How this award-winning optical illusion actually works

The "3D Schröder Staircase", created by Japanese mathematician Kokichi Sugihara, has been crowned the 2020 winner of the Best Illusion of the Year contest – and it’s certainly a bit of brain bender.

The contest annually recognises the best illusion creators worldwide, and is branded as a celebration “of the ingenuity and creativity of the world’s premier illusion research community”.

Schröder staircases cleverly play with perspective, and are usually two-dimensional, showing two interpretations, as seen from above and then from below.

The original, 2D version was published in 1858 by German natural scientist Heinrich G. F. Schröder.

But now Sugihara’s creation is a three-dimensional model, with two interpretations as staircases both seen from above; when the object is rotated by 180 degrees on a vertical axis, it switches from one view to the other.

This new spin on a classic illusion is created with a red cone at the “top” of the steps, which is then rotated, putting the cone at the “bottom” of the steps.

Both times, the staircases seem to be at an incline – but that’s the illusion.

When Sugihara turns the model, he reveals that the two "legs" of the staircase are actually the same length, and the stairs are all on the same level.

Writing on his website, the illusionist explained: "This object is an example of my experimental material to investigate the behavior of the brains, which are apt to misperceive 2D pictures as 3D objects when they are embedded in real 3D structures.”

He went on to say: "The Schroeder Staircase, which is known as an ambiguous picture for more than 150 years, is decorated by real 3D side walls and support columns. As the result, we perceive new ambiguity, which is different from that of the original Schroeder Staircase."

Truly mind boggling stuff – and if you fancy delving further into the world of optical illusions, you can check out all the 2020 finalists here.