Cones and Rods
The retina which is found in the human eye has photo-receptors of two type and they are known as rods and cones. The rods are very many and are in the ranges of more than one hundred and twenty millions in a retina. The rods are more sensitive than the cones although they are not color sensitive. The retina contains an estimation of between six and seven million cones and these are color sensitive. The cones are concentrated on the macula, a yellow spot in the center of the retina. In the center of the macula there is a region that does not contain any rods and has very many cones which are very thin and very densely packed. This area is known as fovea centralis (Palmer, 1999).
Evidence that have been got through experiments have suggested the there exists three different color reception types. The response curves of the three categories of color receptors have already been determined. This is because the color perception depends on the three nerve cells firing (Jameson, 2001).
Can all mammals see color?
Almost all mammals have cones and rods in their retinas. This can explain why almost all mammals do experience different light conditions especially dusk, night, dawn and day. Therefore all eyes of mammals have mechanisms that control the amount of light that goes through the eye. This mechanism helps the eyes in adjusting its perception of light so that during the night and dusk as much light as possible goes through the eye and at this time the retina is very sensitive. However, during a bright day, the excess light will spoil the very sensitive retina and hence the mechanisms control the amount of light entering the eye while desensitizing the retina at the same time. In order for the brain to interpret color, the eyes need to have color pigments. This is why some animals have better vision of color than others. The human beings are not the best in color interpretation because some insects can see colors that are invisible to the human eye. Other animals cannot see any color (Palmer, 1999).
Many mammals, fish and birds have the ability to perceive the entire spectrum. Cones are in different flavors and this is determined by the pigment which they contain. Different pigments have different capabilities of detecting colors. Normally human beings have three pigments which include blue, green and red. However, other mammals do not see color as well as human beings do. Scientists argue that mammals may have less pigments than we do or that they have different pigments from us. That is why most mammals cannot see color as human beings can see color. It is important to note that not all human beings have the capability of seeing color as a normal human being. This is because some people have fewer pigments than we do and this subjects them to a sort of blindness in term of color. This condition is known as color-blindness and this means that some people cannot see some colors. These conditions are brought about by people lacking one or two pigments and thus cannot see all the colors as they are supposed to. In the same respect, the reason why other mammals cannot see color as well as we do is because they do not have the three pigments. In fact some mammals have more color pigments than humans (Jameson, 2001).
References
Palmer, S.E. (1999). Vision Science: Photons to Phenomenology, Cambridge, MA: MIT Press. pp 129 – 142.
Jameson, K. A., Highnote, S. M., & Wasserman, L. M. (2001). “Richer Color Experience in Observers with Multiple Photopigment opsin genes.” Psychonomic Bulletin and Review8 (2): 244–261.