Figure 2.

Evidence of mental fatigue as a function of time-on-task. During the event-related color-word Stroop task, performance on the fourth repetition (compared with the first) produced (a) more congruent errors, (b) less post-error slowing on congruent trials and (c) less % blood-oxygenation-level-dependent (BOLD) signal change to error (compared with all correct trials) in the dorsal anterior cingulate cortex (dACC). (d) Scatterplot showing that higher error-induced BOLD signal change during the first task repetition correlated with respective longer post-error slowing in all subjects. (e) Scatterplot showing that the higher the change in dACC activity (fourth >first repetition), the higher was the sleepiness before beginning the task. Asterisks denote a significant difference between first and last task runs (repetitions).