Human Factors

One of the fundamentally important outcomes of sensory research is the development of an important set of applications based upon a functional knowledge of the operation of our sensory systems. Human Factors is one applied field that has made great use of diverse areas of psychology including sensation and perception. Human Factors refers to the application of scientific knowledge of human capabilities to the development of equipment (Proctor & Van Zandt, 1994). Basically, the idea behind human factors is to make the equipment fit the human user instead of the other way around. In other words, human factors is where we make basic psychology work in the real world, which is a very exciting task.

One vital area of application of visual knowledge in human factors has been the development of displays such as televisions and computer monitors. Historically, the development of color televisions and monitors owes much to the trichromatic theory of color vision. Beginning in 1931, the Commission Internationale de líEclairage (CIE) had formalized human color matching behavior using a quantitative model of the trichromatic theory, with major updates in 1960 and 1976. See Figure 18 for a depiction of the 1931 CIE diagram. Even in the years prior to the measurement of the responses of the cones, engineers were able to make a precise prediction of the human color response. Engineers need only to give a coordinate for a color in this space and, depending on the reliability of the equipment, the color will be precisely duplicated on any television and monitor or even printer.

Figure 18. The 1931 CIE color system. Colors are specified by their chormaticity coordinates (x, y). The spectrum is on the outside with example wavelengths given. The triangle represents the range of colors that can be reproduced on a typical television (Silverstein and Merrifield, 1985).

Because the visual system has a functionally trichromatic receptor layer, there are other important engineering simplifications in developing color television and monitors that have been made possible. In essence the trichromatic theory specifies that three primaries should be sufficient for reproducing most colors we see. Thus, all modern color monitors and televisions use three color elements for color reproduction. These three elements are placed close enough together so that the colors are blended by the spatial summation mechanisms of the eye. To show how this is a real engineering blessing, consider what might happen if we had more than three color systems in our visual system. For each additional color mechanism, the engineer would need another color element in the system to be able to match the color of the scene being caught on film or tape. If we had even octachromatic vision (eight color mechanisms or cones), then there would need to be eight guns on our color television and not three. It might be very hard to fit all eight dots inside the limits of human spatial summation, that is, close enough together so that they are blended together by the visual system.

More recent efforts in display development have been in two primary areas. The first area is in assisting the development of new display technologies so that they have the same visual excellence as the CRT (cathode ray tube, the technology behind the standard monitor). The second area is in developing displays for harsh visual environments such as the airplane cockpit.

When the electron gun of a CRT strikes the surface of the display it stimulates several elements. The elements in the middle are bright and the ones at the edge are dim. This pattern of stimulation can be described as bell shaped or gaussian. Think of the lines on the CRT as being drawn with a bright center and dim slightly fuzzy edges. Thus the dots in the middle of the line are brightest and the dots on the edge are much dimmer. Since the jagged edges of the lines are made by dim dots, they are not as noticeable. If the lines are drawn directly like a pencil on paper as they are on some CRTs, then the jagged edges are all but unnoticeable (Silverstein & Merrifield, 1985). Liquid Crystal Displays (LCDís) and other technologies do not have these bell shaped beams but access each element directly in a digital fashion. Thus, the jagged edges of lines are easily noticeable. Thus, research efforts have determined how to take advantage of the way the visual system operates to most effectively and efficiently minimize the visibility of these jagged edges (Silverstein, Krantz, Gomer, Yeh, & Monty, 1990).

The airplane cockpit is a harsh environment in which to place an electronic display such as a CRT or LCD. If the sun is in front of the pilot, then it might take the pilot a relatively long time to be able to see the much dimmer display (i.e., dark adaptation). In some flight situations even a few seconds might be critical. If the sun enters the cockpit from the side window onto the display, the surface is washed out making it difficult or impossible to read and distinguish the colors of the elements. In the evening, it is important that the display not be too bright that the pilot can not see important but possibly dim targets in the sky or on the land. Visually oriented human factors research has focused on the stimulus intensity needed on these displays so that pilots can read them accurately and quickly under the wide range of conditions. An important goal of these efforts is to develop an automatic control mechanism that senses the ambient light visible out the front cockpit windows and the light falling on the display surface and automatically adjusts the intensity of the display for the pilot (Silverstein & Merrifield, 1985; Krantz, Silverstein, & Yeh, 1992).

One important future direction for sensation and perception's application to human factors will be developing a good general model of visual system-display interaction. With a single TV at home, this was not a big issue, but with scanners and digital cameras, printers, computer monitors, and TVs all at home the difference in color from one display to the next can be very great and disappointing. Obviously the model that is developed should not be tied to any single display type. There are also a plethora of new display technologies coming out. The venerable CRT will still be around for many years, the LCD is found on laptop computers and may be on our walls if HDTV takes off, color printers are coming into the home, and there are many other new display technologies besides. Two difficulties arise with these new technologies. First, the research effort to develop good images on CRTs and LCDs were very expensive and it would be nice if what has been learned from one technology could be applied to another. Secondly, the image reproduced on different displays can look very different, especially the colors. Colors will change and some times so dramatically that we would describe it as a different color on different displays. A good general model of visual system display interaction would allow new technologies to benefit from previous research and to develop images that have the same color from screen to screen and screen to printer.

Whereas studies of sensation and perception comprise a substantial portion of the field of human factors, studies of sensory and perceptual function have also recently made important contributions to the field of neuropsychology. This work has helped us to better understand and characterize a diverse group of neuropathologies and neurodegenerative disorders.