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| Visual Illusions
Perhaps the most important lesson in Flirting With Disaster is that it's not always safe to trust your instincts when it comes to risk. There are a few simple black and white visual illusions in chapter 2 of FWD to try to make this point, but the web provides more scope to use this metaphor to underscore it with somewhat more force. At right is a picture I composited from two photos (and a bit of background to enhance the image) taken just moments apart as my son walked from one side of this Ames Room to the other, a distance of about 15 feet. Created by Adelbert Ames, an American ophthalmologist and pioneering investigator of visual illusions, this distorted room is carefully constructed and lit to fool our brains into thinking that it is rectangular when it is not (see below for its design, and examine the Wikipedia entry for the Ames Room for more detail).The floor, windows, and ceiling are all at precise angles that deny us the usual clues that perspective provides to tell us when things are farther away. The lighting is also arranged so that the left and right sides of the room appear much nearer to each other than they really are. From the viewing point at the right, someone walking from the right to the left side of the room appears to shrink to about half their starting size. The reverse occurs in the opposite direction. It is quite unnerving!Of course, the Ames Room is a visual magic trick. Even the clocks on the wall are distorted in shape so that they appear round when seen from the viewing point. And yet, the message is nevertheless clear: we do not always see what is there, we often see what our brains expect to see, or that which is easily available in memory, or that which makes a good story, or that which fits with the many mental short-cuts humankind has evolved over the centuries. As you read Flirting With Disaster or look at this web site, try to keep in mind that our instincts aren't always the best guide.
Adelson's Checker Shadow Illusion
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Edward Adelson's Checkerboard Illusion. See the instructions at left and the link below for more information.
| MIT professor Edward Adelson has developed a series of breathtaking illusions. My favorite, and perhaps the best known, is a checkerboard on which stands a green cylinder that casts a gentle shadow. See the picture at right.
If you hover your mouse pointer over the picture, you will see two squares highlighted. The question: Which of the squares is darker? The answer seems obvious, but one's instincts are profoundly wrong! (Click on the picture to see only the two squares, and release your mouse button to see the original picture restored.)
It is impossible to believe that the two squares are the same brightness. In fact, when I use this example in talks, many people still do no believe the illusion is not faked. (You can cut holes in a piece of paper and selectively cover the screen if you want to perform your own test. You can also measure the brightness of the squares with a photo editor such as the Gimp or Photoshop.)
The explanation for this illusion is that our brains have evolved to read brightness and color accurately in shadow as well as direct light. This automatic correction is completely unconscious and not controllable. As a result, we see the relative not the absolute brightness, since this is one of the important means we use to pick out objects from their context.
Still, the message from this illusion is clear: you can't always trust your instincts, no matter how sure you are.
The Penrose Triangle (also known as the Penrose Tribar)The Penrose triangle, also known as the Penrose Tribar, is an impossible object. It was first created by the Swedish artist Oscar Reutersvärd in 1934. The mathematician and mathematical physicist Roger Penrose independently devised and popularised it in the 1950s, describing it as "impossibility in its purest form". It is featured prominently in the works of artist M. C. Escher, whose earlier depictions of impossible objects partly inspired Penrose.The tribar appears to be a solid object, made of three straight beams of square cross-section which meet pairwise at right angles at the vertices of the triangle they form.This combination of properties cannot be realized by any 3-dimensional object. Nevertheless, there do exist 3-dimensional solid shapes each of which, when viewed from a certain angle, has the appearance of possessing all the qualities mentioned in the above paragraph.
A "Real" Impossible TriangleA sculpture based upon the Penrose design was erected East Perth, Western Australia. A photograph of the sculpture as an "impossible" object is shown immediately below, and its secret is revealed in the small picture to its right. This exciting new landmark was created through a unique collaboration between a leading Western Australia artist Brian McKay and architect Ahmad Abas.In 1997, a number of local artists were invited to enter submissions for a major commission for the East Perth redevelopment.  The winning submission came from McKay and Abas, and it was accepted with one amendment: to create a bold statement for the wider community, the size of the sculpture was increased by 50 percent from the planned height of 9 meters to 13.5 meters.
The design striations on the polished aluminum reflects both sunlight and artificial lighting and changes dramatically between sunrise and sunset. Toying With Perspective
 Like the impossible triangle, one of the best known aspects of the work of M.C. Escher is his manipulation of perspective. Instead of using three dimensions, as McKay and Abas did above, Escher and others have used the power of two dimensional illustration to suggest three dimensional worlds that cannot exist.
There are many, many examples of such impossible worlds, as it is a favorite theme. A stunning collection is provided in The Ultimate Book of Optical Illusions by Al Seckel. The Impossible Terrace, which sports simultaneous views from above and below is shown here. If you look closely, you will also see that the ladder twists in a rather strange way.
Web ReferencesIf you'd like to explore visual illusions in more depth, the Internet is a wonderful place to start. Here are a couple of sites to get you going:
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