Everything about Necker Cube Illusion totally explained
The
Necker cube is an
optical illusion first published in
1832 by
Swiss crystallographer Louis Albert Necker.
Ambiguity
The Necker cube is an ambiguous line drawing. It is a wire-frame drawing of a cube in isometric perspective, which means that parallel edges of the cube are drawn as parallel lines in the picture. When two lines cross, the picture doesn't show which is in front and which is behind. This makes the picture ambiguous; it can be interpreted two different ways. When a person stares at the picture, it'll often seem to flip back and forth between the two valid interpretations (so-called
multistable perception).
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 don't 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.
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 (Einhauser, et al., 2004).
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.
Sidney Bradford,
blind from the age of ten months but regaining his sight following an operation at age 52, didn't perceive the ambiguity that normal-sighted observers do.
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's no cube there at all: only a
two-dimensional drawing of twelve lines. We see something which isn't 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.
Richard Dawkins in his 1982 book
The Extended Phenotype, and later new preface to a later edition of
The Selfish Gene, uses a Necker cube as an analogy of two ways to view the same object to introduce the
gene-centric view of evolution.
Impossible cube
The
impossible cube or
irrational cube is an
impossible object that draws upon the ambiguity present in a Necker cube illustration. An impossible cube is usually rendered as a Necker cube in which the edges are apparently solid beams. This apparent solidity gives the impossible cube greater visual ambiguity than the Necker cube, which is less likely to be perceived as an impossible object. The illusion plays on the human eye's interpretation of two-dimensional pictures as three-dimensional objects.
In
M. C. Escher's lithograph
Belvedere, the figure of a boy seated at the foot of the building is holding an impossible cube; the rest of the scene is based on the same principle that makes the impossible cube. In the scene, a ladder from the inside of the first story leads to the
outside of the second. However, this isn't appreciated by the prisoner in the basement cell because the basement is a
possible cuboid and he's unambiguously on the inside.
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".
Further Information
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