Tactical Display for Soldiers Human Factors Considerations (1997) / Chapter Skim
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4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN
4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN
Pages 65-116
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From page 65... ...
Next we describe the research base on a series of visual factors to be considered in designing and assessing display devices. These factors include: field of view and resolution, binocular versus monocular viewing, visual perception of the world and pictures, and depth cues.
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From page 66... ...
Functions of the Helmet-Mounted Display In the Land Warrior System, helmet-mounted displays are to serve several functions, the most important of which is to display the output of devices designed to enhance soldiers' perception of their environment. These include the night vision system and the thermal weapon sight.
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From page 67... ...
For example, superimposing symbology on the night vision display would allow users to switch back and forth between these two information sources without making head movements, large eye movements, or changes in accommodation. Similar advantages apply to a case in which the soldier must rapidly switch from using the night vision system for movement across a terrain to acquiring a target with the thermal weapon sight.
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From page 68... ...
. This problem of target detection is in a sense amplified by the greater speed of movement afforded by the Land Warrior System.
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From page 69... ...
Spatial disorientation can be expected; with no external support, such as a seat, a soldier is not provided with tactile information about bodily orientation to help counteract any disequilibrium due to the helmetmounted display. Because the weight, weight distribution, and configuration of some displays interfere with the free head movements that a soldier would otherwise rely on to obtain the visual information that is intimately tied to normal action and locomotion in the environment, the equipment-based deficits offered to the infantry would seem to be considerably more serious than those offered in aviation.
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From page 70... ...
70 TACTICAL DISPLAY FOR SOLDIERS TABLE 4-1 Display System Features, Human Performance Considerations, and Research Issues Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research Head/helmet-mounted display (general issues) · Always available · Does not have to be held in the hand or manipulated · Can easily be aligned on target or terrain feature · Wide field of view · Can be used to guide movement · Added information improves situation awareness of medium to long-range environment · Added weight on head · Off center CG · More complex and fragile than hand-held display Precision/alignment requirements more severe · Wide field of view results in inadequate resolution Display information content may overload or distract user, reducing situation awareness Acquisitic of inform.
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From page 71... ...
- Display prototype data formats, realistic targets at varied ranges and aspects to determine peak performance in optimum conditions · Use head tracker to assess search head movements - Measured day/dusk/ night lighting, conditions controlled display conditions, synthetic and real images, real targets at a controlled distance, camouflage, image stability, information legibility while moving, distracting and/or masking effects of HMD on assessing real targets, varied user population to assess peak r performance In known conditions Percent correct and time to detect Identify targets and terrain features Place reticule on target Percent correct and time to acquire and apply displayed information .
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From page 72... ...
and "cognitive switching" · CG is off sideways as well as forward · Smallest FOV; least information capability; more and larger head movements required · No depth information · Difficulty to navigate on uneven terrain · General H plus: · Effects of rivalry, lo · Effects of r .
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From page 73... ...
Display prototype data formats, realistic targets at varied ranges and aspects to determine nominal performance in known conditions Use head tracker to assess search head movements with real world situation awareness) · Effects of ambient conditions on HMD information delivery, interaction with local environment · Assess stress, fatigue, · Effective use of varied information information, content in operational tasks in a field exercise with/against soldiers with conventional equipment success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA rivalry · General HMD issues, · Laboratory/bench · As general HMD · As general h as target plus: technical test issues HMD issues nvoluntary)
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From page 74... ...
74 TABLE 4-1 Continued TACTICAL DISPLAY FOR SOLDIERS Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research Biocular helmet-mounted display · Wider FOV, more information, easier to navigate · No interocular rivalry · Less complex to adjust than binocular · Heavier than monocular · Poor resolution · Incorrect depth information - Isolates user from environment . · General H plus: · Effects of stereo/par assessmer
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From page 75... ...
VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN 75 Visual Design Test Visual Test Test Research Approach Conditions Criteria · Controlled user field experiments · Operational field testing · Assess possible visual fatigue, disorientation, postural stability/loss of coordination · As general HMD issues plus: · Effects on postural stability, navigational/ vestibular orientation · Assess stress, fatigue, · Effective use of varied information information, content in success and time operational tasks to conduct in a field operational tasks exercise with/against dependent upon soldiers with HMD data, conventional equipment . interference of HMD on local SA Effects on orientation, attention fatigue and possible perceptual adaptation with longer-term usage nonocular · General HMD issues · Laboratory/bench · As general HMD · As general HMD n plus: technical test issues issues h · Effects of anomalous stereo/parallax upon target rom assessment, mobility Controlled user field experiments Operational field testing As general HMD Issues Use head tracker to movements Assess stress varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment · As general HMD issues · Effective use of information, success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA
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From page 76... ...
76 TABLE 4-1 Continued TACTICAL DISPLAY FOR SOLDIERS Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research Binocular helmet-mounted display · Can provide stereo viewing · Better depth information for mobility · Better target recognition · Heaviest optics · Alignment and adjustments more complex and critical · General H plus: · Assess ad of correct mobility, as well as of stereo .
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From page 77... ...
. precision and registration requirements · Operational field testing · Laboratory/bench · As general HMD, technical test plus: · Assess effects of optical misalignment upon performance · As general HMD, issues, plus · Assess effects of optical misalignment upon performance, orientation and postural stability and coordination when moving · As general HMD · As general HMD issues · Effects of postural ability, navigational/ vestibular orientation · Assess stress, fatigue, · Effective use if varied information information, content in operational success and time tasks in a field to conduct exercise with/against operational tasks soldiers with dependent upon conventional HMD data.
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From page 78... ...
. - Display collimation interferes with eye's accommodative response to the real world Display luminance interferes with eye's luminance adaptation to the real world Display content may obscure objects in the real world (clutter)
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From page 79... ...
- Laboratory/bench · As general HMD technical test issues, plus: · Assess registration requirements · Controlled user field experiments Operational field testing · As general HMD issues · Laboratory/bench technical test · Controlled user field experiments · As general HMD · As monocular HMDs · As monocular HMDs · Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment · As general HMD issues · As general HMD · Effective use of information, success and time to conduct operational tasks dependent upon data, interference of HMD on local SA · As general HMD issues · As general HMD
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From page 80... ...
80 TABLE 4-1 Continued TACTICAL DISPLAY FOR SOLDIERS Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research Helmet-mounted display with integrated symbology and sensor image · Much more information can be coded symbolically · Critical features (e.g., targets, navigation way points, supply drops) can be localized and enhanced · Remote sensor and intelligence information can be integrated · Users must be trained to use symbology · Luminance, depth, and apparent size of symbology must be integrated with the sensor image and world · A tendency to load the user with more information than needed avoided - Unstable symbology can induce motion illusions, disorientation, loss of balance · As genera · Effects of collimatia and coots to deal wi environed changing or movie upon post coordinati Assess tra associated formats, e .
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From page 81... ...
location in perception of the real world Optimization of information content for specific tasks Training requirements Effects of unstable symbology on orientation, mobility
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From page 82... ...
82 TABLE 4-1 Continued TACTICAL DISPLAY FOR SOLDIERS Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research
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From page 83... ...
. · As general HMD issues, plus: - Effects on postural stability, navigational/ vestibular orientation - Value added, optimum location, interference effect of each symbolically coded datum must be assessed in isolation, and in conjunction with other display content · Effects of misadjusted symbology luminance, depth, location in perception of the real world - Optimization of information content for specific tasks · Training requirements Effects of unstable symbology - Effective use of information, success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA .
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From page 84... ...
84 TABLE 4-1 Continued TACTICAL DISPLAY FOR SOLDIERS Control or Display Device Sensory and Ergonomic Considerations Benefits Costs Visual Desi Research Helmet-mounted display with remote sensor image (e.g., offset sensor, laser sight on weapon) · Information not locally available may be integrated · Weapons may be aimed without exposure Movement with sensors not collocated with the eye can induce motion and position illusions resulting in errors, disorientation, motion sickness Differences in scale, optical axis, resolution of multiple sources can induce error and confusion .
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From page 85... ...
image sources; assess target/terrain characteristics with nonvisual (e.g., thermal) contrast effects Training requirements associated with using thermal imagery · Controlled user field experiments · As see through HMD · As see through issues, plus: HMD · Assess weather effects (temperature, precipitation, fog/haze)
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From page 86... ...
During daytime operations, an opaque display will be used to provide navigation information, command and control data, and real-world images acquired through the weapon sight; at night, these functions will be integrated with the night vision system. The proposed displays and optical systems pose some risk with respect to problems such as eyestrain, disorientation, and physical discomfort resulting from ergonomic limitations.
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From page 87... ...
. Effective use of information, success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA Effects on orientation, attention fatigue and possible perceptual adaptation with longer term usage .
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From page 88... ...
Visual displays provide layout information through the patterning of light and dark (and color, when applicable) on the surfaces that they present to one eye (monocular)
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From page 89... ...
BFV driver thermal sight M 1 13 M- l 9 driver night sight M 113 vision block (M- 17E4) AN/PVS 7 night vision device Land Warrior System requirement 210° 2° 15° 3.4° to 6.8° 8° 45o 26.8° 98° in the 15° uplook position or 76° in the 20° uplook position; (vertical field of view of 23° up and 21° down in the 15° uplook position)
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From page 90... ...
In biocular displays, both eyes receive the same augmented view. In binocular displays, the two eye's views are disparate so as to provide binocular parallax or stereoscopic depth information, obtained from sensors of fixed vergence.
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From page 91... ...
In the case of a monocular display, we would expect little rivalry at night because the augmented eye will provide a much stronger image than the unoccluded eye. This would tend to negate the ability of the unoccluded eye to provide information useful for detecting targets.
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From page 92... ...
Stereopsis is a particularly potent depth cue for objects close to the observer, and the resulting depth sensitivity declines linearly out to a range of about 30 meters (Cutting and Vishton, 1995~. Stereopsis is only one of many depth cues that are discussed in a later section, as one can readily demonstrate by closing one eye and noticing that depth information hardly changes at all.
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From page 93... ...
In the monocular display, the unoccluded eye will have an even larger field of view, but, as pointed out above, at least part of this view may be suppressed by the stronger image in the augmented eye. Evidence on the Importance of Binocular Displays These considerations suggest that stereo displays should be superior to monocular displays for seeing depth, moving across terrain, avoiding obstacles, perceiving camouflaged objects, and detecting threshold targets.
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From page 94... ...
than with normal vision. It means that the static pictorial depth cues seen through the display (the depth cues are basically shapes, revealing interposition, perspective, etc.)
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From page 95... ...
However, most of the visual tasks that are normally required of infantry soldiers do not depend on information about what contours and points can be distinguished on the surface of a display. They depend on recognizing which
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From page 96... ...
, a viewer can normally draw on various kinds of depth information available to unobstructed vision. Chief among these are pictorial depth cues, motion dependent cues, and cues that involve the adjustment of the ocular system, as we discuss at some length in this section.
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From page 97... ...
In principle, therefore (although it is not contemplated in the programs considered here) , helmet-mounted displays might restore or enhance depth information, might use depth cues to provide simulated environments, or, much more modestly, might use depth cues to enhance the separation of different sets of alphanumeric or graphical data.
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From page 98... ...
If a helmet-mounted display design significantly degrades the depth cues that normally provide the information for depth perception, as most such devices do, performance of any tasks that need such information will take longer and be less accurate. The Helmet-Mounted Display and Task Performance In evaluating the proposed helmet-mounted display and sensors, it would be useful to have some idea of what kinds of visual tasks will be affected by limits in display resolution, field of view, gray scale, etc.
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From page 99... ...
estimates the importance of various depth cues in perceiving depth over three different ranges or action zones. We can use this classification, together with a set of activities a soldier might have to perform using the Land Warrior System equipment, to estimate what kinds of tasks would be affected by limits in display resolution.
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From page 100... ...
out the details of the relationships it proposes. Even more important, it must be expanded greatly if it is to help in considering the effects and aftereffects of the specific displays that are to be used in the various missions of dismounted infantry soldiers.
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From page 101... ...
However, low display resolution can seriously degrade the effectiveness of this depth cue in two ways: (1) The depth information potentially offered where the boundaries of the occluded and occluding objects intersect can normally rest on very fine detail (in normal vision, the threshold for
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From page 102... ...
In a cluttered environment, however, viewers may not discern where one shape ends and another begins. In normal vision, surface quality, color, and texture probably serve heavily in this regard, but low resolution devices lose the texture and sparse gray scales lose the shading.
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From page 103... ...
Lateral head movements would in most cases have to be impracticably larger in this zone, in order for motion parallax to disambiguate the occlusion with the displays being planned, and therefore training should probably reflect this fact. Accommodation, convergence, and binocular disparities are anomalous when using the proposed devices in Zone 2.
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From page 104... ...
Familiar size presumably provides absolute distance information with a single object and should not therefore be so dependent on a large field of view, but it may in fact also be unreliable and slow even under normal vision. This raises another problem that is more serious than loss of depth perception: for familiar size to work as a cue, the object must be recognized, and the low resolution and sparse gray scale of the proposed display may interfere with recognition of all but the most distinctive forms.
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From page 105... ...
Effects of Degradation of Depth Cues Using the above classification, together with a set of activities a soldier might have to perform using the Land Warrior equipment, we now estimate what kinds of tasks would be affected by limits in display resolution. Image intensifiers present essentially photographic images to the eye, although heavily modified by range and atmospheric conditions and limited by resolution, field of view, and sensor offset.
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From page 106... ...
In addition, the restricted field of view (30-40 degrees) could be quite dangerous, because of its negative effects both on situation awareness and on stitching together successive narrow glances at an active and cluttered environment (see examples 1 and 2 below)
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From page 107... ...
· Depth localization and 3D form. With only monocular viewing, the depth perception needed to align parts in the third dimension would most naturally come from small head movements.
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From page 108... ...
Effects of Helmet-Mounted Displays on Depth Information Helmet-mounted displays, like night vision devices, capture optical information about the environment and present it visually to the wearer. If binocular sensors are used, stereopsis may be enhanced (if somewhat distorted)
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From page 109... ...
, depending on the task and on the parameters and combinations of cues (Ellis et al., 1991; McGreevy and Ellis, 1986~. The pictorial depth cues (and stereopsis and motion-based depth information as well)
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From page 110... ...
Yet, the Land Warrior device is one that uses focal visual information, but it has to be integrated with the operator's requirement for carrying out ambient visual activities. Peripheral vision also provides landmarks as to where some detail that was previously fixated (i.e., was clearly seen in central vision during a previous glance)
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From page 111... ...
There may be some minimum field of view below which a wearer will be unable to achieve a coherent grasp of the context, even by making the successive head movements discussed above; this is suggested by aperture-viewing studies and by examining motion picture use of "establishing shots" (Hochberg, 1986~. At a narrow field of view, the facilitating effects of the context on object recognition may be lost, and the context is often necessary for accurate perception.
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From page 112... ...
Similarly, they will have to substitute search through head movements for search through eye movements because of the reduced field of view. Training to criterion in several critical tasks similar to what must be done in the field (e.g., setting fuses, replacing pins in grenades, clearing weapon malfunction in Zone 1 and detecting approaching threats in Zones 2 and 3)
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From page 113... ...
Our review has pointed out that the monocular display may result in rivalry, which can induce fatigue and disorientation. In addition, stereo depth information will be lost, which is an important depth cue when contrast is poor and obstacles are within 30 meters.
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From page 114... ...
One measure is visual acuity, which is usually defined as the reciprocal of the target size in arc minutes (of subtended visual angle)
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From page 115... ...
, at least two lines (a line pair also used as a measure in night vision goggles) are required to represent one cycle of a periodic target.
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From page 116... ...
640 x 480 pixel display. Taking a 0.7 Kell factor into account, however, active lines/pixels are actually 448 x 336, resulting in a resolution of 5.35 arcmin/pixel or a useable resolution of 10.7 arcmin/pixel.
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