Abstract
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
Intermediate M.D.
Physiology Long Essay
University of Malta
(1997 - 1999)
For further information and complete text, please contact the author, Mark A. Fiorentino at mfiorentino@hotmail.com
