Automotive head-up display

Research into the ERB primarily utilizes virtual reality driving simulators to mimic real life driving scenarios while eliminating situational variability. In order to examine HUDs and HDDs, studies often compare hazard reaction time, situational awareness, and quality of driving (such as speed consistency) using both systems. The extent of the ERB on different demographics, particularly those of age and experience level, are of particular interest. The interaction between work-load and the influence of ERB are also frequently examined for research.

Saccadic gaze is the perceptual mechanism through which the eye is inadvertently drawn to external stimulus without the individual's conscious action.[10] An involuntary gaze is most easily drawn by movement or distinct changes in illumination in an individual's visual field.[11] These external stimuli can be beneficial in such situations as the movement of a pedestrian about to walk out onto the road, in turn allowing the driver to take evasive action. Exogenous cues can also be irrelevant, and often dangerous, leading to distraction from goal behaviours, such as the flashing of a cellphone taking one's eyes off the road. By superimposing vital driving information onto the horizon in a driver's direct line of sight, HUDS allow important exogenous cues, like the movements of other vehicles to draw the gaze of a driver whilst they monitor vital vehicle feedback such as speed or revolution count.[12] It is theorized that this can facilitate faster reaction times to hazards and improve situational awareness. A collaborative project between Faurecia Groupe and Indian Institute of Science developed an eye gaze and finger controlled head up display[13] for cars that can also automatically estimate drivers’ cognitive load and distraction.[14]

The ideal visual field is the area in which stimuli are most accurately, rapidly, and efficiently processed by the eye. In humans, this field is thought to be within 20 degrees above or below the vertical meridian of an individual's gaze and 60 degrees either side of the horizontal meridian.[15] If an object is beyond these boundaries it will require eye movement to bring the stimuli out of periphery. By including feedback instruments in the primary field of vision, HUDs allow for the horizon and all associated stimuli to stay in the primary field vision where the information may still be processed and acknowledged by a motorist.[16]

Reaction time, and more specifically delayed reaction, is widely cited as a key contributor to vehicular accidents.[17] Reaction time in relation to the ERB is defined as the time it takes for a motorist to react to an external hazard or stimuli and then carry out the appropriate reaction, or evasive maneuver such as braking when a vehicle in front stops. The feedback offered by a HUD is projected onto the windshield of a vehicle with the aim of integrating outside stimuli and the instrumental feedback; thus removing the need to remove a driver's eyes from the road. Studies of reaction time to hazards in HUD vs HDD designs have found that the average reaction times for HUD are faster.[9] This trend appears to continue across demographics, including both categories of experience level and age.[18][19]

Speed maintenance is the extent to which a driver maintains a speed and adjusts their speed to suit traffic laws and environmental conditions. The use of HUDs appears to produce better speed maintenance in drivers under experimental conditions when compared to HDDs.[6] It is theorized that this is because having the speedometer at the eye level of the vehicle operator allows for continuous monitoring of the vehicle's speed. HUD use also appears to increase general driving quality, including staying within road markings, and increased smoothness of driving and navigation abilities.[7] Drivers’ capacity to focus on external cues, such as road texture, road demarcations and street signs is increased by using a seamless interface where focus on the road isn't interrupted to assess speed and other information.

The influence of ERB on drivers is not universal. There is evidence that as the complexity of driving tasks increases, the benefits of using a HUD are decreased, and in some circumstances, they are no longer statistically significant. The ERB is diminished, for example, when individuals are driving cognitively demanding vehicles, such as industrial vehicles, or when they are asked to multitask while driving.[6] One study has shown that when placed in a cognitively demanding condition, individuals shift their focus from the road alone to focus on other tasks such as shifting gears or talking to others. Subsequently, a driver's ability to process HUD feedback requires diversion of attention, much akin to that which occurs whilst using a HDD.[6]

There are limitations for where a HUD can be placed or projected in a vehicle before it begins to diminish the ERB and becomes more of a distraction. HUDs can be constructed so that the instrumental feedback appears to be projected out into the horizon, rather than displayed directly on the windshield.[20] In test situations, a projected HUD which appears near the nose of the vehicle is said to result in the most rapid response times and best situational awareness on the part of the driver, as well as facilitating better driving quality.[20] For in-glass laminated HUD, the display glass part is integrated in the windshield while the electronics shall be placed and hidden inside the vehicle body. The information is displayed directly on the windshield.