Data from two simulator experiments were examined to investigate whether performing an auditory task influences pilots' gaze behaviour. Gaze behaviour was measured while participants performed a manual flying task with an auditory task (dual-task condition) or without (single-task condition). Experiment 1 took place in a fixed-base, fixed-wing simulator with 15 novice military pilots. Experiment 2 took place in a moving-base, rotary-wing simulator with 13 experienced military helicopter pilots. Percentage dwell time outside significantly increased in the dual-task condition compared to the single-task condition in both experiments, by a factor of 1.2 and 1.5 respectively. Mean duration of fixations outside significantly increased for pilots, while it decreased for novices. In novices, altitude control performance was also significantly reduced when performing the auditory task, whereas bank angle control performance significantly increased in experienced pilots. The impact on gaze behaviour may potentially serve as a behavioural indicator of pilot auditory workload.

Objective
We aimed to find objective measures of the impact of spatially disorienting (SD) stimuli on pilot cognition in an ecologically valid environment.
Background
SD frequently occurs in military rotary-wing operations and often contributes to mishaps. Effects of SD stimuli on pilots are usually quantified using control errors, but effects on cognition have not yet been successfully quantified.
Method
Military helicopter pilots (n = 14) performed scenarios with six SD stimuli (SD condition) and six corresponding control stimuli (NoSD condition) in a motion-base simulator with integrated virtual reality headset. SD stimuli were: false horizon, featureless terrain, leans, brownout, a somatogyral yaw illusion, and loss of horizon due to night vision goggles (NVGs). Mental workload was measured using auditory arithmetic task performance and attentional focus was measured using eye-tracking.
Results
Average arithmetic task performance was significantly impaired, and proportional gaze dwell time on the attitude indicator was significantly increased in the SD compared to the NoSD condition. Of the six SD stimuli, the featureless terrain, the leans, and the brownout induced significant effects on performance, whereas the featureless terrain, brownout, and false horizon significantly affected gaze behavior. The NVGs and somatogyral yaw stimuli did not induce significant effects. Pilots’ self-reports indicated awareness of all SD stimuli, except for the featureless terrain.
Conclusion
The results indicate that SD impacts pilot mental workload and attentional focus.
Application
Modern military aircraft present a large volume of mission-related information to pilots. This study shows that SD stimuli may negatively impact the processing of such information.