Optical illusions

How fast do we actually see the world?

Gianni Sarcone

Our visual system does not work like a camera shooting at a fixed number of frames per second. There is no single human “FPS.”

Reality is continuous, but our brain processes visual information on different time scales. Some visual mechanisms are remarkably fast; others are much slower. What we perceive depends on what we are looking at, the stimulus, its brightness and contrast, and even where it falls on the retina.

Flicker is a good example.

When a light flickers fast enough, we stop seeing individual flashes and perceive a steady light. But there is no universal cutoff such as 30 or 60 FPS. Under some conditions, humans can detect flicker well above 60 Hz, and the threshold changes with luminance, contrast, stimulus size, retinal location, and other factors.

And detecting a very brief visual event does not mean that we see at 250 FPS. Temporal resolution is not a single number. Different visual tasks have different limits.

Then there is the famous wagon-wheel illusion.

A spinning wheel can appear to slow down, stop, or even rotate backward. In films, this is a straightforward consequence of the camera sampling the motion at discrete intervals. Interestingly, similar effects can also occur under continuous illumination, suggesting that temporal sampling or aliasing may also occur within the visual system itself. The exact mechanism, however, is more complicated than simply saying that the brain “takes snapshots.”

And what about the feeling that time slows down during danger?

It can certainly feel that way. But experiments have found no evidence that frightening situations suddenly increase our temporal resolution—as if the brain switched to a higher frame rate. Instead, the experience seems to involve changes in attention, memory, and the way the event is reconstructed afterward.

So forget the idea that your brain runs at 30, 60, or 250 FPS.

There is no single frame rate for human vision.

We don’t simply record reality.

We construct our experience of it.

How minimal can a drawing be?

Gianni Sarcone

How far can you strip away a design and still leave it readable? Take almost everything out, and your brain will still fight to make sense of what’s left.

Here are two experiments in pushing that boundary:

  • 24 Configuration: The curve of the 2 flows straight into the diagonal of the 4. The brain uses the Gestalt principle of closure—filling in the missing pieces so you see two distinct digits sharing a single outline.
  • 45 Configuration: Standard typography is stripped back to raw vertical and horizontal lines. The crossbar of the 4 turns directly into the top curve of the 5, relying on your memory of numbers to decode the abstract shape instantly.

When you remove the noise, viewing becomes interactive. You aren’t just looking at a drawing—your mind is actively completing it.

👉 For more patterns, and mathematical curiosities, explore these number facts.

Train your brain by questioning your eyes

Gianni Sarcone

For many years, I collaborated with Publications International Ltd. (PIL) on the Brain Games™ series, creating hundreds of optical illusions for three books designed to challenge visual perception, observation, spatial reasoning, attention, and visual logic.

Optical illusions are more than visual tricks: they make the brain question its first interpretation, detect discrepancies, and construct a different explanation of what it sees. In that sense, they provide a stimulating workout for perception and reasoning.

I now put my expertise in visual perception and optical illusions at the service of publishers, educational institutions, medical centers, and other organizations looking for engaging ways to challenge and stimulate the mind.

Challenge your eyes. Make your brain work.

👉 Discover the latest book on Amazon

optical illusions - Brain Games

The Deceptive Oriental Fan

Gianni Sarcone

One of my earliest color illusions, created back in the 1990s, when I was immersed in exploring the physiology of color perception.

Do the pleated sections of the fan really have two different shades of brown?

They don’t. Every pleated “accordion” section is exactly the same brown. Only the thin light and dark bands bordering each fold differ. Those subtle edge contrasts trick your visual system into seeing alternating tones where none exist.

The color is perfectly uniform, but your brain interprets it differently depending on the surrounding contrast—a classic example of simultaneous brightness contrast.

Topsy-Turvy Illusions from the Past

Gianni Sarcone

“The Lawyer and the Client” (1790), an etching by John Kay, is a clever visual joke—and a rather pointed one about the legal profession.

The Lawyer and the Client - Etching

Look at it one way and you see a smug lawyer. Turn it upside down and the same face becomes a worried client. A simple rotation changes the character completely, showing how appearances—and perhaps even justice—can depend on the point of view.

Below, another of Kay’s reversible caricatures: “Before and After Marriage.”

Before and After Marriage - Etching

John Kay (1742–1826) was a Scottish caricaturist and etcher known for his satirical portraits of Edinburgh society. Topsy-turvy caricatures were popular in the 18th and 19th centuries because they combined visual wit with social criticism, hiding two meanings in a single image.

The Geometry of Wonder

Gianni Sarcone
impossible objects: nested tribars

One of my finest sculptures: nested triangles, the central one in wood, the others in stainless steel…

nested tribars

Just kidding. It’s an impossible tribar composition — a sculpture that can exist only in the eye and the mind.

The Penrose triangle (or Penrose tribar) is generally credited to Roger Penrose, who, together with his father Lionel Penrose, published it in 1958 as an “impossible object.” However, the visual idea of creating paradoxical triangular forms and impossible geometries has older precedents.

Japanese visual culture is often mentioned in discussions of geometric illusion because Edo-period (1603–1868) art, decorative motifs, and craft traditions reveal a deep fascination with complex patterns, ambiguous spaces, and unconventional perspectives. Elements found in traditions such as sankaku mokkō (triangular motifs), karakusa patterns, architectural ornamentation, and woodworking designs show how Japanese artists and craftsmen explored visual structures that challenge perception. While no confirmed direct predecessor of the Penrose tribar has been identified in Japanese art, these examples belong to a broader historical tradition of creating forms that play with geometry and the limits of visual interpretation.

Japanese tribar

A glimpse below into traditional Japanese fabric patterns, where triangular designs reveal how interlaced geometry can create the sensation of impossible structures.

Kagome patterns

To round things off, it’s worth mentioning the Valknut, a Scandinavian symbol dating back to around the 7th century whose interlocking triangles closely resemble the tribar.

valknut

Your Brain vs. Geometry: Rooftop illusion

Gianni Sarcone

Believe it or not, the green and purple rooftops are congruent—identical in shape, size, and angles. What changes is not the geometry, but your perception of it. Perspective, orientation, and contextual cues lead your visual system to interpret the same form as two different structures.

rooftop illusion, related to shepard tables

This effect is closely related to Shepard’s tabletop illusion and earlier studies in which identical parallelograms (A and B), when rotated (and superimposed), are perceived as different shapes, as the brain prioritizes interpretation over measurement.

Since some still insist these roofs are not congruent, I’ve put together a short animation that shows otherwise.

animated rooftop illusion

Bear-ly Seal

Gianni Sarcone

People often ask where my ideas come from. There is no single answer. They tend to surface quietly, shaped by places I’ve seen and cultures I’ve crossed.

“Seal or Bear?” grew out of that kind of moment. An animal suspended in the vastness of a frozen world—emerging from an ice hole, yet refusing to settle into a single identity. Is it a polar bear? A seal? Or something that holds both readings at once?

Bear of seal?

The idea came to me while traveling through northern Canada, surrounded by the stillness of Arctic landscapes and the deep presence of Inuit traditions. That silence has a way of sharpening perception—of making ambiguity feel natural rather than puzzling.

First created in the 1990s, the illusion went on to become a reference point in visual perception studies and later found its way into textbooks.

More recently, the “Seal or Bear?” illusion will be featured by the NHK Educational Corporation as part of a 2026–2027 educational series on psychology and visual perception.

The Borromean Tribar

Gianni Sarcone

This form belongs to the family of impossible figures, more specifically to the Penrose triangle, or tribar.

impossible figure

At first glance, it looks entirely manufacturable. The structure appears to be made from three identical square rings (Fig. 1), each pierced by a circular opening and arranged in three mutually perpendicular planes (Fig. 2). Together, they seem to interlock seamlessly, forming an impossible three-dimensional tribar that evokes a trefoil knot and its endless over-under weaving.

If this sculpture looks physically realizable to you, congratulations: your visual system has just accepted a geometric impossibility.

the making of the borromean tribar

Could such an object be built? Not exactly. One solution would be to twist one of the junctions slightly, but that trick would be immediately noticeable here because some of the angles would no longer appear perfectly square (90°), as shown in the picture below. Another possibility would be to leave a small gap at one junction and view the sculpture from a carefully chosen angle, allowing perspective to hide the discontinuity.

This is how a real 3D Borromean Tribar would appear…