Effects of search mode and intertrial priming on singleton search (original) (raw)
2006, Perception & Psychophysics
Attention refers to the mechanisms involved in the selection of those portions of the available sensory information that will receive processing priority. Two sources of control over attentional selection have been distinguished. Attention may be captured by a salient visual event (stimulusdriven, or bottom-up, control of attention), or attention may be directed to objects that possess task-relevant properties (goal-directed, or top-down, control of attention). There has been considerable debate over how these factors interact to determine processing priority (for recent reviews, see Rauschenberger, 2003; Ruz & Lupiáñez, 2002). Theeuwes (e.g., 1992) proposed that in parallel search, attention is automatically directed to the most salient object. He showed that when observers are engaged in parallel search for a particular singleton (e.g., a unique circle among diamonds), an irrelevant singleton that is more salient than the target singleton (e.g., a red element among green ones) interferes with search, even though the observers know that they have to ignore the irrelevant singleton. On the basis of such findings, Theeuwes (1992) concluded that parallel search 1 is driven exclusively by bottom-up factors, because knowledge of the target feature failed to override bottom-up interference from the most salient item in the display. Bacon and Egeth (1994) questioned this conclusion. Using a distinction initially suggested by Pashler (1988), they proposed that in Theeuwes's (1992) experiments, two search strategies were available: (1) the singleton detection mode, in which attention is directed to the location with the largest local feature contrast, and (2) the feature search mode, which entails directing attention to items possessing a specific visual feature. Indeed, in Theeuwes's (1992) experiments, the target was defined as being a singleton and as possessing the target attribute. If subjects used the singleton detection mode, both relevant and irrelevant singletons could capture attention, depending on which exhibited the greatest local feature contrast. Bacon and Egeth first conducted a replication of Theeuwes's (1992) study. They presented subjects with displays consisting of colored circles or diamonds arranged on the circumference of an imaginary circle. Line segments varying in orientation appeared inside each item. The subjects were required to determine the orientation of the line segment within a target item. The target item was defined as the unique green diamond among green circles. As was expected, time to find the target shape singleton increased when an irrelevant color singleton (a red circle) was also present. Bacon and Egeth then introduced two manipulations designed to render the singleton detection mode inappropriate for performing the task. They presented either