Neat.

I was pausing and playing the video to see the exact moment my brain failed when I noticed something even more odd. When he drags the pencil from one boundary to the other the colour darkens on the left side of the pencil first. Its almost as if he is dragging a shadow across the paper.

I got the whole flag to look one shade by staring at the center line keeping my eyes still. Try it.

Huh, this must be some sort of retinal blue-yellow channel adaptation. That's a cool effect. Nice demonstration.

When he removes the pencil, rather than "popping" back in, the separating line gradually "reappears." Stupid brain, outwitted by a bloody #2!

dude its like the matrix!

Actually, the delayed color change in the first move is caused by video compression, watch in HD and the effect is still there, but not as much. If you watch the lowrez , you will notice small black artifacts at the top of the paper in the first second after he moves the pencil.

When I stared at it I saw a 3D stegosaurus.

I was kinda noticing how, to me anyway, the shades actually look like gradients (each panel, not the whole thing) without the pencil, darker on the left side than the other.

If you cover all 3 borders simultaneously, you'll see that all 4 rectangles are the same color! Looks like the borders are the only "illusion" here

http://en.wikipedia.org/wiki/Cornsweet_illusion

*brain failure

Adding video to channels (Brain) - requested by xxovercastxx.

Not to be picky, but this is actually a retina failure.

>> ^Payback:
I was kinda noticing how, to me anyway, the shades actually look like gradients (each panel, not the whole thing) without the pencil, darker on the left side than the other.


That's because of the mach band illusion (pointed out in that link posted by berticus). The mach band illusion can be seen with any slight step change. The cause is well worked out and has to do with the fact that the retina primarily encodes contrast instead of luminance. What happens is that the edges are amplified making the adjacent side appear brighter/darker accordingly. As you move away from the edge, you perceive the appropriate brightness. That creates the gradient effect you pointed out.

Stupid easily-tricked brain fails me again.

>> ^deathcow:
dude its like the matrix!


The greatest trick the Matrix ever pulled was convincing the world it did not exist.

fascinating - and helps to explain why I came back into the party with my pants around my ankles.

I was hoping for a final, "and here's what happens when you put a pencil over all three borders at once."

This post has been removed from the Brain channel by channel owner jonny. Please review the FAQ to learn about appropriate channel assignments.