Keywords

1 Introduction

In the wake of the rapid development of photoelectric technology and human-computer interaction interface, Helmet Mounted Display System (HMDs) has become the key link in information transfer and interaction control of modern fighters, and the research on the system interface is of great importance. HMDs interface, as the sub-interface in the complicated system of fighters, is characterized by large amounts of information, intricate information structure and information continuity, due to that various dynamic changes and targeting system of fighters are centralized in HMDs. In actual combats, human-computer system matching shall be more restrict, with more scientific information coding and structure. An irrational and unscientific design of HDMs interface will lead to the wrong decisions of pilots with serious results.

With the transparent HMDs interface, pilots shall not only observe the dynamic change information in it, but also the external targets through it. Thus, the background brightness of the interfaces will impact pilots’ observation on destination icons. A long-term literature investigation on existing HMDs has shown that the great majority of HMDs have focused on interface design, including icon shape, size and color and the change of brightness of the entire interface, with little on the brightness changes. In particular, little China’s research on HMDs, on the early stage, has focused on the brightness of HMDs interface. This paper proceeds from this aspect aiming at optimizing the brightness of existing icons.

Color is one of the essential elements in traditional interface design of avionics systems. Color coding acts two roles. On the one hand, it can highlight important information in the complicated avionics systems, to guide pilots for quick target lock and upgrade the system efficiency. On the other hand, users have different psychological experience and feelings for different colors and there are related standard requirements in the avionics subsystem interface for the use of different colors, including red, yellow and green. In design of avionics subsystem interface, besides simple use, color coding can also express the logical structure and subsystem of information [1]. The use of color can integrate and classify the functions and levels of interface information, to effectively express the heterogeneousness and similarity among information cells, for the convenience of pilots to get interface information, understand and study the avionics system interface. Icon characters displayed in HMDs interface include flight parameters, tracking and aiming information. Icon characters of flight parameters include: flight path and direction icons, attitude information (pitching and rolling), speed, height, heading and vertical velocity (climbing and diving); tracking and aiming characters include: target line of sight, aiming characters, target guide, velocity of approach and slant-range of target, etc., as shown in Fig. 1.

Fig. 1.
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HMDs interface icons

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The development avionics system interface will follow the systematic, complicated and integrated trend. HMDs will be the representative interface of human-computer interaction of fighters in the future. Along with the transformation of war modes and the revolutionary advance of weapon performance, battlefield situation information under the background of bid data will also feature multiple dimensions, dynamics and complication. Hue, brightness, purity and contrast ratio can be used as the features of color coding to express the prosperities of information in different dimensions and upgrade pilots’ information understanding and identification efficiency. As Fig. 2 shows, the node design of next generation monitoring interface information network applies the scientific color coding to enhance the use efficiency of monitoring interface substantially.

Fig. 2.
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The node design of next generation monitoring interface

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HMDs interface design enhances the brightness of information color to attract the attention of pilots, in order to highlight and feature the important information. Users will experience the strength of simulation to search and orient the information zone quickly. Similarly, the coordination utilization of color coding, size, shape and layout of icons and characters can function to significantly enhance pilots’ performance of information searching and cognition degree of interface information. A scientific and rational color coding is of great importance for visual guidance of pilots. Many of experts and scholars have conducted researches in this aspect. Laar (2001) suggested that color difference can enhance the visual display and help users search visual clues [2]. Jen-Her Wu et al. (2003) conducted experimental analysis on the cognitive performance of hue, brightness and saturability in foreground and background assortment [3]. Peter (2003) conducted the significance level experiment on the differentiation degree and detectability of colored text [4]. Ahlstrom et al. (2005) adopted hierarchical brightness coding to optimize the design of avionics system interface [5]. Dennis (2008) proposed to structure the visual advantage via color perception; the hierarchical color combination could promote the importance ranking of interface information [6] (Fig. 3).

Fig. 3.
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Mapping of color anti-interference performance to visual perceptive layer

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In terms of complicated system interfaces such s HMDs interface, Wu and Sun [7] proposed to test the azimuth angle and pitch angle of HMD relative to fighters, based on video picture processing methods, in order to optimize the existing angle of HMD for head tracking. Niklas [8] applied multi-sensor information combination to enhance the visual display effect of HMD. Xiaoli et al. [9] conducted experimental research on the visual limitation of target searching in radar situation interface, based on information erroneous judgment and careless omission of pilots. Jing et al. [10] launched the research on information coding of balancing time pressure in complicated system interface. Zhang and Zhuang [11] analyzed the influence of text and location coding on information cognition based on eye movement data, through measurement of accuracy and respond time of testees to complete operation tasks. Knalb and Többen [12] developed icon system covering barriers and route information and threatening the regional conformal presentation. Wilson et al. [13] measured the prospective memory and attention diversion of pilots based on eye movement tracking technology to confirm the complicated factors influencing cognition. Cheng and Sun [14] proposed the methods for tracking human-computer eye movement oriented to mobile devices. Xiaoping et al. [15] proposed the methods to optimize the layout of human-computer interface layout of vehicles. Haiyan et al. [16] proposed the methods to assess the interface of driving display and control system of fighters, based on eye movement tracking technology. Weinreich et al. [17] conducted the eye movement research on enterprise website and SE interface. The literatures have shown that the research on HMDs interface mainly focuses on helmet mounted display technology and physiological assessment method of eye movement in complicated system interface, with little research on HMDs interface from the perspective of color brightness.

2 Methodology

2.1 Participants

17 subjects (9 males and 8 females) were present undergraduates (n = 5), postgraduate (n = 6) and doctoral candidates (n = 6) from Southeast University. They ranged in age from 20 to 35 years, with a mean age of 24 years. They had no color blindness or hypochromatopsia, with the corrected visual acuity over 1.0. They were required to practice and train to know the experimental procedure and operation requirements. Each participant sat in a comfortable chair in a soft light and soundproofed room, and eyes gazed at the center of the screen. A 17-in. CRT monitor with a 1024 × 768 pixel resolution was used in the experiment. The distance between participant eyes and the screen was approximately 60 cm, while the horizontal and vertical picture viewing angle was within 2.3°.

2.2 Experimental Equipment and Experimental Procedures

Five values of brightness, including 10 %, 30 %, 50 %, 70 % and 90 %, are used in the experiment. There is a horizon in the center of the display, while sky and ground are simulated in upper and lower parts. Five values of brightness of sky are compared with those of ground. The interface is shown in Fig. 4. Through random combination, 25 pictures are obtained for simulating background brightness.

Fig. 4.
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Simulated picture for comparing brightness between sky and ground

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There are two experiments, including Experiment 1 and 2. Experiment 1 focuses on exploring whether pilots’ reaction time will be shortened when the target frame is regulated based on background brightness. The target frame used is rectangular. In this experiment, it is designated to be 50*50 large, 0.7 mm wide and green (wavelength: 500–560 mm). In the control group of Experiment 1, brightness is a constant and equals to 100 %, just as shown in Fig. 5. Aforementioned 25 pictures are separately taken for 3 times to simulate brightness. Each time, 3, 5 and 7 disturbances appear in different positions at random. Subjects need to make responses by clicking the button as soon as possible. In experimental group, when background brightness isn’t above 50 %, brightness of the target frame will keep 100 %. As background brightness is higher than 50 %, the brightness will be automatically declined to 40 %, just as shown in Fig. 6. Other experimental requirements are completely the same as those of the control group.

Fig. 5.
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Simulated picture of control group in experiment

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Fig. 6.
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Simulated picture of experimental group in experiment


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Experiment 2 intends to examine if it is more effective to use dotted target frame than the solid one under backgrounds of different brightness. The experimental methods won’t be illustrated here in detail because they are completely the same as those mentioned above. In this experiment, dotted target frame is used in the experimental group and solid target frame is utilized in the control group for comparisons.

3 Analysis and Results

The experiment selects 17 testees; removes 10 % of testees with high error rate; and selects 14 groups of available data. Then, the experiment selects the reaction time and accuracy data of each testee for each picture; finally, the experiment summarizes the mean value of reaction time and accuracy of 14 testees in different disturbances to get Tables 1, 2 and 3.

Table 1. Mean values of reaction time and accuracy of effective testees in control group
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Table 2. Mean values of reaction time and accuracy of effective testees in experiment group 1
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Table 3. Mean values of reaction time and accuracy of effective testees in experiment group 2
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3.1 Line Chart Analysis

Summarize the mean values of testees’ reaction time in the experiment to get this line chart as in Fig. 7.

Fig. 7.
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RT line chart (Color figure online)

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The line chart above has visually shown that the existing target frame, target frame with changeable brightness and dotted target frame are increased, along with the increase of disturbance number. The dynamic change of line chart has suggested that the fold lines of design plans of three target frames are roughly paralleled without cross. However, in the wake of the increase of disturbances, the increase trend of reaction time has been slightly reduced. And the dotted target frame features the most significant decreasing trend, compared by target frame with changeable brightness with the most unapparent decreasing trend. In addition, it is visual that the reaction time of dotted target frame is the longest, followed by that of existing target frame, and the reaction time of target frame with changeable brightness is the shortest, among the design of three target frames.

3.2 Anova

ANOVA on reaction time shows that the between-group main effect shall be significant as (F = 15.772, P = 0.001, P < 0.05), the main effect of disturbances shall be significant as (F = 3.262, P = 0.042, P < 0.05), showing the significant influence of experiment groups and disturbance number on reaction time.

The multi-comparison test results on reaction time based on LSD are shown as Tables 4 and 5. The table has shown that there are significant differences in reaction time of experiment group 1 and 2, compared by reaction time of disturbances only when there are 3 and 7 disturbances, showing that the slight change of disturbance number will not bring about significant difference of reaction time.

Table 4. LSD multi-comparison test of experiment groups
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Table 5. LSD multi-comparison test of disturbance number
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Conclusions have been made based on the data of 14 effective testes: (1) In case of three disturbances, respondents’ reaction time is the shortest regardless of dotted or solid lines. With the increase in disturbances, respondents’ reaction time gets longer. (2) In the same background brightness, respondents’ reaction time may be effectively shortened when the brightness is 40 %. (3) Under the same experimental conditions, it takes a longer reaction time for respondents to observe the dotted target frame than the solid one.

4 Conclusions

  1. 1.

    Significant differences exist in reaction time among existing target frame, target frame with changeable brightness and dotted target frame. The reaction time also significantly differs for 3, 5 and 7 different disturbances. Experimental data have effectively indicated the changes based on background brightness and demonstrated that the design scheme of brightness for optimizing target frame is feasible. On the whole, cognitive effects are better for the target frame with changeable brightness as compared with existing target frame no matter how many disturbances there are. The reaction time is about 12 % shorter on average for the former target frame.

  2. 2.

    Respondents’ reaction time is longer in observing dotted target frame, which reflects that it is more reasonable to design solid target frame.

  3. 3.

    From the increase in reaction time, it may be observed that the longer the reaction time, the smaller the increase, which may be reflected most evidently when the number of disturbances increases from 5 to 7 for the dotted target frame. In addition, it may be discovered from the experimental data that the target frame with changeable brightness narrows by 100 ms on average compared with existing target frame.