<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2010) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> The Necker cube is an optical illusion first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker . It is a simple wire - frame drawing of a cube with no visual cues as to its orientation, so it can be interpreted to have either the lower - left or the upper - right square as its front side . Necker cube is used in studies of human visual perception . </P> <P> The Necker cube is an ambiguous line drawing . </P>

A necker cube is an example of a(n)