Task switching

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Abstract

Everyday life requires frequent shifts between cognitive tasks. Research reviewed in this article probes the control processes that reconfigure mental resources for a change of task by requiring subjects to switch frequently among a small set of simple tasks. Subjects' responses are substantially slower and, usually, more error-prone immediately after a task switch. This ‘switch cost’ is reduced, but not eliminated, by an opportunity for preparation. It seems to result from both transient and long-term carry-over of ‘task-set’ activation and inhibition as well as time consumed by task-set reconfiguration processes. Neuroimaging studies of task switching have revealed extra activation in numerous brain regions when subjects prepare to change tasks and when they perform a changed task, but we cannot yet separate ‘controlling’ from ‘controlled’ regions.

Section snippets

Task switching: basic phenomena

In a task-switching experiment, subjects are first pretrained on two or more simple tasks afforded by a set of stimuli (Fig. 1, Fig. 2 provide examples). Each task requires attention to, and classification of, a different element or attribute of the stimulus, or retrieval from memory or computation of a different property of the stimulus. Then, a stimulus is presented on each of a series of trials and the subject performs one of the tasks. There are several methods for telling the subject which

Time taken by control operations

To change tasks, some process or processes of ‘task-set reconfiguration’ (TSR) – a sort of mental ‘gear changing’ – must happen before appropriate task-specific processes can proceed. TSR can include shifting attention between stimulus attributes or elements, or between conceptual criteria, retrieving goal states (what to do) and condition–action rules (how to do it) into procedural working memory (or deleting them), enabling a different response set and adjusting response criteria. TSR may

Issues for further research

Unfortunately, the foregoing consensual account of the preparation effect is not without problems. First, there are studies in which the opportunity for preparation with either full [33] or partial [34] foreknowledge of the upcoming task does not reduce the switch cost, even though it improves overall performance. Second, in task-switching experiments, to know whether TSR is necessary, a subject must discriminate and interpret an external cue (with unpredictable switching), retrieve the

Brain correlates of task switching

At first glance, task switching lends itself well to the subtractive methodology of neuroimaging and electrophysiology. We can compare event-related activation in trials that differ only in whether they do or do not follow another of the same task. Numerous brain regions, usually in medial and lateral regions of the prefrontal cortex, but sometime in parietal lobes, cerebellum and other subcortical regions, are reported to be more active on switch than on non-switch trials. As one example, left

Acknowledgements

Thanks to Hal Pashler, Nachshon Meiran, Ulrich Mayr and an anonymous reviewer for their comments on an earlier draft of this article.

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