Friday, June 30, 2006

Color vision continued: What role do rods play in color vision, if any and how many dimensions/ variables we need.



There is a very descriptive and helpful book eye, brain and vision on Hravard's site and I was going through the chapter on color vision. It is posited there that color blindness occurs if one of the 3 cone pigments are not present and consequently one is not able to distinguish white light from a monochromatic light of certain wavelength. It is also posited that for color vision only 3 types of receptors are required (and are present in the form of 3 types of cones in the retina). Now here is some experimental work that I would like done for this experiment. What happens to someone who lacks the green pigment and who is exposed to light in the wavelength of light between the non-overlapping visual fields of blue cone and red cone. As per the arguments in the book, that should lead to total loss of color (and actual colorblindness as opposed to color-defectiveness for that range of colors) and thus ability to use only rods and thus get a black and white view of world for those wavelengths. Is that really so, as per color blind people with the green cone not present?

The other thought that passed while reading the article is that it uses projection of 3 types of monochromatic light with same intensities as the metaphor of choice while describing how the brain processes color. Unfortunately as we know, the blue color cone does not overlap with red color cones and this metaphor may not be right. Even, with this metaphor it strikes one as to how black is perceived, because the picture that is shown of 7 colors (including white) produced depends on a dim room in which the 3 lights are projected and the rods that would be useful in producing this black color are integral to the experimental setup of demonstrating the tri-color sufficiency of explaining the color vision. I , personally believe that rods do have a role in color perception and color perception may more involve the CMYK model than the RGB. This also brings the 'image formation' metaphor over the 'laser beam' model. Also, at the same time, due to Kline-bottle associations I may even venture forth and propose that in reality 6 types of colors/ color detecting devices may be required to fully apprehend the colors and we may still be in the process of evolving/ detecting such pigments. Maybe the rods themselves of nocturnal animals like wild cats may throw some light. Total armchair speculation!

Interestingly, the author of the above book concedes that Brown color is a bit difficult to explain, though purple can be easily explained or be intuitive. As per this article on color naming universals which references the article Berlin and Kay (1969) published under the title 'Basic Color Terms, their Universality and Evolution'. the brown appears in stage VI of a language evolution, where apparently as per my initial eight fold developmental model, a qualitatively different sort of leap needs to be taken. The original Harvard's book excerpt from "Eye, brain and vision" takes recourse to Herring theory of opponent processes, specifically that of red and yellow mixing to give orange and that when seen through black contrast giving appearance to brown. Thus for brown to be explained,, the 2 extreme edges of blue-yellow dimensions and red-green dimensions have to mix spatially at a point and then this has to be seen in contrast to another extreme of black-white dimension. Seems a complicated explanation and involves taking recourse to brains excitatory and inhibitory processes to provide explanation. I might revisit this later if some more suitable explanations in terms of some other inherent property of cooler like using both the hue, saturation, value and R,G,B model may explain brown. While HSV explains purple (in the sense of it being complement of green and actually lying in the region that sort of make ultra-violet and infra-red meet), it is surprising why it is not one of the words that are found while going from stage V to stage VI of language evolutions.

Endgame: Is CMYK actually CMYKW model, with white of paper acting as background essential for the CMYK to work in reproducing images?

Sphere: Related Content

No comments: