# Necker cube

The Necker cube: a wire frame cube with no depth cues.

The Necker cube is an optical illusion first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker.[1]

## Ambiguity

The Necker cube is an ambiguous line drawing.

Necker cube on the left, impossible cube on the right.
One possible interpretation of the Necker cube, often claimed to be the most common interpretation[citation needed]
Another possible interpretation

The effect is interesting because each part of the picture is ambiguous by itself, yet the human visual system picks an interpretation of each part that makes the whole consistent. The Necker cube is sometimes used to test computer models of the human visual system to see whether they can arrive at consistent interpretations of the image the same way humans do.

Humans do not usually see an inconsistent interpretation of the cube. A cube whose edges cross in an inconsistent way is an example of an impossible object, specifically an impossible cube (compare Penrose triangle).

With the cube on the left, most people see the lower-left face as being in front most of the time. This is possibly because people view objects from above, with the top side visible, far more often than from below, with the bottom visible, so the brain "prefers" the interpretation that the cube is viewed from above. Another reason behind this may be due to the brain's natural preference[citation needed] of viewing things from left to right,[2] therefore seeing the leftmost square as being in front.

There is evidence that by focusing on different parts of the figure one can force a more stable perception of the cube. The intersection of the two faces that are parallel to the observer forms a rectangle, and the lines that converge on the square form a "y-junction" at the two diagonally opposite sides. If an observer focuses on the upper "y-junction" the lower left face will appear to be in front. The upper right face will appear to be in front if the eyes focus on the lower junction.[3] Blinking while being on the second perception will probably cause you to switch to the first one.

 This is an example of two identical necker cubes, the one on the left showing an intermediate object (blue bar) going in "down from the top" while the one on the right shows the object going in "up from the bottom" which shows how the image can change its perspective simply by changing which face (front or back) appears behind the intervening object. It is possible to cause the switch to occur by focusing on different parts of the cube. If one sees the first interpretation on the right it is possible to cause a switch to the second by focusing on the base of the cube until the switch occurs to the second interpretation. Similarly, if one is viewing the second interpretation, focusing on the left side of the cube may cause a switch to the first.

The Necker cube has shed light on the human visual system. The phenomenon has served as evidence of the human brain being a neural network with two distinct equally possible interchangeable stable states.[4] Sidney Bradford, blind from the age of ten months but regaining his sight following an operation at age 52, did not perceive the ambiguity that normal-sighted observers do.[5]

## Apparent Viewpoint

The orientation of the Necker cube can also be altered by shifting the observer's point of view. When seen from apparent above, one face tends to be seen closer; and in contrast, when seen from a subjective viewpoint that is below, a different face comes to the fore.[6]

## Epistemology

The Necker cube is used in epistemology (the study of knowledge) and provides a counter-attack against naïve realism. Naïve realism (also known as direct or common-sense realism) states that the way we perceive the world is the way the world actually is. The Necker cube seems to disprove this claim because we see one or the other of two cubes, but really, there is no cube there at all: only a two-dimensional drawing of twelve lines. We see something which is not really there, thus (allegedly) disproving naïve realism. This criticism of naïve realism supports representative realism.

A rotating Necker cube was used to demonstrate that the human visual system can recruit new visual cues that affect the way things look.

A doctored photograph purporting to be of an impossible cube was published in the June 1966 issue of Scientific American, where it was called a "Freemish Crate".

## References in popular culture

The Necker cube is discussed to such extent in Robert J. Sawyer's 1998 science fiction novel Factoring Humanity that "Necker" becomes a verb, meaning to impel one's brain to switch from one perspective or perception to another.[7]

In Grant Morrison's Doom Patrol comic book, issue 36/September 1990 page 14, a character named Mr. Jones constructs a three-dimensional Necker cube out of paper, meditates upon it in order to create new agents for his organization, and uses it as a weapon by forcing others to look into it.

Peter Watts postulates in his novel Blindsight that consciousness serves as a set of training wheels for reality; this manifests in our ability to see only one aspect of the Necker cube at a time. In the novel, vampires have a more advanced perception of the universe because they can hold both aspects of the Necker cube in their head simultaneously.