Response conflicts in visually guided movements under mental fatigue.

Mental fatigue induced by prolonged task performance (time-on-task [ToT]) is typically perceived as an unpleasant state and is associated with compromised performance. Operations requiring cognitive control, such as resolving response conflicts, are particularly sensitive to ToT-related detrimental effects. As cognitive control is critical for precise movements, ToT likely impacts movement performance. Two experiments explored this by examining the resolution of response conflicts in pointing movement with increasing ToT. In Experiment 1, participants performed a flanker task with congruent, neutral, and incongruent pointing trials. The results revealed slower movement initiation and execution, especially in incongruent trials, and ToT-related impairments in leftward movements possibly due to rightward attentional bias under fatigue. Experiment 2 introduced ‘leap trials,’ where spatial target locations shifted unexpectedly. While leap trials required high cognitive control, they resisted ToT-related deterioration, suggesting that phasic changes in spatial orientation resist fatigue. The performance of frequent normal trials with stable target locations declined over time, indicating that reduced tonic vigilance may worsen movements. Across both experiments, motivation manipulations after ToT periods mitigated declines in performance, reflecting the compensatory role of increased task engagement. These findings highlight the interplay between fatigue and cognitive control in motor tasks, offering insights into mechanisms underlying performance under mental strain.