Effects of task duration on mental fatigue: A multimodal analysis based on subjective, behavioral, and electrophysiological measures

Mental fatigue is typically induced by prolonged cognitive tasks. However, the task durations employed across studies vary significantly, potentially influencing the sensitivity of different assessment measures. This study evaluated the effects of three task durations on subjective, behavioral, and neurophysiological measures of mental fatigue. Twenty-two healthy adults completed the Stroop tasks under three duration conditions (30-, 60-, and 90-minute) on separate days in randomized order. Mental fatigue was assessed using subjective measures [Brunel Mood Scale-Chinese version (BRUMS-C) and Visual Analogue Scale (VAS)], behavioral measures (response times and accuracy), and neurophysiological measures (P300 amplitude and latency). Results indicated that subjective ratings indicated increased subjective mental fatigue under all three conditions, the 90-minute task led to a significantly greater increase in VAS score. Behaviorally, both the 60-minute (p = 0.009) and 90-minute (p = 0.006) Stroop tasks led to prolonged response times, but a reduction in accuracy was observed only in the 90-minute condition (p = 0.039). Neurophysiologically, a decrease in P300 amplitude was observed only after completing the 90-minute task (p < 0.001), whereas P300 latency remained stable across all conditions. These findings indicate that commonly used measures of mental fatigue differ in their sensitivity to task duration. Subjective, behavioral, and neurophysiological indices did not respond uniformly across task durations, highlighting the importance of employing multimodal assessment strategies when evaluating mental fatigue induced by prolonged cognitive engagement.