Ramachandran, V.S., “Phantoms in the Brain”

William Morrow and Company, 1998, ISBN 0-688-15247-3

Book Review by Paul Harris

I saw this one while browsing in the Barnes and Noble as well.  I recognized the name right away.  Dr. Ramachandran was a guest speaker at one of the COVD annual meetings in the past and I was not only very informative but was very entertaining.  Most of his work as been in dealing with phantom limb problems and elucidating those neurological mechanisms whereby this occurs.  He uses his vast clinical experience with many phantom limb patients to educate us about various aspects of brain function many of which impact on our understanding of vision and the visual process.  His writing style is very easy to read and he has quite sense of humor that comes across throughout the book.  What follows are a few quotes that I found interesting:

 

(Page 56) The brain’s connections are extraordinarily labile and dynamic.  Perceptions emerge as a result of reverberations of signals between different levels of the sensory hierarchy, indeed even across different senses.  The fact that visual input can eliminate the spasm of a nonexistent arm and then erase the associated memory of pain vividly illustrates how extensive and profound these interactions can be.

 

 To me this also adds weight to our assertions of vision being the dominant process in humans.

 

(Page 59) ….the single most important principle underlying all of perception – that the mechanisms of perception are mainly involved in extracting statistical correlations from the world to create a model that is temporarily useful.

 

Within each of us we build a representation of reality.  By its very nature it is incomplete.  Here he states what we really do when we sample the world those 4-5 times a second, we are extracting statistical correlations to make that internal representation of reality relevant for problem solving to do the things we do.

 

In talking about the dual neurological pathways between the eyes and the brain he made a distinction that goes well beyond the staid “where” and “what” differentiations that I find is very significant.

 

(Page 77) Actually the term “where” pathway is a little misleading because this system specialized in not just “where” – in assigning spatial location to objects – but in all aspects of spatial vision: the ability of organisms to walk around the world, negotiate uneven terrain and avoid bumping into objects or falling into black pits.  It probably enables an animal to determine the direction of a moving target, to judge the distance of approaching or receding objects and to dodge a missile. If you are a primate, it helps you reach out and grab an object with your fingers and thumb.  Indeed, the Canadian psychologist Mel Goodale has suggest that this system should really be called the “vision for action pathway” or the “how pathway” since it seems to be mainly concerned with visually guided movements.

 

Ramachandran takes a good part of the book to talk about how we build our internal representation of reality and how we do it so economically.  He uses the phenomena of “filling in” of the blind spot to demonstrate how this is done.  He states that the filling in of the blind spot is not just something we do for the blind spot but is indicative of processes that are used throughout the field of vision to help us handle the volume of data needed to function in “real time.”

 

(Page 88) It turns out that the human visual system has an astonishing ability to make educated guesses based on the fragmentary and evanescent images dancing in the eyeballs. 

 

(Page 90) Bear in mind that the filling in is not just some odd quirk of the visual system that had evolved for the sole purpose of dealing with the blind spot.  Rather, it appears to be a manifestation of a very general ability to construct surfaces and bridge gaps that might be otherwise distracting in an image – the same ability, in fact, that allows you to see a rabbit behind a picket fence as a complete rabbit, not a sliced-up one.

 

Everything that the visual system does is based on such educated guesswork.

 

(Page 103) One of the most important principles in vision is that it tries to get away with as little processing as it can to get the job done.  To economize on visual processing, the brain takes advantage of statistical regularities in the world – such as the fact that contours are generally continuous or that table surfaces are uniform – and these regularities are captured and wired into the machinery of the visual pathways early in visual processing.

 

(Page 110) …the primary visual cortex, far from being a mere sorting office for information coming in from the retina, is more like a war room where information is constantly being sent back from scouts, enacting all sorts of scenarios, and then information is sent back up again to those same higher areas where the scouts are working.  There’s a dynamic interplay between the brain’s so-called early visual areas and the higher visual centers, culminating in a sort of virtual reality simulation of the cat.

    

Later in the book Ramachandran finally made real for me what “neglect” is really all about and the underlying neurological mechanisms.  The entire explanation is beyond the scope of this “book review” but the following quote should give you a sense of the explanation.

 

(Page 117) We know that the left hemisphere is specialized for many aspects of language and the right hemisphere for emotions and “global” of holistic aspects of sensory processing.  Given its role in holistic aspects of vision, the right hemisphere has a broad “searchlight” of attention that encompasses both the entire left and entire right visual fields.  The left hemisphere, on the other hand, has a much smaller searchlight, which is confined entirely to the right side of the world.  As a result of this odd arrangement, if the left hemisphere is damaged, it loses its searchlight, but the right can compensate because it casts a searchlight on the entire world.  When the right hemisphere is damaged, on the other hand, the global searchlight is gone but the left hemisphere cannot fully compensate for the loss because its searchlight is confined only to the right side.  This would explain why neglect is only seen in patients whose right hemisphere is damaged.

 

And one final quote from this masterful work:

 

(Page 227) Everything I have learned from the intensive study of both normal and patients who have sustained damage to various parts of their brains points to an unsettling notion: that you create your own “reality” from mere fragments of information, that what you “see” is a reliable – but not always accurate – representation of what exists in the world, that you are completely unaware of the vast majority of events going on in your brain.