Silhouette Illusion

from Michael’s   Visual Phenomena & Optical Illusions

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What to see

One the right you see the silhouette of a spinning figurine. Does she spin clockwise or counterclockwise?

What to do

After you have decided which way she spins, mentally try to make her spin the other way. Yes, this is possible. But difficult. It may help to blink, or to look a special features. People differ markedly here. While it may be very difficult to voluntarily flip the direction, it may also occur spontaneously.

Note: Silhouettes are ambiguous – they can turn either way and it would look exactly the same.

But it is very difficult to flip the spin direction. Tick the checkbox “Spheres”. With a little effort, e.g. “lock hand to the spheres”, you can make the silhouette go either way too.

If you press the button “🚶 ↺⇄” the silhouette itself reverses motion direction. Wait, I just said silhouettes are ambiguous, yes, but if you tick “Lighting” you will see a full 3D model which totally disambiguates the rotatation direction.

If you tick the Eyes checkbox, you will see black eyes when the model looks at you. That also disambiguates the direction, although less then via Lighting.

Comments

Sources

Website of the original author, Nobuyuki Kayahara

Troje NF, McAdam M (2010) The viewing-from-above bias and the silhouette illusion iPerception 1:143–148 [PDF]

Nice variation by Marcel de Heer

I thank Vijai in Irvine, who pointed me to threejs, which sped up loading by a factor of 50!