The state of the art in assessing mental fatigue in the cockpit using head-worn sensing technology

Mental fatigue is an important construct for aviation as it can impact pilots' performance. However, its assessment has been and still is challenging. Most research done in this field is based on basic laboratory experiments, and the measurement methods in use have certain limits one needs to overcome in order to apply them in a cockpit. In this review, we present an overview of research on mental fatigue, its assessment and the gap between fundamental research and its application in aviation. We provide an overview over classical experimental paradigms for mental fatigue induction and subjective measures, as well as advanced head-worn sensing technologies (or such that target head and face), namely electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS) and eye-tracking. For each measure, we discuss limitations and open challenges. Finally, we draw conclusions on the feasibility of integrating the measurements into the cockpit. We also highlight gaps that future research needs to bridge.