An Evaluation of Color Patterns for Imaging of Warning Signals in Cockpit Displays Tatiana Evreinova Tampere Unit for Computer-Human Interaction Pinninkatu 53B, University of Tampere FIN-33014 Finland +358 3 215 8569
[email protected] ABSTRACT
The quality of information perception in an aircraft cockpit depends on the way of interacting with display units, including modality, interface structure, and external exploitation conditions. The goal of this work is to find a solution that would allow real-time imaging or doubling of audible warning signals through spatial-temporal color coding. Software emulation of the peripheral display was built. The development and pilot evaluation of the method were both performed. Presentation of visual signals in paracentral field is efficient, but their optical and temporal parameters are critical in relation to distraction effect. Keywords
Cockpit display, audible signals, spatial-temporal color coding, visual distractor INTRODUCTION
In aircrafts, human-machine interaction is the key issue to providing situational awareness and maintaining safety. The pilot functions as an observer who monitors the displays and information from the flight computer, pays attention to the environment and concentrates on communication tasks. To facilitate the amount of work and tasks he or she has to accomplish, the aircraft becomes more and more computerized. However, the displays in the cockpit of an aircraft can be quite complex and have to function in a harsh visual environment that may strongly affect the image quality of the displayed information [4]. The lack of operational feedback regarding the functions of different systems as well as missions performed with these aircraft can lead to serious consequences. Audio, visual and tactile feedback cues are used for these purposes as well as flight crew communication. The aviation environment is characterized by multiple sources of noise, both on the ground and in the air.
Noise is produced by aircraft equipment – jet efflux, rotors,
Roope Raisamo Tampere Unit for Computer-Human Interaction Pinninkatu 53B, University of Tampere FIN-33014 Finland +358 3 215 7056
[email protected] transmission systems, propellers, hydraulic and electrical actuators, cabin conditioning and pressurization systems, cockpit advisory and alert systems, communication equipment, and aerodynamic effects [1]. Noisy cockpits make communication between pilots difficult, increasing the potential for errors. According to the statistics, more than 70 percent of pilot errors occur because pilots in noisy jet cockpits may not hear important instructions, special audible alert and warning signals or not perceive the appearance of an alarm situation [7]. Through time, pilots’ hearing of jet aircrafts and helicopters is decreased. Due to vibration disease, some pilots have low tactile sensitivity. The use of tactile displays is not always possible. The surveys of the German Pilot Association have shown that 31% of the pilots who used conventional tactile displays said that they would like to have a higher degree of sensitivity in such kinds of devices to avoid incorrect control of the aircraft [6]. For many years, color has been used successfully in aircraft cockpit displays. The use of this parameter has many reasons. One of them is an opportunity to present complex information, which can appear during the flight, through colored symbols in a limited space. The use of color to provide key information for air traffic controlling duties is rapidly evolving. For instance, to monitor both ground and air traffic, such as flight strips, weather radar, navigation lights, direct visual logo recognition, air traffic controllers use traditional color-based markers. They have red, blue, green, yellow and neutral, which is a grey color and three luminance contrasts, corresponding to day, night and twilight [4]. However, visual displays should be arranged in a way to reduce information access costs. Displays and panels must be scanned frequently and searched for relevant information. The reaction time can be a crucial issue, particularly, in the case, when the pilot needs to receive alarm and warning signals [6]. Modern aircraft displays provide high density of displayed information. It means that a signal can be localized independently among a large variety of other values by changing the contrast or
flickering the critical value on the display. This could be done with a rapid change in the luminance, brightness or color. Color is appropriate to find a certain target or to project specific information on the display that is not related to another feature. It is important that only a small number of colors are used to ensure absolute judgment and correct identification and to avoid distracting the pilot. An illusion of clarity exists where we see the entire visual field in color and with equal high resolution, but this cannot be true because the fovea only has such resolution within 1/2 - 2 degrees. Eye movements must bring each part of a scene or an image nearer the fovea to be processed with ample resolution. However, within paracentral area (?20?) color vision is still possible and could be used for the imaging of coded light sequences [2].
frequency of use of coded warning signals, color patterns are coupled into the spatial groups.
Figure 2. Snapshot of the program during testing; strips B1B4 are color indicators for imaging of warning signals
Figure 1. Features of visual perception The goal of this work is to find a solution that would allow real-time imaging or doubling of audible warning signals through spatial-temporal color coding. METHODOLOGY
An assistive method for spatial-temporal coding of speech messages and non-speech audible signals into visual color patterns was developed. To simplify the perception of the signals, semantic groups of color patterns should include not more than seven coding elements. Spatial grouping of the elements reduces cognitive load based on complementary strategy [3] and provides unconscious associative perception of color patterns during imaging. To evaluate recognition of signals with the help of a new method of the spatial-temporal color patterns, a test program was written in Microsoft Visual Basic 6.0. A snapshot of the program during the test is shown in Figure 2. Figure 3 shows a snapshot of the program in the editorial mode in which test parameters can be changed. Each audible signal is displayed with the help of a spatial pair of four strips. The strips are placed close to peripheral unfocused position. Diffused three-level luminescence does not require recognition of clear shape of signals. That layout is not a distractor like special soft indicators, and does not create obstacles within the central field. Strips provide only direction detection, colors and brightness of the light sources. Based on functional similarity and
Figure 3. Snapshot of the test program in editorial mode Task-dependent software permits it to display audible warning signals through the spatial-temporal color patterns consisting of eight light units with three gradations of brightness (0, 0.5 and 1.0) and three colors (background, red and green). The light units within pattern characters are not separated. A variant of light code for basic audible warning Q-signals is shown in Figure 4. They are used for air-toground communication and reduce many important phrases during radio signaling with the help of three letters [5]. Exposition duration of light equivalents of coding warning signals depends on a latent period of the visual perception. Therefore it should not be less than 640 ms for perception of all light units.
Figure 4. Spatial-temporal coding for audible Q-signals We suggest that such a way of audible signal doubling could be more suitable than radio paging in noisy jet
cockpits. By using minimal resources of visual perception such a layout provides maximal information capacity of imaging
EXPERIMENTAL EVALUATION
At the exposition time of 800 ms the amount of recognized test symb ols was about 77 percent. If exposition duration is increased up to 960 ms the amount of recognized test symbols grows to 94 percent. The full analysis of recognition of all test sequences shows that the average value of recognized test symbols among hindering ones was 87.24 percent (? = 14.4%). The better exposition time for recognition of color patterns within paracentral area (?20?) is 960 ms. The average value of recognized test symbols among hindering patterns was 94.8%, ? = 15%.
Participants
CONCLUSION
Four subjects participated in this pilot experiment. Subjects' ages ranged from 22 to 47 years old, and all had a normal color sight but different visual and hearing acuity. There were 2 males and 2 females.
The comparative analysis of the amount of detected test symbols among noise symbols has shown that probability of error depends on color pattern similarity of detected test symbol to noise pattern and of the exposition duration. One of possibilities to decrease the amount of errors is to develop color code with alternative or adaptive exposition duration of light units within the color pattern.
T = S ? log2 (kb + 1)N where, S is an amount of spatial positions of indicators groups, N is an amount of indicators per symbol, k is an amount of colors and b is the number levels of brightness. The information capacity of proposed system is 27.86 bit.
Procedure
The main research method in this work is empirical research. We studied visualization efficiency of audible signals transforming into color patterns. We recorded the amount of recognizable test symbols among noise symbols – visual distractors by test-persons. During the test session, the task of the test person consisted of remembering the first color combination and counting the amount of these color patterns appearing within the presented sequence or test symbols among hindering ones. Test sequences were composed equally of ten test symbols and ten noise symbols. A color pattern recognition of signals was tested at the exposition time 640 – 1280 ms when the duration of one light unit was varied randomly from 80 up to 160 ms. Discussion of results
The color pattern recognition for QTH signal shown in Figure 5.
The proposed method for real-time imaging or doubling of audible warning signals requires minimal resources of visual perception and has to be useful for pilots to decrease recognition errors in alarm situations. ACKNOWLEDGMENTS
This work was financially supported by the Academy of Finland (grant 73987), and by the Nordic Development Centre for Rehabilitation Technology (NUH). REFERENCES
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Figure 5. Color pattern recognition at exposition time 6401280 ms for QTH signal At exposition time 1280 ms the amount of recognized symbols is almost always more than ten test symbols. If the exposition time is too long and hindering symbols include a sequence of light units, similar to the test symbol, the test pattern can be perceived within hindering symbols. Even in a case when sequences are not equal, a perceived noise symbol is added proceeding from the existing signal model in the short-term memory of the user.
4. Operational color vision in the modern aviation environment. RTO Technical Reports, RTO-TR-016 AC/323(HFM-012)TP/6. Available at: http://www.rta.nato.int/Rdp.asp?RDP=RTO-TR-016 5. Q-signals for amateur radio operators. Available at: http://www.qsl.net/ad4dx/indexGQ.html 6. Schmelzer R. Human interaction with aircraft cockpit displays. Available at: http://www.eas.asu.edu/~humanfac/ringo.html. 7. The role of human factors in improving of aviation safety. Available at: http://www.boeing.com/commercial/aeromagazine/aero_ 08/human.html
