Editing Optical illusion (section)

== Physical visual illusions ==
A familiar phenomenon and example for a physical visual illusion is when mountains appear to be much nearer in clear weather with low humidity ([[Foehn wind|Foehn]]) than they are. This is because haze is a cue for [[depth perception]],<ref name="Goldstein">{{cite book |last= Goldstein|first= E. Bruce|date= 2002|title= Sensation and Perception| location= Pacific Grove, CA|publisher= Wadsworth| isbn=0-534-53964-5}}, Chpt. 7</ref> signalling the distance of far-away objects ([[Depth perception#Aerial perspective|Aerial perspective]]).

The classical example of a physical illusion is when a stick that is half immersed in water appears bent. This phenomenon was discussed by [[Ptolemy]] ({{Circa|150}})<ref>{{cite book |last= Wade |first= Nicholas J. |date= 1998 |title= A natural history of vision |location= Cambridge, MA |publisher= MIT Press}}</ref> and was often a prototypical example for an illusion.