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

Optical Performance 135
Figure 5.13. Human visual system’s binocular FOV.
amount of visual information available to the aviator is provided via the
display imagery. In principle, the larger the FOV, the more information
available. The maximum FOV target value would be that currently
achieved by the unobstructed human visual system.
The human eye has an instantaneous FOV that is roughly oval and
typically measures 120º vertically by 150º horizontally. Considering both
eyes together, the overall binocular FOV measures approximately 120º (V)
by 200º (H) (Zuckerman, 1954) (Figure 5.13). The size of the FOV that an
HMD is capable of providing is determined by several sensor and display
parameters including size, weight, placement, and resolution. Designs
achieved so far all provide restricted FOV sizes. As FOVs decrease, head
motion becomes greater and increases head and neck muscle fatigue. This
also reduces the amount of background information about the area (target)
of interest and induce “tunnel vision” (Biberman and Alluisi, 1992).
In ANVIS, the FOV of a single I 2 tube is a circular 40º. The two tubes
have a 100º overlap; hence, the total FOV is also 40º. This FOV size seems
small in comparison to that of the unobstructed eye. But, the reduction
must be judged in the context of all of the obstructions associated with a
cockpit, e.g., armor, glareshield, support structures. Still, the aviator must
use continuous head movements in a scanning pattern to help compensate
for the limited FOV.