These three horizontal lines are all the same length.  Does the middle line appear to be longer than the top line? The arrows on the end of the lines give the impression that the lines are different lengths.  The red horizontal lines help to show that they are all equal.  This is known as the […]

In 1939, William Orbison described the following illusion where the red square appears to be distorted by the presence of the angled blue lines. It does not look to be a perfect square, but if you take a sheet of paper or something else with a straight edge and line it up, you will see […]

Do the black lines presented below appear to be parallel? The black lines are indeed parallel even though they do not appear to be.  In 1860, this classic optical illusion was discovered by Johann Karl Friedrich Zöllner.  This illusion was the basis for the discovery of the Poggendorff illusion.