Mental fatigue and task control: Planning and preparation

The effects of mental fatigue on planning and preparation for future action s were examined, using a task switching paradigm. Fatigue was induced by "t ime on task," with subjects performing a switch task continuously for 2 hr. Subjects had to alternate between tasks on every second trial, so that a n ew task set was required on every second trial. Manipulations of response-s timulus intervals (RSIs) were used to examine whether subjects prepared the mselves for the task change. Behavioral measurements, event-related potenti als (ERPs), and mood questionnaires were used to assess the effects of ment al fatigue. Reaction times (RTs) were faster on trials in which no change i n task set was required in comparison with switch trials, requiring a new t ask set. Long RSIs were used efficiently to prepare for the processing of s ubsequent stimuli. With increasing mental fatigue, preparation processes se emed to become less adequate and the number of errors increased. A clear po ststimulus parietal negativity was observed on repetition trials, which red uced with time on task. This attention-related component was less pronounce d in switch trials: instead, ERPs elicited in switch trials showed a clear frontal negativity. This negativity was also diminished by time on task. ER P differences between repetition and switch trials became smaller with incr easing time on task.