Optical illusions: illusioni ottiche (it), illusions d'optique (fr), ilusiones ópticas (sp), optische Täuschungen (ger),
ilusões de ótica (por), optische illusies (du), optické klamy (cz), oculorum fallaciae (lat).

"The organizational mechanism of vision are best demonstrated
by illusions. Illusions illustrate that perception is a creative
construction that the brain makes in interpreting visual data..."
- Eric Kandel, in Principles of Neuronal Science.

Vision isn't always WYSIWYG
What are optical or visual illusions? In the fewest words, they are particular illusions that deceive the human visual system perceiving something that is not present or, incorrectly perceiving what is present. In English, there are 2 essential words to express the faculty and the act of seeing : 1) see, 2) view. The etymological sense of the words see and view are “follow something with the eyes” (from the indo-european *seq) and “have learnt” (from the indo-european *weid). So, for our ancestors an image is something to shape with the eyes (follow with the eye) and an information taken from the real world (having learnt from this visual perception).

Unfortunately (or fortunately?), seeing isn’t some kind of direct perception of reality. Actually our brain is constantly interpreting and giving structure to the initial visual input from our eyes. If this was not the case, we wouldn’t see colors and we probably would see the world upside down! Another interesting everyday paradox of our vision is that we don’t see the edges of our visual field! In fact, we should see black zones outside of our visual field, but our brain cancels out these zones with a smooth fade-out effect. In the following webpages we have included classic and new optical illusions that will delight children and grown-ups as well as inquisitive minds in search of solid, accessible material on this amazing subject.

Vision is allusion...
We all know that since ancient times immediate perception is not a reading of physical reality. This is specifically illustrated by Plato’s allegory of the cave: humans are likened to prisoners chained in a cave, unable to turn their heads and thus to see any real object. All they can see are shadows of objects projected by a light source on the wall of the cave. Then, what the prisoners perceive are just shadows and echoes cast by objects that they do not see at all. Such prisoners would mistake appearance (shadows) for reality.

Well, but what is actually seeing? what is vision, what is exactly the visual experience? Vision is the most creative act that a human being is capable of. Seeing is depicting the world on the living canvas of our mind. As we depict well only what we really know, our mind is both the canvas and the artist. In this creative process, the eyes represent nothing other than a medium with which our mind interprets and ‘reconstructs’ the reality around us. The poet Novalis said: “the eyes is a ‘superficial’ organ”. In fact, we will never perceive the real world because it is strongly dependent of our body and our mind. Yes, vision isn’t quite a 100% natural process as folk may think... It depends for a large part on learned skills that are helpful in interpreting our near environment, but can sometimes deceive. That’s why the study of visual illusions and mental fallacies is important: they reveal the magic and the limits of our perception (or consciousness). Some illusions teach us to doubt and to question the many appearances of the reality, they are a kind of school for life.

[Excerpts from the works of Gianni A. Sarcone, © 1992-2006]

The Authors
Gianni A. Sarcone and Marie-Jo Waeber, designers and writers, are specialists in creative learning. They create and invent educational manipulatives and thinking games which help teach mathematics, visual and plastic arts. Their maxim is: “be curious first!”. Gianni A. Sarcone and Marie-Jo Waeber are also regular authors of educational and recreational puzzle and math columns for newspapers and magazines. They have published several books in English, French and Italian on puzzles and on the mechanism of vision: MateMagica, New Optical Illusions, Dazzling Optical Illusions, Almanach du Mathématicien en Herbe... Click here to get more info about the authors.

All the images shown on this page are copyrighted, © 2006, G. Sarcone

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