Book review: Sleights of Mind

Authored by Stephen L. Macknik and Susana Martinez-Conde in 2010 (ISBN 978-0-8050-9281-3). The authors interviewed many magicians and got themselves invited to magicians' trade shows, and these experiences form the basis of the book. They provide some very nice examples on their website.

This is another book in the vein of how our brains fail to grasp reality. I have enjoyed magic since I was a child. One of my fondest memories is of a David Copperfield show I attended in my 20s in Boston. Among other things, he performed card tricks with a camera and an audience member watching from inches away. The things he did were plainly impossible, yet they were happening. He closed his show by flying around the stage, through hoops to show that no wires were involved. To this day I do not know how he did that, and I am ambivalent about knowing.

The book describes how magic tricks work, both from a general theoretical perspective and a this-is-how-this-particular-trick-is-performed perspective. The latter is called out by "Spoiler Alert" in bold letters before and after each such section, and such sections comprise a good quarter or third of the book. I skipped these sections, as I hope to attend more magic shows in my life and do not want the tricks "spoiled".

The general theoretical perspective is this: our brains excel at recognizing patterns, to the extent that we tend to observe patterns even when they do not exist. Further, our brains try to reach conclusions quickly, as that gives us our best chances in identifying prey and avoiding predators. The modern world does not resemble the world of 10,000 years ago, even though our brains have changed little, so magicians, through careful analysis of how our brains short-circuit careful observation with pattern recognition, can devise sequences that encourage, perhaps demand, careless observation.

One common illusion is that our eyes see everything there is to see. The invisible gorilla is one example of this falsehood. It is true that all available light enters your pupil. But your retina contains a blind spot and unevenly distributed rods and cones. It converts the light energy into electrical energy, which triggers certain neurons. These neurons trigger certain emotions that adjusts the "plain" light energy, and that is what you "see". You are not a video camera.

Optical illusions are commonplace. Staring at a waterfall causes the objects nearby to appear to float upward. Observe a flash of light contemporaneously with hearing multiple beeps and you report that you saw multiple flashes. We learn as infants and toddlers that objects have size, shape and color constancy. The magician need only change one or more of those things to cause you to (falsely) believe an object is moving. The McGurk effect shows that what we hear is influenced by what we see.

Beyond visual illusions there are cognitive and memory illusions. For an example of a cognitive illusion, a magician named Apollo pickpockets a man on stage, taking advantage of the fact that we can really concentrate on only one thing at a time, no matter how much folks want to brag about their multitasking abilities. An example of a memory illusion is the common trick of misstating what is transpiring. The magician will pull a cloth here, wave a wand there, position a person, and so on. Near the end of the trick the magician will repeat, in words, what has happened, and will lie about it, and because our memories are confused by the constant patter and unusual circumstances, we believe the lies.

The next Informatica World conference is in Las Vegas. I attended the 2009 version, also in Las Vegas. It was my first visit to that city and I will not be unhappy if it is my last, also. If I end up going, though, I will be sure to take in a magic show.