Get a Headache Watching Avatar in 3D?

I saw it in 3D.  The visual effect was indeed stunning.   I'm not sure if it is heightened awareness associated with Avatar's market presence, but suddenly, headaches are being reported as a common side effect.  Understanding how the brain sees and interprets depth may shed some light on why.

 

First, it helps to know that the brain uses many clues to interpret depth, besides the classic "3D sensation" that these movies evoke. They including things like the familiar size of objects that we know, the relative size of objects seen together, relative speed (motion parallax), color and luminance cues (distant objects have less contrast), accommodative (near focus) cues, and eye alignment clues, among others.  The brain takes all visual cues and integrate them into "vision," including the sensation we take for granted as depth.

The "3D sensation" evoked in the recent spate of 3D movies is based on the phenomenon we call stereopsis.  The brain uses distance parallax clues (ie, from which angle does each eye see the object) for this special sensation and is considered the highest form of visual processing, or "binocular vision."  The technologies that stimulate your stereopsis typically offer your brain a false sense of parallax, but don't often address the many other clues we use to sense depth.  Our natural visual system is overwhelmingly complex. Vision is a sensation that arises from such an impressive array of processing layers, that duplicating it perfectly is currently impossible using artificial means.

If you experienced a headache while watching a 3D movie, it may be due to miscues of your eye-alignment systems.  It may also be due to the high rate of switching vision between right and left eye that happens with the new 3D technology, which appears seamless at 140 cycles per second.  But as far as we know, watching a 3D movie is perfectly harmless and the headache temporary, if it happens to you.   Enjoy the new fascination with 3D entertainment.  It really has improved significantly, Toying with your stereopsis creates a real sense of wonder and appreciation for the genius of vision.