Poggendorff Illusion

“The Poggendorff illusion is named for Johann Poggendorff (1796-1877), a German physicist who first described it in 1860. Poggendorff had received a letter from astronomer Johann Karl Friedrich Zöllner, describing an illusion created by a fabric design.”

The Poggendorff illusion is an interesting optical phenomenon that challenges our perception of parallel lines and angles. It consist of a line at an angle where the middle connection is covered by a rectangle. There is then a decoy line that is drawn that seems like it must connect to the original but in fact does not. Being able to change the opacity of the rectangle allows the user to easily convince themselves of the reality of the situation.

This illusion can be attributed to a phenomenon known as "misalignment of contours," where the brain struggles to accurately decipher the intersection of the diagonal line and the parallel lines. This is due to the way our brains interpret depth and perspective and the introduction of the rectangle disrupts the continuation of the parallel lines. Our brains try to correct this conflict by creating the easiest parallel line continuation it can find.

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