1080: "Visual Field"

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Re: 1080: "Visual Field"

Postby jpers36 » Wed Jul 11, 2012 6:31 pm UTC

Somewhat tangential, but I have voluntary nystagmus.

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Re: 1080: "Visual Field"

Postby Nexxo » Wed Jul 11, 2012 6:32 pm UTC

I have just been awesomed.

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Re: 1080: "Visual Field"

Postby Angua » Wed Jul 11, 2012 6:34 pm UTC

You know what's fun - get someone to follow your finger as you move it back and forth across their vision (don't do it too fast for easy tracking). Then ask them to do the same eye movement without you moving a finger for them to track.
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Re: 1080: "Visual Field"

Postby Pfhorrest » Wed Jul 11, 2012 6:48 pm UTC

Timst wrote:Alright, so the floaters have an explanation. On to another thing that bug me since childhood: Am I the only one, at night (or I guess anytime it's completely dark), to see the dark not uniformly black, but rather composed of a myriad of tiny color pixels on a black background? I mean it's not like a confetti party or anything, but it's not just a black shape either. When I focus at the center of my field of vision I can even see some kind of spinning diamond shape, and I remember observing it since I was a child. Ol' diamond, I call him.

I've noticed that as well. Not necessarily a diamond, but shifting symmetrical abstract geometric shapes something like a kaleidoscope. Pressing my palms against my closed eyelids seems to amplify the effect.
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Re: 1080: "Visual Field"

Postby WizenedEE » Wed Jul 11, 2012 7:01 pm UTC

xkcd wrote:Google "stopped clock illusion".
Google Trends wrote:Your terms - stopped clock illusion - do not have enough search volume to show graphs.


So I'm guessing that either
1) Most xkcd readers don't read the title text or
2) Most xkcd readers clicked on the large picture and forgot about the titile-text like I did.

It was a direct order; I would've expected more people to search for it.

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Re: 1080: "Visual Field"

Postby emtee » Wed Jul 11, 2012 7:53 pm UTC

The explanation for chronostatis is interesting... the brain "filling in" the time while your eyes were just coming to a halt with the subsequent (stable) image.

It doesn't quite explain something which must be related, which is that when I first look at the clock sometimes the second hand appears to move backwards for one tick.

Any theories?

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Re: 1080: "Visual Field"

Postby Paulmichael » Wed Jul 11, 2012 7:54 pm UTC

Oh me yarm Oh me yarm Oh me yarm thank you Randall! I had recently (within the past year or so) noticed that whenever I stared up into the daytime blue sky, I could see thousands of mostly translucent specs flashing back and forth. I thought they were cells of some kind, but I didn't really know what to Google for. Cool to think I'm looking directly at white cells! Does he also mean white blood cells? :shock:

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Re: 1080: "Visual Field"

Postby Timst » Wed Jul 11, 2012 8:10 pm UTC

Pfhorrest wrote:
Timst wrote:Alright, so the floaters have an explanation. On to another thing that bug me since childhood: Am I the only one, at night (or I guess anytime it's completely dark), to see the dark not uniformly black, but rather composed of a myriad of tiny color pixels on a black background? I mean it's not like a confetti party or anything, but it's not just a black shape either. When I focus at the center of my field of vision I can even see some kind of spinning diamond shape, and I remember observing it since I was a child. Ol' diamond, I call him.

I've noticed that as well. Not necessarily a diamond, but shifting symmetrical abstract geometric shapes something like a kaleidoscope. Pressing my palms against my closed eyelids seems to amplify the effect.


Awesome. Now I can sleep more easily (in my brightly colored darkness).

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Re: 1080: "Visual Field"

Postby Uzh » Wed Jul 11, 2012 8:30 pm UTC

"The problem is that humans have these darn biological limitations and if it gets too far from 293 K they'll start complaining, or die." http://forums.xkcd.com/viewtopic.php?f=60&t=106000#p3483385

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Re: 1080: "Visual Field"

Postby wbeaty » Wed Jul 11, 2012 9:07 pm UTC

The keyword everyone is really after: ENTOPIC

http://en.wikipedia.org/wiki/Entoptic_phenomenon

http://en.wikipedia.org/wiki/Blue_field_entoptic_phenomenon or "Sheerers"

The blue-yellow-quadrants polarization thing is found under http://en.wikipedia.org/wiki/Haidinger%27s_brush

Back before flatscreens we had to go outdoors in the early morning or late evening, stare straight up into the clear blue sky, then spin around until dizzy. Haidinger's Brushes would appear at the center of vision since there's a band of strong polarization in sky light positioned 90deg from the Sun's location.

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Re: 1080: "Visual Field"

Postby bmonk » Wed Jul 11, 2012 9:10 pm UTC

reitsma wrote:brilliant comic, but it still hasn't addressed a strange visual phenomenon that I experience - if you stare at an LED clock, and 'crunch' on something (causing jaw, and i guess one's whole head to move), the glowing numbers 'jump' around independently.
does anyone else have this experience?

Not me--but when my alarm goes off at 5:25, the numbers look crooked, but at 5:26 and other times, they are aligned properly. The same thing happens also at 12:52 and 2:52.
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Re: 1080: "Visual Field"

Postby flicky1991 » Wed Jul 11, 2012 9:38 pm UTC

So what I want to know is, what about the multicoloured shapes that appear when you close your eyes?

----

highlyverbal wrote:This hemi-green is an imaginary color in the sense that no natural phenomenon produces it or even could (light at that wavelength would strike and stimulate all relevant cones). What will your brain perceive then? What will that feel like?


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Re: 1080: "Visual Field"

Postby ivnja » Wed Jul 11, 2012 9:51 pm UTC

Bossi wrote:Also curious- if I fall asleep in the sun on a bright day, I'll often wake up to find that I can't see the color red for the next 5-10 minutes.

I'd assume it's a matter of your red cones are getting overworked - if you close your eyes and face up at the sun, what you see inside your eyelids is mostly red. Even if you're asleep and not consciously seeing anything, I imagine the cones themselves don't stop receiving.
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Re: 1080: "Visual Field"

Postby Jeff Bobbo » Wed Jul 11, 2012 10:22 pm UTC

ivnja wrote:
Bossi wrote:Also curious- if I fall asleep in the sun on a bright day, I'll often wake up to find that I can't see the color red for the next 5-10 minutes.

I'd assume it's a matter of your red cones are getting overworked - if you close your eyes and face up at the sun, what you see inside your eyelids is mostly red. Even if you're asleep and not consciously seeing anything, I imagine the cones themselves don't stop receiving.

Aye, this is the same thing that also causes pins and needles/numbness if you sit on your foot or such.

This is the sciencey bit:
The neurotransmitter chemical (acetylcholine), which is used to transmit signals between neurons binds to a receptor on the second neuron, an enzyme then comes along and splits it up into two parts (acetate and choline), which then detach from the receptor. This can then be remade by another enzyme (acetylcholinesterize). But when this process happens constantly (sitting on your foot), the enzyme which rebuilds the neurotransmitter doesn't work as fast as the deconstructor enzyme, so you 'run' out of neurotransmitter, resulting in numbness (or seeing red, in Bossi's situation).

On the other hand, I learnt this stuff like two years ago, and didn't do particularly well in biology, so there's probably some error there, or spelling (although I generally find my nervous system knowledge is 'good').

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Re: 1080: "Visual Field"

Postby whateveries » Thu Jul 12, 2012 1:25 am UTC

OK, so, now, now I am completely aware of the floaters, thanks Randall. Maybe I can take my mind of it by breathing manually for a while, whilst increasing my awareness of my tongue.

p.s. I hope you sit on a nut.
it's fine.

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Re: 1080: "Visual Field"

Postby reitsma » Thu Jul 12, 2012 7:56 am UTC

thanks to all who answered my question! Fantastic and comprehensive explanations offered. :D

those jumpy numbers don't make me feel so crazy now.

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Re: 1080: "Visual Field"

Postby orthogon » Thu Jul 12, 2012 7:58 am UTC

Pfhorrest wrote: Pressing my palms against my closed eyelids seems to amplify the effect.

I noticed the other day that if I push my palms against my closed eyelids I see something that looks remarkably like a tinned pineapple slice, in the right colour yellow and complete with a jaggedy hole in the middle. I spent some time wondering why. Any suggestions?
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Re: 1080: "Visual Field"

Postby jackal » Thu Jul 12, 2012 8:18 am UTC

jonsimon wrote:
jqubed wrote:
dzamie wrote:Hmm... Wikipedia doesn't really have too much about chronostasis aside from its name and description. Oh well.


So, basically, it's our brain's image stabilization initially not realizing the clock hand is still supposed to be moving?


No. When you move your eye too quickly, it proudcues a blur image for the milliseconds it took to move your eye. Because your brain doesn't bother processing the blur, it replaces those miliseconds in your visual memory with the image of the thing you moved to. Essentially, it rewrites the history of what you perceived.


Amazing that this was posted when it was. I was just watching a YouTube video about this the day before the comic was posted.

keithl wrote:BTW, another note on LED clocks - if you can still find them, get red LED clocks for bedroom and nighttime bathroom.


If you can get your hands on one, take it into a dark room, hold it up, and jiggle it at about two or three shakes per second, give or take. An odd phenomenon appears (and I've only noticed it with red LEDs, although I didn't have any green or blue LED clocks to test with): the numbers appear to oscillate opposite where your brain expects them to based on the position of your hand.

Jeff Bobbo wrote:This is the sciencey bit:
The neurotransmitter chemical (acetylcholine), which is used to transmit signals between neurons binds to a receptor on the second neuron, an enzyme then comes along and splits it up into two parts (acetate and choline), which then detach from the receptor. This can then be remade by another enzyme (acetylcholinesterize). But when this process happens constantly (sitting on your foot), the enzyme which rebuilds the neurotransmitter doesn't work as fast as the deconstructor enzyme, so you 'run' out of neurotransmitter, resulting in numbness (or seeing red, in Bossi's situation).


According to my understanding of retinal cells (largely from http://en.m.wikipedia.org/wiki/Photorec ... #section_3), the cells actually work in reverse: when light stimulates them, they stop transmitting the neurotransmitte (glutamate). I'm not a biologist, but it seems to me that the cells actually work harder (transmitting more glutamate) in the dark, perhaps leading to odd nighttime visions.

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Re: 1080: "Visual Field"

Postby Angua » Thu Jul 12, 2012 12:05 pm UTC

jackal wrote:
Jeff Bobbo wrote:This is the sciencey bit:
The neurotransmitter chemical (acetylcholine), which is used to transmit signals between neurons binds to a receptor on the second neuron, an enzyme then comes along and splits it up into two parts (acetate and choline), which then detach from the receptor. This can then be remade by another enzyme (acetylcholinesterize). But when this process happens constantly (sitting on your foot), the enzyme which rebuilds the neurotransmitter doesn't work as fast as the deconstructor enzyme, so you 'run' out of neurotransmitter, resulting in numbness (or seeing red, in Bossi's situation).


According to my understanding of retinal cells (largely from http://en.m.wikipedia.org/wiki/Photorec ... #section_3), the cells actually work in reverse: when light stimulates them, they stop transmitting the neurotransmitte (glutamate). I'm not a biologist, but it seems to me that the cells actually work harder (transmitting more glutamate) in the dark, perhaps leading to odd nighttime visions.

Actually, the reason you get bleaching is because the pigment which detects light gets broken down when it does so. If you break all of it down too quickly, you can't detect anything until you make some more. This is also why night vision takes a while to kick in, as our rods spend their time bleached in higher light levels.

It has nothing to do with the neurotransmitters.
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Re: 1080: "Visual Field"

Postby Jeff Bobbo » Thu Jul 12, 2012 12:23 pm UTC

Angua wrote:Actually, the reason you get bleaching is because the pigment which detects light gets broken down when it does so. If you break all of it down too quickly, you can't detect anything until you make some more. This is also why night vision takes a while to kick in, as our rods spend their time bleached in higher light levels.

It has nothing to do with the neurotransmitters.


... I remember being told that now. T_T

*Goes off to be incorrect about other biology stuff else where*

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Re: 1080: "Visual Field"

Postby GulliNL » Thu Jul 12, 2012 12:59 pm UTC

dexeron wrote:The best part of today's comic is that it reminded me of something ELSE that's been bothering me, and I finally looked it up. I've never met anyone else who's experienced it (in fact, people look at me like I'm crazy when I describe it) but when I I turn my head while looking at a colored light source (so that I end up seeing it out of the corner of my eye) the light source will often MOVE in relation to the background. In other words, looking at the little red "message" light on my desk phone... if I turn my head back and forth, the light will actually move left and right while the phone remains stationary! This is most pronounced with red lights, I think. Also, sometimes (depending on the kind of light) a light will actually seem to CHANGE color if moved away from the center of vision, changing from red to blue and back!

Turns out it's called Chromatic Abberation and it is, as I thought, the result of my glasses. It's probably more pronounced for me because of the extreme curvature of my lenses.

So I'm not actually going crazy. At least not in that way. ;)

Well, not to ruin your little party over there, but I have it too, and I don't wear glasses.

When I am in a dark environment and I look at a light source, for instance the screen of my cellphone, and I jiggle it (or just when walking while watching the screen) it seems the screen moves first and the darker image (of the bezel of the screen and your hand holding it) follows shortly after that.

Also I think Chromatic Abberation is when you look at a picture with high contrast, for instance a tree backlit by the white clouds behind it, there appears to be a very thin purple outline of the leaves. This is why it is sometimes called Purple Fringe. So maybe you're not using the correct term, or different effects have the same name, anyways I see it too :)

EDIT;
Glasses can produce Chromatic Abberation, indeed because of the curvature of the lens. This is why many lens manufacturers for digital camera's use special High Dispersion glass or filters to counter this effect.
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Re: 1080: "Visual Field"

Postby RuthR » Thu Jul 12, 2012 3:17 pm UTC

Enjoyed your comic on peripheral vision today, as my lab studies aspects of peripheral vision. I did want to make a clarifying comment about the text which reads, "We only see at high resolution over a small area in the center of our vision where retinal cells are densest (the fovea)". There's a bit of a common misconception that the fovea has high resolution and everywhere else the resolution is terrible. But it's more like the fovea has way more resolution than we need, and then there's decent resolution for quite a distance out from the fovea.

For instance, for a typical reading distance of about 15 inches from the page, an individual letter in an 11 pt font can be read out at about 13 degrees of visual angle. (That's a threshold, meaning it wouldn't be very pleasant to read letters that far out, but you could do it right way above chance.) That's pretty darn good acuity outside of the fovea.

We can't actually read that far out, but that's because of visual crowding rather than loss of acuity. Crowding refers to an effect in which, in the periphery, it's hard to read a letter if it is flanked by other letters which are too close to it. With typical font spacing, crowding for an 11 pt font becomes a problem at about 1.5 degrees eccentricity. Crowding is the big fish in terms of determining what we can and cannot do in the periphery.

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Re: 1080: "Visual Field"

Postby _iCeb0x_ » Thu Jul 12, 2012 7:01 pm UTC

The TLC joke was THAT negligible? I almost LOL'd, but I'm at the office...


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Re: 1080: "Visual Field"

Postby ThirstyMonkey » Thu Jul 12, 2012 7:44 pm UTC

I'm wondering if anyone else has experienced the following eye-related phenomenon:

If I close my eyes and rub them, occasionally I won't be able to see for a few seconds afterward. I mostly see splotchy dark red spots that quickly go away. I suppose this has something to do with damaging cells in my eye, but that isn't the curious part. After I experience this, if I rub my eyes again, I don't experience the temporary vision loss, and I won't experience it again for at least a few minutes. (I have no idea how long it takes to experience it again. Usually my mind has wandered and I don't think to check again.)

Does anyone know why this happens?

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Re: 1080: "Visual Field"

Postby Korbl » Thu Jul 12, 2012 8:32 pm UTC

I just came to say:
"Thank you, Randy, for finally explaining fucking darkvision in D&D." (albeit probably unintentionally).

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Re: 1080: "Visual Field"

Postby mattholimeau » Thu Jul 12, 2012 9:17 pm UTC

reitsma wrote:brilliant comic, but it still hasn't addressed a strange visual phenomenon that I experience - if you stare at an LED clock, and 'crunch' on something (causing jaw, and i guess one's whole head to move), the glowing numbers 'jump' around independently.
does anyone else have this experience?


Assuming noone else has addressed this...
And assuming I am correct in what I think you're talking about...

I'm guessing you wear thick glasses, and its the glasses that are warping the light slightly differently based on wavelength difference.

For example, say there's a lot of black text on a white background, then one word is in blue. I happen to wear thick glasses - if I tilt my head up and down, the blue word seems to move up and down in comparison to the rest of the text.

I noticed this (quite) a few years ago, took off my glasses and did the same thing and the bounce went away. Neat stuff.

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Re: 1080: "Visual Field"

Postby CharonPDX » Thu Jul 12, 2012 9:41 pm UTC

Chronostasis and computer clock apps do not mix well.

The first time I tried, I loaded up my "full screen clock app" on my iPad. Looked away for a few seconds, then looked back quickly.

"It's true! The second hand was stopped for what felt like five seconds!"

Then the second hand jumped forward ten seconds - the app had frozen for a while, starting before I looked back, and including the few seconds after I looked back again... :oops:

Happened the second time, too.

Since then, I don't seem to experience chronostasis properly. The first second seems just as long as the following few.

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Re: 1080: "Visual Field"

Postby TheBlackCat » Thu Jul 12, 2012 9:46 pm UTC

If you want a couple interesting eye facts:

1. The photoreceptors in your eyes are turned off by light. They are essentially modified chemical receptors, with a light-sensitive chemical in them. When they are exposed to light, the chemical changes shape and pops out of the receptor, turning it off. So ours eyes are most active in the dark.

2. Your optic nerve does not generally carry information from solid-colored areas. Instead, it carries information about edges, where color and/or brightness changes. Your brain then fills in the solid-colored areas. This is all done by the retina. If you optic nerve carried all the information from your retina, it would be about the size of a donut.

3. Although it has not be conclusively confirmed, due to the genetics involved it is possible that the mothers of some color-blind men have an additional photoreceptor and thus might be able to see colors other people can't (that is, two colors that seem the same to most people might seem different to them). Although even if they have the photoreceptor there is no guarantee they would actually be able to use it.

4. When fully dark-adjusted, humans can perceive an individual photon hitting their retina.

5. There are many specialized cells in the retina doing fairly complex tasks. For instance there are cells in the retina that respond to objects moving in a particular direction.

6. The eye is the only sensory organ in the body that develops directly out of brain tissue.

Speaking of Chronostasis, I noticed that with the seconds in my digital watch when I was little, but always assumed it was just because I hadn't seen the previous second change so it just seemed longer.

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Re: 1080: "Visual Field"

Postby Max™ » Thu Jul 12, 2012 10:15 pm UTC

orthogon wrote:
Pfhorrest wrote: Pressing my palms against my closed eyelids seems to amplify the effect.

I noticed the other day that if I push my palms against my closed eyelids I see something that looks remarkably like a tinned pineapple slice, in the right colour yellow and complete with a jaggedy hole in the middle. I spent some time wondering why. Any suggestions?

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Re: 1080: "Visual Field"

Postby ShadedKnight » Thu Jul 12, 2012 11:50 pm UTC

Timst wrote:
Pfhorrest wrote:
Timst wrote:Alright, so the floaters have an explanation. On to another thing that bug me since childhood: Am I the only one, at night (or I guess anytime it's completely dark), to see the dark not uniformly black, but rather composed of a myriad of tiny color pixels on a black background? I mean it's not like a confetti party or anything, but it's not just a black shape either. When I focus at the center of my field of vision I can even see some kind of spinning diamond shape, and I remember observing it since I was a child. Ol' diamond, I call him.

I've noticed that as well. Not necessarily a diamond, but shifting symmetrical abstract geometric shapes something like a kaleidoscope. Pressing my palms against my closed eyelids seems to amplify the effect.


Awesome. Now I can sleep more easily (in my brightly colored darkness).


I'm not sure about the geometric shapes, but I think I do see the pixels and I have always wondered about it. Sometimes it doesn't happen when it's completely dark, just mostly dark, and I'd be very interested to know about the cause of that.

I remember telling my dad at some point about the floaters, but without reference I just sort of described them wierdly and I think he just sort of forgot about it, and whenever I saw them it plagued me as to their cause. Glad I finally learned about that.

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Re: 1080: "Visual Field"

Postby TheBlackCat » Fri Jul 13, 2012 1:19 am UTC

ShadedKnight wrote:
Timst wrote:
Pfhorrest wrote:
Timst wrote:Alright, so the floaters have an explanation. On to another thing that bug me since childhood: Am I the only one, at night (or I guess anytime it's completely dark), to see the dark not uniformly black, but rather composed of a myriad of tiny color pixels on a black background? I mean it's not like a confetti party or anything, but it's not just a black shape either. When I focus at the center of my field of vision I can even see some kind of spinning diamond shape, and I remember observing it since I was a child. Ol' diamond, I call him.

I've noticed that as well. Not necessarily a diamond, but shifting symmetrical abstract geometric shapes something like a kaleidoscope. Pressing my palms against my closed eyelids seems to amplify the effect.


Awesome. Now I can sleep more easily (in my brightly colored darkness).


I'm not sure about the geometric shapes, but I think I do see the pixels and I have always wondered about it. Sometimes it doesn't happen when it's completely dark, just mostly dark, and I'd be very interested to know about the cause of that.

I remember telling my dad at some point about the floaters, but without reference I just sort of described them wierdly and I think he just sort of forgot about it, and whenever I saw them it plagued me as to their cause. Glad I finally learned about that.

It might be due to thermal activation of the photoreceptors. As I mentioned before, the photoreceptor is really just a chemical receptor that is pre-loaded with a light-sensitive molecule. That molecule changes shape and pops out when it interacts with light of the appropriate frequency, turning off the receptor.

At least ideally. But nothing in biochemistry is ideal, it is all based on random events that have been somewhat biased in one direction or another. in the case of photoreceptors, the light-sensitive molecule will sometime change its shape just due to thermal energy around it. In brightly-lit environments this is overwhelmed by real photodetection events so you don't notice it, but in very dark environments it can make up a significant fraction, even a majority, of such events. They are amplified by your visual system and you perceive them as light

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Re: 1080: "Visual Field"

Postby PM 2Ring » Fri Jul 13, 2012 6:06 am UTC

On seeing stuff when you press your eyes:

http://en.wikipedia.org/wiki/Phosphene wrote:A phosphene is a phenomenon characterized by the experience of seeing light without light actually entering the eye. The word phosphene comes from the Greek words phos (light) and phainein (to show).[1] Phosphenes are flashes of light, often associated with optic neuritis, induced by movement or sound.[2][3]

Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex as well as by random firing of cells in the visual system.

[...]

The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks.[6] The pressure mechanically stimulates the cells of the retina. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light.

Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene. Hermann von Helmholtz and others have published drawings of their pressure phosphenes. One example of a pressure phosphene is demonstrated by gently pressing the side of your eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.

and
MadSci wrote:It has been widely reported that prisoners confined to dark cells often see brilliant light displays, which is sometimes called the "prisoner's cinema." Truck drivers also see such displays after staring at snow-covered roads for long periods, and pilots may experience phosphenes, especially when they are flying alone at high altitudes with a cloudless sky. In fact, whenever there is a lack of external stimuli, these displays can appear. They can also be made at will by simply pressing your fingertips against closed eyelids.

In addition, they can also be produced by an electrical shock. In fact, reportedly, it was high fashion in the eighteenth century to have a phosphene party. It is noted that Benjamin Franklin once took part in such an encounter where a circle of people holding hands would be shocked by a high-voltage electrostatic generator, so that phosphenes were created each time the circuit was completed or broken.

The earliest account of phosphenes is given by the Bohemian physiologist Johannes Purkinje in 1819. [...] Oster (1970) suggests that, because phosphenes originate within the eye and the brain, they are a perceptual phenomenon common to all mankind. The visual areas of the brain at the back of the head (occipital lobe) can also be stimulated to produce phosphenes.

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Re: 1080: "Visual Field"

Postby marsman57 » Fri Jul 13, 2012 12:30 pm UTC

morgothcr wrote:
marsman57 wrote:I felt like I did it correctly, but I could see the blind spots without any problem. Did anyone else have this experience?

I think it's because each eye is compensating for the blind spot on the other one, so you really don't have a blind spot while looking with both eyes.
Try covering one eye at a time: The blind spot on the corresponding side magically, well, disappears...


Thanks. The left eye one disappeared about 90% when I did that. The right eye was still there, but kind of fainter. I am supposing the positioning was just a little bit off for me in that case.

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Re: 1080: "Visual Field"

Postby tastelikecoke » Fri Jul 13, 2012 12:44 pm UTC

PM 2Ring wrote:it was high fashion in the eighteenth century to have a phosphene party.

I've known phosphenes, but a phosphene party? Are the phosphenes really fun and exciting to get a shock for it?

Edit: I remembered one fun phosphene I had that appeared like a red star row field. So I think I solved my question.

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Re: 1080: "Visual Field"

Postby J Thomas » Fri Jul 13, 2012 5:56 pm UTC

tastelikecoke wrote:
PM 2Ring wrote:it was high fashion in the eighteenth century to have a phosphene party.

I've known phosphenes, but a phosphene party? Are the phosphenes really fun and exciting to get a shock for it?


Think about it. It's 1790. Paris. You are at a party. Everybody sits in a circle, you're between two ladies, and they tell you all to hold hands. They turn off the lights. If you aren't touching both of the ladies -- somewhere -- when the spark comes then everybody will know somebody has broken the chain. But any kind of skin-to-skin contact in the dark is OK.

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Re: 1080: "Visual Field"

Postby Richard Kirk » Fri Jul 13, 2012 10:30 pm UTC

Angua wrote:Of course, one of the reasons the body filters out the blue from the fovea is due to the fact that red and green are nice and close together, so you get less difference in focusing them as different wavelengths focus differently. It also helps increase the resolution as you only have to go two cells apart rather than 3.


As always, it is a bit more complicated than that. The eye lens has pretty terrible chromatic aberration, so even if you had the resolution off the eye axis, you would not be able to see much. We have only a few percent of blue cells compared to red and green, and they are connected slightly differently, so even if you projected a perfect image onto the retina, we still could not resolve much in the blue. Anyhow, the centre of the eye is not flat, but has a pit in the middle. This helps cram in more cone cells but it must also mean that having a flat plane of focus is not as important as the other physical constraints. Hemholtz th physicist said if he had a camera that was like the human eye, he would send it back to the shop: the optics are pretty rubbish but the post processing is awesome.

If you are as old as I am, you may see a brownish, long, wiggly floater. This is easy to spot if you look up, then down at something like the sky. This is probably a blood vessel that went from the back of your eye to the lens, and supplied oxygen to it until you are born, when it detached. I don't know where it was all the time in between, but there it is now.

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Re: 1080: "Visual Field"

Postby PM 2Ring » Sat Jul 14, 2012 2:22 am UTC

TheBlackCat wrote:3. Although it has not be conclusively confirmed, due to the genetics involved it is possible that the mothers of some color-blind men have an additional photoreceptor and thus might be able to see colors other people can't (that is, two colors that seem the same to most people might seem different to them). Although even if they have the photoreceptor there is no guarantee they would actually be able to use it.


I know a female optometrist who suspects she may be a tetrachromat. She has no children, but several of her male relatives, including a brother, have some degree of red-green colour-blindness.

Wikipedia
Possibility of human tetrachromats

Humans and closely related primates normally have three types of cone cells and are therefore trichromats (animals with three different cones). However, at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space.[8]

In humans, two cone cell pigment genes are located on the sex X chromosome, the classical type 2 opsin genes OPN1MW and OPN1MW2. It has been suggested that as women have two different X chromosomes in their cells, some of them could be carrying some variant cone cell pigments, thereby possibly being born as full tetrachromats and having four different simultaneously functioning kinds of cone cells, each type with a specific pattern of responsiveness to different wave lengths of light in the range of the visible spectrum.[9] One study suggested that 2–3% of the world's women might have the kind of fourth cone that lies between the standard red and green cones, giving, theoretically, a significant increase in color differentiation.[10] Another study suggests that as many as 50% of women and 8% of men may have four photopigments.[9]

Further studies will need to be conducted to verify tetrachromacy in humans. Two possible tetrachromats have been identified: "Mrs. M", an English social worker, was located in a study conducted in 1993,[11] and an unidentified female physician near Newcastle, England, was discovered in a study reported in 2006.[10] Neither case has been fully verified.

Variation in cone pigment genes is widespread in most human populations, but the most prevalent and pronounced tetrachromacy would derive from female carriers of major red-green pigment anomalies, usually classed as forms of "color blindness" (protanomaly or deuteranomaly). The biological basis for this phenomenon is X-inactivation of heterozygotic alleles for retinal pigment genes, which is the same mechanism that gives the majority of female new-world monkeys trichromatic vision.
[...]

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Re: 1080: "Visual Field"

Postby Boppre » Sat Jul 14, 2012 6:36 am UTC

This comic prompted me to test my blind spot. How big, vibrant and fast can objects be and still be completely invisible? The answer is a lot:
http://www.swfcabin.com/open/1342241982

The squares are 60 pixels wide, suggestions welcome. I'm now thinking how to exploit this on a game, but making the player close an eye will be hard.

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Re: 1080: "Visual Field"

Postby Max™ » Sat Jul 14, 2012 8:20 am UTC

I think we've been cheated.
Spoiler:
Image
mu

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Re: 1080: "Visual Field"

Postby Pfhorrest » Sat Jul 14, 2012 9:48 am UTC

Any word on whether those shrimp perceive in a 13-dimensional color model the way we perceive in a 3-dimensional one, or do their brains just give up on that shit and map things to a linear continuum at that point?
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