Eye-tracking based mental fatigue assessment in VR environments

While "stress" measured by wearable devices typically reflects autonomic nervous system responses to external pressures, a deeper form of fatigue—mental fatigue—is becoming more prevalent in today’s information-rich society. Characterized by decreased cognitive and attentional capacity, mental fatigue is harder to detect and slower to recover from, often not resolved by sleep alone. Early detection and management are crucial to prevent its chronic progression. Mental fatigue differs from peripheral stress in that it is characterized by impaired cognitive function and attention span. Mental fatigue often goes unnoticed and is not easily relieved by sleep alone. Early assessment and intervention are essential to prevent its chronic progression. We have developed ZEN EYE Pro, a VR-based eye-tracking system that allows for rapid (approximately 1 minute) and non-invasive assessment of mental fatigue in a real-world context. The purpose of this study was twofold: first, to evaluate the feasibility of ZEN EYE Pro as an objective assessment tool for mental fatigue. The second was to test the validity of our developed assessment by examining the impact of two established stress reduction interventions - mindfulness-based stress reduction (MBSR) and inhalation aromatherapy. In an experiment with 61 Japanese adult participants, the mean mental fatigue score was 44.20% (SD = 9.93). (1) A 5-minute mindfulness session with Apple Vision Pro reduced fatigue scores by 18.85% (p < 0.001). (2) A 2-minute inhalation aromatherapy session with a blend of aromas reduced fatigue scores by 14.47% (p < 0.001). These results demonstrate the feasibility and validity of objective and time-efficient mental fatigue assessment using the ZEN EYE Pro and suggest its applicability in a variety of real-world settings.