Meagan L. Anderson
Stephen F. Austin State University
The planet Earth is covered with many colors, both natural and man-made. The human perception of color is more frequently discussed than the actual visible radiation. This may be due to the emotional link that humans have to their perceptions of colors (Color and Acuity, 1998). Artists who use certain colors to depict particular emotions, and the new field of study, which has recently developed, connecting colors to emotional meanings both show this link. Most everyone has a favorite color with which they identify themselves. Color is therefore not only a prominent part of human vision, but is an important part of emotion.
Although some animals are not capable of color perception (as found through scientific study), the ability to discriminate between colors serves an important function to those who are (Williams & Hogan, 1994). Humans use color as a means to separate and organize the environment (Goldstein, 2002). For example, when cooking meat, the percentage of red or pink in the center allows the chef to determine when it has been cooked thoroughly. Also, when shopping for fresh fruit, the color sends a signal as to the readiness of the pieces. Even picking out a white bloom on a green plant requires color vision. Some animals must rely on their ability to discriminate colors in order to hunt, spot predators, or gather fruit. They may also use color to indicate sexual availability, which aides in reproduction (Color Experience, 2001). Though humans may rely on color for certain activities, other animals use it to escape being captured by prey, and perpetuate life through reproduction. This is why evolution is thought to be responsible for color vision. The animals with color vision were better suited to survive, as well as seek out mates, and pass on their genes.
According to Hartmann, Dobson, and Hainline (2000), about five percent of humans do not have normal color vision. Females are much less likely to have any type of color-deficiency due to its genetic properties. Color deficiency in humans is the inability to perceive some of the colors in the normal spectrum of vision for humans (Goldstein, 2002). People who have a color-deficiency have the ability to adapt to their environment, much the same way other animals are expected to adapt, although certain tasks, such as picking out objects against a textured background (with one eye only), will always be more difficult (Corn & Webne, 2001).
The most common form of color-deficiency is red-green deficiency, which is often indicated by the inability to discriminate between the two (Effective Color Contrast, 2002). The two forms of red-green deficiencies are protanopia and deuteranopia (Goldstein, 2002). For people with deficient color vision, particular color schemes are easier to look at and use (Merchant, 2000). An example of a particularly difficult set-up is a green object on a red background. This color scheme is thought to be difficult for humans as well as dogs.
Popular belief about the color vision of dogs was that they had none, and were therefore colorblind (What Do Dogs, 1998). Total colorblindness indicates that their entire world would be shades of gray. Now, many researchers believe that dogs are able to see very similarly to an average human deuteranope (Color and Acuity, 1998). It is therefore assumed that dogs also lack the red cone type. Dogs have excellent night vision, and therefore they have a large number of rods. In order to have room for so many rods, they have fewer cones, which sacrifices color vision. This allows them to be better adapted for their lifestyles. This also backs up the theory that evolution caused color vision or a lack of it. When looked at, dogs' central retinas only contain twenty-percent cones, leaving the other eighty-percent to be rods (used for dim lighting). The central retinas, or fovea, of humans are made up entirely of cones. This would explain why humans can see colors better, but lack the night vision that dogs possess (Performance Descriptors, 2000).
Many tests have been run in order to determine what colors dogs can see, but no information was found on the ability to differentiate between shades of the same color. In the following experiment, the dogs' ability to discriminate colors will be more closely tested. It is expected that the dogs will be able to choose more accurately between shades of blue and yellow than shades of red and green.
All of the participants will be randomly selected dogs of various breeds and combinations of breeds from no-kill adoption agencies. There will be both male and female dogs of varying ages. They will receive extra treats, play time, and affection after each testing session, regardless of ability to cooperate with the experimenter. No dog will be withheld any of the former due to an inability to participate.
There will be nine 12" by 12" squares of cardboard. Three of them will be white, three will be gray, and the remaining three will be black. Also, twenty-four small fish bowls will contain water with food coloring of different concentrations (to create different shades of colors). In previous research, many different stimuli have been used, but these will be used because of availability. Dog treats will be used in order to reinforce correct behaviors during training. Tennis balls will also be used as reinforcement, by allowing the dogs to play with them at the end of the trials.
Each dog will undergo preliminary training with the experimenter(s), in which they will learn to touch the odd-colored stimuli with their noses. The initial stimuli will be the cardboard squares. They will be presented in groups of three, with two of them matching in color. The odd-colored square must not be put in the same place every time. A dog treat will be placed under the square that does not match. Upon nosing the correct square, the dog will receive the treat. Once the dog begins to make the correct selection on the first time for each trial, the experimenter should hold the treats and hand feed them to the dog for further correct choices. If the dog fails to make the transition to the new form of reinforcement, the training will start over. On the other hand, if the dog makes the change well, then the training phase may be ended.
The testing phase will begin by using the water stimuli, which will consist of two bowls with identical concentrations of coloring, and one of a different concentration. This will create a setup in which three stimuli will be presented, with one being different. The dogs will be tested for shades of blue, green, yellow, and red. Records should be kept for which color combinations they accurately discriminate as well as those they do not. Each color combination should be tested, and treats should be given after each trial in which a correct response is made.
This will be a two-factor within-subjects design. The levels of the first independent variable will be the colors (blue, red, yellow, and green). The second IV will be the shade of the colors with four levels (5, 10, 15, or 20 drops of fodd coloring in 8 oz. of water). The dependent variable will be the ability to detect the stimuli that differ in color. The ability to discriminate will count as a correct answer, while the inability will be shown as an incorrect answer.
The data that will be collected will be based on a correct or incorrect response for each trial. The results of the within-subjects experiment should support the hypothesis that dogs can discriminate between shades of blue and yellow with much better accuracy than they can with red and green. The results will be submitted to a two- factor within-subjects ANOVA. A main effect for color is expected, with blue and yellow being easier to discriminate. No main effect is expected for shade. An interaction effect is expected in that the darker shades of the yello w and blue lead to slightly better accuracy. The color(s) which has(have) the highest rate of correct responses will be assumed to be easier for dogs to discriminate between.
The results of this experiment should provide a clear evaluation of dogs' ability to discriminate between shades of colors. This experiment should also have results that are consistent with the color spectrum shown on Dr. P's Dog Training (1998). Because studies such as the ones on the Dr. P's web site have found that dogs see in shades of blue, yellow, grey, and white, it would be reasonable to assume that they could therefore discriminate between shades of these colors much better than other colors.
The hypothesis and experiment assumes that the dogs have normal vision for canine standards. It is however, important to remember that dogs have vision problems unique to the individual. For example, rod-cone degeneration occurs in some genetically predetermined dogs. Kommonen, Kylma, Karhunen, Dawson, and Penn (1997) state that this impairs the visual acuity as well as color perception. This type of problem would be a factor in skewed results, but due to the participant pool, these types of problems are not tested for.
The results of this experiment should lead to further experimentation into the shades of blue and yellow that are most easily seen or discriminated. This research could benefit dog owners, veterinarians, as well as breeders.
Color and Acuity Differences between Dogs and Humans. (1998). Dr. P's Dog Training: Vision in Dogs & People. Retrieved March 2, 2002 from: http://www.uwsp.edu/psych/dog/LA/davis2.htm
Color Experience and the Human Animal. (2001). AIC Color '01 Rochester. Retrieved March 3, 2002 from: http://www.iscc.org/aic2001/abstracts/symposium/What_is_Color/Hardin.doc
Corn,E., & Webne,S. (2001). Visual impairments and what they mean for participation in activities. Journal of Visual Impairments & Blindness, 95(2), 110-118.
Effective Color Contrast: Designing for People with Partial Sight and Color Deficiencies. (2002). Lighthouse International. Retrieved March 4, 2002 from: http://www.lighthouse.org/color_contrast.htm.
Goldstein, E. Bruce. (2002). Sensation and Perception. Pacific Grove, California: Wadsworth.
Hartmann, E., Dobson, V., & Hainline, L. (2000). Preschool vision screening: summary of a task force report. Pediatrics, 106, 1105-1112.
Kommonen, B., Kylma, T., Karhunen, U., Dawson, W., & Penn, J. (1997). Impaired retinal function in young Labrador retriever dogs heterozygous for late onset rod-cone degeneration. Vision Research, 37 (3), 365-370.
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