Helmet-mounted Display Symbology Research Articles

Attentional Tunneling in Pilots During a Visual Tracking Task With a Head Mounted Display.

We examined whether active head aiming with a Helmet Mounted Display (HMD) can draw the pilot's attention away from a primary flight task. Furthermore, we examined whether visual clutter increases this effect. Head up display symbology can result in attentional tunneling, and clutter makes it difficult to identify objects. Eighteen military pilots had to simultaneously perform an attitude control task while flying in clouds and a head aiming task in a fixed-base flight simulator. The former consisted of manual compensation for roll disturbances of the aircraft, while the latter consisted of keeping a moving visual target inside a small or large head-referenced circle. A "no head aiming" condition served as a baseline. Furthermore, all conditions were performed with or without visual clutter. Head aiming led to deterioration of the attitude control task performance and an increase of the amount of roll-reversal errors (RREs). This was even the case when head aiming required minimal effort. Head aiming accuracy was significantly lower when the roll disturbances in the attitude control task were large compared to when they were small. Visual clutter had no effect on both tasks. We suggest that active head aiming of HMD symbology can cause attentional tunneling, as expressed by an increased number of RREs and less accuracy on a simultaneously performed attitude control task. This study improves our understanding in the perceptual and cognitive effects of (military) HMDs, and has implications for operational use and possibly (re)design of HMDs.

Hypoxia impairs reaction time but not response accuracy in a visual choice reaction task

We investigated the effect of hypoxia on the reaction time (RT) and response accuracy of pilots performing a visual choice reaction task that corresponded to the scanning of helmet mounted display (HMD) symbology. Eighteen male military pilots performed the task in a hypobaric chamber at two simulated altitudes (92 m and 4572 m) in a single-blinded repeated measures and counter-balanced design. The visual stimuli were displayed in low and high contrast and at a 30- and 50-degree field of view (FoV). We measured the pilots' RT and response accuracy. Using an eye tracker, we measured the pilot's glance time at each stimulus location. Finally, we collected subjective ratings of alertness. The results show that hypoxia increased the RT and glance time. Lowering the stimulus contrast and increasing the FoV further increased the RT, independent of hypoxia. These findings provide no evidence for hypoxia-induced changes in visual contrast sensitivity or visual field. Instead, hypoxia seemed to affect RT and glance time by reducing alertness. Despite the increased RT, the pilots maintained their accuracy on the visual task, suggesting that visual scanning of HMD symbology may be resistant to the effects of acute hypoxia.

Modeling perceptual color confusion of helmet-mounted display symbology as a function of see-through contrast

In military aviation helmet-mounted displays (HMDs) or head-up displays, light from the ambient scene is added to the symbology to create a complex mixture of colors, textures, and luminances. In the case of color mixing, the color of the transparent symbology symbols shifts toward the colors of the ambient background that the symbology overlays. The magnitude of the shift depends on the contrast of the symbology against the background. Against a darkened background, there is negligible shifting of symbology color. However, during daylight conditions, symbology colors shift toward the background hue. Using CIELAB distances between symbology colors as a measure of color discrimination, confusion contrast thresholds are calculated for each of seven symbology colors mixed with fourteen different background colors over a wide range of luminance contrasts. Confusion contrast thresholds are calculated for color normal and color vision deficient (CVD) observers. For CVD observers, colors are filtered using the RGB coefficients developed by Machado. Using the color discrimination data presented here as well as previous assessments of HMD luminance requirements based on observer ratings of the quality of symbology, luminance guidelines for see-through displays are presented, which correct for a calculation error made previously.

Development of the Non-Distributed Flight Reference Off-Boresight Helmet-Mounted Display Symbology

The U.S. Air Force Research Laboratory (AFRL) is developing helmet-mounted display (HMD) symbology to support its acquisition development programs that in turn transition the latest advances in crew systems to the operational user. This HMD symbology is being designed to provide aircrew with the ability to maintain spatial orientation and awareness of aircraft state while performing off-boresight tasks across day, night, and all-weather conditions. Requirements dictate that the HMD symbology must perform at least as well as the existing head-up display symbology for off-boresight piloting tasks, as well as target acquisition and designation across air-to-air and air-to-ground missions. This paper summarizes the research conducted by AFRL investigating the non-distributed flight reference (NDFR) HMD symbology. The research describes the necessity of having off-boresight symbology on the HMD, how the NDFR symbology has been evaluated and designed to date, and most importantly, the benefit to the pilot when using off-boresight symbology compared to using the HUD alone.

The OKCR and Pilot Performance during Transitions between Meteorological Conditions Using HMD Attitude Symbology

Research has shown that spatial disorientation often occurs when pilots transition between real-world visual cues and head-down attitude instruments. Recent studies investigating the opto-kinetic cervical reflex (OKCR) indicate that when pilots transition between these two types of visual cues, they are also transitioning between frames of reference. Limited research has been conducted investigating pilots' response during transitions between real-world visual cues and helmet-mounted display (HMD) attitude symbology. Eleven pilots performed vertical “S” maneuvers in and out of clouds to simulate frequent transitions between visual meteorological conditions and instrument meteorological conditions using both primary flight symbology on an HMD and traditional head-down primary flight instruments. Because pilots focused primarily on the symbology during the task, the OKCR was not found. Results also revealed that pilots were better able to maintain commanded vertical velocity when using the HMD compared to the head-down instruments, which is attributed to the head-up location of the symbology. Having the HMD symbology superimposed on the real-world visual scene can provide additional visual cues that pilots can use to perform their task more efficiently.

Helmet-Mounted Display Symbology for Terrain Avoidance During Low-Level Maneuvers

A simulation study was performed to evaluate helmet-mounted display symbology for fighter aircraft ground collision avoidance systems. Four visual alert symbologies were tested: an iconic cue, an aircraft-fixed (AF) guidance cue, a head-fixed (HF) guidance cue, and an HF guidance cue with a pitch ladder. Participants were given audio and visual side tasks and responded to alerts in different aircraft attitudes. Shorter reaction times were observed when a HF visual alert was given in addition to the standard audio alert. No significant differences in recovery performance (measured by response time and altitude loss) were observed between display formats. However, the display format had a significant effect on participant head motion. With HF guidance cues, pilots were able to perform the recovery maneuver with their heads off axis; with AF guidance cues or no guidance cues, pilots consistently turned their heads to face forward before maneuvering the aircraft.

Practical Considerations for Fixed Wing Helmet-Mounted Display Symbology Design

Helmet-mounted displays (HMDs) may become a primary source of head-up information in future tactical aircraft. In evaluations, HMDs have produced improved situation awareness and mission performance. To realize this improved performance, HMD equipped pilots spend significantly more time looking off-axis, away from traditional displays. Accordingly, it is important that HMD information be designed so targeting and ownship status symbology is effective and safe. The U. S. Air Force Research Laboratory is working to develop an optimized HMD symbology set. Toward this end, symbol designs must accommodate the conditions of intended use, technology limitations, and integration with other displays. This paper discusses efforts to design target tracking/location and ownship status symbologies for the day/night all weather fixed-wing tactical aircraft application. Design principles derived from both laboratory and flight test are presented. These principles relate to symbology frame of reference, orientation, compression, and line of sight mechanization. Evaluation methodologies are also discussed.

Toward an Empirically Based Helmet-Mounted Display Symbology Set

The helmet-mounted display (HMD) affords continuous availability of critical flight information independent of head orientation. With appropriate information presented on a HMD, aircraft control can be maintained regardless of where the pilot is looking. This research addresses the development of an empirically based HMD symbol set. Three attitude formats and three altitude formats were evaluated within a composite fixed-wing HMD symbology layout. The attitude formats varied in basic form and symbol compression ratio. Symbol compression ratio is the ratio of the angle represented by the symbol to the symbol's subtended visual angle. High symbol compression results in symbols which represent large angles, and therefore have slow rate-of-motion relative to their uncompressed counterparts. The altitude symbologies were formed of both vertical scale and dial formats and included vertical velocity indicators. Subjects performed a flight-path maintenance task within sessions of differing “real” horizon presence and orientation. The formats were evaluated under a task which was designed to require high-accuracy flight-path maintenance. This type of task is traditionally thought to require less symbol compression. The results showed that performance was influenced by the manipulation of the attitude symbology formats. The results also suggest that symbol compression may be advantageous.