Two Eyes, Two Views: Your Brain and Depth Perception

[n2doc]

Insights into the nuances of depth perception provided by our two eyes' slightly different views of the world
By Vilayanur S. Ramachandran and Diane Rogers-Ramachandran

Humans enjoy stereoscopic vision. As we mentioned in our essay last issue, because our eyes are separated horizontally images we see in the two eyes are slightly different and the difference is proportional to the relative depth. The visual areas in the brain measure these differences, and we experience the result as stereo—what we all have enjoyed as children playing with View-Master toys.

Visual-image processing from the eye to the brain happens in stages. Rudimentary features such as the orientation of edges, direction of motion, color, and so on are extracted early on in areas called V1 and V2 before reaching the next stages in the visual-processing hierarchy for a progressively more refined analysis. This stage-by-stage description is a caricature; many pathways go “back” from stage to stage—allowing the brain to play a kind of 20-questions game to arrive at a solution after successive iterations.

Returning to the concept of stereo, we can ask: At what stage is the comparison of the two eyes’ images made? If you are looking at a scene with hundreds of features, how do you know which feature in one eye matches with which feature in the other eye? How do you avoid false matches? Until the correct matching is achieved, you cannot measure differences. In stereopsis, this conundrum is called the correspondence problem.

more:

http://www.scientificamerican.com/article.cfm?id=two-eyes-two-views

[Captain Hilts]

1. It's the 'relative speeds' vision test that most of those who fail vision tests in flight school

fail. It's not just regular vision.

[hunter]

2. My binocular vision is defective, always has been.

:(

3-D movies are no fun at all.

[eppur_se_muova]

3. Have you talked to a specialist about this?

I completely lost my depth perception in my late 20's/early 30's -- not properly diagnosed for a long time, and it made work with my hands very difficult. I found a very good ophthalmologist who referred me to a specialist. Turned out I was repressing the vision in one eye almost completely, as my eyes failed to converge properly due to a large accumulated overcorrection in one eye. Lots of therapeutic exercises with stereoscopic tranaglyphs eventually restored normal depth perception -- completely, as far as I can tell.

http://en.wikipedia.org/wiki/Convergence_insufficiency

http://en.wikipedia.org/wiki/Orthoptist

A book on this topic, which I *must* get around to reading: http://www.powells.com/biblio/1-9781135983994-0

[hunter]

4. Mine's anisometropia.

The odd thing is I never developed the commonly associated amblyopia, where the input from one eye is mostly ignored. Instead I've got one eye that's only slightly nearsighted and useful for seeing things in the medium distance (I can pass the the DMV vision test with that eye) and one nearsighted eye good for reading a newspaper or a computer monitor.

Thus far my presbyopia seems to be progressing in a way that will let me get away with not wearing glasses in most situations, so maybe it's a feature and not a bug... :P

Susan Barry's book looks very interesting. One of my brothers has eyes similar to hers and had the muscle surgeries and all that, but binocular vision still eludes him. I can't even begin to guess what's going on in my head.

Your story is interesting. I suspect their are stages of brain development past puberty. There's no flag that pops up signaling "adulthood" and bringing brain development to a halt. A grandma brain may differ from a mom brain in the same way an adolescent brain differs from a mom brain. During these transitions there could be, perhaps, changes in the visual circuitry where missteps might occur. ***wild speculation, but fun nevertheless***

[eppur_se_muova]

5. Well, you've obviously looked into it pretty thoroughly.

When I first started losing my depth perception I had no idea what was really going on. I was really lucky my opthalmologist knew just the right specialist to refer me to.

[hunter]

6. That must have been really alarming to have your vision change like that.

I never missed what I never had.

The only reason I know anything about my eyes is that I get migraine headaches so wretched I can hardly see anything, which forced me to see specialists in the bad old days before there were effective migraine drugs. (I don't ever go to the doctor unless I have to. These days it's usually my wife telling me I have to!)

I have a regular optometrist because my night vision is not so good for driving. Every year or two we fuss around a bit to get me a prescription that makes me feel more comfortable driving at night without being distracting or disorienting. Thinking about the book you mentioned, I could probably get glasses that corrected my vision 100% and maybe remodel my brain to achieve binocular vision... hmmmmm...