Optical illusions are puzzles for the eye. They reveal how different combinations of images — light and shadow, shape and density, foreground and background — can trick viewers into seeing something unexpected.

And we are still discovering new illusions that deceive and delight us.

In the above image, pairs of wavy lines run horizontally across the screen. In the white and black corners, they’re fine. But in the gray area, half of those wavy lines suddenly look like zigzags.

The only difference? The alternating pattern of light and dark patches on each line. In lines where the peaks of the waves are dark and the valleys are light, the wavy pattern remains.

But when the dark and light patches are the ascending and descending parts of the wave, our eyes interpret them as lines forming corners instead of wavy lines.

This is known as the curvature blindness illusion.

As with many optical illusions, this is all about contrast. The white and black backgrounds allow you to view the alternating pieces as one continuous wavy line, whereas the gray background forces you to regard those alternating pieces as individual segments.

Those individual segments are granted the illusion of three-dimensions, and our minds process the lighter ascending line and the darker descending line as “walls” forming a corner, rather than the rising and falling of a sine wave.

It’s amazing how distinctly different the pairs of lines look with just those small variations. Even knowing how I’m being manipulated, it’s still hard to convince myself that I’m not actually seeing what I’m seeing.

Very cool stuff.

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