By Shannon Crouch
Humans have visual cues that they naturally use to perceive their motion through the environment. There are numerous human factors that are associated with being able to navigate a vehicle safely while adhering to signal lights, signs and other traffic road markings. There needs to be vast improvement in the way that information is presented to drivers for many reasons. One example is that the placing of the sun during a particular part of the day prohibits one from distinguishing whether a traffic light is green or red. The elderly have difficulties reading certain signs or differentiating among the color of signal lights, even with their glasses on. Most everyone has less visual acuity at night and certain road markings or traffic lights are harder to perceive. Color blind people canÕt always tell the difference between a red light and a green light, and they may also have a hard time seeing brake lights, blinkers, etc. All of the situations mentioned above can lead to serious fatal accidents. Extensive research in this area has been conducted for many years and is still going on today.
Driving is a complex task which involves a variety of interactive parallel and serial processes that depend on various visual functions. Vision plays a vital role in safe, proficient driving even though there are other sensory and motor systems that are used in driving. It has been estimated that 90% of the information used in driving is visual and that visual information alone might be sufficient for safe driving (Fox, 1997). Beyond these general statements, it has been difficult to determine what specific visual skills are used for driving that are important.
Safe and efficient driving is Òa matter of perceptual-motor sensitivity to perceptual laws of locomotion in a spatiotemporal fieldÓ (Fox, 1997). Specifically, the driver must be aware of two fields: (1) the field of safe travel and (2) the minimum stopping zone. The field of safe travel refers to a field surrounded by actual and potential obstacles to locomotion. The minimum stopping zone refers to a field that is determined by variables like speed, visual/road conditions, etc. Car crashes occur when another car or stationary object is not perceived accurately. In order to guide a vehicle, the driver must (1) abstract important sensory information from the environment, (2) process this information accordingly to complete visuospatial tasks and (3) act accordingly to achieve task goals. The driver must maintain awareness of his/her path and of non-moving and moving objects.
To safely navigate a vehicle in a consistent manner with the driverÕs goals is dependent upon a current assessment of the altering situation and also requires stable attentional mechanisms to keep up with ongoing environmental information and evaluate relevant information.
The goal of navigation is to achieve movement through space and because large movements are typically more significant than small one, it is apparent that the task must be fundamentally stored in our understanding of space. We need to understand how people judge their movement through space and how displays may be designed to facilitate this judgement. We also need to consider how navigational performance can be supported through the design of maps and instructions (Wickens, 1992).
The human factors problems associated with mas and navigation should be self-evident to anyone who has ever come across the following situations: (1) driving through a confusing series of intersections; (2) following directions on how to get somewhere and missing a turn; and (3) having known the area of a place and then become unable to locate oneÕs position on the map because the surrounding landmarks are all unfamiliar (Wickens, 1992). We need to be able to navigate from one location to another, using landmarks or other features (visual) to trigger the decisions as to which direction to go at a given intersection.
Reaction time (RT) is a human factor that affects signal information processing. RT is lengthened as a set of stimuli are made less discriminable from one another. These discriminability difficulties can be minimized by deleting shared and repeated features where possible. RT is lengthened as the discriminability between the responses is reduced (Wickens, 1992).
As we move through an environment in an automobile, our judgements of the direction and speed with which we are moving depend on information distributed across the visual field, not just in the area of foreal vision, but in the peripheral vison as well. Although peripheral vision is not highly effective for recognizing objects, it is more proficient at conveying information about motion and orientation (Wickens, 1992).
A potential bias in human perception occurs because our subjective perception of speed is heavily determined by global optic flow (the velocity of points traveling across the display surface and the retina as we navigate). We feel as if we are traveling at a greater speed in a sports car than a bus, in part because the sports car is lower to the ground. The global optical flow can be affected by the density of texture over which a vehicle passes. As this density increases (texture is finer), the global optical flow increases and the driver perceives a faster velocity (Denton, 1980).
The issues of whether different tasks are served differently by more or less integrated displays is represented in the proximity compatibility principle (Andre & Wickens, 1990), which states that Òto the extent that information sources must be integrated, there will be a benefit to presenting those dimensions in an integrated format.Ó It should also be noted that two items on a cluttered display will be more easily integrated or compared if they share the same color (different from the clutter), but the shared identity of color may disrupt the ability to focus attention on one while ignoring the other (Andre & Wickens, 1990). A unique color code will help this focusing process, just as it disrupts the integration process. Cluttering of signs and signals can cause confusion. A study conducted by Culler, Holahan and Wilcox (1978) found that the ability to locate and respond to a stop sign in a cluttered display is directly inhibited by the proximity of other irrelevant signs in the field of view.
The proximity compatibility principle also applies to spatial distance in a cluttered display. Two pieces of information that need to be integrated on a cluttered display should be placed in close spatial proximity, as long as this proximity does not also move them closer to irrelevant clutter (Andre & Wickens, 1990).
Color blind individuals cannot differentiate among colors, which makes it difficult to perceive traffic signals of any kind. Color blind people are technically termed dichromats, meaning, Òtwo-colors.Ó Dichromats can see only two hues whereas people with normal vision can distinguish over one hundred hues. Most dichromats can see blue and yellow; for them, there is a region of the spectrum between blue and green which has no color and appears gray or white. All colors appear to them as combinations of black, white and gray with either yellow or with blue. Many dichromats will claim that they can easily tell the red from green in a traffic signal. In the United States, the go-light is blue-green so that color blind people can distinguish it from red. Even though they can discriminate between the two, the go-light falls into the colorless region of the spectrum for many, and it is indistinguishable from the color of automobile headlights at night. They have become accustomed to using brightness and saturation differences as cues and they have learned to call these differences ÒcolorsÓ (Neitz, 1997).
Another way color can affect visual processing is when isoluminant displays are used. leClerc, Malbert, Montagnon, & Troscianko (1991) revealed that certain color gradients (at isoluminance) markedly affected the perceived depth. A gradient in saturation (e.g. red-to-gray) was particularly effective in allowing depth perception, while a red-green hue gradient had no effect on perceived slant. Their data suggests that while color can encode depth, its contribution is contingent on the presence of texture cues. This contingency implies strong links between texture and color processing in human vision.
There have been several proposed solutions to the above-mentioned problems. To reduce the speed of individuals in vehicles, since speeding plays a major role in traffic accidents, the AAA Foundation for Traffic Safety is planning a test series using converging patterns of stripes on the road to give drivers the illusion of excessive speed; this should, in turn, cause them to reduce their speed. The only problem foreseen with this method is that varying speeds can themselves pose problems, since fewer accidents occur when all traffic drives at the same speed (Science News, 1996).
Denton (1980) did a similar study on the previously mentioned research. He exploited the characteristic of the perceptual experience, when the global optical flow increases and the driver perceives a faster velocity, in an ingenious application of perceptual research to highway safety. His concern was with automobile drivers in Great Britain who approached traffic circles at an excessive rate of speed. DentonÕs solution was to minimize the spacing between road marks at a gradual and continuous rate as the distance to the stop point minimized. A driver who may be going at an excessive speed would see the global optical flow as increasing. This would cause the driver to compensate by imposing a more appropriate degree of braking or slowing down (Wickens, 1992). Results of his study showed significantly slower speed following introduction of the markers and the rate of fatal accidents was greatly decreased.
Another current research project being conducted involves dynamic driving situations by using a version of the flicker technique developed by Dr. Rensink of Cambridge Basic Research Center for studying the ability of people to perceive changes in static scenes. An advantage of the flicker technique over others is that awareness is probed while the subject is in the situation and not afterwards. The repeating flash can be somewhat annoying, but it does not affect the normal perception of a situation as it unfolds. Motion perception remains normal between flashes; this would create a Òquasi-realistic but totally safe and controlled driving environmentÓ (Fox, 1997).
This area of applied research in perception deserves further research. Our environment needs to be as safe as possible for all humans, with visual handicaps or not, to be able to drive and process all signals and markings efficiently.
References
Andre, A.D., & Wickens, C.D. (1990). Proximity compatibility and information display: Effects of color, space and objectness of information integration. Human Factors, 32, 61-77.
Culler, R.E., Holahan, C.J., & Wilcox, B.L. (1978). Effects of visual distraction on reaction time in a simulated traffic environment. Human Factors, 20, 409-413.
Denton, G.G. (1980). The influence of visual pattern on perceived speed. Perception, 9, 393-402.
Fox, C.R. (1997). Reducing accident rates among elderly drivers. 14th Biennial Eye Research Seminar, 11-12.
Illusions: The route to safer roads? (1996, July 13). Science News, 150, 31.
leClerc, J. Malbert, E., Montagnon, R., & Troscianko. (1991). The role of color as a monocular depth cue. Vision Research, 31, (11), 1923-1930.
Neitz, M. (1997). Society and color blindness: A view in need of correction. 14th Biennial Eye Research Seminar, 64-66.
Wickens, C.D. (1992). Engineering psychology and human performance (2nd Ed.) New York: Harper Collins.