"Did you see Avatar? Could you see the 3D?"
Since I was cross-eyed and stereoblind until I underwent optometric vision therapy at age 48, my friends keep asking me this question. Yes, I saw Avatar, and I saw all the 3D. What I particularly liked was the way the forest appeared to recede far into the distance and the way the seeds of the Tree of Life floated forward in the space between me and the movie screen. Those seeds reminded me of the lovely comb jellies or "sea walnuts" that inhabit the waters around Woods Hole, MA in late summer. 
Sea walnuts are bioluminescent so at night while swimming you can see them floating at different distances in the dark waters around you.
I was curious about other people's reaction to Avatar in 3D. Did they feel any of the sensations I experienced when first seeing in stereo? My friends, particularly those who saw Avatar in IMAX, described an enhanced sense of immersion while watching the film, a feeling of being surrounded by the movie scene. A sense of immersion is one of the most powerful effects of being able to see in 3D. That's why I was very pleased when Oliver Sacks ended "Stereo Sue," his story about me, with my description of seeing a snowfall in stereo for the first time: how I felt myself in the midst of the snowfall and was completely mesmerized by the enveloping snow.
While watching Avatar, the movie screen appears to transform into an open window because objects or people on the screen seem to come out toward you or recede into the distance. I see a similar view when looking through a real window now. In my stereoblind years, any scene framed by a window or mirror always appeared at the plane of the frame. Now with stereovision, when looking out a window, I see the pockets of space between the window pane and the trees outside. I was very startled the first time I looked in a mirror and noticed my own reflection not at the plane of the mirror but some distance behind it. I finally understood the phrase, "Through the Looking Glass."
Recently, I had an email conversation with Almont Green, a talented 3D photographer who writes a fascinating blog. After watching Avatar, Almont Green wrote that "things looked eerily more sharply defined at the edges," and this effect lasted about 30 minutes. As I wrote to Almont Green, an enhanced sense of stereo depth provides an enhanced sense of edges and borders. Watching the movie may tune up the stereo system. I see this same sharpening effect after practicing vision therapy each day.
However, not everyone is delighted with 3D movies. Some complain of headaches or general feelings of discomfort. Headaches may result from the effort necessary to position the eyes for 3D movie viewing, but there may be additional reasons. 3D movies challenge our spatial relationship to the things around us. Although people and objects in the movie appear to float forward or back, you can't actually reach out and touch those movie figures. What you see contradicts the information you're getting from other sensory systems. When we feel a disconnect between our senses, we need to re-interpret where we and other things are in space, and this confusion may induce bodily discomforts.
I became very well aware of this while going through optometric vision therapy. As I gained stereovision and also a much better awareness of my visual periphery, I developed a new spatial connection with everything around me. In my stereoblind years, I could infer distance and depth from monocular cues (perspective, shadows etc.), but this was very different from feeling myself in a volume of space with solid, space-filling objects all around me. While practicing vision therapy procedures, I know when my spatial sense is transforming because I might feel a twinge of nausea, slightly sweaty, or even a tremor in my right hand. We experience many of the same feelings with motion sickness, another situation in which our spatial sense is disrupted.
Why should a change in our spatial sense bring on such visceral reactions? Our sense of ourselves is rooted in our understanding of where our bodies end and the rest of the world begins and in our interpretation of where we are located relative to everything else in space. If we disturb our spatial sense, not only do we upset our sense of security and our ability to move, but we also challenge a fundamental aspect of our identity.
(Comb jelly photo: http://www.aquariumofpacific.org/images/olc/1_comb.jpg)
(Teaser photo: http://jennyleewilliams.files.wordpress.com/2009/11/1950s-3d-movi...)
