Human Colour Perception
Colour vision is a complicated process, beginning at the retina and ending at the higher cognitive centres of the brain. In this essay, I try to take a look at the various levels of this processing, from the retina and then moving stepwise to higher level processing. It is important to note that processing of the visual image does not start at the level of the primary visual cortex, but much lower down - at the level of the retina, where initial modifications of the visual scene enable the cortex to better process what is being seen. The retina is not just the analogue of the film within a camera. It is also a processing station within itself.
However, the real true analysis of the colour of the visual scene only begins within the association areas of the visual cortex, namely but not selectively Area V4. It is here that colour is in fact separated from wavelength, and this process is further enhanced within Area V8. The phenomenon of colour vision is greatly challenged in the condition of cerebral achromatopsia, where the patient sees the world in shades of grey. However, the fact that the patient can detect isoluminant chromatic borders has challenged the way in which we understand colour processing within the brain, and has complicated (but rendered further interesting) our theories about the subject.
Mark A. Fiorentino
Physiology Long Essay
University of Malta
(1997 - 1999)
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