Goosenecks of the San Juan Illusion

I thought I would point out an interesting illusion that I accidentally discovered with a friend a number of years ago. I was showing him some photographs in Stokes' Geology of Utah. One shot was an b/w aerial view of the Goosenecks of the San Juan. Anyhow, we were sitting at a table across from each other with the book between us. I pointed to the river, he responded "What river?" I said, "That river there, that's the San Juan river." He responded again, "I just don't see which river you're talking about." I was very confused for a moment, then I decided I should take a look at what HE was looking at. The book was oriented so the right side up was in line with my view...basically he was looking at it upside down. When I flipped it around and looked at it, I realized why he wasn't seeing it.

I have photographed the page of Stokes book and rotated the image to demonstrate the illusion. It's amazing how our brains can be tricked. If you have Stokes book (or feel like printing the image) try the following: Place the book/image upside down ... then slowly rotate the book around and see if you can maintain the illusion, before it snaps back. Once it snaps back, can you make it invert again? I can't.

Stefan Folias :: 10.15.06