Biopsychology: Colour Vision Theories - Essay Example

Biopsychology Introduction Colour vision is one of the most important human abilities or other organisms’ abilities which endow them to make their worlds multi-sided and full of colours. Colour vision represents another important component of human lives making people able to live their lives to the fullest extent. A combination of biopsychological factors and mechanisms initiates the process of objects’ distinction based on the wavelengths of the reflected light. These signals reach nervous system through the cone photoreceptors in our eyes (Malacara, 2002). Isaac Newton said: “All colourd Powders do suppress and stop [absorb] in them a very considerable Part of the Light by which they are illuminated. For they become colourd by reflecting the Light of their own Colours more copiously, and that of all other colors more sparingly." (Opticks, Book I, Part II, Experiment 15)   Generally, colour vision is merely a physical ability of an organism or human being. A colour is perceived by the human eye as a combination of different wavelengths. The ability of humans to distinguish colours is an interesting question, which has been discussed by scientists for many years. Thus, a number of theories have been created. These theories will be discussed in the present paper. Trichromatic colour vision theory According to Peter Gouras “color vision is an illusion created by the interactions of billions of neurons in our brain. There is no color in the external world; it is created by neural programs and projected onto the outer world we see. It is intimately linked to the perception of form where color facilitates detecting borders of objects” (Gouras , 1969). There are two main theories explaining the ability of humans to distinguish colours: trichromatic colour vision and opponent process theory. The researches devoted to the development of trichomatic colour vision were initiated in 18th century by Thomas Young. This scientist claimed that human vision is caused by interaction of three different kinds of photoreceptor cells. Later on, claims of this scientist were experimentally proven by Hermann von Helmholtz. Therefore it was proven that a human required 3 wavelengths in order to distinguish all colours. More detailed discussion of this theory requires additional facts. There are 3 kinds of cones in the retina of the eye; each of these 3 cones has various photosensitive pigments. Different kind of pigment is sensitive to different light wavelength. Cones are of three different types: long, medium and small, ranging from 560 nm to 420 nm respectively (Dacey, 2000). Not only has the longitude of the wave of light influenced colour vision, but also intensity of this wave of light. Information about colours read by the brain differs with regard to every type of cone. Cones in their interaction enable brain to perceive colour. This explanation requires additional clarifications: for example, moderate simulations of M cone cell could result from bright red colour’ stimulation, or by yellowish-green light of medium intensity. Cell responses depend on intensity of colour light. A combination of cell responses is another important factor in trichromatic colour vision theory. Peter Gouras states “in order to detect objects by differences in spectral reflectance, two or more different types of cones are needed. This is an important concept for understanding color vision. For divariant color vision, two cone types must exist and be sensitive to different parts of the visible spectrum, preferably as different as possible. The range of the visible spectrum depends on the ability of light to penetrate the eye and be absorbed by the photoreceptors” (Gouras , 1969). It is a well-known fact that each of 3 cone types in the human retina can accumulate nearly one hundred different kinds of gradations. Brain, in its turn, combines these gradations in various manners and thus a human being has an ability to differentiate nearly one mln of different kinds of colour (Mausfeld, 1998). The colour opponent theory An opponent theory also presents an interesting vision. In accordance with the colour opponent theory a process of colour vision interprets signals about colour obtaining it from rods and cones in an opposite manner. According to this theory, there are three types of cones. Their wavelengths overlap on each other and differences between these wavelengths lead to different responses which are easily fixed by each type of cone’s individual response. The secret of opponent theory is rooted in its name: colours are fixed in accordance with “3 opponent channels: red VS green, blue VS yellow and black VS white” (Delahunt, Brainard, 2000). Responses to colours of different channels are in opposition. The difference between two main theories of colour vision is the following: the trichromatic theory detects the process of colour detection by visual system with 3 types of cones by the retina of the eye; the opponent process theory is based on mechanisms that get and process information from cones (Delahunt, Brainard, 2000). There is a theoretical background in accordance with which signals about colours are really obtained from 3 types of cones, but they are processed on a complex level. Biological background of the opponent theory explains this process in accordance with bipolar cells and ganglion cells interaction. The process of information about colour is processed in the following way: information (from cones)–to bipolar cells–information is processed. In this simple manner information is obtained and processed involving both bipolar cells of the retina and cones. Further stage is the information transfer to ganglion cells. There are two classes of this kind of cells: magnocellular class and parvocellular class (P class); large and small-cell layers respectively (Mausfeld, 1998). On the small-cell layer the largest part of information is processed. Two groups of information processing occur at this stage: one group processes “information about differences between firing of L and M cones” (Mausfeld, 1998). Another group process information about differences between S cones and a mutual signal from both L and M cones. Thus the first subtype of cells processes red-green differences; the second subtype processes blue-yellow differences. Information about intensity of colour is transferred by P cells. Visual impairment: colour blindness Unfortunately, some humans are unable to see all range of colours and thus they live a defective life (Kaiser, Boynton, 1996). One kind of such visual impairments is colour blindness. Humans with this physical disorder can’t distinguish some colours which can be distinguished by others. This disorder is caused genetically though it may be caused by eye damages, nervous or brain disorders (Neitz & Neitz, 2000). This illness is named after its developer, John Dalton at the end of eighteenth century. This scientist suffered from colour blindness himself. Colour blindness isn’t considered to be a serious disability; it is generally perceived as a mild disorder. This illness can be inherited or physical factors can cause it. For example, in case of cones’ absence or defect a human doesn’t have an ability to distinguish colours (monochromacy); or absence of retinal cones can lead to achromatopsia (Delahunt, Brainard, 2000). Other forms of colour blindness (dishromacy, protaponia etc) can be caused by absence, damage or malfunction of cone pigments, retinal photoreceptors and other factors. Therefore it is relevant to consider colour blindness in terms of two main theories of colour vision. A detailed discussion of this disorder, more studies and researches on this theme would decrease cases of this illness. Conclusion 1 Colour vision is an integrative part of human lives. The studies and researches in this field are directed on mechanisms of colour’s perception. Detailed discussions of physical, nervous and psychological peculiarities of humans are decisive factors in differentiation of colour vision mechanisms. It is relevant to refer to the most famous colour vision theories in order to explain human ability of colour vision. In accordance with trichromatic theory only 3 types of colour receptors (red, green, blue) are decisive ones. Opponent Process theory makes an emphasis on opposition of one colour receptors’ to others. Nevertheless only 2 colour receptors are distinguished as decisive ones: one for red and green, one for blue and yellow. In the modern science there is a tendency to refer to trichromatic theory in the majority of cases. This theory was chosen because 3 types of retinal receptors absorbed certain band wavelengths distinct for each separate group of receptors. It is also proven that simultaneous interaction of three types of cones can be explained on genetic level: M and L wave curves are rooted in a common gene and their interaction is caused by the X chromosome (Neitz & Neitz, 2000). Though the role of genes is unquestionable in the process of colour vision, other biological, physical and psychological components and activities should be also taken into account. In the majority of cases all these components work for colour vision, but there are visual impairments, like colour blindness, when they can negatively influence on colour vision. Therefore a detailed discussion of colour vision theories and their practical implementation next to innovative researches and studies in this field would benefit both for medicine and society. Works cited 1. Malacara, D. Colour vision and colorimetry: theory and applications. SPIE Press, 2002. 2. Dacey, D. M. (2000) Parallel pathways for spectral coding in primate retina. Annual Review of Neuroscience, 23, 743±75. 3. Delahunt, P. B., Brainard D. H. (2000). Control of chromatic adaptation: Signals from separate cone classes interact. Vision Research, 40, 2885±903. 4. Gouras P (1969) Antidromic stimulataion of orthodromically identified ganglion cells in monkey retina. J Physiol 204:407-419. 5. Kaiser, P. K., Boynton, R. M. (1996) Human Colour Vision, 2nd edn. Washington, DC: Optical Society of America. 6. Mausfeld, R. (1998) Colour perception: From Grassman codes to a dual code for object and illumination colours. In: Backhaus, W. G. K., Kliegl, R., Werner J. S. (Eds.) Colour Vision Perspectives from Different Disciplines. Berlin: Walter de Gruyter, 219±50. 7. Neitz, M., Neitz, J. (2000). Molecular genetics of colour vision and colour vision defects. Archives of Ophthalmology 118, 691±700. 8. Opticks (4th Ed) by Isaac Newton Read More