From their subsequent book, published 26 years later, Brain and Visual Perception: The Story of a 25-year Collaboration (OUP), it would seem that this general characterization remains largely the same, in spite of further discoveries of theirs and those made by other researchers, such as Ramachandran.
Understanding of this large and indispensable organ [the brain] is still woefully deficient. This is partly because it is very complex, not only structurally but also in its functions, and partly because neurobiologists' intuitions about the functions have so often been wrong (p. 150).
In the primary visual cortex the map is uncomplicated by breaks and discontinuities except for the remarkable split of the visual world down the exact middle, with the left half projected to the right cerebral cortex and the right half projected to the left cortex (p. 150).
Important as the advances in mapping cortical projections were, they tended for some time to divert thought from the real problem of just how the brain analyzes information. It was as though the representation could be an end in itself instead of serving a more subtle purpose--as though to cater to some little green man who sat inside the head and surveyed the images playing across the cortex. [F]or vision, at least, the world is represented in a far more distorted way; any little green man trying to glean information from the cortical projection would be puzzled indeed (p. 152).
It follows that this [the visual cortex] cannot by any stretch of the imagination be the place where actual perception is enshrined. Whatever these cortical areas are doing, it must be some kind of local analysis of the sensory world. One can only assume that as the information on vision or touch or sound is relayed from one cortical area to the next the map becomes progressively more blurred and the information more abstract (p. 152).
It is important to realize that this part of the cortex [the visual areas] is operating only locally, on bits of the form; how the entire form is analyzed or handled by the brain--how this information is worked on and synthesized at later stages, if indeed it is--is still not known (p. 155).
Saturday, October 16, 2010
Brain Mechanisms of Vision (Hubel & Wiesel)
With the proverbial appeal to authority, it might prove useful at this juncture to review a few key passages from an article entitled "Brain Mechanisms of Vision" written in 1979 by Nobel laureates David Hubel and Torsten Wiesel for Scientific American in a special issue devoted to the brain (Vol. 241, No. 3), two years prior to receiving their Nobel Prize, which they shared with Caltech biologist, Roger Sperry, in 1981: