Before I begin a discussion of web design and color, I would like to say a few things about the fundamentals of how we see color. When I was a Psychology professor, I taught classes on Sensation and Perception and Neuroscience that covered much of this, and I can’t resist the opportunity to share some of the things that I learned (and can remember) from my experience teaching these classes. Color TheoriesAt one time, there were thought to be two competing theories as to how the human visual system processes color. The first, trichromatic theory, is based on the idea that the visual system is maximally responsive to three colors and that color vision is a result of the combination of differential responses of these three components. As evidence for the theory, proponents cited the fact that all the colors that can be perceived can be created by mixing three colored lights that differ in wave length. All you have to do is to differentially vary the intensity of the three lights, so long as they are different wave-lengths (colors), and you can get the three of them to mix to display virtually any color. The second, opponent-process theory, is based on the idea that the visual system is responsive to three color pairs (green-red, blue-yellow, and black-white) and that color vision is due to the combined differential response of these three different components. Evidence that supports this is the opponent color after-image effect. When most people stare at a bright green color for several seconds and then look away at a white field they will perceive a red color, and vice versa when looking at red. The same thing occurs with blue and yellow. It turns out that both theories are accurate; they simply apply to different levels of the nervous system. Somewhere along the line I’m sure you have heard that we have rods and cones in our eyes. These are special types of neurons called receptors, which convert a physical signal (e.g., light) into a neural signal. Receptors in the visual system are called photoreceptors. The cones are responsible for our color vision and, it so happens, for those with normal color vision, there are three specific types of cones, which are maximally responsive to three different wave lengths. For most people, these preferred wave lengths represent the colors red, blue, and green. Therefore, for visual processing in the eye (on the retina) trichromatic theory applies. Once the neural signal passes beyond the retina on its way to the brain, the nature of the cells change and, in fact, the cells respond in an opponent fashion, consistent with opponent process theory. So, for example, a green photoreceptor and red photoreceptor might each send a signal to a single blue-red opponent cell farther along in the system. Opponent cells, like all nerve cells, fire periodically just for grins, establishing a sort of base line firing rate. For a red-green opponent cell the base-line rate will decrease when it gets a green signal and increase when it gets a red signal (or vice versa). There are also blue yellow and black-white opponent cells as well. (If you'd like to know more about opponent process and trichromatic theory, Kaiser, 1997) Light vs. PigmentYou may have heard, at some point, that white is the presence of all color. You may have also tried the experiment that I tried when I was in grade school, which was to mix together all of your paints, in which case it probably appeared to you that you had disproved this theory, because you end up with a dark brown color that gets closer to black every time you add another color. (This is one of those many things that leads us not to question what we here from grown ups. :) The problem with our grade school research model and the conclusion we drew, was that white is the presence of all color when you are mixing light, but it works the exact opposite when mixing pigment. You can demonstrate that white light contains all colors by shining it through a spectrum or watching a rainbow, both of which split white light into it’s component parts. However, we usually see color in the form of pigments, not light. Most of the time the light that exists in our environment is some variation on white. This white contacts some pigment such as a red shirt. The shirt then sucks up all of the colors from that white light except for the red and reflects the red. So, when you were doing your ingenious experiment with your paints as a kid, you started with something like green, which sucked up everything but green from the white light reflecting on it. Then you add another colored pigment and more of the color in the light is sucked up, etc., until you end up with some muddy color. White ambient light is the constant, most of the time, and changes in our perception of color are due to pigment changes. If your teacher had given you a bunch of different lights to play with and allowed you to shine them on a white background you could have done a cooler experiment. You could have shined one colored light on the background, then another, and another and, each time you added a color the background, instead of looking more and more like mud, would have looked more and more white. Unfortunately, my teacher was barely willing to let me play with paint, much less a bunch of electrical equipment, so I only know about this process hypothetically. If you're interested in learning more about color perception in general, see the section on Color Perception in Peter Kaiser's excellent web book referenced below. ReferencesWhat is the opponent process theory of color vision? The opponent process theory suggests that the way humans perceive colors is controlled by three opposing systems. We need four unique colors to characterize perception of color: blue, yellow, red, and green. According to this theory, there are three opposing channels in our vision. They are:
We perceive a hue based on up to two colors at a time, but we can only detect one of the opposing colors at a time. The opponent process theory proposes that one member of the color pair suppresses the other color. For example, we do see yellowish-greens and reddish-yellows, but we never see reddish-green or yellowish-blue color hues. The theory was first proposed by German physiologist Ewald Hering in the late 1800s. Hering disagreed with the leading theory of his time, known as the trivariance of vision theory or trichromatic theory, put forth by Hermann von Helmholtz. This theory suggested that color vision is based on three primary colors: red, green, and blue. Instead, Hering believed that the way we view colors is based on a system of opposing colors. As mentioned above, Hering’s opponent process theory clashed with the trichromatic theory that dominated his time. In fact, Hering was known to strongly oppose von Helmholtz’s theory. So which is correct? It turns out that both of these theories are necessary to fully describe the intricacies of human color vision. The trichromatic theory helps to explain how each type of cone receptor detects different wavelengths in light. On the other hand, the opponent process theory helps explain how these cones connect to the nerve cells that determine how we actually perceive a color in our brain. In other words, the trichromatic theory explains how color vision happens at the receptors, while opponent process theory interprets how color vision occurs at a neural level. In the 1970s, psychologist Richard Solomon used Hering’s theory to create a theory of emotion and motivational states. Solomon’s theory views emotions as pairs of opposites. For example, some emotional opposing pairs include:
According to Solomon’s opponent process theory, we trigger one emotion by suppressing the opposing emotion. For example, let’s say you receive an award. The moment you’re handed the certificate, you may feel a lot of joy and pleasure. However, an hour after getting the award, you may feel a bit sad. This secondary reaction is often deeper and longer lasting than the initial reaction, but it gradually disappears. Another example: small children becoming irritable or crying on Christmas a few hours after opening presents. Solomon thought of this as the nervous system trying to return to a normal equilibrium. After repeated exposure to a stimulus, eventually the initial emotion wanes, and the secondary reaction intensifies. So over time, that “after-feeling” can become the dominant emotion associated with a particular stimulus or event. You can test out the opponent process theory with an experiment that creates a negative afterimage illusion. Stare at the image below for 20 seconds, and then look at the white space that follows the image and blink. Note the color of the afterimage you see. If you prefer to do the experiment offline, you can do the following: Materials
Method
The afterimage should have the opposite color of what you just stared at because of a phenomenon known as cone fatigue. In the eye, we have cells called cones, which are receptors in the retina. These cells help us see color and detail. There are three different types:
When you stare at a specific color for too long, the cone receptors responsible for detecting that color become tired, or fatigued. The cone receptors that detect the opposing colors are still fresh, however. They aren’t being suppressed any longer by the opposing cone receptors and are able to send out strong signals. So when you then look at a white space, your brain interprets these signals, and you instead see the opposing colors. The fatigued cones will recover in less than 30 seconds, and the afterimage will soon disappear. The results of this experiment support the opponent process theory of color vision. Our perception of the image’s color is controlled by Hering’s opposing systems. We only see the opposing color when the receptors for the actual color become too fatigued to send out a signal. Solomon’s opponent process theory may explain why unpleasant situations can still be rewarding. It could be why people can enjoy horror movies or thrill-seeking behaviors like skydiving. It may even explain phenomena such as the “runner’s high” and self-injurious behaviors, like cutting. After developing his theory, Solomon applied it to motivation and addiction. He proposed that drug addiction is the result of an emotional pairing of pleasure and withdrawal symptoms. Drug users feel intense levels of pleasure when they first start using a drug. But over time, the pleasure levels decrease, and withdrawal symptoms increase. They then need to use the drug more frequently and in larger quantities to feel pleasure and avoid the pain of withdrawal. This leads to addiction. The user is no longer taking the drug for its pleasurable effects, but instead to avoid withdrawal symptoms. Some researchers don’t completely support Solomon’s opponent process theory. In one study, researchers didn’t observe an increase in withdrawal response after repeated exposure to a stimulus. There are good examples that suggest the opponent process theory is valid, but other times it doesn’t hold true. It also doesn’t completely explain what would happen in situations involving several emotional stresses occurring at one time. Like many theories in psychology, Solomon’s opponent process theory shouldn’t be considered the only process involved in motivation and addiction. There are several theories of emotion and motivation, and the opponent process theory is just one of them. Most likely, there’s a range of different processes at play. |