Science & Technology

Curvature Blindness Is an Optical Illusion That Will Rattle Your Brain

We've all seen the one where it's either two faces or a vase. And that one that shows an old lady and a young woman at the same time. Been there, done that. Thanks to a November 2017 discovery, a brand new optical illusion is here to trip you up all over again. Curvature blindness is both mind-blowing and frustrating, as any good illusion should be.

Curves in All the Places

The curvature blindness illusion is neat little design made up of rounded wiggly lines and jagged zigzags over areas of black, white, and gray — at least, that's what it looks like. What if we told you there were no sharp zigzag lines in this image? Each line is an identical sine curve. Look at it again. And again. You might need a few close examinations, and you still may not be able to grasp the truth.

This optical illusion was introduced to the world by psychologist Kohske Takahashi of Chukyo University, Japan in a November 2017 paper published in the journal Perception. Takahashi describes what happens here: "a wavy line is perceived as a zigzag line." He also notes the unusual strength of this illusion, saying "unless one carefully stares at the region that looks like a corner, it is hard to find that all lines are physically wavy. Despite the simplicity and effect magnitudes, to the best of our knowledge, no one has reported about this phenomenon."

Do My Eyes Deceive Me?

You may have noticed that where the dark gray and lighter gray segments meet in high and low points, they appear to have sharp edges over the gray background but rounded edges over the white and black backgrounds. When one shade makes up the entire high or low point, you see the rounded curves over any background. How is that happening? Takashi notes that your brain gets a little confused with the ambiguity and defaults to seeing corners when the segments meet at the highs and lows: "The underlying mechanisms for the gentle curve perception and those of obtuse corner perception are competing with each other in an imbalanced way and the percepts of corner might be dominant in the visual system."

Playing with where the different shades meet up on the line is one thing, but the background plays a vital role in this illusion too. The switch-up is only apparent against a gray background, not the white or black background. This suggests that, in order for the illusion to work, the lines must have one shade that's lighter than the background and one that's darker. The next question to answer: Why does the brain default to seeing sharp corners? Hopefully, Takashi will tackle that next. In the meantime, enjoy this visual adventure!

For more visual trickery, check out "The Ultimate Book of Optical Illusions" by Al Seckel. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

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Written by Joanie Faletto January 5, 2018

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