Escherian Stairwell...

Via reader and friend Simon M.  Watch this video first:


Then for an explanation, watch this:

Shake Your Head!

Carefully, though, don't hurt yourself!  If you shake your head side-to-side while staring at the picture at right, it becomes more obvious what the picture is showing. 
I've noticed a similar phenomenon when looking through window screens, or (better yet) picket fences.  It's a terrific example of how your brain puts assembles information gathered over time...

This isn't really an illusion in the usual sense, but more a demonstration of the brain's contribution to perception...

Via friend and reader Simon M...

Audio Illusion...

Known as the “McGurk Effect”, this is simply awesome.  I must have watched this 10 times and I can still hardly believe it.  Via reader Simon M.:

Optical Illusion of the Year...

The colors on the dots below are changing the entire time the video is playing, but when the wheel starts jogging, they appear to stop.  Awesome!

Great Illusion...

The four ramps in this device actually slope down toward the center, so the balls are really just rolling downhill, powered by gravity.  The illusion is created by making the ramps non-rectangular in a very specific way.  From one particular perspective, this tricks your brain into thinking that the ramps slope upward toward the center – thus creating the illusion of balls rolling uphill.  You can see this for yourself as the demonstrator rotates the entire assembly – you'll suddenly see it as it really is, with all four ramps sloping down toward the center...

Awesome Optical Illusion...

That is not a blue spiral, but rather concentric blue circles...

Great Optical Illusion...

The image at right won the “Best Visual Illusion of the Year” award.

Why?

Because the two halves are identical!

Read all about it here.

Your Lyin' Eyes...

The picture at right (click to enlarge) appears to show a pair of blue spirals and a pair of green spirals on a red/purple background. That's what your eyes are plainly telling you.

Your eyes are lying.

Both of those spirals are exactly the same color.

I didn't believe it either, so I enlarged the picture in GIMP and examined it under extreme magnification. Those colors really are the same!

All is explained here and here.

Just Weird!

I ran across this on BoingBoing, where they showed the picture of the girl at right. Not a real girl, BTW — just a little photoshopping. The weird part is how this affects one’s perceptual system. When I look at those pictures (especially the girl, for some reason), I feel a bit like I’m cross-eyed, and no matter how long I stare at it, I don’t feel like I’ve actually clearly seeing the picture. It’s a very strange feeling, hard to put into words.

Click on either thumbnail to get a larger image. And if you’re intrigued by these, there are many more here.

I speculate that the slightly alarming visual effects are caused by the special sensitivity of our perceptual system to human faces; that somehow these faces are “wrong” in a way that our perceptual system just cannot handle. Kind of like what happens when you get dizzy, because your perception (the combination of spatial and visual, in that case) is getting conflicting inputs.