Limitations on the parallel guidance of visual search: Color?×?Color and Orientation?×?Orientation conjunctions.

In visual search for a conjunction it is much more difficult to search for the conjunction of 2 colors or 2 orientations than for Color?×?Orientation or Color?×?Shape conjunctions. The result is not limited to particular colors or shapes. Two colors cannot occupy the same spatial location in Color?×?Color searches. However, Exps 6 and 7 show that Color?×?Shape searches remain efficient even if the color and shape are spatially separated. Our guided search model suggests that in searches for Color?×?Shape a parallel color module can guide attention toward the correct color, whereas the shape module guides attention toward the correct shape. Together these 2 sources of guidance lead attention to the target. However, if a target is red and green among red–blue and green–blue distractors, it is not possible to guide search independently toward red items and green items or away from all blue items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning and attention: Brain and behavioural approaches the 1995 Banff Annual Seminar in Cognitive Science.

The Banff Annual Seminar in Cognitive Science (BASICS) was founded in 1982, and thus the meeting this past May marks the 14th anniversary of this conference. Many recent talks have stressed the importance of studying these processes in conjunction with each other. In keeping with this theme, the focus of BASICS 1995 was on recent neuropsychological, neurophysiological, and behavioural findings with respect to attention and learning. Further, many of the talks provided evidence in support of attentional organization centered around objects, rather than locations. The first talk, from world-renowned scientist Michael Posner, centered on his work involving neuroscientific approaches to the study of high-level skills such as reading. Steven Luck's talk also emphasized the use of multiple neurophysiological techniques to study high-level cognitive function, in this case, the binding of features. The talk by Lynn Robertson about her work in collaboration with Anne Treisman, switched to a focus on neuropsychological, rather than neurophysiological, findings regarding attention in humans. The last speaker of the first afternoon, Patrick Cavanagh, gave a talk replete with impressive visual demonstrations regarding his work in the behavioural analysis of spatial visual attention. The first speaker of the following morning session, Jeremy Wolfe, began his presentation by comparing his theory of visual search, which he calls Guided Search, to the more traditional theory of search, Feature Integration Theory (FIT), as proposed by Anne Treisman. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of items in working memory on the deployment of attention and the eyes during visual search.

Paying attention to an object facilitates its storage in working memory. The authors investigate whether the opposite is also true: whether items in working memory influence the deployment of attention. Participants performed a search for a prespecified target while they held another item in working memory. In some trials this memory item was present in the search display as a distractor. Such a distractor has no effect on search time if the search target is in the display. In that case, the item in working memory is unlikely to be selected as a target for an eye movement, and if the eyes do land on it, fixation duration is short. In the absence of the target, however, there is a small but significant effect of the memory item on search time. The authors conclude that the target for visual search has a special status in working memory that allows it to guide attention. Guidance of attention by other items in working memory is much weaker and can be observed only if the search target is not present in the display. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory for where, but not what, is used during visual search.

Although the role of memory in visual search is debatable, most researchers agree with a limited-capacity model of memory in visual search. The authors demonstrate the role of memory by replicating previous findings showing that visual search is biased away from old items (previously examined items) and toward new items (nonexamined items). Furthermore, the authors examined the type of memory representations used to bias search by changing an item's individuating feature or location during search. Changing the individuating feature of an item did not disrupt normal search biases. However, when the location of an item changed, normal search biases were disrupted. These results suggest that memory used in visual search is based on items' locations rather than their identity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New objects dominate luminance transients in setting attentional priority.

Both the sudden appearance of an object and sudden changes in existing object features influence priority in visual search. However, direct comparisons of these influences have not been made under controlled conditions. In 5 visual search experiments, new object onsets were compared directly with changes in the luminance of old objects. Factors included the luminance contrast of items against the background, the magnitude of luminance change, and the probability that these changes were associated with the target item. New objects were consistently more effective in guiding search, such that a new item with very low luminance contrast was equivalent to an old item undergoing a large change in luminance. An important exception was an old item changing in contrast and polarity, which was as effective as the appearance of a new object. This indicates that search priority is biased toward object rather than situational changes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implications of visual search deficits for cognitive theory.

Neuropsychological evidence was presented and found to be consistent with Treisman's Feature Integration Theory (FIT). Several studies were reported using groups of patients with unilateral visual neglect, stable patients with known lesion loci, and a single patient with bilateral parietal-occipital lesions. Collectively, the data support a distinction between feature and conjunction search. They also support arguments for the primary role of spatial representation in forming correct conjunctions between features and for individuating objects. Nevertheless, the data do call for some refinements in FIT. The spatial maps involved in feature integration for serial visual search and for the experience of an accurately conjoined object appear to be relatively late. Features are likely to be integrated in the nervous system at sub-threshold levels in early vision (e.g., vl or v2), but it requires supra-threshold spatial knowledge to successfully conjoin features in visual experience (Wojciulik, Robertson & Kanwisher, 1994). The evidence as a whole, however, is consistent with FIT in that spatial information is necessary for controlled visual search and for the accurate conjunction of features in multi-item arrays. In addition, it suggests that explicit access to relatively late spatial information is necessary to correctly conjoin features in the experiences percept. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conjunction search revisited.

Search for conjunctions of highly discriminable features can be rapid or even parallel. This article explores three possible accounts based on (a) perceptual segregation, (b) conjunction detectors, and (c) inhibition controlled separately by two or more distractor features. Search rates for conjunctions of color, size, orientation, and direction of motion correlated closely with an independent measure of perceptual segregation. However, they appeared unrelated to the physiology of single-unit responses. Each dimension contributed additively to conjunction search rates, suggesting that each was checked independently of the others. Unknown targets appear to be found only by serial search for each in turn. Searching through 4 sets of distractors was slower than searching through 2. The results suggest a modification of feature integration theory, in which attention is controlled not only by a unitary "window" but also by a form of feature-based inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual marking: Prioritizing selection for new objects by top-down attentional inhibition of old objects.

The authors propose a new mechanism for prioritizing the selection of new events: visual marking. In a modified conjunction search task the authors presented one set of distractors before the remaining items, which contained the target if present. Search was as efficient as if only the second items were presented. This held when eye movements were prevented and required a gap of 400 ms between the old and new items. The effect was abolished by luminance changes at old distractor locations when the new items appeared, and it was reduced by the addition of an attention demanding load task. The authors propose that old items can be ignored by spatially parallel, top-down attentional inhibition applied to the locations of static stimuli. The authors discuss the relations between marking and other accounts of visual selection and potential neurophysiological mechanisms. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

No emotional “pop-out” effect in natural scene viewing.

It has been shown that attention is drawn toward emotional stimuli. In particular, eye movement research suggests that gaze is attracted toward emotional stimuli in an unconscious, automated manner. We addressed whether this effect remains when emotional targets are embedded within complex real-world scenes. Eye movements were recorded while participants memorized natural images. Each image contained an item that was either neutral, such as a bag, or emotional, such as a snake or a couple hugging. We found no latency difference for the first target fixation between the emotional and neutral conditions, suggesting no extrafoveal “pop-out” effect of emotional targets. However, once detected, emotional targets held attention for a longer time than neutral targets. The failure of emotional items to attract attention seems to contradict previous eye-movement research using emotional stimuli. However, our results are consistent with studies examining semantic drive of overt attention in natural scenes. Interpretations of the results in terms of perceptual and attentional load are provided. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A neural theory of attentive visual search: Interactions of boundary, surface, spatial, and object representations.

Visual search data are given a unified quantitative explanation by a model of how spatial maps in the parietal cortex and object recognition categories in the inferotemporal cortex deploy attentional resources as they reciprocally interact with visual representations in the prestriate cortex. The model visual representations are organized into multiple boundary and surface representations. Visual search in the model is initiated by organizing multiple items that lie within a given boundary or surface representation into a candidate search grouping. These items are compared with object recognition categories to test for matches or mismatches. Mismatches can trigger deeper searches and recursive selection of new groupings until a target object is identified. The model provides an alternative to Feature Integration and Guided Search models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Serial deployment of attention during visual search.

This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 (RTs) were measured. For many unpracticed subjects, the slopes of the resulting RT?×?Set Size functions are too shallow to be consistent with A. Treisman's (see record 1988-00255-001) and A. Treisman and G. Gelade's (see record 1980-04680-001) feature integration model, which proposes serial, self-terminating search for conjunctions. Searches for triple conjunctions (Color?×?Size?×?Form) are easier than searches for standard conjunctions and can be independent of set size. A guided search model similar to J. E. Hoffman's (see record 1981-04707-001) 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early, Involuntary Top-Down Guidance of Attention From Working Memory.

Four experiments explored the interrelations between working memory, attention, and eye movements. Observers had to identify a tilted line amongst vertical distractors. Each line was surrounded by a colored shape that could be precued by a matching item held in memory. Relative to a neutral baseline, in which no shapes matched the memory item, search was more efficient when the memory cue matched the shape containing the target, and it was less efficient when the cued stimulus contained a distractor. Cuing affected the shortest reaction times and the first saccade in search. The effect occurred even when the memory cue was always invalid but not when the cue did not have to be held in memory. There was also no evidence for priming effects between consecutive trials. The results suggest that there can be early, involuntary top-down directing of attention to a stimulus matching the contents of working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Signals of threat do not capture, but prioritize, attention: A conditioning approach.

Research suggests that threatening information captures attention more rapidly than neutral information. However, in most studies threat stimuli differ perceptually from neutral stimuli and are instrumental to perform the task, leaving the question unanswered whether threat is sufficient to capture attention. In experiment 1, we designed a visual search task with stimuli of equal salience (colored circles) that have the potential to lead to efficient search (10 ms/item). In experiment 2, one of the colors (conditioned stimulus, CS+) was made threatening by means of fear conditioning. Participants responded to a target presented in one of the circles. Overall, the search was faster on congruent trials (where the target was presented in the CS+) than on baseline trials (where the CS + was absent). Furthermore, the search was slower on incongruent trials (where the target was presented in another color than the CS+) than on baseline trials. The search on congruent trials was affected by set size (90 ms/item), but to a lesser extent than on baseline trials (105 ms/item). We conclude that threat prioritizes, but does not capture attention. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Has feature integration theory come unglued? A reply to Tsal.

Y. Tsal (see record 1989-31807-001) presented a critical review of feature integration theory (FIT) and of a number of studies that have purported to show a direct relationship between focal attention and the perception of illusory conjunctions. Conceptual difficulties with the theory are highlighted, and Tsal concluded that the reviewed studies have not provided sufficient empirical support. We argue that neither Tsal's conceptual criticism nor his empirical ones are convincing enough to warrant rejection of FIT and that he has not suggested an obvious and unique theoretical alternative that inspires an appropriate empirical test. A problem for FIT that Tsal did not raise is discussed. That is, the visual primitives assumed by the theory are not clearly specified or related to known neurophysiological or psychophysical evidence concerning early vision. Nevertheless, we conclude that FIT remains a viable theoretical framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postattentive vision.

Much research has examined preattentive vision: visual representation prior to the arrival of attention. Most vision research concerns attended visual stimuli; very little research has considered postattentive vision. What is the visual representation of a previously attended object once attention is deployed elsewhere? The authors argue that perceptual effects of attention vanish once attention is redeployed. Experiments 1–6 were visual search studies. In standard search, participants looked for a target item among distractor items. On each trial, a new search display was presented. These tasks were compared to repeated search tasks in which the search display was not changed. On successive trials, participants searched the same display for new targets. Results showed that if search was inefficient when participants searched a display the first time, it was inefficient when the same, unchanging display was searched the second, fifth, or 350th time. Experiments 7 and 8 made a similar point with a curve tracing paradigm. The results have implications for an understanding of scene perception, change detection, and the relationship of vision to memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search for motion–form conjunctions: Is form discriminated within the motion system?

Motion-form conjunction search can be more efficient when the target is moving (a moving 45° tilted line among moving vertical and stationary 45° tilted lines) rather than stationary. This asymmetry may be due to aspects of form being discriminated within a motion system representing only moving items, whereas discrimination of stationary items relies on a static form system (J. Driver & P. McLeod, 1992). Alternatively, it may be due to search exploiting differential motion velocity and direction signals generated by the moving-target and distractor lines. To decide between these alternatives, 4 experiments systematically varied the motion-signal information conveyed by the moving target and distractors while keeping their form difference salient. Moving-target search was found to be facilitated only when differential motion-signal information was available. Thus, there is no need to assume that form is discriminated within the motion system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual search for conjunctions of motion and form: Display density and asymmetry reversal.

In visual search for motion-form conjunctions, search rates have been reported to be faster for moving than for stationary targets if the target-nontarget discrimination is easy (45° target line tilt from vertical), but this asymmetry is reversed if the discrimination is difficult (9° tilt) (J. Driver & P. McLeod, 1992). Driver and McLeod proposed that gross aspects of form discrimination are performed within a motion filter that represents only the moving items, whereas fine discriminations rely on a stationary form system that is poor at filtering by motion. However, H. J. Muller and J. Maxwell (1994) failed to observe the asymmetry reversal, possibly because they used lower density displays. The study did not yield an effect due to varying display density. This lends support to the notion of a unitary form system, with the role of the motion filter being limited to guiding the search to the moving items or the stationary items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)