Which side is the front? Stare at either side and imagine "Front" or "Back" for 5-10 seconds, and you'll be able to change the orientation of the stairs!

What: This finnicky optical illusion is called schroders stairs, which is aptly named after it’s author, Heinrich Schröder, who published the illusion in 1858 [1] The illusion uitilizes a phenomena Multistable perception, which is a type of perceptual ambiguity that occurs when an image can be seen in multiple ways. In this case, the stairs can be seen as either going up or down, depending on which side you focus on.

How To Experience: This illusion is a tricky one, for some people it will come easy, for some it will take time. I’ve placed the letters A & B on the top and bottom side to give you a focal point. As you focus on this point, you should imagine in your mind that the side of the stairs you’re looking at is the “front” of the staircase. After 5-10 seconds, the stairs should orient into this position in your mind! If you already see that side as front, then look to the other dot and imagine “front” there, and again after 5-10 seconds the stairs should flip!

If this doesn’t work for you, there is an option in the controls to add the words front/back, which can help with the visualization. There’s also some settings to change the stair count and size, which I have found can help triggering the flip as well.

And finally, if this doesn’t work for you, there’s some controls in there to change the top and bottom colors, you can fade these so one side looks more shadowed than the other, then try to switch them quickly.

Explain it: This illusion is a great example of multistable perception [2], where the brain can interpret the same image in multiple ways.

Bistable perception is a perceptual phenomenon characterized by changes in subjective perception while sensory input remains constant

There are no true “three” dimensions to the lines drawn on screen, but naturally the brain will try to assign a shape to them, especially since they appear so commonly in our world. As the brain is assessing, there are seeming flips to your perception, which your brain will convay to you as a change in the orientation of the stairs.

It is reported that the activity in the visual cortex is what correlates with the dominant perceptual appearance is responsible for the flip, but the exact mechanism is still not fully understood.

Cites and Extras:

I've researched these optical illusions in my spare time but am clearly not any kind of expert and my explainations are pretty smooth brained, if you find something mis-cited, earlier examples, or general mistakes please new let me know via, be kind!