Simulator sickness (SS)-virtual environment (VE) sickness is expected to become increasingly troublesome as VE technology evolves. This paper investigated using an independent visual background (IVB) to reduce SS and VE sickness. The IVB is a visual scene component that provides visual motion and orientation cues that match those from the vestibular receptors. In this study, the IVB was stationary, fixed with respect to inertial space. Two experiments were conducted. The first experiment examined the differences in visual motion-induced postural disturbance as a function of simultaneous exposure to an IVB. Subjects exhibited less balance disturbance when the IVB was presented. An expected statistically significant interaction between IVB presence-absence and visual scene motion oscillation frequency was observed. In the second experiment, subjects reported less SS when the IVB was presented during the VE exposure. We suggest that an IVB may alleviate disturbance when conflicting visual and inertial cues evoke SS.

The operation and performance of a six degree-of-freedom (DOF) shared-aperture tracking system with image overlay is described. This unique tracking technology shares the same aperture or scanned optical beam with the visual display, virtual retinal display (VRD). This display technology provides high brightness in an AR helmet-mounted display, especially in the extreme environment of a military cockpit. The VRD generates an image by optically scanning visible light directly to the viewer's eye. By scanning both visible and infrared light, the head-worn display can be directly coupled to a head-tracking system. As a result, the proposed tracking system requires minimal calibration between the user's viewpoint and the tracker's viewpoint. This paper demonstrates that the proposed shared-aperture tracking system produces high accuracy and computational efficiency. The current proof-of-concept system has a precision of +/− 0.05 and +/− 0.01 deg. in the horizontal and vertical axes, respectively. The static registration error was measured to be 0.08 +/− 0.04 and 0.03 +/− 0.02 deg. for the horizontal and vertical axes, respectively. The dynamic registration error or the system latency was measured to be within 16.67 ms, equivalent to our display refresh rate of 60 Hz. In all testing, the VRD was fixed and the calibrated motion of a robot arm was tracked. By moving the robot arm within a restricted volume, this real-time shared-aperture method of tracking was extended to six-DOF measurements. Future AR applications of our shared-aperture tracking and display system will be highly accurate head tracking when the VRD is helmet mounted and worn within an enclosed space, such as an aircraft cockpit.

Image quality issues such as field of view (FOV) and resolution are important for evaluating “presence” and simulator sickness (SS) in virtual environments (VEs). This research examined effects on postural stability of varying FOV, image resolution, and scene content in an immersive visual display. Two different scenes (a photograph of a fountain and a simple radial pattern) at two different resolutions were tested using six FOVs (30, 60, 90, 120, 150, and 180 deg.). Both postural stability, recorded by force plates, and subjective difficulty ratings varied as a function of FOV, scene content, and image resolution. Subjects exhibited more balance disturbance and reported more difficulty in maintaining posture in the wide-FOV, highresolution, and natural scene conditions.