Switch costs in task switching are commonly attributed to an executive control process of task-set reconfiguration, particularly in studies involving the explicit task-cuing procedure. The authors propose an alternative account of explicitly cued performance that is based on 2 mechanisms: priming of cue encoding from residual activation of cues in short-term memory and compound cue retrieval of responses from long-term memory. Their short-term priming account explains the repeated cue encoding benefit, switch cost, reduction in switch cost with preparation time, and other effects. The authors develop a mathematical model of their priming account and fit it to data from 3 experiments, demonstrating that a set of basic psychological processes can produce several effects-including putative switch costswithout switching tasks.Keywords: task switching, switch cost, priming, compound cue retrieval A remarkable property of the human cognitive system is its flexibility. As human beings, we can adapt to changing circumstances in a fraction of a second, often using external cues as indicators of change. However, interpreting these cues in the context of the other stimuli available to our senses is not always straightforward, and occasionally it seems as if a modicum of control is required to guide our actions. We are then confronted with a fundamental issue in cognitive psychology: how the mind controls itself. Many complex cognitive processes have been attributed to mechanisms of executive control, such as selecting and modifying task goals, devising strategies to achieve these goals, programming and coordinating the subordinate processes needed to implement the strategies, and monitoring and troubleshooting performance (Logan, 1985(Logan, , 2003Monsell, 1996;Norman & Shallice, 1986). Many situations are thought to engage executive control, with recent research focusing on task switching.In this article, we propose a short-term priming account of explicitly cued task-switching performance that does not require an executive control mechanism to switch tasks. We develop a priming model based on our short-term priming account that is written in the language of Logan's (2002) instance theory of attention and memory, which integrates Bundesen's (1990) theory of visual attention, Logan and Gordon's (2001) theory of executive control, Nosofsky's (1986) generalized context model of categorization, Logan's (1988) instance theory of automaticity, and Nosofsky and Palmeri's (1997) exemplar-based random walk model in a common mathematical framework. These theories account for numerous phenomena in cognitive psychology, and our priming model extends their coverage to the task-switching domain with the modeling of cue encoding and response selection processes. We develop the modeling of cue encoding processes (Arrington & Logan, 2004;Logan & Bundesen, 2003 in greater detail by linking them to repetition and associative priming effects in short-term memory (STM). We integrate mechanisms from models of categorization and memory retrieva...

Multitasking was studied in the stop-change paradigm, in which the response for a primary GO1 task had to be stopped and replaced by a response for a secondary GO2 task on some trials. In 2 experiments, the delay between the stop signal and the change signal was manipulated to determine which task goals (GO1, GO2, or STOP) were involved in performance and to determine whether the goals were activated in series or in parallel. As the delay increased, the probability of responding on stop trials changed very little, but GO2 task reaction times decreased substantially. Such effects are consistent with both a nondeterministic serial model (in which the GO1 goal is replaced by the STOP goal, which is subsequently replaced by the GO2 goal) and a limited-capacity parallel model (in which stopping and GO2 processing occur concurrently) with a capacity-sharing proportion that resembles serial processing.

Hierarchical control of cognitive processes was studied by examining the relationship between sequenceand task-level processing in the performance of explicit, memorized task sequences. In 4 experiments, switch costs in task-switching performance were perturbed by sequence initiation times that varied with sequence complexity, preparation time, and type of sequence transition (repetition or switch). Hierarchical control was inferred from these sequence initiation time effects and the recurrent finding of no switch cost at the first serial position across sequences, the point at which sequence-level processes are likely active in maintaining or instantiating a hierarchical control structure in working memory. These findings resonate with past research on motor programs and serial memory and provide new insights into the concepts of task set and control.

Six experiments were conducted to separate cue encoding from target processing in explicitly cued task switching to determine whether task switch effects could be separated from cue encoding effects and to determine the nature of the representations produced by cue encoding. Subjects were required to respond to the cue, indicating which cue was presented (Experiments 1, 3a, and 4a) or which task was cued (Experiments 2, 3b, and 4b), before performing the cued task on the target. Cue encoding was successfully separated from target processing when the cue response indicated which task was cued but not when it indicated which cue was presented. Task switch effects were found when this separation was successful, suggesting that there are "true" task switch effects independent of cue encoding. Analysis of the conditions required for successful separation suggested that cue encoding results in a semantic categorical representation of the task to be performed rather than verbal or phonological representations of individual cues. Implications for the authors' past modeling of task-switching performance are discussed.

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