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...tly discussed in the literature: the storage of information (which is affected only by the number of task sets) and the manipulation of information (which is primarily affected by task ambiguity; see =-=Baddeley, 1986-=-; Baddeley & Logie, 1999). To enable a comparison between the experiments, we used variants of the same paradigm in both of them. Participants switched between two main tasks: color discrimination and...

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...ts. We find it interesting that this notion of competition management goes perfectly in line with one of the first theories of executive functions delivered by Norman and Shallice (1986; but see also =-=Desimone & Duncan, 1995-=-; Miller & Cohen, 2001), who suggested that top–down control biases the bottom–up competition between task sets or schemata according to intention. How Do Our Results Relate to the Existing Theories i...

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...g that this notion of competition management goes perfectly in line with one of the first theories of executive functions delivered by Norman and Shallice (1986; but see also Desimone & Duncan, 1995; =-=Miller & Cohen, 2001-=-), who suggested that top–down control biases the bottom–up competition between task sets or schemata according to intention. How Do Our Results Relate to the Existing Theories in the Task-Switching L...

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...ed paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De Jong, 1995b, 2000; Goschke, 2000; Mayr & Keele, 2000; Meiran, 1996; =-=Rogers & Monsell, 1995-=-). In most cases, switching tasks is accompanied by a robust performance cost, seen both in reaction time (RT) and error rates, indicating switch cost. A recent conceptualization that incorporates kno...

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...es. However, it is possible that the DLPFC activation in these studies was related to the component of WM that is responsible for manipulation of information and not to mere storage (for support, see =-=Smith & Jonides, 1999-=-). Another possibility is that our results can be taken as a further example for the fact that brain activation and RT are not always completely parallels, a fact that is sometimes overlooked in the c...

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...the original version of this paradigm, performance in blocks of trials in which a task is repeated is compared with performance in blocks in which the participants switch between two different tasks (=-=Allport, Styles, & Hsieh, 1994-=-; Jersild, 1927; Spector & Biederman, 1976). More recent studies have used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed t...

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... used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De Jong, 1995b, 2000; Goschke, 2000; Mayr & Keele, 2000; =-=Meiran, 1996-=-; Rogers & Monsell, 1995). In most cases, switching tasks is accompanied by a robust performance cost, seen both in reaction time (RT) and error rates, indicating switch cost. A recent conceptualizati...

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...erpreted as supporting the WM hypothesis. Specifically, some studies found activation in the dorso-lateral prefrontal cortex (DLPFC) during performance of mixed blocks (e.g., D’Esposito et al., 1995; =-=Koechlin, Basso, Pietrini, Panzer, & Grafman, 1999-=-). The DLPFC is widely believed to be involved in WM processes. However, it is possible that the DLPFC activation in these studies was related to the component of WM that is responsible for manipulati...

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...epetition. In contrast, other theories emphasize the role of preparation in both trial types—switch and repetition. These theories focus on processes like task decision (e.g., Dreisbach et al., 2002; =-=Rubinstein et al., 2001-=-; Sohn & Anderson, 2001). By simultaneously exploring three trial types—switch, repetition, and single task—we demonstrated that a large part of the preparation control process that occurs in mixed-ta...

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...adigm, performance in blocks of trials in which a task is repeated is compared with performance in blocks in which the participants switch between two different tasks (Allport, Styles, & Hsieh, 1994; =-=Jersild, 1927-=-; Spector & Biederman, 1976). More recent studies have used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De ...

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... the literature: the storage of information (which is affected only by the number of task sets) and the manipulation of information (which is primarily affected by task ambiguity; see Baddeley, 1986; =-=Baddeley & Logie, 1999-=-). To enable a comparison between the experiments, we used variants of the same paradigm in both of them. Participants switched between two main tasks: color discrimination and shape discrimination. T...

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...ixing cost and switching cost might reflect somewhat different control processes. Accordingly, mixing cost but not switching cost may reflect global control mechanisms or sustained control processes (=-=Braver, Reynolds, & Donaldson, 2003-=-; Koch, Prinz, & Allport, 2005; Kray & Lindenberger, 2000), whereas switching cost appears to be exclusively related to specific or transient control mechanisms (Braver et al., 2003; Logan & Bundesen,...

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... switching cost, and the difference between repetition trials (in mixed-tasks blocks) and single-task trials (in pure blocks) is termed mixing cost (Fagot, 1994; Kray & Lindenberger, 2000; Los, 1996; =-=Meiran, Chorev, & Sapir, 2000-=-). These two cost components compose the alternation cost—the difference in performance between switch trials (in mixed blocks) and single-task trials (in pure blocks). While switching cost has receiv...

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... recent studies have used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De Jong, 1995b, 2000; Goschke, 2000; =-=Mayr & Keele, 2000-=-; Meiran, 1996; Rogers & Monsell, 1995). In most cases, switching tasks is accompanied by a robust performance cost, seen both in reaction time (RT) and error rates, indicating switch cost. A recent c...

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... other task, then this condition is a bivalent one. However, if the value never appeared in the other task, then this condition is not bivalent because the stimulus could not be bound with that task (=-=Waszak et al., 2003-=-), and it could not prime a competing response. In our experiment, all target stimuli contained two dimensions (color and shape), each relevant for only one of the tasks. In the shape task, participan...

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...& Donaldson, 2003; Koch, Prinz, & Allport, 2005; Kray & Lindenberger, 2000), whereas switching cost appears to be exclusively related to specific or transient control mechanisms (Braver et al., 2003; =-=Logan & Bundesen, 2003-=-; Mayr & Kliegl, 2003). Orit Rubin and Nachshon Meiran, Department of Behavioral Sciences, Ben-Gurion University of Negev, Beer-Sheva, Israel. This project was supported by German–Israeli Foundation f...

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...ials (in mixed-tasks blocks) is termed switching cost, and the difference between repetition trials (in mixed-tasks blocks) and single-task trials (in pure blocks) is termed mixing cost (Fagot, 1994; =-=Kray & Lindenberger, 2000-=-; Los, 1996; Meiran, Chorev, & Sapir, 2000). These two cost components compose the alternation cost—the difference in performance between switch trials (in mixed blocks) and single-task trials (in pur...

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...is the following behavioral double dissociation. Kray and Lindenberger (2000) found that whereas switching cost was relatively unaffected by old age, mixing cost was strongly affected by it (see also =-=Mayr, 2001-=-). However, Capeda, Capeda, and Kramer (2000) showed that children suffering from attention-deficit/hyperactivity disorder exhibit disproportionately large switching cost but normal mixing cost. In li...

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...uld predict that preparation (CTI) would have little or no effect on mixing cost. In contrast, theories of goal setting suggest that this process is common to switch and repetition trials (especially =-=Sohn & Anderson, 2001-=-). In this case, one would predict a similar preparation effect on mixing cost and switching cost. There are actually different findings that might support each of the predictions mentioned above. In ...

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... Prinz, & Allport, 2005; Kray & Lindenberger, 2000), whereas switching cost appears to be exclusively related to specific or transient control mechanisms (Braver et al., 2003; Logan & Bundesen, 2003; =-=Mayr & Kliegl, 2003-=-). Orit Rubin and Nachshon Meiran, Department of Behavioral Sciences, Ben-Gurion University of Negev, Beer-Sheva, Israel. This project was supported by German–Israeli Foundation for Scientific Researc...

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...nce in blocks of trials in which a task is repeated is compared with performance in blocks in which the participants switch between two different tasks (Allport, Styles, & Hsieh, 1994; Jersild, 1927; =-=Spector & Biederman, 1976-=-). More recent studies have used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De Jong, 1995b, 2000; Goschke,...

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...) is termed switching cost, and the difference between repetition trials (in mixed-tasks blocks) and single-task trials (in pure blocks) is termed mixing cost (Fagot, 1994; Kray & Lindenberger, 2000; =-=Los, 1996-=-; Meiran, Chorev, & Sapir, 2000). These two cost components compose the alternation cost—the difference in performance between switch trials (in mixed blocks) and single-task trials (in pure blocks). ...

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... research on task switching, there is a robust finding that switch cost is reduced (and sometimes eliminated) when participants have sufficient time to prepare for a task switch (e.g., De Jong, 2000; =-=Gopher, Armony, & Greenshpan, 2000-=-; Meiran, 1996; Meiran et al., 2000; Rogers & Monsell, 1995). Some authors interpreted this finding as evidence for the involvement of internal control in the process of task switching and proposed va...

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.... For example, it was found that explicit probabilistic task information provided to the participants in advance affects switch and repetition trials similarly (Ruthruff, Remington, & Johnston, 2001; =-=Sohn & Carlson, 2000-=-). Additionally, Meiran, Hommel, Bibi, and Lev (2002) found that the number of task alternatives has equal effect on switch and repetition trials. Although our interpretation of these findings as bein...

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...ing cost and not that of switching cost. For example, it was found that explicit probabilistic task information provided to the participants in advance affects switch and repetition trials similarly (=-=Ruthruff, Remington, & Johnston, 2001-=-; Sohn & Carlson, 2000). Additionally, Meiran, Hommel, Bibi, and Lev (2002) found that the number of task alternatives has equal effect on switch and repetition trials. Although our interpretation of ...

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...r should be considered: When using bivalent stimuli, in addition to the potential bottom–up interference, participants also need to filter out irrelevant stimulus variation (in the sense discussed by =-=Garner, 1970-=-, 1974). Specifically, Garner showed that performance in a single-task condition is impaired when stimuli contain an irrelevant attribute that varies randomly across trials. On the basis of these resu...

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...e two block types: working memory (WM) demands, division of attention between perceptual dimensions, degree of arousal and effort, response criterion, and so on (Meiran, 1996; Rogers & Monsell, 1995; =-=Ward, 1982-=-). However, recently, it has become increasingly evident that mixing cost may be at least as important as an indicator of executive control as switching cost. This is because mixing cost seems to capt...

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...robabilistic ratios, different task sequences, etc.). It has been implicated before that task uncertainty is related to mixing cost because it affects switch and repetition trials to the same degree (=-=Dreisbach, Haider, & Kluwe, 2002-=-; Meiran et al., 2002; Ruthruff et al., 2001). We therefore suggest that for a given degree of task uncertainty in the mixed blocks (which, in our experiments, was 50%), univalent stimuli reduce task ...

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...repetition trials (in mixed-tasks blocks) is termed switching cost, and the difference between repetition trials (in mixed-tasks blocks) and single-task trials (in pure blocks) is termed mixing cost (=-=Fagot, 1994-=-; Kray & Lindenberger, 2000; Los, 1996; Meiran, Chorev, & Sapir, 2000). These two cost components compose the alternation cost—the difference in performance between switch trials (in mixed blocks) and...

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...eflect somewhat different control processes. Accordingly, mixing cost but not switching cost may reflect global control mechanisms or sustained control processes (Braver, Reynolds, & Donaldson, 2003; =-=Koch, Prinz, & Allport, 2005-=-; Kray & Lindenberger, 2000), whereas switching cost appears to be exclusively related to specific or transient control mechanisms (Braver et al., 2003; Logan & Bundesen, 2003; Mayr & Kliegl, 2003). O...

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...he conditions was as follows: single-task 3 mixed-tasks 3 single-task. In the mixed-tasks condition, the tasks were ordered randomly and were cued by instructional cues (De Jong, 1995a; Meiran, 1996; =-=Shaffer, 1965-=-). We manipulated task preparation time by varying the cue target interval (CTI) using two randomly determined CTIs: 100 ms (affording little or no preparation) and 1,000 ms (long preparation time). I...

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...lusion is in line with that of a number of recent articles, all showing that preparation overcomes bottom–up influences (Koch & Allport, in press; Meiran & Daichman, in press; Rubin & Koch, in press; =-=Yeung & Monsell, 2003-=-). In several previous studies, a significant reduction in switching cost was found when the stimuli were univalent (Allport et al., 1994; Meiran, 2000; Rogers & Monsell, 1995; Spector & Biederman, 19...

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...k sequences, etc.). It has been implicated before that task uncertainty is related to mixing cost because it affects switch and repetition trials to the same degree (Dreisbach, Haider, & Kluwe, 2002; =-=Meiran et al., 2002-=-; Ruthruff et al., 2001). We therefore suggest that for a given degree of task uncertainty in the mixed blocks (which, in our experiments, was 50%), univalent stimuli reduce task uncertainty (because ...

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...an, 1976). More recent studies have used a modified paradigm that makes it possible to contrast task-switch trials and task-repetition trials within blocks of mixed tasks (e.g., De Jong, 1995b, 2000; =-=Goschke, 2000-=-; Mayr & Keele, 2000; Meiran, 1996; Rogers & Monsell, 1995). In most cases, switching tasks is accompanied by a robust performance cost, seen both in reaction time (RT) and error rates, indicating swi...

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...ated. This result was later replicated by Spector and Biederman (1976) and by Allport et al. (1994, Experiment 4). An even stronger result was recently found by Waszak, Hommel, and Allport (2003; cf. =-=Allport & Wylie, 2000-=-). These authors showed that a single trial was sufficient to link a specific stimulus (picture–word combination) with a specific task set (picture naming) and that later encounters with the same stim...

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...cy between RT and imaging results might be an indication that the cognitive system can compensate for the extra WM load, without a cost in response time (for direct evidence for this discrepancy, see =-=Rubin, Brass, Koch, Ruge, & Meiran, 2004-=-). The evidence in favor of the task-ambiguity hypothesis emphasizes the important role of competition management in task switching and in executive control. Specifically, it shows that, in the task-s...