It's official! The best visual illusion, as voted for 2007, is this Leaning Tower Illusion by Kingdom, Yoonessi & Gheorghiu from McGill, 2007.
Here is a novel illusion that is as striking as it is simple. The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more, as if photographed from a different angle. The reason for this is because the visual system treats the two images as if part of a single scene. Normally, if two adjacent towers rise at the same angle, their image outlines converge as they recede from view due to perspective, and this is taken into account by the visual system. So when confronted with two towers whose corresponding outlines are parallel, the visual system assumes they must be diverging as they rise from view, and this is what we see. The illusion is not restricted to towers photographed from below, but works well with other scenes, such as railway tracks receding into the distance. What this illusion reveals is less to do with perspective, but how the visual system tends to treat two side-by-side images as if part of the same scene. However hard we try to think of the two photographs of the Leaning Tower as separate, albeit identical images of the same object, our visual system regards them as the 'Twin Towers of Pisa', whose perspective can only be interpreted in terms of one tower leaning more than the other.
Very cool. I also recommend the Bouncing Brains by Hansen, Hamburger and Gegenfurtner (researcher involved with the blue banana). Check out all the 2007 winners and finalists, now available online! The winners are...us.
Comments
What happens when it's three in a row?
Posted by: derek | May 15, 2007 1:06 PM
I don't know, Derek, perhaps that's a question toward the 2008 contest.
Posted by: Sandra | May 15, 2007 1:34 PM
I'm actually pretty sure the picture of the third would just be an empty landscape since the building would be so tilted that it would have fallen over.
Posted by: Steve | May 15, 2007 1:50 PM
Here it is with three, if you are curious:
3 pisas
Posted by: gertie | May 15, 2007 4:21 PM
Thanks, Gertie.
Posted by: Sandra | May 15, 2007 6:22 PM
Whoa, that's freaky: B is leaning more than A, and C is leaning more than B by the same amount, and C is leaning more than A by the same amount, not twice as much. Intuitive proof that 1+1=1!
Thanks gertie!
Posted by: derek | May 16, 2007 6:30 PM
I'm not sure about this winner ... I think its weak sauce (get it?) :o|
Posted by: ArtM | May 21, 2007 12:57 PM
I notice that if they are stereo fused (I'm cross viewing them), I get a false stereo depth percept.
Posted by: Mark Dow | May 21, 2007 3:13 PM
Can anyone explain why, if the two photographs are identical, one sees the right tower as leaning more than the left? Why not the left leaning more than the right? Or does this involve eye dominance?
Posted by: Howard | May 21, 2007 4:54 PM
dandik
Posted by: motta | May 22, 2007 1:56 PM
I am a musician and a psychiatric survivor. This song is brilliant and everyone who works in the 'mental health system' should be forced to listen to it to experience what it is like to have the boot on the other foot!!
Posted by: DDos Protection | November 7, 2009 2:31 AM