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wildflower's avatar

Brain's reaction to total darkness vs. blindness?

Asked by wildflower (11098 points ) July 13th, 2008

I visited Aillwee Cave yesterday (really cool cave, btw!) and the tour guide stopped at one of the deepest points of the cave to give a demonstration of total darkness. It really was total darkness, your eyes couldn’t make out a single outline or shape or anything.
As a bit of trivia the guide also told us that if one were to stay in total darkness for extended period of time, the brain would start to react by exaggerating sounds (water dripping would become conversation, etc.) and eventually create full blown hallucinations.
This sounds really fascinating – and an interesting (albeit time-consuming) alternative to drugs – but now I’m curios about the difference between being in total darkness and being blind. I’m pretty sure blind people don’t walk around with full blown hallucinations, but why does the brain behave differently in these situations?
I’ve tried googling all morning, but haven’t found anything that explains this, so I thought I’d try here…..neurologists, ophthalmologists, physicians, psychiatrists, etc…...anyone with knowledge/experience of these things: please enlighten me!

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6 Answers

arnbev959's avatar

Maybe this can get you started.

Great Question. I can’t wait to hear other responses.

Curious404's avatar

I think the difference is the seclusion of being in an open, dank, hole with echos, and bats vs being blind in an area of familiarity- human voices, cars, warmth, etc. I’d bet that even a blind person would hallucinate in those cave conditions. It would be torture to leave anyone in those conditions.

jonno's avatar

I agree with Curious404, it isn’t so much the darkness, but the isolation and conditions. Imagine if you had to walk around for a week in your day-to-day life wearing a 100% effective blindfold – you wouldn’t go crazy then, would you? Maybe a little bit annoyed, though.

I’ve always wondered though, does a blind person ‘see’ darkness, or do they just have a total lack of vision? (Perhaps it depends on if they were born blind or whether they became blind after a life of being able to see?)

marinelife's avatar

From a cavers FAQ: “Within a few hours of total darkness you would find yourself experiencing auditory and visual hallucinations as your mind attempted to compensate for the lack of sensory input. Cavers who have spent days in caves while surveying report that they soon find themselves in a sort of quasi-hibernation where they sleep for 12 hours and then work for 12 hours. Upon returning to the surface, these speleologists report they experience heightened sensitivity to light, sound and temperature for several days.”

Compare that to this account of Charles Bonnet Syndrome, which afflicts people who are beginning to lose their sight.

“For those stricken with Charles Bonnet Syndrome, the world is occasionally adorned with vivid yet unreal images. Some see surfaces covered in non-existent patterns such as brickwork or tiles, while others see phantom objects in astonishing detail, including people, animals, buildings, or whatever else their minds may conjure. These images linger for as little as several seconds or for as much as several hours, appearing and vanishing abruptly. They may consist of commonplace items such as bottles or hats, or brain-bending nonsense such as dancing children with giant flowers for heads.

Most of those afflicted with Charles Bonnet Syndrome are people in the early stages of sight loss, and the hallucinations usually begin while their vision is still present but slowly diminishing. The most common culprit is macular degeneration, a disease where certain light-sensing cells in the retina malfunction and cause a slowly worsening blind spot in the center of one’s vision. Other eye diseases such as glaucoma and cataracts can cause the symptoms as well, and in a few rare cases it has been diagnosed in people without any detectable vision problems whatsoever. The likelihood of Bonnet visions also seems to increase in people who have limited social interaction, such as people who live alone.”

Harp's avatar

If an area of the brain that is dedicated to processing input from a specific sense is deprived of input for a length of time, well then, by golly, those neurons will just start making stuff up. This has been well documented in the case of hearing, as well. Deprived of sound by either the onset of deafness or by one’s environment, it’s not uncommon to hear full-blown orchestral music as if it were actually present.

All this is contingent, though, on having fully developed those regions of the brain prior to losing the sensory input. In the case of someone who is blind from birth, that region would likely have been appropriated for some other cognitive or sensory function, and so wouldn’t be generating hallucinatory sensations. But the extra processing power that comes from repurposing those brain regions will augment other sensory experience.

KendraThePirate's avatar

I work in a cave, so I have a bit of experience with it. It has happened to me when my batteries have died in the center of the cave. Hallucinations are really no fun at all in this case.

The majority of blind people do not see just pitch black, even if you are born blind. Only about 10% actually see black. Most cases its not that you can’t see, its that the receptor cells in your retina that send the message of “sight” to your brain to interpret is damaged or malfunctioning. It can still sense light.

In Cave darkness, there is no light whatsoever. Your eyes will work so hard trying to help you interpret darkness and your brain not being able to will start to send you images of what you want to see, usually something you have seen before or experienced. The begining stages of hallucination is whats called Residual (Visual) Memory. If you wave your hand infront of your face you may or may not see it. It you study your hand infront of your face then wave it about, you would be able to see the shadowy outline. That, my friend, is a hallucination (though mild)! Your brain knows what your hand looks like and where it is, so it will send you an image of it.

There is a common myth that if you are exposed to those extreme conditions for prolonged periods of time (a matter of months) you will go blind.

Completely false. Since your eyes are dilated to their fullest for that prlonged time, when light hits your retina it could seriously damage your sight possibly causing you to go blind. When I got ut of that cave i was super sensitive to light. I had to sit in a dark room for about an hour just so i could walk outside without getting painful migranes due to brightness, and it still hurt. I saw an eye doctr the next day and had t hae my perscription changed because my eyes were damaged my the sun. Being in Cae darkness can cause your eyes to atrophy, but it will not cause you to go blind.

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