The Droste effect is an endless picture-in-picture—a part of the picture contains the whole picture, which contains the picture, which contains the picture, and on.

Most of us are likely familiar with it from the fun visual effect you often see when sharing your screen on a video call, which contains the video call where you're sharing your screen, on which is the video call where... Always entertaining. Google calls it an infinity mirror.

The name derives from a Dutch brand of cocoa powder, Droste, where the classic advert was a picture of a nurse carrying a tray with a box of the cocoa powder, with the picture of the woman on it carrying the tray with a box of the cocoa...

Articles about the Droste effect often mention the amazing M.C. Escher's Print gallery, a picture without beginning or end.

The Droste effect

Yes, the two train track pieces are the same lengths. I know this because we have a basket of toy train tracks, and I took two identical curves and lined them up for the outline of this sketch. But it's easy to be fooled and think the one at the top is shorter than the one at the bottom.

While there may be other factors to help explain the ring-segment illusion, a common one is that our brains compare the short inner side of the top track against the longer outer side of the lower track leading us to believe the top one is shorter. Aligning the top track to the outer left point of the lower track enhances the illusion by increasing the horizontal contrast.

I like the ring-segment illusion as the name for it. It's also known as the Jastrow illusion after the Polish-American psychologist Joseph Jastrow, also known for the ambiguous figure of the rabbit-duck, who published a tapered version of the ring-segment illusion. In his paper, he gives a related example of how a square sitting on a point can look larger than one sitting on a side as we subconsciously compare the longer diagonal length with the shorter side length. You can test that in the sketch.

The ring-segment illusion

It's been called the expectation effect. Is it a B or a 13? It appears that how we see depends on the context and what we expect to see.

This neat example is from a 1955 experiment by Jerome Bruner and A. Leigh Minturn. One of the findings, other than people seamlessly identifying a B or 13 when surrounded appropriately by letters or numbers, was that when asked to draw what they saw "as is" participants were more inclined to draw a closed or partially closed B when it was surrounded by letters. What participants expected to see appeared to affect what they did see.

Context is king

The reason, generally, is simply that all those times previously we weren’t tuned in to notice what’s top of mind now. The frequency likely hasn’t changed a bit just our noticing of it has.

Also known as the Baader-Meinhof Phenomenon.

The frequency illusion: we notice what’s top of mind

How we choose to separate objects from the background. Also see FedEx. Travel is good for resetting our figures and grounds.

The classic vase/faces illustration is an example of an ambiguous figure—or sometimes a reversible or bistable figure.

Figure and ground

The moon seems smaller when up in the sky and bigger when on the horizon. I was surprised to learn that the real cause is still disputed.

The moon illusion

The Hermann Grid, the Necker cube, and the Blivet

Sketchplanations tagged with illusion