Assignment 300 words
Color is all around us, but just how deeply integrated is the phenomenon of color into our senses and neural pathways? Describe trichromatic theory and opponent-process theory of color vision, including the observations on which it is based and the physiological basis of each theory. Lastly, watch the video on synaethesia below, and discuss what it means to say that color is created by the nervous system. Explain what everyday life would be like for an individual with the disorder, including its impact on occupation, relationships, and leisure time. Be sure to include how the disorder might affect the persons behaviors and experiences in these settings.
PSYC304 | LESSON 5: COLOR PERCEPTION
Topics to be covered include:
The influence of wavelength on color
The proposals of trichromatic theory
The proposals of opponent process theory
The explanations of composite theory
Why are people colorblind or color weak?
Light is transmitted in waves that determine color based on frequency and amplitude. It is then processed through the visual perceptual systems as light waves until the rods and cones transform the information to neural signals the brain is able to understand. Color perception and processing are covered under a few different theories: trichromatic color processing theory, opponent-process theory, and composite theory. Each theory looks at the processing of color perceptions. Color perceptions are not always accurate, and some people experience color blindness or color weakness, each of which is dependent upon genetic makeup.
The Rainbow after the Rain
Think about the last time you were out in a pouring rain. When it finished, the sun came out. What did you do? Did you see a rainbow, with its vibrant colors arrayed across the sky? Light, of course, has everything to do with color as we will see in this lesson. When we look at the rainbow, we see certain colors. These colors are part of the visible portion of the electromagnetic spectrum. How do we recognize colors? What helps us separate one color from another? Imagine having no color. The world would be a very drab place. Thankfully, we do have color and the rainbow to remind us of how much color information we perceive each and every day.
Wavelengths of Light
In order to explain our perception of color, we are going to do a little bit of a review to set the stage. Light is transmitted in waves, which vary in frequency and amplitude. The frequency of a wave is the number of cycles of a wave in a one second time period. The amplitude of the wave is the highest point, or crest of the wave The higher the crest, the more frequent the waves will be. The wavelength is the distance between crests. The wavelengths are measured in nanometers, which are billionths of a meter. As you can guess, that is very, very small. Humans are only able to perceive a limited span of wavelengths from 400 to 700 nanometers. The size of the wavelengths determines the color we perceive, which means different wavelengths lead to different perceptions of color. The longer wavelengths around 700 nm are red hues, and as the wavelengths decrease, the colors advance through the spectrum ending with violet around 400 nm (Griggs, 2016). Light can be considered a stream of photons. Any one photon has is characteristic wavelength, which determines its color.
If you look at the visible spectrum, or what the human eye can perceive, you will see that we perceive a small part of a greater range. Of course, not all living beings perceive color as humans do. Other primates have the ability to perceive colors, but some other mammals do not (Carlson & Heth, 2010). Most mammals see more in black and white. Birds and fish, on the other hand, have very advanced color perception, which makes sense if you think about all of the brightly colored lures on the market today for fishermen (Carlson & Heth, 2010). Bees can see ultraviolet light, which is the light past the blue end of our visible spectrum.
How many of you remember acronyms from elementary school? Do you remember ROY G. BIV? That is the acronym or the colors of the spectrum, and the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet (Griggs, 2016). The colors of the spectrum are called spectral colors (Carlson & Heth, 2010).
Hue, Brightness, and Saturation
The colors determined by the different wavelengths are called hues (Carlson & Heth, 2010). The longer the wavelength, the closer the color gets to red, while the shorter the wavelength, the closer the color gets to violet (Griggs, 2016). Amplitude, on the other hand, pertains to the number of photons of light per unit of time. The more photons that strike your retina per unit of time, the brighter the light seems to you. The amplitude thus determines the level of brightness, or intensity of light being perceived (Carlson & Heth, 2010). The more photons a wave has, the brighter the light, indicating brighter colors. The smaller the amplitude, the fewer the number of photons striking the retina, and thus the duller the intensity of the colors (Griggs, 2016). It is also important to note that color can either be pure of mixed. The level of purity of a perceived color is the saturation of the color. A color that consists of only one wavelength would be a pure color (Carlson & Heth, 2010). Every different wavelength is a different color, but it takes more than a one wavelength difference for us to recognize a different color. For these color mixtures the light has photons with different wavelengths.
Remember in a previous lesson we talked about transduction. Transduction is the conversion process that occurs as sensory information is converted from physical energy to neural signals that are transmitted to the brain in a way that it can understand. The transduction process is how light energy is converted to neural messages the brain can process. The transduction process takes place in the retina. The retina is a thin, light sensitive layer of the eye located toward the back of the eye. The retina contains three cell layers, the ganglion cells, the bipolar, and the receptor. When the light waves enter the retina, they first pass through the ganglion and bipolar cells on their way to the receptor cells. The receptor cells are comprised of the rods and cones, where visual processing and transduction begins (Griggs, 2016). Once the information is transduced, the neural signals are sent to the bipolar cells, which, in turn send them to the ganglion cells. The ganglion cells are responsible for moving neural information on to the optic nerve.
The rods process dim light and colorless, or achromatic, visual information. The cones process bright light and visual information containing color. There are many more rods (around 120 million) than cones (around 6 million) in the retina, which means rods outnumber cones by about 20:1. Cones are located toward the center of the retina in the fovea, which makes sense since this would be where bright light is processed. The rods, on the other hand, are located on either side of the fovea in the periphery of the retina. The cones produce a clearer image of the visual stimulus because they are located on a more direct route to bipolar and ganglion cells as they process the information. So how do rods and cones impact how we perceive color?
The easy answer would be that rods do not process color, yet that is not completely true. Research indicates that rods, which do not process color perceptions, do show a greater sensitivity to blue and green wavelengths. This means that in the dim light of night, blue or green would show up brighter in our visual perception than yellow or red. Have you noticed that more emergency vehicles have added blue lights? It is because the rods, which process the dim light of night, are better able to pick up this light. So, even though rods do not necessarily process color perceptions, they are sensitive to the brightness of certain colors over others. Cones, on the other hand process yellows as brightest. Think about how many fire departments have changed the color of fire trucks from red to yellow. It was due to the perceived brightness during the day as the cones process the yellow color (Coon & Mitterer, 2015).
Color and the Cones in the Retina: Trichromatic Theory
Thomas Young initially, and then Hermann von Helmholtz subsequently proposed that there are three different cones that react to three different colors of light (Griggs, 2016; King, 2012). This is the basis of trichromatic theory. The three cones correspond to short, medium, and long wavelengths, and involve just three wavelengths of light: blue, green, and red. Based on this theory, there are only the three colors, and all other colors we perceive are mixtures occurring based on different proportions of activity by each of the three cones. When all three cones are active at the same level, color would be perceived as white. It is also important to note that with this theory, black and white would be processed by the rods rather than the cones (Coon & Mitterer, 2015). This makes sense because in dim light, most of our world appears as either black or white. Watch this Ted Talk about how we see color: How We See Color.
Open file: Transcript
When these three colors of light, called primary colors, are directly mixed together, it is called an additive mixture. With an additive mixture, all of the wavelengths of light from a visual stimulus are processed in the retina and our brains process them so that we experience one color of light. On the other side of this, if some wavelengths are absorbed before they reach retina, they are subtracted from the mixture, resulting in a subtractive mixture (Griggs, 2016).
Early television screens were based on trichromatic theory, using red, green, and blue dots. Broadcasts were designed to activate the three types of cones using these dots.
Research does seem to agree that there are actually three types of cones, each of which contains photopigments that seem to respond selectively to red, green, or blue wavelengths. Yet, this theory does not completely explain some aspects of color. Red-green and blue-yellow wavelength pairs are considered complementary colors because when the pairs are added together the produce white. This negates the ability to create additive mixtures of red and green or blue and yellow. If we cannot produce these colors, then every color cannot be an additive mixture based on the three primary colors, as trichromatic theory proposes (Griggs, 2016).
Another interesting point is that when we stare at a red object for a period of time, and then look away at a white sheet of paper, we see green (Griggs, 2016). This also works with yellow and blue. When you stare at one color, and then look away to a white sheet of paper, you will see the other color as an afterimage. Afterimages are the visual perceptions that occur after you finish looking at something like when you stare at a light and then look away (Coon & Mitterer, 2015). The afterimage is the spot of light you still see even though you are no longer looking at the light. When we look at an image containing one complementary color, and then look away to a white page, we see the other color in the complementary set. This is a concept called complementary-color afterimage.
The trichromatic theory of color vision does not explain complementary color processes. Yet, as you can see from the flag, complementary colors do have an influence in how we perceive color. So, what does explain this? Lets look at another theory.
Opponent Process Theory
The opponent process theory has a different take on complementary colors. Opponent process theory proposes that we have three opponent-process systems that include red-green, blue-yellow, and black-white color combinations that come into effect after the cones have processed color information. This theory as it proposes that when one of the opponent colors is stimulated, the opposing color is inhibited. Research has indicated that some of each of the following types of cells seem to respond based on opposing colors ganglion cells, thalamus cells, and visual cortex cells (Griggs, 2016). Again, cells involved in color processing after the cones.
This theory would explain why the complementary pairs in trichromatic theory are not additive and do not appear as combinations of one another. With opponent-process theory, only one of the colors would be stimulated at a time because the other would be inhibited. So, instead of red and green adding together in color perception processing, either red of green would be processed, and the other color in the pair would be inhibited. Now, this processing of one color over the other can be tiring for the system processing this color. So, when you stare at the green and yellow flag, the visual systems processing green and yellow can become fatigued, and need the opportunity to rest the neural components involved in sending that signal (Griggs, 2016). Remember, you were looking at it for at least 30 seconds, and it was processing that entire time, meaning the same neural signal was firing along neuronal networks and needs to rest.
On the other side of this, the opposing colors of red and blue have been inhibited from sending their specific signals. Thus, as the stimulated colors fatigue their processing systems while you stare, the opposing inhibited colors have not been taxing their processing systems. This is based on the rebound effect, in which the retinal ganglion cells that were inhibited fire faster, and the formerly excited cells fire slower (Carlson & Heth, 2010). When you look away from the green and yellow flag, the afterimage is dominated by the opposing inhibited colors because their systems are rested and ready to go. Remember that both opposing colors are competing for processing at the same time, so even if you are looking at something green, red is still trying to process too. When you look away from green, reds take the opportunity to take over with the afterimage.
Which Theory Fits Better? A Look at Composite Theory
As we have seen, both trichromatic and opponent process theories have some supporting research. So, how do we determine which theory is a better fit to explain color perceptual processing? It is possible that both trichromatic theory and opponent-process theory have merit. Composite theory proposes that, based on trichromatic theory, color information is processed by the cones, but, like opponent-process theory, after the cones send their signals, color information is processed by cells beyond the receptor cell level, including ganglion, thalamic, and cortical cells (Griggs, 2016). Processing occurs on a few levels that include components of both theories. So, trichromatic theory explains what happens as the light waves are processed in the eye, and opponent-process theory explains what happens once the eye is finished processing the information and it moves through the rest of the systems as the information travels to the brain (Coon & Mitterer, 2015). Of course, this is all rather simplistic since we tend to have more complex experiences with color.
Think about the rainbow you see after the rain. You are looking at all of the colors of the spectrum at once and they each appear separate, yet create a total picture. If you removed one of the colors, the entire perception would alter based on that change. This means that the perceived color of a stimulus is influenced by the colors of other stimuli in the same visual field (Coon & Mitterer, 2015). This is called simultaneous color contrast. This adjustment is the result of brain cell activity in different parts of the cortex, with one area registering the field of colored objects, and sending that information on. When a color adjustment comes in, it creates a domino effect, causing color perception of the field of objects to adjust. When even one of the colors of the objects in the field change, the color perception of all of the objects in the field changes. This occurs as the brain processes the information, sometimes adding colors that are not there (Coon & Mitterer, 2015). Now, what happens when the brain does not accurately recognize colors?
TYPES OF COLOR BLINDNESS
ISHIHARA COLOR TEST
The perception of color is not an accurate process at any point, as you can see from all we have looked at so far. But, what happens when the color pigments are not recognized as color pigments? Someone who is colorblind is unable to perceive color, and instead views the world in black and white (Coon & Mitterer, 2015). As we discussed earlier, black and white are processed in the rods, while color is processed in the cones. Thus, if someone who is colorblind is able to see black and white but not color, the issues would lie in the cones. When colorblindness occurs in an individual, it is because they either do not have any cones, or the cones are not functioning correctly. Fortunately, total colorblindness in very rare. More people experience color weakness, which is a partial form of colorblindness in which an individual is unable to perceive some colors (Coon & MItterer, 2015).
Color seems like such a straightforward concept. A rainbow shows us spectral colors across the sky. We recognize the names of these colors and enjoy the beautiful view. Yet, there is a lot that goes into this process starting with the wavelengths of light that are transmitted through the visual processing systems on their way to the brain as they are identified and perceived. Different theories cover different areas of the color perception processing system. Some cannot perceive all of the colors of the rainbow accurately, and a few cannot perceive the colors of the rainbow at all.
Carlson, N. R., Miller, H. L., Heth, D. S., Donahoe, J. W., & Martin, G. N. (2010). Psychology: The science of behavior (7th ed.). Boston, MA: Allyn & Bacon.
Coon, D., & Mitterer, J. O. (2015). Introduction to psychology: Gateways to mind and behavior (14th ed.). Boston, MA: Cengage Learning.
Griggs, R. A. (2016). Psychology: A concise introduction (5th ed.). New York, NY: Worth Publishers.
King, L. A. (2012). The science of psychology modules (2nd ed.). New York, NY: McGraw-Hill Companies, Inc.
A rainbow over a mountain and a lake by https://pixabay.com/en/rainbow-canim-lake-british-columbia-142701/.
Different colored pencils together by https://pixabay.com/en/colour-pencils-color-paint-draw-450621/.
A drawing that shows the difference between saturation, hue, and lightness by https://earthobservatory.nasa.gov/blogs/elegantfigures/files/2013/08/hsl_diagram_618.png.
A close up of rods and cones in the eye by By Helga Kolb Adapted from Photoreceptors by Helga Kolb http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=61447752.
Mixed colors of light by 27328481.
Complementary color example, using clothes pins. Yellow and purple, white and black, orange and blue and red and green. by By Robertgombos Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=58981707.
Colored circles with numbers using different colored dots to test color blindness. The circle on the left shows the red and green dots. The circle on the left is in black and white to show what a color blind person might see by By Dan-yell Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=33501972.