Distinct oculomotor signatures for task disengagement and reduction in vigilance during a supervisory task

Technological advancements in human-machine interfaces increasingly confine human operators to the role of passive supervisors. Under such conditions, the out-of-the-loop phenomenon, driven by vigilance decline and task disengagement, can result in degraded performance, when automated systems fail unexpectedly. Despite decades of research on the topic, characterizing, quantifying and predicting these performance problems remain difficult. This study aimed at identifying distinct oculomotor signatures associated with task disengagement and vigilance reduction during a specifically designed supervisory task. Participants viewed a simplified aircraft interface and were asked to monitor an autopilot system and validate or reject its decisions. Task disengagement was manipulated by varying the time delay before participants were required to intervene: in some cases, responses were frequent, while in others participants had to wait longer before having to intervene. Vigilance was manipulated through time-on- task. Results showed that participants' performance was negatively impacted by task disengagement (slower reaction times when less solicited). Although visual exploration decreased both under low vigilance and low engagement, other oculomotor markers (i.e., saccades, fixations, eyelid opening and blinks) could dissociate the two states. Finally, logistic classifiers revealed that specific oculomotor features predicted participants' reaction times above chance. In summary, this study identified distinct oculomotor patterns linked to vigilance decline and task disengagement, two factors contributing to the out-of-the-loop phenomenon, which were also predictive of individuals' performance. These results are not only relevant for the monitoring of piloting activities, but contribute to the general knowledge of the impact of task disengagement on human performance.