Changing Your Mind: On the Contributions of Top-Down and Bottom-Up Guidance in Visual Search for Feature Singletons Jeremy M. Wolfe Brigham and Women’s Hospital and Harvard Medical School Serena J. Butcher, Carol Lee, and Megan Hyle Brigham and Women’s Hospital Observers, searching for targets among distractor items, guide attention with a mix of top-down information— based on observers’ knowledge—and bottom-up information—stimulus-based and largely independent of that knowledge. There are 2 types of top-down guidance: explicit information (e.g., verbal description) and implicit priming by preceding targets (top-down because it implies knowledge of previous searches). Experiments 1 and 2 separate bottom-up and top-down contributions to singleton search. Experiment 3 shows that priming effects are based more strongly on target than on distractor identity. Experiments 4 and 5 show that more difficult search for one type of target (color) can impair search for other types (size, orientation). Experiment 6 shows that priming guides attention and does not just modulate response. When you look at Figure 1, your attention is probably attracted to the spiky diamond. It is a salient item, and, all else being equal, salient items that are different from their neighbors tend to attract attention (Egeth, 1977; Julesz, 1986; Moraglia, 1989). The infor- mation that guided your attention to that item can be labeled as bottom-up—meaning that it did not depend on the observer’s knowledge of the stimulus. The stimulus itself provides the guidance. If you are now asked to find the white vertical lines, you can do this with no particular difficulty. The stimuli did not change when you performed the second task. Instead, you changed your mind in response to the suggestion that you look for white verticals. You can find white verticals by guiding your attention to the intersec- tion of the set of white items and the set of vertical items (Wolfe, Cave, & Franzel, 1989). The information that guided your atten- tion in this case can be labeled top-down—meaning that it de- pended on the observer’s knowledge. The white verticals would not have attracted attention in the same way without that knowl- edge (though there is evidence that the white vertical lines actually become more salient if you are looking for them; Blaser, Sperling, & Lu, 1999). Top-down information can come in several other forms. Posi- tion information can be used to guide attention. Instead of being told explicitly that the target is white and vertical, the observer might be told that the target is the item in the upper left corner. Implicit information can also be considered a form of top-down information. Maljkovic and Nakayama (1994, 1996) showed that attention was more swiftly deployed to a red item if recent target items had also been red. They dubbed this priming of pop-out (see also Kristjansson, Wang, & Nakayama, 2002). Because it relies on what the observer has learned about the prior trials and does not rely solely on the state of the stimulus, we consider this to be a form of implicit top-down guidance. The positional analogue of priming of pop-out is the contextual cuing effect studied by Chun and Jiang (1998). If observers see the same random scene multiple times and if the target is always in the same location in that scene, they learn to direct attention to that location more efficiently even if they never explicitly realize that they are seeing the same stimulus on different trials. As with priming, because this effect relies on the observer’s implicit knowledge, it can be considered a form of top-down guidance. The purpose of this article is to examine the contributions of top-down and bottom-up guidance in some of the simplest of visual search tasks—search for a salient singleton target in a homogeneous array of distractors. Previous work, reviewed later in this article, has examined the role of bottom-up guidance, but under conditions in which observers have still had substantial top-down knowledge about target features (e.g., red) or feature dimensions (e.g., color). In this article, we substantially reduce that top-down knowledge. It cannot be fully eliminated except in a hypothetical study in which observers are asked to search for something among something else and those things change on every trial. By reducing explicit top-down information, we can more closely examine the role of priming and defend our description of priming as an implicit form of top-down guidance. The visual system requires attention and guidance of that atten- tion because the eyes provide the central nervous system with more information than it can process. It is simply not possible to Jeremy M. Wolfe, Visual Attention Laboratory, Department of Surgery, Brigham and Women’s Hospital, Boston, Massachusetts, and Department of Ophthalmology, Harvard Medical School; Serena J. Butcher, Carol Lee, and Megan Hyle, Visual Attention Laboratory, Department of Surgery, Brigham and Women’s Hospital. This research was supported by National Eye Institute Grant EY05087. Carol Lee was supported by the Research Science Institute of the Center for Excellence in Education. We thank Glyn Humphreys, Jan Theeuwes, Jennifer DiMase, and Nayantara Santhi for comments on drafts of this article. Correspondence concerning this article should be addressed to Jeremy M. Wolfe, Visual Attention Laboratory, 333 Longwood Avenue, Suite 402, Boston, Massachusetts 02115. E-mail: wolfe@search.bwh.harvard.edu Journal of Experimental Psychology: Copyright 2003 by the American Psychological Association, Inc. Human Perception and Performance 2003, Vol. 29, No. 2, 483–502 0096-1523/03/$12.00 DOI: 10.1037/0096-1523.29.2.483 483