Pinna’s Illusory Intertwining Effect

Estimation 9 December 2013 0 Comments

Pinna's illusory intertwining effect

This figure looks like a warped spiral made up of white and black squares on a gray background.  If you examine it more closely, however, you will find that it is actually made up of four concentric circles.  This illusion was first described by Baingio Pinna and Richard L Gregory in a 2002 article titled […]

Fraser Spiral Illusion

Estimation 22 March 2012 0 Comments

Fraser Spiral

Do you see a spiral in the image below? There is no spiral.  This drawing consists of a series of concentric circles.  This illusion, called the Fraser spiral was discovered by British psychologist James Fraser in the early 20th century.