Though he had been weak at mental visualization, now when he looks at something, then closes his eyes, he continues to experience not just an afterimage lasting seconds, but a super-clear "persistence of vision" lasting many minutes, as if he hadn't closed his eyes at all. This signals his brain's slowness to erase, but also that he is developing a powerful ability to visualize. When he closes his eyes and imagines his arms, he now sees them in much more vivid visual detail than before.
But, alas, his tumour returns; then he loses depth perception, his precious "stereo vision," so that his reflection in the mirror no longer seems behind the mirror. He loses peripheral vision on his right, too, so that he is, for practical purposes, blind in his right eye. As of this writing, though not totally blind, if he wishes to go for a walk in his New York neighbourhood, it must be with the help of friends.
This is a deeply moving book, and one can only imagine the duress under which it was written, and yet, as it rises to the concluding essay, The Mind's Eye, one begins to forget that duress as Sacks outlines the surprising range of neuroplastic reorganizations that occur in blindness. There are those, such as U.K. religion professor John Hull, who went blind at 48, and eventually lost not only his visual memories, but also "the very idea of seeing," so that the sense of objects as having appearances vanished. He surrendered to this change "with acquiescence and joy," thinking he had entered a new order. His writing became stronger. His case reminds us that visual imagery is not essential to thought, as many argue.
At another extreme, blind Zoltan Torey, an Australian psychologist, declined switching to a more auditory mode, and uses his freed-up visual cortex to expand his mental eye, making it so vivid that he is able to climb a ladder and replace his entire roof guttering single-handedly. Similarly, Jacques Lusseyran, a French Resistance fighter, though he forgot the face of his mother and stopped caring what people looked like, developed (along with an infallible "nose" for detecting traitors) a vast stage on his mind's eye, filled not with darkness but all the colours of the rainbow. He was capable of giving his walking companions a visual inventory of all they would see that far exceeded what they were able to observe with the naked eye. Which of these developments will occur will depend in part on one's history, and how one trains oneself.
The New York Times has called Sacks "the poet laureate of medicine." Blind poets, such as Homer and Milton, have long been symbols of a special power conferred by blindness, allowing them to see what the sighted can not, and develop superior oral memories that enable them to compose hundreds of pages of verse by recitation. Perhaps, in addition to crediting their talent, we can also credit these powers to their brains' neuroplasticity. When input to the visual cortex - almost half our cortex - is blocked with an absolute blindfold, all that cortical real estate is reallocated, within hours, to processing touch and sound. But now we learn, it can also be neuroplastically reassigned to the mind's eye.
We tend to think of vision as a primary experience that connects us directly with reality, and the mind's eye, and language, as merely reflecting, or describing, reality. But if seeing is our only direct access, then how do we account for the scientific report and EEG study by Helder Bértolo that found congenitally blind people actually see visions in their dreams and can draw them out? And some congenitally blind people, such as Helen Keller, write in a way that "startles one with its brilliantly visual quality."
Sacks concludes with a profound paradoxical question: "If there is a fundamental difference between experience and description, between direct and mediated knowledge of the world, how it is that language can be so powerful? Language, that most human invention, can enable what, in principle should not be possible. It can allow all of us, even the congenitally blind, to see with another person's eyes." Thus can blind poets see, and make us see.
Norman Doidge is a psychiatrist and author of The Brain That Changes Itself. His website is www.normandoidge.com. Copyright © 2010 by Norman Doidge