Task asymmetries in switch costs and voluntary choice have typically been interpreted as evidence for the effects of between-task competition: Weak tasks must be strongly imposed and are therefore difficult to switch away from, resulting in high levels of competition and correspondingly poor performance on subsequent trials.
Previous behavioral studies have revealed a surprising bias toward performing the weaker task of a pair, evident as decreased switch costs for this task and a bias in voluntary task choices toward performing this weaker task.
An implication of this hypothesis is that repetition of the weaker task becomes, paradoxically, the default voluntary choice when choosing between tasks that differ in relative strength.
Hence, parieto-occipital alpha power was modulated by the task and transition type early in the RSI, being selectively stronger in repeat trials of the weaker task.
Switch costs were usually larger when individuals needed to switch to the stronger (more dominant) task than to a weaker task.
Allport and colleagues [ 16] have argued that the extra inhibition of the stronger task set is required to enhance performance with the weaker task set, and therefore, inhibition carries over to the next trial.
Taken with the finding that CNV amplitude in our study tended to be increased on trials with faster RTs (cf. Lavric et al. 2008), these results suggest that the CNV provides an index of active intentional control and that advance preparation of the stronger task requires more intentional control than advance preparation of the weaker task.
These CNV findings complement and extend existing theoretical accounts of switching asymmetries observed behaviorally, which have typically been taken to show that execution of the weaker task makes the switch toward the stronger task more difficult (Gilbert and Shallice 2002; Yeung and Monsell 2003).
Accordingly, later in the preparation interval, switch-related activity would only be detected for weaker tasks and for slower trials the pattern we observed.
Furthermore, the distributed group displayed a weaker task-related power decrease in upper alpha in both clusters of electrodes in the second practice block.
