Human Factors in the Design of Tactical Display Systems for the Individual Soldier (1995)

The U.S. Army has launched a major research and development effort to equip infantry soldiers for the high technology battlefield of the future. The Mission Needs Statement for 21st Century Land Warrior (21 CLW) System (Department of the Army, September, 1993) calls for improvement in lethality, command and control, survivability, mobility, and sustainability in support of individual, dismounted infantry soldiers. More specifically, the Land Warrior System is tasked to provide vision enhancement (under both day and night conditions), secure voice communication, greater protection, reduced load, and adequate support for individual maintenance in the tactical environment. The operational concept is stated as follows (Operational Requirement Document, Department of the Army, 1994):

The [system] will be used by dismounted combat soldiers. The system will significantly enhance the soldier's ability to engage and defeat enemy targets while minimizing friendly casualties. The command, control, communications, computer and intelligence (C4I) subsystem will facilitate dynamic transmission of battlefield information, and enable soldiers to access the digitized battle field.

Guided by these requirements, military planners have conceptualized an ensemble of equipment that includes new protective garments, armaments, and information processing elements. The visual display component of the information processing subsystem is envisaged as an opaque, monocular presentation device mounted on a soldier's helmet. The land warrior helmet-mounted displays are to serve several functions: output and control of the thermal weapon sight; reception of navigation information, such as maps and current location from the global positioning satellite system; and various command and control functions, such as messages regarding danger and troop movements.

Interest and plans for providing individual, dismounted soldiers with new tactical information systems has been partly motivated by combat experiences in recent conflicts. Specifically, accomplishment of an assigned mission and soldiers' survival appear to be correlated with the amount and quality of information provided to each soldier (see Franks, 1994).

Plans have also been affected by advances in technology. Such advances include both hardware and software innovations in information processing systems. Likewise, sensor technology has been changing. These changes are most apparent in the area of night operations. Individual soldiers already have access to ambient light intensification and infrared detection equipment that has been used in combat, and those devices have shown sufficient promise to warrant continuation of their development.

At the same time, the whole domain of tactical intelligence has expanded. For example, satellites can now detect tactical targets and transmit the information almost instantaneously to command centers for relay to a combat unit. Other satellite arrays and packet switching¹ make it possible for soldiers to determine their location within a radius of a few meters from any site on the surface of the earth with direct downlinks from satellites. When one's own location can be determined and that information is used in conjunction with laser range finding, it can be as if an individual soldier has whole batteries of artillery under direct control. Thus, overall, there appear to be opportunities to use the advances in technology to provide information that will help soldiers perform their missions, avoid tactical mishaps, and improve survivability.

Whether these opportunities can be realized depends on the implications for human performance of design alternative tradeoffs: that is, the specific configuration of the physical equipment that will be used to convey this information--particularly the equipment that the individual, dismounted soldier will carry. Two related issues that may be equally important are the content of the information to be provided and the format of the messages. Concerns have been raised about the degree of control of the information flow that will be given to a soldier. The system development problem becomes increasingly serious when it is recognized that issues of format, content, and display design all interact. For example, a particular category of information may call for a format that is not compatible with an otherwise promising display device.

The charge to the panel is to examine the relationship among the tactical information needs of individual soldiers; the possible devices available now or in the near future for processing, transmitting, and displaying such information; and the human performance implications of the use of such devices. The study plan incorporates a two-phase approach. Phase I is an initial exploratory step in the panel's deliberations. In Phase II we will continue our examination of the issues raised in Phase I (see below) and cover: (1) the design of control systems; (2) the implications of 21 CLW concepts for information flow and

command control; (3) the use of helmet-mounted displays in a team context; (4) the need for additional data on such topics as infantry tasks, the effects of battle related stress on performance, and the interaction between physical and cognitive workload; (5) the tradeoffs associated with utilization concepts, training, and personnel selection based on individual differences; and (6) appropriate field-based methodologies for testing and evaluating the benefits and costs of head-mounted displays for the infantry soldier (including ergonomic considerations). The report on Phase II will include recommendations for specific empirical studies.

In this report on Phase I, we provide a preliminary review of design issues related to perception, cognition, situation awareness, and workload. In the perceptual area, the focus is on issues of sensory fidelity, depth cues, and field of view; in later stages of our work (Phase II) we plan to examine the implications of the design for head loading and disruption of the vestibulo-ocular reflex. Because the framework for our analysis is soldiers' performance with the system in the full range of environments and missions, we discuss both the military context and the characteristics of the infantry soldiers who will use the system. Although the current concept for 21 CLW is a monocular, opaque device that is mounted on a soldier 's helmet, our analysis also includes opaque and see-through devices that are either helmet mounted or hand held. The review of helmet-mounted technology covers monocular, biocular, and binocular displays.

The first chapter of this report provides contextual background: a brief review of the military environments in which the new systems and subsystems will be used. It emphasizes that the conditions under which military missions are (or are likely to be) conducted are increasingly varied with respect to both the physical environment and the task conditions, which include antiterrorist operations, catastrophe relief, and peacekeeping. Chapter 2 discusses the capabilities and limitations of infantry soldiers as users of the system and discusses how training, system design, or both might enhance the utility of the system.

Chapter 3 covers psychobiological factors in the use of tactical information displays. Each design feature is examined within the framework provided by human factors criteria. For some of these criteria (e.g., luminance and contrast requirements for reading, distance limits for accommodation and binocular disparity, color cuing, icon displacement), sufficient empirical data and well-grounded principles exist so that the tradeoffs of a given design alternative can be made reasonably explicit. For some other criteria (e.g., the extent to which the degraded resolution drastically diminishes depth cues and greatly reduced field of view restricts performance), particularly those that are tied to specific combat missions and conditions, new field research will be needed to provide a solid base of evidence for future engineering design decisions. Issues associated with workload measurement are discussed in an appendix.

The introduction of innovations always entails both immediate costs and risks of future ones. The equipment array contemplated for 21 CLW includes dozens of technological advances. The tactical information system concept and the helmet-mounted display that might represent this concept also represent major departures from past technology and past battle practices. In short, a helmet-mounted display is a potentially high-risk innovation.

The human factors approach to innovation serves to lower the risk. Such mitigation happens in two ways. First, the human factors approach raises a series of broad systems analytic questions: Can the soldiers who will be issued the equipment operate it correctly--in a virtually error-free manner? If not, can only certain soldiers do the job? To what extent can training expand the population of soldiers who can use the system effectively? Does use of the proposed ensemble cause any impairment in the baseline level of soldier functioning? For example, is the weight of the device debilitating so that use can go on for only a relatively short time? Does use of the device change the center of gravity for the user--leading to such negative side-effects as motion sickness or spinal injury? Does use of the system conflict with any mental processes, such as maintaining a sense of the immediate and likely future tactical situation? If a proposed configuration passes the tests implied by these questions, building advanced prototypes and fielding the system in an exercise mode should be undertaken. This approach is dependent on the helmet-mounted display prototypes having data hooks so that evaluators can precisely determine how individual soldiers are using the devices.

However, if not all the implied tests are passed, the second form of risk mitigation can be put in place: a low-cost assessment of alternative configurations. For example, if it appeared that an opaque, monocular display would give soldiers problems with visual interference effects, such as interocular conflicts, one alternative would be to provide an opaque binocular or biocular display that is deployed in the line of sight only infrequently and temporarily--particularly in daytime when normal vision would be key in an engagement situation. In other words, provide the soldier with a larger flip-up/flip-down display. The relative likelihood of this configuration working well or working better than the monocular option could be determined by human factors analysis, and its actual superiority or inferiority could be determined by narrowly targeted field experiments.

Another feature of the second approach is that it can be used to generate rich data about individual differences. It is reasonable to assume that some people will “get more” from a given system than others. The question is what psychobiological attributes allow some people to exploit the properties of a given system better than others. Often, the answer to that question is counterintuitive: it may not be the youngest, strongest, or brightest person who does best with a given device. Indeed, the relationship between personal attributes and a performance measure can be nonlinear. The average person can, in some cases, do better than those who are rated quite high on particular attributes or more poorly than those who

are rated quite low. In any case, well-designed empirical tests of system effectiveness can also reveal which individuals should be issued a specific pieces of gear.

Evaluation of the effectiveness of helmet-mounted displays involves questions of whether they will help soldiers move, detect, recognize, evaluate, and make correct decisions about objects on the battlefield. Different display technologies possess different attributes that affect a soldier's sensory, perceptual, and cognitive tasks. The tasks themselves vary across missions and environments. Tradeoff evaluations must take into account the interactions between soldier task demands and the attributes of different devices because these interactions affect the perception, attention, situation awareness, and workload of the soldiers using the devices. A device that assists a soldier under one task in one environment may detract from the soldier's performance on a different task or in a different environment. To yield valid predictions about the effectiveness of helmet-mounted displays, the devices must be tested under realistic field conditions as well as in the laboratory.

The panel's work in Phase I identified several specific issues that deserve special consideration. These issues are summarized here.

• The Land Warrior System and its head-mounted display system must be systematically tested in a range of realistic battle conditions, not only to aid th development and refinement of employment doctrine, but also to validate technical capabilities, system performance, and development priorities.

• To achieve the expected enhancements in performance, the Land Warrior System and its head-mounted display must be compatible with the mental, psychological, and physical characteristics of the infantry soldier. Complex displays will not achieve the Army's goals if they provide overwhelming levels of information that may be unneeded or may exceed the ability of a soldier to process. Furthermore, physical ergonomics will play a critical role in the system's success.

• Little in known about the relationship between design attributes, human attributes, and successful performance for the Land Warrior System. Effective personnel selection for the system relies on understanding these relationships.

• Embedded training solutions may be an appealing option when training time is limited. However, to employ embedded training, hardware and software needs have to be specified early in the system design. Of particular importance are computer memory, processing speed, input and output devices, display characteristics, and system architecture.

• Opaque monocular displays can lead to visual rivalry. By occluding one eye, visual rivalry can remove targets from either eye through monocular suppression, thus causing such problems as temporary blindness in the unrestricted eye, temporary total blindness, and vomiting. These problems may be reduced by using the system in an intermittent fashion or by designing a fully synthetic environment.

• Opaque monocular displays and see-through displays can lead to loss of stereoscopic depth perception. Such loses are likely to impose important costs on infantry soldiers, such as reducing the ability to see through camouflage (to distinguish the camouflage surface from its surround). Devices that eliminate stereopsis and that degrade other depth cues collapse everything into one depth plane and make it difficult to use attention effectively.

• Current technology offers less than optimum sensor and display resolution, field of view, contrast, and chromaticity. These factors, coupled with absent or anomalous stereo depth information, tend to keep the human accommodation and vergence systems running open-loop. The result can be eyestrain, fatigue, and, possibly, disorientation.

• Since pictorial and motion-based depth cues can be generated by computers, a helmet-mounted display might be used to restore or enhance lost depth information. Tradeoffs associated with enhancing or degrading depth cues can probably be estimated by assembling a series of matrices, based on the following: the distances for particular tasks, the distance ranges over which each class of depth cues are effective, the depth cues offered in each environment, and the effects of different display properties on different depth cues.

• Restriction of field of view interferes with the normal means by which humans deploy attention across the visual field. Although a viewer can compensate to some extent for a small field of view by making more head movements to obtain a series of small glimpses of the environment, there is currently no single accepted cognitive theory from which one can set the bounds of one glimpse. How are successive views of the display directly placed by the visual system into a single perceptual setting? How much structural overlap is required? Over how much delay? Over how many shifts in view?

• Since information can be provided by means of several modalities, it is important to determine the most appropriate modality for a given message in a given situation and evaluating the value added by using multiple modalities to provide redundant information (e.g., an auditory signal to direct the gaze of a soldier or to indicate the onset of an incoming text message).

• The weight of helmet-mounted display optics must be placed largely in front of the eyes, adding poor center of gravity to the weight problem. Better optics tend to be more complex and heavier than less capable optics.

• When a soldier is wearing a helmet-mounted display, the potential for attentional narrowing (paying exclusive attention to one source of information at the expense of other channels of information) is a significant concern: users may dwell on compelling and complex graphics and text displays at the expense of attending to otherwise available environmental cues. In a situation in which information overload occurs, users may be unable to efficiently use any of the available information or may be significantly delayed in locating the necessary information. Yet helmet-mounted displays can aid situation awareness by improving a wearer's ability to localize targets and self, to navigate in the environment, to keep up to date on situational factors, and to share information among team members. Furthermore, a helmet-mounted display can aid situation awareness by presenting information in a format that is compatible with a soldier's needs.

• Design of the helmet-mounted display may be able to remedy the main factors that limit situational awareness: for example, there may sensory enhancements that can improve a wearer's ability to localize self and targets and navigate in the environment, improve information sharing among team member, keep soldiers and commanders up to date, and allow soldiers to look at information in different ways to support decision making.

• Physical factors in the battlefield--such as heat, cold, vibration, and noise--all have some implication for the design of helmet-mounted displays and the information they provide to soldiers. Research is needed to explore the relationship between battlefield stress and performance. One important area is the potential effects of vibration (caused by walking) on the effective use of a helmet-mounted display. Another is examining the positive and negative influences of noise (i.e., noise can be distracting to the soldier but at the same time it may act as a deterrent to the enemy).

Many sensory-perceptual issues raised in this report are not new to the those working on development of the 21 CLW systems. Reactions on the part of soldiers in the Soldier Integrated Protection Ensemble (SIPE) Demonstration trials held at Ft. Benning in September, 1992, included motion sickness and disorientation. Reactions also included praise by the soldiers for the functions of improved interunit communications and the thermal sight and the navigational information provided by the Global Position System (GPS).

The SIPE demonstration did not include formal field or laboratory experiments, and the need for such experiments using rigorous research procedures is of critical concern to staff at the Army Research Laboratory and the Natick Research Development and Engineering Center. The second phase of the present project should help establish the priority level of design option testing and the methodological framework that will enable effective field research.

From a research perspective, much of what is known about visual performance comes from laboratory investigations using standard, highly simplified visual tasks. Unfortunately, a soldier's visual tasks are nonstandard and complicated. This means that system-specific research in both the laboratory and the field will be needed to provide the knowledge base

for solid engineering design decisions. When possible, such studies should incorporate some of the stresses of battlefield conditions in order to evaluate the potential for loss of situation awareness on the part of the soldier. Research plans should include procedures for detecting design features that might actually support situation awareness by directing the soldiers' attention to salient aspects of a scene or circumstance that otherwise might be missed. Implications for doctrine, personnel selection, training, and employment concept are significant. The Land Warrior System requires the full attention of the Army's MANPRINT community.