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?

BARRY: While an infant brain rewires itself in response to many strong stimuli, an adult brain changes largely in response to stimuli that are behaviorally relevant. These ideas became clear to me when I underwent optometric vision therapy. 

I did not use my eyes in the way that people with normal vision do. Since my former way of seeing - looking with one eye and turning in the other - allowed me to move about with reasonable accuracy, my visual habits became entrenched. Optometric vision therapy made me aware of how I used my two eyes and then provided me with tasks that could be completed only if I consciously changed my viewing habits. Only then did I learn to aim the two eyes simultaneously at the same point in space. This new ability then promoted changes in brain circuitry which led to the ability to see in 3D. Since this new way of looking provided me with a more efficient and more informative way of seeing, these changes became automatic. 

My experience, as well as that of several others also described in my book, have taught me that you cannot understand brain plasticity by studying brain circuits in isolation from the whole person. To rewire your adult brain, to rehabilitate yourself, you need to understand how you interact and cope with the world, and then put yourself in situations which teach you to perform differently.  If you can learn a better way of negotiating the world, you can change the circuitry in your brain.

LEHRER: In Fixing My Gaze, you describe what happens at a cellular level when we learn something new, be it  seeing in 3-D or learning how to read. What can educators and teachers learn from this new science of learning?

BARRY: Science is revealing what every good teacher already knows. We can change the synapses and wiring in our brain and thus learn new things if we are exposed to and pay attention to novel situations, if we stay motivated, and if we practice. Novel experiences, as well as the anticipation of a reward, stimulate ancient areas of our brain, such as the brainstem and basal forebrain. Activation of these areas liberate powerful neuromodulators, including dopamine and serotonin, onto our cortical neurons and circuits, and these neuromodulators facilitate and strengthen synaptic changes which underlie learning. Practice and repetition are necessary to make these changes long-lasting. Optometric vision therapy provided me with the novel and rewarding experiences that triggered synaptic rewiring in my brain. In fact, I wonder if an infant's brain is so malleable in part because everything is new to them; their neuromodulatory areas must be continually active.