
With increased use of stereoscopic devices, it is important to emulate real-world practices and study physiological and perceptual effects over long viewing periods. Stereoscopic channels may not always be perfectly aligned, and alignment may shift with use. In this experiment, we investigated the impact of vertical misalignment between left and right-eye imagery during stereoscopic remote vision system (sRVS) use. For three-hour periods, participants performed a simulated aerial refueling task. Their goal was to fly the boom into a receiver aircraft receptacle as quickly as possible without scratching the aircraft. After each successful connection, the participant monitored several systems, which required changes to version and vergence position. Binocular eye position was recorded throughout the task. While performance increased over time, the survey results showed that participants were experiencing strain over time and with increased misalignment. However, only one oculomotor change – horizontal vergence – was observed over time. Time series analysis revealed a more complex relationship between pupil size and time within each block. To further investigate the relationship between eye movement behavior and vertical misalignment, a principal component analysis was performed. These results identified eye movement behaviors that are sensitive to changes in stereoscopic misalignment and have the potential to be used to indicate oncoming fatigue. This experiment highlights the importance of considering the visual system as a whole when assessing stress and not simply relying on performance metrics.

United States Air Force (USAF) vision tests have largely remained unchanged since WWII and therefore, it is unclear whether current standards are applicable for users of new humane-machine interfaces (e.g., stereoscopic remote vision system (RVS) in the KC-46 refueling tanker). This study examined the relationships between a range of early vision assessments, including Operational Based Vision Assessment (OBVA) lab-developed tests, an electronic version of the standard Titmus test, and the current Armed Forces Vision Tester (AFVT), and air refueling task performance using a stereoscopic RVS. Additionally, the relationships of these vision test scores to operationally-relevant subjective measures of visual fatigue were assessed. Results showed that OBVA measures of disparity discrimination, horizontal fusion, and horizontal phoria correlated with air refueling performance. OBVA measures of acuity, contrast sensitivity, disparity discrimination, and radial motion sensitivity were significantly associated with subjective measures of discomfort and visual fatigue. Notably, neither the electronic Titmus results, nor the AFVT measures were not associated with either air refueling task performance or subjective measures of discomfort and visual fatigue. Adjustments to the vision standards and test methods used for USAF aeromedical vision screening should therefore be considered.