EXPRESS: No effect of mental fatigue on perceived hand weight.

Fatigue has a profound impact on various sensory and perceptual processes, yet its effects differ depending on whether it arises from physical or mental exertion. While physical fatigue is known to alter body weight perception, it remains unclear whether mental fatigue has a similar effect. This study tested the hypothesis that mental fatigue, like physical fatigue, would influence the recently identified perceptual bias of hand weight underestimation, where individuals perceive their hand as lighter than its actual weight. Twenty-four participants completed a validated mental fatigue induction task, followed by pre- and post-fatigue assessments of hand weight perception using a weight judgment paradigm. As expected, the fatigue task significantly increased subjective ratings of mental fatigue. However, contrary to the hypothesis, the degree of hand weight underestimation remained unchanged between pre- and post-fatigue sessions, a Bayesian analysis strongly supported the null hypothesis. These results suggest that mental fatigue, unlike physical fatigue, does not significantly alter sensory mechanisms underlying hand weight perception. This study underscores the distinct pathways through which physical and mental fatigue interact with perceptual processes.