How does this work?

[Unabogie]

Does anyone know why this works the way it does? I've seen several variations of the trick.

http://twitpic.com/7mipik

For people who don't want to click, you see what looks like a reverse negative image with a red dot on it. When you stare at the red dot and then look at the wall and blink, you see the image in full color.

 

[ceptimus]

In simple terms, the colour receptors in your retina get 'tired' after continuous exposure, so they don't work as well for a short while afterwards.

If you stare at red for a while, then look away at a medium gray, then the blue and green receptors in your eye will fire more strongly than the tired red ones, so the gray will look more like cyan blue for a while.

 

[Unabogie]

In simple terms, the colour receptors in your retina get 'tired' after continuous exposure, so they don't work as well for a short while afterwards.

If you stare at red for a while, then look away at a medium gray, then the blue and green receptors in your eye will fire more strongly than the tired red ones, so the gray will look more like cyan blue for a while.

But why do I see skin tones? Maybe I don't understand colors enough. Can you elaborate?

 

[ehcks]

But why do I see skin tones? Maybe I don't understand colors enough. Can you elaborate?

The color receptors you're using get tired, so the ones you're not using are stronger when you look at white. The ones that are now stronger are the opposites of the ones you were using earlier, so you see the opposite of the inverted image.

 

[Unabogie]

Thanks, guys!

 

[casebro]

I know that occasionally I 'rest my eyes' at the computer, and when they re-open colors are waaay too bright, for just a couple seconds. So receptors do get tired. And re-energized. Now, how to keep them working at full power all the time? Vitamin? Mineral? Exercise?

 

[dlorde]

In simple terms, the colour receptors in your retina get 'tired' after continuous exposure, so they don't work as well for a short while afterwards.

The coloured after-images aren't directly the result of colour receptor fatigue, but of the fatigue of the next level of colour processing neurons, the 'opponent cells', as described in section 3 'Opponent Cell Fatigue and Colored After-images' of this (literally eye-opening) document.

Incidentally, if you want to get the full effect of the 'impossibly dark', the 'self-luminous', and the 'hyperbolic' after-image colours using the colour plates in the document, it should be printed out using a reasonably colour-accurate printer, rather than viewing on-screen.

 

[Stomatopoda]

Now, how to keep them working at full power all the time? Vitamin? Mineral? Exercise?

You don't. The effect is due to the way human eyes are structured and interact with the brain, not due to any damage or fatigue (in the sense of muscle fatigue).