Portable faceted simulator systems are relatively easily deployable to numerous locations around the globe. Although these uncollimated, faceted displays allow for a relatively small footprint, the viewing distance for faceted simulator screens can vary significantly as a user moves their head and direction of gaze. When binocular head mounted displays (HMDs) are used in tiled simulators to overlay symbology, the difference between the focus and vergence of the HMD and the out-the-window view can cause human factors issues. These issues can manifest themselves as blurred imagery, doubled imagery or eyestrain. These effects are not normally observed in flight, where the pilot's "real world" is at or near optical infinity.
We performed preliminary experiments in a faceted simulator using a number of different display conditions for overlaid symbology: on-screen, monocular HMD and binocular HMD. The HMD conditions were tested with a range of image distances from 36 to 55 inches, which represent the range of viewing distances in a faceted display system used by the Air Force (M2DART). Subjects were queried for apparent distance of the overlaid symbology, blurriness of symbology, presence of doubled imagery and viewing comfort.
The preliminary results showed no obvious blurring of the imagery due to focus mismatch, but large effects due to vergence mismatch. These effects included symbology which appeared to "float" in front of or behind the out-thewindow view, doubling of the imagery or symbology, and uncomfortable viewing of the overlaid symbology and imagery. No single binocular symbology convergence setting prevented reports of double vision, apparent distance effects and/or viewing discomfort. Monocular symbology alleviated the vergence mismatch, but was judged less comfortable to view. These results indicate that for the M2DART, and other faceted simulators with similar viewing distances, some method of vergence mismatch mitigation is required to permit the integration of binocular HMDs for training applications.