Looking for two targets at the same time: One search or two?

Abstract

A considerable amount of evidence suggests that, under conditions of high discriminability, subjects are able to process multiple elements in a visual display simultaneously when searching for a single target among distractors. Relatively little emphasis, however, has been placed on the question of whether subjects can search for and detect multiple targets simultaneously. This latter question is the focus of the present report. In two experiments, we compare performance in single-target and multiple-target detection tasks in order to investigate whether or not multiple targets can be detected simultaneously. In Experiment 1, subjects searched for one or two targets that were defined by color. In Experiment 2, subjects searched for a color and/or a letter target. When the two targets were presented in the same location (e.g., a red X when Target 1 was red and Target 2 was an X), they seemed to be detected simultaneously. Implications for object-based processing of visual information are discussed.Much work in the area of visual search has focused on questions concerning the spatial "mode" of search. Specifically, investigators have tried to determine under what conditions (if any) subjects are able to process all elements of a visual display simultaneously and under what conditions they must process each item in turn. The former mode is known as spatially parallel search; the latter mode is known as spatially serial search.One method of distinguishing between spatially parallel and spatially serial search is to manipulate the number of elements in a display and observe how response time varies as a function of the number of elements present (e.g., Egeth, Jonides, & Wall, 1972;Neisser, 1967;Treisman, Sykes, & Gelade, 1977). Typically, a single target item is specified (e.g., an X), which subjects are to detect from among displays of distracting items. The number of distractors in the display can be varied from few to many. If each element is processed in turn, then each element that is processed before the target item is found will add to total search time. Spatially serial search therefore predicts a positive, monotonic relationship between the number of elements in the display and the time required to find the target. In contrast, if all elements are processed simultaneously, search time should be determined only by the processing of the target. Spatially parallel search therefore predicts that the time required to find the target should be unaffected by the number of elements in the display. This method has been used extenWhile conducting this research, the first author was supported by a National Science Foundation graduate fellowship. The authors are grateful to Toby Mordkoff, Charles Eriksen, Jeff Miller, Hal Pashler, Jeremy Wolfe, and two anonymous reviewers for their helpful comments on earlier drafts of this work. Correspondence should be addressed to C. M. Moore, Department of Psychology, University ofCalifomia, San Diego, La Jolla, CA 92093-0109 (e-mail: cmoore@ucsd.edu). 381 sively to identify conditi...

Visual detection and perceptual independence: Assessing color and form

“…This result supports the assumption that, although focused attention is not needed to detect the targets, relative spatial location influences target detection both within and between dimensions. This conclusion is consistent with other published reports (Moore & Osman, 1993).…”

Visual search within and across dimensions: A case for within‐dimension grouping

“…There was no interaction between task and display set size and, most importantly, between task, display set size and search context. The mean differences between the one-and two-feature conditions at display set sizes four, six and eight respectively were 96, 82 and 102 ms in the within-dimension search contexts, and 59, 75 and 68 ms in the across-dimension ones (see also Moore and Osman, 1993, on within-colour search). The trend for a larger increase for within-dimension search was not reliable.…”

Matching of visual input to only one item at any one time

“…The limited matching capacity can explain why subjects require more time if they have to search for multiple targets in conventional search tasks (Linnell & Humphreys, 2002;Moore & Osman, 1993;Quinlan & Humphreys, 1987). In this situation subjects will have to switch between searchtemplates and match one at a time.…”