A Googler showed me an optical illusion, and another Googler commented that they weren't fooled by it because they didn't have stereo vision.  This caused me to look into stereo vision (depth perception, seenig things in 3D).

I experience the following, which makes me think that I might be partially stereoblind (some studies estimate that 5-10% of people are stereoblind):

  • I have more or less the same perception of depth when I have one eye closed as when I have both eyes open.
  • I have more or less the same perception of depth when watching a 2D movie as when I am experiencing real 3D things.
  • When watching a well-made 3D movie (eg, Avatar or some of the OK Go 3D videos on YouTube), I experience a sense of depth and fullness that I normally don't experience either with 2D movies or in real life.
  • Sometimes, if I squint in just the right way and stare at something really hard, I begin to see a depth to it.

It hard to describe because, often, when people talk about stereo vision, they simplify the discussion to just the perception of distance.  I do have a fairly decent perception of distance, but I suspect that most of it comes from 2D inferrences rather than stereo vision (since I can also tell how far something is from me with one eye closed), much like how you can tell how far things are when watching a 2D movie even though you don't benefit from stereo vision there.  

I brought up the issue with a friend, and I discovered that he thinks of stereo vision differently.  Try looking at something in the distance.  Now, put a hand a couple inches in front of your face so that it blocks one eye's vision of the thing you're looking at but the other eye can still see it.  You should see your hand superimposed over the thing you're looking at.  I see superimposed images in some rare occurrences like that or like when I look far off to one side and can see my nose, but my friend sees most things like that.  One of his eyes is weaker than the other, and when he wears glasses (which he usually doesn't), he doesn't experience the same superimposition.  That makes me think that he might be partly stereoblind due to amblyopia (lazy eye), which is sometimes correctible.

I am interested in getting more perspectives on this.  How do you experience depth?  Am I stereoblind?