Sue Barry is a neuroscientist at Mount Holyoke College. She's also the author of the newly released book Fixing My Gaze, which tells the story of how Barry, at the age of 48, finally learned to see in 3-D. Mind Matters editor Jonah Lehrer chats with Barry about what a flat world looks like and what her own experience can teach us about brain plasticity and education.
LEHRER: You begin your new book, Fixing My Gaze, by describing the moment you realized that you lacked stereoscopic vision, which underlies the ability to see in 3-D. Could you describe that moment?
BARRY: I was sitting in my college neurobiology class, somewhat bored and distracted, when the professor began to describe experiments done on wall-eyed and cross-eyed cats. He mentioned that vision in these cats had not developed normally and that these animals probably lacked stereovision or the ability to see in 3-D. What's more, these animals could never gain stereovision because this skill developed only during a "critical period" in early life. What was true for cats was also thought to be true for people.
The professor's words jerked me right out of my daydream. I realized that I was like the cats in the scientists' experiments, since I had been cross-eyed since early infancy. Three childhood surgeries made my eyes look normal so I assumed that I saw normally, as well. Yet, I had just learned in class that I lacked a fundamental way of seeing.
After class, I went straight to the college library and read up on stereovision. I searched out and tried every stereovision test I could find and flunked them all. This is how I learned that I was stereoblind.
LEHRER: How did you regain 3-D vision at the age of 48?
BARRY: Even though I had three childhood surgeries to "correct" my crossed eyes, I still did not see in 3-D. After the operations, my eyes looked cosmetically straight but they were still slightly misaligned. The conflicting input coming into my brain from my crossed eyes not only prevented stereovision but also gave me an unstable gaze. I rapidly switched my view between my two misaligned eyes so that my view of the world was jittery especially when I looked in the distance.
In my late forties, I consulted a developmental optometrist who prescribed for me a program of optometric vision therapy designed to stabilize my gaze. Since I was cross-eyed, I looked at visual targets with one eye and turned in the other. The vision therapy procedures provided me with the feedback I needed to know where in space each eye was looking. With this feedback, I learned to aim the two eyes at the same location in space at the same time and, to my astonishment, began to see in 3D. Further therapy taught me how to integrate my new 3D views with my former ways of judging depth and distance.
LEHRER: What was it like to see the world in 3-D? Could you describe your first reactions?
BARRY: Many people tell me that the world looks about the same to them whether they look with one eye or with two. They don't think stereovision is all that important. What they don't realize is that their brain is using a lifetime of past visual experiences to fill in the missing stereo information. Seeing in 3-D provides a fundamentally different way of seeing and interpreting the world than seeing with one eye. When I began to see in stereo, it came as an enormous surprise and a great gift.
For the first time, I could see the volumes of space between different tree branches, and I liked immersing myself in those inviting pockets of space. As I walk about, leaves, pine needles, and flowers, - even light fixtures and ceiling pipes - seem to float on a medium more substantial than air. Snow no longer appears to fall in one plane slightly in front of me. Now, the snowflakes envelope me, floating by in layers and layers of depth. It's been seven years since I gained stereovision, but ordinary views like these still fill me with a deep sense of wonder and joy.
LEHRER: Scientists used to assume that the adult brain was a relatively fixed organ. What can your experience teach us about the plasticity of the brain?