Monitoring army drivers’ workload during off-road missions: An experimental controlled field study

•Army drivers performed real off-road training exercises of different complexity.•Exercises were performed with and without a secondary vocal task.•Drivers’ EEG power spectra and gaze dispersion changed over the exercises.•The EEG-based workload index was sensitive to task complexity.•Drivers’ gaze entropy was sensitive to task complexity and dual tasking. We studied the validity of electroencephalographic (EEG) and gaze indices to discriminate task load variations in professional Army drivers while performing real training exercises with a Light Multirole Vehicle in non-combat scenarios. Twenty-two non-commissioned officers from the Spanish Army carried out two sets of standardized driving exercises, with low and high maneuver complexity (off-road navigation vs. slalom on dirt road). They performed both exercises with and without a secondary auditory-vocal digit span forward task. Throughout the exercises, we simultaneously recorded drivers’ EEG and gaze activity. We also assessed perceived task load and performance. We found that drivers’ neural activation changed with exercise complexity. Particularly, the EEG signal ratio between Frontal-Theta and Parietal-Alpha power spectra, known as the EEG workload index, was higher during the most complex exercise. This index was not affected by dual tasking. Furthermore, the level of uncertainty of the gaze position, as measured by gaze entropy, increased during the most complex exercise. Dual tasking did increase drivers’ gaze dispersion, but only when performing the less complex exercise. Perceived task load was sensitive to maneuver complexity and dual tasking. Performance indices did not vary across exercises. Our results support that physiological monitoring in real training, even in extreme environments, is feasible and can give objective measurements of changes in task load over time in a minimally invasive fashion.