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Another Cool Color Illusion:

From Discover's Bad Astronomy blog. Thanks to Tim Sandefur (Panda's Thumb) for the pointer.

wolfefan (mail):
Very cool indeed - thanks!
7.13.2009 3:28pm
Go Horns!:
I wonder if a defense attorney has ever used a similar image to discount eyewiness testimony.

So you say that the car/jacket/etc. was blue. Could you please describe this picture? What colors do you see? Really, green and blue . . . So maybe what you say was green and not blue.

Really, the lines are continuous? Well, upon closer examination we can see that they are not . . . Maybe your mind was just filling in the blanks.

Anyone ever seen an exchange like this in Court? Should a judge allow something like this to happen or would it just be a worthless stunt?
7.13.2009 3:31pm
traveler496:
This is the best static color contrast illusion I've seen; thanks! It's not the best illusion I've heard of, though; that is the following (apologies for going from memory on this, but I can't find a reference and I'm hoping one of you can debunk or substantiate).

Setup:
Subject is shown a black-on white spiral which is rotated clockwise for 30 sec in pink light, then counterclockwise for 30 sec in green light. This is repeated a few times.

Illusion A:
If the spiral is now rotated clockwise in white light, subject reports seeing a black-on-green spiral. When the rotation is reversed, the spiral becomes black-on-pink.

Alternate Illusion B:
If the spiral is stationary, and bathed in green light - you guessed it - it appears to rotate clockwise. Switch to pink light, and the rotation appears to reverse.

Assuming this is for real, it is of course the interaction of the two different modalities (color controlling motion perception, and vice versa) that is so compelling. There's an Isaac Asimov Mystery plot device in there somewhere:-)
7.13.2009 3:46pm
corneille1640 (mail) (www):
I'm willing to buy into the notion that the image is an optical illusion. But if most people (that is, most people who are not colorblind or who otherwise have difficulty distinguishing colors) see the different "green" and "blue" colors, then aren't the colors, for most practical purposes "different"?

In other words, if I were to ask people to point out which spirals are "green" and which are "blue," people likely, with great consistently, would choose the illusory color.
7.13.2009 4:28pm
TNeloms:

In other words, if I were to ask people to point out which spirals are "green" and which are "blue," people likely, with great consistently, would choose the illusory color.


Why does consistency of opinion between viewers discount anything about this? This is true of pretty much all optical illusions; in fact, if this weren't the case then they wouldn't be very compelling, since many people wouldn't "get it."

The main points of these illusions are to point out the strong subconscious processing power that the brain performs automatically when processing stimuli, and to challenge the notion that what you perceive is an accurate reflection of the objective stimuli. I think this illusion does both of those things very well.
7.13.2009 4:53pm
subpatre (mail):
corneille1640 writes: "... aren't the colors, for most practical purposes "different"?"

True. The illusion is from the 'blue' color —made up of two colors like a halftone— has one of its constituent colors the same as one of the two that make up the 'green' color.

An easy test is to sub-sample, forcing an integration. In a photo-editor like Paint, reduce the size to one-tenth (50X50 pixels) and promptly enlarge the size ten times to get the original size. You will have slightly fuzzy spirals of pink, light blue, pink, and light green.

Of course the real illusions are these webpages, since our monitors only show one shade of red, one shade of green, and one shade of blue. There is no yellow, yet the spiral had orange stripes. Spooky ;-)
7.13.2009 5:14pm
Leo Marvin (mail):
The apparently blue spirals bitterly resent being equated with the apparently green ones.
7.13.2009 9:23pm
Skyler (mail) (www):
I think it's a stretch to say that a spiral that is half green and half blue is either one color or another.
7.13.2009 10:26pm

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