Mental fatigue does not impede visuomotor adaptation driven by implicit processes

• Visuomotor adaptation to a small cursor distortion is not impacted by mental fatigue. • Implicit visuomotor adaptation is preserved when mentally fatigued. • Mental fatigue does not hinder engagement of automatic processes during visuomotor adaptation. We have recently shown that mental fatigue impairs visuomotor adaptation when both explicit (i.e., conscious strategy) and implicit (i.e., unconscious) processes are engaged (Apreutesei and Cressman, 2024). Specifically, mental fatigue led to decreased initial visuomotor adaptation, and increased mental fatigue was correlated with decreased explicit engagement. Extending from this work, the current research looked to establish the impact of mental fatigue on implicit visuomotor adaptation, when explicit contributions were negligible. Participants trained to reach with distorted cursor feedback that was rotated 20° clockwise relative to hand motion in a virtual environment. These rotated training trials were completed following a mentally fatiguing time load dual back task (TLDB) lasting 32 min (Mental Fatigue (MF) group) or watching of a documentary for the same duration (Control (CTL) group). Mental fatigue increased significantly for the MF group following the TLDB task, while the CTL group did not exhibit a similar increase in mental fatigue after watching the documentary. The extent of visuomotor adaptation was similar for both groups across all rotated training trials and this adaptation was shown to arise implicitly. Furthermore, no significant difference in implicit adaptation was observed between groups, and correlations between mental fatigue and implicit adaptation were weak. These results suggest that mental fatigue does not interfere with visuomotor adaptation when it is driven implicitly, supporting our proposal that mental fatigue interferes with the engagement of conscious reaching strategies.