Necker Cube

What is happening

First try seeing the square face at the bottom left as facing toward you. Then try reading the square face at the top right as the near one instead. Holding both readings clearly at once may be difficult. There is no right or wrong answer if it doesn’t flip right away.

Why it looks that way

When reading depth from a line drawing, there isn’t enough information to decide which face is closer. The same network of lines supports more than one three-dimensional interpretation, so what you see can flip depending on where your attention goes. The figure itself never actually reverses.

How to check

Revealing the answer distinguishes the candidate faces by color and dotted lines. The coloring is there to help support one reading — it is not the single correct answer to the original figure. The rotating ring of dots is another figure that similarly lacks depth information, letting you compare the difference between a still image and one in motion.

Try a related illusion

For reference: explanation and research. The figure here is an original implementation.

First described

After Louis Albert Necker, 1832

Necker was drawing a crystal figure when he noticed its depth spontaneously flipped.

See it in the timeline