Sleights of Mind
Stephen Macknik, Susana Martinez-Conde & Sandra Blakeslee
fm01
-
Cognitive neuroscience experiments are strongly susceptible to the state of the observer. If the experimental subject knows what the experiment is about, or is able to guess it, or sometimes even if she incorrectly thinks she has figured it out, the data are often corrupted or impossible to analyze. Such experiments are fragile and clunky. Extraordinary control measures must be put in place to keep the experimental data pure. Now compare this with magic shows. Magic tricks test many of the same cognitive processes we study, but they are incredibly robust. It doesn't matter in the slightest that the entire audience knows it is being tricked; it falls for each trick every time it is performed, show after show, night after night, generation after generation.
Chapter 1
-
Magicians understand at a deeply intuitive level that you alone create your experience of reality, and, like Johnny, they exploit the fact that your brain does a staggering amount of outright confabulation in order to construct the mental simulation of reality known as "consciousness."
-
Perception means resolving ambiguity.
-
You don't consciously know how big your pupil is at any given time. Part of the reason for this is that the irises adjust for light level and help to make differently lit environments accessible for neural processing. In low light, your irises open to allow in more photons, and in high light your irises close to keep your retina from becoming blinded by glare. That's why a light level expert such as a photographer must use an objective light level measuring device called a photometer, rather than her own subjective visual estimates of light level, before she can determine the best f-stop to use with her camera lens.
-
Magicians are constantly exploiting these features of your visual system in their tricks. They use illusions of depth in card tricks. They use context to mislead your perceptions. They count on your filling in the missing pieces of a scene. They draw on edge-detecting neurons to convince you they can bend spoons.
-
Black light—what scientists call ultraviolet light—vibrates at a shorter wavelength than visible violet light, and it is called "black" because it is invisible. Fluorescence occurs when one wavelength of light is converted into another.
-
Being a magician, he says, is the most honest living he has ever made—he promises to deceive you, and then he does.
-
Magicians use tension and relaxation to manipulate your judgment of where the hidden object is and is not. (We realized we would have to apply this principle to our audition at the Magic Castle.)
Chapter 2
-
Sleight of hand magic, when done well, is miraculous to behold. (The word "sleight" comes from Old Norse and means cleverness, cunning, slyness.)
-
The reason for this is that your visual system has very poor resolution except at the very center of your gaze. The cards are so thin that your vision is not up to the task of distinguishing them, especially in the hands of a skilled card sharp. Your center of gaze is called the macula—the region near the center of your retinas packed with photoreceptors. It, along with the fovea (the very center of the macula and the part with the very highest resolution), is responsible for high-acuity vision. It's a piece of your anatomy that is so specialized it has its own set of diseases, including age-related macular degeneration. In fact, macular degeneration is the most common form of blindness in older people, as maculas slowly die over the course of a few years. Without maculas, you can see only with your peripheral vision, which has very low resolution. You navigate by seeing the world in terms of what appears off to the sides of your head.
-
Two normal depth perception cues—occlusion and perspective—have conspired to fool you. These processes are automatic and occur without your being aware of them, which is why the trick works.
-
Occlusion refers to the fact that if one person is partly hiding behind another person, you naturally assume that the person who is not occluded is closer to you. The same goes for playing cards. This is a logical deduction made by your brain, done automatically and virtually instantaneously, without conscious thought.
-
Hillis once showed a magic trick to Richard Feynman, the Caltech physicist widely regarded as one of the most brilliant people who ever lived. "I'd do the trick and challenge him to figure it out. He'd go off for a day or two, think it through, and come back with the correct answer," says Hillis. "Then I would repeat the trick using an entirely different method. And it drove him crazy. He never got the meta principle that I changed methods. This may be because of how scientists are trained to use the scientific method. You keep doing experiments until you find the answer. Nature is reliable. The idea that someone would switch methods just flummoxed him."
-
Your brain cannot deal with zero sensory input, so it makes up its own reality. The point here is that your brain is constantly making up its own reality whether it receives actual reality-driven input from your senses or not. In the absence of sensory input, your brain's own world making machinations keep on truckin' nevertheless.
Chapter 3
-
Op artists were also interested in kinetic or motion illusions. In these eye tricks, stationary patterns give rise to the powerful but subjective perception of illusory motion. An example is Enigma by Isia Leviant.
-
The only difference between these two faces is their degree of contrast. Yet one appears female and the other male. That's because female faces tend to have more contrast between the eye and mouth (think how makeup exaggerates these features) and the rest of the face than males. Richard Russell, the Harvard University neuroscientist who created the illusion, has found that increasing the contrast of a face (more makeup!) makes it more feminine. Conversely, reducing contrast makes it look more masculine.