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

Visual Performance 6
William E. McLean
Clarence E. Rash
Introduction
The discussions of physical FOMs above did not attempt to relate the
measured values to the visual performance of the user. However, in some
cases, it was appropriate to provide limited comments on the impact of the
FOMs on user visual performance. In the following sections, system
performance as a function of user visual performance is explored in greater
depth. The eye has its own transfer function which must be considered
when the display image is viewed. Previously, the FOMs for displays were
categorized into four domains: Spatial, spectral, luminance, and temporal
(Table 5.2). These image domains parallel analogous human visual
performance domains. The spatial domain includes those display
parameters associated with angular view (subtense) of the user and coincide
with user’s visual acuity and spatial sensitivity. The spectral domain
consists of those parameters associated with the user’s visual sensitivity to
color (wavelength). The luminance domain encompasses those display
parameters identified with the overall sensitivity of the user to illumination
levels. The temporal domain addresses display parameters associated with
the observer’s sensitivity to changing levels of light intensity.
The human eye has an extraordinary visual capability. It can perceive
light within the spectral region of 0.38 �m (violet) to 0.78 �m (red). It
consists of a central region, containing cone detectors, which provides
detail and color perception (decreasing with decreasing cone density away
from the center, fovea); and a peripheral region, containing rod detectors,
which provides black and white perception and motion detection. The
maximum sensitivity of the cones is about 555 nm and is 507 nm for the
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