I am a physicist, with a specialty in optics, so I was especially interested in The Mind’s Eye, by Oliver Sacks (not to mention the less well known The Island of the Colorblind). The Mind’s Eye is a fascinating book about the visual system, many of the things that can go wrong with it, and what we learn from them. It is also the book in which Dr. Sacks reveals that he suffers from prosopagnosia, or face blindness; is not a surgeon because he cannot visualize; and functions only with great difficulty now that he has monocular vision as a result of a retinal cancer. I have great difficulty recognizing faces, but nothing approaching prosopagnosia, and it is a marvel to me that he could cover it up for the better part of 80 years.
Dr. Sacks claims to have had a very acute stereoscopy and even belongs to a Stereoscopy Society. When he lost the vision in one eye, he obviously lost stereo vision, but he also completely lost depth perception. I find that extremely peculiar, because most of us, as far as I know, can walk around with one eye closed and still see depth as a result of what you might call psychological cues; we do not bump into door jambs just because we have a patch over one eye. Indeed, I always walk around an art museum with a program to cover my weaker eye: When I look at a painting, the stereoscopy I get due to having binocular vision tells me that the painting is flat; when I cover one eye, that clue is absent, and the painting pops into life, almost as if I were seeing in stereo. (I would have called it “cyclopean stereo,” because it is what I see with one eye, but that term seems to mean something else. Let us call it “monocular stereo.” Learning it takes only a few minutes practice.)
What is odd is that, unlike Dr. Sacks, I have always had very poor stereoscopy. Then, when I was perhaps 65 years old, I developed a slight diplopia, or double vision, due to a membrane growing on my retina. I visited an optometrist for perhaps 6 months or a year and did a battery of eye exercises during that time and for several years thereafter. One day, while I was still seeing the optometrist, I looked out my window and noticed that everything popped into stereo – for the first time, the leaves in the foreground stood out from the house in the background as they never had before. I have since acquired a smidge of macular degeneration, so the diplopia is not so important, and I stopped doing the exercises a few years ago. I am looking out my window right now, however, and the enhanced stereoscopy remains. I still walk around art museums with one eye covered, but I do not think that the monocular stereo effect has changed.
The surprise to me, though, was that my brain was plastic enough to acquire stereo vision after 60-odd years of not having it. I now consider it a miracle that I could play tennis at all.
I billed this as a meditation, not a book review, but I have to say: Read the book! You may find the section about the ocular cancer a little overlong, but otherwise I thought it was typically, Sacksianly fascinating. The only question is why I waited so long to read it.