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Tactical Display for Soldiers: Human Factors Considerations (1997)

Chapter: 4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN

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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

4
Visual and Psychomotor Factors in Display Design

In a working environment that is arguably the most dangerous of any current profession, image intensification and thermal imaging have extended the normal perceptual capabilities of the soldier and allowed vision to operate in conditions in which the unaided eye would be ineffective. The proposed helmet-mounted display is designed to allow various information sources to be displayed in front of one eye on a single screen, thereby reducing the time required to switch from one source to another.

A great deal is known about the human visual system and its strengths and limitations in a variety of conditions. The scientific evidence regarding visual and psychomotor factors is among the most critical the panel has assessed. In this chapter, we identify several human factors issues that should be carefully considered by the system's designers.

In our examination of visual and psychomotor attributes of helmet-mounted displays, we begin with an overview of the proposed hardware for the Land Warrior helmet-mounted display and a discussion of its intended uses in enhancing soldiers' awareness of their environment. We follow this with the advantages and disadvantages of such displays for the infantry soldier. Of particular concern is that the display may degrade or even block out information about the local environment that is normally available through the unaided eye; it may, because of its weight, reduce mobility; and its use may result in spatial disorientation and dizziness. 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. The discussion of depth cues

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

presents a tentative framework for a program of testing, evaluating, and improving military visual displays. We then discuss the value of training in overcoming visual and perceptual distortions. The final section presents our conclusions and design guidelines.

INTRODUCTION

Hardware Configuration

The display in the Land Warrior System is initially to be an opaque screen, with a 40 degree field of view displayed on a monochrome 640 x 480 active matrix electro luminescence (AMEL) display, positioned about 1 inch from the wearer's eye. The display is monocular, leaving one eye available to view the ambient environment. The optics and display are to be suspended from the helmet, with the image intensifier located either on the helmet or in line with the optics.1

Several human factors issues need to be considered in evaluating this design. First, there are ergonomic issues related to placing additional weight on the helmet and ensuring that the display is stable with respect to the head; we discuss these issues in detail in Appendix A. In addition, the monocular display, limited resolution coupled with field of view, and off-axis location of sensors have important implications for perceptual and perceptual-motor performance.

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. The night vision system amplifies ambient illumination and allows soldiers to see night environments that would be essentially invisible to the unaided eye. The thermal weapon sight uses the heat differences between objects and their backgrounds to produce a thermal image of the environment. This image can be useful at night as well as during the day, when smoke and other obscurants can make targets difficult to see with the unaided eye. In addition, the device can display messages regarding danger and troop movements, as well as information useful for navigation, such as maps and location as determined by the global positioning system (GPS).

It should be noted that all of the information listed above can be displayed on devices other than a helmet-mounted display. For example, night vision goggles,

1  

The influence of bandwidth constraints on image quality and refresh rate must be accounted for in the proposed wireless transmission system.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

thermal sights, and GPS are currently used to good effect by the Army. The potential advantage of the helmet-mounted display is to integrate this information on one display, facilitating rapid switching between various sources of information as circumstances demand. 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.

The use of helmet-mounted and head-up displays in aircraft provides some insights into the potential advantages and disadvantages of this display technology. The Army has pioneered in the application of helmet-mounted displays in aviation, with various night vision devices and sensors feeding into the Integrated Helmet and Display Sighting System (IHADSS). It has developed an extensive body of research data on visual performance with sensor displays (Foyle and Kaiser, 1991; Bennett et al., 1988; O'Donnell et al., 1988), human factors and safety problems (Brickner, 1989; Hart and Brickner, 1987; Rush et al., 1990), and field experience with visual illusions (Crowley, 1991). These analyses demonstrate both the great potential and the risks of using helmet-mounted displays. For example, Wickens and Long (1994) have shown that head-up displays do provide an advantage to pilots in terms of staying on course and instrument landings. However, they have also shown that pilots using a head-up display are more likely to miss occasional, low-probability events, such as an aircraft moving onto the runway during an approach for landing. This may be due partly to the cluttering effect of the symbology's being superimposed on the image of the outside world, as well as attentional conflict between the near and far information domains (Fischer et al., 1980; Hoffman and Mueller, 1994; McAnn et al., 1992; Neisser and Becklin, 1975; Wickens and Long, 1994; Wickens et al., 1993).

The use of helmet-mounted displays by the infantry soldier, however, poses its own particular set of constraints that may be different from those encountered in the cockpit. Because the soldier is mobile, the issue of providing a stable base for the display becomes even more important than it is in the cockpit, making helmet fit and weight critical issues (see Appendix B). In addition, part of the advantage of head-up displays in the aircraft is due to symbology that can be made conformal with various aspects of the scene (Weintraub and Ensing, 1992). A symbolic runway with associated symbology can be superimposed on an actual runway scene, which helps to integrate the two sources of information and reduce attentional interference (Wickens and Andre, 1990). It is difficult to see how this sort of conformal mapping between symbology and scene features could be achieved in the infantry environment. It is therefore important to analyze the use of helmet-mounted displays within the context of the physical and task environments in which the infantry soldier operates.

For example, the Land Warrior System, with its associated soldier radio,

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

may allow a squad to operate in a more dispersed fashion that reduces its vulnerability. However, night use of a monocular display may at times reduce the ability to detect a camouflaged ambush site because of a loss of certain depth cues, such as stereopsis (especially if small head and trunk movements are not made to compensate through parallax for the loss of stereopsis). This problem of target detection is in a sense amplified by the greater speed of movement afforded by the Land Warrior System. Thus, overreliance on the visual system and speed of advancement through the terrain could reduce squad attentiveness to other cues. If an ambush occurs, the squad's speed of execution of the counterambush drill may be reduced because of both the time needed to orient to the enemy and the narrow field of view.

As to the presentation of symbolic data in the Land Warrior System, for some tasks it may be better to place the helmet-mounted display screen off the visual axis or use a hand-held device, which would require the wearer to shift gaze in order to access the information on the screen but might more than balance this cost by reducing clutter. It is important to determine when it is advantageous to present information superimposed on the scene image and when it may be better to provide other displays.

Advantages and Disadvantages of Display Devices

The introduction of devices that provide remote or local information in the form of enhanced sensory or symbolic displays may in the proper circumstances contribute greatly to the safety and effectiveness of the infantry soldier. However, the specific means proposed in each case may interfere with the acquisition or use of sensory information, depending on the circumstances, and all such devices are associated with certain general problems. We introduce such problems briefly here and discuss them in more detail in the next section.

First, as we discuss in this section, helmet-mounted displays may degrade or even nullify information about the nearby environment that is normally available through the unaided senses; see the report on the Soldier Integrated Protective Ensemble (SIPE) (U.S. Department of the Army, 1993). They may distract attention in ways that may have a critical effect on some tasks, interfering with the user's situation awareness. Even design factors that may be unimportant under less demanding conditions may seriously contribute to a soldier's workload under combat conditions.

For example, the SIPE squad and team leaders reported to our panel a situation in which they were unable to see an ambush target even though the target presented itself on multiple occasions. The squad positioned itself further from the kill zone (concentrated area of fire) because they felt secure in their ability to observe the site. One possible explanation of why the squad was unable to detect the target is that their attention was distracted: they reported diligently observing the kill zone, which meant that they were focused on an area. If the target passed

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

outside the area of narrowed attention, they may never have noticed it, even though it was in their field of view.

Second, through excessive fragility, bulk, and weight, the equipment by which remote or sensor information is displayed may seriously reduce the mobility of the dismounted infantry soldier; it may also add fatigue and heat stress (U.S. Department of the Army, 1993). In aviation helmet-mounted display equipment, the heavy and off-center optics increase fatigue and headaches, and the close-fitting helmet liners used to hold the optics in position may also increase heat stress. In the infantry, these physical problems are an even greater cause for concern: greater fatigue can be expected because active infantry soldiers do not receive support from a seat, and the equipment may interfere with their ability to move and to take cover rapidly.

The physical effects of the equipment may have perceptual and cognitive consequences as well. 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 helmet-mounted 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.

These two sets of issues, the sensory/perceptual and the ergonomic, not only are problems in themselves, but also may interact in counterproductive ways. They must be kept in mind by both the equipment designers and the users. Cost-benefit analyses after appropriate testing-tests whose results apply to the situations in which the equipment is to be used-should precede commitment to any mode of proposed enhancements and to the means by which they are achieved. Table 4-1 summarizes the major benefits and costs of key factors of helmet-mounted displays as well as the key research and testing issues.

Before examining visual factors in detail, it is useful to compare the potential side effects of the proposed helmet-mounted display with those found in others currently being developed. Much of the recent work on the effects of helmet-mounted displays has focused on their use in creating virtual environments (VE). In VE applications, the user is emersed in a synthetic environment that differs from the real-world environment. Experiences in VE involve remote synthetic images of scenes, auditory displays, and apparent head and body motion. The current state of the art in VE technology permits display of relatively sparse image geometry (supplemented by "wallpaper texture"), updated at low rates (usually less than 30 Hz), and displayed more often than not in a biocular format. Current head and body tracking systems, which are required to synchronize the displayed scene with user movements, have hysteresis problems, are slow, and are inaccurate at the limits of the operating envelope. The result is often a low-

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

TABLE 4-1 Display System Features, Human Performance Considerations, and Research Issues

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

  • Acquisition/application of information on a visual display
  • terrain
  • targets
  • map data
  • overlaid symbology/ text
  • overlaid cursors/reticules
  • placement (location on display) of information
  • information density (and clutter)
  • time for sequencing text, other data
  • display switching (IR/I2)

 

  • Laboratory/bench technical test

 

  • Controlled light conditions, controlled display conditions, synthetic images
  • Assess optical and display parameters (e.g., FOV luminance)
  • Assess off-axis viewing, distortion, off center display, etc.
  • 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

 

  • 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

 

 

  • Controlled user field experiments

 

  • 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 performance in known conditions

 

  • Percent correct and time to detect
  • Identify targets and terrain feature
  • Place reticule on target
  • Percent correct and time to acquire and apply displayed information
  • Effects of mobility upon display usability (especially off- axis viewing, interference
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

Monocular helmet-mounted display

 

  • Minimum weight
  • Simplest HMD; less alignment required
  • Eye with no display remains dard adapted
  • Eye with no display continues to sample real world
  • Severe visual rivalry problems. such as target suppression (involuntary) 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

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

 

  • Assess optical and display parameters (e.g., FOV, luminance)
  • Assess off-axis viewing, distortion, off center display, etc.
  • 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

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment

 

  • Effective use of information, success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA

 

  • General HMD issues, plus:
  • Effects of visual rivalry, loss of stereo
  • Effects of smaller field of vision (FOV) with respect to visual search, reduced information content, more emphasis on format of data

 

  • Laboratory/bench technical test

 

  • As general HMD issues

 

  • As general HMD issue
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

  • Controlled user field experiments

 

  • Assess possible visual fatigue, field experiments disorientation, postural stability/loss of coordination

 

  • As general HMD issues plus:
  • Effects on postural stability, navigational/ vestibular orientation

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment

 

  • 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

 

  • General HMD issues plus;
  • Effects of anomalous stereo/parallax upon target assessment, mobility

 

  • Laboratory/bench technical test

 

  • As general HMD issues

 

  • As general HMD issues

 

 

  • 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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

  • General HMD issues, plus:
  • Assess advantages of correct stereo in mobility, target assessment as well as vulnerability of stereo system to misalignment problems

 

  • Laboratory/bench technical test

 

  • As general HMD, plus:
  • Assess effects of optical misalignment upon performance.

 

  • As general HMD

 

 

  • Controlled user field experiments
  • Effects of stereo vision on object detection and and recognition, mobility
  • Assessment of precision and registration requirements

 

  • As general HMD, issues, plus
  • Assess effects of optical misalignment upon performance, orientation and postural stability and coordination when moving

 

  • As general HMD issues
  • Effects of postural ability, navigational/ vestibular orientation

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment

 

  • Effective use if 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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

Helmet-mounted display with see-through (transparent optics)

 

  • Display content can be integrated with the real world scene
  • Referenced navigational and targeting data can provide "where to look" guidance
  • User retains visual contact with the real world

 

  • 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)
  • Unstable registration of display image on the real world may induce disorientation

Helmet-mounted display without see-through (world occluded)

 

  • Less complex (lighter) optics
  • Minor misregistration with real world less noticeable

 

  • User is isolated from real world
  • Major misregistration with real world is less detectable and can result in serious positioning errors
  • Significant re-adaptation time to real world when display is removed
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

  • As general HMD issues, plus:
  • Effects of display collimation luminance and content upon ability to deal with the local environment, effects of changing display content or moving display content upon postural stability coordination, orientation

 

  • Laboratory/bench technical test

 

  • As general HMD issues, plus:
  • Assess registration requirements

 

  • As general HMD

 

 

  • Controlled user field experiments

 

  • As monocular HMD's

 

  • As monocular HMDs

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment

 

  • Effective use of information, success and time to conduct operational tasks dependent upon data, interference of HMD on local SA

 

  • As general HMD issues

 

  • Laboratory/bench technical test

 

  • As general HMD issues

 

  • As general HMD issues

 

 

  • Controlled user field experiments

 

  • As general HMD

 

  • As general HMD
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment.

 

  • Effective use of information, success and time to conduct operational tasks dependent upon HMD data, interference of HMD on local SA

 

  • As general HMD, plus:
  • Effects of display collimation luminance and content upon ability to deal with the local environment, effects of changing display content or moving display content upon postural stability, coordination, orientation
  • Assess training, time associated with data formats, effects of double imaging on imagery/symbology in overlap regions and/or see through

 

  • Laboratory/bench technical test

 

  • As general HMD, plus
  • Assess registration requirements

 

  • As general HMD, plus:
  • 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 on orientation, mobility
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

  • Controlled user field experiments

 

  • As general HMD issues

 

  • 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

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

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
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

 

 

  • Effects on orientation, attention fatigue and possible perceptual adaptation with longer term usage

 

  • As general HMD issues, plus:
  • Effects of display collimation luminance and content upon ability to deal with the local environment, effects of changing display content or moving display content upon postural stability, coordination, orientation
  • Requirements for integrating scale, resolution, optical axis of image sources: assess target/terrain characteristics with non-visual (e.g., thermal) contrast effects
  • Training requirements associated with using thermal imagery

 

  • Laboratory/bench technical test

 

  • As general HMD issues, plus:
  • Assess registration requirements
  • Non-visual wave lengths characteristics synthetic modeled in synthetic imagery

 

  • As general HMD issues.

 

 

  • Controlled user field experiments

 

  • As see through HMD issues, plus:
  • Assess weather effects (temperature, precipitation, fog/haze) which may produce sensor performance variations, thermal camouflage

 

  • As see through HMD
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Control or Display Device

Sensory and Ergonomic Considerations

 

Benefits

Costs

quality image with conflicting sensory cues that become unstable and uncorrelated when the user moves his head. These features of the VE image have led to a number of reported cases of disorientation and motion sickness-a problem that will continue to hamper the widespread acceptance of this technology. In 1992, a special issue of Presence highlighted work in this area.

The display proposed for the Land Warrior System is a flip-down, monocular display mounted on one side of the soldier's helmet. 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. The risk of inducing disorientation and motion sickness should be significantly less than for VE systems, however, because there are fundamental differences in the technology. These can be summarized as follows:

  • Images to be viewed by the soldier are derived from sensors whereas VE images are generated synthetically. The lags and scene content of the VE system are thus not issues for the proposed infantry system.
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Visual Design Research

Test Approach

Visual Test Conditions

Test Criteria

 

 

  • Operational field testing

 

  • Assess stress, fatigue, varied information content in operational tasks in a field exercise with/against soldiers with conventional equipment

 

  • 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
  • When the displayed image is derived from the night vision sensor, it is correlated with head motion. There are no time lags of the sort that would be induced by a head tracker. As a result, the unstable image problems associated with trackers are not a problem for the proposed infantry system.
  • When the displayed image comes from the weapon sight, it is remote and uncorrelated with head movement. However, the pointing direction and rate of movement are directly under the soldier's control so that he can maintain a stable image at a cost in speed of response. Furthermore, when this image is in use, the soldier is stable and braced in a static position.

A poorly fitted or badly balanced helmet will increase the risk of disorientation because, in addition to physical discomfort, the display will be unstable and will move around unpredictably. Other problems with the proposed display include the lack of binocular optics, lag characteristics of the AMEL displays, and the use of the weapon sight image in any situation other than a static brace. However, if the Land Warrior System is well fitted and properly aligned, the risks of motion sickness should be minimal.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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VISUAL FACTORS IN DESIGNING AND ASSESSING DISPLAY DEVICES

In connection with night vision in helicopters, Weintraub and Ensing (1992) note that, simply considered, some visual information is obviously better than none. However, that point is less clear-cut if the visual information is misleading; if its correct interpretation requires more training, higher mental capability, and better concentration than soldiers have; and if interpretation takes more time than can be spared under the conditions of use. Such potential limitations on information use must be considered in relation to specific tasks.

An example of difficulty in interpretation and perception was the performance of TOW weapon system gunners employing the first thermal night sight. The TOW missile system had been fielded for several years prior to the development of a thermal night sight. When the night sight was added, it clearly enhanced the system's capabilities and potential; however, there were significant problems in training gunners to detect and identify threat targets at ranges of 1,000 meters and beyond. The night sight was capable of detecting the heat difference at extended ranges, but soldiers had great difficulty consistently detecting and then identifying friendly versus enemy targets. Once detected, the probability of a hit was high, but soldiers could not be easily trained to detect targets effectively and to avoid fratricide under varying battlefield conditions. This training problem was not fully resolved until the quality of the thermal image was improved, and soldiers gained confidence in their ability to discriminate images in the sight.

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), to both eyes (biocular), or by different displays to each eye (binocular). For this discussion, a display with high physical fidelity is one that provides much the same effective patterning to the eye as would the layout or environment itself when viewed under good conditions. Task-independent definitions of fidelity are not now available. When effective fidelity is too low for a specific task to be performed, the display may be useless or even harmful. Because increases in physical fidelity will in the short-term entail increased expense, fragility, weight, interference with mobility, and other costs, it is important to achieve an understanding of the effective fidelity needs of different tasks.

Display designs are usually discussed in terms of their sensory properties, that is, in terms of the attributes that the displays can offer to the eye and in terms of which their fidelity limits can be assessed. These sensory properties are readily measured. However, they do not by themselves provide information on whether the display allows the viewer adequate perceptual knowledge of the objects and layout being confronted and adequate situation awareness of the environment in which the actions are to be taken.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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TABLE 4-2 Comparison of Field of View Differences for the Human Eye and for Several Input Devices

Eye or Device

Horizontal Field of View in Degrees

Human eye (using both eyes, with no head movement)

201°

Sniper rifle scope (M 49)

Thermal weapon sight (light)

15°

Dragon sight

3.4° to 6.8°

TOW sight (AN/TAS 4A)

BFV driver thermal sight

45°

M113 M-19 driver night sight

26.8°

M 113 vision block (M-17E4)

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)

AN/PVS 7 night vision device

40°

Land Warrior System requirement

60° (90 desired)

Field of View and Resolution

Augmentation displays are all vastly impoverished in comparison with the light that reaches the unaided eye from a natural environment under good viewing conditions. Of course, image intensification and thermal imagery provide information that is not available to the unaided eye. Nonetheless, it is important to consider how various choices of display resolution and configuration affect the observer's perceptual abilities.

Sensors generally provide a field of view that is much smaller than is generally available during unaided viewing. Small fields of view are undesirable because the observer loses sensitivity to peripheral information and may have trouble integrating the separate views into a coherent whole. Table 4-2 compares the horizontal field of view of the unaided human eye with that of several visual input devices.

A display's resolution (that is, measured by the number of dots [pixelshorizontal] or by the number of stripes [TV lines-vertical] per degree of visual angle that can be discriminated) is virtually always lower than the normal eye's highest resolution.2 The display's contrast (the ratio of its darkest and brightest

2  

Other metrics may also be used to define resolution. For example, resolution in night vision goggles is measured in line pairs (see Technical Note).

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

regions) and the number of intermediate levels between those extremes (if there are any) are far less than the eye normally handles. Approximate guidelines for reading, vernier and stereo acuity, contrast thresholds, and other sensory tasks provide a starting point against which to evaluate the equipment (see Boff and Lincoln, 1988). For the reasons considered below, however, those guidelines are not enough. Tests of the features that permit adequate visual performance under actual or simulated field conditions are needed prior to final design decisions.

The significance of these sensory factors depends on the perceptual and cognitive tasks that a viewer is to perform. At the very least, a display must support the visuomotor actions needed to look at it and retrieve information from it. For example, the display must provide enough contrast to focus the eye on the plane of the display (accommodation) and enough coherence (low enough ''snow" or noise level) to allow purposeful eye movements aimed at some peripherally distinguishable feature. Although such behaviors are largely elective and technically under the control of the viewer, their coordinated use has been extremely well practiced in normal environments, as have relationships between the two eyes and between the eyes and the movements of head, body, and limbs.

Binocular Versus Monocular Viewing

A person's two eyes are separated by an interocular distance of 65 mm, and their lines of sight are normally converged to approximately the angle that matches their accommodation distance. For nearby distances (see Table 4-1), each eye receives a noticeably disparate view of the layout. A point in the world that then falls on corresponding places in the two eyes is seen as a single point in binocular vision; a point that falls on noncorresponding places in the two eyes is seen as nearer or further, depending on the disparity. (For more detailed discussion, see Howard and Rogers, 1955, especially pages 55-58). Artificial displays to the two eyes may depart from this natural arrangement in different ways. Each kind of display interferes in some way with this normal process. In monocular displays, one eye is augmented and the other is unoccluded. 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.

There are several important issues involved in deciding whether the helmet-mounted display should be monocular or binocular (see Table 4-1). Monocular displays have the advantage of economy and lower weight. In addition, the unoccluded eye is allowed to adapt to the dark and is therefore available for detecting targets in the soldier's immediate vicinity. On the down side, monocular viewing necessarily involves a loss of stereoscopic vision and may lead to binocular rivalry.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
Binocular Rivalry

When images shown to the two eyes are sufficiently different, for example, a vertical grating presented to the left eye and a horizontal grating shown to the right eye, the brain is unable to combine the two images together into a single view. A state of rivalry ensues, in which the views provided by the two eyes are seen in alternating fashion. With large images, this rivalry will be piecemeal, with localized patches of one eye's view juxtaposed with patches from the other eye. Several variables influence which eye will dominate this rivalry and how long an image will be suppressed. Generally, the eye with the stronger image will dominate, with stronger images being associated with greater contour, brightness, contrast, and motion (Howard and Rogers, 1995). A closed eye represents an extreme case of low strength, but even a closed eye can sometimes suppress the perception of an eye viewing high contrast, moving lines (Howard, 1959).

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. In addition, there should be occasional brief periods when the unoccluded eye gains dominance and causes a degradation of the augmented eye. This would tend to increase in severity with increases in the ambient illumination. Rivalry would be more severe during the day, when the unoccluded eye is receiving a stronger image than the augmented eye, a topic that deserves research under field conditions. Of course, in this situation the observer has the option of closing one eye and reducing rivalry.

An additional factor in rivalry occurs when observers have unequal acuity in the two eyes. According to AR 40-501, Standards of Medical Fitness, infantry personnel must have corrected visual acuity of at least:

  1. 20/40 in one eye and 20/70 in the other eye,
  2. 20/30 in one eye and 20/100 in the other eye, or
  3. 20/20 in one eye and 20/400 in the other eye.

AR 611-201, Enlisted Career Management Fields and Military Occupation Specialty, puts a further restriction on vision requirements for the infantry soldier. To be awarded the military occupational specialty IIB, personnel must have corrected visual acuity of at least 20/20 in one eye and 20/100 in the other eye. An acuity of 20/20 in one eye and 20/40 in the other meets the clinical definition of amblyopia, which occurs in approximately 1-2 percent of the population (Anne Marie Rohaly, personal communication, May, 1996). Amblyopes essentially rely on their good eye for perception. A somewhat similar condition occurs when contact lens wearers use the 'monovision' system, in which one lens corrects for near vision and the other for far vision. Clear vision is obtained at both near and far ranges with the eye providing the clearest image achieving dominance. In the

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

case of amblyopes, the good eye will tend to dominate, and it may be important to measure acuity in each eye before deciding which eye should view the display.

It is also possible that long periods of monocular viewing may result in changes in normal binocular function, although the evidence on this is sparse. Brown et al. (1978) found that, after 8 days of monocular occlusion, subjects showed large changes in phoria and severe diplopia and failed all tests of stereopsis; after 4 hours of occlusion, much smaller and more transient effects have been found (Sethi, 1986).

Stereopsis

In addition to producing rivalry, monocular displays remove the depth cue of stereopsis. 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. This latter observation is sometimes used to claim that stereo is really not that critical to seeing depth. However, it is a bit misleading. First, at close range, stereo depth acuity rivals vernier acuity in terms of sensitivity and can resolve depth differences as small as 2-6 arc sec (Howard and Rogers, 1995). Second, the stereo system operates by matching local features in each eye and can perceive depth in the absence of any recognizable monocular shapes (Julesz, 1971). This ability is especially important in breaking camouflage, in which an object invisible to a single eye stands out in depth against its background. Stereo depth is therefore likely to be particularly important in the infantry soldier's environment, which places a premium on the perception of nearby edges (branches, a ridge, etc.) and objects. At night, under low light conditions (no moon) in which the night vision image is low in contrast, many of the monocular depth cues will not be useful. In this case, a wire strung across a path may blend in with the background but stand out in clear relief with stereo viewing so long as the wire's line has a significant vertical component relative to the retina's axis.

Viewing with two eyes has also been found to be superior to monocular viewing in detecting targets in which depth plays no role. For example, binocular viewing of a threshold-level flash leads to better detection than monocular viewing. Part of this advantage is due to probability summation. If each eye has an independent chance of seeing the target, then two eyes should see better than one (Riggs, 1971). Stereo-blind viewers show precisely the advantage for binocular detection predicted by probability summation. Viewers with normal stereo depth perception show advantages of binocular viewing that are greater than predicted by probability summation, suggesting that they have binocular mechanisms that can sum information from the two eyes prior to detection.

Finally, stereo displays potentially provide a larger field of view than mo-

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

nocular displays although the difference is negligible in current usage. Each eye receives a separate augmented view with an area of central overlap. 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. However, it is important to go beyond laboratory tasks and determine whether these are important factors in performance within the military context. Some indication that they are comes from interviews with Apache pilots of the AH-64 helicopter (Rush et al., 1990). Thermal images of the outside world are presented to one eye, leaving the unoccluded eye dark-adapted and available for seeing instruments and maps in the cockpit. Rush et al. report that pilots sometimes have trouble switching their attention from the bright display to the dark-adapted eye. Some pilots resort to flying for very short intervals with one eye closed, an extremely fatiguing endeavor (p. 14). Practice is reported to be effective in controlling rivalry, but tiring missions apparently make rivalry an additional stressor.

More direct evidence on the importance of binocular displays in the kinds of tasks relevant to the infantry soldier comes from recent studies by CuQlock- Knopp et al. (1994). They had soldiers walk through an off-road terrain while wearing monocular, biocular, and binocular night vision goggles. Independent raters judged performance with the binocular system to be superior to either the monocular or biocular systems, which were equivalent. In addition, the binocular system was preferred by the users. Additional field studies of this type are needed to compare these display configurations in a variety of other tasks, such as target detection.

Both monocular and biocular displays deprive viewers of stereoscopic depth information; all three displays use collimated light, which does not allow accommodation to provide differential focus for objects at different distances. These conditions tend to keep the human accommodation and vergence corrective feedback systems in conflict, resulting (with sustained use) in eyestrain, fatigue, and possibly disorientation (Ebenholtz, 1988, 1992; McCauley, 1984). Although soldiers may be able to adapt to such a system, there may be both short- and long-term costs.

This disorientation could be a significant detractor on the battlefield, rather than a multiplier of capabilities. Infantry School personnel informally reported to the panel that some soldiers had difficulty using the monocular night vision devices. These problems included vomiting, temporary blindness in the unstimulated eye, and temporary total blindness. Similar reports circulated about the

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Apache equipment, also informally, and may be reflected in the time limits imposed on its continuous use (Brickner, 1989). Visual rivalry is a major contributing factor that can be reduced only by using the system in an intermittent fashion or by designing a fully synthetic environment (virtual reality). Little is known about the distribution of individual susceptibility to visual rivalry or the long-term health hazards that might be associated with prolonged use. Intermittent short-term use may be a solution, but guidelines such as those developed for Army aviation are needed.

Even without eyestrain, fatigue, and disorientation, limited display resources mean limited information transfer, depending on the task. For example, when field of view, resolution, and gray scale are reduced, fewer different patterns and less information can be displayed, whether the display is an electronically transferred image of the optic array that is faced by a sensor mounted on the helmet or a presentation of maps and computer-generated graphics. This means that a viewer can differentiate and recognize fewer shapes (insignia, equipment, landmarks, etc.) 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.) are less effective, and so are the behaviors that depend on them.

Reduced field of view also means that: (1) there are fewer objects or parts seen from any position of the head when the wearer is surveying some part of the environment and that there is less context to provide meaning for any detail or object that is in fact seen; (2) a wearer receives less of the ambient or peripheral vision that is important for orientation in the environment; (3) there is less scope for surveying the environment by making fast and economical eye movements (see Table 4-1) while holding a given head position; and (4) there is more need for head movements, which are relatively slow and cumbersome (especially when wearing helmet-mounted displays and associated sensors). Tasks that require rapid scanning of a wide array, as when coming up out of a ground roll, should become impossible to perform smoothly and rapidly by normal perceptual-motor skills.

A perfect system, without any of these limitations, is not currently available for the dismounted infantry soldier; an acceptable trade-off must match the available system to the users' demand characteristics, given the tasks that the users must perform. Table 4-1 presents a summary of trade-offs for visual displays within different categories of visual tasks.

Visual Perception

Visual helmet-mounted displays, and visual displays generally, communicate in at least two different ways: (1) they may present two-dimensional patterns that have meaning for the user and can guide behavior with no need for the viewer to perceive a three-dimensional world from that pattern and (2) they may

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

present two-dimensional patterns that have no meaning in themselves but that act as cues to the viewer's perception of depth, objects, and surfaces in a three-dimensional world. In many actions in the world, it is those three-dimensional perceptions that guide behavior. Although these two channels of information are usually both used in helmet-mounted displays, they are treated differently by virtually all displays, so we consider them separately.

The laser range finder can provide information about the distance of some object in the field, substituting for at least some of the functions served by the visual depth cues, and often surpassing them in accuracy and precision. But the range finder cannot replace the depth cues in providing an integrated perceptual grasp of size, shape, and layout. An attempt to use range to determine some object's size, for example, would require deliberate calculations based on the measured distance and the measured size of the object's image in the display, a time-consuming procedure and one that is probably error-prone compared with humans' very rapid normal perceptual grasp of size and distance. Similarly, a buddy system that uses radio communication to provide triangulation from two viewpoints can offer distance information that may draw on trigonometric calculations to supplement the visual depth cues when the latter are inadequate (or have been defeated by the helmet-mounted display), but it cannot substitute for the rapid and intuitive grasp of the three-dimensional environment that unfettered depth cues afford. The form in which people normally obtain and use the information that underlies human perception of any situation cannot in general be altered without substantial cost in time, error, and situation awareness.

Some tasks require little more visually than that the viewer detect a particular two-dimensional pattern (or classes of two-dimensional patterns) on the display's surface or in the collimated array that it presents to the eye. For example, judging whether an infrared marker in the field of view falls on the pattern projected by a rifle's target requires only that the user judge whether or not two patches of light coincide on the display. For this task, the equipment used in the SIPE project received favorable testimony from its users (U.S. Department of the Army, 1993). Success on such tasks can probably be closely predicted by existing data on the resolution and contrast that are needed to detect contours and points. Similarly, the detection and reading of graphic symbols requires only that the display's contrast, resolution, and signal-to-noise ratio fit what is known about legibility (Helander and Rupp, 1984; Grandjean, 1987; Human Factors Society, 1988). There are probably many tasks that can be reduced to similar visual questions about the display's surface. The substantial psychophysical research literature on visual detection and research on computer and video displays can provide good bases for design trade-offs (Helander and Rupp, 1984; Grandjean, 1987; Human Factors Society, 1988).

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

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

three-dimensional objects in the environment need action, on perceiving their three-dimensional spatial relationships to each other and to the viewer, and on perceiving the three-dimensional environment in which the actions are to be performed. Those perceptions depend, in turn, on depth cues, which are patterns of light either projected to the eye by the environment or transmitted through the helmet-mounted display. Even when the display shows only maps or diagrams, which can in principle be provided as two-dimensional patterns and evaluated as such, the literature suggests that the information about layout and location is still best conveyed by the same kind of depth cues that are used in pictures of three-dimensional space (Bemis et al., 1988; Burnett and Barfield, 1991).

Depth Cues

For visually guided behaviors in three-dimensional space (advancing, aiming, reconnoitering or scanning the environment, combat, manipulating equipment, etc.), 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. For general references see Cutting and Vishton (1995), Gillam (1995), and Hochberg and Brooks (1996); the interaction of different sources of information in any specific combination of task and environment must be separately addressed.

Pictorial depth cues do not rely on moving pictures. They are essentially patterns in a two-dimensional array of light that the world projects to the eye, patterns that are themselves two-dimensional but that most frequently arise from differences in depth. That is, the various cues are aspects or features of the pattern of light that are likely to be provided both by a three-dimensional scene (layout of objects and surfaces) and by the projective picture of that scene as made by a camera, by an artist, or by a computer. Thus, because the visual angle subtended by an object decreases with its distance, one has linear perspective (e.g., within the display, sizes perpendicular to the line of sight decrease as distance increases) and the related cues of projective relative size (the relative distance of two objects in the world are inversely related to the sizes of their images in the display) and textural density (as distance in the world increases, the density of textural detail in the image of a homogeneous surface increases). Height in field is a powerful depth cue when viewer and target object rest on the same plane (the farther the target, the higher toward the horizon line). Interposition is an exceptionally strong cue whenever the images of two objects overlap (when two contours form a "t," the uninterrupted one is probably the nearer).

Other important depth cues result from motion parallax, in which characteristic patterns of motions in the two-dimensional array normally arise from the relative motion between viewer and environment (motion perspective, the optical expansion pattern, etc.).

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

Finally, there are the depth cues that depend on the adjustments of ocular musculature: stereopsis and accommodation. In stereopsis, or binocular disparity, any point in space on which the two eyes are converged (a voluntary act) falls on corresponding points in the two eyes; any object or point at some other distance near that line of sight projects disparate images to the two eyes. Those disparities, taken with the eyes' vergence, are particularly powerful depth cues for relatively nearby distances (Alpern, 1971). Also, the eye muscles increase the lenses' curvature to focus on nearer objects; such muscular action, or accommodation, is a depth cue within very close distances.

Quite different two-dimensional patterns can thus act as cues to the same three-dimensional situation, providing the same perceived depth. It is normally the perceived three-dimensional situation that determines action and decision, when the viewing conditions permit. Even though they are used to provide information that may be missing from the normal field of view (with dark of night being the extreme case), helmet-mounted displays will generally degrade these depth cues; depending on their design, they will do so to a different extent and in different ways.

For example, where helmet-mounted displays transmit light originating in the scene, collimation places all points at infinity as far as accommodation is concerned. Resolution, gray scale, and field of view of the transmitted or reconstructed image are always impaired relative to unaided vision; this degrades those cues that depend on detail (like textural gradients), on gradations of shade (like modeling), or on expanse (like linear perspective). Other cues used for perceiving the spatial layout of objects and surfaces can be generated by computers. 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.

The effects of degrading or enhancing depth cues, and the trade-offs involved, can probably be estimated. To do so, one would need to assemble a set of matrices around the four variables: (1) which distances are most important for particular tasks, (2) the distance ranges over which each class of depth cues is effective, (3) which depth cues are offered by particular environments, and (4) the effects of different display properties on the different depth cues. A first step toward achieving item (2) has already been taken by Cutting and his colleagues (Cutting and Vishton, 1995); the other items can probably be approximated. Such attempts are necessarily still quite speculative, since at present far less is known in an engineering sense about how the physical properties of a display affect the effectiveness of the depth cues than is known about the display of two-dimensional patterns. They would, however, suggest on a principled basis what research and testing are needed for different tasks and conditions. A discussion

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

of a few examples here illustrates the relationship between these variables and their importance to the design and use of helmet-mounted displays.

First, tasks differ in the ranges of depth information they require. Information about nearby depth (i.e., within 3 meters) is needed in reaching for tools or weapons, for avoiding collision with obstacles (a nearby doorjamb, tree trunk, etc.), and for touching pen to map. Information about whether a moving figure is about to disappear behind a house or wall, or will remain in front of it, involves intermediate distance (say, from 5 meters to 3 kilometers); the same question about a column of moving vehicles and a rise in terrain involves far distances (say, above 5 kilometers). Distinguishing a camouflaged object from its background at any of these distances requires depth information appropriate to the object's scale and distance. 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. However, predicting with confidence what will be recognizable in any situation depends on having a usable model, or generalizing from previous tests in that situation, or both. At our present state of knowledge, neither is sufficiently reliable or complete, and so we must generally use both.

Several recent discussions of models intended to apply to electronic instruments are found in Peli (1995). Models that attempt to take into account how information in the target scene is transformed by the electronic media, the visual optics, and selective retinal sensitivities have increased in sophistication, graduating from point-by-point analyses (from pixel to blur circle to retinal spacing) to modulation transfer functions and numbers of cycles per target, and even numbers of cycles per the details needed to identify a particular vehicle (O'Kane in Peli, 1995). These approaches attempt to model target detection and identification in terms of variables such as contrast and spatial frequency. However, it seems likely that accurate prediction will ultimately have to specify the features or shape primitives that underlie shape recognition by humans. These primitives are not currently known, although there are several promising proposals, such as Biederman's geon theory (Biederman, 1995), that have opened promising avenues of inquiry (Ullman, 1996). In addition, it is clear that top-down effects of familiarity, and priming from prior glimpses, permit extremely efficient search and object recognition, but these factors are at present very difficult to model.

Without an explicit or implicit model, laboratory tests are difficult to apply. In any case, laboratory tests alone are of questionable validity, given the many

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

ways in which field tests may differ from the laboratory; indeed, even individual field tests are of questionable validity if the results are to be applied to other situations, to users with other training, to different tasks, etc. (see O'Kane, 1995). Test conditions should come as close as possible to the situations for which the equipment is intended; the tests should come as early as possible in deciding the costs and benefits of different equipment specifications; and any help from operational units in determining what specifications are needed for different tasks would be welcome.

We have approached the task of estimating the impact of the helmet-mounted display on soldier performance by first recognizing that soldiers have to be able to perform visual tasks at a wide range of distances using a varied set of depth cues. The classification recently undertaken by Cutting and Vishton (1995) 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. These estimates are obviously very rough approximations, but they nonetheless may be useful as heuristics.

Depth Cues Used to Guide Action

There are many different channels (or cues) through which information can be obtained about depth and distances in the environment. These differ in substance and mechanism and are unified only by the fact that the diverse channels bring information from the same world, agreeing with each other to the extent that they are all correct. Although such channels are redundant, they do not measure the same things about layout and are not effective over the same ranges. They therefore differ in terms of which task performance they best support. They are differently affected by the devices that reduce resolution, field of view, binocularity, and free head movement; a detailed study of such differences would probably help as a guide both to actual testing and to training. In what follows we (1) introduce a first pass, based on Cutting and Vishton (1995), at classifying the various major cues in terms of three categories or zones of performance in normal perceptual activity and (2) consider for each of these three zones the likely effects of impoverished and offset displays on the wearer's perception of depth, layout, and orientation and what such an examination suggests in the way of necessary further analysis, research, and training.

Visual Guidance within Three Zones of Action

Figure 4-1 should be regarded as a tentative first step in constructing a framework for a program of testing, evaluating, and improving military visual displays. More data and more extensive analyses are needed to solidify and fill

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

FIGURE 4-1 A framework for testing visual displays in three zones of space. Source: Adapted from Cutting and Vishton (1995). Printed by permission.

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. When so expanded, it must be studied in real or simulated field tests to determine how best to deal with display limitations and to determine the specific cautions and training such effects and aftereffects make necessary. There is not now, and is never likely to be, a way of generating the answer to such questions from first principles or from some look-up table, but the body of perceptual knowledge we now have makes it possible to suggest what should be looked for and what will be found. What follows should be considered sample suggestions; they should not be taken as exhaustive.

The plots in Figure 4-1 suggest that there are three egocentric regions or zones of space: Zone 1 is personal space, extending to slightly beyond arm's reach, and delimits the space used by a static observer. Zone 2 is action space, extending to about 30 meters, and encompasses distances in which an observer can throw an object to another person, throw an object at an animal, or easily talk

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

to others. Zone 3 is vista space, extending beyond 30 meters, and includes an area in which changes in the position of objects is slow as a pedestrian moves through the environment.

For each zone, we list the aftereffects to be expected, as well as the effects that impoverished and offset artificial displays are likely to have on picking up spatial cues, apprehending the shapes and layout of the viewer's environment, carrying out typical actions, and perceiving one's orientation in the environment.

For each of 9 depth cues of the more than 15 depth cues that have been widely discussed and studied, Cutting and Vishton use existing data or plausible assumptions to estimate the barely discriminable (threshold) depth separation between two objects at different distances from the designated viewer D1 and D2. These distance are used to derive a measure of depth-contrast sensitivity (DCS) according to the equation: DCS = 2(D - D2)/(D + D2). Figure 4-1 shows this sensitivity measure as a function of the objects' mean distance from the viewer (D1 + D2)/2). The horizontal line at .1 on the sensitivity scale represents the ''assumed utility threshold for information." That is, Cutting and Vishton assume that depth differences less than this amount do not contribute to perception of layout. Note that small values of depth-contrast sensitivity reflect good sensitivity. For example, occlusion provides extremely fine discrimination of which object is closer and is effective at all distances from the observer for which the objects' junctions with other objects are visible. By comparison, convergence and accommodation are useful primarily at distances less than 10 meters.

Visual Guidance Within Zone 1 Insofar as personal space is concerned, accommodation and convergence are potentially at their most useful with normal vision, but accommodation is anomalous as a differential depth cue with collimated displays, and convergence is typically fixed by the optical design and therefore anomalous as a cue as well. Users of these devices should be thoroughly warned and convinced that they have lost the normally automatic depth knowledge that is based on this information, and they should be trained to use other cues. In addition, it appears that collimation does not necessarily cause observers to accommodate for infinity. Iavecchia et al. (1988) reported that most observers tend to let their accommodation "lapse inward" when viewing collimated displays. Edgar et al. (1995) recently confirmed this finding and showed that it was especially pronounced when observers had to make complex discriminations of helmet-mounted display imagery. The effect of this incorrect accommodation would be to blur the image as well as to affect the perceived size and distance of objects.

Figure 4-1 shows that occlusion is a highly effective depth cue for all zones, including Zone 1. 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

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

misalignment can be as low as 1 arc sec) and in that case will be lost with the low resolution characteristic of electronic displays, such as the image intensifier (I²) device and the thermal weapon sight. Depending on configuration, ambiguity of what depth is in fact perceived and even illusions can result (Chapanis and McCleary, 1953; Dinnerstein and Wertheiman, 1957). Users should be alerted to this fact and informed that moving the head laterally while maintaining fixation on the likely region of intersection should help to alleviate this problem; training will probably be needed because the weight of the headgear may discourage lateral head motion.

Overall shape is also normally used to interpolate the region of the intersection cue supporting occlusion (see Chapanis and McCleary, 1953). 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. Of the two, it is probably most effective (and certainly cheaper) to increase the gray scale and gamma, so that surfaces are distinguished as much as possible by display luminance. Again, training in the use of lateral head movements will help, and any differential displacement of the light source (as would then occur if the infrared sensor were head-mounted) could also prove useful.

Binocular disparities are also at their most effective within Zone 1, and the viewer is completely deprived of these when monocular or biocular displays are used. It is likely that, if the observer makes small lateral head movements, equivalent information can be regained (albeit more slowly and much less instinctively). We emphasize the need for head-movement training because it seems likely that most tasks to be performed within Zone 1 use focused and relatively fixed attention. Even in normal conditions (aside from something done very close up, like threading a needle), this is probably accomplished with a relatively fixed head and with great reliance on the binocular cues. For that reason, we do not expect that reduced field of view will be much of a problem in this zone. For the same reason, however, the novice will probably also need practice in making the required movements habitual in disambiguating the layout at hand, while ceasing such movements when they would interfere with fixed and tightly focused attention. Although a little informal testing should convince the viewer that elective head movements can be brought into service in this way, we know of no actual research on this matter.

The necessity of adapting visuomotor performance (including the head movements mentioned above) to the effects of offset, or displaced viewpoint, should be greatest in this zone. Wearers should be alerted to the nature of the adaptation, to its incompleteness, and to the fact that they should expect involuntary aftereffects to follow any prolonged use of offset displays.

Visual Guidance Within Zone 2 Occlusion remains useful in Zone 2. Its vulner-

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

ability to low resolution could be somewhat lower if the larger objects at issue in action space are smoother shapes (lower perimeter/area ratios and therefore less likely to provide conflicts between the global and local components of occlusion noted above). Their greater separations might make luminance differences more likely within the display, but gray scale will probably continue to be important. 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. It seems likely that the absence of the binocular information is particularly costly in this space, and training should stress the fact that errors are likely to arise from the monocular viewing (probably mainly ones of assuming that objects that are adjacent in the displayed image array are at the same distance from the viewer). As noted above, one cannot expect that comfortable lateral head movements can serve as useful correctives, but lateral body movements or sideways steps should usually serve to disambiguate the layout. Height in visual field is probably a highly useful potential cue in this zone. At this point, however, we should consider the major problems that will surely be introduced by what we have called the viewpoint offset provided by the equipment and that should be addressed in research and training.

A helmet-mounted sensor changes height relative to the ground plane and horizon and also must distort the viewer's perception of the upright (and slants of all surfaces) (Held et al., 1975; Johansson and Börjesson, 1990; Matin and Li, 1992; Proffitt et al., 1995). These are probably minor effects except when shifting between the display and a direct view; the user's sense of the vertical will have shifted when adapting to the offset, and an opposing shift should occur as an aftereffect when shifting to direct viewing. Practice in anticipating such aftereffects may be profitable. A gun-mounted sensor such as the thermal weapon sight, if used for anything other than centering the target, is very much more likely to distort perceived height in field and badly confuse the viewer's perceived slant of upright and ground plane.

Moreover, since the user must integrate information over changing views as the gun's direction changes without the proprioceptive feedback that would usually provide the context for head and trunk movements, the relationship between those views may be badly distorted or chaotic. That is, because of the restricted field of view, the displacements within the visual field will not necessarily be correctly or unambiguously interpretable. This is known in the computer-vision literature as the aperture problem. It can result in extremely robust illusions as to the direction of motion (often known as the "barber pole" illusions). This in turn may scramble the perception of successively viewed objects' lateral spatial relationships.

Even setting aside the gun sight as a source of layout information, the problem remains in diminished form when any offset sensor is used with reduced field

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

of view. Although occlusion may be a potentially useful depth cue for normal vision in Zone 2, it may be highly vulnerable because of restricted field of view. It seems likely that training to achieve a disciplined use of landmarks and of deliberate panning movements may be able to minimize damage from the aperture effect.

Relative size and familiar size are theoretically both valuable depth cues with normal vision in Zone 2. Because relative size depends on the difference in size. of the images provided by two objects at different distances in space, and because there is no reason to believe that it remains effective if the field of view is too small to display both objects simultaneously, relative size may not function reliably with the equipment being considered. This particular issue can probably be tested most cheaply with laboratory simulations. 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. For relative size to work, things that are of very different shape in the world should not end up having similar shape in the display. This is likely to be a problem with the low-resolution images provided by infrared imagery in which shapes may not be recognized and many of the remaining depth cues, such as texture gradients, shading, etc., may not be available. Whether or not this is a problem for familiar size and relative size as depth cues, or for the even more important tasks that hang on object identification, should be tested for specific missions and equipment.

Viewpoint offset probably requires less adaptation in Zone 2 than in Zone 1, and aftereffects are probably correspondingly less disruptive; training here may not be necessary, although that should be determined by research over the appropriate distances. The effects of reduced field of view on integrating an overall picture of the environment should in general be mixed, because larger stretches of the environment are included within the same visual angle, and stable landmarks (large in the world but relatively small within the display) should help the viewer integrate the views obtained from different directions. This requires some degree of shape fidelity between object and display, and we have noted above that, with low resolution and sparse gray scale, this may pose a problem. As with offset, directed research is needed to estimate the extent of the problem.

Visual Guidance Within Zone 3 As Figure 4-1 indicates, in Zone 3, or vista space, binocular disparities contribute little. Infantry soldiers do not normally move far and fast enough to provide useful motion parallax, leaving occlusion, texture gradients (relative density), height in field, aerial perspective, and relative size as more or less effective depth cues for normal daytime vision in much of

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

this space. Visual displays that reduce resolution, gray scale, and field of view should have mixed effects on these cues: relative size and height in field may be damaged less in Zone 3 than in Zone 2, because two relatively distant objects that are not too far apart laterally within the environment are more likely to be simultaneously included within a limited field of view than are two nearer objects. Textural gradients are almost certainly lost with low resolution, and aerial perspective should be rendered useless by eight-bit gray scales.

It is probably not necessary to assess further the effects that such displays have on daytime vision because we assume that (regardless of what designers now intend) most visual tasks during the day will be conducted with unaided vision. At night, moreover, using unaided vision, we should probably expect that Zone 3 will effectively fail to provide information about layout and depth, so that the viewer will have to depend on instrument-provided range information about those distances. Under these conditions and considering the large distances involved, concern about viewpoint offset and corresponding aftereffects does not seem justified. However, the integration of successive views of the sparsely populated nighttime vistas available with small fields of view probably requires both training and the addition to the display of some suitable directional framework, a framework that is salient but that does not obscure the already-restricted visual field.

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. In contrast, thermal imagers depend on characteristic signatures and hot spots; although there are models that seem to predict performance to some extent (O'Kane, 1995), we do not discuss such imagers here.

First, taking several examples from each of the three action zones, we make exceedingly rough estimates of the resolution needed to execute typical tasks in those zones, using equipment that provides the graphic equivalent of image intensifying devices (Table 4-3). (Although the Land Warrior equipment has been forecast as having higher resolution and larger field of view, the panel was unable to obtain specifications, in any case, the same sorts of analyses will be needed with whatever parameters are finally achieved.) We propose that, even if it is necessary to limit display size and processing load to the present 300 K pixels, the user should have available one or two alternatives to the uniformly distributed 640 x 480 format. Specifically, the user should be able to choose a higher resolution in the lower part of the field, at the expense of the upper part.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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TABLE 4-3 Rankings of Information Sources by the Areas under Their Curves in Figure 4-1 within the Three Kinds of Space

 

Action

Space

 

 

Source of Information

Personal Space

All Sources

Pictorial Sources

Vista Space

1. Occlusion and interposition

1

1

1

1

2. Relative size

4

3.5

3

2

3. Relative density

7

6

4

4.5

4. Height in visual field and height in the picture plane

a

2

2

3

5. Aerial perspective and atmospheric perspective

8

7

5

4.5

6. Motion perspective and motion parallax

3

3.5

--

6

7. Convergence

5.5

8.5

--

8.5

8. Accommodation

5.5

8.5

--

8.5

9. Binocular, disparity, stereopsis, and diplopia

2

5

--

7

a Dashes indicate data not applicable to source.

Assuming that the processing limits cannot be exceeded, adding additional sensitive units to the sensor and switching them in and out as desired (trading off density in one region against another) would be one way to achieve this, and probably relatively inexpensive. In general, there are different kinds of evidence that the lower part of the visual field is more important for detailed functions, and that the visual system is equipped with more specialized contour-sensitive mechanisms, than the upper field (Previc, 1996; Rubin et al., 1996). More specifically, as we discuss below, depth perception and manipulation, especially in the absence of binocular vision, is not well served by the existing resolutions.

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). The 640 x 480 array resolution, although sparse for the central 4-8 degrees of central vision, is much higher than is needed for peripheral vision (the ambient system), and some redistribution should make it possible to increase the field of view to something between 50 and 60 degrees by lowering peripheral resolution. (Luminance modulation could be used to obtain higher effective subpixel resolution; such enhancement might help for some environmental tasks and detract in others, so that real and simulated field tests are important.) The additional margin will not help in obtaining information through eye movements, but it should prove useful when the soldier relies on head move-

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

ments, as when walking or surveying the surroundings. This display format should probably be elective.

Zone / Example 1: Disarming mines, cutting wires, adjusting sights, applying first aid, setting fuses, clearing weapon malfunction, etc. Two issues are detection and depth perception (and aligning parts in depth as well as in the frontoparallel plane).

  • Close detail. Assume the following situation: a distance of about 0.5 meter, wires or other parts as small as 1/8 inch, and horizontal display lines (or pixel rows) of about 0.063 degree = 3.75 min (30 degree 480 lines). The 1/8 inch subtends 23 minutes, or is about 8 pixels high and is well above both the 1 min minimum separable for spatial resolution at adequate contrast and the pixel size (3.75 min/pixel) limit of the Land Warrior System. Given the parameters, such features should be visible almost out to 1 meter, at which point the pixel size should exceed the image size, and visual confounding and loss of detail should become a factor.
  • 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. With lateral head movements of about 1 inch, depth differences of about 1/4 inch would be needed at 18 inch (0.5 meter) distance, and about 1.25 inches at 1 yard/meter. Most fine manipulation tasks are conducted within this range or a bit less, and this resolution would likely limit task precision. With twice the resolution in the lower half of the display field, all of these tasks would probably be feasible at 0.5 meter and some even at 1 meter.

Example 2: hand-to-hand combat, breach obstacles, detect branches and handholds, operate controls. At a range of about 1 meter, the field of view should be less than 2 ft. Limbs, weapons, and branches are safely above spatial resolution, but shoulders, limbs, and most of the target body fall beyond the field of view. Something like a 55 degree field of view would include the opponent's head, shoulders, and arms and at a half-normal resolution should then be enough for the ambient system.

Zones 2 and 3 A critical activity occurring in Zones 2 and 3 involves object detection, recognition, and identification (see Technical Note). A soldier needs to detect the presence of another person in the distance, recognize that person as friend or foe, and in some cases identify the individual. The bases for these object recognition tasks are unknown, but we attempt to use some simplifying ideas, similar to the basis of Biederman's geon theory, to provide estimates of what kind of performance might be expected using limited resolution displays. The main assumption of the geon theory is that object recognition is accomplished by recognizing combinations of a small set of component forms. We

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

have no reason to believe that there is a single system underlying object recognition or a single set of criteria. Indeed, it seems reasonable to assume that different classes of objects are recognized and/or identified by different criteria in different zones.

Viewed from 1 meter or less, with a field of view of 30 degrees, a tank's overall silhouette would seem unobtainable. Conversely, viewed from 75 meters, the largest of some soldier's component features (e.g., a 1 inch nose, seen in profile) subtends little more than 1.3 min, whereas the minimum separable angle for reading letters is taken as 1.0 min and, more to the present point, the minimum pixel size is close to 4 min. To pick up the contribution of the nose is barely possible with good unaided vision alone at 75 meters and is not possible with a device of the Land Warrior System's resolution. This is not to say that discerning the target's nose is necessary or sufficient to recognize the soldier (some other feature or clusters of features may be needed). However, if the presence of the largest feature (whatever it may be) cannot be detected, then smaller ones become irrelevant.

Having considered a few examples of resolution effects on specific tasks, we turn to a more general survey of the effects of helmet-mounted displays on depth information.

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) by increasing the separation between them, extending depth information from Zone 1 into Zone 2 (i.e., intermediate distances). If only a single sensor is used, stereopsis is necessarily lost with monocular or biocular head-mounted displays, and accommodation loses all differential depth information in all displays because the light is collimated. Head-motion parallax is seriously distorted whenever the sensors are at a different optical location from the eyes (as in virtually all head-mounted displays) and is lost when a viewer must remain stationary. Without stereopsis or parallax, a viewer is left only with interposition for nearby depth information, and that information is severely limited; objects' images must be overlapping to provide it, and at most it tells only which surface is the nearer.

Because a viewer who must remain stationary but who is concerned more with intermediate and far distances than with near distances must in any case depend chiefly on the pictorial depth cues (see Figure 4-1), the loss of stereopsis and the distortion of head-motion parallax that is imposed by most helmet-mounted displays may not represent significant additional costs. That can only be true, however, if the equipment provides the depth cues in a condition that is adequate to the perceptual needs of the task. Such devices are not equal to what the unaided eye receives under good viewing conditions, but more graded assess-

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

ments are needed for making design decisions, particularly under degraded viewing conditions.

There are data that offer some guidance as to the equipment needed for stereopsis (in the case of binocular displays) and for parallax, obtained as functions of luminance, contrast, and resolution, using very simple displays involving wires, dots, and gratings (Schor, 1987; Schor et al., 1984, Foley, 1987). The pictorial depth cues, however, are another matter. At the most basic level-as two-dimensional patterns-there are various data showing that the exposure time and contrast needed to detect targets vary with their size, background luminance, etc. These could be applied to features of the depth cues that seem amenable to such analysis.

For example, textural gradient and local occlusion may be presented to the sensor by the environment, but they are probably very readily lost at low resolutions; shading cues and the intersections that provide interposition information are degraded or lost with a sparse gray scale; height in field and convergent linear perspective, both of which depend on some extended region of the display, must at some point be degraded as field of view decreases, as aperture-viewing studies confirm (Hart and Brickner, 1987). The effects on these attributes of any display must therefore be assessed before deciding to use the equipment in any task that is likely to call heavily on those cues, and effort should be made to relate, extend, test, and apply the results of such task-oriented analyses.

The same issue arises in the context of computer-generated graphics. One function of the display equipment (including hand-held displays, which do not directly interfere with normal visual perception of the world) is to present maps, diagrams, and charts. Experimental evidence suggests that maps and diagrams that incorporate depth cues may be more effective than traditional displays (see, e.g., Bemis et al., 1988; Burnett and Barfield, 1991), 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) can, in principle, be successfully constructed on computer graphics displays, but they can be used by a viewer only to the degree that the sensory qualities of the display permit. The enhancement and simplification techniques that are available to computer-generated images can provide more robust information, but limitations in field devices such as resolution, contrast, and field of view must still be evaluated as to their effects on depth cues from these artificial sources.

Most familiar classes of objects can be recognized with extreme rapidity even in the absence of any depth information, cued only by their shapes in the display (Biederman, 1985; Peterson et al., 1991). Performance tasks that do not require any specific depth perception-but that can be carried out by recognizing some object(s) or layout (e.g., the presence or direction of a person or group, of a particular kind of equipment, a particular house, etc.)-are therefore probably not badly degraded by the absence of depth information. Moreover, objects' familiar

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

sizes can actually act as depth cues, although such distance information takes longer to extract (Predebon, 1992). Like the depth cues, however, the perception of the objects as shapes necessarily depends on the quality of the display, the field of view, and how the situation prepares or primes the viewer.

In a display that is too coarse to resolve the features that characterize a given object, or with gray scale and contrast inadequate to model its forms, shapes may not be recognizable. Conservative estimates of what tasks can be performed are certainly possible to make (see discussion on action zones). But object recognition cannot be predicted solely from any table of data because objects (and depth cues as well) are normally highly redundant. That is, a part or a feature (or even just an attribute of some object, like its color) may serve instead of the whole object, given an appropriate past or present context (Hochberg, 1980). With training and familiarity, therefore, performance may surpass what would be expected from such tables. Conversely, a given point of view may obscure the relevant features even when display quality is otherwise adequate. As a consequence, trade-off assumptions about any specific equipment need to be tested in the real or simulated missions for which it is intended.

Effects of Helmet-Mounted Displays on Field of View

With a small field of view, some or all of the redundancy in an object or scene is very likely to be lost, because only some portion of either may be included within the display. Moreover, peripheral vision is greatly decreased by the field of view for most displays proposed. This will interfere with object recognition, because the information in peripheral vision normally informs a viewer where to look next in order to obtain some needed feature. In the division of perceptual labor between what have been called the ambient and focal visual systems (Hughes et al., 1996; Leibowitz et al., 1982; Schneider, 1969; Trevarthen, 1968), which are roughly equivalent to peripheral and foveal vision, it is the former that contributes most heavily to orienting (e.g., attentional capture), visual guidance of the limbs, and posture (orientation or vection) (for recent reviews, see Hughes et al., 1996). In normal vision, we bring only a few points in the layout around us to the fovea, relying on the ambient system for the remainder. 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) lay relative to the feature presently being fixated, and these landmarks are likely to be unavailable within a small field of view. A viewer can compensate to some extent for a small field of view by making more head movements to sample the environment. But successive small glimpses of the environment that are obtained by such movements (which are much slower and more cumbersome than eye movements, especially with heavy helmet-mounted displays in place)

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

can provide information about the entire object, or scene, only if they are effectively stitched together in memory, which is not necessarily possible in cluttered or unfamiliar settings.

There is currently no single accepted cognitive theory from which one can set the bounds of an individual glimpse. For example, are successive views of a display ''directly" placed by the visual system into a single perceptual setting, without passing through any memory-like encoding process, just so long as there is enough structural overlap between the views? If so, which seems doubtful (Hochberg and Brooks, 1996), how much overlap must there be? Over how much delay? Over how many shifts of view? Regardless of theory, it is known that reduced fields of view reduce a viewer's ability to grasp things and to maneuver within the visual environment.

According to both a large body of research and common sense, objects and scenes can be identified more rapidly and more correctly when a viewer has been previously set or primed by those objects or by the categories to which they belong (Biederman, 1985; Bachman and Alik, 1976). The context in which an object appears, if it is an appropriate context, can serve much the same function (Biederman, 1981), but that depends on a field of view sufficient to provide that context. Reduced fields of view eliminate or reduce the context and thereby its facilitating effects.

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. Soldiers commonly are required to drop to the ground, roll rapidly, and survey their surroundings. It seems likely that the effects of narrow fields of view (and protruding eyewear) may require special training on such tasks and warnings about specific vulnerabilities.

When it is important for a viewer to have a ready grasp of where people and things are distributed within the visual environment (which must often be the case with infantry soldiers), the higher cost and weight of displays that go with wider fields of view may be unavoidable. Only controlled research under field (or field-like) conditions can inform that decision. In any case, because the sequence of visual queries (e.g., successive glances and head turnings) is elective-depending on a viewer's task, knowledge, and attention as much as on the information provided by the visual display at each step in the sequence-one must consider the situation that the viewer needs to grasp and the factors that affect such situation awareness.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

TRAINING

As mentioned earlier, problems with the monocular display in the Apache helicopter were at least partially alleviated by training. There are at least three quite different areas in which specific training may help infantry soldiers use the helmet-mounted display, and the effectiveness of such training should be evaluated:

  1. Performance of manipulations and locomotion under the offsets described should be practiced, and relearning of behavior during the aftereffects of protracted sessions should be pursued to familiarize the soldier with the existence and nature of the aftereffects.
  2. To execute certain tasks, soldiers will have to substitute head motion parallax for binocular stereopsis in order to gain depth information in Zones 1 and 2. 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) may help decrease the costs of these informational losses.
  3. Objects and terrain seen through these devices, especially narrow field of view thermal imaging, do not present the familiar perceptual units that so quickly and seamlessly serve to build our normal visual world. It is more like recognizing planes by radar signatures, but trying to do so in the course of rapid movement through a cluttered environment. Fortunately, practice with the purely visual task of recognition and identification can be obtained as much as is necessary using recorded and/or simulated displays. How effective such training is, and how much is needed, are questions for research.

CONCLUSIONS AND DESIGN GUIDELINES

The Land Warrior System aims to increase both the effectiveness and the survivability of infantry soldiers, using technologies that include portable computers, satellite navigation, light amplifying and thermal sensors, and both helmet-mounted and hand-held displays. Although such technologies can certainly enhance performance under certain conditions, they incur costs and risks as well. The pros and cons of each innovation must be considered in balance, to avoid net reductions in safety and capability. Evaluations must be informed by real or simulated research in the field; they should not be based solely on analyses of human abilities in laboratory situations.

Field research to test the effectiveness of this equipment has only recently begun. To be effective, the research must be directed toward conditions under which the net benefits from specific sensory enhancements are of questionable

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

value. On the basis of the relevant research literature, this chapter summarizes what planners need to know in order to assess the benefits and costs of the major proposed enhancements. We believe that carefully designed field testing, guided by the kinds of human factors issues that are raised here, together with the concerns expressed by those who use the equipment, will be needed continually as this program evolves.

  1. The proposal to use a monocular display appears to be motivated by the lower weight and cost of this configuration, as well as the desire to maintain dark adaptation in one eye. 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. Field tests tend to support this concern. We recommend that a binocular display be seriously considered and further field tests be conducted to evaluate the effects of display configuration on a variety of soldier tasks.
  2. Our analysis suggests that a variety of depth cues are degraded by limited display resolution and field of view. This in turn should impact task performance within the three different depth zones of action. We recommend that field studies be conducted to determine how resolution and field of view affect performance in the three zones. In addition, training in making head movements and scanning patterns, which may partially alleviate these problems, should be investigated.
  3. Thermal imagery presents a special challenge to the soldier's visual system because many of the usual cues to depth and shape available in visible light are absent in thermal images. Once again, training may be particularly important in the successful use of the thermal images.
  4. The effects of long-term use of monocular displays are unknown. This issue should be investigated before a monocular configuration is adopted.
  5. The use of the helmet-mounted display for maps and other symbology may be problematic. Symbology tends to produce clutter and may interfere with the perception of the sensor imagery. Maps and certain other kinds of symbology might be better displayed on a hand-held or wrist-mounted device.
  6. The use of off-axis sensors, such as the image intensifier mounted on the helmet, may produce a variety of illusions, disorientation, and aftereffects. This placement should be avoided if at all possible.
  7. Placement of additional weight on the helmet raises concern over fatigue, increased physical workload, and related increases in cognitive workload. The helmet-mounted display should be evaluated under the demanding physical conditions in which these interactions are likely to occur.
Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

TECHNICAL NOTE: VISUAL ACUITY AND RESOLUTION

The preferred way to describe the minimum size target that can be seen is in terms of the visual angle it subtends at the viewer's eye in units such as arc minutes (Ogle, 1953). Many other units are also in use (see Figure 4-2). One measure is visual acuity, which is usually defined as the reciprocal of the target size in arc minutes (of subtended visual angle). One implication of the visual acuity unit is that normal vision corresponds to 1 arc minute (equivalent to Snellen acuity of 20/20).

In clinical practice it is common to use the Snellen fraction. The numerator of this fraction is usually taken as 20 and the denominator (usually in multiples of 10) is the range at which a young viewer with no visual abnormalities or dysfunction could discriminate alphanumeric characters that the testee can see at 20 feet (e.g., if your vision is 20/200, that means you need to be at a viewing distance of 20 feet to see letters a "normal" viewer could see at 200 feet, and you would be unable to read this text). While the measure has many limitations and acuity does not equal resolution, it is a commonly used reference.

Line resolution requirements (RCA, 1968): in television terminology, a line refers either to an actual scan line or to the time period allocated for a scan line. By this last definition, commercial broadcast TV in the United States is a 525-line system. Less than 525 actual scans are possible, however, because approximately 35 of the periods are used for the vertical retrace. Thus the number of actual or active TV lines is 490. Applying a Kell factor of 0.7 to this figure gives the equivalent of 343 active lines for use in considering resolution capabilities. (Because the phase relationships between a scanning spot and the objects in a natural scene cannot be controlled, some loss of resolution results. A commonly

FIGURE 4-2 Visual acuity units. Source: Farrell and Booth, 1984. Reprinted by permission.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

TABLE 4-4 Line Resolution Requirements

Task

Line Resolution Per Target Minimum Dimension

Detection

1.0 ± 0.25 line pairs

Orientation

1.4 ± 0.35 line pairs

Recognition

4.0 ± 0.8 line pairs

Identification

6.4 ± 1.5 line pairs

used figure is 30 percent. Thus the number of lines for effectively calculating resolution is 70 percent of the total. This value is known as the Kell factor.)

Furthermore, since an active TV line can represent, at most, one-half of a cycle of a periodic target (a light or a dark bar), 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. It is important to keep this ratio of 2 active TV lines per cycle of spatial frequency in mind when dealing with line-scan systems (note that scan lines typically describe vertical resolution; horizontal resolution measures refer to pixels). This may be mitigated to some extent with helmet-mounted displays in which head movements can cause the sensor to move (i.e., scan line or pixel boundaries can be shifted) but data to demonstrate are not available, and for fixed displays (e.g., maps) the line pair/pixel pair requirement remains.

Angular threshold of the eye (RCA, 1968): the probability of seeing an object is influenced not only by the field luminance, the contrast of the object with respect to the scene background and the complexity of the scene, but also by the angular subtense of that object at the eye of the observer. Whereas under ideal conditions the eye can resolve down to 30 seconds of arc, the common figure used is 1 minute of arc. In most practical situations, however, the angular threshold of the eye is higher. With a high resolution complex image, for which line resolution does not enter as a limiting and confounding factor, it appears that 6 to 12 minutes of arc are required for typical visual acquisition and recognition tasks. Table 4-4 summarizes conclusions from one set of measurements of the capability of humans to perceive single military targets (standing man to tank size) as a function of the limiting resolution per target minimum dimension (Johnson, 1960).

Resolution example: an SVGA computer screen rated at 1,280 pixels x 1,024 lines, at a viewing distance that would result in a horizontal screen subtense of 10° horizontal by 7.5° vertical (with a 3/4 aspect ratio) could be defined as having resolution as follows:

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×

horizontal:

1,280/10 = 128 pixels/degree of visual angle

 

or

 

128/60 = 2.13 pixels/arc minute of visual angle

 

or

 

1.07 pixel pairs/arc minute, which is approximately equivalent to 20/20 Snellen acuity.

In the case of the Land Warrior System, a 40° horizontal by 30° ° vertical field of view is subtended by a (nominal) 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. A Snellen equivalent measure for acuity would be 20/214.

Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
×
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×
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×
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×
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×
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×
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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Suggested Citation:"4 VISUAL AND PSYCHOMOTOR FACTORS IN DISPLAY DESIGN." National Research Council. 1997. Tactical Display for Soldiers: Human Factors Considerations. Washington, DC: The National Academies Press. doi: 10.17226/5436.
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This book examines the human factors issues associated with the development, testing, and implementation of helmet-mounted display technology in the 21st Century Land Warrior System.

Because the framework of analysis is soldier performance with the system in the full range of environments and missions, the book discusses both the military context and the characteristics of the infantry soldiers who will use the system. The major issues covered include the positive and negative effects of such a display on the local and global situation awareness of the individual soldier, an analysis of the visual and psychomotor factors associated with each design feature, design considerations for auditory displays, and physical sources of stress and the implications of the display for affecting the soldier's workload. The book proposes an innovative approach to research and testing based on a three-stage strategy that begins in the laboratory, moves to controlled field studies, and culminates in operational testing.

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