The role of response requirements in task switching: dissolving the residue

Task-switching paradigms, which are regularly used to assay 'executive control' processes in humans, almost invariably reveal a decrement in subjects' performance on the first trial following a switch of task. That is, subjects are slower to respond and more error prone on the switch trial, a difference in performance that has been termed the 'switch-cost'. This switch cost has then been taken to reflect the time taken by neural control processes. Previous studies have shown that while performance improves as more time is provided to prepare for the switch, switch costs persist, even over very long intervals. In the present study, however, we find that changing the response regimen (choice reaction time vs go-no-go) has profound effects on the switch cost. A task switching paradigm was used in which subjects randomly switched between two tasks, based on a cue that was presented at varying intervals prior to the presentation of the imperative stimulus. While switch costs were found in all conditions in the choice reaction time blocks, they were completely abolished in the go-no-go blocks when sufficient preparation time was provided (500 or 800 ms). This is important because the only difference between the choice reaction time and go-no-go conditions was the response requirement: these conditions did not differ in the stimuli used, in the tasks performed or in the preparation time provided. These data call into question models of executive control that interpret switch costs as reflecting the time taken by neural processes to switch the system from a readiness to perform one task to a readiness to perform another.