1) Optical illusion
Found on
https://www.crosswordclues.com/clue/sander-illusion
The Sander illusion or Sander`s parallelogram is an optical illusion described by the German psychologist Friedrich Sander (1889–1971) in 1926. However, it had been published earlier by Matthew Luckiesh in his 1922 book Visual Illusions: Their Causes, Characteristics, and Applications. The diagonal line bisecting the larger, left-hand parallelo....
Found on
http://en.wikipedia.org/wiki/Sander_illusion
No exact match found.
