The Gestalt principles of visual perception describe how our brains make sense of what we see. For example, they explain how we associate a photo with the text of a newspaper article or understand a series of words as a sentence on a billboard. These principles originated from the field of Gestalt psychology in the early twentieth century.

In laying out sketches, I try to consider how a viewer will understand what connects with what, the order in which the viewer will read the sketch with their eye, and how colour or formatting link related elements—skim through the back catalogue to see it in action. In creating each sketch, consciously and unconsciously, I use many of the standard Gestalt principles of design.

There are many Gestalt principles and some variations in the names. I chose seven common principles to illustrate:

Proximity
Objects that are close together are perceived as a group

Similarity
Similar objects are perceived as a group

Continuity
Elements on a line or curve are related

Closure
Completing missing parts of images to create a whole

Figure-Ground
Identifying what's in the foreground or background

Symmetry & Order
Perceiving symmetrical or orderly elements as a group

Common Fate
Objects moving together are perceived as part of a group

The Gestalt principles are helpful for information design, user interface design, user experience design, graphic design and just about any design. It is also fascinating to spot how you unconsciously use them when interpreting designs you see. For example, look at the signs in an airport, a menu, or a page of your favourite app and see which principles are in play.

The Interaction Design Foundation has a great article on the Gestalt principles that explains their use in design in more depth. You'll also find many others.

Gestalt principles

The impossible staircase, also known as the Penrose stairs, is an optical illusion of never-ending stairs.

Named after its inventor, the mathematician Roger Penrose, who first introduced this concept in the 1950s, the illusion uses multiple, conflicting lines of perspective to trick your eye into seeing the stairs continually rise.

I imagined this is what would happen if you visited M.C. Escher's house. Escher made the staircase famous in his drawings Ascending Descending, and Waterfall, after being introduced to it by Roger Penrose, who Escher had inspired to create some impossible shapes.

The mindbending Penrose steps also appear in the movie Inception.

It took quite a long time to get the perspective right. Ultimately, I used the handy tutorial on drawing the Penrose staircase from the excellent Circle Line Art School.

Also see: the ring-segment illusion, the frequency illusion, the moon illusion, and the Hermann Grid, necker cube, and blivet

Impossible staircase

While historic buildings in an ancient city centre make tourist attractions, most people would prefer the giant distribution warehouses that power online commerce and our world of delivery-everything to remain out of sight.

Several recently constructed distribution warehouses have started using enormous blocks of colour at scale to gently lead the eye and help buildings of exceptional size blend better into their surroundings.—greens to blend into countryside or "a beautiful sky blue" (video) to blend better with the sky.

Having passed both buildings with the patterns in this sketch, I can attest that the effect, in the right angles and light, is compelling—even though I noticed them more than ever as I spent time thinking about how well it works.

Read more about buildings designed to disappear into the landscape in Rowan Moore's Guardian article ​"A shed the size of a town:​ what Britain's giant distribution centres​ tell​ us about modern life"

This effect also reminded me of dazzle camouflage.

Blending buildings

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, but 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

You may have noticed that sometimes, when the moon rises over the horizon, it seems unusually large.

On several occasions, I've stopped to wonder at it shining behind the skyline—it's always a treat. However, if you stay awake long enough, you might see that later in the night, once the moon has risen higher in the sky, it has reverted to its expected size. This apparent change in size is known as the moon illusion.

Great minds from Aristotle to Isaac Newton have wondered at its cause, and I was surprised to learn that its cause is still debated. The most accepted explanations suggest the illusion arises from comparing the moon as it passes the horizon with known objects, such as buildings and trees, that provide a sense of scale. Higher in the sky, we can only compare the moon to the vastness of space and the sheer size of the sky itself.

To experience the full grandeur of the moon illusion, try a telephoto lens with the moon rising next to a cityscape.

I updated this sketch for my book Big Ideas Little Pictures (here's the original)

The moon illusion

The Hermann Grid, the Necker cube, and the Blivet

Illusion sketches