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What: This finicky optical illusion is known as Schröder's stairs, which is fittingly named after its creator, Heinrich Schröder, who made the illusion public in 1858. The illusion makes use of a phenomenon called multistable perception, which is a form of perceptual ambiguity that takes place when an image can be perceived in several ways. In this instance, the stairs can be viewed as either ascending or descending, depending on which side you concentrate on.

How To Experience: This illusion is a difficult one. For some people, it will be easy to experience, while for others, it will take some time. I've put the letters A and B on the top and bottom sides to provide you with a point of focus. As you focus on this point, you should envision 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 take on this orientation in your mind! If you already see that side as the front, then look at the other dot and imagine "front" there, and again after 5 - 10 seconds, the stairs should change their appearance! If this doesn't work for you, there's an option in the controls to add the words front/back, which can assist with the visualization. There are also some settings to modify the stair count and size, which I've found can also help trigger the change. And finally, if this still doesn't work for you, there are some controls to alter the top and bottom colors. You can fade these so that one side looks more shadowed than the other, and then try to switch them quickly.

Explain it: This illusion is an excellent example of multistable perception, where the brain can interpret the same image in multiple ways. Bistable perception is a perceptual phenomenon marked by changes in subjective perception while the sensory input remains the same. There aren't any real "three" dimensions to the lines drawn on the screen, but naturally, the brain will attempt to assign a shape to them, especially since they appear so frequently in our world. As the brain is evaluating, there seem to be sudden changes in your perception, which your brain will convey to you as a change in the orientation of the stairs. It is reported that the activity in the visual cortex, which is related to the dominant perceptual appearance, is responsible for the change, but the exact mechanism is still not completely understood.