Gestalt occurs when we only have partial information and we tend to fill in missing info.  For instance, many optical illusions illustrate the concept of GESTALT.   Stereotypes are also a type of GESTALT which are normal for us to use, but can become negative when we rely only on the generalization instead of facts. 

          
   Is it a rabbit or a duck?                                How many legs?
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Where does it all connect?             How many squares do you see?

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MC Escher was also well known for his mathematical Tessellations which played with people's perception...

   
 Where do the pillars settle?                                    Tessellations 

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        Black geese or white geese?                                              M.C. Escher Self-Porttrait

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