The optical illusion your brain can't switch off

The optical illusion your brain can't switch off

There is a black silhouette of a woman spinning on one foot, and no matter how long you look at it, it always turns the same way. Until it stops doing so. The "spinning dancer" — attributed to Japanese designer Nobuyuki Kayahara — is the most cited case of an ambiguous figure: two readings, clockwise and counterclockwise, equally valid, and a brain that picks one and clings to it as if its life depended on it.

The problem is not your eyesight. It's that there is nothing to look at. With no shadows, no perspective, not a single fold to reveal which leg is in front, the flat silhouette offers the same information for both interpretations. The visual system fills in the gap and then defends its fill-in.

Tricks that work and why

The most effective one is to cover with your hand everything above the knees. With no arms or hair distracting you, the foot resting on the ground becomes the only clue and the opposite spin becomes much easier to imagine. The same goes for the swing: focusing on just one of the supports and deciding it is the closest to the viewer is enough to reverse the movement.

Another route is to look out of the corner of your eye. Peripheral vision has less detail and the interpretation changes more easily. Blinking or looking away for a second and returning just as the raised leg passes in front also helps. In the case of the cat, the point of ambivalence comes when the face overlaps with the rear: that's where it's decided whether you see the face or see through the head, and with it the direction of the spin.

Some argue that experience is of no use here. Those who work daily with parts and measurements acknowledge that size illusions — the two equal lines with Müller-Lyer arrows — lose strength with practice, but with ambiguous figures there is no error to correct: both readings are correct and the brain has nothing to grab onto in order to choose.

The cat that only swings back and forth

Not all ambiguous figures behave the same way. With the cat, the most common result is not a complete change of direction but a back-and-forth swing: it turns left and right without ever completing a full turn. The silhouette does not offer enough information to sustain the full rotation and the visual system keeps oscillating between the two readings.

The dancer, on the other hand, allows a full switch, though it takes effort. And there is no magic shortcut: the illusion cannot be switched off, only negotiated.

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That's where the matter gets stuck. You can teach the eye to change its reading, but not to stay with it: as soon as attention relaxes, the brain returns to its preferred version and the other one disappears.