In this chapter we present the conclusions and recommendations given the highest priority by the panel. Each chapter also contains a set of conclusions and design guidelines.

The panel's overarching conclusion, after reviewing the available Land Warrior specifications and the existing human factors research findings that apply to those specifications, is that the proposed monochrome, low-resolution monocular as compared to a binocular display will, in most situations, degrade performance in the field and may have unacceptable implications for training and selection.

The challenges associated with the helmet-mounted display for the dismounted infantry soldier are considerable, and the body of human factors knowledge about the relative merits of the numerous design options is, at present, limited. Although a substantial amount of work on such displays in the aviation environment has been done, the direct transfer of results to the infantry environment is not possible due to differences in task conditions and performance requirements. A major difference is that pilots are relatively stable (not moving) on

a moving platform, whereas the infantry soldier is moving on a fixed platform (the ground). With regard to specific elements of the helmet-mounted display technology proposed by the Army, the panel makes the following conclusions.

After careful review of the available data on the human visual system, the panel concludes that a monochrome, low-resolution, monocular display will, in most situations, degrade human performance compared with a binocular system. The chosen technical approach offers less than optimal sensor resolution, less than optimal spatial and temporal display resolution, and less than ideal field of view, contrast, and chromaticity. These factors, coupled with absent or anomalous stereoscopic visual depth information, tend to keep the human accommodation and vergence systems running open-loop and drastically degrade or even eliminate visual depth information. The result can be eyestrain, fatigue, and possibly spatial disorientation, as well as loss of equilibrium and loss of form and layout perception. One important area of investigation is the potential long-term consequences of monocular viewing and rivalry.

The panel further concludes that, even if the visual perception issues associated with the proposed helmet-mounted display technology are resolved, shifting the infantry soldier's attention away from the battlefield toward a computer-generated display raises other critical issues. The helmet-mounted display may compromise local situation awareness (location, presence of enemies, terrain and object perception) by competing for mental resources and affecting perceptual processes. Also, the potential increase in cognitive workload associated with processing and applying the information may be in itself prohibitive.

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.¹

1. Research should be undertaken about the relationship among design attributes, human attributes, and successful performance for the Land Warrior System. Significant increases or changes in soldier skills and abilities may be required as a consequence of these technologies. Effective personnel selection and training for the system will depend on understanding these relationships.
2. 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.
3. 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 and can compensate for the loss of stereopsis by using small head movements to provide depth information through parallax, the significant optical persistence characteristics proposed for the helmet-mounted display make such corrections problematic. Furthermore, there is currently no accepted cognitive theory from which one can set the bounds of one glimpse. Important research questions include: 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? The overall impact of the system on soldier situation awareness, when used in combination with other equipment and information in the battlefield environment, must be addressed.
4. The provision for remaining in a protected position while extending, aiming, and firing the rifle is laudable. However, the question of rifle stabilization 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, particularly under conditions of sustained performance. The absence of image stabilization associated with a helmet-mounted display is also an issue for viewing and sighting. Even if one assumes the design of a new helmet, skull skin movement can range from 0.5 to 1.5 inches. Tests of the accuracy of the aiming of the rifle should be included in the field research program.
5. Physical factors in the battlefield-such as heat, cold, vibration, and noise-all have implications for the design of helmet-mounted displays and the information they provide to soldiers. Research is needed to explore the relationship between stress on the electronic battlefield and performance. One important area is the potential effects of vibration and small shifts in helmet alignment (caused by walking or more violent motion) on the effective use of a helmet-mounted display. Another is the combined effects of physical and mental workload on soldier performance over extended periods of time.

6. The low-resolution, monochrome, monocular display presents challenges associated with movement, target recognition and identification, hit accuracy, map reading speed, cognitive workload, and functionality. The benefits claimed for the Land Warrior System involve the use of the unaided eye at night as a baseline for comparison-not the unaided eye during the day or with night vision goggles. 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. Comparisons made by researchers at Aberdeen Proving Ground (CuQlock-Knopp et al., 1994) suggest that people navigate their environment better at night with binocular viewing (compared with monocular viewing).
7. In a given battle situation, the pace of engagement would allow only seconds for reading a display. Presenting messages to the ear may be a more effective way to communicate with the engaged soldier. What data are critical to show visually to the infantry soldier during combat must be investigated. The minimum and maximum threshold values of visually displayed data need to be determined. Research is needed on the perceptual narrowing threshold between audio and visual displays. The trade-offs among free field attenuation devices, active cancellation, normal communications traffic, signals, icons, and working memory capacity need research.
8. Helmet weight and the distribution of that weight have the potential to degrade the performance of the infantry soldier. Currently there is no evidence demonstrating the effects of the weight requirement specified for the proposed helmet-mounted display in the Land Warrior System. Likewise, no studies have been done to ensure that freedom of head movement is not impaired and that helmet stability is congruent with aiming a hand-held weapon. As part of the larger program of applied field research, testing and evaluation should be undertaken to ensure that the weight and distribution of the equipment does not interfere with the ability of the soldier to move freely and aim his weapon accurately.

We recommend that the following design guidelines be adopted to maximize the soldier's situation awareness and facilitate his ability to process information efficiently:

1. The helmet-mounted display should minimize the degree to which it is a physical barrier to acquiring information about the world (e.g., occludes or alters normal hearing and vision). It should enhance regular sensory input only when needed (e.g., targeting support, night vision).
2. The helmet-mounted display should minimize both attentional distraction and the cognitive load it places on the user by providing integrated information in

2. task-oriented sequence, by reducing extraneous information, and by minimizing memory requirements.
3. The helmet-mounted display should provide salient cueing-directing the soldier's attention to important information. The audio mode is generally preferable for simple cueing and the transmission of time-critical information.
4. Spatial, topographic, and positional information should be presented by graphics that have been well learned by soldiers (e.g., standardized map symbols) in order to facilitate rapid and accurate interpretation.
5. Whenever possible, the system should simplify the presentation of data entry and system control options. Simplification of these tasks will minimize workload in high-load situations, such as battlefield engagements.