Ординатура / Офтальмология / Английские материалы / Fixing My Gaze_Barry, Sacks_2010

FIGURE 7.6: Atmospheric perspective creates a sense of distance. (© Malcolm Feinstein)

Due to the scattering of light as a result of the atmosphere, objects seen at a distance appear hazier than those in the foreground. Artists call this cue atmospheric perspective. Malcolm Feinstein, a professional artist who also happens to be my father, created the painting in Figure 7.6. Note how the more distant buildings and spire are painted to appear hazier.

Artists use rules of perspective to evoke a sense of depth. All of us learn through real-life experience that parallel lines, such as those outlining the sides of a long road, appear to converge in the distance. This cue is used often in paintings and illustrations. Take a look at how the use of perspective convincingly suggests depth and distance in the painting in Figure 7.7.

FIGURE 7.7: A road painted in perspective. (© Malcolm

Feinstein)

Since artists can evoke a strong sense of three dimensions on a flat canvas using monocular cues alone, I assumed that these cues were sufficient to provide me with a vivid, three-dimensional view of the world. I used shadows and shadings to discern an object’s shape, object occlusion to know which object was in front of or behind another, and perspective to gain a sense of depth and distance. I didn’t need stereopsis to know that the world was in 3D. Gaining stereovision, I thought, would augment my perception of depth but not change it in any fundamental way. So, I was completely unprepared for my new appreciation of space and for the deep feelings of joy and wonder, the enormous emotional high, that these novel sights gave me. To experience for the first time seeing the most ordinary things in stereo feels like scaling a mountain and witnessing your first mountaintop view. Was I being overly dramatic, completely over-the-top? Had other individuals experienced similar visual transformations and responded with similar feelings? I wanted to discuss my story with other neuroscientists but was afraid that most would either discount my experiences as scientifically impossible or dismiss my reactions to gaining stereovision as exaggerated.

I thought back to Oliver Sacks’s story “Hands” in The Man Who Mistook His Wife for a Hat, a true story about a woman who in her sixties had gained the use of her hands and a new way of perceiving and interacting with the world.

I had met Sacks once, years before at a party, and we had talked briefly about my crossed eyes and my perception of the world without stereovision. So, one evening in December 2004, when my husband and children were involved in a late-night Monopoly game, I retired to a quiet room in our house and composed a long letter to Oliver Sacks. To my relief, Dr. Sacks did not dismiss my account but instead wanted to learn more about my vision change. He came to visit and, a year later, wrote an article, “Stereo Sue,” for The New Yorker magazine. A week after the article’s publication, I was interviewed on National Public Radio. The response to my story—hundreds of e-mails and letters—was incredible. I heard from individuals who, like me, had gained stereovision as adults, and all were more than anxious to tell their stories. I quickly learned that I was not alone, that they too were amazed, overjoyed, and sometimes baffled by their new vision.

When I gained stereopsis, borders and edges around objects appeared much sharper and crisper than ever before. This effect was almost as dramatic as my new sense of space. It is part of the reason I was so intrigued by the view of my family’s coats hanging on the pegs outside my laundry room. An engineer would describe the world before my vision therapy as “low pass filtered,” meaning that sharp edges were softened. In my stereoblind years, borders outlining objects were not well defined, but with no reference for comparison, I had no way of knowing this.

One of the people who wrote to me, Stephanie Willen

Brown, put this very well when she described how objects, large and small, from letters on license plates, to items on her desk, and even to buildings in New York City, seemed sharp and clean after she gained stereovision. This clarity, she wrote, is “everything, everywhere. . . . There are edges to everything!”

Lucas Scully, who had been a patient of Dr. Ruggiero, experienced the same heightened sense of clarity, texture, and depth when, at age four, he received his first pair of bifocals to correct a visual condition called accommodative esotropia. Lucas was farsighted, which forced him to focus his eyes with great intensity to see close objects. When we look close, we not only focus our eyes but also turn them inwards. Since these two processes are coupled, some farsighted children overconverge their eyes when they focus on nearby objects. Bifocals reduce the amount of effort needed to focus and prevent the eyes from turning too far inward. When he wore his bifocals, Lucas’s eyes didn’t overconverge, and his stereopsis improved significantly. A letter his mother wrote to Dr. Ruggiero poignantly describes the effects of the new spectacles on her son’s vision:

I will never forget the first day he wore glasses. Walking out to the car, after seeing his optometrist, Lucas was unusually distracted. I asked him several times to climb up into the truck but instead he squatted down and began running his little fingers along the pavement. My first reaction was to tell him

not to touch. . . . My husband stopped me before I could say a word, and together we watched as Lucas experienced seeing texture for possibly the first time in his life. On the drive home he stared out the window watching the trees pass and at home his exploration continued. He walked around the house touching everything. He traced the grout between tiles with his fingers and spent half an hour looking at spices. He sat on the kitchen floor and pulled out jars of dried spices, held each one up to the light and examined the contents. . . . He went up to his room and took out toys and it was as if they were all brand new. He just kept touching them and turning them, inspecting each tiny detail. And that was just the beginning. . . . Now he walks up to children, introduces himself, and plays all sorts of games. As for coloring and painting, he can’t get enough of it. . .

. He loves puzzles. . . . He is writing. . . . Improving his vision has accelerated his social and cognitive skills. My shy, reclusive, difficult boy has become a curious, adventurous, and happy four-year-old.

Most of my friends and acquaintances who gained stereovision as adults experienced the same wonder that Lucas did when he got his glasses at age four. Rachel Hochman, who as an infant had a cataract of her right eye, expresses these feelings beautifully in an essay entitled “The Green World.” A botanist who could always identify a vast variety of plants, Rachel felt that she truly understood

the forest, even though she didn’t initially have stereovision:

Given names, these plants gained meaning. . . .

These plants emerged from the green carpet and canopy. . . . The day I recognized that the world was no longer a sea of green, but rather a mass of specific individuals colored in olive, emerald, celadon, jade, teal, and chartreuse, brought me great joy. . . . The language of botany provided me with a context for perceptual distinction.

But Rachel was frustrated with her vision. She often squinted with her right eye, felt that there was a void in her vision on the right side, and had a hard time visually tracking objects like a moving ball. After hearing about my story, she embarked on a course of optometric vision therapy with Dr. Hans Lessmann. For the first weeks, Rachel worked tirelessly on tasks that taught her to pay attention to the input from her compromised right eye while her left eye was still open. “Every procedure,” Rachel wrote to me, “required my intense, focused, concentration. I couldn’t work while other people were in the clinic. I couldn’t hold a conversation [while doing the exercises]. I can’t believe how extraordinarily difficult it was for me.” But the effort paid off. After six weeks, Rachel was ready to learn to fuse images from her two eyes.

To teach fusion and the use of stereopsis cues to Rachel, Dr. Lessmann had projected a Polaroid vectogram onto a wall so that images on the vectogram covered most

of Rachel’s visual field. A vectogram consists of two clear Polaroid sheets, each containing a similar image. Figure 7.8 shows the two sheets partially overlapping each other. Each sheet contains an image of a rope circle (also known as a quoit). When the viewer is wearing Polaroid glasses, each eye sees the image on only one of the sheets. To see just one image of the rope circle, he or she must fuse the right-and left-eye views.

When the images of the rope circles were projected onto the wall, they provided such a large target that Rachel was able to fuse the two images. Fusing large images, called peripheral fusion, is an important step in gaining stereopsis because it helps align the eyes and trigger accurate convergence and divergence movements. When Rachel could fuse the two images into one, Dr. Lessmann slid the vectogram sheet seen by the right eye to the left and the vectogram sheet seen by the left eye to the right. Now Rachel’s eyes had to turn in to maintain fusion, to continue seeing just one combined image of the circles. To Rachel’s astonishment, this image of the fused quoits appeared to float forward. If Dr. Lessmann slid the sheets in the opposite direction, then Rachel’s eyes had to diverge to maintain fusion, and the fused quoits appeared to recede. She saw the fused image as being located no longer on the wall but in its own plane with a space, a palpable volume of space, between itself and the wall.

FIGURE 7.8: The quoits Polaroid vectogram. (Photo by James Gehrt)

The very next day, Rachel experienced her first stereo view outside of the doctor’s office. She observed a familiar row of trees that were now completely transformed:

I thought that I could see plants clearly. . . . I thought I knew the forest . . . [but] strolling through a humble plantation of pines, I had an epiphany. I was amongst the trees, not looking out at them. . . . [T]hey surrounded me in a way that was different than I’d previously experienced. The crenulations of bark

and appliqué of moss were deeper, the edges clearer, the colors brighter. . . . Most unusual: the space between the trees was apparent. It was as if I had stepped inside a painting that I had spent my whole life observing. I was awed and moved to tears. I had never experienced a forest in this way. The depth of space and emotion was overwhelming.

Intrigued by Rachel’s description of the large, floating rope circle projected into space, I traveled to Dr. Lessmann’s office in Pittsburgh to try out this technique. Dr. Lessmann projected the rope circle onto the wall while I wore the Polaroid glasses and fused the rightand left-eye images into one.

“Where is the rope circle?” he asked.

“I’m not sure,” I said hesitantly. “I think it’s on the wall.”

Dr. Lessmann handed me a long pole and instructed me to place the tip of the pole in the center of the rope circle so that it touched the wall. I put the tip of the pole in the center of the rope circle, but I couldn’t feel the wall. It was disorienting—an uncanny feeling, much like the sensation you have when you descend a staircase and underestimate the height of a step. The wall seemed to have slipped behind the rope circle. Gingerly, I moved the pole through the image of the rope circle into empty space. Eventually, I hit the wall.

“Give the wall a hard tap,” Dr. Lessmann commanded.