Colors Beyond Rainbows We usually associate colors with some wavelength in the visible spectrum. However, there are some colors which do not appear in the visible spectrum, and yet we perceive them in our daily lives. This certainly indicates that perception of color is not just an activity of the eye and the brain, but is a product of the mind. Before moving on to the difference between reception and perception of colors, we shall briefly introduce Qualia. What is Qualia? Qualia are the subjective property of conscious experience [1]. In simple terms, it refers to how we experience our world when we are conscious. Examples of qualia include subjective feelings like redness of an object, the smell of flowers etc. The Mind vs the Brain We often say CPU is the brain of the computer, but never refer to CPU as the mind of the computer. That is because brain just refers to hardware part where different processes/mechanisms are going on. It is the mind which experiences, feels things. To illustrate the difference between the functioning of the mind and the brain, here's an apt example[1]. Examine the following 2 pictures: Inside the brain Inside the mind Image Courtesy:http://www.biotele.com/qualia.htm Both represesnts the same information. In the left, the image shows how our brain responds to the different colors/shades in images as different signals, it only stores the information. On the other hand, it is the mind that manipulates and transforms received signals, into the experience of color and shapes. Mind is the place where the signals are transformed into Qualia. Perception of Magenta How does the eye respond to light? Humans are trichromatic[2]. We have three kinds of cone cells L, M, S in our retina which respond selectively to different wavelengths of light. Different colors are perceived due to difference in ratio of activation of these cells. Response of cone cells to various wavelengths of light Image Courtesy:http://www.biotele.com/color_brain.html If two (or more) reasonably separated wavelengths of light strikes our retina, more than one type of cone cells get activated, and the color experienced in the mind (as expected) roughly corresponds to the average of the wavelengths present in the light[3]. For example, if red light and green light are incident, the color perceived in the mind is yellow, which can be seen as an average of red and green, lying halfway between the two in the visible spectrum. How does the mind perceive light? There is inconsistency between wavelength reception and color perception. What we perceive is not always what our retina detects[2]. If we see a yellow light or a combination of red and green light - in both cases brain perceives it to be yellow color. As mentioned above, we simply don't measure the exact frequency/wavelength of the light incident, but rather have three different types of cells, each sensitive to different range of wavelength[4]. In layman's words, the brain receives an (R,G,B) triplet and the mind performs calculations on this, thus resulting in the perception of color. This simple phenomenon has interesting consequences. Unlike the red-green case mentioned above, when our eyes receives wavelengths from the two ends of the visible spectrum (i.e. red and violet light), instead of summing the input responses to produce a color halfway between red and violet in the spectrum (i.e. ~ green), it invents a new color (Magenta)[3]. Magenta=Red+Blue Image Courtesy:http://www.biotele.com/magenta.html In order to account for the gap between the two extreme ends, our mind constructs magenta, which in reality, does not exist in the visible spectrum[3][4]. The light spectrum Image Courtesy:http://www.kollewin.com/blog/electromagnetic-spectrum/ Scientifically speaking, the visible spectrum is linear , but psychologically we end up thinking of it as a circular color space. This circular color space can be directly attributed to the fact that we receive (R,G,B) triplets in our mind, and not the exact wavelength of incident light. The color loop perceived by the mind Image Courtesy:http://www.regruntled.com/category/color.html Magenta is the complementary color of green. All the colors in the light spectrum have complements that exist within the spectrum - except green[3]. An obvious question : Do we all perceive the same color? In an experiment to study the human retina, David Williams and his team[5] used a disk which could be tuned to obtain different shades of yellow. Each person was asked to tune the disk frequency for pure yellow color as per his perception. Each person selected almost the same frequency, which showed that 3everyone perceived the same wavelength as yellow. However, the distribution of cone cells in the retina varied greatly. Though 1the discrepancy was more than a 40:1 ratio, all the participants were apparently perceiving the same wavelength as yellow color. "Those early experiments showed that everyone we tested has the same color experience despite this really profound difference in the front-end of their visual system", says Heidi Hofer, a member of the research team. This strengthens our belief that the surrounding environment influences our perception of color. Since all of us have been living in the same environment, our perception of colors is the same, to a large extent, even though the mechanisms going on in the brain might vary. Conclusion The perception of magenta is a strong evidence in favor of Qualia. Besides this, many other experiments have shown that though the eyes and the brain are responsible for reception of signals, its the mind that perceives color. For example, in a related experiment[5], subjects were asked to 2wear colored contacts for four hours a day. It was observed, after short while, their eyes got "tuned" to this change, and once again they could perceive colors normally, 1as if they were not wearing the contacts. References [1]http://www.biotele.com/qualia.htm (Retrieved on July 26, 2010) What is Qualia : A brief and easy-to-follow introduction to Qualia [2]http://www.biotele.com/color_brain.html (Retrieved on July 26, 2010) Colour, is it in the brain? : A detailed description of how we receive color, perceive color, and why what we receive is not quite what our mind perceives. However, it does not talk about the perception of magenta in specific. [3]http://www.biotele.com/magenta.html (Retrieved on July 26, 2010) Magenta aint a color : This page gives a general (though not very detailed) introduction to the perception of magenta, and is pretty much self-contained as far as the perception of magenta goes. [4]http://forgetomori.com/2009/science/magenta-and-all-the-colors-of-the-grey-matter/ (Retrieved on July 26, 2010) Magenta and all the colors of grey matter : A detailed description of how we perceive color in general, and also addresses the magenta perception phenomenon in detail. [5] University of Rochester (2005, October 26). Color Perception Is Not In The Eye Of The Beholder: It's In The Brain. ScienceDaily. Retrieved on July 26, 2010 from http://www.sciencedaily.com/releases/2005/10/051026082313.htm This is an excellent reference to some experimental studies performed by a research team at the University of Rochester. These experiments reveal a lot about the retina and its functioning, and also talk about perception of color.