Posted: June 14, 2006
In the June 19 New Yorkerarticle "Stereo Sue" by neurologist Oliver Sacks, Stereo Sue refers to Sue Barry, associate professor of biological sciences, and her story of gaining binocular and stereoscopic vision--essentially the ability to see in three dimensions--after living most of her life without it. Sue developed strabismus, or cross-eyes, in early infancy, and although she had vision in each eye, her eyes didn't work together. She had surgeries when she was a child to align her eyes cosmetically, but her eyes were not well enough aligned to allow her visual system to merge the images from the two eyes into one image seen in depth. As a result, she supressed the images from one eye or the other at any given time.
Sacks writes: "[Sue] no longer looked cross-eyed to a casual observer, but she was half aware that her eyes were still not working together, that there was still something amiss, though she could not specify what it was. 'No one mentioned to me that I lacked binocular vision, and I remained happily ignorant of the fact until I was a junior in college,'" [Sue] wrote [in a letter to Sacks]. Then she took a course in neurophysiology.
In the class, Sue learned that she saw the world as flatter than most people. "I went to the library and struggled through the scientific papers," Sue wrote to Sacks. "I tried every stereo vision test that I could find and flunked them all. I even learned that one was supposed to see a three-dimensional image through the View-Master, the toy stereo viewer that I had been given after my third operation. I found the old toy in my parents' home, but could not see a three-dimensional image with it. Everyone else who tried the toy could."
Sue was told by doctors that there was no therapy that could help her gain stereoscopy. Sue accepted this advice since scientific experiments done in the 1960s indicated that there is a critical period during the first year of life for binocular vision. If binocular vision does not develop during this period, then it can never develop. So when Sue began having increased vision problems 25 years later and consulted an optometrist, it was to everyone's surprise that Sue began to see things differently after just a few vision therapy sessions. "I noticed today that the light fixture that hangs down from our kitchen ceiling looks different," Sue wrote. "It seems to occupy some space between myself and the ceiling. … I went back to my car and happened to glance at the steering wheel. It had 'popped out' from the dashboard. …"
Sue then wrote the letter to Sacks, a neurologist and author who has written several books about his patients' experiences adapting to various neurological diseases and conditions and whom Sue had once met. Since Sue could not find any other stories like her own and everything she read said it was impossible to achieve stereoscopy in adult life, she asked Sacks what he thought of it all.
In 2005, Sacks, along with some of his colleagues, visited Sue twice, performing a number of tests on her and learning about her vision history to try to find out what Sue could see before and after the therapy. They learned that the therapy helped Sue align the images coming from her two eyes and taught her to stop suppressing the image coming from one eye or the other so that the two images could be fused into one image seen in depth. They also met with Sue's optometrist, Theresa Ruggiero. According to Sacks, "Dr. Ruggiero herself was greatly surprised, she said, when, immediately after achieving flat fusion [merging the images from both eyes together], Sue experienced stereoscopy. She speculated that Sue must have had some binocular vision and stereoscopy, even if very briefly, during the critical childhood period, or it would not have been possible for her to have stereo vision now." However, most individuals with Sue's condition, i.e., strabismus, do have a small area of fusion in their visual field, so many others may be able to achieve stereoscopy in adult life.
Sue still does challenging therapy exercises for at least 20 minutes every day. According to Sacks, "Whatever its neurological basis, the augmentation of Sue's visual world has effectively granted her an added sense, a circumstance that the rest of us can scarcely imagine. For her, stereopsis continues to have a quality of revelation."
Sacks quotes from the letter Sue wrote in which she talks about seeing snowfall for the first time in stereo vision: "I could see the space between each flake, and all the flakes together produced a beautiful three-dimensional dance. In the past, the snow would have appeared to fall in a flat sheet in one plane slightly in front of me. I would have felt like I was looking in on the snowfall. But now, I felt myself within the snowfall, among the snowflakes. Lunch forgotten, I watched the snow fall for several minutes, and, as I watched, I was overcome with a deep sense of joy. A snowfall can be quite beautiful--especially when you see it for the first time."