Why do our eyes do this?

[GrandMasterK]

http://www.johnsadowski.com/big_spanish_castle.html

[Dak]

heh, probably the best one of those that i've seen.

 

The chemical processes that translate different wave-lengths of light into electro-chemical signals that our brain can interpret take a slight time to reset.

 

meaning that if you, say, stare at blue for a while, and then look at white, your blue-receptor chemicals will be slightly depleted, meaning that the green and red light will be detected better than the blue, thus over-representing the levels of green and red and making them look yellow.

 

 

colour....light levels....detection....detected levels....colour seen

 

white.....100green.....OK...............100green.........yellow

.............100red.......OK...............100red

.............100blue......suppressed......50blue

 

As for why it happens so fast in this case, or why it persists so long... no idea.

[KLB]

As the say here in New England, that was "wicked good." Often times weird eye trick pictures don't work with my eyes but this one worked very well. What I found weird was that there wasn't a fadding of color, but the picture switched from color to black and white as if a switch had been flipped after a few seconds.

 

Dak thanks for the explaination.

[swansont]

Rods and cones are not equally disributed in the eye. Rods are more peripherally located and are sensitive to movement, so when your eye is still, the peripheral vision tends to fade and blur. It's also an effect in low light — the centrally located cones are less sensitive under those conditions, so looking straight at something in low light will tend to make it seem like it's fading away. (astronomers are very aware of this)

 

wiki entry on rods that has more detail

[Peels]

I think it is caused by the sensory memory.

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

[Edtharan]

The cones in our eyes come in 3 types. One for Red, one for Blue and one for Green. Each of these cones uses a chemical that breaksdown in light of the appropreate wavelength.

 

When we look at something for a while these chemicals get depleated and take a short period of time to replenish. If we rapidly then look at something else (white works best) then the cones that had the chemical depleated will only give a weak (or nonexistant) signal to our brains. The cones that didn't get depleated will give a much stronger signal to the brain.

 

For example: If I was to look at a green image for a while (30 sec is long enough) then I was to look at a white wall, I would see a Red+Blue (Magenta) image.

 

The colours in the castle picture are chosen so as to depleate the cones of the oposite colour from the original picture (in most image manipulation software they have a function to do this). The black and white image is used to give the rods (they only detect the intensity of light not the colour) the corect brightness levels for the picture.

 

An interesting side line of this, is that if you are able to keep your eyes completely still (this is almost imposable unless you use a muscle relaxent injected into the muscles around the eye - don't try this at home, it is usually done for eye surgery) then over a period of time the colour detection chemicals in your eyes will be depleted and you will no longer see anything. If something is moved (or walks past your vision) you will see it as it will activate the cones in your eyes that have not yet been depleted.

[Heretic]

I can't remember the exact term for this, but it happens with ALL senses. It was essential to our survival and is still very helpful.

 

My understanding is:

 

Whenever one of your senses is continually stimulated, whether it be seeing the same colors, hearing the same sounds, etc. your brain tunes it out. I know that in the eyes the response is somewhat different, as the cones and rods actually get "tired".

 

This system helps you find changes in the enviroment. Something that is paramount to survival, whether it is used to find prey or avoid predators it's a handy tool.

 

Take for example you're in the woods and birds are constantly chattering. If you continue to focus on that chatter you might not hear that twig snap behind you. However with your brain getting rid of "background noise" it allows you to focus more clearly on new sounds.

 

It's really fascinating stuff.

[swansont]

I was looking at this again and realized that I never moved the mouse over the picture. My prior explanation only deals with why the image seems to bleed out during the time you are staring at it. The negative image arises basically because your brain assumes a certain white level, so when you stare at colors for a long time, your brain compensates, and then when you look at a neutral area, you esentially see the correction your mind has made. There may (also) be chemical depletions in the pigment reactions that trigger this.

 

I get this "negative" effect when wearing laser goggles that filter red and IR. When you take them off everything has a pinkish hue to it for several seconds.