Switch-related and general preparation processes in task-switching: evidence from multivariate pattern classification of EEG data.

The cued-trials task-switching paradigm is used to investigate the processes involved in preparation to change task. Task switch trials typically show poorer performance than task repeat trials, suggesting that additional or more time-consuming preparation processes are required to switch tasks. However, behavioral and neuroimaging studies have so far been unable to decipher whether preparing for a switch in task involves distinct cognitive processes to those required more generally on both switch and repeat trials. The current study addresses this question using a novel multivariate pattern misclassification analysis of frequency band-specific local topographical patterns in human EEG activity that was elicited by cues varying in information value. Within the alpha frequency band, misclassification analysis produced evidence for an early switch-related preparation process over right frontal cortex, as well as a later task readiness preparation process over right parietal cortex. This represents compelling evidence for dissociable switch-related and task readiness preparation processes that show distinct time course and spatial activation patterns.

Adjustments of response threshold during task switching: a model-based functional magnetic resonance imaging study.

Adjustment of response threshold for speed compared with accuracy instructions in two-choice decision-making tasks is associated with activation in the fronto-striatal network, including the pre-supplementary motor area (pre-SMA) and striatum (Forstmann et al., 2008). In contrast, increased response conservativeness is associated with activation of the subthalamic nucleus (STN) (Frank et al., 2007). We investigated the involvement of these regions in trial-by-trial adjustments of response threshold in humans, using a cued-trials task-switching paradigm. Fully and partially informative switch cues produced more conservative thresholds than repeat cues. Repeat cues were associated with higher activation in pre-SMA and striatum than switch cues. For all cue types, individual variability in response threshold was associated with activation level in pre-SMA, with higher activation linked to lower threshold setting. In the striatum, this relationship was found for repeat cues only. These findings support the notion that pre-SMA biases the striatum to lower response threshold under more liberal response regimens. In contrast, a high threshold for switch cues was associated with greater activation in right STN, consistent with increasing response caution under conservative response regimens. We conclude that neural models of response threshold adjustment can help explain executive control processes in task switching.

Anticipatory reconfiguration elicited by fully and partially informative cues that validly predict a switch in task.

Task-switching studies show no behavioral benefit of partially informative cues. However, ERP evidence of an early cue-locked positivity elicited by both fully and partially informative cues suggests that both cues trigger an anticipatory component of task set reconfiguration (Nicholson, Karayanidis, Davies, & Michie, 2006). We examined this apparent discrepancy using a cued-trials task-switching paradigm with three tasks. The ERP finding of an early cue-locked positivity was replicated for both switch-to cues, which validly predicted an upcoming switch trial and specified the new task set, and switch-away cues, which validly predicted an upcoming switch trial but not the new task set. This component was not elicited by a noninformative cue that did not specify whether the task would switch or repeat. Switch-away cues resulted in more accurate but not faster responding than did noninformative cues. Modeling of decision processes confirmed a speed-accuracy trade-off between these conditions and a preparation benefit for both switch-to and switch-away cues. These results indicate that both fully and partially informative cues elicit an early anticipatory component of task set reconfiguration that is reflected in the early cue-locked positivity. We argue that the pattern of results is most consistent with a task set inhibition account of this early anticipatory component of task set reconfiguration.