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photography and film – facts, ideas, values

Visual illusion

The wiki entry calls them optical illusions

The roller motion visual illusion (explanation from Akiyoshi’s illusion pages) which was shown in 3 Quarks a few days ago without comment seemed as if it was crying out for one. The obvious point is this a moving illusion. Although straightforward visual tricks using ambiguity are fascinating, the motion illusions are to me the most affecting. It seems to be saying something rather powerful about the brain. The traditional reason for studying visual illusions was a way to show how the brain worked in a not dissimilar way to brain-damaged patients do.

An unlikely source of clarification about visual illusions can be found in the Edge article below. In it Nathan Myhrvold [First Day report – Edge 0] discusses priming experiments in behavioural economics. [ Who is Minding the Mind by Dominict Carey in NYT discusses priming in other areas.] Nyhrvold says at the end of the experiments he describes:

…it seems absurd, but cheap metaphors capture our minds. Humans, it seems, are like drunken poets, who can’t glimpse a screen saver in the corner, or plot some points on graph paper without swooning under the metaphorical load and going off on tangents these stray images inspire.


The analogy that seems most apt to me is optical illusions. An earlier generation of psychologists got very excited about how the low level visual processing in our brains is hardwired to produce paradoxical results. The priming stories seem to me to be the symbolic and metaphorical equivalent. The priming metaphors in optical illusions are the context of the image—the extra lines or arrows that fool us into making errors in judgment of sizes or shapes. While one can learn to recognize optical illusions, you can’t help but see the effect for what it is. Knowing the trick does not lessen its intuitive impact. You really cannot help but think one line is longer, even if you know that the trick will be revealed in a moment.

The next section clears it up, though of course he mainly referring to his subject:

Perhaps the same thing is true here—the point of these psychological experiments, like the illusions, is to isolate an effect in a very artificial circumstance. This is a great way to get a clue about how the brain works (indeed it would seem akin to Steven Pinker’s latest work The Stuff of Thought which argues for the importance of metaphors in the brain). But is it really important to day-to-day real world thinking? In particular, can economics be informed by these experiments? Does behavioral economics produce a systematically different result that classical economics if these ideas are factored in?

I can imagine it both ways. If it is important, then we are all at sea, tossed and turned in a tumultuous tide of metaphors imposed by our context. That is a very strange world—totally counter to our intuition. But maybe that is reality.

Try the Stepping Feet illusion which he says he designed from a version from from Stuart Antis, who has a collection of his own illusions. Note the latter has a way of enhancing the illusion by getting you to use peripheral vision.  I think I have linked to it so that the ‘feet move  on the plain background. Click the background button for the dramatic effect.

The Cool Effect Illusion is pretty cool too.  This is unusual in the need to move to make it work.

Mark Bowers has a collection of illusions in a post, including a nice large one of the shades of gray illusion and the ‘red is green’ illusion (remember  the Stroop Effect?)

Simanek (link below) says under the sub-heading ‘Seeing illusions’ :

Some persons look at these illusion pictures and are not at all intrigued. “Just a mis-made picture,” some will say. Some, perhaps less than 1 percent of the population, do not `get’ the point because their brains do not process flat pictures into three dimensional images. These same persons have trouble with ordinary engineering line drawings and textbook illustrations of three dimensional structures.

Others can see that `something is wrong’ with the picture, but are not fascinated enough to inquire how the deception was accomplished. These are people who go through life never quite understanding, or caring, how the world works, because they can’t be bothered with the details, and lack the appropriate intellectual curiosity.

It may be that the appreciation of such visual paradoxes is one sign of that kind of creativity possessed by the best mathematicians, scientists and artists. M. C. Escher’s artistic output included many illusion pictures and highly geometric pictures, which some might dismiss as `intellectual mathematical games’ rather than art. But they hold a special fascination for mathematicians and scientists.

Oscar Reutersvärd – a founding father of impossible figures

78 Optical Illusions and Visual Phenomena

Atlas of Visual Penomena

Grand Illusions

The Principles of Artistic Illusions by Donald E. Simanek

Key to all optical illusions discovered (well, it’s a theory)

Motion ambiguity (

A Short Course in Behavioral Economics (

An online version of

Visual Illusions: Their Causes, Characteristics and Applications by Matthew Luckiesh, first published in 1922.  Visual illusion in nature, architecture and much more.


September 8, 2008 - Posted by | general |

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