NOTICE: Posting schedule is irregular. I hope to get back to a regular schedule as the day-job allows.

Friday, June 29, 2012

The GUIDE: Magic and the Brain - Part 3 - Fooling Ourselves [Full link to blog for email clients.]

After having examined (optical) illusion and misdirection, we come to the final part of how the magician, illusionist or con artist works their "magic" - convincing us to convince ourselves that the magic is real.  For the most part, "fooling ourselves" is part of leading the audience with misdirection, until they come to a conclusion that supports the trick.

In magician terms, this is know as "The Force" (or in confidence games "The Hook"), and is best exemplified by fortune telling and horoscope.  The fortune teller's art is to provide a vague description and fortune that can fit just about any situation.  As long as the participant wants to believe, they'll find a situation that makes the fortune true - for example, "You will meet a tall, dark stranger" may be successfully fulfilled by meeting your child's handsome teacher, yet in the absence of such obvious confirmation, just about any encounter will do - "Well, that guy that crossed my path at the checkout was... maybe... kinda tall, had... oh, a bit of a tan... I suppose he could be called handsome... well, he wasn't ugly..."  [This, by the way, also partially explains "coincidence" and "deja vu" in which what we think we experience, is partially filled in from memory and association!]

One of the most successful - although least obvious to a novice - tricks in a magician's repertoire is the Force.  Through the Force, an audience member seemingly makes random or free choices, but the magician subtly guides that choice in the direction necessary for the trick.  Not to give away any secrets, but an obvious application is used in confidence games where the operator questions a correct choice with "Are you sure?  Are you really sure?" in order to get the "mark" to change their selection from correct to erroneous.  In card magic, a Force is used to guide the audience member's choices to keep narrowing down the possible combinations - for example, cards are laid out in rows and columns, the participant makes a choice of row, the cards are "shuffled" and replaced, then the participant makes a choice of column.  A skillful Force can that only one card can fulfill all of the possible choices. 

A combination of illusion, misdirection and Force is also something that I have successfully used when performing card magic - the first several tricks are performed according to the rules that I establish, with my card decks, and a bit of setup.  About the time the audience begins to suspect that my card decks are rigged, I challenge the audience to provide a deck of their own choosing (this worked especially well with Boy Scouts at summer camp - someone always had their own deck of cards), I then smoothly shift to tricks that work well with any deck, and leave the audience scratching their heads - all with a subtle manipulation of misdirection and Force.

The other great application of "fooling ourselves" that magic tricks employ is violation of accepted norms - the solid steel Chinese Linking Rings cannot possibly pass through each other, therefore the trick must utilize some quirk of either "magic" or laws of physics which have not yet been discovered.  The brain is a powerful organ for processing information and reconstructing information from only partial clues - a bit of song, part of a picture, a smell, a touch - all can evoke powerful, clear memory.  The association cortex of the brain stores and recalls information using only partial matches, and relies on memory to fill in the rest of the information.  In the same manner that dreams result from partial scenes and events, and seem to have complete memory and history, the brain uses our memory to fill in the gaps and blanks similar to what happens in the figure at above - the triangle seems obvious, but it does not really exist.  However, since our visual cortex is tuned more for lines than for curves, the triangle made from straight (albeit broken) lines is more evident than the circles.

The practice of "filling in the gaps" thus explains how the brain can be "fooled" by the illusionist or magician in much the same way as it is fooled by an optical illusion.  This also explains how sleight of hand and misdirection aid the magician in their art - we see what we expect to see, and what we do not see (but expect) we fill in from memory.  So in reality the "magic" is in our brain, and is a part of how we normally interact with the world - which raises a further question of whether "perception" is in fact "reality?"  But that's a question and an issue for later... much later.

Until next time, accept no substitutes and ask for the genuine Lab Rats -  at The Lab Rats' Guide to the Brain!

Wednesday, June 27, 2012

The GUIDE: Magic and the Brain - Part 2 - Misdirection [Full link to blog for email clients.]

This is part 2 of the "Neuroscience of Magic/Illusion" series, and will deal with the second great trick of magicians and illusionists: misdirection.  Misdirection is common to magic acts, illusions, con games and games of chance.  The most common misdirection is that of the operator/illusionist/magician, who keeps up a running patter so that your attention is distracted from what they are really doing, which isn't really magic at all.

Chinese Linking Rings - Magic Masters.*
One of my favorite tricks from my time as an amateur magician is the "Chinese Linking Rings" in which the magician can seemingly pass one ring through another, causing them to link up and separate right in front of your eyes.  One of the best ways that an magician can excite - and at the same time, misdirect - an audience is to give an audience member two rings.  If the rings are linked, the person is challenged to separate them, if separate, that person is challenged to cause the rings to link together.  Of course, the rings are solid and there is no defying the laws of physics and allow one solid ring to pass through another.  However, the act of diverting the audience's attention from the stage magician to the assistant allows the magician to work their "magic" with less scrutiny from the audience.  From my own experience, the audience is much more interested in the facial expressions and frustration of the audience than in noticing that the magician somehow never actually shows how the trick is done

 As discussed in the previous blog, magic, illusion and misdirection all play into how the brain represents and processes information.  If we can make the visual cortex think that something there, when it isn't, we are half way to performing a "magic trick."  Likewise, misdirection relies on the fact that the brain processes familiar stimuli in a manner different than novel stimuli.  Allow a rat to explore a chamber that it has experienced before, and it will usually find a convenient spot and sit down.  Put it in an unfamiliar environment or add a novel feature, and the rat will spend most of its time exploring the novelty.

A similar example of novel information processing can be detected in EEG.  Most EEG analysis consists of quantifying rhythms, oscillations, frequencies and spectra, since the EEG is constantly changing.  However, if a tone, flash of light or photograph is presented very briefly on a computer screen, scientists can synchronize a point in the EEG with the stimulus and look for features that are time-locked to that event.  We call this an "event-related potential," or ERP.  ERPs are pretty small compared to most EEG activity, so it is often necessary to repeat the stimulus a few times to average out the random fluctuations of the EEG.  It's been known for more than 50 years that a particular positive deflection in the ERP occurring at around 300 milliseconds after the stimulus (thus known as P300 or P3) is reduced in amplitude if the stimulus is familiar, and increased if the stimulus is unfamiliar.  Thus we see that the brain "expects" familiar information, and pays more attention to unique information.

So let's look a bit closer at the idea of "expectancy." The brain has several areas that are involved in making predictions about your environment.  The first area involved is cingulate cortex, located on the upper, inner surface of the two halves (hemispheres) of the cerebral cortex.  The role of cingulate is typically to "guess" or make predictions of what comes next - whether reading, moving, tracking, listening - whatever the stimulus, cingulate is typically involved in making predictions.  Next is the amygdala and limbic system located inside the temporal lobe.  Amygdala, hippocampus, and the connected structures compare predicted (or expected) events with what actually happened.  The role of hippocampus is to simultaneously provide memory of prior events, and also to store the new information regarding success of prior predictions.  There are other brain ares involved, such as caudate/striatum, which provides signals indicating value or reward, and this can be very important in gambling or confidence games, but the primary brain ares involved in misdirection are these which process expectancy.

The true "magic" of an illusion or magic trick is to show the subject what they expect to see, and diverting their attention from anything that might reveal any other action or occurrence.  Thus the magician's patter directs our attention to what they wish to show us, and by making that familiar they reduce our attention that would otherwise notice the unexpected events (i.e. linking the Chinese Rings) until after the event has already occurred.  Gambling and confidence games invoke an additional aspect of expectancy, by assigning an arbitrarily high "value" or motivation to the expected outcome.  The "mark" who expects to win a lot of money is influenced by striatal signals which reinforce the potential payoff of the prediction.  An fault of our brain's expectancy circuits is a particular blindness to probability - flipping a coin 100 times means nothing to the probability of heads or tails on a single flip.  However, the "Gambler's Fallacy" which represents the brain's expectancy anticipates that the more consecutive flips resulting in "heads" absolutely must mean that the next flip has a 10-to-1 chance of being "tails" when in fact the real chance is still 1-to-1.

We'll wrap up this section on Magic and the Brain with a final post on "Fooling Ourselves."  In the next blog.  Until then, take care of your brain, and tip the magician on your way to the buffet!


*For anyone interested in learning about and starting an amateur magic career, check local directory listings for a magic club, or check out "Magic Masters" online ( or at one of their retail storefronts.

Monday, June 25, 2012

The GUIDE: Magic and the Brain - Part 1 - Illusion [Full link to blog for email clients.]

At the last "Neuroscience and a Movie," the discussion turned to future programs, and someone mentioned "Neuroscience and Magic."  Several of my colleagues are amateur magicians, and one clinician that I co-taught with last year is actually quite a successful magician.  I have dabbled in the arcane art myself, and while many would term me a "mechanic" (I prefer tricks that rely on a device or physical prop) I do know and understand how a lot of slight-of-hand and illusion work.

Rather than speak directly about magic tricks, I want to devote a few blogs to the two most common features of magic - illusion and misdirection - and how they each play on features of our brain and nervous system. Today I will discuss illusions (and in particular, optical illusions) and the next blog will cover misdirection. [Today's blog is an expansion on a mailbag question from last year.]

Illusions, and in particular optical illusions, are usually caused by one of two processes.  The first is to simply confuse the eyes by playing tricks with what we have come to learn is "normal."  For example, in typical 3-D vision, left is closer to the left eye, right is closer to the right eye, close is big, and far away is small.  A number of the Escher optical illusions take advantage of violating visual rules and conventions.  We can easily follow the lines of the Penrose staircase but the artist violates the rules of perspective by using the same technique of perspective for up/down and near/far.  Likewise the Penrose triangle on the same page violates logic, because instead of consistently shading one surface, Lionel and Roger introduce discontinuities that cannot co-exist, thus creating the illusion.

The second method is to tease the eyes by taking advantage of how the retinal ganglion neurons, lateral geniculate nucleus and V1 visual cortex process vision.  Figure 1 show the distinction between the real world, and the V1 representation.  Because the RGN and LGN are tuned to detect edges, the "fill" in the middle of the text is not represented in V1.  That information is not lost, however, color and fill information is transmitted to V2 and V3 second visual areas, which detect shadings, colorations and start to interpret perspective and parallax. 

Figure 1
When viewed simply as independent lines, the elements of the Vase optical illusion look distinctly like two faces, or a vase (Top of Figure 2).  V1 has no problem distinctly identifying either feature when presented independently.  However, once the lines are put together and shaded, there is a conflict between what V2&V3 say is present (the vase) and what V1 detects (the faces, due to the distinctiveness of the edges of the dark shading).  Thus this second type of optical illusion, like the Necker Cubes (do an internet search, there are way more examples than I can show here).   Rely on the brain being presented with two different interpretations – simply because the visual system processes lines and shading separately.
Figure 2
What about illusions that appear to move, such as in Figure 3?  The "bicycle wheel" illusion at left takes advantage of the fact that the brain and visual system detect motion when successive "line" responsive neurons in the visual cortex are activated.  If one set of neurons, representing a straight line on the left visual field are activated, then a set toward the middle of the visual field, and so on, crossing our vision, the brain interprets the successive activation as indicating motion.  The "ocular dominance" columns of V1 visual cortex consist of groups of neurons that respond to lines of different angles and positions in our visual field.  If the neurons in a given row (i.e. different angles) are activated, we perceive that as rotation of the object - however, in the illusion to the left in Figure 3, we are simultaneously activating the different angle-sensitive neurons, and as our focus shifts to different portions of the figure, the brain interprets the shift as rotational motion of the object.  The parallel lines illusions in Figure 3 again rely on the representation of lines in V1.  Our perception is biased to look for straight lines, and curves are really only detected by difference between the curved and straight line.  Thus the vertical pair of lines at the center of each cluster of four lines is identical, and perfectly parallel, but the differing angles and spacing produced by the curved lines tends to fool the brain into think that all of the lines are curved.
Figure 3
One of the more interesting "psychometric" aspects of neuroscience is that it is possible to detect when a person's perception of an optical illusion shifts.  Most of the motor control are of the brain is in the frontal cortex, just forward of the border with the parietal cortex, and control of the eye muscles is now exception.  It may seem that occulomotor control (Cranial Nerve III, the third "O" in yesterday's mnemonic) is a simple matter of pointing the eyes in the right direction.  However, the process is *much* more complicated, requiring actual target acquisition and identification – in other words, the full suite of visual cortical processing.   Distance and horizontal tracking requires that the eyes move at slightly different angles; focus and lighting changes requires pupil diameter control.  The "Frontal Eye Fields" along (with the Edinger-Westphal nucleus of deep thalamus and the superior colliculi and locus coeruleus of the brainstem) is involved in the complex process of integrating actual vision with the process of adapting the eye to light and motion.   When visual information changes it can be revealed as changes in scanning the environment or reacting to light. 

In fact, it has been demonstrated that if a person is shown a Necker Cube-style optical illusion, and told to press a button whenever their perception of the cubes changes from the "top" to the "bottom" view, the pupils dilate briefly.  This is just one small way in which the operation of the brain (or – dare I say it – The Mind) can be monitored by a physiological reaction. 
Figure 4

One last type of optical illusion that depends on even more complex association of vision and language, and it gets to the types of illusions that magicians employ in their acts:  The "Stroop Interference" effect shown in Figure 4 violates the consistency of line vs. shading, but also introduces understanding of the word meaning.  This process depends heavily on the multi-sensory association cortices at the intersection of Occipital, Temporal and Parietal lobes – with the added involvement of decision making by the Frontal Lobe.  This is one of those phenomena that belies the idea that we only tap a tenth of our brain.

So, how does a magician fool our eyes and our brains?  Rather simple, really, the illusionist knows that the brain is looking for fairly simple features, and that combining vision with other information (such as sound, language, or memory) can cause conflicts between what we think we see, and what is really there.  We perceive closed lines and circles when they are not, or openings where there are none.  We confuse language with color with angle and notice the familiar among  the unusual.  A large percentage of the magician's craft is also misdirection, and we will discuss that in the next blog.

Until then, don't confuse your brain, take care of it, and watch out for illusions!