Editing Optical illusion (section)

=== Object ===
[[File:Shepard tables.jpg|thumb|"Shepard tables" deconstructed. The two tabletops appear to be different, but they are the same size and shape.]]
Just as it perceives color and brightness constancies, the brain has the ability to understand familiar objects as having a consistent shape or size. For example, a door is perceived as a rectangle regardless of how the image may change on the retina as the door is opened and closed. Unfamiliar objects, however, do not always follow the rules of shape constancy and may change when the perspective is changed. The [[Shepard tables]] illusion<ref>{{cite web |url=http://www.michaelbach.de/ot/sze_shepardTables/index.html |first=Michael |last=Bach |work=michaelbach.de |orig-year=16 August 2004 |date=4 January 2010 |title=Shepard's "Turning the Tables" |access-date=27 January 2010 |archive-url=https://web.archive.org/web/20091227121317/http://www.michaelbach.de/ot/sze_shepardTables/index.html |archive-date=27 December 2009 |publisher=Michael Bach |url-status=dead }}</ref> is an example of an illusion based on distortions in shape constancy.