Bent Line Illusion

This page contains information about the bent line illusion, sometimes called the broken line. The topic is related to the optical illusions. To see how the brain could be tricked look below and read the instructions. You will be amazed to know the psychology of the mind and how it reacts to stimulations. For more tricks check our Brain Tricks main page.

Tips for the bent line illusion: In the image at top left you see the basic effect: the two ends of a straight line segment passing behind an obscuring rectangle appear offset when, in fact, they are aligned. Place your mouse pointer over the image to convince you of this.
On the right is a variation where the width of the occluding rectangles can be varied or they can be made partially transparent. I selected the starting value of the rectangle width so that the oblique lines appeared offset by half of their distance.

Notes: This illusion was discovered in 1860 by physicist and scholar JC Poggendorff, editor of Annalen der Physik und Chemie, after receiving a letter from astronomer F. Zöllner. In his letter, Zöllner described an illusion he noticed on a fabric design in which parallel lines intersected by a pattern of short diagonal lines appear to diverge (Zöllner’s illusion). Whilst pondering this illusion, Poggendorff noticed and described another illusion resulting from the apparent misalignment of a diagonal line; an illusion which today bears his name.

Trick of the Day: The moon when close to the horizon looks bigger than when it's in heart of the sky. That's because when it's close to the horizon, your eyes sees it in comparison to other parts of the horizon, such as trees, mountains and houses, and that's what makes it look bigger. For more tricks and illusions of the day check Tricks of the Day.

This Bent Line Illusion is just one of the many resources of the optical illusions showing how the brain can be fooled. Don't you wonder what other aspects in life we take for granted could be very different from how we perceive them? Choose a related page, or simply click on previous/ next.