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People have difficulty performing two tasks at once. For example, maintaining items in working memory (WM) makes people more distractible. However, different types of WM load may have different effects on attentional selection depending on whether WM load overlaps with mechanisms involved in target or distractor processing. Three experiments examined the effect of concurrent WM load on Stroop tasks, a widely used measure of executive control and inhibition. Stroop interference increased when the type of WM load overlapped with the type of information required for the target task (experiment 1). In striking contrast, Stroop interference decreased when the type of WM load overlapped with distractor processing (experiment 2). Experiment 3 replicated these results in a different Stroop task. Thus, concurrent WM load does not always impair executive control; performance depends on how contents of WM and task-relevant information overlap. The results highlight how dissociable components of WM interact with perception and executive control.attention ͉ executive control ͉ Stroop interference ͉ cognitive load I n the face of distracting information, attentional mechanisms help to prioritize and select information that is most relevant for current behavioral goals. However, selection is not perfect. Failure to inhibit unnecessary information (i.e., distractors) causes people to slow down and make mistakes. The Stroop interference effect is one of the most straightforward examples in which uninhibited distractor processing interferes with target processing. People are significantly slower to name the ink color of a colored word when the meaning of the colored word is incongruent with the ink color of the word (e.g., ''red'' in blue ink) as opposed to when it is congruent (1). Stroop and other researchers (2-4) explained this interference with the automaticity hypothesis: Word reading is more automatic than color naming. According to this account, the more arduous, attentiondemanding process of color naming is hampered by the more automatic process of word reading (5). However, contrary to predictions from the word automaticity account, Stroop interference can be observed from color distractors in revised versions of the task (5, 6). Thus, a more general explanation of the Stroop effect simply focuses on the inability to ignore distractor information, which may vary in salience depending on the task. Stroop interference occurs whenever observers fail to inhibit distractor information that is incongruent with the target task and response.An important goal of attention research is to understand the conditions that promote selection and reduce distractor interference. Given such robust interference in the Stroop task, are there manipulations to reduce interference? Stroop interference should be reduced if people's attention can be diverted away from the conflicting information. Indeed, an innovative study by Kahneman and Chajczyk (7) successfully reduced the Stroop effect by presenting additional distractors in the display, wh...

In two experiments using spatial probes, we measured the temporal and spatial interactions between top-down control of attention and bottom-up interference from a salient distractor in visual search. The subjects searched for a square among circles, ignoring color. Probe response times showed that a color singleton distractor could draw attention to its location in the early stage of visual processing (before a 100-msec stimulus onset asynchrony [SOA]), but only when the color singleton distractor was located far from the target. Apparently the bottom-up activation of the singleton distractor's location is affected early on by local interactions with nearby stimulus locations. Moreover, probe results showed that a singleton distractor did not receive attention after extended practice. These results suggest that top-down control of attention is possible at an early stage of visual processing. In the long-SOA condition (150-msec SOA), spatial attention selected the target location over distractor locations, and this tendency occurred with or without extended practice.

There has been a controversy on whether working memory can guide attentional selection. Some researchers have reported that the contents of working memory guide attention automatically in visual search (D. Soto, D. Heinke, G. W. Humphreys, & M. J. Blanco, 2005). On the other hand, G.F. Woodman and S. J. Luck (2007) reported that they could not find any evidence of attentional capture by working memory. In the present study, we tried to find an integrative explanation for the different sets of results. We report evidence for attentional capture by working memory, but this effect was eliminated when search was perceptually demanding or the onset of the search was delayed long enough for cognitive control of search to be implemented under particular conditions. We suggest that perceptual difficulty and the time course of cognitive control as important factors that determine when information in working memory influences attention.

The allocation of spatial attention was measured with detection probes at different locations. Response times were faster for probes at the location of the target digit, which subjects reported, than at the locations of distractor digits, which they ignored. Probes at blank locations between stimuli produced fast responses, indicating that selection was accomplished by inhibiting distractor locations but not other areas. Unlike earlier studies using location cuing with simpler stimuli, these experiments showed no attentional differences across horizontal or vertical midlines. Attention varied little with distance from the target, although blank locations far from the target were somewhat less attended than were those near the target, and attention was only slightly affected by expectations for stimulus location. This task demonstrates a form of feature-driven spatial attention, in which locations with objects lacking target features are inhibited.In the course of visual processing, some regions of the visual field receive more thorough processing than do others. Presumably, when multiple objects appear simultaneously, information from each object can interfere with the processing ofthe others, and this selection process, or spatial attention, limits this interference by favoring the locations of some objects over others. One early demonstration of spatial attention came from experiments using spatial cuing. They established that the presentation of a cue indicating a particular location in the visual field could draw attention to that location, so that subjects responded to a subsequent stimulus at that location more quickly than to a stimulus at some other, uncued location (Eriksen & Hoffman, 1974;Posner, Nissen, & Ogden, 1978;Posner, Snyder, & Davidson, 1980).These cuing experiments stimulated a series of studies that attempted to produce more complete maps of the allocation ofspatial attention across the visual field. In these later studies, the relative positions of cue and test stimulus were systematically varied. For instance, Hughes and M.-S. Kim is currently at the Department of Psychology, Yonsei University, Seoul, 120-749, Korea. This work was supported in part by Grant P30-EY08126 from NEI awarded to the Vanderbilt Vision Research Center. Data from Experiments I and 2 were presented at the meeting of ARVO, May 1995, in Ft. Lauderdale, FL. Thanks to Ben Phillips, Vik Barad, and Tarsicio Duran for help in conducting experiments, and to Volker Thoma, Matthew Heisler, Art Kramer, MaryLou Cheal, Carolyn Backer Cave, Roger Remington, Lynn Zimba, and an anonymous reviewer for comments. Thanks also to Paul Russell and Tom Birkett for providing software to control the Macintosh response keys and a design for the response key interface, and to Lonny Shimp for building the response keys. Correspondence should be addressed to K. R. Cave, Department of Psychology, Vanderbilt University, 301 Wilson Hall, Nashville, TN 37240 (e-mail: kyk.r.cave@vanderbilt.edu). Zimba (1985 showed that responses were uniformly fast w...

Load theory predicts that concurrent working memory load impairs selective attention and increases distractor interference (N. Lavie, A. Hirst, J. W. de Fockert, & E. Viding). Here, the authors present new evidence that the type of concurrent working memory load determines whether load impairs selective attention or not. Working memory load was paired with a same/different matching task that required focusing on targets while ignoring distractors. When working memory items shared the same limited-capacity processing mechanisms with targets in the matching task, distractor interference increased. However, when working memory items shared processing with distractors in the matching task, distractor interference decreased, facilitating target selection. A specialized load account is proposed to describe the dissociable effects of working memory load on selective processing depending on whether the load overlaps with targets or with distractors.

Working memory (WM) has been thought to include not only short-term memory stores but also executive processes that operate on the contents of memory. The present study examined the involvement of WM in search using a dual-task paradigm in which participants performed visual search while manipulating or simply maintaining information held in WM. Experiments 1a and 2a involved executive WM tasks that required counting backward from a target digit and sorting a string of letters alphabetically, respectively. In both experiments, the search slopes in the dual-task condition were significantly steeper than those in a search-alone condition, indicating that performing the WM manipulation tasks influenced the efficiency of visual search. In contrast, when information was simply maintained in WM (Experiments 1b and 2b), search slopes did not differ between the single- and dual-task conditions. These results suggest that WM resources related to executive functions may be required in visual search.

Theories of attention can be separated into those that select by location, and those that select by location-invariant representation. Experiments demonstrating stronger interference or facilitation from distractors grouped by nonspatial features with the target than ungrouped distractors have been considered as evidence for the selection of location-invariant representations. However, few studies have measured spatial attention directly at the locations of the grouped or ungrouped objects. In these experiments subjects responded to spatial probes (dots) while also identifying a cued target letter among distractors. Probe responses were faster for distractor locations with the target color than for those with the nontarget color, implying that target-color locations receive more attention. This pattern of spatial attention may explain why target-color distractors interfere more with target identification than nontarget-color distractors. These results suggest that although attention can be directed by nonspatial properties such as grouping by color or organization of the scene into objects, selection may ultimately be based on location.