Friday, February 5, 2010

Serious pants: Stereo vision in a single eye

This is several kinds of wonderful -- Paradoxical fusion of two images and depth perception with a squinting eye. In strabismus (squint), where one eye is misaligned so that the centre of the field of view is not focussed on the normal fovea, the part of the retina where it is focussed can become a kind of "pseudo-fovea". The brain develops the connections that compare it with the fovea in the other, correctly-functioning eye, thereby providing stereofusion and depth perception.

These authors found 44 people with intermittent strabismus; in the affected eye they had a normal fovea and also a pseudo-fovea off to the side. Their stereo vision worked by 'normal retinal correspondence' with the normal eye when they weren't squinting or 'anomalous retinal correspondence' when they were.

So far so good. But what these 44 patients have also developed -- and this seems quite unfair -- is the neural wiring that can compare the images from the fovea and the pseudo-fovea of the same eye. In other words, if the normal eye was blindfolded and a pair of random-dot hidden-picture images was shown to the squinty eye so that one was focussed onto the fovea and the other onto the pseudo-fovea, they could see the 3D image.*

Indeed the human brain is a wonderful thing, as ZRM has been saying for yonks.

* Ramachandran encountered a similar case in 1994 -- if the fovea of the affected eye saw one texture and the pseudo-fovea saw a differen texture, the patient had 'monocular rivalry' between them, like the normal binocular rivalry between eyes.

UPDATE: in comments, tigris proposes that 'fauxvea' would be a better term than 'pseudo-fovea'.
If she's so smart, why doesn't she HAVE HER OWN BLOG?

19 comments:

ckc (not kc) said...

...and it's all shot to shit when you've had a few too many double scotches

Smut Clyde said...

That gives me an idea for how to spend the rest of Saturday afternoon.

ckc (not kc) said...

...enjoy your Saturday - we'll use what's left of it when it gets here

zombie rotten mcdonald said...

ckc, if you were thinking more clearly, you might use what's left of the scotch when it gets here.

mikey said...

Oddly, I'm spending my friday evening doing the same thing.

Post brings to mind one of the most difficult parts of teaching the art of the combat handgun. To wit: Getting people to keep both eyes open. They are conditioned to look across the sights with one eye closed and the dominant eye squinted. Needless to say, whatever contribution this makes to accuracy is more than offset by it's negative impact on vision and situational awareness.

It was another area where women were just that much better than men. They didn't grow up squinting over toy and pretend guns, so whatever conditioning they might have was much easier to drill out.

ckc (not kc) said...

if I were thinking more clearly...
(there's never anything left of the scotch...damned antipodeans)

Another Kiwi said...

Oh yeah, we should leave our Scotch lying around for greedy Northerners to drink. HAH!!!

M. Bouffant said...

Just 'cause your sun is over the yard-arm sooner & you get a drinking jump on us is no excuse for not sharing.

Stay out of our bourbon, too.

Smut Clyde said...

so whatever conditioning they might have was much easier to drill out.

This sounds best in a sinister German accent, like Laurence Olivier's character in Marathon Man.

Smut Clyde said...

I heard that Another Kiwi keeps his scotch concealed inside a ceramic Lileks bong. Word to the wise.

ckc (not kc) said...

...much easier to drill out

...my contractor (usually accompanied by "don't know what they were thinking putting that in that way!"

(German accent optional)

ckc (not kc) said...

close parentheses also optional (but absence much appreciated by nit-picking, double-scotch consuming intermittent strabismi [I made that up])

mikey said...

Shit.

Too much salt in the goddam salad.

Scotch is a two edged sword...

tigris said...

I demand a rigorous set of retinal training exercises because now my life seems incomplete. And instead of trotting out all the syllables to say "pseudo-fovea" why didn't they just say "fauxvia?" Scientists, hmph.

Smut Clyde said...

why didn't they just say "fauxvia?"
I would have written 'fauxvia' except, Oh look, something shiny!

zombie rotten mcdonald said...

Just 'cause your sun is over the yard-arm

Another artificial constraint that's been conditioned into people, and must be drilled out.

I'll get the hammer drill.....


Wv is fearbulk, which seems to be very pertinent in 2010.

Another Kiwi said...

I don't even have a fucking yard arm!
Unless it's a type of evil robot arm, I got one of them. It has Hadrosaur pelvic blood on it...

tigris said...

Yeah, my arm's only around 30". I shall remain mute on whether it has been involved in fucking.

tigris said...

By around 30" meaning approximately 30" long, not 30" around. Sorry if I frightened anyone.