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An Ecological approach to partial binocular overlap

Authors:

Abstract

A partial binocular-overlap helmet-mounted display (HMD) allows the presentation of wide-field-of-view imagery with no loss of resolution and a reduction in size and weight. One trade-off with these attributes is binocular rivalry created by the edge of the imagery seen by one eye overlaying continuous imagery seen by the other eye. Three distinct methods are considered that reduce this rivalry--and there are trade-offs with each approach. These three methods are the use of optical stops or filters that provide a luminance gradation that softens the overlapping binocular edges, left/right eye assignment for the flanking monocular regions, and contour lines superimposed on the imagery that correspond to the binocular/monocular borders. These approaches to improving the quality of partial binocular- overlap HMD imagery are considered within an ecological framework, where departures from ecological validity may impact visual perception and system performance.
An Ecological Approach to Partial Binocular-Overlap
James E. Melzer and Kirk Moffitt
Kaiser Electronics
2701 Orchard Parkway
San Jose, California 95134
ABSTRACT
A partial binocular-overlap helmet-mounted display (HMD) allows the presentation of wide-field-of-view imagery with no
loss of resolution and a reduction in size and weight. One trade-off with these attributes is binocular rivalry created by the
edge of the imagery seen by one eye overlaying conlinuous imagery seen by the other eye. Three distinct methods are
considered that reduce this rivalry-and there are trade-offs with each approach. These three methods are the use of optical
stops or filters that provide a luminance gradation that softens the overlapping binocular edges, left/right eye assignment for
the flanking monocular regions, and contour lines superimposed on the imagery that correspond to the binocular/monocular
borders. These approaches to improving the quality of partial binocular-overlap HMD imagery are considered within an
ecological framework, where departures from ecological validity may impact visual perception and system performance.
1. INTRODUCTION
A partial binocular-overlap HMD presents the user with a central binocular image flanked by monocular images. This
design offers several advantages over fully- or lOO%-overlapped HMD imagery.
1 Compared with full overlap, a 50% partial
overlap provides a 50% increase in horizontal field-of-view (FOV). This FOV increase, illustrated in Figure 1, is achieved
with no gain in weight or size, or loss of resolution. A wide horizontal FOV is critical for tasks involving balance,
orientation, night pilotage, and situational awareness. Trade-offs to achieving a wide FOV with partial overlap include
problems with distortion, roll compensation, rcquircd overlap, and binocular rivalry.l
Monocular 1 Binocular I Monocular
Figure 1. Partial binocular-overlap results in a gain in the horizontal FOV. The
dashed lines indicalc the boundaries of the binocular region. The center of
the display FOV is the ccntcr of the binocular region.
An ecological approach provides a framework for Lhc design and evaluation of partial binocular-overlap HMDs.
Ecological vision, as used in this paper, considers the human and visual environment to be reciprocally coupled and not
iudependent.2p3 An ecological analysis of a man-machine system begins with an evaluation of the environmental constraints
relevant to the human operator. One criterion of this analysis is the concept of ecological validity, which is based on the
assumption that ecological evaluations or nalural sccncs and Ihe way scenes are viewed by the observer are relevant to
vision.4v5 The quality of display systen~s n~ay bc improved by increasing their ecological validity. The degree of ecological
validity in binocular HMDs will bc: shown to bc linked lo image quality and freedom from display artifacts.
Proc.ofSPIEVol.1456,LargeScreenProjection,Avionic,andHelmet-MountedDisplays,ed.HMAssenheim,RAFlasck,TMLippert,JBentz(Aug
1991)CopyrightSPIE
124
2. RIVALRY AND LUNING
Luning refers to the crescent-shaped dark images that lie on the monocular sides of the monocular/binocular boundaries of
a partial-binocular overlap video display.
The circular aspect of luning is due to the fact that miniature CRTs used with
HMDs have circular images. The dark images are characterized by a tendency to alternate over time with the display imagery,
and to promote oculomotor instability. Image alternation indicates that luning is probably due to binocular rivalry between
the eyes. Luning is exacerbated by the unnatural black edges which surround the HMD imagery.
We have preliminary evidence that luning is primarily a cosmetic problem, and does not affect performance. This
evidence comes from studies at Kaiser Electronics on the presence of luning crescents, and the detection of small targets in and
around tithe luning area of the display. Field reports from simulator and flight tests have revealed that the luning crescents are
frequently not noticed after pilotage activities begin imposing workload. Nevertheless, performance for other types of tasks
could be affected, and distraction and fatigue effects from the rivalry remain unknown.
The results from several Kaiser Electronicsstudies will be described. The reader is cautioned that these are preliminary
laboratory evaluations that lack the richness of the cockpit environment. For example, several of the experiments rcq!?e?
fixation on a target, the tasks were one-dimensional and workload was minimal, and the imagery was static. On Ihc ot!lcr
hand, these experiments did provide a simulation of critical aspecw: of binocular HMDs.
Three methods of attenuating luning with partial binocular-overlap imagery have been identified.
These methods are:
1. Luminance roll-off of the binocular imagery, 2. Left/right eye assignment of the monocular regions, and 3. Drawing
contour lines on the imagery that correspond to the binocular edges. These three methods will be discussed in more detail in
the following section. They will then be considered within an ecological framework.
3. DISPLAY AND IMAGERY CONFIGURATION
3.1 Luminance Roll-Off
The first method of attenuating luning is by softening the high-contrast boundary edge.
Observations at Williams Air
,Force Base6 and at the Air Force Armstrong Aerospace Medical Research Laboratory, and formal studies at Kaiser Electronics,
have indicated that rolling-off the luminance at the edge of the binocular region blends the binocular imagery into the black
region and reduces the perception of luning. For example, one Kaiser Electronicsstudy found that a cosine taper of display
luminance was optimal for reducing luning. In terms of utility for a binocular HMD, luminance roll-off can be implemented
with optical filters or electronically at the CRT. Filters involve introducing optical elements into the HMD system, while
rolling-off the CRT image requires image processing.
3.2 Eye Assignment
The second method of attenuating luning involves the arrangement of the monocular regions.
Partial binocular-overlap
displays may be configured to have either convergent or divergent overlap.
The right side of Figure 2 shows the configuration
of divergent imagery, and the left side of this figure shows a corresponding geometric layout of real-world surfaces.
The reader
can observe the effects of a divergent HMD design by looking at a distant object through two short tubes that are canted
slightly outwards.
Your right eye will see more of the right visual field, your left eye will see more of the left visual field,
and both eyes will view a central binocular region.
Note that the image placement is divergent, and that the eyes are
not
making divergent eye movements.
The left side of Figure 2 shows a real-world geometric arrangement that results in divergent imagery.
A solid object that
is viewed with both eyes is located in front of background imagery and a black surround.
An example would be a book held
at arms length. The depth discrepancies between this geometric arrangement and binocular HMD imagery will be discussed
in the next section.
125
and into a black
outer monocular
images are continuous
and are both coplanar
LE
RE
Figure 2. The geometric and imagery layout of a divergent arrangement. LE=Left eye, RE=Right eye.
We previously stated that we had not observed any left/right eye assignment effects on luning with simulated partial
binocular-overlap imagery.
1 These observations were based on a very small FOV (-10). Subsequent work with larger FOVs
revealed that eye assignment does affect luning.
We also equated a divergent arrangement with placing a septum between the
eyes, but now think that a near object viewed against a more distant background is a better conceptualization.
A convergent overlap image configuration is shown in the right side of Figure 3. Similar to the divergent example, the
reader can observe the effects of this design by looking at a distant object through two short tubes that are canted slightly
inwards. Your right eye will see more of the left visual field, your left eye will see more of the right visual field, and both
eyes will view a central binocular region. This configuration is commonly referred to as the
knothole effect
and is used in
non-pupil-forming head-up displays (typically with a binocular overlap of 5-109, where the exit aperture of the optics forms
the -knothole and the observer views the collimated display imagery. Real-world geometry that provides convergent imagery
is shown in the left side of Figure 3. As an example, a convergent view is present whenever we peer through an opening
such as a Gndow.
T$e cCce of divelgent versus convergent overlap may depend on the packaging difficulties with binocular HMDs.
Factors such as display FOV, eye relief? and exit-pupil diameter determine the size of the combining optics. Large combining
optics may
limit or preclude the necessary interpupillary distance (IPD) adjustment and fitting to the head and face with a
convergent HMD design.
RE Only
LE Only
monocular and
LE Display
RE Display
\ dno6ar /Black
Bi>oc/ular
Image
Figure 3. The geometric and imagery layout of a convergent arrangement. LE=Left eye, RE=Right eye.
  126
3.3 Contour Lines
The third method of attenuating luning requires that explicit contour lines be drawn on top of the HMD imagery, such
that they outline the binocular region.
That is, the binocular imagery is distinguished from the monocular imagery by thin
black lines drawn on the imagery. These contour lines segment the image similar to the close binocular object in Figure 2.
This method can be implemented with either divergent or convergent imagery, and has no impact on HMD optics, mechanics,
or electronics. The use of contour lines to attenuate luning came from an ecological evaluation comparing divergent and
convergent configurations. This evaluation will be discussed further in Section 4.3.
4. AN ECOLOGICAL EVALUATION
An ecological evaluation examines the relationship between the organism and its environment,
The basic approach taken
in our ecological evaluation is to compare partial binocular-overlap HMD imagery with analogous real-world scenes. This
evaluation can provide remedies to lessen the difference between the display and the real-world and to improve image quality.
The three luning-attenuation methods discussed in the previous section will now be evaluated using this ecological approach.
4.1 Luminance Roll-Off
The black surround shown in Figures 2 and 3 is unnatural and is a major contributor to luning. Since a bright surround
is not feasible, tapering the edge of the image provides a means of softening the high-contrast boundary edge.
The effect is
similar to the low to moderate contrasts that predominate in the natural world. We have experimentally shown that a variety
of luminance roll-off functions serve to lessen the perception of luning.
While other researchers have reported success with putting an optical stop into the HMD optical train6, we have observed
a fuzzyimage with the use of a cosine luminance roll-off in a simulated partial binocular-overlap HMD. The rolled-off
image from one eye either combines or rivals the unaltered image from the other eye. The fuzziness problem is not severe,
and is generally preferable to the dark luning crescents that are otherwise present.
4.2 Eye Assignment
With a natural scene, the geometric arrangement of the environment and the separation of the left and right eyes determine
the eye that receives the visual information. With a partial binocular-overlap HMD, this assignment of scenery to eye is no
longer deterministic. Monocular regions of the scene can be assigned to either the left or right eye.
A central point of this
paper is that one of the two eye assignments is more ecologically valid, and results in superior image quality.
Researchers at The Smith-Kettlewell Eye Research Institute in San Francisco have studied the effects of ecological
validity on binocular rivahyp They demonstrated that there are natural opto-geometrical restraints that determine the
combinations of depth and left/right eye views of a display. Violating these constraints with ecologically invalid displays
was shown to result in a significant increase in binocular rivalry at the unpaired monocular regions of the display.
The left half of Figure 2 shows a three-dimensiona scene of a close object occluding the background.
Note that there are
unique (unpaired or monocular) regions of the background seen by each eye (shown as dotted regions). The corresponding
stereogram is shown to the right of the 3D drawing. The binocular object is seen as nearer than the surrounding surface due
to it having more binocular disparity. Reversing the eye that views each monocular region, while maintaining the
object/background depth relationship, results in an ecologically invalid display. The resulting stereogram has no counterpart
in the physical world, and was found to create visual suppression and rivalry.4
Similarly, Figure 3 shows a view through an aperture to a background surface. The unpaired monocular area is now
.
nasal relative to the binocular area for each eye. Reversing the eye that views each monocular region, while maintaining the
aperture/background depth relationship, resulted in an ecologically invalid display and increased rivalryP
Experiments conducted at Kaiser Electronics over the last two years have revealed several interesting eye-assignment
effects. In an informal study, 24 out of 2.5 observers rated a convergent display as having less luning than a divergent display.
127
This comparison was formalized in a study involving convergent and divergent overlap, random-dot and realistic scenery, 45
and 60FOVs, and placement of the superimposed edge on the left or right side of the display. Luning was found to be least
evident with a convergent display and a real-world scene.
We propose that the increased luning found with divergent versus convergent partial binocular-overlap displays results
from the greater ecological invalidity of the divergent configuration. Consider the viewing conditions for divergent imagery.
Binocular imagery in the natural world, such as a book held at arms length, is immediately surrounded by unpaired monocular
regions--sections of the background that are occluded by the book for one eye. The right eye sees part of the right-hemifield
where the left eye sees part of the object. Luning is typically not noticed in such situations when attention is focused on the
book and the eyes are appropriately converged. There are two distinct features of this imagery. The first is that the object is
closer than the background. That is, the object and the background have binocular disparity that is seen as depth. There is
also evidence that the eye assignment of the unpaired monocular regions provides depth information4J
Second, the object
has an explicit monocular/binocular border, and is separate from and occludes the background. Neither of these features exist
with HMD imagery, where the central binocular region is at the same depthas the monocular regions and these regions are
continuous.
Similarly, when viewing a scene through an opening or aperture, the flanking monocular imagery affords the observer
depth information. Convergent HMD imagery is similar to the real world in providing seamless monocular/binocular regions
that are equally distant. In this sense, the convergent HMD is valid with respect to the ecological world. Invalidity may
come from the (black) surround, which is close in the real world but coplanar with the HMD imagery.
If much of the luning with a divergent display is due to the continuous monocular/binocular regions, then luning should
be reduced by making these regions discontinuous. This discontinuity may ameliorate the problem of these coplanar image
regions.
4.3 Contour Lines
Our ecological analysis of divergent HMD imagery led to the prediction that explicitly defining the binocular region
would increase ecological validity and improve image quality.
The near object in the left side of Figure 2 creates borders that
separate the binocular object and the. monocular background. Even though the HMD imagery remains continuous and without
depth, explicit borders should improve the display.
Using a binocular HMD simulation, we experimented with explicitly defining the binocular imagery by drawing black
contour-lines on the continuous imagery that corresponded to the edge seen by the other eye. The binocular imagery was
distinguished from the monocular imagery by a superimposed thin black line, as illustrated in Figure 4. In this
demonstration, the contour line had the predicted effect of reducing luning. In fact, the reduction was frequently total-no!
unlike many of the reports with convergent imagery.
A formal experiment conducted at Kaiser Electronics on the efficacy of contour lines replicated the finding that convergent
overlap produced less luning than divergent overlap, and found that displays with contour lines produced less luning than
displays without contour lines. Naive observers viewed a simulated partial binocular-overlap HMD image for 20 seconds on
each trial, and pushed a button whenever they perceived that luning crescents were dominating the imagery. The results from
this experiment, illustrated in Figure 5, show that
either
converging the imagery or inserting contour lines will reduce the
perception of luning.
The results of this contour-line experiment and previous investigations of luning conducted at Kaiser Electronics suggest
several alternatives for reducing the magnitude of luning with partial binocular-overlap displays. A convergent configuration
is effective at reducing luning compared to a divergent configuration. The use of contour lines is also an effective means of
reducing luning. The results shown in Figure 5 indicate that combining convergent overlap with contour lines would
optimize the display. The trade-off is the design and packaging of a converged optical system and the continuous presence of
contour lines.
  128
Ix
RE
Contour Lines
Figure 4.
Explicit contour lines superimposed on divergent and convergent HMD imagery. The left side
shows the left-eye (LE) and right-eye (RE) views. The right side shows the resulting binocular
view. The Xs designate the center of the binocular region.
9
20
s
E
2
P,
e
i?
-2 10
2
Yt4
.d
b
%
2
G 0
Without
Convergent
Divergent
Overlap
Format
Figure 5. Apparent luning as a function of overlap format and contour lines.
129
The data from this study support an ecological explanation of luning with partial binocular-overlap displays. Increasing
ecological validity lessens the perception of luning.
Departing from ecological imagery results in increasing amounts of
luning.
The first implementation of contour lines with an HMD was with Raisers WideEyeTM partial binocular-overlap HMD,
which has divergent imagery. Informal reports from trade-show attendees were that the contour lines virtually eliminate
hming. The utility of contour lines is that they appear to reduce luning with divergent HMDs, and that they are relatively
easy to generate. The major trade-off is that they are always present on the display.
The data from Figure 5 show that contour lines reduce residual luning with a convergent HMD.
Remaining ecological
problems with convergent configurations include the coplanar, black areas surrounding the imagery that create high-contrast
edges. The contour lines trace these high-contrast edges, and may reduce the negative effects.
5. VIEWING CONDITIONS
An ecological approach may be appropriate for other attributes of HMDs. Table 1 presents a list of attributes of natural
scenes and a list of attributes of partial binocular-overlap HMD imagery. Most of the differences between natural scenes and
HMD imagery are due to limitations in technology and biomechanics. For example, the natural instantaneous FOV for
humans exceeds 2OO, while the HMD FOV ranges from about 60for a lightweight flight-worthy system to about 120for a
heavier and larger simulator system. With a helmet-presented FOV approaching 60, the observer begins to react to the HMD
as his direct view of the world (as opposed to watching a display).
With a FOV of about 90, the observer becomes immersed
in the imagery.7
Advances in optical materials and design, lightweight composite materials, and electronic displays will gradually allow
larger FOVs for flight-worthy HMD systems. Similarly, HMD attributes such as brightness, resolution, and color are driven
by the available technology+urrently miniature CRTs. These quantitative factors can be compared with the last five
attributes listed in Table 1, which represent qualitative differences between natural scenes and HMD imagery. For example, as
the head tilts, the natural world remains gravitationally upright. With an HMD and head tracker, the image of the world will
tilt with the head unless roll compensation is incorporated into the HMD system. There has been speculation that roll
compensation may only be required with larger FOVs, and roll compensation is not currently implemented with a fielded 40
HMD. The question becomes: When does roll compensation significantly improve pilotage? Such qualitative design
decisions are difficult to answer, but offer the promise of immediate and significant improvements in HMD quality and
usability.
Table 1
Comparison of Natural Scenes with
Partial Binocular-Overlap HMD Imagery
Natural Scenes
Very WFOV
High resolution
Extended brightness
No temporal lag
Infrequent distortion
Perfect imagealignment
Full color
Normal stereo
Perfect roll-compensation
Natural eye assignment
No noticeable rivalry
Partial Binccular-OverlaD HMD
Limited FOV
Limited resolution
Limited brightness
Imagery lags head movements
Distortion compensation required
Imperfect image alignment
Monochrome
None or limited, w/ variable sensor separation
Roll-compensation absent or lagging
Arbitrary eye assignment
Noticeable rivalry
  130
6. SUMMARY
The ecological validity of HMD imagery has been considered as a criterion in the evaluation of three methods of
attenuating rivalry or luning with partial binocular-overlap HMDs. Luminance roll-off eliminates the unnatural high-
contrast edge, manipulation of left/right eye assignment increases the binocular cormspondence of the HMD with the natural
world, and contour lines compensate for the unnatural continuity of binocular/monocular imagery and the black surrounding
surface.
Manipulation of eye assignment and/or contour lines appear to offer the most promise for improving the image quality
of a partial binocular-overlap HMD with the least cost or artifact. In either case, luning can be attenuated by implementing
ecological remedies. This approach generalizes to other aspects HMDs, such as color, stereo, and roll compensation. The
challenge with HMDs is to identify those designs that are ecologically valid and provide safe, economical, and useable
hdWiUt%
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131
... Partial binocular overlap results when the two HMD optical channels are canted either inward (convergent overlap) or outward (divergent overlap -see also Figure 3-3, Chapter 3, Introduction to Helmet-Mounted Displays). This latter configuration is similar to human vision with two monocular channels viewing the outward portion of the visual field and a central binocular region (Melzer and Moffitt, 1989;Melzer and Moffitt, 1991). Partial binocular overlap requires two image sources and two video channels with the optics and imagery properly configured to compensate for any residual optical aberrations. ...
... Early efforts attempted to explain the difference in the degree of luning observed between convergent and divergent displays with an ecological vision model. Here, convergent overlap was theorized to induce less luning because it was more "ecologically valid" than the divergent case (Melzer and Moffitt, 1991). Several techniques have been shown to be effective in reducing the rivalry effects and their associated perceptual artifacts (Melzer and Moffitt, 1991;Moffitt and Melzer, 1993). ...
... Here, convergent overlap was theorized to induce less luning because it was more "ecologically valid" than the divergent case (Melzer and Moffitt, 1991). Several techniques have been shown to be effective in reducing the rivalry effects and their associated perceptual artifacts (Melzer and Moffitt, 1991;Moffitt and Melzer, 1993). ...
... Partial binocular overlap results when the two HMD optical channels are canted either inward (convergent overlap) or outward (divergent overlap -see also Figure 3-3, Chapter 3, Introduction to Helmet-Mounted Displays). This latter configuration is similar to human vision with two monocular channels viewing the outward portion of the visual field and a central binocular region (Melzer and Moffitt, 1989;Melzer and Moffitt, 1991). Partial binocular overlap requires two image sources and two video channels with the optics and imagery properly configured to compensate for any residual optical aberrations. ...
... Early efforts attempted to explain the difference in the degree of luning observed between convergent and divergent displays with an ecological vision model. Here, convergent overlap was theorized to induce less luning because it was more "ecologically valid" than the divergent case (Melzer and Moffitt, 1991). Several techniques have been shown to be effective in reducing the rivalry effects and their associated perceptual artifacts (Melzer and Moffitt, 1991;Moffitt and Melzer, 1993). ...
... Here, convergent overlap was theorized to induce less luning because it was more "ecologically valid" than the divergent case (Melzer and Moffitt, 1991). Several techniques have been shown to be effective in reducing the rivalry effects and their associated perceptual artifacts (Melzer and Moffitt, 1991;Moffitt and Melzer, 1993). ...
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Chapter
Helmet-mounted displays (HMDs) have been in development since the 1960s. Now, almost five decades later, the technology has improved significantly; HMDs have made some inroads into commercial applications (Ellis, 1995; Kalawsky, 1993; Pankratov, 1995); their use has become standard within the military community for flight applications, training and simulation (Simons and Melzer, 2003); and they are rapidly expanding into military applications for the dismounted and vehicular-mounted Warfighter (see Chapter 3, Introduction to Helmet-Mounted Displays). Unfortunately, design guidance for HMDs has not kept pace. This is due in part to the rapid advances in enabling technologies (e.g., micro-electromechanical devices, microprocessors, emissive image sources, microdisplays). 1 However, it is mostly because HMDs are both engineering-and human-centered systems; whenever humans are a key system component, their complex sensory, neural mechanisms and their variability across the population makes the design of HMDs and the human-machine interface extremely challenging. This, in turn, makes universal design guidelines equally challenging. This is not to imply that the design community has been negligent in the development of guidelines. In a 1972 symposium on visually-coupled systems sponsored by the U.S. Air Force System Command's Aerospace Medical Division held at Brooks Air Force Base, Texas, participates attempted to address many of the fundamental design issues for HMDs (Birt and Task, 1973). Hughes, Chason and Schwank (1973) provided an overview of the history and the known and potential psychological problems of HMDs and included an extensive annotated bibliography of relevant material on such issues as eye dominance, brightness disparity, helmet-mounted displays/helmet-mounted sights, retinal rivalry, and others identified during the 1972 symposium. Chisum (1975) expanded this discussion by presenting visual considerations associated with the head-coupled aspects of HMDs. As a special subset of displays, HMDs are subject to the practices for display development in general, many of which are based on decades of human performance research. Two of the most comprehensive volumes are Farrell and Booth's (1984) Design handbook for Imagery Interpretation Equipment and Boff and Lincoln's (1988) Engineering Data Compendium: Human Perception and Performance. HMDs are also a specialized class of displays called head-up displays (HUDs), defined as transparent, fixed location displays that present data without obstructing the user's view (Figure 17-1). Developed originally as gun sights for military aircraft, they have expanded into commercial aircraft (Steenblik, 1989) and recently have become an option in some automobiles (Oldsmobile Club of America, 2006). HUD guidelines concentrate mostly on symbology and related display criteria such as clutter, dynamic response and viewing comfort issues, and many of these criteria have a firm foundation in human factors and human perception (Prinzel and Risser, 2004; Ververs and Wickens, 1998; Weintraub, 1992; Wickens, 1997; Wickens, Fadden, Merwin, and Ververs, 1998). Two important reference books on HUDs are Wood and Howells' (2001) Head-Up Displays and Newman's (1995) Head-Up Displays, Designing the Way Ahead. However, of the vast amount of research conducted over the last half-century, only four reference books have been written specifically for HMDs; and the first three of these focus on aviation applications only. The first 1 Suggested reading on these enabling technologies is Brennesholtz: Designing for the User (Melzer and Moffitt, 1997), addresses HMD development for fixed-wing aircraft. It could be considered an engineering guide with its coverage of the traditional engineering design approach, but it also places a significant emphasis on the end user, addressing a wide array of human-centered disciplines required for the design of head-mounted virtual reality, industrial and military displays. Topics include optical requirements, lens designs, cybersickness, eye strain, head-supported weight, 2 stereoscopic imagery, anthropometry, and user acceptance. The book also introduces the potential of HMDs to serve as an interface for brain-actuated control functions, a concept explored in this volume (see Chapter 19, The Potential of an Interactive HMD). Figure 17-1. Examples of head-up displays (HUDs): (left) a HUD in a fighter cockpit and (right) a HUD designed for aircraft simulation (Rockwell Collins).
... The ARU frame's stiffness maintained the critical binocular alignment (Moffitt, 1997) between the two optical relay assemblies while allowing a smooth lateral adjustment for interpupillary distance. To expand the horizontal field of view, the monoculars were canted outward using partial binocular overlap (Melzer & Moffitt, 1991, Melzer, 1998. This provided a total binocular field of view of 40° vertical by 60° horizontal with 20° of central binocular overlap. ...
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In today's increasingly sophisticated simulation world, a realistic, high intensity, task-loaded display of the battlespace environment has become the expectation of the military user community. To effectively train aviation aircrews, the visual system must support realistic collective/combined arms training with the required fidelity to fly nap-of-the-earth (NOE) or conduct multi-ship operations. Meeting this high level of expectations requires that the visual system be capable of performing all necessary collective tasks and supporting individual tasks with no negative training transfer or physical impacts on crewmembers. An evolving technology that can meet these needs is the Head-Mounted Display (HMD). This paper will address the use of HMDs in aviation simulators and will follow the evolution of the SIM EYE XL 100A from its early Wide Eye™ stage, to its current use in the Army's Aviation Combined Arms Tactical Trainer-Aviation (AVCATT-A) Reconfigurable Manned Simulator program. Finally, it will address possible future improvements that can be incorporated into the HMD to further satisfy Army aviation users.
... Each provides a 65° horizontal by 50° vertical field of view. Each monocular is canted outward by 17.5° for a total horizontal field of view of 100° with a central 30° partial binocular overlap region (Melzer and Moffitt, 1991). Each image source assembly contains three miniature XGA (1024 x 768) resolution LCD panels each with a monochrome (red, green and blue) backlight. ...
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The Aviation Combined Arms Tactical Trainer-Aviation Reconfigurable Manned Simulator (AVCATT-A) is the Army's newest aviation training simulator. It is a dynamic reconfigurable system used for combined arms collective training and mission rehearsal through networked simulators in a simulated battlefield environment. AVCATT-A will provide training for both active U.S. Army and National Guard units. AVCATT-A provides five functional cockpits. These are the OH-58D Kiowa Warrior, the AH-64A Apache, the AH-64D Longbow Apache, the CH-47D Chinook, and the UH-60A/L Blackhawk helicopters. To meet the visual needs of all these cockpits, AVCATT-A is employing state-of-the-art technology.
... Several techniques have been shown effective in reducing the rivalry effects and their associated perceptual artifacts. 83 ...
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An introduction to Helmet Mounted Displays in military avionics applications.
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Near-eye display systems for augmented reality (AR) aim to seamlessly merge virtual content with the user’s view of the real world. A substantial limitation of current systems is that they only present virtual content over a limited portion of the user’s natural field of view (FOV). This limitation reduces the immersion and utility of these systems. Thus, it is essential to quantify FOV coverage in AR systems and understand how to maximize it. It is straightforward to determine the FOV coverage for monocular AR systems based on the system architecture. However, stereoscopic AR systems that present 3D virtual content create a more complicated scenario because the two eyes’ views do not always completely overlap. The introduction of partial binocular overlap in stereoscopic systems can potentially expand the perceived horizontal FOV coverage, but it can also introduce perceptual nonuniformity artifacts. In this paper, we first review the principles of binocular FOV overlap for natural vision and for stereoscopic display systems. We report the results of a set of perceptual studies that examine how different amounts and types of horizontal binocular overlap in stereoscopic AR systems influence the perception of nonuniformity across the FOV. We then describe how to quantify the horizontal FOV in stereoscopic AR when taking 3D content into account. We show that all stereoscopic AR systems result in a variable horizontal FOV coverage and variable amounts of binocular overlap depending on fixation distance. Taken together, these results provide a framework for optimizing perceived FOV coverage and minimizing perceptual artifacts in stereoscopic AR systems for different use cases.
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The Warfighter in the modern battlespace has a predetermined, but ever-changing, set of tasks that must be performed. Performance on these tasks is affected strongly by the amount and quality of the visual input, as well as by the resultant visual perception and cognitive performance. Visual perception is defined as the mental organization and interpretation of the visual sensory information with the intent of attaining awareness and understanding of the local environment, e.g., objects and events. Cognition refers to the faculty for the human-like processing of this information and application of previously acquired knowledge (i.e., memory) to build understanding and initiate responses. Cognition involves attention, expectation, learning, memory, language, and problem solving. The direct physical stimuli for visual perception are the emitted or reflected quanta of light energy from objects in the visual environment that enters the eyes. It is important to understand that the resulting perception of the stimuli is not only a result of their physical properties (e.g., wavelength, intensity, and hue) but also of the changes induced by the transduction, filtering, and transformation of the physical input by the entire human visual system. This chapter explores some of the more important visual processes that contribute to visual perception and cognitive performance. These include brightness perception, size constancy, visual acuity (VA), contrast sensitivity, color discrimination, motion perception, depth perception and stereopsis. An analogous discussion of input via the auditory sense is discussed in Chapter 11, Auditory Perception and Cognitive Performance. Brightness Perception In physics, the luminance of an object is exactingly defined as the luminous flux per unit of projected area per unit solid angle leaving a surface at a given point and in a given direction. A more useable definition is the amount of visible light that that reaches the eye from an object. But, when an observer describes how "bright" an object appears, he/she is describing his/her brightness perception of the object. This brightness is the perceptual correlate to luminance and depends on both the light from the object and from the object's background region. Human visual perception of brightness and lightness involves both low-level and higher levels of processing that interact to determine the brightness and lightness of parts of a scene (Adelson, 1999). 1 If a scene was scanned by a photodetector, it would measure the amount of luminance energy at each point in the scene; the more light coming from a particular part of the scene the greater the measured value. The human eye's retinal receptors (cones) respond in a similar manner when a scene is imaged unto it. However the appearance (perception) of a region of the scene can be drastically altered without affecting the response of retinal receptors. The well-known simultaneous contrast effect demonstrates this phenomenon (Figure 10-1). In reality, the two center regions have 1 Brightness is the perceptual correlate of luminance and may be thought of as perceived luminance; Lightness is the perceptual correlate of reflectance and may be thought of as perceived reflectance.
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A stated goal of the US Army has been the standardization of the human computer interfaces (HCIs) of its system. Some of the tools being used to accomplish this standardization are HCI design guidelines and style guides. Currently, the Army is employing a number of HCI design guidance documents. While these style guides provide good guidance for the command, control, communications, computers, and intelligence (C4I) domain, they do not necessarily represent the more unique requirements of the Army`s real time and near-real time (RT/NRT) weapon systems. The Office of the Director of Information for Command, Control, Communications, and Computers (DISC4), in conjunction with the Weapon Systems Technical Architecture Working Group (WSTAWG), recognized this need as part of their activities to revise the Army Technical Architecture (ATA), now termed the Joint Technical Architecture-Army (JTA-A). To address this need, DISC4 tasked the Pacific Northwest National Laboratory (PNNL) to develop an Army weapon systems unique HCI style guide, which resulted in the US Army Weapon Systems Human-Computer Interface (WSHCI) Style Guide Version 1. Based on feedback from the user community, DISC4 further tasked PNNL to revise Version 1 and publish Version 2. The intent was to update some of the research and incorporate some enhancements. This document provides that revision. The purpose of this document is to provide HCI design guidance for the RT/NRT Army system domain across the weapon systems subdomains of ground, aviation, missile, and soldier systems. Each subdomain should customize and extend this guidance by developing their domain-specific style guides, which will be used to guide the development of future systems within their subdomains.
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The applications of color symbology, graphics, and imagery in helmet-mounted displays have the potential to reduce workload and improve piloting performance. Unfortunately, there are three well-recognized paradigms that disallow the use of color in helmet-mounted displays in aviation environments. We provide evidence of three corresponding paradigm shifts that encourage the use of color in these displays. The rationales for these paradigm shifts are based on new methods of training and rehearsing, new lighting environments, and new display technologies.
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Consideration is given to the possible use of a partial binocular overlap configuration to decrease the size and weight of a helmet mounted display while maintaining a wide FOV and adequate image resolution. It is suggested that a partial binocular overlap helmet mounted display would allow the user to see a central binocular image flanked by two monocular images. Under proper conditions, the user would not be aware of the partial overlap, but would benefit from reduced weight, decreased size, and extended FOV. Visual considerations are discussed, including binocular rivalry, distortion and binocular disparity, derotation, and the amount of overlap required.
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[argue] that an ecological approach to human factors is necessary if the gap between the worlds of basic research and applied design are to be bridged / describe in detail the additional benefits adopting an ecological approach to human factors / 1st, a general overview of the ecological approach is presented / the remainder of the chapter will be structured into 4 sections / the 1st 3 sections outline the implications of the ecological perspective for human performance modeling, task analysis, and human factors experimentation / the final section provides an example from the area of cognitive engineering illustrating how application of the ecological approach to human factors can lead to fruitful research (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Distant surfaces are occluded by nearer surfaces to different extents in the two eyes, leading to the existence of unpaired image points visible in one eye and not the other. An ecological analysis of the real world situation that could have given rise to such unpaired points indicates the presence of a depth constraint zone, defined by visibility lines between which possible real world points must lie. The leading edge of this zone starts at the edge of a fused binocular occluding surface and recedes linearly with increases in horizontal distance to the unpaired point. Psychophysical evidence indicates that the human visual system makes use of this unpaired information in a remarkably adaptive manner, showing an increase in perceived depth for increasing horizontal separations between the unpaired target and fused edge, at least over a significant angular range (approx. 25–40 min arc). We also show that unpaired points in binocular images can lead to the formation of subjective occluding contours and surface having the qualitatively appropriate sign of depth. Furthermore, we show that the visual system could not recover depth of unpaired points camouflaged from the other eye against silhouettes. Our findings indicate that the visual system makes use of occlusive relations in the real world to recover depth, contour, and surface from unpaired points. The fact that such processes must utilize eye-of-origin information implies that they share this essential characteristic with classical or Wheatstone stereopsis. The necessity of eye-of-origin information also suggests that the processing may begin relatively early in cortical visual processing, possibly as early as V1. Finally, the novel emergence of subjective occluding contours from unpaired monocular stimuli raises the possibility that this process is mediated by visual experience, built up by the association of unpaired points and occluding contours.
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A surface occluding a more distant surface gives rise to interocularly unpaired regions to its immediate left and right. The unpaired region on the left side is visible only to the left eye, whereas that on the right side is visible only to the right eye. Thus for real world scenes there are opto-geometrical constraints which determine whether particular combinations of relative depth and right-eye-only or left-eye-only stimuli are ecologically valid or invalid. We report a demonstration and experiments to show that opto-geometrically “valid” unpaired regions are seen as continuous with the rear plane and escape interocular suppression, whereas “invalid” unpaired regions are perceived as closer and are suppressed vigorously. An additional experiment indicates that the results cannot be understood in terms of correspondence solving, but require neural mechanisms that embody real-world occlusion constraints. These results suggest a rather close interaction between stereopsis and rivalry “modules”. Since explicit eye-of-origin information is lost relatively early in the hierarchical organization of cortical visual processing, we argue that occlusion-related constraints must be embodied at such early levels.
Wide-Field-Of-View, Helmet-Mounted Infinity Display System Development
  • Cae Electronics
CAE Electronics, "Wide-Field-Of-View, Helmet-Mounted Infinity Display System Development", AF Systems Command AFHRL-TR-84-27, Brooks AFB TX, 1984.