ABSTRACT
Eye activity measures are increasingly employed to evaluate operators’ mental states and the usability of interfaces. This paper focuses on the eye movement activities of operators performing the manually controlled rendezvous and docking (MCRVD) of two space vehicles during spaceflight. Ten male subjects participated in the simulated MCRVD experiments, in which the subject observed the image of the target space vehicle on the computer screen, and regulated the relative position and posture of the two space vehicles by manipulating the control handles. Each subject performed two consecutive RVD tasks of the same difficulty level. Eye movement data were collected by the ASL eye tracker H6. Eye activity measures, such as the blink rate, the blink duration, the Percent Eyelid Closure (PERCLOS), and the fixation related measures were extracted. As pervious research has revealed, manually controlled RVD can be divided into tracking control stage and accurate control stage, eye activity measures in the two stages were also calculated separately. Results show that the blink rate in the accurate control stage is significantly lower than that in the tracking control stage (p < 0.05), while both the PERCLOS and the blink duration in the two stages are low and show no significant
that in the tracking control stage, but no fatigue was found in the subjects during the experiments. For all of the ten subjects, longer control time corresponds to bigger PERCLOS, which means that there is a tendency for operators to be more tired as control time lasts longer, and validates that the PERCLOS is an effective index of mental fatigue. The fixation related measures show that human eyes were fixed on the image of the spacecraft nearly 80% of the time, while the numerical display of the spacecraft state were less fixed on, which validates that the numerical display only provides compensatory information. Among the numerical display areas, the velocity display area attracts more fixations and longer fixation dwell time, which implies that the velocity information is more important for subjects performing the RVD task (more fixations), and is more difficult to extract (longer fixation dwell time). Apparently if the velocity display is designed to be more noticeable, the overall visual workload of the operators may be reduced.
