Poggendorff Illusion

The Poggendorff illusion gets its name from the German physicist Johann Poggendorff, who first explained this illusion in 1860. Although it seems like the black line on the left stretches into a purple line on the right, don't take the bait. The black line is actually lined up with the yellow one, while our brain misinterprets the depth of elements and distorts the perception.

The magnitude of the effect increases as the interrupted line gets more vertical and the width of the interrupting segment grows.

Despite numerous studies, there’s still no consensus found about the Poggendorff effect, and it remains one of the most controversial of the geometrical illusions.