Academic journal article Memory & Cognition

Cue-Based Preparation and Stimulus-Based Priming of Tasks in Task Switching

Academic journal article Memory & Cognition

Cue-Based Preparation and Stimulus-Based Priming of Tasks in Task Switching

Article excerpt

In this study, we investigated the interaction of three different sources of task activation in precued task switching. We distinguished (1) intentional, cue-based task activation from two other, involuntary sources of activation: (2) persisting activation from the preceding task and (3) stimulus-based task activation elicited by the task stimulus itself. We assumed that cue-based task activation increases as a function of cue-stimulus interval (CSI) and that task activation from the preceding trial decays as a function of response-stimulus interval. Stimulus-based task activation is thought to be due to involuntary retrieval of stimulus-associated tasks. We manipulated stimulus-based task activation by mapping each of the stimuli consistently to only one or the other of the two tasks. After practice, we reversed this mapping in order to test the effects of item-specific stimulus-task association. The mapping reversal resulted in increased reaction times and increased task shift costs. These stimulus-based priming effects were markedly reduced with a long CSI, relative to a short CSI, suggesting that stimulus-based priming shows up in performance principally when competition between tasks is high and that cue-based task activation reduces task competition. In contrast, lengthening the response-cue interval (decay time) reduced shift costs but did not reduce the stimulus-based priming effect. The data are consistent with separable stimulus-related and response-related components of task activation. Further theoretical implications of these findings are discussed.

Action control is shaped by numerous interacting factors. These are sometimes partitioned into internal factors (e.g., current intentions, goals) and external factors, such as the tendency of situations (or stimuli) to prime actions associated with them. Recently, the interaction of these factors has been studied using the task-switching paradigm. In task switching, performance in repeated tasks is compared with performance when there is a requirement to switch between different tasks. Typically, reaction time (RT) and error rate are greater on task switch than on repetition trials. These shift costs appear in many studies, in which a variety of tasks and paradigms have been used (see, e.g., Monsell, 2003, for a review).

Interactive Processes in Task Switching

It has been suggested that shift costs in task switching are related to a process of reconfiguring the task set (see, e.g., Goschke, 2000; Meiran, 1996; Rogers & Monsell, 1995). The main empirical support for this suggestion has come from studies exploring the effects of the time available for task preparation. For instance, Rogers and Monsell varied the temporal interval from the preceding response to the onset of the next task stimulus (response-stimulus interval, RSI) in predictable, instructed task sequences (e.g., AABBAABB etc.) and found that longer RSIs were associated with reduced shift costs. They took this reduction of shift costs with long RSIs as evidence for advance preparation for the upcoming task.

However, lengthening the RSI provides time not only for active preparation of the upcoming task, but also for changes relating to the preceding task, such as the decay of activation relevant to that task (Meiran, 1996). Both of these processes could, in principle, affect the size of shift costs. To dissociate the influence of preparation and decay, Meiran ( 1996) used explicit instructional cues in a random task sequence.

Decay of task activation. The cuing paradigm allows the potential effects of decay time on shift costs to be examined, independently of active preparation. To do so, the cue-to-stimulus interval (CSI), which represents the time available for cue encoding and task preparation, is held constant while the prior response-to-cue interval (RCI) is varied. In fact, it has been found that shift costs decrease with increasing RCI (see, e.g., Koch, 2001 ; Meiran, Chorev, & Sapir, 2000), in accord with the idea that task activation decays over time following execution of a response. …

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