Head-up displays and their automotive application: an overview of human factors issues affecting safety

Visual Complexity of Head-Up Display in Automobiles Modulates Attentional Tunneling

OBJECTIVE

To investigate how the visual complexity of head-up displays (HUDs) influence the allocation of driver's attention in two separate visual domains (near and far domains).

BACKGROUND

The types and amount of information displayed on automobile HUDs have increased. With limited human attention capacity, increased visual complexity in the near domain may lead to interference in the effective processing of information in the far domain.

METHOD

Near-domain and far-domain vision were separately tested using a dual-task paradigm. In a simulated road environment, 62 participants were to control the speed of the vehicle (SMT; near domain) and manually respond to probes (PDT; far domain) simultaneously. Five HUD complexity levels including a HUD-absent condition were presented block-wise.

RESULTS

Near domain performance was not modulated by the HUD complexity levels. However, the far domain detection accuracies were impaired as the HUD complexity level increased, with greater accuracy differences observed between central and peripheral probes.

CONCLUSION

Increased HUD visual complexity leads to a biased deployment of driver attention toward the central visual field. Therefore, the formulation of HUD designs must be preceded by an in-depth investigation of the dynamics of human cognition.

APPLICATION

To ensure driving safety, HUD designs should be rendered with minimal visual complexity by incorporating only essential information relevant to driving and removing driving-irrelevant or additional visual details.

Automotive Augmented Reality Head-Up Displays

As the next generation of in-vehicle intelligent platforms, the augmented reality heads-up display (AR-HUD) has a huge information interaction capacity, can provide drivers with auxiliary driving information, avoid the distractions caused by the lower head during the driving process, and greatly improve driving safety. However, AR-HUD systems still face great challenges in the realization of multi-plane full-color display, and they cannot truly achieve the integration of virtual information and real road conditions. To overcome these problems, many new devices and materials have been applied to AR-HUDs, and many novel systems have been developed. This study first reviews some key metrics of HUDs, investigates the structures of various picture generation units (PGUs), and finally focuses on the development status of AR-HUDs, analyzes the advantages and disadvantages of existing technologies, and points out the future research directions for AR-HUDs.

The effect of visual rivalry in peripheral head-mounted displays on mobility

Recent head-mounted displays and smart glasses use vision multiplexing, an optical approach where two or more views are superimposed on each other. In vision multiplexing, augmented information is presented over an observer's natural field of view, providing field expansion and critical information during mobility situations like walking and driving. Yet despite its utility, vision multiplexing may produce visual rivalry, a phenomenon where perception alternates between the augmented information and the background scene for seconds at a time. To investigate, we compared the effect of different peripheral vision multiplexing configurations (unilateral opaque, unilateral see-through and bilateral see-through) on the detection of augmented information, incorporating at the same time real-world characteristics (target eccentricity, depth condition, and gaze movement) for a more realistic assessment. Results showed a persistently lower target detection rate in unilateral configurations than the bilateral configuration, suggesting a larger effect of binocular rivalry on target visibility. Nevertheless, this effect does become attenuated when more naturalistic elements are incorporated, and we discuss recommendations for vision multiplexing design and possible avenues for further research.

Ergonomic Guidelines of Head-Up Display User Interface during Semi-Automated Driving

Self-driving vehicles are emerging as a result of technological advances, and the range of human behavior is expanding. The collateral information on driving is increasing, and head-up displays (HUDs) can be coupled with augmented reality displays to convey additional information to drivers in innovative ways. Interference between the actual driving environment and the displayed information can cause distractions. Research is required to find out what information should be displayed and how to properly display it considering the number of information, as well as the location and arrangement of the HUD. This study aims to examine the types of HUD information presentation that enhance the driver’s intuitive understanding. The first experiment identified which information affects drivers more in self-driving conditions in terms of error rate and importance. As a result, information that the drivers consider to be of greater importance or more relevant to their safety was selected. The level of HUD information complexity was assessed in the second experiment. The independent variables were the number of symbols, location of the HUD, and arrangement of the HUD. The results showed that the number of symbols was most affected and that fewer than six should be displayed. Besides, the arrangement of contents was more intuitive when a vertical alignment was used, and the main content should be placed in the center of the windshield area. Finally, ergonomic design guidelines of the information presentation type are proposed in this study.

Functional requirements of automotive head-up displays: A systematic review of literature from 1994 to present

Despite the long history of automotive head-up displays (HUDs), what information they should display in different situations to best serve the driver remains unanswered. The lack of understanding hinders designing useful automotive HUD systems. In an effort to address this, the current study investigated the developer, researcher and user perspectives on the functional requirements of automotive HUDs through literature review. The review results indicated that: 1) the existing commercial HUDs perform largely the same functions as the conventional in-vehicle displays, 2) past research studies proposed various HUD functions for improving driver situation awareness and driving safety, 3) autonomous driving and other new technologies are giving rise to new HUD information, and 4) little research is currently available on HUD users' perceived information needs. Based on the review results, this study provides insights into the functional requirements of automotive HUDs and also suggests some future research directions for automotive HUD design.

How to warn drivers in various safety-critical situations - Different strategies, different reactions

Technological advances allow supporting drivers in a multitude of occasions, ranging from comfort enhancement to collision avoidance, for example through driver warnings, which are especially crucial for traffic safety. This psychological driving simulator experiment investigated how to warn drivers visually in order to prevent accidents in various safety-critical situations. Collision frequencies, driving behavior and subjective evaluations of situation criticality, warning understandability and helpfulness of sixty drivers were measured in two trials of eight scenarios each (within-subjects factors). The warning type in the head-up display (HUD) varied (between-subjects) in its strategy (attention-/reaction-oriented) and specificity (generic/specific) over four warning groups and a control group without a warning. The results show that the scenarios differed in their situation criticality and drivers adapted their reactions accordingly, which underlines the importance of testing driver assistance systems in diverse scenarios. Besides some learning effects over the trials, all warned drivers showed faster and stronger brake reactions. Some warning concepts were understood better than others, but all were accepted. Generic warnings were effective, yet the warning strategy should adapt to situation requirements and/or driver behavior. A stop symbol as reaction generic warning is recommendable for diverse kinds of use cases, leading to fast and strong reactions. However, for rather moderate driver reactions an attention generic approach with a caution symbol might be more suitable. Further research should investigate multi-stage warnings with adaptive strategies for application to various situations including other modalities and false alarms.

Human Factors Issues Surrounding an Automotive Vision Enhancement System

Although night vision systems have been used extensively for a wide variety of military applications, only recently have such systems been considered for automotive applications. This paper provides a technological primer for an automotive application of a vision enhancement system (or VES), and reviews the human factors literature, general human factors issues, and accident data relevant to such a system. The automotive VES consists of two primary components, an infrared sensor and a display. VES information can be displayed to the driver in a contact analog fashion on a head-up display, or in a non-contact analog fashion on either a head-down or head-up display. The primary potential benefit of a VES is to improve the driver's ability to see critical driving events (e.g., pedestrians, bicyclists, roadway direction) under nighttime driving conditions.

Effect of selected in-vehicle route guidance systems on driver reaction times

Experiments were conducted in a fixed-base, high-fidelity simulator to evaluate selected in-vehicle route guidance systems. Drivers navigated a simulated network using five route guidance systems: paper map, head-down turn-by-turn display, head-down electronic route map, head-up turn-by-turn display, and an audio guidance system. The primary measure of driving performance was the reaction time to a scanning task. Other measures included navigation errors, workload, and perception ratings. Censored regression models were developed to study the effect of route guidance type on reaction times. Results indicated that the drivers responded the fastest while using the audio system and the slowest while using the paper map. The head-up turn-by-turn display was associated with lower reaction times compared with an identically designed head-down turn-by-turn display. The head-down electronic map, despite its complexity, performed better than the head-down turn-by-turn display.

Effect of background scene complexity and field dependence on the legibility of head-up displays for automotive applications

This study examined the legibility of information presented on head-up displays (HUDs) for automotive application as a function of background scene complexity, the position of the HUD within field of view relative to the background scene, and the perceptual capacity of the perceiver. Groups of field-dependent and field-independent subjects viewed video footage from the perspective of following a lead car on an open road with low, moderate, and high scene complexity. Subjects were required to track the lead vehicle and identify HUD-presented targets of a specified orientation and specified changes in a HUD-presented speedometer. The results indicate that (a) HUD legibility deteriorated with increased visual complexity of the background scene; (b) positioning the HUD on the roadway reduced the effect of background scene complexity on HUD legibility; and (c) field-dependent subjects made fewer correct and more false positive target identifications than did field-independent subjects.