The perception of color - Research Paper Example

The Perception of Color The Development of Color Vision in human beings, and the eye itself, is a remarkable evolutionary process. The human eye itself did not develop in a linear straightforward manner. It most likely began as a light sensitive pigment on smaller creatures and then became more differentiated creating light sensitive structures that began to be dispersed inside of a the forming eyeball to become the retina. At first the retina was most likely a movement sensor but over time the ability to delineate details and the ability to see color was developed. (Gordon) The evolution of the eye is a standard development in all vertebrates as well as many non-vertebrate species as well. See the figure below: Figure 1: (Evolution of the Eye 2008) But what exactly is color? Color and light go together and are inseparable companions. One object can emit light and another object can reflect that light. The former is usually undergoing some chemical reactions that create color and is dependent on the material it is combusting for the color spectrum it emits, objects such as the sun, or a light bulb for example. The latter objects which reflect light are a combination of the color range of light hitting their surfaces and the reflective properties of their surfaces. For instance, the leaves of most trees reflect green light because of the chemical chlorophyll, which fuels photosynthesis, however they are also designed to absorb the spectrum of red light which activates the chemical reaction turning carbon dioxide into breathable oxygen. There is also a considerable variance of color by the perceiving entity. There is a wide variety in the range of vision across many different organisms, largely dependent of possible evolutionary and ecological needs. This ranges from seeing only in black and white to an even broader distinction of colors than humans possess. for instance, the ability to see into infra-red or ultraviolet wavelengths “… color is a heterogeneous collection of perceptual concepts generated from wavelength-sensitive data for a variety of specialized purpossess by cognitive systems with different neuro-computational structures and evolutionary histories.” (Matthen 186) Humans possess what is known as trichromatic vision. Tri (three) and Chroma (color). Our human eyes have three color receptors that are individually sensitive to red, green, and blue light . While dcecptively simple these three receptors allow humans to distinguish about 2.3 million different varieties of colors. (Kleiner 12) The following figure is a photoreceptor nerve grouping: Figure 2: Photoreceptor Grouping (Farndon 57) There are two types of light-sensing cells: (1) rods, which are used in most low light situations and distinguish between differing shades of grey and the three kinds of (2) cones, that are sensitive to the color spectrum to the particular wavelength of light as described previously. (Savage) Humans actually perceive quite a very narrow range of the electromagnetic spectrum, from 400 to 700 nanometers. Figure 3: Electromagnetic Range of Human Vision, Rods & Cones (Color Vision A) Trichromatic vision is actually a bit of a rarity when you consider a species wide analysis of all organisms that have optic nerves and eye, even just among the mammals only a few possess trichromatic vision. When comparing dichromatic species, those who perceive only the blue and red zone of the spectrum, with trichromatic species there is no apparent Darwinian direct line of descent. (Matthen) The following figure is a simplistic rendition of this concept: Figure 4: Divergence of color perception over time (History of biological Evolution 2007) Why develop this extra range of color vision, or for that matter why develop color vision at all? Some researchers believe that a declining sense of smell in came hand in hand with the rise in color vision. This newly developed perception allowed those species with color vision to detect edible fruit from greater distances thus improving their change for survival, and pass on the evolutionary trait/mutation. (Kliener) There are other slightly different variations on this theme: In a new wrinkle on this evolutionary mystery, Dominy and Lucas of the University of Hong Kong have recently challenged the dogma that trichromacy evolved for detecting ripe fruits. They argue that this color vision instead helped our primate ancestors find tender red leaves bursting with nutritional value. (Travis 235) However, it must be noted that the use of color has evolved in many organisms for a variety of purposes, perhaps coinciding with the ability to perceive it. It is used as sexual attractors by many species, as well as indication that this is poisonous do not eat it, as well as various other uses. (Savage) Does that mean the trichromates (those with tri-color vision) have a greater advantage over dichromates (those with two-color vision)? An experiment was conducted with new world monkeys, one species with dichromatic vision and the other with trichromatic vision. The trichromates were able to distinguish much riper fruit, with more available energy for their systems, than their dichromate counterparts. "The main finding is that trichromacy confers an advantage when selecting ripe fruits from those at various stages of maturity. This is the first time such an advantage has been demonstrated for primates using naturalistic stimuli." (Travis 236) Why do all species with similar retinal and eye-brain structure not possess full color vision? It would seem from it humble beginnings as a motion detector and limited photoreceptor that they eye should have developed in more of a straight line fashion. However, color vision appears to have evolved in a rather haphazard manner with a good deal of variation among the species. For instance, even though birds have trichromatic vision they use a completely different kind fo chemical to detect the color red. (Travis) One possible explanation is the evolutionary theory of the Principle of Divergence. This hypothesizes that a new species may arise from a sub-population of species which has developed a specialization, such as color vision. This allows it to survive and perhaps overwhelm the original species to the point of extinction since it is taking more of the available resources from it. (Matthen). While theorists vary on the exact origin and need for color vision, it seems to have filled some ecological niche, but it apparently is not an advantage for all species to possess it, only for a select few. Works Cited “The Evolution of the Eye” ScienceDaily.com (2008) 26 Mar 2008 http://www.sciencedaily.com/articles/plants_animals/evolution/3/ Farndon, John. “Color Vision.” Human Body; 2003, p57 Gordon, Ian E. Theories of Visual Perception. Hove, England: Psychology Press, 2004. “The History of Biological Evolutional and Devolution” Nikon (2007) 26 Mar 2008 http://www.nikon.co.jp/main/eng/feelnikon/discovery/light/chap05/sec01.htm Kleiner, Kurt “What We Gave Up For Color Vision.” New Scientist; (2004) 181 p.12 Matthen, Mohan. Seeing, Doing, and Knowing: A Philosophical Theory of Sense Perception. Oxford, England: Oxford University Press, 2005. Savage, Candace. “In Living Color.” Canadian Geographic (1998) Annual First Edition 118. P.47 Travis, John. “Visionary Research.” Science News; (2003) 164 p. 234-236 Read More