Corners are especially important because they provide a point where two lines meet. This is, of course, extremely useful for picking a spot where you’re going to meet up on the street before getting in line for The Last Jedi, or, in the case of your visual perception, providing a point to focus on so that a larger shape can be categorized. There is a (pun intended) kink in this method of processing visual information however, which arises in the form of an illusion in the graphic below. Every line you’re looking at is exactly the same in terms of its curvature, but your brain will think every other set of lines is rigidly bent thanks to how your brain perceives corners.

Image: Takahashi (2017) / iPerceptionDiscover reported on the incredible illusion, which was discovered by psychologist Kohske Takahashi of Chukyo University in Japan. Takahashi’s illusion was published in i-Perception, a peer-reviewed, open-access journal that focuses on “all the senses and the perceptual processes of humans, animals and machines.”

If you’re wondering how exactly this “curvature blindness” illusion takes place in your mind — and it really is an illusion despite every atom of your being probably telling you that you’re looking at two different sets of lines — it’s a bit complicated to say the least.

Takahashi notes in the abstract for the paper that  “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.” Meaning that because corners are so important for how we process visual information, when a curved line appears to be on the cusp of smooth versus zig-zag, we’ll err on the side of zig-zag because we can’t help but try to spot corners anywhere we can due to their importance in helping us make visual sense of the world. This makes sense as a line is really only a line until it turns a corner.

In terms of why exactly we perceive the apparently zig-zagged lines to have corners while they’re still curved exactly like all the others has to do with the bands of coloration, where they meet along the wavy lines, and what backgrounds they’re set against. All of the lines, even those that look zig-zagged, display a sine curve, as you can see in the corners when they’re set against white or black backgrounds. This changes when they’re set against a gray background however, as it seems to “cast a light” against any gray section of line that cuts off in the middle of a curve.

Graphing a sine wave (y = sin x) 

Takahashi claims that this is a “novel illusion,” which shows that “the underlying mechanisms of curve and corner perception could not be independent, but rather would interfere or compete with each other.” Meaning again that when it comes to visual perception, corners and curves compete for our attention, and when it’s a close call, corners win out because they usually help us to determine what shape something is.

Although it’s extremely difficult to instruct your brain to perceive any of the zig-zag lines as genuine wavy lines, it seems like the closest you can get to seeing all the lines as their true wavy selves is to place your fingers over the lines that don’t zig zag and then take another look at the ones that do. Or you can just accept the fact that not everything is as it seems.

What do you think about this “curvature blindness” illusion? Will you ever think of corners in the same way? Give us your thoughts in the comments below!

Images: Takahashi (2017) / iPerception, Orion Pictures

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