The towers were colored concrete gray, were 129 m wide, and
43 m deep along the Y coordinate. From south to north their
heights were 701, 823, 729, 945 and 834 m, with respective
spacings between them 215, 86, 258, and 172 m. At the southeast
corner of each tower adjacent white 45° right triangles were
drawn on the east and south walls with their 90° angle at the
corner at ground level (see Figure 1 inset). Their high point
was at the corner 43 m above the ground, and their bases extended
43 m along the ground. Relative perception references were
towers depth, and triangle heights and bases, all being 43 m.
The large towers and the white triangles were used to ensure that
distinct cues for perceptual reference, and distinct relative
perception cues, were available at the longest expected viewing
distances and from all viewing angles.

The other (3-D with familiar objects) visual database added
to the texture database several types of 3-D objects which are
depicted schematically in Figure 1. The objects included
variable size four-tree "groves," trucks on the roads and
billboards beside them, mobile homes, and a high school type of
football stadium.

The trees were not simple geometric objects. They were of an
evergreen type, had a texture pattern which gave them a somewhat
realistic appearance, and allowed viewing the background between
the "branches." Tree groves consisted of four trees planted ina
square pattern, with the grove edge-to-edge dimensions equal to
tree height. Tree width and the spacing between them in a grove
were one-third of tree height. Tree groves were scaled
proportionally in sixteen equally spaced sizes between 5 and 37 m
for their maximum dimensions. Two maximum size tree groves with
north-south and east-west aligned edges were located just north
and south of the 45° road with centers at X = 514, Y = 851, and X
= 514, Y = 630.

Tree groves and mobile homes were placed within a continuous
200 m wide area (X = -237 to -437) on the west side of the
detailed database. This area of tree groves and mobile homes
extended on indefinitely to the south with the adjacent road
(center at X = -194). A tree grove of randomly determined size
and edge alignment was randomly located along each 75 m north-
south interval of the area, and randomly along its width. The
center of a mobile home (18L x 4W x 3.3H) with length oriented
east-west was located 30 m south of the center of every fourth
tree grove. A second adjacent mobile home with length oriented
north-south was located with its center 14 m south and 14 m west
of the center of the first mobile home. The same tree grove and
mobile home area extended between Y = 1032 to 1232 along the
north edge of the detail area from X = -437 to +613, but with
mobile homes placed south of the adjacent tree grove.



APPENDIX A

Multiple Regressions and Factor Weights



logically due to some combination of image display
characteristics and image content, or to differences in test
conditions.

From a methodological standpoint the results of this
psychophysical research are encouraging. Large and statistically
significant differences were found between most of the
experimental design factors, and between many of their
interactions. Although practical significance may be debatable,
the large number of observations resulted in high statistical
significance for correlations of .04 or greater, and differences
in perceptual accuracy of 3% or greater. The magnitude
production psychophysical method used appears to be sensitive to
the characteristics of visual scene content and user tasks.
These have proven difficult to assess precisely by means of more
global measures of flying or combat performance.

26



An exponent of 1.0 is a necessary, but not sufficient,
condition for reflecting accurate perceptions. If perceptions
are a constant 5% of stimulus magnitudes, for example, an
exponent and slope of 1.0 will be found even though the
perceptions are highly inaccurate. If such a constant perceptual
error exists, it will shift perceptual magnitudes by that
constant, in the same manner that the constant k shifts plotting
levels to reflect the units of measurement. The combination of
these two constant shifts will be reflected as a vertical shift
in the slope line of the log-log plot. Misinformation, that an
exponent of 1.0 represents accurate perceptions, has somehow
permeated throughout a lot of the psychological literature of
authors who are not specialized in psychophysical research (for
example, Kling & Riggs, 1971).

De Maio & Brooks (1982) and De Maio, Rinalducci, Brooks &
Brunderman (1983) investigated the effects of vertical object
density and detail on the accuracy of altitude perceptions, using
the Stevens exponent n as their psychophysical measure. They
recorded simulator visual imagery as photographs, as dynamic
video tape motion segments, and as static video tape views. The
imagery was recorded at eight altitudes in 50 foot increments
from 50 to 400 feet above ground level. The photographic and
video tape records of various visual databases at the eight
altitudes were viewed by groups of pilots on a large classroom
projection screen. For each image or dynamic image segment, each
pilot estimated the height above ground.

The power function exponents obtained from these estimations
varied from a low of 0.20 to a high of 0.84 for the various
visual databases. The higher exponents were obtained for the
visual databases with the highest object density and detail. De
Maio et al. (1983) concluded that the knee in the exponent versus
object density curve at 0.7 (90% of the exponent asymptote just
above 0.8), corresponding to an object density of about 5 objects
per km’, represented the point of diminishing returns in object
density for height perceptions. For the highest exponent of 0.82
that De Maio & Brooks found for the recorded imagery, however,
they report mean estimated altitudes of 25 ft for 50 ft (50%)
actual simulator imagery height, and 257 ft for 400 ft (64%)
actual. These end point heights result in a power function
exponent of 1.12 rather than 0.82. Middle heights or individual
variability must have had substantial effect, therefore, for
their 0.82 result to occur. Although not reported for other
heights, their exponent would have required estimated altitudes
of around 75% of actual at 100 and 150 ft heights, estimates of
less than 50% at 300 and 350 ft, or some similar combination of
higher percentage estimates at lower heights, and lower estimates
at the higher heights.



Procedures for distance and height perceptions. The subject
began the first trial for forward distance estimation by pressing
the trigger switch of the right joystick used for X-Y viewpoint
motion control. This unblanked the image at current helmet
angles. As the image unblanked the first of the sequence of
increasing target values to be estimated (#1, equal to .25
relative or 8 m absolute) appeared on the panel CRT. The subject
used fore-aft joystick input to move the eyepoint rearward along
the rail to a location estimated to match the target value in
distance south of the perceptual reference (the south wall of the
south tower). When this location was attained, the subject
entered the estimate by pressing the push button on top of the
opposite (left) joystick. The next target value (#2) then
appeared on the CRT, and the subject moved the eyepoint rearward
to and entered the estimate for it. This process continued
through estimation of the sixth and farthest target value. Upon
entering the estimate for it, the image blanked to a uniform gray
for 3 seconds as the eyepoint location was reset to start the
sequence of decreasing target values to be estimated on the
trial.

The reset location was at a distance on the rail three times
the largest #6 target value, or at Y = -1032 m for relative
perceptions and Y = -914 m for absolute perceptions. As the
image unblanked, the first decreasing sequence target value to be
estimated (#6) appeared on the CRT, which was the same as the
last value of the increasing sequence. The subject used the
joystick to move the eyepoint forward (or rearward) to a location
estimated to match the target value in distance south of the
reference, and entered the estimate. The next target value (#5)
then appeared on the CRT, and an estimate was made for it.
Estimation then continued through the last decreasing sequence
target value (#1). Upon entering this last estimate for the
rail, the image was blanked to gray and the eyepoint location
reset without unblanking to the starting location for the next
rail. The subject then initiated the trial for the new rail when
ready by pressing the joystick trigger switch. These procedures
continued through the ninth rail. Subjects were free to rest for
a while between rails, but seldom did. The same procedures and
unblanking values for rails were used for perceptions of lateral
distance and height, except that height trials started with
unblanking at 1m above the ground. For height left joystick up-
down inputs were used for viewpoint motions and its trigger
switch for starting the trial, and the right joystick top push
button used to enter estimates. For lateral distance
perceptions, subjects were required to set their eyepoint to the
target value distance east of the east walls of the towers. For
height perceptions, they set their eyepoint to the target value
height above the ground.

° S s i . The first trial for speed
perception started on the highest rail with the helicopter

13



APPENDIX A

Table A-1

Multiple Regressions and Factor Weights for Log of Percent Magnitude
Production Error

Independent Factors
EXP REP vIS BAS ROW coL SGN VAL

Forward Distance

Multiple R: .552
Constant: 2.545

Weight -011 -.012 -.013 .093 .030 .025 .091 -.006
Step Entered 8 7 6 1 3 4 2 5
R After Entry -552 .551 .549 .346 .520 .541 .487 .547

Lateral Distance

Multiple R: .499
Constant = 2.106

Weight -087 -.022 .111 .053 .021 .101 .026
Step Entered 4 Not 7 1 5 6 2 3
R After Entry +448 ~499 .255 .490 .497 .345 .401
Height
Multiple R = .476
Constant = 1.972
Weight .020 .015 -.013. .127 .013 .017 .044 ~.030
Step Entered 6 7 8 1 5 4 3 2
R After Entry ~473 .474 .476 .345 .470 .466 .460 .443
Speed

Multiple R: .681
Constant: 2.268

Weight -107 .096 NA -.088 NA -095 -.011
Step Entered 2 3 Not NA 1 NA 4 5
R After Entry -577  .628 NA -508 NA -674 .681

Note. N for multiple regressions is 5184, except 1152 for speed.
Full labels of the three-letter abbreviations for the independent
factors may be found in Table 1.



FOREWORD

The U.S. Army plans to increase use of computer-generated
imagery for simulation in initial and combat readiness training.
Computer-generated imagery is the key technology in virtual
reality, which is being explored for potential uses in training
and mission rehearsals. How well visual perceptions with
computer-generated imagery compare with real-world perceptions
will be a major factor determining simulation and virtual reality
effectiveness. The accuracy of visual perceptions with computer-
generated imagery, however, remains almost totally undefined
after nearly three decades of application in simulation. Diffi-
culties in conducting research with simulators designed for
training is a major reason for the failure to define their per-
ceptual accuracies in comparison to the real world.

The Simulator Training Research Advanced Testbed for
Aviation (STRATA) at the Rotary-Wing Aviation Research Unit
(RWARU) of the U.S. Army Research Institute for the Behavioral
and Social Sciences (ARI) has a very high quality virtual reality
type of helmet display and is designed for research. STRATA was
configured and used to obtain thousands of psychophysical obser-
vations per subject on distance, height, and speed perceptions.
This allowed high statistical confidence on the effects of the
factors tested.

The results indicate that distance, height, and speed
perceptions with STRATA’s very high quality virtual reality type
of computer-generated imagery are substantially less than simu-
lated physical values or real-world perceptions. The results
suggest that substantial perceptual underestimations may be
expected with existing and at least near-term computer-image
generation technology. These perceptual underestimations may
limit attainment of the highest levels of combat proficiency if
training is limited to only that conducted in simulators which
use computer-image generators. The results also suggest existing
and developmental night vision systems that use similar digitized
image formats might produce similar perceptual underestimations.

This psychophysical research was initiated internally by the
ARIRWARU as the first effort of a series to objectively quantify
the simulation fidelity of STRATA. It will be applied by the
ARIRWARU in planning future STRATA research, and as a knowledge
resource for application to issues concerning aviation simulator
training and development.

EDGAR M. JOHNSON
Director



Discussion

Simulator Versus Real-World Perceptions

The primary issue of concern in simulator or virtual reality
psychophysics is how well perceptions with the visual system
match those in the real-world. These results were not
encouraging. Only height perceptions appear to be reasonably
comparable with the accuracy of perceptions in the real-world.
Real world relative perceptions have been found to be more
accurate than absolute perceptions (Gibson, Bergman & Purdy,
1955), and this also was found for these simulator distance and
height perceptions. Relative height perceptions at 83% of actual
stimuli, in particular, were reasonably accurate.

Median absolute forward distance perceptions with the
simulator visual system were 34% of simulated physical distance,
while typical real-world absolute perceptions were about 91% of
actual physical distances (Gibson & Bergman, 1954). Lateral
absolute distance perceptions in the simulator of 43% of physical
distances also were much less than for real-world perceptions.

Median absolute height perceptions with simulator vision
were 59% of simulated physical heights, while real-world absolute
perceptions over land average 87% of actual heights (Ungs &
Sangal, 1990).

Median speed perceptions with simulator vision were 41% of
simulated physical speeds, while typical real-world perceptions
of speed are 90% of actual (Salvatore, 1968).

Reasons for the large differences in accuracy between
simulator and real world perceptions of distance, height and
speed are not evident. It was hoped the high resolution, wide
field of view, head-slaved, color virtual reality type of display
used in this research would result in close to veridical
perceptions. This did not occur. Characteristics of the display
image, image content, selected test factors and levels, test
procedures, or interactions between these aspects, must be
causing the differences. The current results suggest several
causal factors that may explain some part of the differences, but
are far from providing a complete explanation.

There are trends of more accurate simulator perceptions as
eye height is reduced. The minimum eye height used of 6 m is
about four times the 1.5 m eye heights used in the real world
distance and the primary speed perception tasks used for
comparison. The eye height trends suggest perceptions at 1.5 m
eye height ought to be about 10% more accurate for forward and

24



Three truck types were used. One was an 18-wheel semi type
with box trailer, the second the same with a tank trailer (both
18L x 2.4W x 4H overall), and the third a full size pickup truck
(5.5L x 2W x 1.8H). Billboards 6 m wide by 4 m high were placed
only on the west or north sides of roads, where they always faced
the subject. For contrast with the ground texture, a range of
light bright colors, white and silver, were used for the trucks,
and their wheels were black. The billboard frames were colored
light gray. Truck or billboard objects were randomly placed
along each 75 m interval of the roads, with a restriction of no
overlapping at interval ends of adjacent trucks in the same lane.
The type of object in each interval, and its heading and color if
a truck, were randomly determined. The stadium included a U.S.
football field yard-marked outline with goal posts, a track
around the field, and spectator stands on each side. The
sidelines ran at an azimuth of 155°. The center of the stadium
was located at X = 132, Y = 628.

No roads or 3-D objects existed in the area where viewpoint
motion was allowed to the south of the south tower and east of
the north-south road (see Figure 1). Ground texture was the only
visual cue inside this area. Actual viewpoint motions extended
well below the figure for forward distance perception trials, and
well to the right of it for lateral distance trials. Ground
texture was the only visual cue on the east (left looking south)
side of the road during all speed estimates, and also on the west
side during perceptions with the textured visual database.

eri 1 si

Experimental design in terms of data collection consisted of
the factors outlined in Table 1, with the within factors listed
in order of increasing cycling rate. Each type of perception was
analyzed separately, however, rather than using perception as an
additional factor. Factor levels are indicated in parentheses,
and listed in the order tested for within factors (except for
rows and columns as indicated below). Counterbalancing was not
used. It should be noted this results in a full half-replication
with the 3-D with familiar objects visual database prior to any
perceptual estimates being required with the texture only visual
database. The three-letter abbreviations are used for factor
reference in some of the results later in the report.

10



combined. Nonparametric tests included the sign, Wilcoxon signed
rank, Friedman, and median tests (Norusis, 1993a). Repeated
measures multi-factor ANOVAs (Norusis, 1993b) also were
calculated to compare the other statistics with analyses of
means-based main effects differences, and to assess interaction
effects. For ANOVAs the log transform of magnitude production
percent error was used, with 300 added to Y axis data, and 100 to
X and Z data, to make all points positive prior to
transformation. The log transformation corrected most of the
positive skew and kurtosis in the original data distributions.
Log transformed data also were used for correlations and multiple
regressions. They increased most of the larger correlations over
those for the original error data, and increased multiple R's by
-02 to .06.

Statistical significance of factor main effects were closely
comparable for all the nonparametric tests and correlations.
Some of the ANOVA results were considerably less significant than
the nonparametric and correlation statistics. The differences
appeared to be due mainly to skew aspects which reduced mean log
transformed level differences close to zero where larger median,
rank and correlation differences existed. Probabilities from the
median test were selected for use as the primary statistic for
interpreting results because medians or geometric means usually
are used in psychophysical research. While some reservations
exist as to appropriateness of the median test for this repeated
measures design, it is most directly related to the selected
median measure of central tendency. It also gave slightly less
significant probabilities than the other more powerful
nonparametric and correlation tests.

owe. onents

Psychophysical power function exponents and intercepts
(Stevens, 1957) were computed using median magnitude productions
as the physical parameters and target values as the perceptual
parameters.

The power function exponent for forward distance perception
is 1.00, for lateral distance 0.91, for height 0.88, and for
speed perception 1.03. Respective zero intercepts are -0.76 m, -
0.37 m, 0.41 m, and -4.56 km/hr. The 1.0 exponent for forward
distance indicates overall changes in perceptions are exactly
linearly proportional to median changes in physical magnitude
productions. The 0.91 and 0.88 exponents for lateral distance
and height perceptions indicate their proportions decrease as
physical magnitudes increase. One should note the 1.0 power
function exponent does not reflect accurate perception, but only
changes linearly proportional to physical stimulus changes. For
example, forward distance perceptions are found (see Figure 2) to
be just 41% of the simulated physical distances produced for
then.

16



Table 2

Sequence of Testing of Viewpoint Motion Rails

Column
1 2 3
Row
3 4 7 9
2 2 5 8
1 1 3 6

Prior to the test week, subjects had a helmet liner poured
and helmet display attachment brackets boresighted. A pair of
subjects were tested for 10 to 12 hours each in alternating
sessions over a period of five days. Testing schedules were
adjusted around other simulator uses. Most sessions were about
50 minutes in duration, but varied from 20 to 80 minutes. The
first test morning began with a desktop briefing on the
perceptual tasks and testing procedures, followed by about one
hour of training on them in the cockpit and helmet display.
Training ended with a free-flight period in which subjects were
prompted to visually inspect at very close range, from different
viewing angles, all 3-D objects in the visual database. Subjects
were informed in the briefing that the total length of the 18-
wheelers was 60 feet. No other dimensional information or
feedback on accuracy of magnitude productions was provided to
subjects during training or testing.

ial. Forward and lateral
distance, and height perceptual estimates were conducted with the
simulated fuselage heading fixed to north. Image unblanking
occurred for forward and lateral distance perceptions at the
start of a trial, at an eyepoint on each rail, which was three
times the initial target value from the perceptual reference
corner of the south tower, but opposite in sign. In visual
database coordinates, unblanking occurred for relative forward
distance perceptions at Y = +32, and at Y = +23 for absolute
perceptions. For lateral distance perceptions, unblanking was at
X = -32 for relative, and at X = -23 for absolute perceptions.
The image unblanked for all height perceptions one meter above
the ground. For speed perceptions, the image unblanked with the
fuselage facing south at Y¥ = 0 and X = -184, 10 m east of the
center of the north-south road. No limits to eyepoint motion
existed in either direction along a rail. Subjects could go
below ground level during height perceptions or free-flight, and
several did so a few times during training or in early testing.

12



lateral distance and speed, perhaps more so for the distances.
The larger viewpoint rail column offsets also had a negative
impact on perceptual accuracies. Being closer to, or moving more
directly toward or from the perceptual reference, resulted in
slightly more accurate perceptions.

The minimal improvement over texture in accuracy of distance
perceptions with the high detail 3-D visual database with
familiar objects, and the lack of improvement in height and speed
perceptions, was not expected. Lack of counterbalancing of order
of testing texture and 3-D visuals may have obscured an actual
effect. The 3-D database, with the same texture of the texture
database, was always tested before the texture only condition.
This may have resulted in perceptual calibration of the texture
under the 3-D condition, and masked actual differences.

Rationale for the 3-D condition first was that opportunity
for exposure in flight training to a detailed 3-D part of the
database, will almost always exist before having to fly over the
texture only database areas. The 3-D condition first addresses
the applied issue of acceptability of texture for flight
training, but may have obscured the more fundamental issues of
the effects of visual database detail and content familiarity.
This minimal impact of visual scene detail may be of substantial
consequence from a practical standpoint in visual system design
and application. One should note, however, that Kleiss and
Hubbard (1993) found increasing density of vertical objects
improved altitude change perceptions near the ground surface
independently of ground texture. It should not be surprising
that different visual scene characteristics may be required to
support the different perceptual discriminations involved in
flying.

Co sions

It was hoped that very high quality pilot's virtual reality
type of visual display which was used might reduce or eliminate
the large perceptual errors commonly observed anecdotally for
most flight simulator visual display systems. This hope was not
realized. While similar psychophysical data for other simulator
visual display systems do not exist to provide definitive
comparisons, these results suggest there may not be large
differences. If so, they suggest that head slaving a high
quality very wide field of view display has contributed little to
improving the match of simulator visual perceptions with those in
the real world, except perhaps for height perceptions. The
failure to produce a close match with real world perceptions is

25



Target values to be estimated were presented on a CRT
display in the upper center of the instrument panel, which was
clearly visible through the blanked to black level area of the
helmet display. For relative perceptual estimates, target values
were presented as a single decimal fraction or integer multiple.
For absolute distance or height estimates, target values were
presented with units labels on the top line in feet, on the
jniddle line in yards, and on the lower line in meters. For speed
estimates units labeled target values were provided in statute
miles per hour on the top line, and on the lower line in knots.
The different units were intended to allow subjects to use those
with which they were most familiar. All normal flight
instruments and helmet display symbology were turned off.

Identical spring centered joysticks (Measurement Systems
Model 546) were mounted on the right and left sides of the seat
outside the armorplate. The right joystick controlled viewpoint
fore-aft position and speed by fore-aft inputs, and lateral
positions by right-left inputs. The left joystick was mounted
with a 60° forward tilt. Up-down viewpoint positions were
controlled by similar inputs with it, and right-left inputs used
to control yaw during pre-test training free-flight. The trigger
switch of the control used for viewpoint control was pressed to
initiate a trial, and a pushbutton on top of the opposite control
used to enter estimates for target values during a trial.
Joystick responses were defined so non-helicopter pilots could
rapidly and precisely adjust their position or speed. The center
+/- 2% was a non-response deadband. Stick voltages beyond this
band (minus the deadband) were squared and then multiplied by a
gain which resulted in maximum viewpoint rates of 329 km/hr for
distance and height estimation, and maximum acceleration response
of 4.6 m/s*or 0.47 g for speed estimation. An integration time
constant of one second was used for all control responses except
switch inputs.

Visual Databases

Both visual databases consisted of a visually unlimited
expanse of flat ground surface textured in shades of green. The
detail area (see Figure 1) of the textured visual database added
several roads and five tall skyscraper-type towers with their
east walls aligned on X = 0. Shadows were not used for any type
of object. The east-west visual database axis is labeled xX, the
north-south axis Y, and the height axis Z. All database
coordinates and object dimensions are given in meters. The
database X-Y-Z 0-0-0 and perceptual reference coordinate was at
the southeast ground level corner of the south tower. A 9 m wide
road with center at X = -194 extended infinitely southward from Y
= 22. It turned 45° clockwise at Y = 22 to run northeastward
between the two south towers. Another road ran east-west just
north of the towers at Y = 989.



VIRTUAL REALITY PSYCHOPHYSICS: FORWARD AND LATERAL DISTANCE,
HEIGHT, AND SPEED PERCEPTIONS WITH A WIDE-ANGLE HELMET DISPLAY

CONTENTS
Page
INTRODUCTION . . 1 eee ee ee ee ee eee ee ees 1
Simulator Psychophysical Research . ..- +--+ +++ +s > 1
Real-World Psychophysical Research ee 4
METHOD . 2. ee ee ee ee ee ee ee ee ee ee eee 5
Subjects ee ee ee ee ee ee ee ee 6
Apparatus 2. 6 6 6 ee ee ee ee ee ee 6
visual Databases ...- ee ee eee ee ee ee 7
Experimental Design . . - - + + e+ ee ee ee ee es 10
RESULTS . 2. 6 6 6 ee ee ee ee ee ee ee 14
Power Function Exponents a 16
Main Effects a 17
Correlations and Multiple Regressions ......-+.-. 21
Interactions . 2. 6 ee ee ee ee ee ee eee 22
DISCUSSION . 2. 6 6 ee 6 oe ee ee ee ee ee ee ee 24
Simulator Versus Real-World Perceptions ........ 24
Conclusions . . 1. ee ee ee ee ee ee ee ee 25
REFERENCES . . 1 ee ee ee ee ee ee ee ee ee ee 27
APPENDIX A. MULTIPLE REGRESSIONS AND FACTOR WEIGHTS .. .- A-1
LIST OF TABLES
Table 1. Experimental Design Factors and Factor Levels . 11
2. Sequence of Testing of Viewpoint Motion Rails . 12
3. Magnitude Production Percent Error Distribution
Statistics for Forward and Lateral Distance,
Height, and Speed Perceptions .....-+..-. 15
4. Median Perceptions in Percent of Physical
Magnitude Productions, and Median Test
Probabilities for Factor Level Differences 7 19

xi



account for about one-fourth to one-half of magnitude production
error variance.

Table 5

Factor Correlations (r) for Log of Percent Magnitude Production
Error

Independent Factors
EXP REP VIS BAS ROW coL SGN VAL

Perception
Correlations*

Forward Distance

xr -043°-.046 -.048 .346 .184 .150 .342 -.077
Lateral Distance

xr 201 -.004° -.051 .255 .199 .080 .232 ~-.205
Height

xr .054 .040° -.037° .345 .057 .078 .121 .279
Speed

xr .275 .247 -.002' NA ~.508 NA ~244 -.098

Note. N for correlations is 5184, except for speed N = 1152.

Full labels of the three letter abbreviations for the independent
factors may be found in Table 1.

7one-tailed p < .0005 for all x's without superscript.

‘y= .001. ‘p= .397. ‘p = .002. “p = .004. ‘p = .479.

While the stepwise increases in multiple R generally are
proportional to factor correlation values, some of the factor
weights are not at all proportional. Weights for forward
distance are closely proportional. The VAL weight for lateral
distance is not at all proportional. SGN and VAL weights for
height are not proportional, although they retain an ordinal
relationship. For speed, the ROW correlation is about twice as
large as the other three substantial correlations (EXP, REP, and
SGN), yet its weight is less than theirs.

Interactions

Interactions between the factors in this experiment far
exceed that expected on a chance basis, and are too numerous to

22



Table 4

Median Perceptions in Percent of Physical Magnitude Productions,
and Median Test Probabilities for Factor Level Differences

Factors
Levels

Overall

Helicopter Flying
Experience
None

Replication
First
Second

Visual
Best 3-D
Texture

Basis
Relative
Absolute

Rail Row Offset
6m
24 m
98 m

Rail Column Offset
6m
24 m

98 m (forward 195) 37

Sign of Change
Increase
Decrease

Target Values?
11-8-24
22-15-48
43-30-72
86-61-97
172-152-121
344-305-145

Type of Perception
Forward Lateral
Distance Height
41 50 72
+0000 +0000 +0000
44 57 77
38 45 64
-4874 +3593 -0589
41 50 73
42 50 70
+0000 -0007 +3309
43 52 72
39 49 71
= 0000 +0000 - 0000
48 58 83
34 43 59
-0000 -0000 -0000
47 58 75
39 49 71
37 45 69
-0000 -0010 +0003
46 51 74
42 51 73
48 68
+0000 +0000 -0000
50 57 75
35 44 68
- 0000 -0000 - 0000
46 69 91
37 50 75
38 50 82
38 45 66
42 48 58
44 46 59

Forward

41

-0000
45
38

-0000
39

~2386
41
42

0000
48
43
(24 m) 39
(49 m) 34

-0000
45
38

-0058
38
41
43
43
42
39

"Median test probability

bist relative and 2nd absolute

in meters; 3rd speed in km/hr.

19



VIRTUAL REALITY PSYCHOPHYSICS: FORWARD AND LATERAL DISTANCE,
HEIGHT, AND SPEED PERCEPTIONS WITH A WIDE-ANGLE HELMET DISPLAY

EXECUTIVE SUMMARY

Requirement:

How well visual perceptions with computer-generated visual
systems compare with real-world perceptions remains almost
totally undefined. Such comparisons will determine the effec-
tiveness and acceptance of computer-imaging systems in many
applications for virtual reality, simulator training, and
helicopter systems simulator-based research and development
(R&D). Yet psychophysical research on visual perceptions with
computer-generated visual systems is quite limited. Differences
in visual perceptions between computer-synthesized visual worlds
and the real world are significant factors that should be con-
sidered in planning and conducting simulator training and
research, but have not been available. There is an unmet need,
therefore, for psychophysical data on various types of visual
perceptions with computer-generated imagery for simulator train-
ing research, system development R&D, and operational training
and virtual reality applications.

Research objectives were to quantify psychophysically accu-
racy of forward and lateral distance, height, and speed percep-
tions with the pilot station virtual reality type of helmet
display used in ARI’s STRATA training research simulator. Factors
the literature suggests might influence accuracy of these percep-
tions were included in the research design to assess their
impact. Accuracy of these perceptions was to be related to com-
parable real-world perceptual data available in the literature.

Procedure:

Perceptual estimates were made by subjects viewing a
computer-generated terrain image in a head-slaved, color, high-
resolution, very wide angle helmet-mounted virtual reality-type
display. Subjects used a joystick to adjust their viewing point
to a sequence of six target values along computer-defined invis-
ible rails through space. These rails ran parallel with the
direction of the type of perception being estimated. Nine rails
offset from the reference cue in a 3 by 3 matrix were used for
distances and height perceptions, and four vertically offset
rails used for speed. One visual condition consisted only of
ground texture, roads, and five skyscraper-type towers, one of
which was used as the reference cue. The second visual condition

vii



ACKNOWLEDGMENTS

The author gratefully acknowledges the programming support
and assistance of Rande Doty in data collection, reduction, and
statistical analysis, and of Larry Murdock in statistical analy-
sis. My thanks to John Stewart for running some of the subjects.

CAE, Inc., site personnel headed by Nick Donker are thanked
for their capable support in reconfiguring the STRATA simulator
for this atypical psychophysical testing requirement. Rolf
Beutler programmed the test conditions and sequences, and Fred
Zalzal the test control monitor displays and data recording.
Yves Provencher poured the subject helmet liners and aligned the
helmet displays.

Majors Bill Barker and Dale Weiler are thanked for coord-
inating the scheduling of pilots to serve as subjects. A special
thanks is extended to the subject pilots for their dedicated
motivation in trying to provide accurate perceptual estimates
over the many hours of testing.

vi



ko TOWER

: regtre Toros crrrsisiit
a = | OF T 7

||
Al Y

Figure 1. Detail area for psychophysical estimates. Ground
surfaces within and beyond gaming area were depicted in a
green colored texture pattern. Three forward and lateral
rails (height 6, 24, and 98 m), and four speed rails (6, 12,
24 and 48 m) exist for each rail depicted in this plan view.
Height rails rise from the page.

8



Utilization of Findings:

The findings suggest that substantial perceptual underesti-
mation of distance, speed, and height should be expected with
computer-generated simulator or virtual reality visual systems.
These perceptual errors could promote flying the simulator too
fast and landing short and high. Simulator instructors and
students should be made aware of these tendencies for perceptual
errors with simulator visual systems. Similar error tendencies
may be expected with virtual reality visual systems. The general
psychophysical methodology used in this experiment should be con-
sidered for defining the perceptual characteristics of other
computer-generated visual imaging systems.

ix



stationary and facing south at Y = 0. The #1 target speed for
the increasing values sequence appeared on the panel CRT as the
helmet display unblanked when the subject started the trial with
the right joystick trigger switch. That joystick was used to
accelerate to the speed perceived as equal to the first target
speed, and the estimate entered with the left joystick top push
button. The next target value appeared and estimation continued
through the sixth increasing target value. When this estimate
was entered the image was blanked to gray for 3 s during which
the eyepoint was returned to the Y = 0 starting point, but at a
speed upon unblanking three times the #6 target value, which also
appeared again on the CRT as the initial value of the decreasing
sequence. The subject reduced or increased speed to that
perceived equal to the target value, and entered the estimate.
Estimation continued through the last #1 target value estimate
and image blanking. The eyepoint then was placed on the next
lower rail under the same starting conditions, and the trial
started by the subject when ready. Estimation continued through
the fourth and lowest rail.

Subjects were allowed to take a break from testing at any
time either in or out of the crew station. At the end of each
set of rails, subjects were questioned as to their comfort and
whether they desired a break. Tester set-up of new test
conditions after a set of 9 or 4 rails always imposed at least a
one minute break, during which subjects were encouraged to close
their eyes and relax.

Results

With the magnitude production psychophysical procedure used,
subject perceptions consist only of the six relative or six
absolute target values for each of the four types of perception.
Errors in perception consisted of the difference between a target
distance or speed value to be perceived, and the magnitude of the
viewpoint location or speed produced as the estimate for that
value. Median accuracy of perception in percent of magnitude
production was planned as the central tendency measure for
analysis and presentation of results. However, some forward (Y)
distance estimates were more than 100% under the target values.
When used as denominators for converting magnitude production
errors to perceptual accuracy errors, such values resulted ina
non-continuous data distribution unsuitable for statistical
analysis or meaningful interpretation. (They resulted in
transformed errors that jumped from near plus to near minus
infinity as magnitude production errors changed from just
above to just below -100%.)

Consequently, magnitude production error in percent was used
as the dependent variable measure for all data analyses. It was
obtained by subtracting target value from magnitude production
value, dividing this difference by the target value, and

14



Technical Report 1025

Virtual Reality Psychophysics:
Forward and Lateral Distance, Height,
and Speed Perceptions With a
Wide-Angle Helmet Display

Robert H. Wright
U.S. Army Research Institute

DTIC
(oo ELECTES
bo, MAY 1 1 1995

G

April 1995

19950510 052

United States Army Research Institute
for the Behavioral and Social Sciences

prio quALT +

Approved for public release; distribution is unlimited.



VIRTUAL REALITY PSYCHOPHYSICS: FORWARD AND LATERAL DISTANCE,
HEIGHT, AND SPEED PERCEPTIONS WITH A WIDE-ANGLE HELMET DISPLAY

Introduction

Psychophysical research on visual perceptions with computer
generated visual systems is quite limited. How well visual per-
ceptions of computer generated visual imagery compare with real-
world perceptions remains almost totally undefined. Yet, such
comparisons largely will determine the effectiveness and accep-
tance of such imaging systems in many applications for virtual
reality, training, and simulator-based advanced system
development.

This research psychophysically examines some of the primary
self-motion spatial perceptions involved in helicopter flight
control. It investigates forward and lateral distance, height,
and speed perceptions with a high resolution, computer generated,
color virtual reality type of helmet display.

Simulator Psychophysical Research

Simulator psychophysical research has two primary areas of
emphasis: display hardware and scene content. Psychophysical
criteria and research issues for visual display hardware were
reviewed and defined by Kraft, Anderson & Elworth (1980). Kraft
& Anderson (1980) investigated two of the issues, on display
joints and scene inserts. For target-to-background luminance
ratios above 10, increasing resolution of a targeting display
from .95 to .5 arc min per picture element increased aircraft
plan view aspect recognition ranges by 28%, rather than the 90%
suggested by the resolution ratios (Kennedy, Berbaum, Collyer,
May & Dunlap, 1988). Increasing resolution from 5 to 1.5 arc min
was found to increase vehicular detection and identification
ranges by 30 to 60%, rather than the 333% factor suggested by the
resolution ratios (Barrette et al., 1990). Target detection
ranges and combat flying tasks both improved as display luminance
increased from 2 to 51 cd/m’. Combat flying task performance
improved as lateral field of view increased from 87 to 127
degrees, and binocular viewing increased head-on aircraft detec-
tion ranges by 18% over monocular viewing (Barrette et al.,
1990). Palmer & Petitt (1977) found angular size estimates of
200% of actual for a distant triangle in a computer generated
collimated night scene, and 150% for an uncollimated night scene.
Gilinsky (1955) found 300% estimates for the same task outdoors
in daylight.

More scene content research indicates improved flight
performance for vertical objects than for objects coplanar with
the ground (Buckland, Edwards & Stephens, 1981; Martin &



CONTENTS (Continued)

Page
Table 5. Factor Correlations (r) for Log of
Percent Magnitude Production Error ee we ew 22
LIST OF FIGURES
Figure 1. Detail area for psychophysical estimates .. . 8
2. Median perceptions in percent of stimulus
for type perception and factor levels ..... 18

xii



this include the pilot experience factor for all four perceptions
(p = .25 to .84), the visual factor for forward (.19) and lateral
(.39) distance, the basis factor for lateral distance (.08), rail
column offset for lateral distance (.14), and the sign of change
factor for lateral distance (.04) and height (.10). The reason
for these exceptions primarily appears to be due to skew-related
reduction in factor level mean differences to values less than
median differences. However, the greatly reduced degrees of
freedom and the large mean square of the F test denominator for
the between subjects experience factor probably is the reason for
those exceptions.

lations and Multip] .

Table 5 shows the independent variable multiple regressions
and correlations with the logarithm of the dependent variable,
percent error in magnitude productions. The SPSS multiple linear
regression analysis program with stepwise variable selection was
used for computing the multiple regressions and correlations
(Norusis, 1993a). Independent variable factor levels were coded
with sequential integer values for correlation and regression.
Correlations and regressions were examined for rail offsets and
target values coded with actual test values, found to be lower,
and therefore were not used.

The maximum correlation for distances and height are with
the basis (BAS) relative-absolute factor. For forward distance
the BAS correlation is .346, for lateral distance .255, and for
height .345. Due to the large N's, all correlations above .04
are statistically significant with probability less than .0005.
For distances the second largest correlation is with the sign
(SGN), target values increasing-decreasing factor. For height
error the second largest correlation is with value (VAL) target
values, and the third largest is with SGN. No other height
correlations approach .1. For lateral distance perceptions
experience (EXP), ROW, and VAL all are about .2. ROW is .184 and
column (COL) .150 for forward distance. Speed error correlations
reflect a different pattern, with ROW at -.508 the maximum.

Other substantial speed correlations include EXP at .275,
replication (REP) at .247, and SGN at .244. Only absolute speed
perceptions were required. Therefore, the BAS factor is not
applicable.

Multiple regression R's (see Appendix A) are .552 for
forward distance, .499 for lateral distance, .476 for height, and
681 for speed. Variance (adjusted R square) accounted for by
the regression equations are respectively, .304, .248, .225, and
.461. These R square values indicate the independent variables

21



distance, and 14% for speed. These offsets all are in the
vertical height dimension. For height, the least row offset
results in 6% more accurate perceptions than the most, but this
offset is in the X or lateral distance dimension.

Accuracy of forward distance perception improves by 9% from
the most to the least rail column offset, but only by 3% for
lateral distance and by 6% for height. All these differences are
significant (p < .00005) statistically. For forward distance,
the most offset is 195 m, but is 98 m for lateral distance and
height. For height the column offset is in the Y dimension.

Increasing sequences of target values result in
significantly (p < .00005) more accurate perceptions than
decreasing sequences of target values. The improvement in
accuracy is 15% for forward distance, 13% for lateral distance,
and 7% for height and speed.

Significant differences in perceptual accuracy between
target values exist for all four types of perceptions (p < .00005
for distances and height; p = .0058 for speed). The range
between the least and most accurately perceived target values is
8% for forward distance, 24% for lateral distance, 33% for
height, and 5% for speed.

The accuracy functions across the target values are
different for each type of perception. For forward distance the
function is concave upward, and it is concave downward for speed.
For lateral distance it is relatively flat with an upward jump at
the smallest target value. For height there is a roughly linear
function of improved accuracy as target values decrease, except
for a reversal at the next to smallest value. This appears to be
due to alignment of the tops of the triangular relative reference
cues on the towers for the #3 target value (1.0), which improves
the accuracy of relative perceptions for it considerably.

Rails considered as a nine-level factor had a larger range
of differences than when grouped by threes in either row or
column offsets. The most accurate perceptions generally result
from the least offset in both row and column, and the least
accurate from the most offset in both. The range of difference
in perceptual accuracy between least and most accurate rails (p <
.00005) is 20% for forward distance, 17% for lateral distance,
and 11% for height.

ANOVA probabilities on log mean differences between factor
levels often are equal to the other statistical tests, but

20



added to the first trees and other familiar 3-D objects, such as
trucks on the road. Absolute and, for distances and height,
relative perceptions were made for both increasing and decreasing
sequences of target values along each rail. Tower depth (43 m)
was used as the reference cue for relative distance and height
perceptions. This length also was depicted as the height and
base of two adjoining white triangles painted on the lower right
corner of the towers. Pilots both with and without helicopter
flying experience were used as subjects. Errors found for per-
ceptions with the computer-generated image were compared with
similar perceptions in the real world.

Findings:

Perceptions for forward distance are 41% of the median
simulated physical stimuli, 50% for lateral distance, 72% for
height, and 41% for speed perceptions. These substantial
perceptual underestimates contrast with typical real-world
perceptions of about 90% for all four types of perceptions.
Psychophysical power function exponents were 1.00 for forward
distance, 0.91 for lateral distance, 0.88 for height, and 1.03
for speed. An exponent of one indicates a change in perception
proportional to that in the physical stimulus; an exponent less
than one a decreasing ratio of change in perception with increas-
ing magnitude of the physical stimulus. There were highly signi-
ficant main effect differences between most of the test factor
levels for all four types of perceptions, and numerous signifi-
cant interactions.

Perceptions were more accurate (6 to 13%) for pilots with
helicopter flying experience than for those with none. Relative
perceptions were considerably more accurate (14 to 24%) than
absolute perceptions. Perceptions were more accurate (7 to 15%)
when target values were increasing than when they were decreas-
ing. Forward (4%) and lateral (3%) distance perceptions were
slightly more accurate for the 3-D than for the texture visual
data-base, but no significant visual database differences were
found for height and speed perceptions. Perceptual accuracy
decreased (10 to 14%) as height of viewpoint rails increased, and
also as rail lateral offset from the reference cue increased (3
to 9%).

The magnitude production psychophysical methodology used
appears to be a sensitive approach for determining the impact of
visual system design and task characteristics on perceptual per-
formance. Psychophysical evaluations of other simulator visual
systems and other flying and fighting-related tasks appears to be
warranted. Such evaluations would provide confirmation of these
results and contribute to definition and insight into actual
perceptual capabilities and limitations of simulator/virtual
reality visual systems, which heretofore have been lacking.

viii



Table 1

Experimental Design Factors and Factor Levels

Between
EXP Helicopter Experience (None; Experience)
Pilots (N1; N2; N3; El; E2; E3;)
Within

REP Replication (1; 2)

VIS Visual Database (3-D with Familiar Objects; Texture)
BAS Basis of Estimate (Relative; Absolute)

Type of Perception (Forward; Lateral; Height; Speed)

ROW Row of Viewpoint Offset (6; 24; 98 m)

COL Column of Viewpoint Offset (6; 24; 98 m [Forward 195])
SGN Sign of Target Value Change (Increasing; Decreasing)

VAL Target Values (#1; #2; #37 #4; #57 #6)
Relative ratio: (.25 5 1 2 4 8 )
Relative (m): (11 22 43 86 172 344)
Absolute (m): (8 15 30 61 152 305)
Speed (km/hr): (24 48 72 97 121 145)

Data were collected as a full factorial design, except that
(a) 195 rather than the 98 m column offset was used for viewpoint
rails for forward distance perceptions, (b) for speed only
absolute perceptions were used, and (c) four row height offsets
tested in the order 49, 24, 12 and 6 m, and a single column
offset of 10 m east of road center, were used for speed. The
double offset of the third column for forward distance
perceptions, was used to minimize in one column the perspective
shrinking of the primary relative reference cue (towers' east
wall depth), to a single picture element or less at the longer
viewing distances. For data analyses, an a priori decision was
made to analyze the four types of perceptions separately. This
was based on the logically different nature of these perceptions,
the different factor levels for speed, and limited computer
memory.

Table 2 indicates the fixed rail testing sequence for
distance and height perceptions. This sequence resulted in a
progression from least to most rail vector offset from the 0-0-0
point of visual reference, except for the center rail. Rows
varied in Z and columns in X for forward distance perceptions, in
Z and Y for lateral distance perceptions, and in X and Y for
height perceptions.

11



Fine, B. J., & Kobrick, J. L. (1981). Individual differences in
distance estimation: Comparison of judgments in the field with
those from projected slides of the same scene. (Report M
7/82). Natick, MA: U.S. Army Research Institute of
Environmental Medicine.

Galanter, E., & Galanter, P. (1973). Range estimates of distant
visual stimuli. Perception & Psychophysics, 14(2), 301-306.

Gibson, E. J., & Bergman, R. (1954). The effect of training on
absolute estimation of distance over the ground. Journal of

Experimental Psychology, 48, 473-482.

Gibson E. J., Bergman, R., & Purdy, J. (1955). The effect of
prior training with a scale of distance on absolute and
relative judgments of distance over ground. Journal of
Experimental Psychology, 50, 997-1005.

Gilinsky, A. S. (1951). Perceived size and distance in visual
space. Psychological Review, 58, 460-482.

Gilinsky, A. S. (1955). The effect of attitude upon the percep-
tion of size. American Journal of Psychology, 68, 173-192.

Kennedy, R. S., Berbaum, K. S., Collyer, S. C., May, J. G., &
Dunlap, W. P. (1988). Spatial requirements for visual simula-
tion of aircraft at real-world distances. Human Factors,
30(2), 153-161.

Kleiss, J. A., & Hubbard, D. C. (1993). Effects of three types of
flight simulator visual scene detail on detection of altitude
change. Human Factors, 35(4), 653-671.

Kling, J. W., & Riggs, L. A. (1971). Experimental psychology. New
York: Holt, Rinhart, and Winston.

Kraft, C. L., Anderson, C. D., & Elworth, C. L. (1980).
Psychophysical criteria for visual simulation systems
(AFHRL-TR-79-30). Williams Air Force Base, AZ: Boeing
Aerospace Company, for Operations Training Division, Air Force
Human Resources Laboratory.

Kraft, C. L., & Anderson, C. D. (1980). Psychophysical criteria
for visual simulation systems: Phase IJ—Experimental investi-~
gations of display joints and scene inserts (AFHRL-TR-80-18) .
Williams Air Force Base, AZ: Boeing Aerospace Company, for
Operations Training Division, Air Force Human Resources
Laboratory.

28



Lintern, G., Thomley-Yates, K. E., Nelson, B. E., & Roscoe, S. N.
(1987). Content, variety and augmentation of simulated visual

scenes for teaching air-to-ground attack. Human Factors,

29(1), 45-59.
McCormick, D., Smith, T., Lewandowski, F., Preskar, W., & Martin,

E. (1983). Low-altitude database development evaluation and
research (LADDER). Proceedings, 5th Interservice/Industry
Training Equipment Conference (Vol I, pp. 150-155).

(1983). Low-level flight

Washington, DC.

Martin, E. L., & Rinalducci, E. J.
simulation: Vertical cues (AFHRL-TR~83-17). Williams Air Force
Base, AZ: Operations Training Division, Air Force Human

Resources Laboratory.
Base system users

(1993a). SPSS for Windows:

Norusis, M. J.
quide, Release 6.0. SPSS, Inc., Chicago, IL.
(1993b). SPSS for Windows: Advanced statistics
IL.

Norusis, M. J.
Inc., Chicago,

Release 6.0. SPSS,
Palmer, E., & Petitt, J. (1977). A measure of psychological
realism on a visual simulator. Journal of Aircraft, 14(5),
421-422.
(1968). The estimation of vehicular velocity as a
10(1), 27-32.

Psychological

Salvatore, S.
function of visual stimulation. Human Factors,
(1957). On the psychophysical law.

Stevens, S. S.
Review, 64, 153-181.
(1970). Scaling apparent

Teghtsoonian, R., & Teghtsoonian, M.
Psychonomic Science,

distance in a natural outdoor setting.

21(4), 215-216.

Ungs, T. J., & Sangal, S. P. (1990). Perception of near earth
altitudes by pilots: Ascending vs. descending over both a land
and water surface. Aviation, Space and Environmental
Medicine, 61, 1098-1102.

29



Main Effects

Figure 2 shows median perceptions in percent of magnitude
productions, for the four types of perceptions and for factor
levels. It also shows the range of medians for individual
pilots. The median percent perceptual accuracy values shown are
direct transforms of the median percent error in magnitude
productions that were used for statistical analyses. Accuracy
values are used to facilitate subsequent comparison with real-
world psychophysical data. Median percent perceptual accuracy
for the levels of each factor are plotted as vertical lines
connected by horizontal lines to form a bar. Length of the bar
reflects the relative effect of each factor. Table 4 identifies
the factor levels for these medians, and the median test
probability for the main effect of factor level differences.
Most median test probabilities for factor level differences are
less than .00005.

Overall median perceptions are 41% of the simulated physical
stimuli magnitude productions for forward distance and speed, 50%
for lateral distance, and 72% for height perceptions.

For all four types of perceptions, helicopter flying
experience significantly (p < .00005) improves perceptual
accuracy over just limited fixed-wing flying experience.
Helicopter experienced pilots are more accurate by 6% in forward
distance perceptions, by 12% for lateral distance, by 13% for
height, and by 7% for speed.

Accuracy for replications are about the same for forward and
lateral distance perceptions, and, contrary to expectations,
decreased on the second replication by 3% (p = .0589) for height
and by 5% (p < .00005) for speed. The reduced accuracies on the
second replication for height and speed are observed in the
pilots with helicopter flying experience. Non-helicopter pilots
actually improved slightly.

The best 3-D with familiar objects visual database level
results in only a 4% (p < .00005) improvement in accuracy over
just texture for forward distance perception, and only a 3% (p =
0007) improvement for lateral distance. For height and speed no
significant differences between visual databases are found.

Relative perceptions are significantly (p < .00005) more
accurate than absolute perceptions. The difference is 14% for
forward distance, 15% for lateral distance, and 24% for height.

Less row offset of viewpoint rails results in statistically
significant (p < .00005) improvements in accuracy for all four
types of perceptions. The improvement in accuracy from the most
to the least offset is 10% for forward distance, 13% for lateral

17



Technical Report 1025

Virtual Reality Psychophysics: Forward and Lateral
Distance, Height, and Speed Perceptions
With a Wide-Angle Helmet Display

Robert H. Wright
U.S. Army Research Institute

Rotary-Wing Aviation Research Unit
Charles A. Gainer, Chief

Training Systems Research Division
Jack H. Hiller, Director

U.S. Army Research Institute for the Behavioral and Social Sciences
5001 Eisenhower Avenue, Alexandria, Virginia 22333-5600
Office, Deputy Chief of Staff for Personnel
Department of the Army

April 1995

Army Project Number Education and Training
20262785A791 Technology

Approved for public release; distribution is unlimited.

iii



An in-simulator flying validation experiment by De Maio et
al. (1983) found mean height perceptions to be about 80% of
actual for three higher density and detail visual databases which
had exponents near 0.8 in the above research. For a visual
database with a 0.5 exponent mean, height perception accuracy of
60% of actual was found, and for the 0.2 exponent database,
perceptions averaged 50% of actual heights. However, for two of
the three visual databases with exponents near 0.8, pilots
received 15-minute practice sessions with full instruments. This
practice could be expected to enhance perceptual calibration for
all three of these similar visual databases. The more accurate
height perceptions with them may largely be due to this
perceptual calibration. As conducted, the validation experiment
results do reflect a positive linear relationship between
psychophysical power function exponent and perceptual accuracy in
height perception.

The method used and conclusions reached by De Maio & Brooks
(1982) and De Maio et al. (1983) are based on erroneous
assumptions about the meaning of the power function exponent with
respect to perceptual accuracy. De Maio & Brooks, citing the
experimental psychology textbook of Kling & Riggs (1971), state
"A power (Slope) of 1.0 indicates perfectly accurate estimate of
altitude." This is not true, as indicated above. A power
(slope) of 1.0 only reflects no change in the ratio between
perceptual and physical stimulus magnitudes. A power (slope) of
1.0 will indicate perfectly accurate estimation only if
perceptual and physical magnitudes are equal. This seldom will
be the case for perceptions. Therefore, the conclusions
concerning the power function exponent made by De Maio & Brooks
and De Maio et al., are relatively meaningless with respect to
perceptual accuracy. The power functions they determine for
altitude estimates with the various visual databases, however,
are valid results.

Upon initial casual reading, the results and conclusions of
De Maio & Brooks (1982) and De Maio et al: (1983) appeared to be
the most relevant in the literature to this proposed
psychophysical research on simulator distance, height and speed
perceptions. Upon the more detailed review described above,
however, only the few observations they report on actual accuracy
or percent accuracy, are considered to be germane results.

-Wi Ss 9} si

Real world psychophysical research data on the type of
perceptions used in this research were reviewed to derive single
estimates of perceptual accuracy and power function exponents.
These estimates were desired to allow comparisons with the four
types of perceptions over the ranges used for them in this
research. Where not reported and the data allowed, they were
used to calculate power function exponents.

4



through space). Nine of these rails were defined ina
geometrically spaced matrix of viewpoint offsets in x, y or z
from the visual reference, for each axis of distance or height
perception. Four rails were defined in a vertical column beside
a road for speed perceptions.

Subjects

Six male subjects were used. Three were Army helicopter
pilots with 550, 1000 and 2300 hours of flying experience. The
other three had only light fixed wing flying experience (170, 280
and 340 hours). The latter three had been selected for and were
about to begin their Army helicopter training. All subjects had
normal or corrected-to-normal visual acuity or better.

Apparatus

Subjects viewed a computer generated (Evans and Sutherland
ESIG 1000) visual scene through a color helmet display from an
AH-64 attack helicopter rear pilot station used as a simulator.
It was enclosed by black drapes which reduced the surrounding
dimmed laboratory lighting to scotopic levels. The usual
computer synthesized replacement of the canopy framing in the
helmet display image was turned off. But masking of the terrain
view by blanking fuselage and glareshield areas to black level
was retained. The helmet display allowed normal head movement,
with slight attenuation from weight reduction lines and fiber-
optic ropes used for transmitting images to the helmet. Helmet
display instantaneous field of view was 65° vertical by 125°
horizontal, with a high resolution center inset of 18 by 25°.
Horizontal overlap of 38° existed at the vertical center of the
images for the two eyes, decreasing in 41° circular arcs to 6.5°
at the top and bottom. Non-stereo binocular viewing of partially
identical (in the overlap area) infinity focus images was used.

Background images had 5, and the inset 1.5 arc min TV line
resolution in both axes, for a 10% contrast modulation input.
Display maximum white luminance capability exceeded 103 cd/m’,
and contrast 50:1. For the colors, textures and shading of
features used in the visual database, however, typical contrast
and luminance were only about 10 to 30% of system capabilities.
Inset eye tracking was not functional for this testing, so the
inset was fixed at the center of the display, and therefore was
always viewed with full overlap. A blending algorithm was used
at the edges of the inset, which usually resulted in no awareness
of these edges for normal viewing. The helmet image continuously
tracked the current angles and translations of the helmet. The
simulated helicopter fuselage was fixed facing north for all
distance and height perceptions, and fixed facing south for
speed.



U.S. ARMY RESEARCH INSTITUTE
FOR THE BEHAVIORAL AND SOCIAL SCIENCES

A Field Operating Agency Under the Jurisdiction
of the Deputy Chief of Staff for Personnel

EDGAR M. JOHNSON
Director

LT
Technical review by

John A. Dohme

John E. Stewart -
Dennis C. Wightman [Aecesion For
Bob G. Witmer NTIS CRA&I

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References

Armstrong, R. N., Hofmann, M. A., Sanders, M. G., Stone, L. W., &
Bowen, C. A. (1975). Perceived velocity and altitude judg-
ments during rotary wing aircraft flight (Report 76-3). Fort
Rucker, AL: U.S. Army Aeromedical Research Laboratory.

Barrette, R., Dunkley, K., Kruk, R., Kurts, D., Marshall, S.,
Williams, T., Weissman, P., & Antos, S. (1990). Flight simu-
lator: Advanced wide field-of-view, helmet-mounted, infinity
display system. (AFHRL-TR-89-36). Williams Air Force Base, AZ:
CAE Electronics Ltd., Martin Shenker Optical Design Inc., and
Schott Fiber Optics, Inc.; for Operations Training Division,
Air Force Human Resources Laboratory.

Buckland, G. H., Monroe, E. G., & Mehrer, K. I. (1980). Flight
simulator visual textural cues for landing (AFHRL-TR-79-81).
Williams Air Force Base, AZ: Operations Training Division, Air
Force Human Resources Laboratory.

Buckland, G. H., Edwards, B. J., & Stephens, S. (1981). Flight
simulator visual development and instructional features for
terrain flight simulation. Proceedings of the 1981 Image
Generation/Display Conference II (pp. 351-362). (AFHRL-TR-
81-48). Williams Air Force Base, AZ: Operations Training
Division, Air Force Human Resources Laboratory.

Burney, G. M. (1977). Estimation of distances while driving
(Supplementary Report 262). Crowthorne, Berkshire, England:
Department of Transport, Department of the Environment,
Transport and Road Research Laboratory.

De Maio, J., & Brooks, R. (1982). Assessment of simulator visual
cuing effectiveness by psychophysical techniques. Proceedings
of 4th Interservice/Industry Training Equipment Conference
(pp. 379-381). Orlando, FL.

De Maio, J., Rinalducci, E. J., Brooks, R., & Brunderman, J.
(1983). Visual cueing effectiveness: Comparison of perception
and flying performance. Proceedings of 5th Interservice/
Industry Training Equipment Conference (pp. 92-96).
Washington, DC.

Denz, E. A., Palmer, E. A., & Ellis, S. R. (1980). Effect of

field of view and monocular viewing on angular size judgments
in_an outdoor scene. (TM 81176). Moffett Field, CA: Ames

Research Center, NASA.

Dixon, W. J., Brown, M. B., Engelman, L., & Jennrich, R. I.
(Eds.). (1990). BMDP statistical software manual. Los Angeles:
University of California Press.

27



multiplying by 100. This measure was used as the dependent
variable for a set of nonparametric, correlation, multiple
regression, and repeated measures ANOVA analyses of independent
variable effects. Missing values of this measure were
successfully replaced by BMDP program AM (Dixon, Brown, Engelman,
& Jennrich, 1990). One or two extreme outliers for each type of
perception also were replaced with the average of the two most
extreme (for the first), or next two (for the second), non-
outlier values.

Table 3 contains magnitude production percent error
distribution statistics for the four types of perceptions. The
min-max range for forward distance is about 70% greater than for
lateral distance, and about three times greater than the ranges
for height and speed. All the distributions are positively
skewed and leptokurtic.

The distribution for speed perceptions is remarkable in that
the minimum magnitude production error is 39% more than the
target value. No magnitude productions less than the target
value, as found for the other perceptions, are even approached
for speed. Translating the 39% value into perceptual terms, the
maximum percent perceived speed is only 72% of the simulated
physical speed. All other speed perceptions are less than 72% of
the physical speed.

Table 3

Magnitude Production Percent Error Distribution Statistics for
Forward and Lateral Distance, Height, and Speed Perceptions

Perception
Statistic Forward Lateral Height Speed
Range 1714 1046 502 597
Minimum -231 82 -75 39
10th percentile 17 4 -11 78
25th percentile 69 44 7 105
Median 141 100 40 144
Mean 179 123 56 156
75th percentile 246 183 91 190
90th percentile 376 271 145 244
Maximum 1484 963 427 636
Skewness 1.907 1.172 1.230 1.678
Kurtosis 6.432 2.451 2.198 5.423

All observations involving each level of a factor were used
in computing nonparametric and correlation statistics on the main
effects of the factor, and multiple regressions for all factors

15



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Virtual Reality Psychophysics: Forward and Lateral

Distance, Height, and Speed Perceptions With a Wide-Angle 62785A

Helmet Display 791

6. AUTHOR(S) 2211
HOL

Wright, Robert H.

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13. ABSTRACT (Maximum 200 words) L
Psychophysics of a color, high resolution, very wide angle, virtual reality

type of helmet-mounted display were investigated. Subjects used a joystick to set
their viewpoint within a computer-generated image database to requested target values
in forward and lateral distance, height, and speed. Test factors for each type

of perception included helicopter flying experience, replications, 3-D with familiar
objects or 2-D texture visual databases, relative or absolute perceptions, viewpoint
motion rail row and column offsets, increasing or decreasing change in target
values, and six target values. Median forward distance and speed perceptions were
41% of simulated physical stimuli, 50% for lateral distance, and 72% for height.
These accuracies contrast with typical real-world accuracies for similar ranges of
about 90% for distance, height, and speed. Main effort differences between most of
the test factor levels were highly significant for all four types of perceptions.

14. SUBJECT TERMS 15. NUMBER OF PAGE:
Psychophysics Distance Computer imagery 42 GES
Virtual reality Height 16, PRICE CODE
Perceptual accuracy Speed .

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cover in detail. Excluding interactions with the pilot
experience factor, there are 121 interactions in each of the
ANOVA analyses for distances and height. By chance, 6
interactions of less than .05 probability could be expected, 1.2
interactions of less than .01, and .12 less than .001. For
forward distance, 26 interactions less than .05 were obtained, 18
less than .01, and 10 less than .001. For lateral distance, the
respective numbers were 22, 15 and 5, and for height 22, 5 and 4.
The ratios of obtained to expected significant interactions were
greater for 2-way and 3-way interactions than for 4-way and
higher interactions. In addition, there were about the same
number of significant interactions which involved the pilot
experience factor, although most of them were in the .05 to .01

range.

These much larger than expected numbers of significant
interactions suggest that adoption of certain combinations of
factor levels can be expected to result in much better perceptual
accuracy than for other combinations. The effects of such
combinations were explored with the combination of the best rail
with the best level of the non-rail factors over all target
values. The worst such combination also was examined. For the
best levels median forward distance perceptions were found to be
96% of physical magnitude productions, lateral distance and
height perceptions 99%, and speed perceptions 60%. These all
represent substantial improvements over the median accuracy for
all levels of all factors combined (41, 50, 72 and 41%,
respectively), and three of them are close to perfectly accurate.
The worst combination was found to reduce respective accuracies
to 25, 39, 51 and 32%.

The best combination of factor levels, however, used the
increasing sequence of target values, which involves moving
backward for forward distance perceptions, away from the
reference for lateral distance, and upward for height. In flying
and most other activities, critical forward distance perceptions
must be made while moving forward, and lateral distance and
height perceptions made while moving toward an object or the
ground. The decreasing level of change in target values was
substituted, therefore, to reflect these important aspects of
applied aviation distance and height perception. With this
substitution in the best combination of other factor levels,
median forward distance accuracy dropped to 48%, lateral distance
to 67%, height accuracy remained at 99%, and speed accuracy
dropped to 55%.

23



FORWARD DISTANCE iyo

PILOTS Cr)
EXPERIENCE C_I
REPLICATIONS 0
VISUAL CI)
REL-ABS |
RAIL (|
RAIL ROW a)
RAIL COLUMN Cat
INCR-DECR | |
TARGET VALUES [or]
50%
LATERAL DISTANCE YY
LOTS CTT)
EXPERIENCE Co
REPLICATIONS 0
ELAS —
REL-ABS
RAIL Crt
RAIL Bolun CI
INCR-DECR |
TARGET VALUES a
12%
HEIGHT | 1 aw . 1
PILOTS
EXPERIENCE Co
REPLICATIONS C)
VISUAL 0
REL-ABS a
RAIL co
RAIL ROW C4
RAIL COLUMN a)
INCR-DECR Ce
TARGET VALUES A A A |
41%
SPEED v
PILOTS COT)
EXPERIENCE LJ
REPLICATIONS Cc
VISUAL 0
RAIL ROW a )
INCR-DECR Cj
TARGET VALUES fami)
1 1 1 1 1 1 1
30 50 70 90%

PERCENT OF STIMULUS

Figure 2. Median perceptions in percent of stimulus for type
perception and factor levels. Bar vertical lines are factor
levels.

18



Rinalducci, 1983; Lintern, Thomley-Yates, Nelson, & Roscoe,
1987). The highest detail or least spacings used in ground
texture and between vertical objects provides better performance
(Kleiss & Hubbard, 1993; Buckland, Monroe & Mehrer, 1980;
Buckland et al., 1981). However, the realism of object
appearance has not been found to affect performance (Kleiss &
Hubbard, 1993).

Realistic appearing 1.5, 4.6 and 10.7 m high objects (pine
and oak trees) had no effect on altitude change perceptions in
comparison to inverted geometric tetrahedrons (Kleiss & Hubbard,

1993). Increasing object density from 1 to 13/km? improved both
percent correct and reaction time for altitude change
perceptions, and increasing density to 51/km’ resulted in further
improvement in reaction time. Texture on the terrain surface
also improved altitude change perceptions (Kleiss & Hubbard,
1993).

The best small jet landing performance was found for the
shortest runway grid spacing investigated of only 1.2 m by
Buckland, Monroe & Mehrer (1980). The least checker spacing of
67 m and the presence of vertical objects produced better
performance in jets trying to fly ata 15m height over simulated
rolling terrain (Buckland, Edwards & Stephens, 1981). Holding 30
mor 61 m altitudes and avoiding terrain crashes was better with
3-D than with 2-D visual cues, with 457 m than with 1372 m cue
spacing, and with higher contrast cues (Martin & Rinalducci,
1983). However, for a higher speed, McCormick, Smith,
Lewandowski, & Preskar (1983) found 46 m ground texture squares
to result in slightly higher altitudes than 91 m squares, and a
mixture of 3-D objects slightly lower altitudes than single types
of objects, or none. A landscape scene that contained buildings,
roads and rectangular fields gave better performance than a
schematic grid pattern for both training and transfer of a dive
bombing task (Lintern et al., 1987).

Since its introduction, Stevens (1957) power law exponent
(the "n" in the formula Y = kx") has been a primary metric used
for psychophysical scaling of the relationship between perceptual
magnitude (Y) and physical stimulus magnitude (X). The
logarithmic form of the formula usually is used: log Y = log k +
n(log X). The k in the formula is a scaling constant which is
usually reported to reflect units of measurement. When the
logarithm of Y is plotted against the logarithm of X, a 45°
straight line results when the ratio of perceptual to physical
magnitude is a constant. This 45° straight line has a slope of
1.0, and graphically reflects a power function exponent, n, of
1.0. When the ratio of perceptual to physical magnitude
decreases as physical magnitude increases, n and the slope of the
log-log plot will be less than one. When the ratio increases, n
and the slope will be greater than one.



Typical distance perceptions were found to be about 90% of
actual distances, and the power function exponent to be 1.00
(Gibson & Bergman, 1954; Gilinsky, 1951; Teghtsoonian &
Teghtsoonian, 1970; Galanter & Galanter, 1973; Burney, 1977;
Denz, Palmer & Ellis, 1980; Fine & Kobrick, 1981). Primary
weight was given to the pretesting data of Gibson & Bergman for
92 subjects, which were far more than used by any other
researchers. Calculations from their data indicated average
perceptions to be 91.3% of actual distances, and the power
function exponent was calculated to be exactly 1.00.

Real world research on helicopter height perceptions (Ungs &
Sangal, 1990; Armstrong, Hofmann, Sanders, Stone & Bowen, 1975)
indicate average perceptions are 87% of actual heights, and the
power function exponents calculated from their data are 1.00.
Ungs & Sangal found mean perceptions over land of 102% of actual
heights if ascending to target heights of 7.6 to 61 m, but 76% of
actual if descending to the same target heights. Their results
suggest ascending or descending to target values is a factor
which should be controlled in psychophysical research test
design.

Real world research on speed perception by Salvatore (1968)
and Armstrong et al. (1975) agree in indicating typical
perceptions for normal vision should be about 90% of actual
speeds, and power function calculations with their data indicate
exponents of 1.00.

Definitive psychophysical data on simulator or virtual
reality visual system distance, height and speed perceptions were
not found. The few research results available tend to be
preliminary non-definitive findings for jet aircraft that are not
directly relevant to combat helicopter heights and speeds, or the
visual databases used for helicopter simulation. There is a
need, therefore, to quantify the accuracy of basic perceptions
which result from viewing computer generated imagery, and the
effects of factors which might influence that accuracy. The
objective of this research is to respond to that need. Using the
very high quality computer generated imagery of the STRATA,
accuracy of perceptions of forward distance, lateral distance,
height, and speed will be quantified psychophysically. Effects
of a selected set of factors on these perceptions also will be
assessed.

Method

A magnitude production psychophysical procedure without
feedback was used in which subjects adjusted their helmet display
viewpoint with joysticks to requested relative or absolute target
values in forward and lateral distance, height and speed.
viewpoint motions were constrained to move in only the axis of
perception along computer defined invisible rails (straight lines

5