Sleights Of Mind Part 2

Another great illusionist is the Dutch lithographer and woodcut artist Maurits Cornelis (better known as M. C.) Escher. Early in his career, Escher carved realistic scenes based on his observations and travels. Later, he turned to his imagination, rendering some of the most brilliant visual illusions in the history of art. When he was in high school, one of Steve's favorite posters was an Escher print of the never-ending staircase (Ascending and Descending, 1960), in which a group of robed monks perpetually climb or descend an impossible staircase situated at the top of a temple. It was impossible because it circled around on itself and never ended. So how could it be drawn if it was physically impossible? Escher must have cheated somewhere in the print and failed to depict the proper structure of a real staircase. But Steve couldn't find it, no matter how closely he looked. He realized he should examine the structure as a whole to see if there was a small systematic warp along the entire structure that allowed for the illusion.

And that's when Steve found that he couldn't look at the structure globally. He could only really see one area of the staircase at a time. His vision could process the details of the staircase when he centered his gaze on a specific part. But when he did that, every other area of the staircase, in his visual periphery, was left in a blur. And he realized that that was how Escher must have done it: since you can see only one local area at any given time, small, gradual errors along the entire structure could not be seen with the naked eye.

This effect challenges our hard-earned perception that the world around us follows certain inviolable rules. It also reveals that our brains construct the feeling of a global percept by sewing together multiple local percepts. As long as the local relation between surfaces and objects follows the rules of nature, our brains don't seem to mind that the global percept is impossible.

Susana's formal introduction to visual illusions came in 1997 when she arrived at Harvard University to study under David Hubel and Margaret Livingstone. At the time, Harvard was the mecca for the study of illusions, and in fact this is where she met Steve. Not only were Livingstone and Hubel leading the field in the study of illusions in the brain, but a number of Harvard psychologists were discovering an array of completely new phenomena.

As part of her postdoctoral training, Susana decided to choose a visual illusion and investigate its effects. Leafing through an art book, she found the perfect playground for her curiosity: op art, a field that explores many aspects of visual perception, such as the relations between geometrical shapes, variations on "impossible" figures that cannot occur in reality, and illusions involving brightness, color, and shape perception.11 Susana settled on op artist Victor Vasarely, whose Nested Squares series exhibited an odd illusion: the corners of the squares looked brighter than their straight-edged sides. But the effect wasn't just about the lightness of the corners, because if Vasarely reversed the order of the nested squares from white-to-black (center to exterior) to black-to-white, now the corners were darker than the sides. So it seemed to be an illusion concerning contrast, and not lightness per se.

Susana searched the vision research literature and found that only a couple of people had discussed this effect previously and n.o.body had investigated its neural bases. And no one had looked at shapes other than squares. Squares are a special type of shape in which all of the corners are convex (all point away from the center of the square). But n.o.body had examined the effect for nonsquare shapes with concave corners or for shapes with corner angles other than 90 degrees. Susana realized there were many aspects of this illusion that she could study perceptually, followed by physiological research in the brain.

After several years, first as a trainee at Harvard and later as the director of her own research team, Susana learned one of the most fundamental secrets of the visual system. The previous dogma in the field had been that neurons in the first few stages of the visual system were most sensitive to the edges of object surfaces. Susana's results showed instead that neurons of the visual system are more sensitive to the corners, curves, and discontinuities in the edges of surfaces, as opposed to the straight edges that had previously been thought to reign.

Vasarely's Utem (1981). Nested squares of increasing or decreasing luminance produce illusory diagonals that look brighter or darker than the rest of the squares. (Courtesy of Michele Vasarely) 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.

Reinterpretation of Enigma (Created by and courtesy of Jorge Otero-Millan, Martinez-Conde Laboratory, Barrow Neurological Inst.i.tute) This static image of regular patterns elicits powerful illusory motion in most of us and has generated an enormous amount of interest in the visual sciences since it was created in 1981. However, the origin of the illusion-is it the brain, the eye, or a combination of both?-remains, appropriately, an enigma.

In 2006 we designed an experiment to probe this question. We asked observers to say when illusory motion sped up or slowed down as they looked at the image. At the same time, we recorded their eye movements with high precision. Before they reported "faster" motion periods, their rate of microsaccades-tiny eye movements that occur during visual fixation of an image-increased. Before "slower" or "no" motion periods, the rate of microsaccades decreased. The experiment proved that there is a direct link between the production of microsaccades and the perception of illusory motion in Enigma. The illusion starts in the eye, not the brain.

Another of our favorite visual illusions is Mona Lisa's smile. Her expression is often called "enigmatic" or "elusive" but, as our mentor Margaret Livingstone at Harvard University observed, the illusory nature of her smile is explained when you consider exactly how the visual system works. When you look directly at the Mona Lisa's mouth, her smile is not apparent. But when you gaze away from her mouth, her smile appears, beckoning you. Look at her mouth, and the smile disappears again. In fact, her smile can be seen only when you look away from her mouth. This is due to the fact, mentioned earlier, that each eye has two distinct regions for seeing the world. The central area, the fovea, is where you read fine print and pick out details. The peripheral area, surrounding the fovea, is where you see gross details, motion, and shadows. When you look at a face, your eyes spend most of the time focused on the other person's eyes. Thus, when your center of gaze is on Mona Lisa's eyes, your less accurate peripheral vision is on her mouth. And because your peripheral vision is not interested in detail, it readily picks up shadows from Mona Lisa's cheekbones that enhance the curvature of her smile. But when your eyes go directly to her mouth, your central vision does not integrate the shadows from her cheeks with her mouth. The smile is gone.

Mona Lisa (Leonardo da Vinci).

The Best Illusion of the Year contest, mentioned in the introduction, has been a huge success. You would think that after generations of talented, dedicated, sometimes obsessively driven visual artists and scientists tinkering and laboring at their easels, drafting tables, scratch pads, darkrooms, and PC graphics programs, this particular vein of ore would be all mined out. But it isn't.

Consider the Leaning Tower illusion discovered by McGill University scientists Frederick Kingdom, Ali Yoonessi, and Elena Gheorghiu, which took first prize in 2007.

The two images of the Leaning Tower of Pisa are identical, but to you it seems that the tower on the right leans more. This is because your visual system treats the two images as if they were part of a single scene. Normally, two neighboring towers will rise skyward at the same right angle, with the result that their image outlines converge as they recede from view. This is one of the ironclad laws of perspective, so invariant that your visual system automatically takes it into account. Since the outlines don't converge in the images above, your visual system is forced to a.s.sume that the two side-by-side towers must be diverging. And this is what you "see."

Mona Lisa up close. The three panels are simulations of how your visual system sees Mona Lisa's smile in the far periphery, the near periphery, and the center of gaze. The smile is more p.r.o.nounced in the left and middle panels. ("Blurring and deblurring" by Margaret S. Livingstone, Harvard Medical School) The Leaning Tower illusion. (F. A. A. Kingdom, A. Yoonessi, and E. Gheorghiu, McGill University) This illusion is so basic, so simple, it is almost beyond belief that no one ever reported it before 2007. It just goes to show that there is still plenty of low-hanging fruit just waiting to be discovered in the world of illusions. Each new illusion adds depth and definition to perceptual and cognitive theory, bolstering certain hypotheses while weakening others or inspiring new ones. Some suggest new experiments. Each inches us just that much closer to understanding perception and awareness.

The illusion of s.e.x (Richard Russell).

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.

Next, the Rotating Snakes illusion, which was presented at the 2005 contest.

The perception of motion need not arise from actual action in the world. Rather, the perception of motion occurs when dedicated motion processing neurons in your brain are activated by specific patterns of light intensity changes in your retina.

The Rotating Snakes illusion (Akiyos.h.i.+ Kitaoka).

Some stationary patterns generate the illusory perception of motion. For instance, in this illusion invented by the scientist Akiyos.h.i.+ Kitaoka, the "snakes" appear to twist. But nothing is really moving other than your eyes. If you hold your gaze steady on one of the black dots in the center of each "snake," the motion will slow down or even stop. Because holding the eyes still stops the illusory motion, eye movements must make the snakes twist. This is supported by the fact that the illusory effect is usually stronger if you move your eyes around the image.

Finally, there is the Standing Wave of Invisibility illusion, which we hope to turn into a totally new magic trick and someday in the future unveil at the Magic Castle. This is the illusion Steve discovered while working on his thesis in graduate school. He wondered what is required for an object to be visible. You might think that visibility should require only that light fall on your retina. But it can be more complicated. Illusions of invisibility show that a stimulus can be projected onto your retina and nevertheless be wholly or partly invisible.

A cla.s.sic example is visual masking. In this illusion, a visual target-for instance, a black bar against a white background-is rendered invisible when two ab.u.t.ting black bars appear a tenth of a second after the target. What's cool is that a target that is seen initially by the brain can be erased by a mask that enters the brain afterward.

Steve's graduate thesis showed how the illusion works in the brain. As it turns out, the target causes two responses in your visual pathway. One, the onset response, occurs after the target turns on. A second, the after discharge, occurs after the target turns off. Other labs had ignored the after discharge because it occurs after the stimulus turns off. But Steve showed that if you inhibit the after discharge, the stimulus disappears. The same also happens if you inhibit the onset response but not the after discharge. So both the onset response to a stimulus and the after discharge contribute to the neural representation of a stimulus. He realized that if this was true, we should be able to predict a new and very powerful illusion in which a flickering target is perpetually rendered invisible by inhibiting both the onset response and the after discharge of each flicker. It worked!12 We called the new illusion the Standing Wave of Invisibility, and it unites our interest in visual illusions and magic. It is this illusion that we plan to turn into a new stage effect to wow magicians with the power of neuroscience on their own turf. To make this happen we are going to need the help of a magic studio that specializes in electrically engineered lighting effects. For now the trick is on our "to do" list.

Welcome to the Show but Please Leave on Your Blinders.

Cognitive Illusions.

Apollo Robbins is sweeping his hands around the body of the fellow he has just chosen from the audience. "What I'm doing now is fanning you," the master pickpocket from Las Vegas informs his mark, "just checking to see what you have in your pockets." Apollo's hands move in a flurry of gentle strokes and pats over the man's clothes. More than two hundred scientists are watching him like hawks, trying to catch a glimpse of fingers trespa.s.sing into a pocket. But to all appearances this is a perfectly innocent and respectful frisking. "I have a lot of intel on you now," Apollo continues. "You scientists carry a lot of things."13 Apollo is demonstrating his kleptic arts to a roomful of neuroscientists who have come to Las Vegas for the 2007 Magic of Consciousness symposium. The idea behind this evening is to show these researchers that magicians have much to teach them about the subjects of their life's work: attention, perception, and even the holy grail, consciousness. Magicians and neuroscientists share a pa.s.sion for understanding the nuts and bolts of the human mind, but we have been developing our respective arts and theories more or less in dependently of each other for generations. Starting tonight, if all goes as planned, our two communities are going to pay close attention to each other's discoveries.

Apollo has dared everyone in the auditorium to try to catch him pilfering this man's belongings up on stage in plain view. We watch intently just like everyone else, but none of us really stand a chance. This is Apollo Robbins, the infamous "Gentleman Thief" who once pickpocketed ex-president Jimmy Carter's Secret Service detail, relieving them of their watches, wallets, badges, confidential itinerary, and the keys to Carter's limo. He can keep the joke on us for as long as he feels like it, but at least we know one thing he doesn't. As soon as we see who Apollo has plucked randomly from the crowd, we exchange amused glances. This man isn't a scientist at all, as Apollo a.s.sumes, but the New York Times science reporter George Johnson, who will be explaining to the wider world what transpires here tonight. George is a man of great humor and intelligence, but he is quite shy. His awkwardness makes for great theater.

The fanning continues as Apollo engages in his highly honed rapid-fire patter. "You have so many things in your pockets I'm not sure where to begin. Here, was this yours?" he asks, thrusting something into George's hand. George frowns down at it. "You had a pen in here," Apollo says, opening George's breast pocket, "but that's not what I was looking for. What's in that pocket over there?" George looks over. "There was a napkin or a tissue, maybe? You have so many things it's confusing to me. You know, to be honest I'm not sure that I've pickpocketed a scientist before. I've never had to do indexing as I went through someone's pockets."

Patter, it turns out, is one of the most important tools in the magician's toolkit for attention management. There are only a dozen or two (depending on whom you ask) main categories of magic effects in the magician's repertoire; the apparent wide variety of tricks is all in the presentation and details. Sleight of hand is of course critical to a pickpocket, but so is patter-the smooth and confident stream of commentary that can be used to hold, direct, or divide attention. Apollo tells George one thing while doing two other things with his hands. This means that in the best-case scenario, George has only a one in three chance of noticing when something of his gets s.n.a.t.c.hed. His real chances are actually far below one in three: in the psychic sparring ring of attention management, Apollo is a tenth-degree black belt. By continually touching George in various places-his shoulder, wrist, breast pocket, outer thigh-he jerks George's attention around the way a magnet draws a compa.s.s needle. While George is trying to keep track of it all, Apollo is delicately dipping his other hand into George's pockets, using his fast-driving voice to help keep George's attention riveted on Apollo's cognitive feints and jabs and away from the pockets being picked.

SPOILER ALERT! THE FOLLOWING SECTION DESCRIBES MAGIC SECRETS AND THEIR BRAIN MECHANISMS!.

Apollo steals George's pen, notes, digital recorder, some receipts, loose cash, wallet, and, very early on, his watch. One cla.s.sic way to lift somebody's watch is to first grab his wrist over the watchband and squeeze. This creates a lingering sensory afterimage. You know about visual afterimages from chapter 1-the red dress, the vanis.h.i.+ng coin-but afterimages can occur in any sensory system. Apollo is exploiting the same principle, only in this case the afterimage is tactile. The afterimage renders the touch neurons in George's skin and spinal cord less sensitive to the watch's removal and creates a conveniently lasting perception of the watch long after it has disappeared. George simply doesn't notice his watch is missing because his skin tells him it is still there. We notice the watch when we see Apollo folding his arms behind his back, buckling it onto his own wrist as his patter leads George down some new garden path of attention.

END OF SPOILER ALERT.

On Adaptation.

At one point or another in your life you surely tore your living s.p.a.ce apart in search of your gla.s.ses-"They can't have just disappeared!?"-only to realize that you were wearing them. When you first put them on an hour ago, the touch receptors in the skin of your face and head gave you a rich sensory impression of their location, their weight, their tightness against your temples. But since then they have become an in effective stimulus and you feel nothing.

Or try to touch the elastic band of your sock without looking, while you keep your legs and feet still. Chances are you will miss it by at least a couple of inches. This same elastic band was very noticeable against your skin when you first put your socks on this morning. But because nothing has changed since, it has become undetectable to your touch sensors. Or put your hand on a table and hold it completely still. At first you will feel it; after a short time, you no longer notice it.

Adaptation is a critical and ubiquitous process in the nervous system, not just in sensory processing but in all brain systems. It saves energy by reducing the metabolism in neurons that do not receive new information.

A few times during the fleecing, Apollo holds a pilfered object high up behind George's head for the audience to see. This makes everyone laugh but George, who smiles and looks around sheepishly, wondering what the joke is. Then, to more laughter, Apollo returns all of George's belongings one by one. "If you're recording, I think we have evidence," he warns as he hands over the digital recorder. Proffering a folded stack of bills, he says, "I presume this is your gratuity money?" Finally he turns to George and says, "We all pitched in to buy you a watch, very similar to the one you were wearing when you got here." He unstraps George's watch from his own wrist and pa.s.ses it over. George gasps and then rolls his eyes.

How could George be so inattentive? Why can some joking thief manipulate his attention like a matador leading a bull? It's truly amazing that this can happen to a professionally trained observer like George while he's onstage (and therefore has heightened attention) and has been told what is about to happen to him. It makes you wonder, what is attention? Can you look directly at something and literally not see it?

Magicians are masterminds of human cognition. They control very sophisticated cognitive processes, such as attention, memory, and causal inference, with a bewildering combination of visual, auditory, tactile, and social manipulations. The cognitive illusions they create, unlike the visual illusions discussed so far, are not sensory in nature. Rather, they involve higher-level brain functions. By toying with your cognition-even if they don't know which neural circuits they are tapping-magicians make it impossible for you to follow the physics of what is actually happening. They leave you with the impression that there is only one explanation for what just happened: pure magic.

Possibly the best definition of attention was put forth in 1890 by William James, author of The Principles of Psychology and the philosopher king of modern psychology. He wrote: "Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others."

James elegantly describes the phenomenon of attention, but he says nothing about how it is generated by your brain or how it is modulated in everyday experience. In William James's day, attention could be studied only in terms of introspection-the reflective looking inward on your own thoughts and feelings.

For the next one hundred years, researchers groped in the dark for new and better ways to understand attention. In experiments, subjects wore headphones that piped different words into their left ear and right ear and were asked to listen to just one side, to see if attention could be divided. Some scientists studied radar operators and combat pilots to see how well they could split attention. Others examined the "c.o.c.ktail party effect," which enables you, in a noisy ballroom filled with loud inebriated people, to hear your name spoken from across the room.

But such studies were observational, meaning the brain was still a black box. Neuroscientists could examine the brain's mechanisms of attention in animals, or in human patients undergoing neurosurgery for diseases such as epilepsy, but there was simply no way to probe the inner cogs and wheels of the brain's attentional circuitry in healthy humans. That changed in the 1990s with the advent of modern brain imaging techniques that allow us to peer into the black box and look for the location of neural correlates of attention. Now we can also begin to figure out how magicians twiddle your attentional circuits with such consummate skill.

Already neuroscientists have learned that attention refers to a number of different cognitive processes. You can pay attention to your TV show voluntarily, which is one process (top-down attention), or your baby's crying can draw your attention away from the TV, which is a different process (bottom-up attention). You can look right at what you are paying attention to (overt attention), or you can look at one thing while secretly paying attention to something else (covert attention). You can draw somebody's gaze to a specific object by looking at it ( joint attention), or you can simply not pay attention to anything in particular. Some of the brain mechanisms controlling these processes are beginning to be understood. For example, you have a "spotlight of attention," meaning that you have a limited capacity for attention. This restricts how much information you can take in from a region of visual s.p.a.ce at any given time. When you attend to something, it is as if your mind aims a spotlight onto it. You actively ignore virtually everything else that is happening around your spotlight, giving you a kind of "tunnel vision." Magicians exploit this feature of your brain to maximum effect.

It is not yet clear whether there is a single center in your brain that controls attention. Given how many types of attentional effects there are, multiple attention control centers may work in concert. One critical clue is that many of the same brain circuits that control your eye movements are involved with changing the location of your attention in the world. This makes sense, because eye movement circuits are responsible for orienting your eyes to specific areas of visual s.p.a.ce, and it seems logical that those same circuits could operate to orient your attentional spotlight, too. Determining what's interesting in the world with attention is undoubtedly critical to deciding where you should look next. Magicians intuitively grasp this, and they control your eyes and your attention as if they were marionettes on a string.

As mentioned, humans have the capacity for overt and covert attention. When a soccer goalie watches a soccer ball fly toward the goal, she is overtly attending to the ball. But that cagey forward on the opposing team, who's trying to make a shot toward the goal, may intentionally divert the goalie's attention from the ball by looking away from the goal (as if to nonverbally communicate, "Hey, look! I'm going to go over there next!" when in fact the next turn will be in the opposite direction). The move is called a "head fake" in sports, and the idea is to trick the goalie into directing attentional resources to the wrong location. The forward, all along, may have looked toward the fict.i.tious region of interest, but was instead covertly attending to the goal so as to plan her shot.

Too much attention can be a bad thing, too. As social beings, humans and other primates often have to process visual information without looking directly at each other, which could be interpreted as a threat. For example, we all intuitively know not to walk up to a cop, look him or her in the eye, and say, "Hey, what you looking at? You looking at me?" The ability to attend covertly stems from the social circ.u.mstance that we do not always want people we are watching to know that we are attending to them.

You also have the ability to engage in joint attention. You can gaze at another person, wordlessly pointing to an object with a simple gesture (including a s.h.i.+ft in your gaze). By doing so, you may induce that person to look over at the object overtly, or you may induce them to covertly attend to that object. Likewise, when the soccer forward faked out the goalie, she did so by pretending to pay attention to an irrelevant section of the field. She initiated joint attention. Babies as young as nine months display joint attention, as do great apes. Dogs are even better than chimps at some forms of joint attention. A dog will look in the direction you point to. A chimp will not.14 Apollo the Gentleman Thief could write the playbook on how to commandeer joint attention.15 *

A Failure of Joint Attention.

In March 2009, we went to Muhlenberg College, in Allentown, Pennsylvania, to attend the Theory of Art and Magic workshop. Each day of the workshop was filled with theoretical lectures, hands-on seminars, and performances. We witnessed a virtuoso performance by Roberto Giobbi of Switzerland, who also gave a full-day workshop on card tricks that complemented his highly regarded five-volume set Card College. (So when we say Roberto wrote the book on card tricks, he really wrote five.) We were sitting in what clearly used to be an upscale private home, now used by Muhlenberg College to host small conferences and meetings with donors. Roberto worked miracle after miracle, and then he performed his version of the famous Bitter Lemon trick. In this trick, a magician asks a spectator to pick a card and sign it, only to find that the card has been transported to the inside of an uncut piece of fruit. The fruit is given to the spectator along with a knife, and when she cuts it open, she finds a rolled-up card. You guessed it-it's hers.

Roberto, a traditionalist, actually uses a lemon. But his trick adds a twist. In his version, Roberto lays a handkerchief over his empty hand and the lemon appears under the handkerchief as if from nowhere. It's a beautiful sleight that fooled everybody in the room. Except Susana.

SPOILER ALERT! THE FOLLOWING SECTION DESCRIBES MAGIC SECRETS AND THEIR BRAIN MECHANISMS!.

Susana, you see, was pregnant with our second son, Brais, and suffered from all-day morning sickness during Giobbi's workshop. She wasn't paying attention. Whereas Giobbi had the rest of the crowd concentrating, Susana was busy trying not to puke. Then a flash of yellow finally caught her attention. She gazed at the magician to see, plain as day, that he was stuffing a lemon up underneath the handkerchief into the palm of his other hand. Later, she mentioned to Steve that she thought that trick was uncharacteristically sloppy. She didn't understand why the professional magicians attending the cla.s.s were so amazed. Steve had no idea what she was talking about. He thought the lemon sleight had been seamless. That's when Susana realized that she had been able to detect the method behind the trick only because of her queasiness-induced attention deficit. Roberto controls people's perception by focusing their attention on his face just as he unceremoniously shoves the lemon up under the handkerchief. This is joint attentional control at its finest. But Susana's attention was fully focused on her barf control mechanism, and thus was unmanageable even by a master magician.

END OF SPOILER ALERT.

Attention is also linked to your short-term memory and your ability to tune out what is happening around you. Sometimes a stimulus is so demanding, so salient, that you cannot help but pay attention-an ambulance siren, an infant's cry, a dove fluttering out of a top hat. This information flows in a bottom-up fas.h.i.+on-from your primary senses to higher levels of a.n.a.lysis in your brain. It is called sensory capture.

Other times you can s.h.i.+ft your attention around, as you choose, in a top-down fas.h.i.+on. Signals flow from your prefrontal cortex (the CEO of your attentional networks) to other regions that help process information. This is the spotlight of attention that is under your control. You don't hear the siren or the baby or see the dove because you are attending to something else, such as the last page of that gripping mystery novel you are reading. Research shows that the greater your capacity for short-term or working memory, the better you are at resisting sensory capture.

Neuroscientists have begun to dissect the nature of attention and identify its neural correlates. The initial brain areas that process a visual scene use circuits that lay out visual s.p.a.ce like a map. These first few stages of visual processing (the retina, the visual thalamus, and the primary visual cortex discussed in chapter 1) are organized so that the neurons that process one part of the visual field are positioned directly next to neurons that process the adjacent parts of the visual field. As your eyes move around, your retinas and the visual input move around, too. But no matter where you look, some neurons are a.s.signed to your central vision, and the other neurons are a.s.signed to specific peripheral positions of input from your retinas. The retinal positions of these visual neurons never change.

When you decide consciously to pay attention to a specific location of this "retinotopic" s.p.a.ce, neurons from higher levels of your visual system increase the activation of the low-level circuits and enhance their sensitivity to sensory input. At the same time, neurons in the surrounding regions of visual s.p.a.ce are actively inhibited. We recently worked with a group of colleagues led by neuroscientist Jose-Manuel Alonso at the State University of New York and showed that the neurons in the primary visual cortex not only enhanced attention in the center of the spotlight and suppressed attention in the surrounding regions, but their degree of activation was modulated by the amount of effort used to accomplish a given task. In other words, the harder the task, the more the central region of attention was activated and the more the surrounding region was suppressed.

In a magic show, you face an incredibly difficult task: to peel away all the layers of misdirection and figure out the secret method underlying each magic effect. But the harder you try, the harder it gets: the more your attention is enhanced on the center of the attentional focus, the more your attention is suppressed in all other locations. Of course, the center of the attentional focus is right where the magician wants it-where nothing of particular interest is going on. The locations surrounding your spotlight of attention-where the real action is happening-are now conveniently suppressed by your brain. The armies of neurons that suppress perception in those regions are the magician's confederates.

Apollo works his marks as if he knew about these neuronal circuits all along. He'll pull a quarter from your breast pocket and ask, "Is this yours?" You know full well that it's not yours (who keeps quarters in their breast pocket?). But you can't help it, you inspect George Was.h.i.+ngton's face as if you might find your initials engraved on his forehead. "What year is the coin?" Apollo asks. And you dutifully try to make it out, but the letters are too small and blurry, so you reach for your reading gla.s.ses...in your breast pocket. They are missing. "Try these gla.s.ses," Apollo kindly offers as he hands you the gla.s.ses off his face. Your own gla.s.ses, as it turns out. While you were busy attending to the quarter, which you knew didn't actually come from your pocket, Apollo's hands absconded with those gla.s.ses literally right under your nose while you suppressed all visual motion surrounding the quarter.

If neuroscientists had known-as Apollo seems to know-that attention works in this way, it would have saved a whole lot of research time. So now we study magicians.

On Misdirection.

You don't have to be a magician to be skilled at attentional misdirection. When a conversation edges into uncomfortable territory, your natural instinct is to change the subject. Often the other person plays along, as if you weren't just talking about your testicular cancer, and pretends that yes, we really are talking about last night's Red Sox score. Our brains are designed to be flexible with regard to what we are paying attention to, at both the sensory and the cognitive levels. Without this flexibility we would be unable to drive home thinking about what's for dinner and then instantaneously swerve the car to avoid the child chasing her ball into the street.

After fleecing George, Apollo turns to the audience and says, "Now would you like to see the behind-the-scenes of how I did all that?" Magicians are famously loath to give away their secrets, but Apollo is here in Las Vegas tonight to instruct, not just to entertain. He calls the ever amiable George back for more pilfering, but this time he explains what he is doing. He slows his techniques way down, occasionally pausing and rewinding.

Most people call what magicians do "misdirection," explains Apollo, but that is like saying doctors make people well with their curing skills. The term is so broad that it is next to meaningless. He prefers to discuss specific principles and techniques such as "frames" and "attention management." It's not true, he says, that the hand is quicker than the eye. Most manipulations are carried out at a normal pace. Success relies on the magician's skill in diverting your attention away from the method and toward the magical effect.

SPOILER ALERT! THE FOLLOWING SECTION DESCRIBES MAGIC SECRETS AND THEIR BRAIN MECHANISMS!.

Frames are windows of s.p.a.ce that the magician creates to localize your attention. A frame can be the size of a whole room or a tabletop or no bigger than a business card. "You have no choice but to watch in the frame," says Apollo. "I use movement, context, and timing to create each frame and control the situation." Apollo demonstrates by moving very close to George. He grabs George's hand and pretends to press a coin into it, though all he is really placing there is another sensory afterimage with his thumb. "Squeeze hard," says Apollo. George gazes intently at his hand, now caught within a frame. He squeezes. "Do you have the coin?" teases Apollo. George nods. He thinks so. "Open your hand," says Apollo. The palm is empty. "Look on your shoulder," says Apollo. George glances to his shoulder, where a coin is resting.

Apollo explains that if a subject's attention is localized to a frame, then maneuvers outside the frame will rarely be detected (such as placing a coin on a shoulder). Magicians, he says, thoroughly manage attention at all times. People tend to think of misdirection as the art of making someone look to the left while some fast move is pulled on the right, but Apollo says it is more about force-focusing your spotlight of attention to a particular place and at a particular time.

Magicians exploit several psychological and neural principles to focus your spotlight of attention. Recall that when you see an object that is new, bright, flashy, or moving-think of that white dove fluttering out of a top hat-your attention is driven by increased activity in your ascending sensory system, which simply means that salient information from your senses flows up into your brain. It arrives from the bottom and travels up. You are strongly drawn to the object. Neuroscientists call it sensory capture. Psychologists call it exogenous attentional capture. Magicians call it pa.s.sive misdirection.

In pa.s.sive misdirection, you are attending to the fluttering bird while the magician gains a few unattended moments to carry out a sneaky maneuver. It is pa.s.sive because the magician lets you do all the work. He just sets up the condition. In Penn & Teller's version of the cups and b.a.l.l.s, Penn uses his juggling skills to draw your attention while Teller does a secret move. Penn actually tells you what he's doing. "This is not juggling," he says as the three little aluminum foil b.a.l.l.s cycle in front of his face, "this is misdirection." You of course helplessly watch the juggling show intently right up until the point Penn informs you that you've been duped.

If more than one movement is visible-the flying dove arcs overhead while the magician reaches his hand into a box to set up the next trick-you will naturally follow the larger, more salient movement. You track the bird, not the hand. Hence the magician's axiom, "A big move covers a small move." In fact, a large or fast-moving stimulus, such as the fluttering dove, can literally decrease the perceived salience of a small or more slowly moving stimulus, such as the magician's hand in the box, so that your attention is drawn to the bird, not the hand. You already know the reason: when you pay attention to a particular location in s.p.a.ce, the neurons responsible for processing information in the surrounding regions are inhibited.

When two identically salient actions start simultaneously, the one you notice first captures your attention. It not only becomes more salient, but the other action is suppressed, becoming less salient. Furthermore, things that are novel (the unexpected dove) produce stronger responses in parts of your brain that are critical to the allocation of attention (namely, the inferotemporal cortex, the hippocampus, the superior colliculus, the prefrontal cortex, and the lateral intraparietal area; these areas receive the bottom-up sensory signals and then activate circuits that enhance the attended object while suppressing other objects in your visual field). The salience of an object also increases when a magician actively directs your attention to it. For example, Apollo may ask you to leaf through the pages of a book while he places your stolen wallet in his pocket. You become absorbed in the task of turning pages. This is active misdirection. (Psychologists call it endogenous attentional capture.) Your top-down attentional control is focused on the book and you ignore the hand. The magician's actions enhance the firing of neurons involved in your attention to turning the pages of the book, whereas neurons that might attend to the magician's hands are suppressed.

Apollo messes with your head in other ways as well. His patter aims to generate an internal dialogue in your mind-a conversation with yourself about what is taking place. This, he says, results in a great deal of confusion. It slows your reaction time and leads you to second-guess yourself.

Many magicians use comedy and laughter to reduce your focused attention at critical points in their acts. Remember the Great Tomsoni and his corny jokes? He takes advantage of your diminished attention in those offbeat moments when you relax after a joke. Or Magic Tony and his leopard shoes? Tony's magical patter aims toward plays on words and homespun rhetoric. He's created a character who fully embodies one of the primary stereo types of a magician: the corny joking uncle. Tony says that his goal is for his patter to be "so lame that it's cool." We couldn't help but wonder why he chose a persona that is, well, overwhelmingly lame. Tony says that the accidental cornb.a.l.l.s create an atmosphere in which you may laugh at their jokes, but it's because you feel you have to be polite, not because it's funny. Without the fake laughter, the show would be embarra.s.sing for everyone, so you laugh. But Tony realized that an unrepentant, over-the-top, intentionally corny punster can make you into a willing executioner of his humor. And that can be very useful to him as a vehicle for misdirection. An honest groaning response to a pun is more attention-grabbing than a fake laugh, says Tony. It's hard to stay focused on the method of a trick when you're busy cringing or rolling your eyes.

In many magic tricks the secret action occurs when you think that the trick has not yet begun or when you think that the trick is over. Magicians call this time misdirection. They can also introduce delays between the method behind a trick and its effect, preventing you from causally linking the two. Arturo de Ascanio, the great magic theorist and father of Spanish card magic, refers to this specific type of time misdirection as the "parenthesis of forgetfulness." Essentially, it means that the magician must separate the method from the magical effect. This separation messes up the spectators' reconstruction process.

Imagine that a magician fakes a coin transfer from his left to his right hand, and then opens his right hand to reveal that it is empty. Because there is no separation between the sleight (the fake transfer) and the magical effect (the vanished coin), you may easily conclude that the coin was never actually transferred but remained concealed in the magician's left hand. A more accomplished magician will introduce a separation-a parenthesis of forgetfulness-between the method and the effect. For example, after the fake coin transfer, and before revealing his empty right hand, he may reach into his pocket for the overt purpose of retrieving a magic wand, but in fact he is also dropping the palmed coin inside his pocket. Then, touching the magic wand in his left hand to his right hand, he shows that the coin has disappeared. When you rewind the scene in your mind, you will have a harder time figuring out where the vanished coin might be hidden.

One of Magic Tony's tricks involves misdirection based on what psychologists call a habituation-dishabituation paradigm. This means he specifically tries to make you complacent (that is, bored, lazy, or otherwise not carefully attending to what he is doing) by apparently repeating the same action over and over, and to lull you into a false sense of security. That's habituation. And then bam! he changes the method, leading you to the resultant spectacular effect.

n.o.bel laureate Eric Kandel and our friend Tom Carew showed that one of the neural correlates of habituation-dishabituation is a change in the strength of connections between neurons in your brain. When habituation occurs, neurons send less signaling chemicals (neurotransmitters) to the neurons they are connected to, thus decreasing the response downstream. When the same connection becomes dishabituated, the signaling neuron sends lots of neurotransmitters once again, thus restoring the bigger reaction in the downstream neuron. Tony elegantly switches the audience's neurons from habituation to dishabituation modes. His initial repet.i.tions lull the spectators' brains into mind-numbing habituation, only to be brusquely awakened (dishabituated) by the shocking magic effect he finally achieves.

END OF SPOILER ALERT.

Another important concept, Apollo tells the scientists gathered in Las Vegas, is that tricks are embedded in natural actions. He demonstrates by making a pen disappear. He dangles it in front of the audience with one hand. When he flicks his other hand past his ear, as if to scratch, no one notices. The movement is natural, unremarkable, quick. Suddenly everyone sees the pen has vanished. Apollo turns his head around to reveal the pen tucked behind his ear.

Teller, the shorter half of the duo Penn & Teller, sheds his mute persona to describe the same concept. A former high school Latin teacher, Teller is far from mute offstage. He has a love for words, and his explanations are not only scholarly but unexpectedly eloquent. "Action is motion with a purpose," he says. In normal social interactions, we constantly search for the purpose motivating other people's actions. An action with no obvious purpose is anomalous. It draws attention. However, when the purpose seems crystal clear, we look no further. Teller explains that he will draw suspicion if he raises his hand for no apparent reason, but not if he performs a seemingly natural or spontaneous action like adjusting his gla.s.ses, scratching his head, draping his coat over the backrest of a chair, or reaching into his pocket for a magic wand. Teller calls this "informing the motion." He says, "Skilled magicians inform every necessary maneuver with a convincing intention."

Neuroscientists now have a good idea why such decoy actions are so good at fooling us. It comes from a remarkable type of brain cell called a mirror neuron. You are familiar with the idea of the "mind's eye": pretty much at will, you can conjure a quasivisual experience of just about anything that can be seen or depicted in images. You also have your "mind's ear," with which you can replay songs and noises and voices you are familiar with. Similarly, there is your "mind's body." This is your brain's virtual representation of your physical self. When you plan out how you are going to cook tonight's dinner, when you daydream that you are an action hero, whenever you relive a painful memory of gym-cla.s.s humiliation, you are running a virtual simulation of those actions in your mind's body. It is an invaluable psychic tool for planning and executing actions, learning motor skills and remembering them. Mirror neurons form an important part of your mind's body because they help you understand the actions and intentions of other people. They do this by automatically mimicking others' actions and a.s.suming their intentions using your own mind's body. So when you see Teller reach for a gla.s.s of water, you instantly do the same thing in your mind's body. You also ascribe a simple, natural motivation to him, namely, that he is thirsty and will raise the gla.s.s to his lips and take a drink. In your mind's body, you do this, too. Literally: many of the same neurons that are active when you take a drink are active when you think someone you can see is about to take a drink. Your brain makes a prediction and runs a simulation, automatically and usually subconsciously.

Mirror neurons are an important element of human social intelligence. They are part of how we are able to understand each other, to imitate, to learn and teach, to empathize. But they can also mislead us. A good magician can disguise one action as another or convincingly fake an action he isn't really performing, prompting your mirror neurons to feed you false inferences about what he is actually doing or not doing. You see Teller raise the gla.s.s to his lips and seem to drink, and your automatic prediction seems to be fulfilled. But did he really take a drink? Maybe he transferred something from hand to mouth, or from mouth to hand.

On Autism.

Joint attention is the mechanism by which you can share another person's experience by following the direction of his or her gaze and pointing gestures. A common and medically established symptom of many autism patients is that they have a deficit in joint attention which can be measured by tracking their eye movements. For instance, autistic patients tend to not look at other people's faces, even the faces of actors in movies or subjects in photographs.16 Magicians rely on joint attention as a form of social misdirection, to divert your attention from the method behind the trick and toward the intended perceptual effect. If the magician wants your eyes focused on his face, he will look directly at you. If the magician instead wishes you to s.h.i.+ft your gaze to a particular object, he himself will turn his body, head, and eyes toward that object, and your head and eyes will quickly follow. This is the magician manipulating your joint attention. In a double act such as Penn & Teller's show, the opportunities to capitalize on joint attention increase twofold. When Penn Jillette performs a routine, Teller's body, head, and gaze are intently oriented to the location of attention the duo wishes to impose on the audience (Penn's hands, face, a specific object onstage) and vice versa. We were careful to apply this same principle when practicing our joint act for the Magic Castle. Joint attention is critical for language acquisition and cognitive and social development. But it also makes you susceptible to magic tricks that exploit your natural impulse to pay attention to the same places and objects attended to by the people around you.

Our hypothesis is that autism patients who suffer from problems of joint attention should respond abnormally to magic tricks that rely on joint attention. They will not be duped by social misdirection, so they will be more likely to "catch" the magician's secret action than normal observers. Failure to be fooled by magic tricks that rely on social misdirection would thus indicate that joint attention is impaired, which could help the diagnosis of autism-spectrum disorders. It would also help evaluate the success of therapies directed to improving joint attention: as the patients' joint attention improves, they should become more and more susceptible to social misdirection and thus more likely to "fall" for magic tricks that rely on joint attention cues. We have written a grant proposal to fund a study to determine whether our hypothesis is correct.

Unlike people with autism, most of us turn our gaze and attention to the faces of people in photographs. However, our intense focus on faces is at the expense of other potentially interesting information. Have you noticed anything strange about this picture? Look more carefully, and you may see that the girl has an extra finger on her right hand. Observers with autism may be quicker to notice details such as these because their attention is not fixed on the faces. (Photocomposition by Smitha Alampur, Thomas Polen/iStockphoto) *

Social misdirection onstage, as used by the magician, is only a more refined form of the social misdirection used by our primate cousins to procure themselves better access to food and other resources. Ethological studies have shown that a macaque will avoid looking at a hidden food cache so as to keep potential compet.i.tors away. Consciousness researchers say that such macaques have a theory of mind. That is, they know to interpret the gaze, head, and body orientation of their peers as indicators of their location of attention and interest. They also know how to adjust or redirect their own body and gaze to fake interest in an undesired object so as to draw compet.i.tion away from the object of desire. In this sense, both macaques and humans are proficient mind readers. But magicians are best. And Apollo, as you'll see in the next chapter, has even more tricks up his proverbial sleeve.