Helmet-Mounted Displays: - USAARL - The - U.S. Army

Optical Performance 151
Figure 5.16. Luning in partial overlap HMDs.
regions, most pronounced near the binocular overlap borders (Figure 5.16).
This phenomenon, like visual fragmentation, is due to the nature of the
dichoptic stimulation of the monocular regions, meaning that each eye is
receiving dissimilar stimulation in corresponding locations, instead of the
similar stimulation of normal unaided vision. In this situation, dichoptic
competition occurs. Here, the monocular region of the FOV presents a
portion of the visual world to one eye and the black background, rather than
the visual world, to the other eye. This results in various forms of
binocular rivalry, where these inputs compete for awareness with the inputs
of each eye alternating in suppressing the input of the other eye.
Phenomenally, this is experienced as the darkening effect of luning, which
is most prevalent when the eye receiving the wrong image of the black
background dominates and suppresses the eye receiving the right image of
the visual world.
Third, this competing visual input can result in less detectable targets
in the monocular regions of the partial overlap FOV (Klymenko et al.,
1994c). Melzer and Moffitt (1997) have proposed blurring the binocular
edges or putting in dark contour lines to separate the binocular and
monocular regions to alleviate the detrimental visual effects. In dichoptic
competition, sharper edges are stronger competitors than smooth edges