Impossible Object

An impossible object is a type of optical illusion consisting of a two-dimensional figure that is instantly and naturally understood as depicting a projection of a three-dimensional object, even though the object it depicts could not actually exist as a solid in ordinary space. Well known examples include the Penrose triangle, described by its popularizers as impossibility in its purest form and originally created by Oscar Reutersvard in 1934 before being popularized by Roger Penrose; the Penrose stairs, devised by Lionel and Roger Penrose; the impossible cube, invented by M. C. Escher; the impossible trident, also called a blivet or a devil's tuning fork; and figures such as the Borromean rings and the impossible waterfall. Impossible objects are of interest to psychologists as well as to mathematicians and artists, since they demonstrate how the visual system's habit of interpreting two-dimensional line drawings as representations of three-dimensional objects can be exploited to produce a drawing that different parts of the visual system interpret in locally consistent but globally contradictory ways, creating a persistent sense of cognitive confusion the longer different regions of the image are compared against each other.