Psychologist Kohske Takahashi, from Chukyo University in Japan, has discovered that the human brain may experience the so-called curvature blindness that swaps waves for corners.

Curvature Blindness Illusion

In a new study, which was published in the journal i-Perception, Takahashi presented an optical illusion dubbed the curvature blindness illusion to prove this phenomenon. The simple image is consist of light and dark gray dashes that were linked to make parallel lines in waves and zigzags across a white, gray, and black background.

The psychologist showed the image to a small group of students and asked them what they could see in the gray middle area of the picture. All of the study participants saw alternating rows of wavy and zigzag lines.

In experiments, the researcher realized that the only time that the curved lines appear as ziggags was when the lines changed color directly before and after the peak or valley of individual curves, when the lines had a gentle curve, and when the lines are over a gray background that appear in contrast to the dark and light tones of each of the lines.

The final image of the illusion shows each line appearing curved when viewed over the black and white backgrounds. In the gray and middle section, only the lines that change color before and after the peaks of the curves appear zigzagged. Two colors that intersect the peak of the curve produce a subtle vertical line, which exaggerates the sharpness of the peak.

"This illusion implies that, in order to perceive a gentle curve, it is necessary to satisfy more conditions—constant contrast polarity—than perceiving an obtuse corner. It is notable that observers exactly "see" an illusory zigzag line against a physically wavy line, rather than have an impaired perception," the researcher wrote.

Mechanisms Behind The Illusion

Takashi acknowledged that the reason why the illusion works is unclear but he has several hypotheses.

Takahashi said it is likely that the human brain has separate mechanisms that identify curved shapes and angular shapes and these mechanisms may interfere or compete with each other.

"I'd say that our eyes and brain may have been evolutionarily adapted to detect corners more efficiently than curves," he said. "We are surrounded by artificial products, which have much more corners than natural environment does, and hence our visual."

Other scientists also offered other explanations. Many think that the gray and white dashes in the image trick the brain into thinking that it is looking at shadows. Another idea is that this could be a defensive mechanism.

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