<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 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>
a necker cube is an example of a ( n )
a necker cube is an example of a ( n )
an optical illusion
an optical illusion