The proposed helmet-mounted display of the Land Warrior System is one part of a major research and development effort by the U.S. Army to equip infantry soldiers for the high-technology battlefield of the future. The Mission Needs Statement for the 21^st Century Land Warrior System (U.S. Department of the Army, 1993) calls for improvements in lethality, command and control, survivability, mobility, and sustainability in support of individual, dismounted infantry soldiers. The Land Warrior System is planned to provide vision enhancement (under both daytime and nighttime 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 (U.S. Department of the Army, 1994):

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 envisioned as a flip-down monocular presentation device mounted to one side of the soldier's helmet. The display proposed for daytime operations is an opaque display that can be used to provide the soldier

with navigation information, such as maps and current location from the global positioning system; various command and control functions, such as messages regarding danger and troop movements; and images of the real world acquired through the thermal weapon sight. The display proposed for nighttime operations is integrated with a monocular night vision system or thermal weapon sight when switched on, it appears in the middle of the night vision field of view. This display is used, as is the one designed for daytime, to provide digital data and weapon sighting information. These are two distinct pieces of equipment that are selected for use based on conditions.

The Army's interest in providing individual, dismounted infantry soldiers with new tactical information systems has been partly motivated by combat experiences in recent conflicts. Specifically, the individual soldier's accomplishment of an assigned mission and his survival appear to be correlated with the amount and quality of information he is provided (Franks, 1994). The plans have also been influenced by advances in technology. Such advances include both hardware and software innovations in information-processing systems. Similarly, sensor technology has been changing. These changes are most apparent in the area of nighttime 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 entire 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 whether the information can be presented to the soldier in ways that do not hamper human performance. Of paramount interest 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. Three related issues that may be equally important are the content of the information to be provided, the format of the messages, and the visual quality of the scene depicted on the screen. Concerns have been raised about the degree of control over the information flow that will be given to the soldier. The problem for system development becomes increasingly serious when it is recognized that issues of format, content, and display design all interact. For example, a particular type of information may call for a format that is not compatible with an otherwise promising display device.

Since the land warrior will view the world through the display at night, the quality of the image is critical to his performance.

The panel's work focuses on the compatibility between the characteristics of the proposed equipment and the capabilities and limitations of the target population. Our analysis has been guided by the context in which the helmet-mounted display would be used and the tasks that would be performed by infantry soldiers and squad leaders equipped with the display. Military environments are increasingly varied with respect to both their physical aspects and their task conditions.

In addition to warfare, military missions include antiterrorist operations, catastrophe relief, and peacekeeping, among other operations. Equally important are the capabilities and limitations of infantry soldiers as users of the helmet-mounted display. Both system design and training must support their effective use of the system.

One important set of questions raised in this analysis concerns the increased capabilities of the new helmet-mounted display and their effect on individual soldier's ability to think and act independently. Is the Army's intention to empower the soldier to make decisions that are now being made at higher levels? Although such matters of doctrine are beyond the panel's charge, we raise this issue for consideration because it is central to decisions about the ultimate disposition and use of the equipment.

The panel has assessed the scientific evidence regarding the major technical issues, design considerations, and testing approaches associated with the proposed helmet-mounted display. Most critical are the visual and psychomotor factors associated with each design feature. In addition, the stress of the battlefield, including physical sources such as heat, noise, and vibration, as well as cognitive sources such as information overload, complexity, and distraction, affect the soldier's ability to perform with speed and accuracy. And his awareness of his situation, both global and local, is affected in important ways by the wearing of a display capable of providing many types of information in many possible formats. These effects interact in ways that are not yet well understood for the circumstances of an individual dismounted soldier.

The panel proposes an innovative approach to research and testing by the

Army that incorporates critical human factors considerations for the Land Warrior System's helmet-mounted display. This approach is based on a three-stage research and testing strategy that begins in the laboratory, moves to controlled field studies, and culminates in operational testing. It brings the user into the testing and evaluation process earlier, through controlled testing that combines the environmental variations of operational testing with the controlled conditions of laboratory testing.

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 performance. The tasks themselves vary across missions and environments. Trade-off 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 with one task in one environment may impair his 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 in the laboratory, in controlled field studies, and in realistic field conditions.

After reviewing the available Land Warrior specifications and the existing human factors research findings that apply to those specifications, the panel developed a set of conclusions and recommendations for research and design. They are summarized below and provided in more detail in the final chapter of this book. For some areas, such as the visual properties of the system, there are sufficient data to make concrete suggestions. For other areas, such as the implications of the system for altering workload or situation awareness and the effects of these alterations on performance, additional data are needed before recommendations can be made.

The panel's overarching conclusion is that the proposed monocular system as compared to a binocular system will degrade user performance in the field, and it may also have unacceptable implications for training and selection. As a result, the panel recommends that the Army should proceed in an experimental mode, comparing the positive and negative performance implications of the monocular helmet-mounted display with alternative technologies.² Moreover, even if the visual issues are resolved, shifting the infantry soldier's attention away from the

battlefield toward a computer-generated display may compromise situation awareness and increase workload. The panel recommends that, if the display of digital data partially occludes the soldier's view of the environment, then hand-held or wrist-mounted displays should be considered as an alternative to the helmet-mounted display for digital data in order to reduce the likelihood of negatively affecting the soldier's local situation awareness.

The proposed Land Warrior System can be a valuable research tool, if the Army takes an experimental approach to its development. If put into the hands of users in a experimental mode, the Army can establish baseline data and threshold values for future developmental efforts. The panel identified eight general areas for which research is needed:

• Understanding the relationship between design attributes, human attributes, and successful performance for the Land Warrior system is needed for effective personnel selection and training.
• Threshold values are needed for screen clutter, gray scale, limits of spatial and temporal resolution, the impact of visual acuity differences in soldiers, short-term memory limits in processing the information, individual susceptibility to various levels of incapacitation associated with visual rivalry, depth cues, field of view (versus resolution) values, delivery modality preferences and trade-offs, and the impact of attentional narrowing.
• There are several questions associated with the small field of view provided by the proposed helmet-mounted display that require additional study: How are successive glimpses of the display organized by the visual system into a single perceptual image? How much structural overlap is required? Over how much delay? Over how many shifts in view? How is this information combined with outside information? What is the overall impact of the system on soldier situation awareness, when used in combination with other equipment and information in the battlefield environment?
• The question of rifle stabilization when the rifle is extended, aimed, and fired from a protected position has not been adequately addressed. In the current weapon system, the sighting device may be considered accurate, but the aiming variance associated with holding the unsupported weapon stable is large, particu-

• larly under conditions of sustained performance. Tests of the accuracy of the aiming of the rifle should be included in the field research program.
• Additional data are needed on the relationship between physical sources of stress on the electronic battlefield (e.g., temperature, vibration, noise) and performance. One important area concerns the potential effects of vibration and small shifts in helmet alignment (caused by walking or more violent motion) on the effective use of the helmet-mounted display. Another area is the combined effects of different levels of physical and mental workload on soldier performance over extended periods of time.
• Comparisons of the Land Warrior monocular system should be made with the existing biocular night vision goggles worn by infantry soldiers and the binocular night vision goggles worn by aviators to determine if significant differences in task performance exist.
• In a given battle situation, the pace of engagement would allow only seconds for reading a display. Determination should be made of what data are critical to show visually to the infantry soldier during combat versus presenting them to the ear.
• Testing and evaluation should be undertaken to ensure that the weight and distribution of the helmet and the display do not interfere with the ability of the soldier to move freely and aim his weapon accurately.

The panel recommends a series of design guidelines for maximizing the soldier's situation awareness and facilitating his ability to process information efficiently. The most important of these include:

Much of the technology being considered for the Land Warrior program and the helmet-mounted display subsystem in particular-is in the early stages of development and the effects of this technology on human perceptual and cognitive performance are, as yet, not well understood. The primary criteria must be based on the soldier's ability to survive and perform. Equipment choices that impede mobility or local situation awareness or both are poor choices regardless of cost.