Eyes on the Brain

A neurobiologist explores the amazing capacity of the brain to rewire itself at any age

What Do Astronauts and Cross-Eyed People Share in Common?

What do Astronauts and Cross-Eyed People Share in Common?

 

Between 1992 and 2005, my husband Dan was a NASA astronaut and flew on the Space Shuttle three times. When he returned from his first trip to outer space, I realized that his experience in microgravity and my experience with crossed eyes shared something in common.

Dan will tell you that gravity is a real drag. He loved being in the free fall of outer space where there is no "up" or "down," He could float about in the Space Shuttle and fly like Superman from module to module on the International Space Station. Right after his return to earth after his first flight, our daughter Jenny, who was ten years old at the time, decided to do her science fair project on her dad's re-adaptation to earth's gravity. She had him close his eyes and point straight upward, a task that most of us can do easily, but Dan raised his arm and pointed about thirty degrees from the vertical. If he tried to balance on one foot with his eyes closed, he immediately fell over. And when he tried to walk, blindfolded, in a straight line, he veered off at a thirty degree angle and crashed into a bookcase.

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What had happened to our space hero? Had his ability to balance and judge direction degenerated while he was in space? In fact, Dan's skills had not deteriorated; instead, he had adapted to a radically new environment, one that is never experienced on earth. (Despite what you might have read or seen in the movies, there are no such thing as anti-gravity rooms.)

For all of us to move through the world, our sensory systems have to work together. For example, when you move your head downward, your visual systems tells you that your head has moved down because the visual world appears to move upward. Sensors in your neck also report the downward motion of your head as do gravity sensors in your inner ear. In the microgravity of spaceflight however, Dan experienced conflicting information from these three sensory systems. While his eyes and neck sensors reported the downward movement of his head, the gravity sensors in his inner ear did not. To cope, Dan, like all orbiting astronauts, learned to ignore the confusing information from the inner ear. In this way, he maintained a coherent, unitary perception of his environment. Experiences like his teach us that people can adapt to totally new environments, even unearthly ones.

So what does all this have to do with crossed eyes? When I was an infant, my two eyes were pointed in different directions. If I looked at you with my right eye, my left eye turned in and vice versa. So, my two eyes saw different things and presented conflicting input to my brain. I suffered from double vision. In order to gain a single view of the world, I learned to ignore or suppress the input from one eye. Now I had a single view of the world, but I did not see in 3D.

Both Dan and I found ways to adapt to our particular situations. Since information from our sensory organs conflicted, we had to suppress some information in order to perceive the world as single and whole. Adaptations such as these are helpful under some circumstances but not others. When Dan returned to earth, the information from his inner ear no longer conflicted with his other senses and, within three days, he paid attention to the gravity sensors in his inner ear again. When, through optometric vision therapy with a developmental optometrist, I learned to aim my two eyes simultaneously at the same point in space, the information from my two eyes no longer conflicted so I no longer suppressed the input from one or the other eye. For the first time in my life, I began to see in 3D. Our brains, even as adults, are in a dynamic state, constantly learning and adjusting to the environment around us.

(I describe the changes in my vision and the vision therapy that brought about these changes in my just published book, Fixing My Gaze.)

Susan R. Barry, Ph.D., is a professor of neurobiology in the Department of Biological Sciences at Mount Holyoke College and the author of Fixing My Gaze (June, 2009).

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