The Necker cube
A cube that flips
A flat drawing of a wire cube can be seen in two orientations. Keep looking, and it may suddenly reverse.
Flips counted: 0. This is just your tally, not a laboratory measurement.
Another example of ambiguity and object reversibility is the Necker cube, which may seem to flip-flop. Britannica Scholars: illusion
The percept of a three-dimensional wireframe cube is already an interpretation, performed on the two-dimensional visual input of a flat line image. Michael Bach: Necker cube Many interpretations of that flat image are possible, but the usual choice is a cube, and both orientations are about equally likely. Michael Bach: Necker cube
If you view a Necker cube for a prolonged time, you may perceive a sudden reversal, typically every three to five seconds, between the two cube orientations. Michael Bach: Necker cube
Can you “hold” one orientation? Normally this is not possible. After about ten seconds or so, it will flip again. Michael Bach: Necker cube
L. A. Necker was a Swiss mineralogist. He discovered the reversals by accident when looking at the drawing of a cube-like crystal. Michael Bach: Necker cube Necker published an account of the phenomenon in 1832. Michael Bach: Necker cube
Some studies have suggested that younger people tend to perceive these reversals more readily than do their elders. Britannica Scholars: illusion
Typical times, not a stopwatch for every viewer
“Typically every three to five seconds” and “after about ten seconds or so” are the figures Michael Bach gives for a Necker cube. They are typical, not a promise that every viewer will flip on that schedule, and some people with normal vision do not see a given illusion at all.