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

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Clarence E. Rash and William E. McLean
(Kaufman, 1963). The blurring works by weakening the competitive
dichoptic strength of the wrong image, and the placement of dark contours
works by enhancing the strength of the right image. Klymenko et al.
(1994d) have confirmed that the placement of contours reduces luning.
A remaining issue is the choice of whether the partial overlap should
be convergent or divergent (Figures 1.9 and 1.10). [In the convergent
design, the right monocular image is presented to the left eye, and vice
versa; in the divergent design, the right monocular image is presented to the
right eye and the left monocular image is presented to the left eye.]
Klymenko et al. (1994d) have found that there is less luning in convergent
FOVs compared to divergent FOVs, and, while luning is reduced by the
placement of dark contours in both cases, the convergent FOV still induces
less luning. Klymenko et. al (1994a) found more fragmentation in
divergent than in convergent displays, and in displays with smaller as
opposed to larger binocular overlap regions. This increased luning and
fragmentation of divergent displays also affects target visibility, where
Klymenko et al. (1994c) found that targets were less detectable in divergent
than in convergent displays, and less detectable in both of these than in full
overlap displays. The differences in target visibility, thought small in terms
of the contrast required to detect the target, were systematic and significant.
In view of these issues, it generally is recommended that full overlap
be implemented wherever, unless the increased FOV provided by partial
overlap is essential (Kalawsky, 1993).
Monochrome vs. Color
All fielded HMDs in Army aviation are monochromatic (having no
variation in hue). ANVIS and IHADSS are green on black. Color HMDs
have not been fielded to date due mostly to their high cost and weight; color
displays also require resolution and luminance tradeoffs. Also, the use of
color image sources increases the complexity of the relay optics design
since a polychromatic design must be used. However, these factors have
not decreased their desirability to the user. This desirability lies in the fact
that color is a very conspicuous attribute of objects. Color can facilitate
three functions: Serve as the actual work object, support cognitive
functions, and to assist in spatial orientation (Spenkelink and
Besuijen, 1996). Overall, color has the potential to reduce workload and
improve visual performance.
The “color”of monochrome CRT and I 2 displays is defined primarily