Optical illusions!

http://snarkmarket.com/blog/snarkives/optical-illusion.gif
Both central circles are of the same size :)

Yes, the IMAGES of the bulls are the same size, but if this painting is supposed to represent a real scene than the brown bull is bigger. Just like the images of the bricks in the walls are different sizes due to perspective, but the real bricks would be the same size.

Good point, OsakaGuy.

Usually in that illusion the image is more abstract, and the converging lines don't necessarily represent perspective. I just thought this was an amusing version.

http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html

Thisi s my favorite illusion. The Two squares are the same color.

I thought I'd seen every optical illusion, until I found this one:

http://www.cheswick.com/ches/me/

The effect is similar to any after-image illusion, but it lasts for hours, in many cases more than a full day.

For those not knowing images of M.C. Escher:

http://images.google.com/images?q=escher

This one that flew the internets last year is my favourite:
http://www.johnsadowski.com/2006/05/lil-color-illusion.html

There were many of them around and they are easily made apaprently.

I am still looking for info on an illusion of movement called the "ghost coin." Just rub two coins together, up and down, with the index finger of each hand. You will see a third coin appearing between and below the two moving coins. I assume it is due to retention of the visual image, but I have not found any formal work on this and also have not figured out why the third illusory coin always appears below the other two.

Actually what is illusiory here is the claim that Bovril is always the same. It used to be made from beef extract, and was heavily marketed as such (hence the bulls). Now it is completely vegetarian. (It tastes the same to me though, although one wonders how good our gustatory memory really is.)

Very fun! I will put your link in my next post!

Haven't seen enough illusions?

The moire's the merrier, I say.

The Akiyoshi one is fascinating. Also because when I unfocus my eyes even slightly, the illusion completely disappears.

Curious - can someone with poorer eyesight examine the Akiyoshi illusion and comment on whether or not it works with and without glasses. (I have better than normal vision.)

Agoodspellr,

I am somewhat nearsighted (enough to have a restriction on my license and to think the font styles on this site is too tiny at night). And I also have never been able to do stereograms. So I am a mild example of your question and it does work both with and without glasses. It didn't work at all the first time I looked at it, but now I can't look at it at all without seeing them float.

Also followed the link to his other illusions and I felt that the roller I'm focused on moves faster. This may be similar to what you report. I'm thinking the rollers might be an interesting image to play with on our eye tracker screen but have not thought of a way to record the *perceived* motion. (Maybe talk-aloud with a facilitator trying to record, or maybe three different keys--could even use a mild deception and tell a naive participant it's a reflex game. So now I'm trying to remember if ClearView records keystrokes.)

There seems to be a stray quote at the end of the URL for SandLot Science. (It's encoded as %22.)

The correct URL is:

http://www.sandlotscience.com/Illusion_Jump_Main/Master_Jump.htm

Thanks, Michael. It's fixed now.