Illusion

[A.Saturnus]

I'm no medic, but I surmise that it would probably have something to do with the rods and cones in the retinae.

Where's Rory when you need him?

The cones in the retinae are the color receptors. The rods have nothing to do with it. And believe, it's me who should know how it works, not Rory.

Colors absorb light, and every color has it's counterpart. The counter is always 180 degrees further on the circle. If you look at that picture, all the colors are the opposite of the 'real' picture, when you look at the black and white picture after focussing on the dot, your brain makes a negative (like foto's), and in this case the negative is the way it should normally look.

In principle you're right. Though the thing that interests me is the "your brain makes a negative"-part. How does the brain make a negative?
Well, actually it isn't the brain, it's the retinae, or more precisely the cones. If you look the center point, the same cones get stimulated by light of the same color over a period of time. This saturates those cones that respond to that color, that means they get harder to be activated by further stimulation (that is so because their synapses run out of neurtransmitter - but that would lead to far now). If you then look at a white or a black sheet or screen, you'll see what we call an afterimage. This is generated by the remaining cones that are not saturated. Normally all cones would be stimulated equally when you see something colorless, but since some can't be stimulated, those that can create the perception of color.
So far everything is clear to me. The interesting part is that the negative creates an afterimage of exactly the positive when you look at the black-and-white picture. What I'd like to know is whether there's a special trick to it (like a precise calculation of light intensities in the b&w-picture) , or whether this will always happen to any b&w-picture that is preceded by a negative.

[InsaneApache]

The cones in the retinae are the color receptors. The rods have nothing to do with it. And believe, it's me who should know how it works, not Rory.



In principle you're right. Though the thing that interests me is the "your brain makes a negative"-part. How does the brain make a negative?
Well, actually it isn't the brain, it's the retinae, or more precisely the cones. If you look the center point, the same cones get stimulated by light of the same color over a period of time. This saturates those cones that respond to that color, that means they get harder to be activated by further stimulation (that is so because their synapses run out of neurtransmitter - but that would lead to far now). If you then look at a white or a black sheet or screen, you'll see what we call an afterimage. This is generated by the remaining cones that are not saturated. Normally all cones would be stimulated equally when you see something colorless, but since some can't be stimulated, those that can create the perception of color.
So far everything is clear to me. The interesting part is that the negative creates an afterimage of exactly the positive when you look at the black-and-white picture. What I'd like to know is whether there's a special trick to it (like a precise calculation of light intensities in the b&w-picture) , or whether this will always happen to any b&w-picture that is preceded by a negative.

I bow to your superior knowledge and aplogise for any hurt that I caused. It was not my intent. I know that you are a psychologist, someone who collects the rent, from castles in the sky, built my psychiatrists.

However I believed this to be more of a physical phenomenon than a psychological one.

Wait!!!

They are one and the same.

[Alexanderofmacedon]

That's crazy!

[Zalmoxis]

Neat trick.

[Fragony]

So far everything is clear to me. The interesting part is that the negative creates an afterimage of exactly the positive when you look at the black-and-white picture. What I'd like to know is whether there's a special trick to it (like a precise calculation of light intensities in the b&w-picture) , or whether this will always happen to any b&w-picture that is preceded by a negative.

Will always happen, try it yourselve. Take a white peace of paper, and put a smaller green one on top of it, stare at it, and then remove it. What you will see is a red afterburn. If you use blue, you will see orange. If you want a precise calculation, the color circle I posted before is just that. It isn't the intensity of light by the way, color doesn't really exist. White light has all the colors, and when we 'see' a color part of the light's energy is absorbed by the surface it's projected on, and the filtered light that bounces back we percieve as color. The energy that is absorbed is the negative, it's like black and white.

[David]

Will always happen, try it yourselve. Take a white peace of paper, and put a smaller green one on top of it, stare at it, and then remove it. What you will see is a red afterburn. If you use blue, you will see orange. If you want a precise calculation, the color circle I posted before is just that. It isn't the intensity of light by the way, color doesn't really exist. White light has all the colors, and when we 'see' a color part of the light's energy is absorbed by the surface it's projected on, and the filtered light that bounces back we percieve as color. The energy that is absorbed is the negative, it's like black and white.

If I may add:

As far as I know there are three types of cones (rods dont matter, they sense movement). They are sensitive to three different wavelenghts of light (red, blue and greenish-yellow kinda). So if you look at the picture, the cones get saturated as A.Saturnus described: but only the cones that are sensitive to the corresponding wavelength of light. Then if you move the mouse over the picture, your retina gets bombarded with "white" light again (so all wavelengths). However, your blue / yellow are not working (saturated) in certain areas (therefore if you move your head the image shifts over your retina, and therefore uses different (unsaturated) cones). What you see is every wavelength (white), except the wavelengths of saturated cones.

So blue saturated = red + yellow = orange, and the yellow sky becomes blue.

NB. In normal situations this wont happen, cause your eyes and head are constantly moving/scanning.

Another small addition:
Saturation is not caused by lack of neurotransmitter, but by repolarization time of the neurons. Sight works via negative signaling as Fragony explained. As paradoxal as it may be, if cones get activated they hyperpolarize.

I cant remember completely, I should have some books on this...