
Eigengrau - ekpyrotic
http://en.wikipedia.org/wiki/Eigengrau
======
jlgreco
I use to do some spelunking and on many occasions lost light while underground
(usually failed batteries, one time my light took a bad hit. Thankfully I
always had backups). I wouldn't really describe the color as "gray" though,
there is too much randomly colored static for that. More of a very dark soupy
brown. Sort of like construction paper perhaps.

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agf
Definitely mirrors my experience.

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xyzzy123
For full sensory deprivation this becomes especially trippy when you can only
hear the white noise of rushing water and you're numb from cold.

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josht
Or you can find yourself an isolation tank.

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wahnfrieden
Are there tanks engineered for those with tinnitus? Sensory deprivation +
tinnitus only means screamingly loud ringing for me - nightmarish.

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maaku
This is a total aside, but I've always wondered: is the ringing a repeating
waveform? If you could discover its structure through trial and error (e.g,
cycling through pure tones and looking for beat frequencies), could you create
an anti-ringing real waveform that nullifies the tinnitus? In other words make
a hearing aide + your ear physiology act like a noise cancelling headphone, at
least as far as your auditory nerves are concerned.

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wahnfrieden
My limited understanding is that it is from one of the hairs in your inner ear
being bent or broken in some way - the hair itself doesn't move, but since
it's bent in the way airwaves could are able to bend it momentarily, the brain
interprets it as it being in that momentary state permanently. Waveform
cancellation happens at a physical level - it wouldn't "unbend" the hair as
the hair isn't actually moving.

I don't actually know though, this is just my understanding.

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kmm
Some people get surgery to cut their cochlear nerve, and they still hear it.
Tinnitus often originates in the brain.

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jpatokal
I'd be quite keen to hear how they determined that #16161D is _the_ color of
Eigengrau. Stick somebody in a pitch black room, show him various shades of
grey on an illuminated display, stop when indistinguishable? But alas, the
[citation needed] suggests it was simply pulled out of someone's Eigengrau-
colored orifice...

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huhtenberg
@coldarchon - you are hell-banned.

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dbbolton
How could you tell?

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ColinWright
Turn on "showdead" in your profile.

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ElongatedTowel
I wonder how that is connected to phenomena like visual snow. Many people
including me see similar effects not only in dark environments but troughout
the day. Some resembling swarms of color, some seeing snow or something that
resembles television static. For me there is no evenly colored surface anymore
because a very faint swarm of colors washes over them.

It affects my vision rather negatively and the darkness magnifies the effect
immensely making it hard for me to be aware of the countours of objects.

There are forums on the net were people experiment with various drugs with
bizarre effects, spontaneous healing or no improvement at all were others see
immediate effects.

My doctor send me to the optometrist, his assistant wondered why he didn't
send me to a neurologist, the optometrist dismissed it because there wasn't
anything wrong with my eyes.

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spullara
IANAD but that sounds serious to me. Visual field distortions are often brain
issues. I would go to a neurologist to be sure. Could be a tumor applying
pressure to your optic nerve or something.

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ElongatedTowel
I've became aware of it about 15 years ago, so it would probably have already
killed me if it was anything like that.

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shardling
No, not necessarily. I've met someone who had a benign brain tumor -- it
caused them to have mood swings, but was not in any danger of spreading.

In their case the doctors didn't remove it because the operation would have
been more dangerous than the tumor itself, and the symptoms were not too
severe. But it's obviously better to be aware of such things.

~~~
pavel_lishin
My wife had a growth removed from her brain a few years ago. Apparently it had
quietly sat around since she was a child, not doing anything, until it decided
to get its shit together and try to kill her.

ElongatedTowel ought to go to the doctor and deal with a few weeks of feeling
like an embarrassed jerk by demanding that they scan his/her brain.

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agf
I've experienced this any number of times, mostly when backpacking in the
Adirondacks in overcast conditions. I've woken up in the middle of the night
with no feeling of vision at all -- no sense of light or dark. It can be
extremely disconcerting and similar to the feeling of drowning, for anyone
who's also experienced that.

The article also suggests the phenomenon is temperature related, which I'd
confirm. The times I've approached true panic for feeling "blind" have been
between -20 and 30 degrees Fahrenheit, while I've always seen more of a mid to
dark brown at warmer temperatures, from 50F up.

~~~
salmonellaeater
I'm pretty sure the temperature of the rhodopsin in your eye was above 30
degrees Fahrenheit :)

A toad's eye temperature can vary because it's cold-blooded. If humans'
experience of eigengrau varies with outside temperature, well that's
interesting and deserves study.

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agf
Sure. I assume I'd be truly blind if the fluid in my eye eve went below zero
C. I'm talking about the perception only.

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shardling
I found wikipedia's section on "The mathematics of color perception" very,
err, illuminating. It made me realize just how complicated the topic is...

[http://en.wikipedia.org/wiki/Color_perception#Mathematics_of...](http://en.wikipedia.org/wiki/Color_perception#Mathematics_of_color_perception)

~~~
alok-g
A question also comes on why humans have three color channels. Or more
generally, why is the number of cones relatively small (some species have more
than three).

While I cannot find the reference, some researchers recorded full visible-
range spectrum for a very large number of naturally occurring objects. Then
they performed principle components analysis of these spectra and found that
for naturally occurring reflection spectra, nearly all signal energy is
recovered with a small number of independent components like three or four. In
other words, the spectra of naturally occurring materials does not vary as
widely as it could to exercise the full Hilbert space available. A downside of
having a larger number of cones is of course that the percentage area
available to each cone will be less, so a higher density of cells would be
needed to maintain the resolution and color perception under dark will suffer
more. The nature then has chosen a near optimal number of cone types for
vision.

One issue I had discovered with the above study was that it was possibly
cyclic. The database of spectra they used did not had too many samples of
(different) objects with the same apparent colors since the latter was
collected primarily to count the number of human-distinguishable colors
occurring naturally in nature.

If the number of primary colors visible to humans were significantly larger, I
can on the very least say that TVs and printers would have been significantly
different than what they are, if at all they would have been practical.

The above however does not answer the question of the electromagnetic
radiation frequency span sensed by the eyes. In other words, why is the
visible range not wider than what it is. Again, some animals do have a wider
range. Had the visible range been wider, it may have required a larger number
of primary colors to cover the expanded Hilbert space. What a physicist once
told me is that the range of frequencies that are visible to humans and
animals correlates very well to the frequency range under which water is
transparent. See [1]. This according to him offers a solid indication that
life originated in water.

A few more interesting thoughts:

1\. Figure out what determines the shape of the locus of the spectrum
(monochromatic) colors on the color chart [2]. It is an interesting exercise
to derive this locus from the measurements of the spectral responses of the
three cone types. Note that the outer boundary of the color chart has a
straight line bottom with purple to magenta in the middle. While the non-
straight boundaries span monochromatic colors, the colors on the straight edge
at the bottom cannot be monochromatic. Figure out why.

2\. A question comes if the spectral responses of the cones could have been
such that the above locus would have concavities. I am not sure of the answer,
though am sure colors outside of the locus but within its convex hull would
still have been visible.

[1]
[http://en.wikipedia.org/wiki/File:Absorption_spectrum_of_liq...](http://en.wikipedia.org/wiki/File:Absorption_spectrum_of_liquid_water.png)

[2]
[http://en.wikipedia.org/wiki/File:Cie_Chart_with_sRGB_gamut_...](http://en.wikipedia.org/wiki/File:Cie_Chart_with_sRGB_gamut_by_spigget.png)

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nhaehnle
> What a physicist once told me is that the range of frequencies that are
> visible to humans and animals correlates very well to the frequency range
> under which water is transparent.

I always thought that it was related to the spectrum of sunlight.

~~~
alok-g
Well, that too. While UV is nearly absent in sunlight at the sea level, there
still is a lot of energy in infrared that is not visible to the human eyes.
See here for examples:
[http://en.wikipedia.org/wiki/Infrared_photography](http://en.wikipedia.org/wiki/Infrared_photography)

~~~
nhaehnle
It's probably just a matter of trade-offs. The visible range does cover the
peak energy of the spectrum of sunlight, and covering more of the infrared may
just not be worth the cost of a more complicated eye.

It would be interesting to see some type of measure of the information content
of adding more infrared in typical nature scenes.

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endgame
Let's post random wikipedia articles without commentary, turning HN into
/r/todayilearned.

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d0m
Go ahead, post all random wikipedia articles you want. The cool thing is how
only the most interesting ones will be upvoted. Now that I think of it, that
could be a neat small script to hack.. post random wiki articles on HN, let
HN-ers upvote the good ones, and only read the best ranked ones.

~~~
endgame
Voting works well with small-to-medium communities of readers invested in the
quality of discussion, but breaks down in large groups. Look at some of the
larger subreddits - people in the comments complain about the quality of
frontpage articles because the voting group becomes much larger than the
commenting/discussion group.

I wonder what's going to be the next big innovation in filtering the firehose?

~~~
eru
There are more interesting algebraic operations you can do on the voting
vector than just adding it up..

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illtakesix
Another interesting color is _Cosmic Latte_ :
[http://en.wikipedia.org/wiki/Cosmic_latte](http://en.wikipedia.org/wiki/Cosmic_latte)

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schoper
Didn't Goethe describe this in his Theory of Color? Amazing
physical/physiological study of sight.

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program
I find the Eigengrau to be a very relaxing color and I use it as the
background of my desktop. It always puzzled me that it's not a pure grey but
it has a little blue. I thought he had more sense that there was a little red
because of the minimal amount of light that passes through the capillaries of
the eyelids.

I suffer from epilepsy and often I see scintillating scotoma, visual snow and
other strange light phenomena. Given this I came to the conclusion that my
brain associate this color to a quiet mental state.

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beemoe
1) Close eyes. 2) Point flashlight at eyes.

I observe that the intensity of the "Eigengrau" depends on how tightly I close
my eyes. With the flashlight, the image is clearly more red than gray. This
could explain some reports of "brown", to the extent that brown is a dark red.

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dave809
when it says that the half-life of the rhodopsin molecule is about 420 years,
does that mean that if we would live that long, half of our rhodopsin will be
gone? how would that affect our eyesight?

~~~
eru
Your rhodopsin get replenished.

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lifeformed
How did they decide on the RGB values? Or did someone just make that up?

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anigbrowl
Yes.

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tuneafish
this isn't particularly surprising. every photo-sensor known to man has "dark"
noise and it is indeed temperature dependent. noise goes up for a fixed
temperature for sensors that are sensitive to longer wavelengths, so the fact
that people report a more brownish color makes more sense than perfectly grey
to me. the sensors in your eyes that are sensitive to deep red will be noisier
than ones sensitive to blue.

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jkuria
Why is this #1 on the front page? And how is it useful? I think a common
pitfall for techies is amassing lots of useless knowledge (a habit I have
weaned myself off over the last few years).

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pcl
I kinda feel like _useless knowledge_ is an oxymoron.

If knowledge about our world is a pitfall, then I'm happy to seek out new
traps.

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tagabek
Neat find! I really dislike the feeling that 'seeing' this causes. I can only
describe it as helpless and vulnerable, while I search for light.

