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

Visual Coupling 93
areas.
If the Comanche decides to mount the I 2 sensor exocentrically on the
nose, collocated near the FLIR sensor, then the displaying of both
imageries on the HIDSS will not introduce any human factors problems
other than those just cited. [Remotely locating the I 2 sensor will affect
resolution, system lag, and contrast.] However, if the FLIR remains
exocentrically located and the I 2 sensor(s) is integrated into the HIDSS,
then additional issues associated with mixed sensor location modes and the
resulting switching of visual reference points must be considered. One
study (Armbrust et al., 1993) looking at these potential issues was
conducted using the AH-64 with its exocentrically located FLIR and
several HMDs with integrated I 2 sensors. Aviators were tasked with
performing a set of standard maneuvers (i.e., precision hover, lateral hover,
rearward hover, deceleration, and pirouette). At designated points during
each maneuver, the aviators were required to switch from one sensor to the
other. For the hover maneuvers, the switch occurred at the maneuver
midpoint. For the deceleration maneuver, the switch occurred immediately
after the start of the deceleration. For the pirouette, switches were required
every 90º. The direction of the switch (from aircraft nose to head and vice
versa) was counterbalanced across subjects. The objective of this study
(phase) was to investigate the effects of switching sensor perspective on
measured performance and subjective aviator workload. Measured
performance was based on monitoring of drift, altitude, and heading data.
Aviator workload was measured by the Subjective Workload Technique
(SWAT) (Armstrong Aerospace Medical Research Laboratory, 1989). The
study found significant degradation in performance for all maneuvers,
regardless of direction of switching. SWAT scores indicated higher
workloads associated with sensor switching. Over 80% of the aviators
reported that targets appeared to be at different distances as a result of
switching, targets in the I 2 imagery appearing closer than in the FLIR
imagery. Over a third (37%) of the aviators reported apparent changes in
attitude or flight path when switching; three-fourths (75%) stated that
switching caused disorientation in one or more of the maneuvers due to
switching. And, of most concern, should be the fact that one-half (50%)
had to transfer controls to the safety pilot during one of the maneuvers. All
of the aviators in the study stated that sensor switching increased
workload. In view of these results, careful consideration should be given
to HMD designs which require the user to switch between noncollated
sensor sources.
In a related study (Rabin and Wiley, 1994) investigating transitory