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  #1  
Old 26 May 2007, 05:49 PM
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Vanishing Cave blindness

Comment: I could find no mention of this "cave blindness" syndrome that some guide at
Skyline View Caverns in Virgina told us about. I'm a skeptic. The guide
said that after 3 days in total cave darkness people will go blind
(generic statement I suppose but still). I'm pretty sure some folks have
been rescued from being underground longer than that and sight loss, other
than maybe temporary discomfort, doesn't seem likely or it might have been
more newsworthy in the past.
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  #2  
Old 27 May 2007, 07:16 PM
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Silas Sparkhammer Silas Sparkhammer is offline
 
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Whalephant

I can't address this claim directly, and I suspect it's wrong.

But the subject of visual accomodation is fascinating!

The first time many of us go into a cave, we are "blind"
in the sense that we don't really know what we're looking
at. It is difficult for us to judge distances or directions.
It is all just a weird blur of alien textures.

Given a little time -- a couple of hours goes a long way
toward this -- the brain starts to work it out. We
start to "get it."

There is another famous effect of visual accomodation:
subjects wore goggles that flipped the visual image
vertically, so that they saw the world around them...
upside down. For a while, they were confused and
clumsy -- but soon, their brains started to compensate
for this, and, within a day or two, they could walk and
run normally, and even read books. In fact, after a
few days of this, when they took the goggles off
again, they went through a similar period of adjustment
and confusion!

So: if you or I were lost in a cavern in total darkness
for three days, we would "forget" how to depend on
our eyesight for getting around. Even when we no
longer needed to feel our way with our hands, we
would continue to do so for a while, decause we had
become so dependent on this as our primary physical
sense. We'd be able to see...but would still grope at
walls and furniture and things. (Heh. And people!)

In that way, then, the legend in the OP is "a little
right," while also being (I think) rather a lot wrong.

Silas
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  #3  
Old 28 May 2007, 09:08 PM
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D'oh!

Quote:
Originally Posted by Silas Sparkhammer View Post
There is another famous effect of visual accomodation:
subjects wore goggles that flipped the visual image
vertically, so that they saw the world around them...
upside down. For a while, they were confused and
clumsy -- but soon, their brains started to compensate
for this, and, within a day or two, they could walk and
run normally, and even read books. In fact, after a
few days of this, when they took the goggles off
again, they went through a similar period of adjustment
and confusion!
I remember hearing about this study and thinking it was very interesting - amazing how the brain can readjust inputs to make better sense of the world around us!

To address the OP, I've visited Mammoth Cave several times (born and bred in KY) and have never heard any reference to cave blindness - either through hearsay or from one of the guides on the tours. If I ever get back again (getting older and less limber, you know ) I'll make a point of asking them specifically.
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Old 28 May 2007, 10:13 PM
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There are several well documented cases of people hiding in sewers during the war. One family hid for almost 18 months in almost total darkness. When freed by Russian forces, their sight was normal, although it took several days to get used to sunlight again.
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Old 28 May 2007, 10:25 PM
jimmy101_again jimmy101_again is offline
 
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Another example of "visual accommodation" is the complete inability of a person to see his/her own blind spot, at least under normal circumstances.

Everyone has a blind spot caused by the discontinuity of the retina where the optic nerve passes through the back of the eye. No visual data is sent to the brain from this area of the retina. The brain somehow completely eliminates this gap in the visual field.

In horror / science fiction flicks they always present "what the bug/spider/creature with multifaceted eyes sees" as a collection of identical images (the bug-eye lens). I would think that a creature with multifaceted eyes, or even multiple regular eyes, perceives a single image, exactly like we do.
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  #6  
Old 28 May 2007, 10:33 PM
Troodon Troodon is offline
 
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Quote:
Originally Posted by jimmy101_again View Post
Another example of "visual accommodation" is the complete inability of a person to see his/her own blind spot, at least under normal circumstances.

Everyone has a blind spot caused by the discontinuity of the retina where the optic nerve passes through the back of the eye. No visual data is sent to the brain from this area of the retina. The brain somehow completely eliminates this gap in the visual field.

In horror / science fiction flicks they always present "what the bug/spider/creature with multifaceted eyes sees" as a collection of identical images (the bug-eye lens). I would think that a creature with multifaceted eyes, or even multiple regular eyes, perceives a single image, exactly like we do.
Each facet of a compound eye (bug eye) is not a complete, working eye. It can sense brightness (and perhaps color - I do not know if bugs see in color), and that's it. The actual sensor in each facet is at the bottom of a tube so it receives only the light coming from the direction towards which the eye is oriented. The combined image from all the facets can be imagined as a low-resolution computer screen, with each facet corresponding to a pixel.

Compound eyes are actually an awful design. Eyes with lenses (like the ones we and octopuses have) are far superior, because the lens eliminates the need for long tubes and allows for much higher resolution vision with smaller eyes.
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  #7  
Old 28 May 2007, 11:03 PM
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Silas Sparkhammer Silas Sparkhammer is offline
 
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Whalephant

Quote:
Originally Posted by jimmy101_again View Post
Another example of "visual accommodation" is the complete inability of a person to see his/her own blind spot, at least under normal circumstances.
Excellent example!

I would bet that it is entirely possible to build a set of goggles, using clever lenses and mirrors, that would "eliminate" the blind spot, by re-mapping that area to parts of the retina that actually sense light. But the overall personal perceptual effect would be next to nil!

I have heard that there are wrap-around goggles for bicyclists that extend their peripheral vision a bit. Forward vision is undistorted, but the last fifteen degrees or so on either side are stretched to cover 30 degrees of vision, thus providing 15 degrees beyond what could normally be seen at all, although compressed.

And, of course, a great many of us are accustomed to driving with "fish-eye" rear view mirrors, which give a wider field of view, at the cost of diminution and distortion of the image.

Silas (my car has a warning label: "Objects in mirror are uglier than they appear.")
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