Sleights Of Mind Part 6

Mac asks how many people saw him slip the rock into his shoe, and about half the hands in the room go up. "I'm so happy that some of you noticed," Mac says. "I've been a little worried that it wouldn't get easier for any of you the second time!" And then Mac asks if he should do it again, a third time. Murmurs of a.s.sent. But this time Mac changes the method and produces another surprise. He does not reach for his back pocket to bring out the now familiar rock. Instead, he simply tips the shoe and shakes it, and when nothing comes out he reaches in and-pulls out a huge rock! Only this time it turns out to be a sponge rock. He had it stuffed in his shoe the whole time.

END OF SPOILER ALERT.

Mac's demonstration ill.u.s.trates how apparent, but not actual, repet.i.tion is a powerful ally to the magician. You become habituated to seemingly repeated actions and gloss over the details. For a magician, the devil is in those details. The audience has a deep-seated bias to a.s.sume that effects that look the same are done in the same fashion. It's human nature.

In your everyday life you deduce how things work by observing them repeatedly. Hammers drive nails. Cups hold liquid. Micro wave ovens heat food. You don't have to think about them. Magicians use this habit of your mind against you to hide the method behind many of their tricks. They know that when you see an effect repeated-the rock drops out of the shoe-you naturally a.s.sume that the repet.i.tion is accomplished by the same method. But then comes a surprise when the rock is made of sponge.

Mac used a different method on the third iteration to throw the audience off track, eliciting a big surprise. Remember the story from chapter 2 in which Danny Hillis fooled Richard Feynman day after day with the same trick, not because Feynman couldn't correctly guess at the method after a day of pondering it (he could), but because Hillis kept changing the method, and so Feynman's explanations were demonstrably wrong. Feynman was flummoxed by apparent repet.i.tion.

Using apparent repet.i.tion, a magician can deliberately raise suspicion about a possible method, and then at the very end show you that the only theory you've got is wrong. This principle, known as the Theory of False Solutions, was formulated by Juan Tamariz, the Spanish magician in the crazy hats introduced in chapter 5. Johnny Thompson calls it "closing all the doors," which means reducing all of the possible explanations of an effect down to none, until only impossible (magical) explanations remain.

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

The whole point of apparent repet.i.tion is to set up false expectations. The magician shows a trick using method number one, and you form a theory of how he did it. Next, he apparently (not really) does the same trick again, but wait-now that you are watching for the telltale sign that your theory is correct, you can see that your theory is impossible. Hmm. Okay, you form a new theory. The magician does the trick again (no, he doesn't really, it just looks as if he did), oh, drat, your second theory is wrong, too, because now that you try to see if your second theory holds water, you can see that the magician is not hiding the card on the back of his hand (though that's exactly what he was doing the second time).

The magician is one step ahead of you, setting up expectations with each iteration and then crushing them just as you begin to understand.

END OF SPOILER ALERT.

One of the greatest weapons magicians have going for them is that your mind operates via prediction. To grasp the meaning of this, imagine what you "knew" as a newborn infant. You could root for a nipple and stick out your tongue, but otherwise the world was mostly a background curtain of meaningless sights, sounds, and sensations. You could feel the pull of gravity and sense light and dark patterns, but nothing made sense. You were not even aware that you had a body. It's doubtful you could be called conscious the day you were born.

Fortunately, infants and babies rapidly race out of this twilight to build up representations of the outside world, their bodies, other people, their feelings and emotions. Every experience is carved into the developing brain's neural circuitry via plasticity, the lifelong ability of the brain to reorganize itself based on new experiences. In this way, each person builds up models of what to expect throughout life.

Early on, you learned that the feet and hands you liked to put in your mouth were your own; you taught yourself to roll over, sit up, crawl, and walk until your movements became engrained in areas of your brain that plan and carry out movements. Then you walked, ran, and-if you practiced a lot-played a sport without thinking about or planning the required motions. But now imagine you are walking down a city street and are so engrossed looking up at some signs that you don't notice a six-inch curb is just ahead. Your distracted brain predicts that the sidewalk is flat while the road is six inches lower. You take a step with the exact precision needed for your foot to land on the sidewalk. And what happens? Surprise! Your foot crashes into the roadway. You failed to predict a common feature of an ordinary walkway.

Early in life you learned to recognize faces and voices. You figured out how to manipulate adult caretakers to get what you needed. If you had nurturing parents, you learned that your cries would be met with love and attention. If you had emotionally unstable parents, you learned that your cries might be met with indifference or punishment. If you had parents who experienced good days and bad days (who hasn't?), you learned how to cope with emotional ups and downs. Most importantly, you learned what to expect from intimate relationships in your life long before you could talk.

You learned to speak based on expectation. Toddlers extract the meaning of their native language from a stream of syllabic sounds and gradually become proficient in vocabulary and syntax. Thus if someone says to you "how now brown," your brain will predict the word "cow" in a flash. But if the person instead says "wolf," your prediction fails and you are surprised.

The same principle applies to vision, hearing, touch, and all your cognition, including your beliefs, which are, after all, constructs of your learned predictions. In other words, perception is not a process of pa.s.sive absorption but of active construction. When you see, hear, or feel something, the incoming information is always fragmentary and ambiguous. As it percolates up the cortical hierarchy, each area, having its own specialized set of functions, a.n.a.lyzes the data stream and asks: Is this what I expect based on my very last experience? Do I need to fill in some of the gaps in the data stream? Does it jibe with my other past experiences? Does this conform to what I already know about the world? Your brain is constantly comparing incoming information to what it already knows, expects, or believes. Every experience is measured up against prior beliefs and a priori a.s.sumptions.

Indeed, all great art is based on violation of prediction. When you go to the movies, you see the same twenty plots unfold over and over. Often the film is boring because it's predictable. But a talented director challenges your predictions. You are surprised, entertained. The same goes for painting, poetry, novels, and great magic acts.

Alas, the automaticity of predictions can get you into hot water. For example, NASA put commercial airplane pilots into a flight simulator and asked them to do a set of routine landings. On some of the approaches a huge commercial aircraft was plopped on the runway. One-quarter of the pilots landed on top of the airplane. They never saw it because they had been led to believe that there was nothing unusual and the runway would be clear.

James the Amaz!ng Randi is a short man with a long Santa Claus beard and a gigantic personality. He's the guy who showed that Uri Geller's spoon bending could be done with mundane methods and who introduced us to Teller and other leading magicians. Randi commands the room wherever he goes. It is no wonder that he plays the role of elder statesman for the American magic community. As founder of the James Randi Educational Foundation, he protects society at large from charlatans and frauds of the paranormal. The foundation offers a one-million-dollar challenge to anybody who can prove paranormal powers of any kind. After more than twenty years and numerous challenges, no one has qualified to collect the money.

Randi moves slowly up to the podium at our Magic of Consciousness symposium. He's getting on in age, but the twinkle in his eyes is youthful and beguiling. Randi explains that you will easily accept unspoken a.s.sumptions and that you tend to believe information that you learn for yourself as opposed to being told it. Prediction at work.

"My purpose here today is to show you that audiences will easily accept their own a.s.sumptions, but not a.s.sertions made by the conjurer," says Randi. "In other words, when we tell them something is so, they have good reason to doubt us because we're there to trick them. So we should try to allow them, as much as we can, to a.s.sume things. Conjurers do well to take advantage of the spectator's misplaced confidence in his own ability to arrive at a correct solution."

Randi demonstrates. "I have already deceived you folks," he says. "When I walked onstage, you a.s.sumed I was talking into this mike." He pushes away the large microphone affixed to the lectern. The real mike is tiny, clipped to the top of his lapel. "Why did you believe it? If you were asked specifically 'Did he use the house amplification system,' you'd say yes, he did. And you wouldn't be telling a lie when you reconstructed the experience for others later on. You'd be telling what you believe to be true. But it wouldn't be true."

Another example: "Many of you think I'm looking straight at you. But no, I'm looking at a blur of faces out there. I can't see you, because I normally wear gla.s.ses with corrective lenses." Randi removes the gla.s.ses from his head and pokes his fingers through empty frames. "Now why would someone come up before you wearing empty frames? What's the use of that? To make a point, ladies and gentlemen." The point being that people don't question lies that have no reason to be lies.

But why don't people question unspoken a.s.sumptions? The reason is that such a.s.sumptions have already been questioned and established as fact. As children, we pulled our grandparents' gla.s.ses off of their faces, stuck them in our mouths, and tested the lenses with our tongues. As adults, we feel no further need to continue to lick the gla.s.s. We've become habituated to the fact that gla.s.ses frames have actual lenses in them. But this is just an observation, not an explanation. It is critical to go further into the neuroscience here and ask how the brain actually accomplishes habituation, and why.

The why is easy: thinking is expensive. It requires brain activity, which takes energy, and energy is a limited resource. More important, thinking takes time and attention away from other tasks, like finding food and mates and avoiding cliffs and saber-toothed tigers. The more you can safely file away as established fact, the more you can concentrate on your current goals and interests. The less you wonder whether somebody's gla.s.ses frames actually contain gla.s.s, the better off you are.

Habituation is created through a neuronal process called synaptic plasticity. Eric Kandel of Columbia University recently won the n.o.bel Prize for his work establishing this process in a little-appreciated sea slug called an aplysia. Kandel recorded from a variety of neurons in the aplysia's nervous system while blowing air onto the slug's gill. Aplysia don't like air puffs on their gill, so they retract it. But air puffs aren't really harmful, and retracting the gill is tiresome and burns precious calories, so as the air puffs are repeated, the aplysia habituates and eventually stops retracting the gill in response. The neural signals concerning the air puffs become more and more minute until neurons eventually stop signaling the air puff altogether. That's synaptic plasticity, and it's the neural mechanism of habituation. We humans do the exact same thing as the lowly sea slug, only we do it with more fancily processed perceptions and behavioral options. We don't question whether every pair of gla.s.ses we see contains gla.s.s, because experience has taught us that we can safely a.s.sume they do, and the synaptic pathways responsible are habituated to that fact. There's no longer a need to lick the gla.s.s.

Once you've habituated to a feature of the world, it becomes a humdrum and seemingly immutable part of the fabric of life. Stable, reliable, unchanging. That's why magicians prefer to rely on unspoken a.s.sumptions over explanations whenever possible.

Mentalism, the subject of the next chapter, is a specific branch of what magicians call the conjuring art, and its success relies on the audience's a.s.sumptions. "Mentalism deals with things that are apparently extrasensory, precognition, divination of various kinds, but it's all a form of conjuring," says Randi. "There is nothing to it in reality. They are tricks. You see, the mentalist does very well by allowing his audience to a.s.sume things."

Mac King is standing in Susana's lab at the Barrow Neurological Inst.i.tute during a doc.u.mentary shoot for the Australian Broadcast Company's weekly Catalyst science show. Two cameras are rolling: one was brought by the show's producers and one is ours. Max Maven told us that Mac was the very best there is at tossing coins from one hand to the other, so here he is. It's not that he drops them less than most people. It's that Mac can toss a coin through the air only to have it disappear upon landing. You see it clear as day. Mac tosses the coin up in the air one, two, three times in his right hand, then tosses it to his left hand. You see it fly through the air. His hand closes to catch the coin, and then opens wide to show that the coin is gone. Incredible.

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

Here's how it works. Mac is in fact tossing the coin vertically in his right hand. But when he makes the toss to his left hand, his right thumb surrept.i.tiously holds the coin in his palm and stops it from flying. So he's only pretending to throw the coin. The left hand closes as if the coin is in flight and "catches" it. But of course the coin was never there-so why do you see a coin flying through the air?

The trick takes advantage of an implied or inferred motion illusion stemming from the motion-sensing portions of your brain. First, a visual region of your brain that tracks the movement of objects or targets in s.p.a.ce and time-called the lateral intraparietal, or LIP-receives information about the actual motion of Mac's right hand. Neurons in this area predict the trajectory of the flying coin based on his hand movements. Then, when Mac's right hand abruptly stops, the motion-selective neurons of two other visual areas (the primary visual cortex and a specialized motion-sensitive visual area called MT) sense the motion of Mac's left hand closing. A major component of this trick is that Mac closes his left hand at the same moment that the coin would have flown through the air had it actually been launched. Without his closing his left hand, there is no motion for the motion areas of your brain to detect. Without the closing of the left hand, the trick is much more likely to fail. But because motion information of the closing hand closely matches the implied motion of the fake-launched coin from the right hand, the predicted trajectory of the illusory coin jibes with the actual trajectory of the left hand's closing fingers, and your brain is satisfied-incorrectly!-that the coin actually flew into the left hand. In fact, only Mac's fingers were moving.

Similarly, have you ever pretended to throw a stick for your dog during a game of fetch? The dog spins around and starts to take off, expecting the stick to follow the implied trajectory. This is because circuits in her brain that are active during the perception of real motion also respond to implied motion. Her brain tells her there is a stick in flight and off she goes.

END OF SPOILER ALERT.

During a magic act, you are as easily duped by implied motion as your dog. Take the vanishing ball illusion, a dumbfoundingly simple trick. A magician throws a little red ball into the air three times. On the first two throws, he catches it in his hand. But on the third throw the ball mysteriously vanishes. You "see" it go up and then it disappears. Amazing.

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

The magician pulls this off by capturing your gaze with joint attention. Each time he throws the ball, he moves his head up and down to exaggerate the ball's trajectory. But on the third toss, he only pretends to throw the ball. He hides it in his hand while his head moves up to track the ball's apparent path. But you, a slave to social cues, move your head up along with his. And that is when you get the sudden sensation that the ball-which you think you've been following with your eyes-has disappeared in midair.

END OF SPOILER ALERT.

Gustav Kuhn, a psychologist and magician at the University of Durham in the UK, showed a film clip of the vanishing ball illusion to thirty-eight students and carefully tracked their eye movements as they watched. Two out of three reported that they saw the ball leave the magician's hand on the third toss.

The eye tracking revealed that the students were not looking at the point in s.p.a.ce where they thought the ball vanished. Rather, the magician used his gaze to covertly direct their attentional spotlights to the predicted position of the ball. His eye movements overruled what the students' own eyes were seeing. The illusion works in part because your brain pathways for eye movement and perception operate in dependently, and in part because you have low-resolution vision outside the center of your gaze, meaning that you are not surprised that you don't see the ball as it is thrown. Your attention follows the presumed trajectory of the ball because of the magician's gaze. Once you catch up to the ball with your eyes, it literally disappears, because now you can see with your high-resolution central vision that the ball is gone. It proves again that the direction of your gaze can be separated from attention.

The effect may be related to the same kind of representational momentum we saw in Mac King's tossed coin trick-the final position of a moving object that suddenly disappears is perceived farther along the path of motion than its actual final position. If so, the neural correlate of the effect lies in area LIP of your posterior parietal cortex.

The vanishing ball also ill.u.s.trates priming. You are more likely to see it vanish in midflight after real tosses have primed you to know what an actual tossed ball looks like.

Priming is a powerful force in everyday life, by which subtle suggestions made to your subconscious mind can influence your subsequent behavior. Try this: Answer the following questions out loud and quickly. Don't stop to think about your answer. What color is snow? What color are clouds? What color is whipped cream? What color are polar bears? What do cows drink? If you said cows drink milk, you were primed by the previous questions to choose something white (cows drink water, Farmer John).

Psychologists are fond of studying priming in laboratory settings. Here are a few examples of some recent experiments.

Subjects were asked to read a list of words related to old age and infirmity-wrinkled, gray, nursing home, dementia-interspersed with neutral words. Afterward, they walked more slowly toward the campus elevator than did others who did not read such words. The effect did not last long, but the change in their behavior was noticeable.

Chinese female students took a math test after filling in ethnic or gender information. Being reminded of their gender resulted in lower test scores (the gender stereo type is that girls are bad at math), whereas being reminded of their race resulted in high scores (Asians are good at math).

Half of the partic.i.p.ants in another study were subliminally primed with the words "Lipton Ice"-repeatedly flashed on a computer screen for 24 milliseconds-while the other half was primed with a control that did not consist of a brand. Priming the brand name Lipton Ice made those who were thirsty want the Lipton Ice. Those who were not thirsty, however, were not influenced by the subliminal message, since their goal was not to quench their thirst.

Advertisers use priming to trigger consumption of junk food. In an experiment, elementary school children watched a cartoon that contained either food advertising or advertising for other products. While watching, they were given goldfish crackers. Kids who saw the food advertising ate 45 percent more crackers.

Prime Mentalism Tricks.

Magicians, especially mentalists, often use priming to bias your responses. For example, here is a mentalist trick normally done with either three or seven spectators, but it should work on you just as well. Please get a pen or pencil and follow these instructions, in the order they are presented, and follow them as quickly as possible.

Choose a number between 1 and 50.

But there are a few rules to your choice.

The number must be double-digit.

Both digits must be odd numbers.

One number must be larger than the other.

Write it down quickly.

Okay, now we are reading your mind. Look at the number and concentrate hard on its value. We're starting to pick up your thoughts. Once we have the number solidly, we'll write it into this book and send that ma.n.u.script off to the printers so that you can read it here.

You guessed the number 37. Yes? Yayy! We read your mind backward in time. No, we got it wrong? Well, clearly, either you didn't follow the instructions or you didn't concentrate hard enough. Maybe you should go buy another copy of this book and see if it works better with that one.

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

Want to know how the trick works? In the first place, n.o.body really knows. But here's what we do know. We reduced the number of choices by requiring a double-digit number. That narrows it down to between 10 and 50. Then we said both numbers must be odd. That leaves only ten choices, between 11 and 39. Then we said you couldn't have duplicates, leaving you with just eight choices: 13, 15, 17, 19, 31, 35, 37, and 39. Okay, narrowing fifty choices down to eight leaves us with a 12.5 percent chance of getting the guess correct, which is better than our original 2 percent chance, but still quite low. So why do people tend to choose 37? Well, we primed you to think about 3 and 7 by starting off our discussion by saying that the trick works best on groups of three or seven. That's not true. The trick is generally done on one person, not on a group. There are certainly other contributors to why this trick works, since it still works most of the time even without the priming, but the other factors are currently not well understood.

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Priming can also lead to perceptual misinterpretations in the form of expectations gone wrong, which can get you into serious trouble. For example, our colleague Peter Tse at Dartmouth College served as an expert witness in a recent case of a man who shot at what he thought was a bear and killed a man instead. According to Tse, the twenty-one-year-old hunter was primed to see a bear. He had seen his younger brother kill a bear earlier that day and he wanted to bag one for himself. The victim was out picking berries in the Vermont woods during bear hunting season without the reflective orange clothing that hunters wear to avoid shooting each other. (This is almost grounds for the Darwin Award, but no matter.) The hunter saw the bushes shake, took aim, and, seeing a bear in his sights, sent a bullet through the victim's shoulder, both lungs and his heart, and out the other shoulder. The berry picker was dead in less than a minute.

The hunter and his brother fled the scene once they realized their mistake. Their uncle later talked them into turning themselves in. The verdict was negligent manslaughter with a one-year prison term.

Tse made his case on the idea that priming-seeing the brother's successful kill earlier that day-had lowered the hunter's ability to detect a false alarm, which in this case meant the erroneous detection of a bear. It was, he said, an example of signal detection theory. Signal detection theory was invented during World War II to help determine when British radar operators should scramble fighters to shoot down German bombers. False alarms were bad because if you scrambled fighters to defend against a nonexistent attack, the country was left vulnerable to a real attack from a different direction for a lengthy period of time while fighters flew home, landed, reserviced their planes, rested the flight crews, and prepared for another scramble event. False alarms were expensive and dangerous. On the other hand, failing to scramble at the earliest possible moment might mean that bombs would fall in the heart of London. Scientists refer to this kind of mistake as a "miss." The question was how to determine ideal criteria for minimizing both false alarms and misses. And how do the radar operators set their own internal criterion for deciding when a blip on the screen is a n.a.z.i bomber?

In the case of the bear hunter, he was single-mindedly determined to kill a bear that day. Never mind that n.o.body holding a gun should be single-minded about anything-the fact is that our desires lead us to see what we want to see. The hunter's ability to detect a bear was heightened to the maximum level, but this same criterion also heightened his ability to mistake a man for a bear. He was in the perfect trigger-happy mood to act on a false alarm. In the end, that's exactly what he did, and it all came down to how he handled the inevitable tension between false alarms and misses.33 Like priming, your tendency to hold biases and stereo types makes false alarms more likely. For example, Keith Payne, a psychologist from the University of North Carolina, Chapel Hill, asked people to sort guns of various kinds from hair dryers and caulk guns and other gun-shaped tools. He used a bias measurement technique championed by Harvard psychologist Mahzarin Banaji. With this method, the level of a person's bias (racial, gender, or other) is determined by measuring their reaction time to concepts that conflict with their belief system. Payne found that American experimental subjects linked black people more easily to guns, whereas they a.s.sociated white people with tools.

This stereo type turned lethal in 1999 when a twenty-three-year-old African student, Amadou Diallo, was killed in New York City because he reached for his wallet when police ordered him to halt. In his country of Guinea, you are supposed to take out your wallet when approached by police. Diallo was shot at forty-one times and hit nineteen times. The cops claimed they saw a gun, not a wallet, and were acquitted, resulting in riots.

Given that false alarms are prevalent, what can we do to decrease their occurrence? One idea is to manipulate the observer's expectations. This is the philosophy of the Transport of London campaign to get drivers to be more aware of cyclists on the road. Car drivers are constantly on the lookout for other cars, but they often miss bicycles and motorcycles. Transport of London uses gorilla-in-our-midst-like demos in television commercials in an attempt to increase driver awareness and reduce the likelihood that drivers will hit a cyclist. It should work. In the Simons and Chabris gorilla demonstration, people are more likely to see the gorilla if you tell them that there could be a gorilla in the movie.

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

Magicians use both bias and priming to cause false alarms, which relates back to Tamariz's Theory of False Solutions. Recall that one way to create strong misdirection is to give clues that a certain method is being used to accomplish a trick when in fact it's a different method altogether. Well, magicians also use prior biases to accomplish false detections. Remember Mac King's fake coin toss and Kuhn's disappearing ball? When you see the coin and ball tossed in the air for real, it serves to plant the bias that the magician always tosses the object. In these tricks, the magicians use repet.i.tion to increase your bias toward making a false alarm (detecting a coin or ball when none is there), but also to decrease the possibility of your missing an actual coin toss. Imagine a card sharp playing three-card monte-an ancient confidence game in which the victim bets he can find a target card among three facedown playing cards. The magician gives the observer several trials to see where the target-say, the queen of spades-correctly lies. This increases the victim's confidence and shifts the criterion (the victim's sensitivity to the position of the queen) up. Then wham! the card sharp uses sleight of hand to swap out the queen, causing a miss during a trial with a large bet.

END OF SPOILER ALERT.

When our son Iago was two, Steve showed him a magic trick. Steve felt he had gotten pretty good at the trick and wanted to show off. But Iago was unimpressed. Here was a kid who was endlessly delighted and entertained by the fact that he could blow out a candle but found something utterly impossible to be utterly ba.n.a.l. You already know why. His brain was still naive enough about the laws of physics and causality that he had no predictions on which to base a sense of surprise. He was still young enough that we could show him how to make an object travel through a magic s.p.a.ce-time wormhole and he would simply note it, and maybe play around with this new fact for a while-in exactly the same way he played around with pouring liquid from one container to another, or pulling his socks on and off, on and off-and that would be that.

Mac King agrees with us. Kids are harder to fool, he says, because they don't have strong expectations about the world. They just think magic exists. Some people really can make a coin dematerialize. If you believe in Santa Claus, what's not to believe in a magic show? It's just a bunch of adults magically transporting a coin around or making cards disappear into thin air. What they really want to see is something difficult and funny, like a triple somersault resulting in the seat of the jumper's pants splitting up the middle.

Randi agrees. Children are notoriously difficult to deceive, he says, because they're not sophisticated enough to be fooled. They have not built up bulletproof models of probability and impossibility.

Thus we can ask: When does a child's mind reach a level of maturity that allows her to be delighted or amazed by a magic trick? How does she acquire expectations? Indeed, what do babies know? When do they learn to predict the world? When are their expectations violable?

Such questions raise a deeper quandary. When infants are born, how much of their brains are preloaded for acquiring knowledge about the world? Are their brains blank slates, or do they possess innate structures that are locked and ready to absorb knowledge? In the 1920s, the Swiss developmental psychologist Jean Piaget pioneered this inquiry and concluded that infants younger than nine months have no innate knowledge of the world. He said they have no sense of object permanence-the idea that a thing can exist even when you don't see it. Piaget also argued that babies gradually construct knowledge from experience, including the capacity for empathy, which he suggested came rather late in development.

Modern cognitive neuroscientists challenge many of Piaget's conclusions and a.s.sume that infants are born with some knowledge of the physical world. They are "statistical learning machines" who have a rudimentary capacity for math and language. Young babies have everyday ideas about psychology, biology, and physics.

Because babies can't talk, developmental psychologists have devised numerous strategies for gleaning information about infant cognition. In "baby labs," infants sit in high chairs or on their parents' laps and observe simple scenarios. The experimenter then measures how long an infant looks at one object compared to another or at a series of events. The idea is that their gaze reveals how interested they are in the object or if they can detect something out of the ordinary-indications that they have simple models of how the world works. For example, babies may become less interested when they see the same event happen over and over. They grow bored. When a new event comes along, they will look longer at it, as long as they notice the difference.

Elizabeth Spelke, a developmental psychologist at Harvard University, has carried out scores of experiments on the reasoning abilities of children. In one, Spelke showed that babies as young as three and a half months will look longer at impossible events (such as a hinged wooden panel moving through a box) than at possible ones. They have, she says, a basic understanding of physical events that appear to violate gravity, solidity, and contiguity.

Such research also shows that infants have a sense of object permanence far earlier than Piaget postulated. In an experiment, babies watched a toy car move down an inclined track, disappear behind a screen, and reemerge from behind the screen farther down the track. Then the researchers put a toy mouse behind the track, raised the screen, and rolled the train again. No problem. Finally, they put the mouse on the track, lowered the screen, then secretly removed the mouse and rolled the train. Infants as young as three and half months looked longer at the possible mouse-crushing event, suggesting they had a sense of object permanence. They knew the mouse existed, and they knew it was located where the train should hit it.

David Rakison, a psychologist at Carnegie Mellon University in Pittsburgh, also uses toys to explore what babies know. Rakison studies infants' abilities to categorize objects. You might think young children naturally lump cows and horses in one group and cars and planes in another. But does that mean they know what the objects are? When Rakison removed legs and wheels from such toys, the babies put cows and cars together. He notes that infants can tell that dogs are different from cats when they are three months old, but they do not know that dogs and cats are alive until they are three years old.

Our son Iago first saw a giant tortoise at the age of eighteen months, during a visit to the Phoenix Zoo. The enormous animal (the size of a kiddie pool) was stationary for a long time, and then it started to walk laboriously toward us, along the fence. Iago exclaimed "Vroom vroom," as if encouraging the reptile to move faster. Lacking any experience of tortoises, he had simply decided that the strange approaching object was some sort of slow-moving car.

Other researchers use animals or dolls to explore what is called the theory of mind-the innate ability of one person to sense the state of mind of another person. A great example of theory of mind in chimps was presented in the 1999 Scientific American Frontier television program Animal Einsteins. In this episode, Alan Alda was dressed up like a veterinarian, wearing scrubs and a mask, as he marched into the chimpanzee enclosure at Georgia State University. He held what looked like a spear, a one-meter-long metallic post with a huge needle on the end. His host, Sue Savage-Rumbaugh, knew that this getup would definitely get the attention of her chimps. It was the same outfit any one of the veterinary staff would wear when they entered the enclosure with the intent to give a shot to one of her animals. She had a "theory of mind" concerning her chimps: that they would see a syringe-wielding vet and be very unhappy about it. She was right.

As Alan walked down the caged hallway, a chimp sitting above the chain-link ceiling, several animal holding cages farther down the hall, watched him like a hawk. A second chimp was released from its holding cell behind the enclosure and entered the chain-link cage. This second chimp could see the first chimp above the hallway outside the cage, but because of a cage separation wall made of brick, the second chimp could not see Alan. But after seeing a signal made by the first chimp, the second chimp stopped in his tracks and looked at the separation wall as if it were the devil himself. He clearly knew that something evil his way came. And this was possible only because the first chimp knew that the second chimp could not know that Alan was coming, and so he signaled him. This incredibly complex behavior shows that the first chimp had a theory of mind. He knew that the second chimp had a mind and that he could not possibly know about the impending doom. So he warned him.

The famous Sally-Ann test is used to look for the emergence of theory of mind in young children. A child is introduced to two dolls, Sally and Ann, and is shown that each doll has her own box, with a candy or toy hidden inside. Then the child is told that Sally is going out for a minute. The experimenter removes the Sally doll from the scene, leaving her box behind.

Next, the child is told that Ann is going to play a trick on Sally. Ann opens Sally's box, removes the candy, and hides it in her own box. Sally returns, unaware of what has happened. The child is asked where Sally will look for her candy. A child with a theory of mind will realize that Sally doesn't know that Ann has played a trick on her. She predicts that Sally will look in her own box for the candy and discover it is missing. But a child lacking a theory of mind will see the situation based on what she knows in her own mind to be true and will predict that Sally will look for the candy where it actually is: in Ann's box.

Very small children tend not to guess correctly in this test, since theory of mind takes time to develop. Most children get it right by age six or seven, although some three-year-olds are capable of it (our son Iago, three years and seven months old at the time of this writing, failed the test).34 Babies and young children also differ from adults in the styles of their attention, their ability to lie, and their sense of time. In her book The Philosophical Baby, Alison Gopnik, a developmental psychologist at the University of California, Berkeley, explains that in order to focus attention, you need strong input from your prefrontal cortex, which is the last brain area to develop in humans. With the help of mature circuitry, your attention works like a narrow spotlight, focusing on one thing at a time. In babies and young children, Gopnik says, attention operates more like a lantern, casting a diffuse light on its surroundings.

"We sometimes say that adults are better at paying attention than children," writes Gopnik. "But really we mean just the opposite. Adults are better at not paying attention. They're better at screening out everything else and restricting their consciousness to a single focus."

"Adults can follow directions and focus, and that's great," says John Colombo, a psychologist at the University of Kansas. "But children, it turns out, are much better at picking up on all the extraneous stuff that's going on. And this makes sense. If you don't know how the world works, then how do you know what to focus on? You should try to take everything in."

These ideas are consistent with the neural correlates of attention that we discovered in collaboration with Jose-Manuel Alonso's lab, described in chapter 4. Attention results from the activation of inhibitory neurons, which in turn suppress neurons in the surrounding visual regions that could cause distractions. When and where you focus your attention, you are also suppressing the potential surrounding distracters. The harder you concentrate, the larger your central attentional activation and surround suppression become. Gopnik and Colombo's studies suggest that babies and children don't suppress surrounding distracters as well as adults do.

In an experiment by John Hagen, a developmental psychologist at the University of Michigan, children are given a deck of cards and shown two cards at a time. They are instructed to remember the card on the right and to ignore the card on the left. Older children and adults direct their attention to the card on the right and remember it. But young children often remember the cards on the left, which they were supposed to ignore.

Gopnik also argues that children under five experience a different sense of time. The world is less ordered. They forget what happened a minute ago and how they felt. They don't seem to antic.i.p.ate their future states. They don't project what they will think and feel later on. They don't have the concept of logical, internally driven thought.

But kids above the age of five have started to develop a sense of consecutive time and a stream of consciousness that flows in an unbroken stream with a unified self at the center. Magicians need these functions in order to make magic magical. Without these processes, there is no strong sense of cause and effect, and therefore no inviolable rules that can be violated. Before you're five years old, your entire life is a magic show, so what's one more trick? We have often asked magicians how early a child can understand and enjoy magic. The usual answer is five years old.

So what kinds of magic tricks do appeal to children younger than five years of age? What would surprise our little Iago? We decided to ask one of the world's premier children's magicians, Silly Billy, aka the New York City performer David Kaye, how he deals with this issue. Not surprisingly, he says the magic tricks that work with children tap into a child's basic knowledge about the world.

For example, pulling a coin from a child's ear is deeply magical. Kids have had ears for their entire lives. They use them to listen and learn. But producing money is not a familiar characteristic of the human ear. So, says Kaye, when a magician pulls a coin from a child's ear, it is magic.

The needle through the balloon is another trick that works on kids. They know balloons can pop. They know a needle will pop a balloon. So when the magician inserts a needle into a balloon and it does not pop, the child sees it as magic.

If you take a crayon and rub it on a surface, it leaves a mark, says Kaye. But the Magic Drawing Board trick, developed by Steve Axtell, goes way beyond the familiar. The magician draws a face on a large board. Suddenly the eyes start moving, the mouth opens and closes. The face becomes animated and carries on a conversation with the magician. This breaks natural laws related to drawing with a crayon.

If you hold a cup of water and turn it upside down, water will spill out. But in the Slush Powder trick, says Kaye, a magician pours water into a Styrofoam cup and turns the cup upside down and the water has vanished. Similarly, a magician can make a cone out of a newspaper, pour milk into it, unfurl the paper, and show that the milk is gone. Kids go wild when they see this.

Finally, if you put small items into a container and move the container across the room, the objects will still be inside. Young children know this. But when the magician places an object in a "change bag" and says the magic words, the object is no longer there. This is magic that a child can believe in. None of it requires a theory of mind.