Components of Switching Intentional Set

Components of Switching Intentional Set Matthew F. S. Rushworth, R. E. Passingham, and A. C. Nobre Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/14/8/1139/1757675/089892902760807159.pdf by guest on 18 May 2021 Abstract & Despite the intuition that we can shift cognitive set on required shifts of intentional set; subjects selected between instruction, some behavioral studies have suggested that set responses according to one of two conflicting intentional sets. shifting might only be accomplished once we engage in The results demonstrated the existence of more than one performance of the new task. It is possible that set switching constituent process. Some of the processes were linked to the consists of more than one component cognitive process and initiation and reconfiguration of the set prior to actual that the component processes might segregated in time. We performance of the new task. Other processes were time recorded event-related potentials (ERPs) during two set- locked to performance of new task items. Set initiation started switching tasks to test whether different component processes with modulation of medial frontal ERPs and was followed by were responsible for (i) set initiation and reconfiguration modulation over parietal electrodes. Implementation of when presented with the instruction to switch, and (ii) the intentional set was associated with modulation of response- implementation of the new set once subjects engaged in related ERPs. & performing the new task. The response switching (RS) task INTRODUCTION Styles, and Hsieh (1994) have argued that switching The neural mechanisms for directing selective attention costs that are protracted over several trials of the new to stimuli or locations are increasingly well understood task indicate that active task set reconfiguration did not (Colby & Goldberg, 1999; Corbetta & Shulman, 1999; occur. The debate is important because if task switching Desimone, 1999; Hillyard, Vogel, & Luck, 1999). How- costs are just the consequence of passive dissipation ever, in most situations people must also be able to then the widely held assumption (e.g., Kimberg et al., switch attention from one set of stimuli to another, or to 2000) that task switching is a useful index of executive switch how they respond to stimuli. Such switching is control may be incorrect. usually referred to as task or set switching. The study of The analysis of RT changes across behavioral para- set switching has attracted interest because it is thought digms has demonstrated that set-switching does com- to be a clearly defined, tractable, and central aspect of prise separable component processes (Meiran et al., the executive control of cognitive processes. Indeed, 2000; Monsell, Yeung, & Azuma, 2000; Wylie & some authors have referred to it as an ‘‘operational Allport, 2000; De Jong, 2000; Meiran, 1996; Rogers & measure of executive control’’ (Kimberg, Aguirre, & Monsell, 1995; Allport et al., 1994; Allport & Wylie, D’Esposito, 2000). Since at least the time of Jersild 1999). A prospective process of ‘‘task-set reconfigura- (1927) an important tradition of work has used reaction tion’’ (Rogers & Monsell, 1995), prior to task perform- times (RTs) to study set switching; subjects perform a ance, has been invoked because the cost of switching, task more slowly after previously performing a different as measured by RT increase, is lower when subjects task (‘‘task-switching cost’’). have greater opportunity for advanced preparation. An The constituent components of task switching are alternative account, however, proposes switching costs currently debated (Meiran, Chorev, & Sapir, 2000; Wylie are the consequence of the persisting activation of & Allport, 2000; Rogers & Monsell, 1995). Central to the processes related to the first task ( Wylie & Allport, debate is the degree to which task-switching costs are 2000; Allport et al., 1994; Allport & Wylie, 1999). due to prospective, active reconfiguration for the new According to this theory, advance preparation reduces task prior to its performance or passive dissipation of switching costs because it allows time for interfering the old task set. A related issue concerns the degree to ‘‘task set inertia’’ from the previous task to dissipate. By which switching costs continue beyond the first trial of altering the time when an instructional cue was pre- the new task; Wylie and Allport (2000) and Allport, sented within a preparation interval, Meiran et al. (2000) provided evidence that both passive dissipation of the old task set and active reconfiguration for the University of Oxford new task set occur. Notwithstanding this debate, most D 2002 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 14:8, pp. 1139–1150 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/089892902760807159 by guest on 28 September 2021 Despite the success of RT-based analyses of set RS task switching complementary neuroimaging experiments may be informative. For example, Meiran et al. (2000, pp. 250–251) point out that it can be difficult to decide if small switching costs indicate a lack of engagement of left task-switching control processes or, the opposite, very efficient engagement of task-switching processes. In the following experiments we have used event-related potential (ERP) recording to measure activity first when Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/14/8/1139/1757675/089892902760807159.pdf by guest on 18 May 2021 stay a cue instructed set switches and subsequently when subjects began performing the task in a new way. We have referred to the two epochs as ‘‘set initiation’’ and right ‘‘set implementation’’ periods. If active task set reconfiguration occurs then it should be detected in the first period, the set initiation period. Processes related to left residual switching costs should be recorded in the second period, the set implementation period. Intentional set switching requires subjects to change right the rules by which they select between motor responses while attentional set switching requires subjects to change the rules by which they select between sensory stimuli. Although there has been little attempt to distinguish such paradigms, both types of set switch- switch ing are possible (Pollman, 2001; Rushworth, Paus, & Sipila, 2001; Rushworth, Hadland, Paus, & Sipila, 2002; Dove, Pollman, Schubert, Wiggins, & von Cramon, right 2000). The present experiments required subjects to switch between intentional sets and used what we have previously referred to as a response switching (RS) left paradigm (Figure 1). The task was divided into blocks of 8 to 17 trials, and on each trial subjects were presented with either a rectangle- or triangle-shaped stimulus. Subjects started Figure 1. Response switching (RS) paradigm. In the RS paradigm by responding to rectangles and triangles with right- and subjects were presented with a series of task items. The items were left-hand responses, respectively (Figure 1), but on always either rectangles or triangles. Subjects alternated between two other blocks the stimulus-response translation changed; conflicting intentional sets: either triangle stimulus-left hand response and rectangle stimulus-right hand response or triangle stimulus-right hand response and rectangle stimulus-left hand response. Every 8–17 trials a white cue shape instructed subjects either to stay with the current selection rule or to switch to using a selection rule based on stay switch the other stimulus dimension. Stay or switch cues were differentiated cue cue by a ‘‘+’’ or ‘‘Â’’ at their center. The meaning of the ‘‘+’’ and ‘‘Â’’ was counterbalanced across subjects. In the example shown, the ‘‘+’’ and items . items . the ‘‘Â’’ mean stay and switch, respectively. The figure shows an example where the subject started by selecting left-hand and right-hand responses to the triangle and rectangle, respectively, and then later switches to the selecting right-hand and left-hand responses to the triangle and rectangle, respectively. stay switch block block authorities agree that ‘‘residual’’ RT costs can be ob- Figure 2. The RS task involved a succession of blocks of 8–17 items served despite advance preparation. The nature of the interspersed with cues instructing subjects to stay with the current residual component of task switching, however, is not selection rule or to switch selection rule. The ERP analyses were based clear (Meiran et al., 2000). It may be a consequence of on two time periods. (1) The cue ERP period was the 1400 msec that a second executive control process that only occurs followed the presentation of stay and switch cues (indicated by gray after onset of the first stimulus in the new task or it rectangles). The ERPs that followed switch cues were compared with those following stay cues. (2) The item ERP period was the 1000-msec may be a reflection of interference from the old task period that followed the presentation of items (indicated by small gray (Meiran et al., 2000; Monsell et al., 2000; Wylie & rectangles). The brain activity after the first two items following switch Allport, 2000). and stay cues was compared. 1140 Journal of Cognitive Neuroscience Volume 14, Number 8 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/089892902760807159 by guest on 28 September 2021 left- and right-hand responses were made to the rectangle and triangle, respectively. Blocks of trials were separated by presentation of either ‘‘switch’’ or ‘‘stay’’ cues. Switch cues instructed subjects to switch the intentional set guiding response selection. Stay cues cue period instructed subjects to continue with the current intentional set. As explained above, the ERP analysis centered on two 2µV epochs, the set initiation and the set implementation Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/14/8/1139/1757675/089892902760807159.pdf by guest on 18 May 2021 periods (Figure 2). The set initiation period analysis involved the comparison of the ERPs that followed the switch and stay cues. The set implementation period analysis involved the comparison of ERPs that followed the task items subsequent to either switch or stay cues.

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