Critique of Animal Psychology Research at the University
of California at Berkeley
Brandon P. Reines, D.V.M.
Color perception research: Dr. Russel DeValois
Funded largely by the National Eye Institute, DeValois has received $1,458,989 in tax dollars since 1958. DeValois has drilled holes in the skulls of macaque monkeys in order to attach a specialized helmet known as a "stereotaxic device" (although currently he glues the device to the skull). Then, for a period of 44 straight hours per monkey, DeValois threads an electrode through the device into individual cells in the brain called neurons. He then shines different colors of light into the monkey's eyes and records electrical impulses from individual neurons. DeValois explored the region of the brain known as the lateral geniculate nucleus (LGN) in his early studies, and he is now monitoring the region known as the striate cortex. DeValois has, used approximately 15 macaque monkeys and 10 cats per year in his research.
The goal of this research has been experiments to answer the question:
How do human beings perceive color? This has been the subject of psychological investigation for more than a century. Long before DeValois began his animal research, two major theories of the mechanism of color perception existed. In 1801, Thomas Young proposed the "Trichromatic Theory" (1801). In essence, Young maintained that there are three types of receptor in the retina: red-sensitive, green-sensitive, and blue-sensitive. Each receptor type inputs information through a distinct pathway to the brain. Young imagined that there are separate neural pathways for red, green, and blue.
Based on his knowledge that virtually any color can be created by mixing some combination of red, green, and blue, Young postulated that the three colors are mixed somewhere in the nervous system to create the actual color of the object. The other major theory is the "Opponent Theory" of Karl E. Hering, a 19th-century psychophysicist. By performing simple psychological tests with human subjects, Hering (1874) deduced that human beings perceive different colors by matrixing input signals into pairs: black-white, yellow-blue, and red-green. He held that black is antagonistic to white, yellow to blue, and red to green. According to Hering, input from the retinal receptors would be "sorted out" by a neural system of "opponent color pairs" before reaching the cortex.
Apparently in an effort to clear up the confusion surrounding the "mechanism of color vision" in human beings, DeValois began his studies of macaque monkey vision in the 1950's. In particular, DeValois used micro-electrodes to record electrical activity in single neurons of the lateral geniculate nucleus (LGN), part of the "visual pathway" in the macaque. DeValois (1958) found that there are three types of neurons in the LGN of the macaque: "On" neurons, "On-Off' neurons, and "Off' neurons. Each designation refers to whether or not the neuron type responds to light. "On" neurons always "fire" in response to light; "Off' neurons never "fire" in response to light; and "On-Off' neurons may or may not "fire" depending upon the wavelength of light, and are known as "opponent cells." Such opponent cells occur in antagonistic red-green, yellow-blue, and black-white pairs.
DeValois' results were hailed in the popular science media as providing the first genuine insight into the mechanism of human color vision (Wright 1969, p. 3). Of course, DeValois' conclusion that the mechanism of color vision is a system of opponent pairs of neurons was really just a slight modification of Hering's theory. Though many modern psychologists undoubtedly believe that the opponent theory was first espoused by DeValois, one psychologist recently pointed out the fact that researchers such as DeValois probably would have "missed" the on-off nature of certain LGN neurons without the guidance of Hering's theory, which was actually based on psychological studies of humans:
...in color vision, the notion of an opponent process coding system came out of psychology, in particular phenomenology and psychophysics (Hering's studies with human subjects). The physiological realization of neural systems behaving in accordance with opponent-process principles occurred over 75 years after they were first suggested, and only after neurophysiologists had begun to take the opponent-process model seriously and thus to look for units with both excitatory and inhibitory responses to different wavelengths. It is very easy to miss an inhibitory response if one is not looking for it. (Rozin, 1976, p. 8).
While the popular science press proclaimed that DeValois had provided the first real "proof' of Hering's theory, in reality, DeValois' results could be used to buttress either of the two major theories of color vision. The existence of "On" cells could be used to support Young's theory, and the existence of "On-Off' cells could be used to support Hering's theory. In many of his publications, DeValois claimed that his findings support Hering's theories (see, for example, DeValois, 1960, p.153), but in other documents he contended that his results support Young:
Our results from the on-cells provide a certain amount of support for a Young-Helmholtz type of theory, as opposed to a Hering-type opponent-color theory, in that it is clear that there are channels up to the cortex for response to just single wave-length bands (DeValois, 1959, p. 640).
Not only has DeValois' monkey research failed to help resolve the controversy over mechanisms of color vision in human beings, it has not brought medical science any closer to a solution for human color blindness. Ironically, while neurophysiologists such as DeValois have failed to provide sufficient insight into the problem of color blindness to remedy the condition, molecular biologists may have the answer. Researchers at the Stanford University School of Medicine have found the defective gene that apparently underlies red-green blindness, the most common form of human color blindness. Even with this knowledge, which may be the biggest advance in the understanding of color blindness of this century, investigator Jeremy Nathans concedes that molecular biology will not lead to a cure for color blindness - nor does Nathans believe that color blindness is sufficiently debilitating to warrant treatment. He commented, "There's no reason to treat it - it's not at all a serious clinical disorder. Besides, I think having some variation in the gene pooi is a good idea (Stephenson, 1986, p. 24)."
Clearly, DeValois' research on color vision in the macaque monkey could be eliminated without endangering the health and welfare of the American public, which foots the bill for his research.
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