Prolonged use of conventional stereo displays causes viewer discomfort and fatigue because of the vergenceaccommodation
conflict. We used a novel volumetric display to examine how viewing distance and the sign of the
vergence-accommodation conflict affect discomfort and fatigue. In the first experiment, we presented a fixed conflict at
short, medium, and long viewing distances. We compared subjects' symptoms in that condition and one in which there
was no conflict. We observed more discomfort and fatigue with a given vergence-accommodation conflict at the longer
distances. The second experiment compared symptoms when the conflict had one sign compared to when it had the
opposite sign at short, medium, and long distances. We observed greater symptoms with uncrossed disparities at long
distances and with crossed disparities at short distances. These findings help define comfortable viewing conditions for
stereo displays.
In stereo displays, binocular disparity creates a striking impression of depth. However, such displays
present focus cues-blur and accommodation-that specify a different depth than disparity, thereby
causing a conflict. This conflict causes several problems including misperception of the 3D layout,
difficulty fusing binocular images, and visual fatigue. To address these problems, we developed a
display that preserves the advantages of conventional stereo displays, while presenting correct or
nearly correct focus cues. In our new stereo display each eye views a display through a lens that
switches between four focal distances at very high rate. The switches are synchronized to the
display, so focal distance and the distance being simulated on the display are consistent or nearly
consistent with one another. Focus cues for points in--between the four focal planes are simulated by
using a depth-weighted blending technique. We will describe the design of the new display, discuss
the retinal images it forms under various conditions, and describe an experiment that illustrates the
effectiveness of the display in maximizing visual performance while minimizing visual fatigue.
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