by Oliver Sacks
My experiences with Stereo Sue and her lyrical delight when she gained stereo vision after a lifetime of stereo blindness reinforced my feeling of appreciation for stereo vision. Indeed, I had spent much of 2004 and 2005 preoccupied with stereo vision, thinking and writing about it, and corresponding with Sue.
And then, in June of 2007, when the melanoma encroached on my fovea and had to be lasered, I lost all the central vision in that eye and, with it, stereoscopy. The complete and sudden flattening of the visual world I had experimented with as a boy by closing one eye now became a permanent condition. Some people have little stereo vision to begin with, or else they make so little use of binocular cues that they scarcely notice the difference if they lose stereoscopy. My situation was very different. Stereoscopy had been a central part of my visual life, and its loss had a profound impact at many levels, from the practical challenges of daily life to the whole concept of “space.” Indeed, these changes were so radical that I was slow to recognize them fully.
Stereoscopy is most important in one’s immediate vicinity, and it was here that I had initial problems of all sorts, some comic and some dangerous. When I reached out my hand for a canapé at a cocktail party, I might find myself grasping at air, missing the mark by six inches or more. I once poured wine into a friend’s lap, missing the glass by almost a foot.
More dangerously, I fail to see steps or curbs, and may trip or come down with a jolt. If there are no shadows or ancillary cues, I see steps only as lines on the ground and have no idea how deep they are, let alone whether they go up or down. Particularly treacherous are those I cannot anticipate, such as a couple of steps in an outdoor plaza or in someone’s sunken living room (often these also lack railings, which can serve as a visual cue). Going down a flight of stairs is a real and sometimes terrifying hazard, and I need to feel my way cautiously, testing for each step with my foot. Sometimes there may be such a compelling sense of flatness to my eye that it competes with what my foot says. Even when every other sense, including common sense, tells me that there is another step, if I cannot see its depth, I hesitate, confounded. After a long pause, I will trust my foot, but the dominating power of vision makes this far from easy.
These experiences (like many others in the past two years) set me to thinking of Edwin Abbott’s classic 1884 book Flatland, where the inhabitants of his two-dimensional world are themselves two-dimensional geometric figures. Occasionally they are confronted by spontaneous changes in the appearance of things which can only be explained, their theorists tell them, if one postulates the existence of three-dimensional objects moving in a three-dimensional space, presenting slices of themselves as they intersect the plane of Flatland. Thus Flatlanders infer the existence of a spatial dimension they cannot see. This is a far-fetched analogy to my own situation, but it always comes to mind when I have to infer depth, despite the at times overwhelming flatness presented to my eye.
Paradoxically, I have lost my fear of heights. I used to feel a sort of frisson, a slight sense of alarm, when I looked down from a tall building to the street below. When I lived in Topanga Canyon, I would avoid getting near the precipitous edges of the winding canyon road. The thought of falling gave me the chills. But now that I have lost depth perception, these feelings have disappeared, and I can look down from great heights with complete indifference.
Occasionally, I have pseudo-stereo experiences, as when something flat, like a newspaper lying on the floor, looks to me as if it is sticking up in the air. Opening my door, I have mistaken my doormat for a table and come to an abrupt, confounded halt. Sometimes I imagine that there may be steps when I see lines on the ground, the edge of a rug, or some other boundary. Does the boundary go with a step, or not? So I have to stop and carefully test with a toe. I rarely experienced such misperceptions when I had both eyes, for stereoscopy serves to clarify and disambiguate situations where monocular cues may be ambiguous or deceiving.
Crossing streets, dealing with steps, just walking around—things that needed no conscious attention before—now require constant care and forethought. People who have spent most of their lives without stereo vision, like Sue, may adapt relatively easily to these challenges, but having been exceptionally and perhaps excessively biased to binocular cues for stereoscopy, I was finding it extremely difficult to function without two eyes.
I wake every morning to a cluttered world, everything on top of everything else. There is no room anywhere, no space between things.
I used to enjoy the tiny light bulbs strung on city trees at Christmas—they seemed to create globes of twinkling lights suspended in midair. Now I see a tree full of such lights as a disk, with no more depth than a sky full of stars. And when I go to the botanic garden, I can no longer gaze, as I once loved to do, at the thick foliage of trees and bushes and see layer after layer, depth upon depth—it is all a flat confusion now.
My reflection in the mirror no longer seems to be behind the mirror; it appears on the same plane as the mirror’s surface. I see spots on my clothes in the mirror and try to brush them off, only to realize that they are spots on the surface of the mirror itself. A similar confusion made me think, one February day, that it was snowing inside the kitchen—“outside” the window seemed no farther away than “inside.”4
While, for the most part, I hate the flatness of everything and lament the loss of depth, I occasionally have a sense of appreciation for my two-dimensional world. Sometimes I see a room, a quiet street, or a laid table as a still life, a beautiful visual composition, as I imagine it might be seen by a painter or a photographer constrained to a flat canvas or film. I find a new pleasure in looking at paintings or photographs, now that I am more conscious of the art of composition. They can be more beautiful in this sense, although they no longer yield me even the illusion of depth.
One afternoon I went to a nearby Japanese restaurant for sushi—one of the attractions of my sidewalk table being the sight of a ginkgo tree across the road. In the middle of the day, at that time of year, the sun’s rays would cast a detailed shadow of the tree and its delicate leaves onto the yellow wall about five feet behind it. But, without stereoscopy, I now saw the tree and its shadow on the same plane, as if both were painted on the wall—a vision both alarming and exquisite, for the 3-D reality had turned into a Japanese painting.
Stereo vision at a distance may be less immediately important, but not being able to judge distance opens me to deep and often absurd doubts and illusions. In Edgar Allan Poe’s story “The Sphinx,” the narrator sees a gigantic jointed creature climbing a faraway hillside; only later does he realize that what he is seeing is a minute insect, practically in front of his nose. I found “The Sphinx” a little far-fetched until I lost stereoscopy. Now I have such experiences constantly. The other day I saw a piece of lint on my glasses and tried to clean it off, only to realize that the “lint” was a leaf on the sidewalk.
It is not just the sense of depth and distance which is undermined but, occasionally, the sense of perspective itself, so crucial to the recognition that one is in a world of solid objects arrayed in space. When I visited a friend’s barn on Long Island, I first failed to recognize it as a barn, for I saw only vertical, horizontal, and diagonal lines, like a geometrical diagram inscribed on the sky. Then, all of a sudden, it acquired perspective and became recognizable as a barn, though still flat, like a photograph or a painting.
My inability to see depth or distance leads me to combine or conflate near and far objects into strange hybrids or chimeras. One day I was puzzled to find a gray web between my fingers, before I realized that I was seeing the gray carpet three feet below—now seen on the same plane as my hands and construed as part of them. I was horrified once, looking at a friend in profile, to notice twigs or slivers of wood coming out of her eyes—but these belonged, I soon realized, to a tree across the road. I spotted a man crossing the road in Union Square, with an enormous scaffolding on his shoulders—he is crazy to be carrying such a thing, I thought—a
nd then I realized that the scaffolding was thirty feet behind him, another conflation. Another time I saw the top of a fire engine apparently impaled on the roof of my car, and then realized that the fire engine was a dozen yards behind the car. But knowing this, or moving my head to demonstrate it by motion parallax, makes strangely little difference to the illusion.
A gigantic pontoon a hundred feet high, spotted at a traffic jam, turns out to be the side-view mirror of a car just in front of me. A woman’s strange green umbrella turns out to be a tree a hundred feet behind her. Most frighteningly, as I was reading in bed one night, I “saw” the ceiling fan about to crash into the reading light just above my head—I “know” that the two objects are at least four feet apart, but this did not prevent the sudden illusion.
Nothing protrudes or recedes from me anymore; there is no direct sensation of “before” or “behind,” only an inference based on occlusion and perspective. Space was once a hospitable, deep realm in which I could locate myself and wander at will. I could enter it, I lived in it, I had a spatial relationship to everything I could see. That sort of space no longer exists for me visually—or mentally.
After two years without stereoscopy, I now function pretty well. I have learned how to shake hands, pour wine, and negotiate steps. I have returned to bicycling and driving my car—these are made possible by motion parallax and the fact that perception is being complemented by action, that I am acting in a three-dimensional world, even though it still looks two-dimensional to me. Most of the time, I can “see through” my illusions and conflations. But this does not alter my sense that a fundamental aspect of the visual world has been taken away and that things will never look as they did before, will never look right. The visual reality I face is utterly wrong—for I know so well how things used to be, and should be.
The only time I see in stereo now is in dreams, for I have had occasional stereo dreams all my life—usually dreams in which I am looking through a stereoscope at an exquisite pair of stereo photographs, perhaps at an urban landscape or the depths of the Grand Canyon. I wake from these to a reality which is incorrigibly, irreversibly, maddeningly flat.
My vision remained in this state, fairly stable, for two years. I was able to do most of the things I wanted—for having peripheral vision in my right eye still allowed me a full visual field, even if it lacked straight-ahead depth. With this peripheral vision, I maintained a small crescent of stereopsis near the bottom of the visual field, and this was important in giving me some implicit or unconscious sense of depth and space, even if there was no stereopsis in the rest of the visual field. But it could be very tantalizing, too, for the region of stereopsis lay below my fixation point, and whenever I tried to focus on something with my one good eye, it immediately flattened out.5
All this was to change on September 27, 2009. The day opened like any other; I had my swim, ate breakfast, and was cleaning my teeth, when it seemed to me that a film came over my right eye. Its peripheral vision, the only vision it still had, was hazy. I wondered if my glasses had misted over, so I took them off and cleaned them—but the film was still there. I could see objects through it, but their outlines were indistinct.
“One of those things,” I thought (although it was unlike anything I had ever experienced before). “It will clear in a few minutes.” But it did not clear. It grew denser and denser. A feeling of fear and danger took hold of me—what was going on? I phoned Dr. Abramson’s office; he was away, but his colleague suggested that I come to the office straightaway. Looking into the eye, Dr. Marr confirmed my suspicion: there was bleeding, probably from the retina, and the blood was now seeping into the vitreous humor at the back of the eye. The cause of the hemorrhage was unclear, but the tumor, irradiation, and repeated laserings might well have scarred the retina, making it more fragile, increasing the chances of a blood vessel being eroded or giving way. There was nothing to be done at this point.
By late afternoon I could not count my own fingers or see anything distinctly with the right eye. I could only sense diffuse illumination from the window and some movement, the way one can see, in bright light, a hand waving in front of the eyes even when the eyelids are closed. The blood would eventually clear, I was told, but this could take six months or more—now, for all practical purposes, my right eye was completely blind.
I could not help thinking of that other day, the day everything started to go wrong, at the end of 2005—and of the nearly four-year fight in which the eye carried on, with ever more of the retina being nibbled at or blasted away. Was this the final knockout blow?
To take my mind off things visual, I went to the piano, closed my eyes, and played for a while. Then, to dull my feelings and prevent rumination, I took two sleeping tablets and went to bed.
I slept deeply. Awakened by my clock radio, I listened with my eyes closed, in that dreamy state between wake and sleep, and it was only when I opened my eyes and saw nothing with the right eye but a vague dim light where the morning sun was flooding in that the memory of what had happened suddenly came back to me.
On Monday morning, Kate came over and suggested that we go for a walk together. As soon as we emerged into the morning bustle of Greenwich Avenue, crowded with people balancing coffee cups and cell phones, people walking dogs, parents with children going to school, I realized that I was in trouble. I was startled, even terrified, because people and objects suddenly seemed to materialize, to loom at me on the right side without any warning. Had Kate not been walking on my right, protecting my blind side, I would have been colliding with everything, tripping over dogs, crashing into strollers, without the least awareness that they were there.
We do not honor our peripheral vision as much as we should, for most of the time we have little explicit consciousness of it. We look, we fixate, we target with our foveas, our central vision. But it is peripheral vision, surrounding this, which gives us a context, a sense of how whatever we are looking at is situated in the wider world. And it is especially movement that peripheral vision is tuned to: peripheral vision alerts us to unexpected movements on either side, and then central vision moves in to target these.
For me, now, a biggish slice of the periphery to my right—forty degrees or more, like a very large slice of cake—has been carved out of my vision. I see, roughly speaking, nothing to the right side of my nose.6 I had lost central vision in the eye earlier, but I still had enough peripheral vision to give me a forewarning, an intimation, of things happening on that side. But now I have lost even this. I have no awareness here, and whatever comes into my visual field from that side is unexpected and startling. I cannot overcome the sense of bewilderment, even shock, when people or objects appear suddenly to my right. A massive slice of space no longer exists for me, and the idea that there could be anything in that space has likewise disappeared.
Neurologists talk of “unilateral neglect” or “hemi-inattention,” but these technical terms do not convey how outlandish such a state can be. Years ago, I had a patient with a startling neglect of her own left side, and the left side of space, due to a stroke in her right parietal lobe.7 But this had not prepared me at all to find myself in a virtually identical situation (though caused, of course, not by a cerebral problem but by an ocular one). This came home even more forcefully when Kate and I finished our walk and headed back to my office. I walked ahead and got into the elevator—but Kate had vanished. I presumed she was talking to the doorman or checking the mail, and waited for her to catch up. Then a voice to my right—her voice—said, “What are we waiting for?” I was dumbfounded—not just that I had failed to see her to my right, but that I had even failed to imagine her being there, because “there” did not exist for me. “Out of sight, out of mind” is literally true in such a situation.
NOVEMBER 9, 2009
Six weeks have passed now since the hemorrhage. I had expected, in time, to accommodate to my semiblindness, my hemispace, but that has not happened. Every time someone or something suddenly appears to my r
ight, it is just as unexpected as the first time. I am still in a world of suddenness and discontinuity, of sudden apparitions and disappearances.8
I can deal with this only by constantly turning my head to monitor what is going on in the blind area. (Indeed, I have to twist my entire upper body around to compensate for the sixty degrees or so I am missing.) But doing this is not only wearisome, it feels absurd, because so far as my own perception is concerned, I have a full visual field—nothing is missing for me, subjectively, and so there is nothing to look for. It may appear odd to other people, too, who feel that I am acting bizarrely, contorting my body or turning around and staring at them.
There are parallel experiences with senses other than vision. If one has a complete spinal anesthesia, for instance, one loses all sensation and power of movement in the lower half of the body. But this description does not do full justice to the strangeness one can encounter. One’s awareness, the sense of one’s body, is sharply terminated, in effect, at the level of the anesthetic, and what lies below is no longer felt as part of oneself, for it is not sending any information to the brain testifying to its own existence. It has disappeared, taking its place, its space with it.
One can, of course, look at one’s “missing” legs, and this is even stranger in a way, for the legs seem curiously unreal, alien—almost like wax models from an anatomy museum. It has been shown, with functional imaging, that the anesthetized parts of the body actually lose their representation in the sensory cortex. So it seems with the right side of my visual field—it no longer sends any signals to the brain, no longer has any representation there. As far as the brain is concerned, it does not exist.
DECEMBER 6, 2009
It is now ten weeks since my hemorrhage, and I have still achieved surprisingly little in the way of accommodation. I must remind myself again and again to check, to make sure that nothing on the blind side is being ignored or forgotten—it is still far from automatic. I wonder if I will ever accommodate, and I think of something one of my correspondents, Stephen Fox, wrote:
