Do children see darkness as "blacker" than adults?
April 9, 2006 7:05 AM   Subscribe

Do children see darkness as "blacker" than adults?

When I was a child, I noticed that in supposed "pitch darkness", I actually saw a large number of really small red, blue, green, and other colored points (somewhat like if you look at a low res digital camera photo of darkness). As an adult, it seems that there are more of these points than there used to be.

I can think of 3 possible likely interpretations:
1) Adult eyes, for some reason, do in fact see more of these dots.
2) It varies from person to person
3) It's my imagination that the number has increased.

Which is it? And, if #1 or #2, why is it?
posted by Bugbread to Science & Nature (21 answers total) 2 users marked this as a favorite
 
I am not sure what you mean by the colored points, but I have always been under the impression that night vision improves dramatically during adolescence, so I guess you could be right.
posted by tastybrains at 7:12 AM on April 9, 2006


I've thought about this, though my most clear memory from being a kid is wondering why there was so much noise in my night vision, and I also recall wondering why night vision was monochrome.

So...as the opposite of you if anything I notice an improvement in the signal:noise ratio as an adult, though this too could be mere imagination.

How would you test this?
posted by jimmythefish at 8:04 AM on April 9, 2006


this paper, or rather the abstract since the paper itself is behind the usual pay-per-view wall, if i understand correctly, says that dark vision gets worse with age, based on a study with people from age 5 years upwards.
posted by andrew cooke at 8:06 AM on April 9, 2006


Andrew Cooke:

Thanks, that was interesting, but it doesn't look quite like it addresses the "lack of blackness" thing.

Jimmythefish is kinda on the money in terms of seeing noise in the night vision. I'm not so much talking about night vision (in the sense of seeing actual things), as I am about "what one sees in the absence of pretty much all light", for example when you turn out the lights in a windowless room, or when you go to visit some caverns and the tour conductor turns out the lights to show you what pitch blackness looks like.
posted by Bugbread at 8:33 AM on April 9, 2006


Black is the visual equivalent of silence. It is what we "see" when no radiation hits our eye. We think we "see" black in the everyday world partly because most blacks are not true blacks, and also because they are surrounded by radiation (colors). But "seeing" black is as much an illusion as "hearing" a moment of silence in a world of sound. But even when you experience true silence, as in an anechoic chamber, you can still hear your nervous system and circulatory system. Similarly, when you experience true darkness, as in a photographic darkroom, you will see visual effects produced by your own body, as you do when you rub your eyes. It makes sense that as we age, we see more of these, just as older people hear sounds from changes in their auditory system, even when deafness prevents them from hearing the full spectrum coming from the outside world.
posted by weapons-grade pandemonium at 8:39 AM on April 9, 2006


weapons-grade pandemonium : "Similarly, when you experience true darkness, as in a photographic darkroom, you will see visual effects produced by your own body, as you do when you rub your eyes. It makes sense that as we age, we see more of these, just as older people hear sounds from changes in their auditory system, even when deafness prevents them from hearing the full spectrum coming from the outside world."

That was pretty much my thinking. I guess what I'm looking for is: does anybody know if this is true, or just something that makes a lot of logical sense, but isn't actually the case? And if this is true, why? Is it because receptors in the retina trigger more randomly as one grows older, or because the mind makes up noise to fill the absence of stimuli, or because low level crosstraffic within the brain that is normally covered up by images is brought to the fore?
posted by Bugbread at 8:52 AM on April 9, 2006


oh, i was assuming that the dots were single photon detections. do you think they're noise in the "hardware" rather than the "input"?
posted by andrew cooke at 8:55 AM on April 9, 2006


not an answer, but an interesting paper on the Molecular origin of continuous dark noise in rod photoreceptors (skimming it, i don't see anything about age).

(i'd always been told that eyes can detect single-photon events - there's a famous experiment in atomic physics that, if i recall correctly, required it - so i'm surprised by the statement that 5 - 7 are required; a later section suggest single photon events are detected, but at lower efficiency, so i'm a bit confused).
posted by andrew cooke at 9:04 AM on April 9, 2006


If they were input, as opposed to hardware noise, those with the best visual systems (children) would see more of them, no?
posted by weapons-grade pandemonium at 9:11 AM on April 9, 2006


Andrew Cooke:

From what I could tell from that abstract, that's what I'm talking about (continuous dark noise). Also, I wasn't aware that people could see even 5-7 photon events. That's incredibly cool, and knocks out a few of my theories. Thanks.
posted by Bugbread at 9:24 AM on April 9, 2006


i'd always been told that eyes can detect single-photon events - there's a famous experiment in atomic physics that, if i recall correctly, required it

Certainly there's an infamous one. I'd heard eye sensitivity on the order of 10 photons, but can't remember where.
posted by Aknaton at 9:32 AM on April 9, 2006


those with the best visual systems (children) would see more of them

yes, that's what i thought (so i was implying "3"), but it turns out that i was ignoring a significant amount of noise in the detector.
posted by andrew cooke at 9:53 AM on April 9, 2006


On a (perhaps) practical note but not to answer the question-
Aldous Huxley improved his vision using techniques developed by Alan Bates MD ("Better Eyesight Without Glasses"). One of those techniques is Palming, where you seal out light from your eyes with your palms and imagine seeing a true blacky black (I am sure those where his words). If I remember right Bates built most his exercises on relaxing the muscles around the eye but I don't believe that was the rational for this one. He may have suggested that rods and cones get habituated to firing and so fire even in the absence of stimulation. I have tried these exercises and they do work but it was an incredible commitment to keep it up. If wikipedia was working for me a would put a link here. But it isn't.
posted by pointilist at 12:51 PM on April 9, 2006


The term for the artifactual or noise-related experience of brief bright flashes even in total darkness is "phosphenes." This can be productively Googled or PubMed'd. As far as I can tell, this varies from person to person; people with retinal damage, especially that due to acute optic neuritis, experience more phosphenes than, say, Joe Average over here.

I've also heard that the eye can detect single photons at some frequencies, but I'm not aware of the experiment that proved this. (The Michelson-Morley experiment did not use an eye as the detector.)
posted by ikkyu2 at 1:50 PM on April 9, 2006


Wikipedia also apparently has an article on phosphene, but I can't access Wikipedia today for some reason.
posted by ikkyu2 at 1:51 PM on April 9, 2006


ikkyu,

It isn't so much bright flashes as a constant background of noise.

If true black is supposed to look like this:


Then what I see is more like this:

posted by Bugbread at 2:12 PM on April 9, 2006


sorry for the derail, but since people keep adressing my half-remembered experiment - i can't recall the details, but it was something to do with radioactive decay and, possibly, counting scintillations on a phosphor screen (think early atomic physics, possibly cambridge). however, i can't get from that to an argument that requires single photons, unless it's something to do with quantised energy and a lower limit (but that sounds like i'm confusing it with the photoelectric effect). all i (half-)remember is questioning the lecturer because it seemed to require single photon detection and being assured that was possible....

back on topic, i have no idea how you'd measure this because presumably there's not just a signal from the eye (which could be measured), but some kind of filtering/processing before the "image" is consciously available. personally, when i close my eyes what i see (once after-images die away) seems to be very infleunced by what i'm thinking. i can sometimes get myself to "see" outlines of specific objects, for example. it doesn't seem that big a leap from that to a child being afraid of the dark (unknown) and so seeing the dark as particularly dark.
posted by andrew cooke at 3:13 PM on April 9, 2006


Speaking of noise and phosphenes, I found that after the one and only time I took mushrooms (and I may have taken too much because I lost consciousness) that the experience had completely wiped the "noise" from my system. When I closed my eyes to go to sleep it was pitch black - the usual hypnagogic effects were gone, and it was the same for when I was walking around at night. It lasted about a week and may have been brought to an end by a combination of marijuana and alcohol on a Saturday night.
posted by hifimofo at 5:59 PM on April 9, 2006


It's noise. What happens is that your cones (which provide color sensing) need a substantial amount of light to function properly (at least compared with the rods). In low-light conditions, the cones are trying to see something and for a lack of substantial input can't manage it and the opsins misfire. If you're a careful observer, you'll also notice that you see far more color blips in the center of your vision. This is the macula, which has the highest concentration of cones. There is a higher density of rods in the periphery of your retina, so you are able to see more at the edges of your vision in low light, but it also looks more grayish.

Some theorize that this difference in densities makes us less susceptible to night time predators (which tend to attack from the side or back, not front on). This also explains our tendency to see movement in the dark when there might not be any. Paranoia is not just a Kinks song, it's a survival trait.

From my recollection, I see as much colored noise as I ever recall seeing, and I have some pretty clear memories of that.

Another thing to keep in mind is that rhodopsin (the opsin in rods IIRC) has a fairly slow response in terms of returning to "normal" when really hit with a lot of input. Try this: go into a room that is pitch dark and wait until your eyes "relax". Take a flash picture trying to avoid looking at any light (if you're using a digital camera, shut off the LCD display, cover up LEDs etc.). After the flash, close your eyes and a few seconds later a fabulously clear black and white image of the room should form and fade away a few moments later.
posted by plinth at 7:31 PM on April 9, 2006


Plinth: Thanks, both for explaining why the noise occurs, and providing what, I think, might explain my situation, which is that most of the absolute dark conditions I am in now are self-imposed and very brief (turning off all the lights for a second to see just how dark the room is with the new thick curtains, etc), while when I was a kid, they were probably longer (playing in the dark), which means that perhaps the rhodopsin response slowness results in more noise during my brief testing than during my more extended darkness testing as a kid.
posted by Bugbread at 12:55 PM on April 10, 2006


I just happened across a Wikipedia article on "Visual snow" today. I'd never heard of it.

Bugbread: I am not as certain as plinth is that what you describe is actually normal. I certainly am not able to detect anything similar in my own vision, once I am dark-adapted. I don't mean to suggest that it's definitely not normal or that you or plinth are mistaken; just that I've never come across it in my rather wide-ranging reading on vision and visual abnormalities, and that strikes me as a bit odd if it is indeed a well-known phenomenon.
posted by ikkyu2 at 4:28 PM on April 12, 2006


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