altered but not when global information is changed. Experiment 2 showed that scene-target covariation is learned more slowly when local, but not global, information is repeated across trials than when global but not local information is repeated. Thus, in naturalistic scenes, observers are biased to associate target locations with global contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search asymmetries within color-coded and intensity-coded displays.

Color and intensity coding provide perceptual cues to segregate categories of objects within a visual display, allowing operators to search more efficiently for needed information. Even within a perceptually distinct subset of display elements, however, it may often be useful to prioritize items representing urgent or task-critical information. The design of symbology to produce search asymmetries (Treisman & Souther, 1985) offers a potential technique for doing this, but it is not obvious from existing models of search that an asymmetry observed in the absence of extraneous visual stimuli will persist within a complex color- or intensity-coded display. To address this issue, in the current study we measured the strength of a visual search asymmetry within displays containing color- or intensity-coded extraneous items. The asymmetry persisted strongly in the presence of extraneous items that were drawn in a different color (Experiment 1) or a lower contrast (Experiment 2) than the search-relevant items, with the targets favored by the search asymmetry producing highly efficient search. The asymmetry was attenuated but not eliminated when extraneous items were drawn in a higher contrast than search-relevant items (Experiment 3). Results imply that the coding of symbology to exploit visual search asymmetries can facilitate visual search for high-priority items even within color- or intensity-coded displays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search for orientation among heterogeneous distractors: Experimental results and implications for signal-detection theory models of search.

Three experiments tested a signal-detection theory (SDT) model of visual search (e.g., as described in J. Palmer, C. T. Ames, & D. T. Lindsey, 1993). In Experiment 1, participants searched for a 0° line among distractors at (a) 30°; (b) ? at 30°, ? at 50°; (c) ? at 30°, 50°, and 70°; and (d) ? at 30°, ? at 70°. The SDT model predicts improved performance in the more heterogeneous conditions, as some distractors are more discriminable from the target. In contrast, in Experiment 1 human performance degraded in the more heterogeneous conditions (c and d). In Experiment 2, sparser displays improved the performance of the SDT model. In Experiment 3, search for θ° among homogeneous θ?+?20° distractors was compared with search for θ° among θ?±?20° distractors. Performance in the latter condition was often worse, relative to performance in the homogeneous condition, than predicted by the SDT model; however, this depended greatly on the identity of the target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fractionating the binding process: Neuropsychological evidence from reversed search efficiencies.

The authors present neuropsychological evidence distinguishing binding between form, color, and size (cross-domain binding) and binding between form elements. They contrasted conjunctive search with difficult feature search using control participants and patients with unilateral parietal or fronto/temporal lesions. To rule out effects of task difficulty or loss of top-down guidance of search, the authors made conjunction search easier than feature search. Despite this, parietal patients were selectively impaired at detecting conjunction targets in their contralateral field. In contrast, the parietal patients performed like the other participants with form conjunctions, with form conjunctions being easier to detect than difficult feature targets. These data indicate a qualitative difference between binding in the form domain and binding across form, color, and size, consistent with theories that propose distinct binding processes in vision. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning by selection: Visual search and object perception in young infants.

The authors examined how visual selection mechanisms may relate to developing cognitive functions in infancy. Twenty-two 3-month-old infants were tested in 2 tasks on the same day: perceptual completion and visual search. In the perceptual completion task, infants were habituated to a partly occluded moving rod and subsequently presented with unoccluded broken and complete rod test stimuli. In the visual search task, infants viewed displays in which single targets of varying levels of salience were cast among homogeneous static vertical distractors. Infants whose posthabituation preference indicated unity perception in the completion task provided evidence of a functional visual selective attention mechanism in the search task. The authors discuss the implications of the efficiency of attentional mechanisms for information processing and learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Automatic guidance of visual attention from verbal working memory.

Previous studies have shown that visual attention can be captured by stimuli matching the contents of working memory (WM). Here, the authors assessed the nature of the representation that mediates the guidance of visual attention from WM. Observers were presented with either verbal or visual primes (to hold in memory, Experiment 1; to verbalize, Experiment 2; or merely to attend, Experiment 3) and subsequently were required to search for a target among different distractors, each embedded within a colored shape. In half of the trials, an object in the search array matched the prime, but this object never contained the target. Despite this, search was impaired relative to a neutral baseline in which the prime and search displays did not match. An interesting finding is that verbal primes were effective in generating the effects, and verbalization of visual primes elicited similar effects to those elicited when primes were held in WM. However, the effects were absent when primes were only attended. The data suggest that there is automatic encoding into WM when items are verbalized and that verbal as well as visual WM can guide visual attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pip and pop: Nonspatial auditory signals improve spatial visual search.

Searching for an object within a cluttered, continuously changing environment can be a very time-consuming process. The authors show that a simple auditory pip drastically decreases search times for a synchronized visual object that is normally very difficult to find. This effect occurs even though the pip contains no information on the location or identity of the visual object. The experiments also show that the effect is not due to general alerting (because it does not occur with visual cues), nor is it due to top-down cuing of the visual change (because it still occurs when the pip is synchronized with distractors on the majority of trials). Instead, we propose that the temporal information of the auditory signal is integrated with the visual signal, generating a relatively salient emergent feature that automatically draws attention. Phenomenally, the synchronous pip makes the visual object pop out from its complex environment, providing a direct demonstration of spatially nonspecific sounds affecting competition in spatial visual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Efficiency of Feature-Based Subitization and Counting.

The enumeration of small numbers of objects (～4) proceeds rapidly, accurately, and with little effort via a process termed subitization. Four experiments examined whether it was possible to subitize the number of features rather than objects present in a display. Overall, the findings showed that when features are presented randomly and are uncorrelated with object numerosity, efficient enumeration is not possible. This suggests that the visual system does not have parallel access to multiple feature maps and that subitization processes operate exclusively on representations coding the locations of objects. The data are discussed with respect to theories of visual enumeration and search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)