Academic journal article Canadian Journal of Experimental Psychology

The Influence of Cue-Task Association and Location on Switch Cost and Alternating-Switch Cost

Academic journal article Canadian Journal of Experimental Psychology

The Influence of Cue-Task Association and Location on Switch Cost and Alternating-Switch Cost

Article excerpt

Abstract Task-switching performance is strongly influenced by whether the imperative stimulus uniquely specifies which task to perform: Switch cost is substantial with bivalent stimuli but is greatly reduced with univalent stimuli, suggesting that available contextual information influences processing in task-switching situations. The present study examined whether task-relevant information provided by task cues influences the magnitude of switch cost in a parallel manner. Cues presented 500 ms prior to a trivalent stimulus indicated which of three tasks to perform. These cues either had a preexisting association with the to-be-performed task (verbal cues), or a recently learned association with the task (spatial and shape cues). The results paralleled the effects of stimulus bivalence: substantial switch cost with recently learned cue-task associations and greatly reduced switch cost with preexisting cue-task associations. This suggests that both stimulus-based and cuebased information can activate the relevant task set, possibly providing external support to endogenous control processes. Alternating-switch cost, a greater cost for switching back to a recently abandoned task, was also observed with both preexisting and recently learned cue-task associations, but only when all tasks were presented in a consistent spatial location. When spatial location was used to cue the to-be-performed tasks, no alternating-switch cost was observed, suggesting that different processes may be involved when tasks are uniquely located in space. Specification of the nature of these processes may prove to be complex, as post-hoc inspection of the data suggested that for the spatial cue condition, the alternating-switch cost may oscillate between cost and benefit, depending on the relevant task.

Task switching is currently attracting considerable research attention, largely because it provides a controlled method for the study of executive control processes (Meiran, 1996; Rogers & Monsell, 1995, but see Allport & Wylie, 1999) and the need for executive control is not eliminated with modest amounts of practice (Rabbits, 1997). The logic of the method is to compare performance on Task A following Task A to performance on Task A following Task B. Response is consistently slower for the switch situation, an effect known as "switch cost."

Research has isolated several factors that influence the magnitude of switch cost, including the presence of contextual cues as to the currently appropriate task set: When Tasks A and B are unambiguously associated with different stimuli, costs to switch between the tasks are much smaller than when one stimulus type is associated with both tasks (Allport, Styles, & Hsieh, 1994; Poulsen & Segalowitz, 1999; Rogers & Monsell, 1995). For example, Rogers and Monsell (1995) had participants categorize letters as vowel/consonant and digits as odd/even. When the stimulus display included both a letter and a digit character (i.e., bivalent stimuli), switch cost was 289 ms, as compared with 161 ms for stimulus displays with a nonalphanumeric (e.g., #) distractor (i.e., univalent stimuli; Rogers & Monsell, 1995, Experiment 4). This is likely because bivalent stimuli are associated with both task sets, and thus encoding such stimuli would activate competing stimulusresponse associations in a bottom-up fashion (Allport & Wylie, 1999). Greater switch cost with bivalent stimuli would thus reflect the time necessary to select between competing processing options, which presumably requires executive control. Conversely, univalent stimuli would activate only the relevant stimulus-response association, resulting in much less cost to switch between tasks because the need to recruit executive processes to resolve competition would be reduced. This effect of stimulus ambiguity on switch cost has been replicated in a number of studies (e.g., Allport et al., 1994; Rogers & Monsell, 1995; Poulsen & Segalowitz, 1999). …

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