The many faces of preparatory control in task switching: Reviewing a decade of fMRI research

Abstract

A large body of behavioural research has used the cued task-switching paradigm to characterize the nature of trial-by-trial preparatory adjustments that enable fluent task implementation when demands on cognitive flexibility are high. This work reviews the growing number of fMRI studies on the same topic, mostly focusing on the central hypothesis that preparatory adjustments should be indicated by enhanced prefrontal and parietal BOLD activation in task switch when compared with task repeat trials under conditions that enable advance task preparation. The evaluation of this straight-forward hypothesis reveals surprisingly heterogeneous results regarding both the precise localization and the very existence of switch-related preparatory activation. Explanations for these inconsistencies are considered on two levels. First, we discuss methodological issues regarding (i) the possible impact of different fMRI-specific experimental design modifications and (ii) statistical uncertainty in the context of massively multivariate imaging data. Second, we discuss explanations related to the multidimensional nature of task preparation itself. Specifically, the precise localization and the size of switch-related preparatory activation might depend on the differential interplay of hierarchical control via abstract task goals and attentional versus action-directed preparatory processes. We argue that different preparatory modes can be adopted relying either on advance goal activation alone or on the advance resolution of competition within action sets or attentional sets. Importantly, while either mode can result in a reduction of behavioral switch cost, only the latter two are supposed to be associated with enhanced switch versus repeat BOLD activation in prepared trial conditions.

Switch-Related and General Preparation Processes in Task-Switching: Evidence from Multivariate Pattern Classification of EEG Data

“…All data were current-source-density (CSD) transformed before analyses (Kayser and Tenke, 2006). CSD is a high-pass spatial filter that minimizes volume conduction by removing large spatially broad (and therefore likely volume conducted) activities (Srinivasan et al, 1996(Srinivasan et al, , 2007, also called scalp Laplacian). This sharpening filter limits spatial autocorrelation as well as the spread of any residual oculomotor artifacts, making the data more amenable to spatial multivariate pattern analysis based on local topographical features.…”

“…However, while ERP studies consistently report differential activation for switch relative to repeat trials (Karayanidis et al, 2010) many fMRI studies do not find any differential switch activation (Ruge et al, 2011), leaving unanswered the question of whether a switch-related preparation process can be dissociated from more general preparation processes. We used a paradigm that differentiated between these processes by including some cues that specified with certainty that the task would change (switch-to, switch-away) and some cues that specified with certainty what the upcoming task would be (repeat, switch-to).…”

“…Within the cue-to-target interval, event-related potentials (ERPs) show an early centroparietal positivity that is greater for switch than repeat trials (Kieffaber and Hetrick, 2005;Nicholson et al, 2005) and a frontocentral pretarget negativity that is similar for both trial types (Nicholson et al, 2005;Jamadar et al, 2010). Consistent with a switch-related preparation process, the early cue-locked positivity is elicited only by cues that predict a definite change in task, regardless of whether they identify the upcoming task (Karayanidis et al, 2009).…”

“…We hypothesized that (1) a switch-related preparation process would be evidenced by switch-away trials being misclassified as switch-to trials in the latency range of the cue-locked positivity and (2) a task readiness process would be evidenced by repeat trials being misclassified as switch-to trials in the latency range of the pretarget negativity. These effects were expected to be represented in the alpha band (Serrien et al, 2004;Sauseng et al, 2006) and at frontal and parietal areas, respectively (Ruge et al, 2011).…”

Selecting and inhibiting responses: Common cognitive and neural substrates?

“…However, one potential alternative explanation for such co-activation of a common executive control network (Duncan & Owen, 2000) might stem from studies that underestimate the important role of proactive (preparatory) and reactive (online) control functions ) because these models are often based on fMRI designs that do not have the temporal resolution to disentangle target-related and preparation-related BOLD activation (see Ruge, Jamadar, Zimmermann, & Karayanidis, 2013 for discussion).…”