Table Of Contentlnterservice/lndustly Training, Simulation, andEducationConference (l/ITSEC) 2009
Improving the Utility ofa Binocular HMD in a Faceted Flight Simulator
Michael P. Browne KirkMoffitt MarcWinterbottom
SA Photonics Human FactorsConsultant AirForceResearch Laboratory
San Francisco, CA La Qninta,CA Mesa, AZ
[email protected] kirkmoffittiu)earthlink.net Marc.'V,'!interbottom@,mesa.afmc.af.mil
ABSTRACT
Faceted simulator displays are widely used because they are relatively compact and economicaL One drawback,
however, isthatviewing distance changes dependingonwhere users arelooking. Thisvariation creates achallenge
for the integration ofbinocular head mounted displays (HMDs), because confusing imagery and visual fatigue can
result when the user views symbology presented by the HJ'v1D at one distance and simulator imagery at different
distances. Understandingthe best approach to presenting symbology with abinocularfllv1D in afaceted simulator
has hecome an important issue, with the deployment of the F-35 Joint Strike Fighter and its hinocular HMD.
Successfulintegration ofabinocularHMDwouldnotonly allowcurrentfaceted simulatorsto beretrofitwiththeF
35 simulatorHMD, hut would also allow future simulators to have either adome or faceted design, thus affording
acquisition agencies greater 'flexibility. BinocularHI'v1Ds are becoming more prevalent, so solving this integration
issuewill likelybecomeimpOltantformultipleplatforms.
We performed an experimentto quantifytbebestmethod ofpresentingsymbologyon abinocularHMD when used
with a faceted simulator display. Five viewing conditions were tested: 1) HMD converged to 36", 2) HMD
converged to 42", 3) dynamic HMD vergence, 4) monocular presentation on the HMD, and 5) on-screen
l
presentation. Screendistancesrangingfrom 36' to 54" weretested.
Our results.suggest that adaptive vergence is the preferred solution. Both static vergence conditions and the
monocular condition resulted in lower comfort scores and poorer performance. The on-screen conditionlalthough
rated comfortable, does notrepresentthe real-world flight condition where symbology is displayed using an HMD.
Although additional evaluations under more operational conditions remain to be completed, these results indicate
that adaptive vergence is a viable solution for the integration of binocular 1:IJ\1Ds into faceted flight simulator
displays.
ABOUTTHE AUTHORS
Michael Browne is the Vice President ofProduct Development at SA Photonics in San Francisco, California. He
has a Ph,D. in Optical Engineering from the University of Arizonals Optical Sciences Center. Mike has been
involved in the design, test and measurement ofhead mounted display systems since 1991. At Kaiser Electronics,
Mike ledtbe design ofnumerous headmounted display and rear-projection display systems, including those forthe
F-35 Joint Strike Fighter. Mike leads SA Photonics' efforts in the design and development of person-mounted
informationsystems, includinghead-mounted displays andnightvision systems.
Kirk Moffitt is ahuman factors consultantspecializing in real and virtual displays and controls. He holds aPh.D.
in Engineering Psychology, and has 28 years ofindustry experience. He is the co-editor ofthe McGraw-Hili text
Head Mounted Displays: Designing for the User. His clients have included military, medical, industrial and
entertainment companies. Dr. Moffitt has also taught courses in human factors and statistics for the University of
SouthernCalifornia,andseminarson fllv1Ddesignfor SPIEand otherorganizations.
Marc Winterbottom is a Research Psychologist at the Air Force Research Laboratory in Mesa, Arizona. His
research focuses on immersive decision environments, intuitive learningl and visual perception, particularly as it
relates to display technologies for simulation and training applications. He received a M.S. degree in Human
FactorsPsychology from WrightStateUniversityand aB.A. degreeinPsychologyfrom PurdueUniversity.
2009PaperNo. 9178Page1of11
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Interservice/lndustry Training, Simulation, andEducationConference(I/ITSEC) 2009
Improving the Utility ofa Binocular HMD in a Faceted Flight Simulator
MichaelP. Browne KirkMoffitt MarcWinterbottom
SAPhotonics Human FactorsConsultant AirForceResearchLaboratory
San Francisco,CA La Quinta,CA Mesa,AZ
m.brownera>saphotonics,com kirkmoffitt(akarthlink,net Marc.Winterbottom(a)mesa.afmc.af.mil
INTRODUCTION
Our previous work (Browne, Moffitt, & Winterbottom
2008) investigated visual anomalies while using a
binocular head mounted display (HMD) in a faceted
flight simulator (a simulator with multiple flat "tiles"
instead ofa dome). These anomalies included subject
reports of floating buried or confusing symbology,
l
doubling of symbology or the background imagery,
symbology slanted relativetothe simulatorscreen, and
general viewing discomfort. Our primary conclusion
was that these visual anomalies could be problematic
when integrating binocular HMOs into faceted flight
simulators.
The viewing discomfort subjects reported was likely
Figure I. Graphical Depiction OfDiplopia Caused
caused by diplopia - or double imaging. Diplopia
By Concentrating On Two Objects At Different
occurs often inthe realworld whenwe lookatmUltiple
Distances Simultaneously. Concentrating On The
objects located at different viewing distances. When
OTW Scene (Shown To The Left) Causes A
directing our attention to a given object, we
Diplopic Image OfThe Reticle. Concentrating On
subconsciously suppress double vision of objects at
The Reticle Causes A Diplopic Image OfThe OTW
other distances, Diplopia is problematic when using a
Scene.
binocular HMD in a faceted simulator because there
are some circumstances, such as targeting an enemy
The specific flight simulator display design ofinterest
aircraft where the user must view both the out the
l forthis investigation istheM2DART(MobileModular
windowdisplay (target) andtheHMD image(targeting
Display for Advanced Research and Training), a
reticle)simultaneously,asshown inFigure},
simulatordisplay system that can be reconfigured and
deployed for a variety of training tasks around the
Vergence angle is a strong depth cue - an object is
globe yet still provide panoramic imagery (Wight, Best
seen as closer in depth when the eyes are converged
& Peppler, 1998). The key to this design is the use of
(angled inward) and more distant when the eyes are
a faceted display and rear projection. These facets
diverged (becoming more parallel). Figure I-left
range in viewing distance from as close as 36inchesto
showstheposition ofthetwo eyes when verged forthe
a practical maximum of 54 inches. This range of
out tbe window (OTW) image. If the HMD
viewing distances creates the potential for vergence
symbology is in front of the OTW image, as could
mismatch centraltoourinvestigations,
occurinafaceted display,thenthat imagefalls onnon
matching locations in the two eyes, creating a double
Figure 2demonstrates asimplified overhead view ofa
image ofthe HMO symbology. Alternatively, iftbe
faceted simulator like the M2DART. The green line
user shifts their vergence to the HMD symbology's
represents the HMO symbology, presented at a fixed
depth, tben the OTW image will appear doubled
vergence distance. Shown also are two OTW display
(Figure I-right).
facets (one straightabead,oneangled ontheright). As
the user looks at different locations within the faceted
simulator, the difference in distance between the HJvlD
symbology (green line) and the display facet changes.
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Whenthe user is looking straight ahead (Figure 2-left), designed the performance experiment to test this
there is no distance difference. Whenthe user looks at hypothesis.
the seam between the display facets (Figure 2-center)
there is asignificantdistance difference atthe centerof Future military aircraft are likely to have an HMO that
tbe field of view. When the user looks at the right supports visual cueing with symbology and imagery.
facet (Figure 2-right) there is a constantly varying The Joint Strike Fighter (.1SF) will be the first US
distance difference. If these distance differences get fighter jet with a binocular IDvID that serves as a
too large, the user will report visual anomalies, primary flight instrument. Although a dome display
includingeyestrain, confusing imagery anddiplopia. may be a good solution for the 1'-35 and other
platfonns, a number of concerns have been raised
about using dome simulators. The first is that if all
faceted simulators have to be replaced with dome
simulators, it will be at a large cost. The second
concern is the size ofthe training system footprint and
visual system complexity, which drive cost factors
associated with training device installation and
sustainment. These issues make the integration of a
Figure 2. Simplified Overhead View Showing The binocular HMO into smaller, more cost-effective
Distance Difference Between The HMD Image faceted displaysofparticularinterest.
Plane And Two Adjoining Screens Of A Faceted
DisplaySystem. The above concerns make the compatibility offaceted
simulators with binocular HMDs an urgent problem in
Since the development of the M2DART, a variety of training F-35 pilots. The goal of the present
manufacturers have developed similar faceted display experiment was to quantify vergence mismatch effects
designs (e.g. Boeing vms, L3 SimnSphere, Glass identified in our first experiment(Browne, Moffitt and
Mountain Optics WASP). These display systems are Winterbottom, 2008). We also wanted to identify the
usedwidely across the servicesfor avarietyoftraining best solutions for improving symbology appearance,
applications. As such, we expect that as long as there viewing comfort and pilot perfonnance for a binocular
are faceted simulators, the potential exists for vergence HMDintegrated with afaceted display.
mismatchwhenusingabinocularIlMD.
In our previous work, we tried a number of HMD
In an aircraft, all ofthe informationthatthepilotviews viewing conditions but no single HMD configuration
outside the cockpit is at or near optical infinity prevented all the problems associated with integrating
(distances from 30 feet and beyond). No matterwhere a binocular HMD with a faceted display. Binocular
the pilot looks, the vergence is ba\)ically the same. symbology converged to one simulator viewing
Therefore, the HMD can be designed such that for distance appeared diplopic or doubled at other
aircraft use, its symbology is also converged to optical distances. Monocular symbology avoided this
infinity. Because of this, there is no vergence vergencemismatch, butwas rated by mostobservers as
mismatch between the OTW scene and the HMD less comfortable to view compared to binocular
symbology for an HMD used in an aircraft. The symbology. Both binocularand monocularsymbology
monochrome HMD symbology in an aircraft will appeared slanted relative to the simulator screen
appear distinct from the real world, and may appear whenever the symbology was not viewed straight
closer in distance, but should not appear blurry, ahead. On-screen symbology exhibited no binocular
doubledorslanted relativetotheOTWscene. problems and was rated as comfortable to view, but
this solution does not utilize an H:MD and creates a
Despite the optical equivalence of the HMD training situation that is not representative of what
symbology andreal-world imagery, there is substantial userswill see in flight.
evidence that the pilot switches attention between the
two (e.g., McCann, Foyle, & Johnston, 1993;McCann, In the virtual world ofHMD symbology, vergence can
Lynch, Foyle, & Johnston, 1993). This attention be manipulated electronically by adjusting the
switching is not driven by binocular disparity and horizontal binocular disparity. Electronically shifting
focus, but by dissimilar visual imagery and the left- and right-eye symhology creates the
infonnation. We postulated that increased visual perception of a change in depth. An inward shift
disparity.will lead to an increase in attention switching brings the symbology forward, while an outward shift
(and an increase in time to perform a task) and pushes the symbology away. We used this concept to
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design an adaptive viewing condition that
electronicallyandautomatically adjuststhevergenceof
the HMD depending on where the user is looking
within the faceted display. One of the goals of our
current experiment was to validate this approach both
intenns ofcomfortandperformance.
METHODS
Observers
Thirteen observers (twelve male and one female), ages
25 to 63, participated in our experiments. All had
experiencewiththedesign, marketingoruse ofHMDs.
Four participants described themselves as "very Figure3. SimEyeSXLSO HMD,
familiar" with HMDs. Four subjects were fighter
pilots, three of whom had extensive experience with A Souy SXRD 3-panel LCOS (liquid crystal on
the monocular joint helmet mounted cueing system silicon) 1920 x 1080 pixel monitor witb a nominal
(JHMCS) HMD. The interpupillary distance (IPD) of luminance of35 fL (atthe brightestportion ofthe sky)
each subject was measured with an L8 pupilometer, was used to present the out-the-window (OTW)
model NH-L8. Eye dominance was determined by imagery. The Sony monitorhadahorizontal dimension
noting which eye was used for sighting through an of 52", as shown in Figure 4. The straight ahead
aperture. Eight participants were right-eye dominant viewing distance was 36" and the nominal viewing
and five were left-eye dominant. Following helmet position was 9" in from the left edge of the screen.
fitting and HMD adjustment, the resting position of This allowed us to testviewing distances ranging from
vergence was measured using nonius targets with a 36" (straight ahead) to 54" (near the upper right hand
dark background. Intact stereo vision was ascertained comer). These distances encompassed the minimum
by presenting three depth planes of symbols, and and maximumviewingdistancesoftheM2DART.
asking the subject to identify the close, intermediate
'I
and distant figures. Finally, abinocular acuity level of 52"
2.6 minutes or 20/52 was verified with on-screen "
"tumbling Es" presented at the straight-ahead viewing
distance of 36 inches. Six of the participants wore
eyeglasses, threeofwhomhadprogressive lenses.
Stimuliaud Apparatus (nearupper
rightcomer)
A Rockwell-Collins Optmnics SimEye SXL50 STM
binocular see-through HMD was used for our
experiment. This HMD, shown in Figure 3, was
designed as asimulatorHMD forthe F-35 Joint Strike
Fighter. It has a 1280 x 1024 pixel format, 40 x 30 Figure4: LayoutofSimulatorScreen
degree field-of-view (FOY), and monochrome green andSubjectPositioning
imagery. Focus of this unit was 0.9 diopter (not The trade-off involved with replicating the M2DART
accounting for chromatic aberration) with a nominal viewing conditions on a single monitor was that our
optical vergence distanceof34.5"(88 cm). This HMD experiment presented symbology at a more severe
has a see-through transmission of>70% and was setto apparent slant angle than found in the M2DART.
anominal luminanceof6.5 fL. This lfMD clasps onto Someobservers commented on this slant but we think
an HGU-55/P military flight helmet. Three helmet that overall the conclusionsfor ourexperimenttransfer
sizes wereavailableforthis study: M, L& XL. totheM2DART.
A PC computer with nYidia GeForce graphics cards
provided the imagery for both the HMD and monitor.
A Polhemus Liberty tracker transmitted head position
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and angle relative to the OTW display. Testing took performance. Eachofthese activities arediscussed
place in an area surrounded by black curtains with a furtherinthenextsections.
nominal illuminance of 1.5 fc. HMD luminance,
monitor luminance and room illuminance were Boresighting
periodically tested to ensure nominal levels were To calibrate the head-tracker prior to each series of
maintained. trials, the system was boresighted to the relevanttarget
locations. To do this, a target was presented on the
The experimental tasks used an HMD reticle and an OTW display and the subjectaligned the HMD reticle
OTW image of a desert scene including sky, withthetargetandpressed amousebutton.
mountains, andadistantcity. TheHMD reticle, shown
in Figure5, subtended atotal of8x6degrees,witbthe ReticleDistancePreference
center circle subtending 1.5 degrees. Each target on The apparent viewing distance ofthe HMD reticle can
the OTW display was a51 x 22 pixel helicopter image be changed by electronicallyshifting the images onthe
subtending 2.1 x0.90 degrees atthe straight-ahead 36" left and right eye microdisplays inside the HMD. We
screen position. The helicopter was gray with a green measured the preferred reticle distance for each often
center dotto aid in centering the reticle on it. A photo screen targets located along horizontal lines that
ofaperson wearingtheHMD andviewingthemonitor divided the display vertically into quarters, and at
is shown inFigure6. distances of36"to 54" in 2" increments. The primary
purpose of this exercise was to establish preferred
positions for the HMD vergence as a function of
viewing distance. We used this information to set
vergence dynamically for the adaptive viewing
condition in the viewing comfort and petfonnance
experiments.
Participants began with the straight-ahead 36" target
and adjusted the apparent viewing distance of the
HMD reticle inward and outward using the left and
right buttons ofa mOlise. They were instructed to put
the reticle atthe positionthatthey felt would work best
forthemto completeatargetingtask, notnecessarily at
the same distance as the screen. Target presentation
Figure5. TargetingHMD Reticle progressed from left to right until the final 54" target
was completed. For each target, head-tracker
infonnation was recorded with the reticle distance
(stored as the lateral shift ofthe left- and right-image
on the HMD display). Figure 7 shows approximately
how the HMD imagery appeared relative to the OTW
image for near, approximately equal, and more distant
vergence settings.
Figure6. SubjectLookingForATarget
Procedure
Weaskedsubjectsto completefouractivities aspartof Figure 7. Appearance Of HMD Symbology
ourexperiment: boresighting, reticledistance Relative To OTW Imagery As The Viewer
preference,viewingcomfortandvisual searchand Electronically Adjusted Vergence Settings On The
HMD
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Interservice/lndustry Training, Simulation, andEducationConference(l/ITSEC) 2009
if visual performance was also affected. Palticipants
ViewingComfortRating were asked to search for helicopter targets located at
We expanded on our initial work to check viewing ten locations on the screen. These locations ranged in
comfort as afunction ofviewing condition(Browne et distance from 36" to 54" in 2" increments. The
al.). We changed the experiment to include better helicopter could appear in any of 10 positions, but all
control overthe reticle distance independent ofsubject positions were randomly presented three times during
interpupilliary distance. We also checked viewing the course of the experiment. \Vhen a target was
comfort over more distances and included an adaptive located, the subject aligned the I-L1\1D reticle with the
condition along with the fixed binocular, monocular target and the reticle changed to a "missile lock"
and on screen conditions. For this adaptive condition, configuration (four alTOWS sUlTounding the targeting
we.used the head trackerto indicate where the subject reticle, as shown in Figure 8). After one second of
was looking and changed the vergence such that the accurate alignment (representing a "missile lock"), a
reticle viewing distance was approximatelythe same as three-digit number was displayed on the reticle and
thedistancefrom theusertotheOTW display. another three-digit number was displayed on-screen,
For the on-screen viewing condition, both numbers
Each trial started with practice targets located at three were displayed on-screen. These spatially adjacent
screen positions. Subjects were instructed to first numbers were compared by the participant. The
preview the task by rotating their head to position the participantwas instructedtopushthe leftmousebutton
reticle over each target to see what different vergence ifthey were the same, and the rightbutton ifdifferent.
mismatches lookedlike. Ifan errorwas made, the subject was required to enter
the correct response. After a correct response, a new
Once the practice session was over, the subject target randomly appeared at one of the remaining
returned to the starting position, positioned the reticle locations, and the subject continued the search task.
over the 36" straight-ahead target and called out a The numbers were displayed against a dark
rating of viewing comfort: "Not uncomfortable to background to ensure consistent contrast across all
view", "Somewhat uncomfortable to view" or "Very target locations.
uncomfortable to view". This sequence was repeated
for seventargets locatedfrom 36to 54inches alongthe
horizontalmid-line in 3"increments.
The not/somewhat/very uncomfortable ratings were
adapted from similar scales with approximately equal
intervals (e.g., Babbitt & Nystrom, 1989). Subjects
were instructed that "Not uncomfortable to view"
means thatthe imagemay look unusual, butnotblurry,
doubled or confusing. You could easily view this
image for a period oftime. "Very uncomfortable to
view" means the image may be blurry, doubled or
confusing--something youwould notwantto view for
Figure8: LockReticle
any length of time. "Somewhat uncomfortable to
view" describes a viewing comfort between these two
The five viewing conditions tested in the viewing
extremes.
comfort experimentwere also used forthis experiment.
The preference data from the first experiment were
Five viewing conditions were tested: 1) Vergence set
used to adjust reticle distance for the adaptive
to the preferred reticle distance for the 36" target, 2)
condition. Three sequential trials were run for each
Vergence set to the preferred reticle distance for the
condition. Werandomizedtheorderofpresentation of
42" target, 3) An adaptive distance that adjusted the
each viewing condition across subjects to minimize
reticle to the userpreferred distance for each target, 4)
learningand fatigue effectsontheaggregatedata.
Monocular, presented in the right-eye, and 5) On~
Screen, where the reticle was drawn on the OTW
We designed this experiment to replicate conditions in
display.
a real simulator environment where operators must
redirect their attention between HMD symbology and
Visual Searchand Performance
on-screen imagery. The primary data from this task
In this experimentwe investigatedwhethertheviewing
were total timeto find and compare numbers at theten
condition is simply acomfort and perception issue, or
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target locations. We also recorded single target times
from acquisitionto response.
ofeach cell which is shaded white gives an indication
RESULTS of the comfort of each viewing condition. For
example, all subjects rated the on-screen viewing
ViewingComfortRatings condition at 36" (located in the lowest, left-most cell)
as comfortable, thus it is shaded completelywhite. On
The results of the viewing comfort experiment are the other hand, the binocular 36" viewing condition at
shown in a Marimekko chart (Figure 9). We feel this a 54" target distance was rated very uncomfortable by
type ofchart provides a good graphical representation almost every subject, so that its cell (upper right-most
ofusercomfortasafunction both ofviewingcondition cell) is shaded almostcompletely hlack.
and ofviewing distance. Each cell depicts the countof
eachratingchoicefor 13participants. Theproportion
Binoc
3611
Not
Binoe
LJncomfortable
:~ 42"
""
" Somewhat
0
U Binoc Uncomfortable
•
OJ) Adapt
.5
~ Very
;;
Uncomfortable
1\fonoc
On
Screen
36 39 42 45 48 51 54
ScreenTargetDistance(incbes)
Figure9. ComfortRatings ForTheFiveViewingConditionsAtSeven TargetDistances
The rating ofviewing comfortat each on-screen target The binocular adaptive viewing condition used the
distance was dependenton theviewing condition. The preference data from the first experiment to adjust the
binocular 36" reticle shows a striking decrease in HMD reticle distance based on target distance. The
comfort as the target distance moves beyond 36". For results in Figure9show mostlycomfortableviewingat
the 42" reticle, the most comfortable viewing is found all target distances. The few somewhat or very
at 42" and 45", while nearer and further target uncomfortable ratings for the more distant targets may
distances resulted in greater reports of discomfort. result from the increase in reticle/screen slant angle.
These results indicate that a fixed-distance HMD This angle may look confusing to some participants
reticle only results in comfortable viewing at or near a when presented in the context of this experiment.
corresponding target distance, in general agreement Despite these minor issues, the binocular adaptive
withBrowne,etal. viewing condition was very successful at mitigating
vergence mismatch compared to the otherHMD-based
methods.
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The aggregate median response times across viewing
Results from Browne, et aI, plus our previous conditions are shown in Figure 10. The adaptive
experience with monocular HMDs indicate that viewing condition had the quickest aggregate median
monocularviewing is problematic, and the data forthe response time of 1115 msec, Just slightly slower was
monocular condition appear to confinn this theonscreen condition, with atime of1157msec, The
expectation. The most discomfort was found at the fixed vergence conditions were more than 10% slower
closer target distances but some subjects even found than the adaptive or onscreen cases and the monocular
the more distant targets uncomfortable to view with a viewingcondition provided the longestresponsetimes.
monocularpresentation.
The data show rather large error bars (standard
The on-screen reticle was in perfect correspondence deviation), representing the significant subject to
with the screen target and imagery in terms ofdepth, subject variation for each viewing condition, but we
but it resulted in a high degree ofslant relative to the believe that the trend is obvious with adaptive and
line-of-sight, and it decreased in angular size with onscreen taking the least time and monocular taking
distance. Even so, this viewing conditionwas rated as the most. This indicates that not only are the fixed
most comfortable to view, in agreement with Browne, vergence conditions and the monocular condition less
etal. (2008). comfortable, but they also have an impact on user
performance,atleastforatargetingtask.
VisualSearchandPerformance
a"
Figure 11 shows how the response time varies a
We calculated the median search time (time to find the function not only of viewing condition but also of
target and achieve "lock"), the median response time target location, We split the viewing conditions into
(time between "lock" and a correct response on the two graphs so that the data is easier to visualize. The
number matching task) and the total time (sum of adaptive dataappears on both graphs. Since itwas the
search and response times). The average search time most likely condition to be implemented in a real
for all ten targets ranged from 38 to 41 seconds, and system, we wanted to ensurethatwe could compare all
the effect of viewing condition was not significant. otherviewing conditionsto it
Although we measured large differences in the ratings
of comfort for the five viewing conditions, it did not There is a large variation in response time across
translate into adifference in overall performance or in viewing conditions for the very near targets, with
search time. Both of these metrics include a relatively rapid responses for some viewing conditions
disproportionate amount oftime searching for the next (on-screen and adaptive) andothers (binocular36"and
target. The amount oftime spent on searching for a 42") with significantly slower response times, In the
target might be too coarse of a measure to identify mid-distances, there were differences between the
differences inperfonnance amongviewingconditions. viewing conditions, but no obvious trends. At the far
distances perfonnance for all viewing conditions
In contrast, response time was directly related to the worsened, while corresponding ratings of"somewhat"
reticleviewingcondition. We definedresponsetime as and "very uncomfortable" were only found with
the elapsed time between target acquisition and a binocular 36" and 42" conditions, We attribute this
correctmanual response. We feel that response time is increased response time at the longest target distances
a good metric for proving our hypothesis that the to the fact that the font size and contrast were reduced
bigger the disparity is between HMD and OTW when viewed from these distances, Numerous subjects
imagery, the longer it will take the subject to make a stated that the numbers were very hard to read at the
correct response, While differences in background longer target distances. We tried to balance the
imagery and target location could affect the time to experimentby notmakingthenumberstooeasyto read
find each target, the effect on response time should be at the short distances so that there would be the
minimaL potential for a noticeable difference between different
viewing conditions. We may need to increase the
We found significant effects for Viewing Condition readability of the compared numbers for future
[F(4, 48) ~ 3.69, P< .05]; TargetPosition [F(9,108) ~ experiments.
5.07, P < .001]; and the interaction of Viewing
Condition and Target Position [F(36,432) ~ 1.74, P <
.0I].
2009PaperNo. 9178Page8af11
lnterservice!lndustry Training, Simulation, andEducationConference(l/lTS'EC) 2009
F
~
1800
.§
1600 ~~..
I- 1400 +,~+~~~-1
"
~ 1200 --rr-I---f""'1I---+---
~
1000 1.
"
0:: 800
~
'g"
600
:l; 400 1·+ 1 I I --I-j_._--
"
'"
f! 200
~
«
Binocular Binocular Adaptive Monocular Onscreen
36" 42"
Figure 10. AverageMedian ResponseTimeAs AFunctionOfViewingCondition
1506 1500 Binocular36"
"" '"
!~ 1460 .~s 1406 ,,n4B,iutlCular42'l
, \
5~ 1300 "5 1300 , \,
f= i: f \ .......
~ 1200 ~ 1200 ! "
ccCo CEo "........./,<1
~ 1100 ~ 1100
0: 0:
1000 1000
36 38 40 42 44 46 48 50 $2 54
NominalScreenTargctDlstancc(inches) NominalScreenTargetDistance(inches)
Figure11.AverageMedian ResponseTimeAsAFunctionOfViewingCondition And TargetDistance
DISCUSSION more distant OT\\! positions will be uncomfortable to
view. Ifthe dioptricaverage distanceof42" is chosen,
We investigated the effect of five viewing conditions most users are not satisfied with the viewing comfort
on viewing comfort and visual performance for a straightaheadat36",orat largerdistancesof54".
binocular HMD integrated with a faceted OTW
display. Our experiments confirmed that setting the Monocular viewing was also found to be
Hl\1D reticle to asingleviewing distance is not agood uncomfortable to view, primarily at close screen
solution for the 36" to 54" range ofviewing distances distances, but some users found it uncomfortable even
found in the M2DART faceted simulatordisplay. We at the longer target distances. These problems
notonly found thatastatic vergenceviewing condition extended to the perfonnance task as well, where the
was uncomfortable to view over many viewing monocular condition produced the slowest response
distances but also that a static vergence negatively times ofall conditionstested atanyviewingdistance.
impacted perfonnance on a targeting task. In addition,
for a fixed vergence the question always remains to These problems with monocular imaging are
what distance should thevergence beset? Ifit is setat interesting because most currentHI\1D systems used in
the straight ahead distance of 36", all other locations U.S. fighter jets and helicopters are monocular
have a vergence setting which is too close and the (JHMCS, DASH, lHADSS). In fact, a number ofthe
2009PaperNo. 9178Page9of11
