http://www.npr.org/templates/player/mediaPlayer.html?action=1&t=1&islist=false&id=93465269&m=93465237
http://smc.neuralcorrelate.com/files/publications/martinez-conde_macknik_nature07.pdf
http://www.mindscience.org/index.cfm

THE ART (AND SCIENCE) OF AUDIENCE MANIPULATION
http://www.boston.com/bostonglobe/ideas/articles/2008/08/03/how_magicians_control_your_mind/
Magic isn’t just a bag of tricks – it’s a finely-tuned technology for
shaping what we see. Now researchers are extracting its lessons.
BY Drake Bennett  /  August 3, 2008

In September of 1856, in the face of a growing rebellion, Napoleon III
dispatched Jean-Eugene Robert-Houdin to Algeria. Robert-Houdin was not
a general, nor a diplomat. He was a magician – the father, by most
accounts, of modern magic. (A promising young escape artist named
Ehrich Weiss would, a few decades later, choose his stage name by
adding an “i” to “Houdin.”) His mission was to counter the Algerian
marabouts, conjurers whose artful wizardry had helped convince the
Algerian populace of Allah’s displeasure with French rule.

A French colonial official assembled an audience of Arab chieftains,
and Robert-Houdin put on a show that, in its broadest outlines, would
be familiar to today’s audiences: he pulled cannonballs out of his
hat, he plucked lit candelabra out of the air, he poured gallon upon
gallon of coffee out of an empty silver bowl.

Then, as he recounted in his memoirs, Robert-Houdin launched into a
piece of enchantment calculated to cow the chieftains. He had a small
wooden chest with a metal handle brought onto the stage. He picked a
well-muscled member of the audience and asked him to lift the box; the
man did it easily. Then Robert-Houdin announced, with a menacing wave
of his hand, that he had sapped the man’s strength. When the volunteer
again took hold of the box, it would not budge – an assistant to
Robert-Houdin had activated a powerful magnet in the floor of the
stage. The volunteer heaved at the box, his frustration shading into
desperation until Robert-Houdin’s assistant, at a second signal, sent
an electric shock through the handle, driving the man screaming from
the stage. The chieftains were duly impressed, and the rebellion
quelled.

The story of Robert-Houdin’s diplomacy by legerdemain is well-
established in magic lore, in large part because it is the only
documented instance, at least since antiquity, in which a conjurer
changed the course of world affairs. Stage magic, after all, isn’t
statecraft, but spectacle and entertainment.

In the past year, though, a few researchers have begun to realize that
magic represents something more: a deep and untapped store of
knowledge about the human mind. At a major conference last year in Las
Vegas, in a scientific paper published last week and another due out
this week, psychologists have argued that magicians, in their age-old
quest for better ways to fool people, have been engaging in cutting-
edge, if informal, research into how we see and comprehend the world
around us. Just as studying the mechanisms of disease reveals the
workings of our body’s defenses, these psychologists believe that
studying the ways a talented magician can short-circuit our perceptual
system will allow us to better grasp how the system is put together.
“I think magicians and cognitive neuroscientists are getting at
similar questions, but while neuroscientists have been looking at this
for a few decades, magicians have been looking at this for centuries,
millennia probably,” says Susana Martinez-Conde, a neuroscientist at
the Barrow Neurological Institute and coauthor of one of the studies,
published online last week in Nature Reviews Neuroscience. “What
magicians do is light-years ahead in terms of sophistication and the
power of these techniques.”

As magicians have long known and neuroscientists are increasingly
discovering, human perception is a jury-rigged apparatus, full of gaps
and easily manipulated. The collaboration between science and magic is
still young, and the findings preliminary, but interest among scholars
is only growing: the New York Academy of Science has invited the
magician Apollo Robbins to give a presentation in January on the
science of vision, and a team of magicians is scheduled to speak at
next year’s annual meeting of the Society for Neuroscience, the
world’s largest organization of brain researchers. And in a world
where concentration is a scarce resource, a better understanding of
how to channel it would have myriad uses, from safer dashboard
displays to more alluring advertisements – and even, perhaps, to
better magic.

A great deal of the success of a piece of magic is simply getting the
audience’s attention and sending it to the wrong place – to a right
hand flourishing a wand while the left secrets a ball away in a pocket
or plucks a card from a sleeve. Magic shows are masterpieces of
misdirection: they assault us with bright colors and shiny things,
with puffs of smoke and with the constant obfuscatory patter that many
magicians keep up as they perform.

For years, cognitive scientists thought of perception as like a movie
camera, something that reproduced the world in its panoply of detail.
Over the past decade, though, that model has been increasingly
questioned. For one thing, people have a pronounced tendency to miss
things that are happening right in front of them. Daniel Simons, a
psychologist at the University of Illinois, did a series of now-famous
studies in the late 1990s that showed the extent of this cognitive
blindness. In one, people were approached by someone asking them for
directions, only to have, in the middle of the conversation, that
person replaced by another. Only half noticed the change.

In another study, people were shown a movie clip of two teams, one in
black shirts and one in white, each passing a basketball around. The
subjects were asked to count the number of passes one of the teams
made. Half said afterward that they hadn’t noticed the woman in a
gorilla suit who, midway through the clip, strolled through, paused,
and beat her chest.

Because of work like this, a new model has arisen over the past
decade, in which visual cognition is understood not as a camera but
something more like a flashlight beam sweeping a twilit landscape. At
any particular instant, we can only see detail and color in the small
patch we are concentrating on. The rest we fill in through a
combination of memory, prediction and a crude peripheral sight. We
don’t take in our surroundings so much as actively and constantly
construct them. “Our picture of the world is kind of a virtual
reality,” says Ronald A. Rensink, a professor of computer science and
psychology at the University of British Columbia and coauthor of a
paper on magic and psychology that will be published online this week
in Trends in Cognitive Sciences. “It’s a form of intelligent
hallucination.”

The benefit of these sorts of cognitive shortcuts is that they allow
us to create a remarkably rich image of our environment despite the
fact that our two optic nerves have roughly the resolution of cell-
phone cameras. We don’t have to, for example, waste time making out
every car on the highway to understand that they are, indeed, cars,
and to make sense of how they are moving – our minds can simply
approximate from the thousands of cars we have already seen in our
lives.

But because this method relies so heavily on expectation – not only to
fill in the backdrop around us but to determine where to send what
psychologists call our “attentional spotlight” – we are especially
vulnerable to someone who knows our expectations and can manipulate
them, someone like a magician. “In magic,” says Teller, half of the
well-known duo Penn & Teller and one of five magicians credited as
coauthors of the Nature Reviews Neuroscience paper, “we tend to take
the things that make us smart as human beings and turn those against
us.”

Misdirection is, in a sense, the conjurer’s tool that is easiest to
understand – we miss things simply because we aren’t looking at them.
Martinez-Conde is particularly interested in misdirection, and the
question of what it is about certain movements that attract and hold
our attention. Robbins, a performing pickpocket and another of the
magicians to coauthor the Nature Neuroscience paper, has found, he
says, that semi-circular gestures draw people’s attention better than
straight ones. “It engages them more,” he says. “I use them when I’m
actually coming out of the pocket.”

Martinez-Conde is intrigued by this distinction, and has hypothesized
that the particular magnetism of curved motions might spring from the
fact that they don’t map as easily onto the quick, straight movements,
or saccades, that our eyes instinctively use to focus on objects. As a
result, she suggests, curved motions might require more sustained
attention and concentration to follow.

Other effects, though, are more befuddling. Often eye-tracking studies
show that subjects can be looking right at an object without seeing it
– car accident survivors report a similar paradox. Or, with just a
little encouragement, a person can be made to see something where
there’s nothing.

The vanishing ball illusion is one of the most basic tricks a magician
can learn: a ball is thrown repeatedly into the air and caught. Then,
on the final throw, it disappears in midair. In fact, the magician has
merely mimed the last throw, following the ball’s imagined upward
trajectory with his eyes while keeping it hidden in his hand.

But if the technique is easily explained, the phenomenon itself is
not. If done right, the trick actually makes observers see the ball
rising into the air on the last toss and vanishing at its apex. As
Rensink points out, this is something more powerful than merely
getting someone to look in the wrong direction – it’s a demonstration
of how easy it is to nudge the brain into the realm of actual
hallucination. And cognitive scientists still don’t know exactly
what’s causing it to happen.

For the moment, the cognitive scientists looking at magic are
confining themselves to these sorts of simple effects, and the
fundamental questions they raise. Eventually, though, Rensink
envisions a sort of periodic table of attention effects: methods for
getting someone’s attention, methods for deflecting it, methods for
causing someone to be blind to something they’re looking directly at.
Such a taxonomy, he argues, wouldn’t just be helpful to magicians. The
control and management of attention is vital in all sorts of realms.
Airplane cockpits and street signs would be designed better, security
guards would be trained to be more alert, computer graphics would feel
more natural, teaching less coercive.

Still, even if none of this came to pass, there’s a value in simply
coming to grips with the gaps and limits in our awareness. Like Robert-
Houdin’s audience, awed by a magnet, we are more easily manipulated
and more likely to put ourselves in compromising situations if we
don’t know what we don’t know. “The main thing is knowing that you’ve
got limitations,” says the cognitive researcher Daniel Simons. “Most
people don’t understand the extent to which talking on a cellphone
affects their driving.”

According to Teller, magic, more than anything else, serves as that
reminder. And that explains why, despite its comparatively humble
effects, it continues even in the age of Imax to attract practitioners
and audiences. “The fundamental thing we do every day is ascertain
what is reality, it’s this diagnosis of what the signals coming into
our eyes are supposed to mean,” he says. “We say, ‘That’s a fence, I
must not walk into it,’ or, ‘Is that a car coming around the corner?
How much can I see of it? Oh, no, it’s only a bicycle.’ ” What draws
people to magic, he believes, is an appreciation of how slippery that
seemingly simple diagnosis can be. “They realize,” he says, “that the
best way to grasp the power of deception is to do it themselves.”

CONTACT
Susana Martinez-Conde
http://smc.neuralcorrelate.com/
email : smart [at] neuralcorrelate [dot] com

SUPPLEMENTARY INFO
http://www.nature.com/nrn/journal/vaop/ncurrent/fig_tab/nrn2473_T1.html
http://www.nature.com/nrn/journal/vaop/ncurrent/box/nrn2473_BX1.html
http://www.nature.com/nrn/journal/vaop/ncurrent/box/nrn2473_BX2.html
http://www.nature.com/nrn/journal/vaop/ncurrent/box/nrn2473_BX3.html
http://www.nature.com/nrn/journal/vaop/ncurrent/suppinfo/nrn2473.html

THE PAPER
http://www.nature.com/nrn/journal/vaop/ncurrent/full/nrn2473.html
Nature Reviews Neuroscience, advance online publication, 30 July
2008 / doi:10.1038/nrn2473

Science and society: Attention and awareness in stage magic: turning
tricks into research
BY Stephen L. Macknik [1], Mac King, James Randi [2], Apollo Robbins,
Teller, John Thompson & Susana Martinez-Conde [1]

Abstract
Just as vision scientists study visual art and illusions to elucidate
the workings of the visual system, so too can cognitive scientists
study cognitive illusions to elucidate the underpinnings of cognition.
Magic shows are a manifestation of accomplished magic performers’ deep
intuition for and understanding of human attention and awareness. By
studying magicians and their techniques, neuroscientists can learn
powerful methods to manipulate attention and awareness in the
laboratory. Such methods could be exploited to directly study the
behavioural and neural basis of consciousness itself, for instance
through the use of brain imaging and other neural recording
techniques.

Magic is one of the oldest and most widespread forms of performance
art [1] (Fig. 1). It is also a discipline with a long legacy of
informal experimentation. This informal research by magicians aims to
determine what conditions allow for the maximum manipulation of human
attention and perception. Much as early filmmakers experimented with
editing techniques to determine which technique would communicate
their intent most effectively, magicians have explored the techniques
that most effectively divert attention or exploit the shortcomings of
human vision and awareness. As such, magic is a rich and largely
untapped source of insight into perception and awareness. Insofar as
the understanding of behaviour and perception goes, there are specific
cases in which the magician’s intuitive knowledge is superior to that
of the neuroscientist. In this Perspective, we underline potential
areas in which neuroscientists stand to reap great benefits from
collaboration with the magic community (Box 1 highlights one such
potential area of collaboration).

Using completely natural means, magicians create effects (magic
tricks) that seem to be outside the laws of nature. One should note
that, unlike so-called psychics, magicians do not claim to possess
supernatural powers. The devices used by magicians can include one or
more of the following: visual illusions (after-images), optical
illusions (‘smoke and mirrors’), cognitive illusions (inattentional
blindness), special effects (explosions, fake gunshots, et cetera),
and secret devices and mechanical artifacts (gimmicks).

Visual illusions — and other sensory illusions — are phenomena in
which the subjective perception of a stimulus does not match the
physical reality of the stimulus. Visual illusions occur because
neural circuits in the brain amplify, suppress, converge and diverge
visual information in a fashion that ultimately leaves the observer
with a subjective perception that is different from the reality. For
example, lateral inhibitory circuits in the early visual system
enhance the contrast of edges and corners so that these visual
features seem to be more salient than they truly are [2, 3, 4, 5, 6].
Unlike visual illusions, optical illusions do not result from brain
processes: they manipulate the physical properties of light, such as
reflection (using mirrors) and refraction (a pencil looks broken when
it is placed upright in a glass of water owing to the different
refraction indices of air and water). Cognitive illusions can be
distinguished from visual illusions in that they are not sensory in
nature: they involve higher-level cognitive functions, such as
attention and causal inference (most coin and card tricks used by
magicians fall into this category).

The application of all these devices by the expert magician gives the
impression of a ‘magical’ event that is impossible in the physical
realm (see Table 1 for a classification of the main types of magic
effects and their underlying methods). This Perspective addresses how
cognitive and visual illusions are applied in magic, and their
underlying neural mechanisms. We also discuss some of the principles
that have been developed by magicians and pickpockets throughout the
centuries to manipulate awareness and attention, as well as their
potential applications to research, especially in the study of the
brain mechanisms that underlie attention and awareness. This
Perspective therefore seeks to inform the cognitive neuroscientist
that the techniques used by magicians can be powerful and robust tools
to take to the laboratory. The study of the artistic intuitions that
magicians have developed about attention and awareness might further
lead to significant new scientific insights into their neural bases.

Visual illusions in magic
Visual illusions are often used by neuroscientists to dissociate the
neural activity that matches the perception of a stimulus from the
neuronal activity that matches the physical reality. Those neurons,
circuits and brain areas with activity that matches the physical
stimulus rather than the subjective perception can be excluded from
the neural correlates of consciousness. Visual illusions are also used
by magicians to fool their audiences, often to enhance cognitive
illusions. Here we discuss a few categories of visual illusions that
have contributed to magic tricks, as well as their neural bases.

Spoon bending. In this illusion the magician bends a spoon, apparently
by using the power of the mind. In one part of the trick, the magician
holds the spoon horizontally and shakes it up and down. This shows
that the neck of the spoon has apparently become flexible [7]. The
apparent rubberiness of the spoon is an example of the Dancing Bar (or
Rubber Tree) illusion [8], in which an oscillating bar (or rubber
tree) seems to bend when it is bounced rapidly. The neural basis of
this illusion lies in the fact that end-stopped neurons (that is,
neurons that respond both to motion and to the terminations of a
stimulus’ edges, such as corners or the ends of lines) in the primary
visual cortex (area V1) and the middle temporal visual area (area MT,
also known as area V5) respond differently from non-end-stopped
neurons to oscillating stimuli [8, 9, 10, 11]. This differential
response results in an apparent spatial mislocalization between the
ends of a stimulus and its centre, making a solid object look like it
flexes in the middle.

The Retention-of-Vision Vanish. Persistence of vision is an effect in
which an image seems to persist for longer than its presentation time
[12, 13, 14]. Thus, an object that has been removed from the visual
field will still seem to be visible for a short period of time. The
Great Tomsoni’s (J.T.) Coloured Dress trick, in which the magician’s
assistant’s white dress instantaneously changes to a red dress,
illustrates an application of this illusion to magic. At first the
colour change seems to be due (trivially) to the onset of red
illumination of the woman. But after the red light is turned off and a
white light is turned on, the woman is revealed to be actually wearing
a red dress. Here is how it works: when the red light shuts off there
is a short period of darkness in which the audience is left with a
brief positive after-image of the red-dressed (actually white-dressed
but red-lit) woman. This short after-image persists for enough time to
allow the white dress to be rapidly removed while the room is still
dark. When the white lights come back, the red dress that the
assistant was always wearing below the white dress is now visible.

This same illusion is the basis for perceptual stability during the
viewing of motion pictures (the image seems to be stable when in fact
it is flickering). On a neural level, both turning on and turning off
a stimulus generate responses in visual neurons that result in the
perceptual visibility of the stimulus [15]. The neural response that
is generated by turning off a stimulus is called the after-discharge,
and it has the perceptual consequence of a positive after-image that
persists for approximately 100 ms after the termination of the
stimulus [16, 17, 18].

Jerry Andrus’s Trizonal Space Warp. In this illusion the audience
stares for several seconds at a spinning disk with three zones of
expanding and contracting motion. They are then asked to look at a
different object on stage that consequently seems to both expand and
contract. Motion after-effects, more commonly known as The Waterfall
Illusion, are the oldest-recorded visual illusions. First reported in
his Parva Naturalia, Aristotle noticed that if one fixates a moving
stream of water and then looks away, the rocks at the side of the
stream will seem to move in the opposite direction to the water. This
effect is caused by neural adaptation — that is, by the decrease in
responsiveness of a neural system to a constant stimulus. In the
Trizonal Space Warp illusion, adaptation to expanding and contracting
motion occurs in three different parts of the visual field.

The above illusions are examples of magic tricks that could have been
used to help elucidate the underpinnings of visual perception. There
might be other fundamental visual processes that could be discovered
by studying magic (Box 1). Further, we propose that there are
cognitive processes that will be better understood as we learn more
from magicians, as discussed in the next section.

Cognitive illusions in magic
Inattentional blindness and change blindness. Attended objects can
seem to be more salient or to have higher contrast than unattended
objects [19, 20, 21, 22]. These perceptual effects have well-
documented neural correlates in the visual system [23]. Magicians use
the general term ‘misdirection’ to refer to the diversion of the
spectator’s attention away from a secret action. Thus, misdirection
can be defined as drawing the audience’s attention away from the
‘method’ (the secret behind the ‘effect’) and towards the effect (what
the spectator perceives) [7, 24]. Misdirection can be applied in an
overt or a covert manner. Here we use the term ‘overt misdirection’ to
indicate cases in which the magician redirects the spectator’s gaze
away from the method. In the more subtle ‘covert misdirection’, the
magician draws the spectator’s attentional spotlight (which can be
thought of as the spectator’s focus of suspicion) away from the method
without redirecting the spectator’s gaze. Thus, in covert misdirection
the spectators can be looking directly at the method behind the trick
and yet be unaware of it because their attention is focused elsewhere.

The concept of covert misdirection is exemplified by the cognitive-
neuroscience paradigms of change blindness and inattentional
blindness. With change blindness, people fail to notice that something
is different from the way it was before. This change can be expected
or unexpected, but the key is that it requires the observer to compare
the post-change state with the pre-change state. Change-blindness
studies have shown that dramatic changes in a visual scene will go
unnoticed if they occur during a transient interruption [25], such as
a blink [26], a saccadic eye movement [27] or a flicker of the scene
[28, 29, 30, 31], even when people are looking right at the changes.
However, observers can also miss large gradual changes in the absence
of interruptions [32]. A dramatic example of change blindness is
illustrated in the Colour-Changing Card Trick video by Richard Wiseman
and colleagues (available online at YouTube.com). In this
demonstration, the viewers fail to notice colour changes that take
place off-camera.

With inattentional blindness, people fail to notice an unexpected
object that is fully visible in the display. Thus, inattentional
blindness differs from change blindness in that no memory comparison
is needed — the missed object is fully visible at a single point in
time. In a classic example of inattentional blindness, Simons and
Chabris [33] asked observers to count how many times the members of a
basketball team passed a ball to one another, while ignoring the
passes made by members of a different team. While they concentrated on
the counting task, most observers failed to notice a person wearing a
gorilla suit walk across the scene (the gorilla even stops briefly at
the centre of the scene and beats its chest!). In this situation no
acute interruption or distraction was necessary, as the assigned task
of counting passes was absorbing. Further, the observers had to keep
their eyes on the scene at all times in order to accurately perform
the task. Memmert showed, using eye-tracking recordings, that many
observers did not notice the gorilla even when they were looking
directly at it [34].

The magic community considers the covert form of misdirection to be
more elegant than the overt form [7]. Few studies have addressed their
relative efficacy, however. Kuhn and Tatler [35] measured the eye
movements of observers during the presentation of a magic trick (a
magician made a cigarette ‘disappear’ by dropping it below the table).
To our knowledge, this is the first study to have correlated the
perception of magic with any physiological measurement. The goal of
the experiment was to analyse the scan paths of subjects to determine
whether observers missed the trick because they did not look at it at
the right time or because they did not attend to it (irrespective of
the position of their gaze). The results showed that the detection (or
not) of the cigarette drop could not be explained at the level of the
retina. That is, detection rates were not significantly influenced by
blinks, saccadic movements or how far the cigarette was from the
centre of vision at the time of the drop. The authors concluded that
the magician primarily manipulates the spectators’ attention rather
than their gaze, using similar principles to those that are used in
inattentional-blindness studies. Thus, to overcome the magician’s
misdirection, spectators should reallocate their attention — rather
than their gaze — to the concealed event (that is, the cigarette drop)
at the critical time [36]. Recent studies have found that the
directions of microsaccades can also be used as an indicator of the
spatial allocation of covert attention [37, 38, 39]. Future research
could aim to measure the microsaccade direction biases of spectators
during successful and unsuccessful magic tricks.

A recent study of the Vanishing-Ball Illusion further supports the
conclusion that the manipulation of gaze position is not critical for
effective covert misdirection. In the Vanishing-Ball Illusion, a ball
thrown by the magician vanishes mid-flight. To achieve this effect,
the magician begins by tossing the ball straight up in the air and
catching it several times without event; then, on the final toss, the
magician only pretends to throw the ball. The ball is in reality
hidden in the magician’s hand, but most spectators perceive it
ascending and then vanishing mid-flight. During the execution of this
trick, the magician’s head and eyes follow the trajectory of an
imaginary ball being thrown upwards. Kuhn and Land [40] found that the
magician’s use of such social cues was critical for making the
spectators’ perceive the illusion (that is, the ball vanishing mid-
flight). However, observers did not direct their gaze to the area in
which they claimed to have seen the ball vanish, suggesting that the
oculomotor system is not fooled by the illusion. Instead, the illusory
effect is presumably caused by covert redirection of the attentional
spotlight to the predicted position of the ball. This result is
consistent with previous studies that suggested that there are
separate mechanisms for perception and visuomotor control [41, 42, 43,
44, 45, 46, 47, 48]. For instance, the eye movements of blindsight
patients are biased towards stimuli that the patients do not
consciously perceive [49, 50, 51]. Kuhn and Land [40] further proposed
that in the Vanishing-Ball Illusion the covert redirection of the
attentional spotlight to the predicted position of the ball might be
related to “representational momentum” (Ref. 52). That is, that the
final position of a moving object that suddenly disappears is
perceived further along the path of motion than its actual final
position. The neural correlates of representational momentum might be
located in the posterior parietal cortex in the primate [53].
Observers of the Vanishing-Ball Illusion might also be tricked by the
strong implied motion that is suggested by the magician’s moves.
Recent studies have focused on the neuronal mechanisms that underlie
the perception of implied motion (some examples of implied motion are
the speed lines that are used by cartoonists, and still photographs of
people running or dancing). Neurons that respond to implied motion are
found in extrastriate visual areas of the dorsal stream, and they are
thought to be also sensitive to real motion [54, 55]. Thus, implied
motion might activate similar circuits to those that are active during
the perception of real motion, and this might result in perceptual
illusions. Another example of this might be when one pretends to throw
a stick for a dog during a game of fetch.

How do magicians misdirect the audience’s attentional spotlight?
Magicians can effectively control an object’s salience by manipulating
the audience’s bottom-up and/or top-down attentional control
mechanisms. Objects that are new, unusual, of high contrast or moving
are salient, and the audience’s attention is more strongly drawn
towards them. such object properties induce bottom-up control of
attention (and are used to accomplish ‘passive misdirection’ in magic
theory [7, 56] or ‘exogenous attentional capture’ in psychology)
because the attention is driven by increased activity in the ascending
sensory system. One way in which a magician might control bottom-up
attention is by suddenly producing a flying dove. The spectators’ gaze
and attention will focus on the dove’s flight, and this will give the
magician a few unattended moments in which he or she can conduct a
secret manoeuvre.

Another facet of bottom-up attention that magicians exploit is the
fact that if more than one movement is visible, spectators will tend
to follow the larger (that is, the more salient) motion [7]. Hence the
magician’s axiom, ‘A big move covers a small move.’ A neural process
that might underlie this axiom is the low-level mechanism of contrast-
gain control (or contrast-gain adaptation) [57]. In contrast-gain
control, the perceived contrast of a stimulus is affected by the
contrast of surrounding stimuli (whereas in contrast-gain adaptation,
the perceived contrast of a stimulus is affected by that of a
preceding stimulus) [58]. A large or fast-moving stimulus might
therefore decrease the perceived salience of a small or more slowly
moving stimulus that is presented either simultaneously (in contrast-
gain control) or subsequently (in contrast-gain adaptation). Novel
stimuli are known to produce stronger neural responses in the
inferotemporal cortex (area IT), the hippocampus, the prefrontal
cortex and the lateral intraparietal area [59, 60, 61, 62, 63]; these
effects are attributed to bottom-up attentional processes.

The salience of an object can also be increased by actively directing
attention to it. For example, a magician might ask a subject to
perform a task that involves one specific object, so that any changes
that are occurring in a second object are missed. Such techniques are
considered to induce top-down attentional control (and are used by
magicians to accomplish ‘active misdirection’ (Refs 7, 56) or by
psychologists to accomplish ‘endogenous attentional capture’) because
they modulate (increase or decrease) neural activity in low-level
brain areas through feedback pathways from high-level brain areas that
are involved in cognitive functions [64]. One example of top-down
attentional modulation is provided by recent work by Chen and
colleagues [65], which shows that neural responses in the primary
visual cortex, an early visual-processing area, are enhanced as a
function of task difficulty during attentional tasks. Another example
of top-down attentional control is when a magician asks the audience
to watch carefully an object that is being manipulated in one hand,
while at the same time conducting a secret action with the other hand.

The principles that underlie attentional capture and contrast-gain
control and adaptation also apply to other sensory systems, for
example the somatosensory system. Pickpockets use techniques similar
to those that are used by magicians (for instance, sleight-of-hand
manoeuvres) to manipulate the awareness and attention of their marks.
One way in which pickpockets manipulate the somatosensory system by
applying the axiom ‘A big move covers a small move’ is as follows. To
steal a watch directly from the wrist of a mark, the pickpocket might
first squeeze the wrist while the watch is still on [66] (invoking
contrast-gain adaptation). This has two effects. First, it makes a
high-contrast somatosensory impression that adapts the touch receptors
in the skin, making them less sensitive to the subsequent light
touches that are required to unbuckle and remove the watch. Second,
the high-contrast impression leaves behind a somatosensory after-
image, giving rise to the illusion that the watch is still on after it
has been removed.

Another way in which magicians can alter an object’s salience is to
split the audience’s attention by introducing several concurrent
actions [24]. If two actions start almost simultaneously, the one that
begins first will usually attract more attention [7, 67]. Social cues,
such as the magician’s gaze (for instance, in the Vanishing-Ball
Illusion), their voice and verbal communication and their body
language (pointing, tension/relaxation), also play an important part
in manipulating the spectator’s attentional spotlight [7].

Misdirection occurs not only in space (what the audience looks at) but
also in time (when the audience looks). Thus, magicians strive to
redirect the audience’s attention away from the moment of the method
and towards the moment of ‘magic’. Indeed, in many magic tricks the
secret action occurs when the spectators think that the trick has not
yet begun, or when they think that the trick is over. Many magicians
use comedy and laughter as a way to reduce focused attention at
critical points in time. The magicians’ term ‘time misdirection’
refers to the deliberate separation of the moment of the method from
the moment of the effect. Usually a delay is introduced between method
(that is, cause) and effect, preventing the spectator from causally
linking the two [7].

Memory illusions and illusory correlations. Magic works in adverse
circumstances: an important part of the entertainment is that
spectators are naturally suspicious and will try to discover the
method behind the trick. Thus, observers of a magic trick will often
try to reconstruct events to understand what happened. However, a
successful magician will either have made it impossible to discover
the method, or will seem to have ruled out all possible methods
(including the actual method) until magic is the only apparent
explanation [7, 68] (see Supplementary information S1 (movie)). The
magician can also influence the spectators’ recall of the performance
by using misdirection: events that draw the spectators’ attention will
be better remembered than less salient events [7, 24, 69]. An
apparently natural or spontaneous action, such as scratching one’s
head, will not be memorable (although it might be critical to the
execution of the trick). Unspoken assumptions and implied information
are also important to both the perception of the magic trick and its
subsequent reconstruction [7]. J.R. has observed that spectators are
more easily lulled into eagerly accepting suggestions and unspoken
information than into accepting direct assertions [70] (see
Supplementary information S2 (movie)). Thus, in the process of
reconstruction, implication can be remembered as direct proof. The
magician can further influence future recollection by describing past
events in a manner that will bias the reconstruction process [7]. This
is known in cognitive science as the ‘misinformation effect’ — that
is, the tendency for misleading information presented after the event
to reduce one’s memory accuracy for the original event. This effect
can even lead to the creation of a ‘false memory’ for events that
never took place [69]. The famous Indian Rope Trick legend might have
partially resulted from the misinformation effect. In the Indian Rope
Trick, a boy climbs a magically suspended rope and disappears at the
top. The magician follows the boy up the rope into the invisible area
at the top and cuts him into pieces (evidenced by the bloody body
parts falling from the invisible area down to the ground). The
magician then descends the rope and magically reintegrates the boy
with no harm done. In fact, the Indian Rope Trick has never been
performed, despite numerous witness accounts [71, 72, 73].

Although the study of false memory and misinformation effects has
become a mainstream topic in cognitive science over the past few
decades, it is possible that the field would have advanced faster if
scientists had looked at the magicians’ intuition of human memory
earlier. Even today, despite the substantial progress that scientists
have already made in this area, the misinformation effect as used by
magicians could be robustly reproduced in the laboratory to study the
neural underpinnings of memory mechanisms and, in particular, false-
memory mechanisms.

Magicians can also make their audiences incorrectly link cause and
effect. We all infer cause and effect in everyday life. When A
precedes B, we often conclude that A causes B. The skilled magician
takes advantage of this inference by making sure that event A (for
example, pouring water on a ball) always precedes event B (in this
case, the ball disappearing). However, A does not actually cause B:
the magician only makes it seem so [74, 75]. This type of illusion —
seeing a correlation that is not there — is termed an ‘illusory
correlation’. Illusory correlations can arise from unequal weighting
of information, from the participants’ expectancies (such as prior
beliefs or stereotypical knowledge) and/or from selective attention
and encoding. In this third possibility, illusory correlations arise
when some events capture more attention or are more likely to be
encoded in memory and remembered than other, less salient, events
[76]. Thus, the magician can effectively use misdirection techniques
to draw illusory correlations between two unrelated events. Just as
visual scientists use visual illusions to identify the neural
mechanisms of perception, neuroscientists could use illusory
correlations to identify the neural mechanisms that underlie the
cognitive computations of cause and effect. In a recent study by
Parris and colleagues [77], participants underwent functional MRI
(fMRI) while watching films of magic tricks that involved apparent
cause–effect violations. The brain activation that was induced by the
watching of these films was compared with the activation that occurred
in a control condition in which participants watched video clips of
events that did not involve apparent causal violations. The results
showed greater activation in inferior medial frontal areas during the
viewing of magic tricks than during the viewing of the control videos.

The illusion of trust. Pickpockets rely heavily on social
misdirection. Gaze contact, body contact [7] and invasion of the
mark’s personal space [24] are effective misdirection techniques (see
Supplementary information S3 (movie)). Further, magicians and
professional pickpockets use established techniques of persuasion to
manipulate the trust of their audiences/marks. Some of these
principles are also used by confidence artists in various scams and
frauds. Brain-imaging studies of subjects playing online trust-
building games show that activation in the paracingulate cortex is
critical to building a trusting relationship. This activation seems to
be related to inferring the partner’s intentions so as to predict
their behaviour [78]. Once trust was established, activity in the
ventral tegmental area, which is linked to the evaluation of expected
and realized reward, was correlated with the maintenance of
‘conditional trust’ (Refs 79, 80). ‘Unconditional trust’ was
correlated with activity in the septal area, which is linked to social
attachment [81, 82, 83]. Future research will determine the role of
conditional versus unconditional trust in confidence fraud schemes.
Neuroscientists can take advantage of the persuasion techniques that
are used by magicians and pickpockets to identify the neural circuits
that underlie feelings of trust and mistrust.

Magic principles
Various principles of stage magic aim to manipulate attention and
awareness. These principles have been identified by magicians and have
been refined over the centuries to great effect. The time is now ripe
to take them into the laboratory and use them to guide new and more
powerful experimental testing and careful quantification. This would
elucidate the mechanistic pathways in the brain that allow magic
tricks to work and would also generate novel and robust laboratory
techniques for studying attention and awareness. A number of magic
principles were discussed during the Magic of Consciousness symposium
during the 11th Annual Meeting of the Association for the Scientific
Study of Consciousness (Box 2); they are reviewed below.

An action is a motion that has a purpose. During the execution of a
magic trick, it is necessary to use unnatural actions. Thus, the
magician needs to reduce the audience’s suspicion about such actions.
One way to do this is to justify unnatural actions so that they seem
natural [7]. Teller [74] refers to this principle with the aphorism,
“An action is a motion with a purpose.”

In everyday life we categorize the motions made by others by
interpreting their intentions. If we see somebody pushing their
glasses higher on the bridge of their nose, we assume that the glasses
needed adjustment, and no further interpretation is made. A good
magician makes use of such innocent actions to hide ulterior motions
in a process called ‘informing the motion’. For instance, magicians
with a mute on-stage persona, like Teller, can take advantage of the
glasses-pushing action to discreetly hide a small object in their
mouth (being mute, they have no lines to garble). A less clever
magician might do the same motion (moving the hand over the mouth)
without informing it with a purpose (adjusting one’s glasses). Such a
motion will be subject to suspicion and scrutiny. In that case, even
if the spectators have not seen exactly how the trick works, they
might feel that something is amiss. The skilled magician informs every
motion with a convincing intention (see Supplementary information S4
(movie)).

Apparent repetition, priming and ‘closing all the doors’. In everyday
life, by repeatedly observing a process we are able to deduce its
workings. Priming is a type of repetition effect in which the
presentation of a stimulus that is similar to a target makes
subsequent presentations of the target perceptually more salient [84].
Priming is used experimentally, and by the magician, to affect the
subject’s sensitivity to a later presentation of a particular
stimulus. Moreover, repetition can be used to induce sensory
illusions, as in the Vanishing-Ball Illusion described earlier.
Spectators are more likely to perceive the illusory ball vanishing in
mid-flight if an actual ball has been tossed several times first, so
that they are primed to know what an actual tossed ball looks like
[85]. Thus, priming and repetition can be helpful in inducing some
illusory effects. Magicians also use repetition to hide the method
behind the trick: when observers see an effect repeated, they
naturally assume that each repetition is done by the same method. But
the magician can covertly change the method that underlies each
apparent repetition of the effect. Indeed, when a good magician
repeats an effect, the method is varied in imperceptible ways and in
an unpredictable rhythm. That way, each time observers suspect one
method is being used, they find their suspicion disproved by the
subsequent repetition [74] (see Supplementary information S4 (movie)
and S5 (movie)). The magician might even deliberately raise suspicion
about a possible method and then show that suspicion to be unfounded
[7]. In this way, the magician closes the door on every possible
explanation for the trick [68, 73, 86], until the only remaining
possibility is ‘magic’. This tactic is referred to as Tamariz’s Theory
of False Solutions (see Supplementary information S1 (movie)). The use
of apparent repetition has the added benefit of confusing the
spectators’ reconstruction process. Further, the specific weaknesses
of each method will cancel each other out [7].

Never do the same trick twice. The corollary of the closing all the
doors principle is that if the magician performs the same trick twice
for the same audience, there is an increased chance that the audience
will identify the method that is being used and figure out the trick
[87] (see Supplementary information S5 (movie)). In several studies by
Kuhn and colleagues, most observers caught the method when the trick
was shown a second time [35, 36, 40, 88]. Similarly, most
inattentional-blindness demonstrations are a one-time-only kind of
effect. Observers are much more likely to see the gorilla the second
time they watch the basketball video described earlier [33].

Conclusions
Magic combines multiple principles of attention, awareness, trust and
perception to both overtly and covertly misdirect the audience.
Whether they are used for performance art or as a means to illicitly
separate victims from their money and valuables, the accomplished
performer uses robust and intuitive manipulative devices that are of
great interest to neuroscientists pursuing the neural underpinnings of
cognition, memory, sensation, social attachment, causal inference and
awareness. Among these devices, we would like to emphasize the use of
misdirection as a means to generate cognitive illusions such as
inattentional blindness, change blindness, memory illusions and
illusory correlations. Magicians are able to obtain these effects
under conditions of high scrutiny show after show. Some of the crucial
principles one needs to take into account when designing a robust
trick are the understanding that every motion should seem to have a
purpose, that the magician should not perform the same exact trick
twice, and that the most successful tricks use apparent repetition to
close all the doors on every possible explanation of the trick except
for ‘magic’ itself.

Cognitive neuroscience endeavors to reverse-engineer the entire
spectrum of cognition by determining the neural correlates of the
various cognitive processes that make up our lives. Magic techniques
can provide methods and insights that could help to explain what
happens in the brain when a spectator thinks he knows what happened on
stage [73]. The possibilities of using magic as a source of cognitive
illusions to help isolate the neural circuits that underlie specific
cognitive functions are endless. For example, the magicians authoring
this article emphasize the use of humour as a critical aid to the
successful implementation of many tricks. Their intuition is that when
the audience is laughing it is as if time stops and the attentional
spotlight is put on hold. That is, the magician can do virtually
anything when the audience is laughing, and nobody will notice.
Recording neural activity (by fMRI, electroencephalogram,
magnetoencephalography, et cetera) in someone who is watching magic
tricks that are accompanied by humour might help researchers determine
the potential interaction between the allocation of attention and the
sensation of mirth. Further possibilities range far beyond the uses of
magic that have already been tried experimentally in cognitive
science, such as the employment of magic palming techniques to direct
subjects into confabulating their reasons for choices that they did
not actually make [89, 90] (Box 3). Magical cognitive illusions are
furthermore an outstanding method by which to dissociate the perceived
contents of awareness from the actual physical events. That is, one
primary purpose of magic is to segregate those events that the
magician does not want the observers to be aware of from those that
the magician does want them to be aware of. We propose therefore that
magical techniques that manipulate attention and awareness can be
exploited to directly study the behavioural and neural basis of
consciousness itself, for instance through the use of brain imaging
and other neural recording techniques. If neuroscience researchers
succeed in adopting magical methods with the same alacrity as
professional magicians, they too should be able to control sensory
awareness precisely and in real-time, while at the same time assessing
the neural activation that is associated with it.