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WIREs Cogn Sci
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Visual search

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Abstract Visual search is the act of looking for a predefined target among other objects. This task has been widely used as an experimental paradigm to study visual attention, and because of its influence has also become a subject of research itself. When used as a paradigm, visual search studies address questions including the nature, function, and limits of preattentive processing and focused attention. As a subject of research, visual search studies address the role of memory in search, the procedures involved in search, and factors that affect search performance. In this article, we review major theories of visual search, the ways in which preattentive information is used to guide attentional allocation, the role of memory, and the processes and decisions involved in its successful completion. We conclude by summarizing the current state of knowledge about visual search and highlight some unresolved issues. WIREs Cogn Sci 2013, 4:415–429. doi: 10.1002/wcs.1235 This article is categorized under: Psychology > Perception and Psychophysics

Stimuli and results from Cave and Zimmerman's experiment. Participants searched for a target letter among similar or dissimilar distractor letters. In some trials, a probe dot appeared and participants made a speeded response to it. Results showed that probe dot RTs were faster at the target location and slower at distractor locations, and this difference is larger for similar than dissimilar conditions. This result reflects different degrees of attentional facilitation and inhibition in each condition, suggesting that the strength of attentional engagement is variable upon task demands. (Reprinted with permission from Ref 85. Copyright 2013 SAGE)

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Stimuli and results from Woodman and Luck's experiment. Participants remembered locations of two objects, performed a serial search during the retention period, and were tested on their memory. Results showed that search was less efficient with increases in memory load, and memory accuracy traded off with set size. Both results suggest that serial visual search requires spatial memory to operate. (Reprinted with permission from Ref 73. Copyright 2013 Springer)

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Searching for the oblique T on the left panel is easy, but the presence of a red singleton distractor can slow search. Interestingly, a similar distractor does not influence performance in serial searches (e.g., when you search for the flipped L on the right panel). Bacon and Egeth suggest that a singleton distractor captures attention only when an observer adopts a singleton‐detection strategy. In contrast, when a search is configured for a specific feature, attention is not captured by a singleton distractor.

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There are three unique objects in this display, but it is not equally easy to find them. Finding the red L should be easy, because preattentive processing supports detection of a single feature (obliqueness), and it tends to ‘call’ attention. Searching for the blue L should be a little harder, because attention is required to combine two features (color and letter identity). Try to find the remaining unique item. It should be even harder, because this time you do not know its features. Top‐down selection of features appears to help guide attention to the target.

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Probability density function of a typical conjunctive search. Although participants make slower responses for target‐absent trials, the RT distributions of target‐present and target‐absent trials generally overlap. This overlap speaks against a deadline model in which people give up a search by the time that most of the targets, if present, should be detected. Thus, participants must be using some other information to terminate their search.

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