​In a new article published in the journal i-Perception, researcher Kohske Takahashi presents a new optical illusion, which he calls the "curvature blindness illusion." It's pretty trippy. 

Take a look at the image below. As you can see in the top left, against the white background, every set of lines has the same shape (a sine curve). But when viewed against the gray background, the lines where the top curve is black and the bottom curve is white still look rounded, while the lines where each curve is half-black and half-white look like sharp angles:

It's unclear exactly why our brains perceive this, but Takahashi proposes that our brains default to seeing corners rather than curves when they get confused:

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.

[via Smithsonian]