The applet design by prof Hwang, modified by Ahmed.
original applet [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2054.0]illusion_Ebbinghaus: Are they the same size?[/url]
The Ebbinghaus illusion or Titchener circles is an optical illusion of relative size perception. In the best-known version of the illusion, two circles of identical size are placed near to each other and one is surrounded by large circles while the other is surrounded by small circles; the first central circle then appears smaller than the second central circle.
You can drag the top blue dot to check if they are all the same size.
Try to drag the sliders to discover the wonder of illusion!
data from http://en.wikipedia.org/wiki/Ebbinghaus_illusion