Visual behaviour in acute stress during simulated and on-road driving.

Driving frequently exposes individuals to conditions triggering acute stress, but its effects on drivers' visual behaviour remain insufficiently understood. We used the heart rate dynamics to label acute stress episodes in recordings from 881 participants who performed simulated and on-road driving. Considering acute stress as a phased process, we analysed eye gaze metrics during stress activation and stress resistance periods. In simulation, stress activation was accompanied by more frequent and shorter fixations, greater fixation area, higher stationary gaze entropy, and lower gaze transition entropy. In on-road driving, significant effects were more selective, with the most consistent changes observed for the horizontal diameter of fixation area and entropy-based gaze measures. During stress resistance, many measures partially returned toward non-stress levels, suggesting a transition from initial reactivity toward stabilisation. These findings support gaze-derived measures as candidate indicators of changes in visual behaviour related to acute stress during driving, while highlighting the importance of considering acute stress as a phased process. They also indicate that multimodal context-aware validation is needed for translation into real-time driver state monitoring and safety-relevant assistance applications.