The illusion dubbed as “curvature blindness” is described and explained in the journal i-Perception, which provides scientific breakdown and analysis of the optical illusion. It describes how a wavy line can be perceived as a zigzag line on a white, grey and black background. “Here, we report a novel illusion —— Curvature Blindness Illusion —— that will provide novel implications for contour perception, in particular, for the underlying mechanisms of curve and corner perception,” Takahashi wrote. In the image below, which displays the illusion, one can see pairs of wavy lines and pairs of zigzag lines against a grey background. Despite how they appear, all the lines are exactly the same.
The lines in the top left and bottom right corner when viewed against the grey background appear curvy like sine waves, while those with the grey background appear to have a sharper zig-zag-like pattern. However, a closer look at the grey background reveals that the curved, dark lines that are running from top to bottom appear to carry the zig-zag pattern, although they are curved in reality. In simpler words, the image consists of light and dark grey dashes linked to make parallel lines in waves and zig-zags on a white, grey and black background. But in reality, the zig-zags don’t actually exist. “Physically, however, all lines are wavy lines with an identical shape; there is no triangular wave and hence there is no corner,” Takahashi said. “Despite the simplicity and effect magnitudes, to the best of our knowledge, no one has reported about this phenomenon.” It’s unclear exactly why human brain perceive the zigzag contour as a sharp corner. According to Takahashi, when our brains are confused and there is ambiguity over whether a line is a smooth curve or not, it is easy for the brains to see corners rather than curves our brains. “We propose 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 a corner might be dominant in the visual system,” Takahashi explained. “As the effect magnitudes are quite strong, unless one carefully stares at the region that looks like a corner, it is hard to find that all lines are physically wavy,” added Takahashi.
