We evaluated the prediction that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator. Participants sat in a cockpit in a video projection dome and were exposed to optical flow that oscillated in the roll axis with exposure durations typical of flight simulation. The frequencies of oscillation were those that characterize spontaneous postural sway during stance. Head motion was measured prior to and during exposure to imposed optical flow. Of 14 participants, 6 were classified as motion sick, either during or after exposure to the optical oscillation. Prior to the onset of subjective symptoms, head motion among participants who later became sick was significantly greater than among participants who did not become motion sick. We argue that the results support the postural instability theory of motion sickness. Actual or potential applications include the prevention or mitigation of motion sickness in virtual environments.

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Advances in helmet-mounted displays (HMDs) have permitted the design of "see-through" displays in which virtual imagery may be superimposed upon real visual environments. Such displays have numerous potential applications; however, their promise to improve human perception and performance in complex task environments is threatened by numerous technological challenges. Moreover, users of HMDs may be vulnerable to symptoms associated with simulator sickness. The primary objective of this investigation was to assess subjective ratings of simulator sickness as a function of time delay, time on task, and task complexity. Participants attempted to center a reticle over a moving circular target using a see-through HMD while concurrently performing a visual monitoring task displayed on a computer monitor. Results indicated that simulator sickness ratings varied directly with time on task, while performance efficiency and ratings of perceived mental workload were not mediated by this factor. Furthermore, the time delay manipulation that affected performance efficiency and operator workload did not generally influence SSQ ratings. These findings are discussed in terms of their implications for practical implementation of see-through HMDs in multi-task environments.

The objective of this research was to assess the effects of two biodynamic stressors, noise and acceleration, commonly experienced in the aircraft cockpit, on human operator performance and workload. Thirteen workload measures, including one subjective, four performance and eight physiological, were recorded on subjects performing a dual psychomotor task. The results indicate that biodyanmic stressors such as noise and acceleration can adversely affect subjective operator workload without affecting objective task performance.