Ready to have your mind boggled? Take a look at the image above. What shape are the lines? Do they look like curves, or zigzags?
The image, spotted by Digg, is a new type of optical illusion published in the aptly named journal i-Perception. Discovered by Japanese psychologist Kohske Takahashi, it’s called the “curvature blindness illusion,” because—spoiler—the contrast of the lines against the gray background makes our eye see some of the lines as zigzags when, in fact, they’re all smooth curves.
The illusion relies on a few different factors, according to the three experiments Takahashi conducted. For it to work, the lines have to change contrast just at or after the peak of the curve, reversing the contrast against the background. You’ll notice that the zigzags only appear against the gray section of the background, and even against that gray background, not every line looks angled. The lines that look curvy change contrast midway between the peaks and the valleys of the line, whereas the lines that look like they contain sharp angles change contrast right at the peak. The curve has to be relatively gentle, too.15