Decomposing Externally Cued Task Switching Costs

Decomposing Externally Cued Task Switching Costs Christina Wasylyshyn (christina.wasylyshyn@nrl.navy.mil) Naval Research Laboratory, 4555 Overlook Ave., S.W. Washington, DC 20375 USA Abstract The double-cued task switching procedure has recently been introduced as a new way to measure externally cued switch costs. In the present individual differences study, two hundred fifty young adults completed measures of task switching, inhibition, and long-term memory. A latent variable approach was taken to examine the relationships among these cognitive measures. Decomposing the externally cued task switching costs into a cue switch component and a task switch component indicated that individual differences in these costs could be explained by benefits of repeated cues rather than by changes in tasks. Individual differences in the cue switch component were predicted by long-term memory scores. Keywords: cued task switching; switch costs; individual differences; long-term memory; inhibition Introduction Recent interest in understanding how people shift their mental sets in response to external cues has led to the development of a new method of measuring task switching costs: the double-cued procedure. In traditional, single-cued procedures, cues and tasks are mapped one-to-one, leading to the possibility that the components of cue switching and task switching are confounded. When there is a change in cue, there must be a change in task; when there is no change in cue, it follows that the task will repeat from the previous trial. Both cue switching and task switching then contribute to the overall switch cost in an undifferentiated manner. One way to distinguish between cue switching and task switching is to use a double-cued procedure, that is, to have two cues to indicate each task. This leads to three types of trials: cue repeat, cue switch, and task switch. In cue repeat trials, both the cue and the task repeat; this is a traditional nonswitch trial. In cue switch trials, the cue changes but the task remains the same; this is also classified as a nonswitch trial. In task switch trials, both the cue and the task change. The latency differences between cue switch and cue repeat trials are thought to indicate encoding benefits from repeated cues. The latency differences between task switch and cue switch trials are thought to reflect the act of task switching. In task switching paradigms, responses to the current stimulus trial are slower (and typically less accurate) if the task differs from that completed on the previous trial. Switch costs are thought to indicate how flexibly one can change his/her cognitive configurations, or task sets, to accommodate newly relevant task demands. In order to establish a task set, one must activate relevant task rules (e.g., Mayr & Kliegl, 2003; Rubinstein, Meyer, & Evans, 2001) and minimize interference from competing task sets, possibly through inhibition processes (e.g., see Mayr & Keele, 2000). It has therefore been suggested that one’s task set reflects the interaction of task set inertia from previous trial(s), exogenous task set activation from the stimulus itself, and endogenous control input needed to overcome the other two biases and to reconfigure the cognitive system for a change in task (Aron, Monsell, Sahakian, & Robbins, Mayr and Kliegl (2003) suggest that performance in double-cued procedures can be explained by two processes: cue-based retrieval of task rules from memory and the application of task rules to the target. The retrieval of task rules produces the cue encoding benefit, while the time involved in applying the mapping rules produces the actual switch cost. Retrieval and loading of task rules from long- term memory is necessary for both nonswitch and switch trials. A repetition of the immediately preceding cue leads to a reactivation of the most recent retrieval process (i.e., positive priming); a cue change, however, requires activation of a new (or less recently activated) retrieval process. Logan and Bundesen (2003) offer a similar explanation, but one that assumes there is no endogenous control component. The explicit task cue provides enough information to uniquely indicate a response on each trial. There is no task set reconfiguration process between the cue and the target stimulus. Instead, any switch costs that remain beyond the act of cue switching are the result of encoding benefits on nonswitch trials, or priming from related cues, not task switching (see Logan & Bundesen, 2004, for explanation of the process of mediator repetition, and see Schneider & Logan, 2005, for formal model). Using double-cued procedures, several studies have shown evidence for cue encoding benefits (i.e., responses were faster for cue repeat trials than for cue switch trials). However, after cue encoding effects have been accounted for, the remaining task switch costs have been negligible in some studies (e.g., Logan & Bundesen, 2003, 2004; Monsell & Mizon, 2006 Experiment 1) and substantial in others (e.g., Mayr & Kliegl, 2003; Arrington & Logan, 2005 Experiment 3; Monsell & Mizon, 2006 Experiments 2-6). There are several procedural differences between these studies that may explain some of the differences in results, including type of task cue and frequencies for task switches. Evidence that switch costs result from the processing of the task cue rather than from the switching of tasks has been shown in studies that use salient verbal or pictorial task cues and/or 50% task switch frequency. Evidence for substantial task switch costs over and above any effect of a cue change