Mind tricks: Six ways to explore your brain
19 September 2007
NewScientist.com news service
Graham Lawton

http://www.newscientist.com/channel/being-human/mg19526221.300-mind-tricks-six-ways...

1 Seeing isn't believing
TAKE a moment to observe the world around you. Scan the horizon with your eyes.
Tilt your head back and listen. You're probably getting the impression that your
senses are doing a fine job of capturing everything that is going on. Yet that
is all it is: an impression.

Despite the fact that your visual system seems to provide you with a continuous
widescreen movie, most of the time it is only gathering information from a tiny
patch of the visual field. The rest of the time it isn't even doing that.
Somehow from this sporadic input it conjures up a seamless visual experience.

What is going on? Bang in the middle of your retina is a small patch of densely
crowded photoreceptors called the fovea. This is the retina's sweet spot, the
only part of the eye capable of seeing with the rich detail and full colour we
take for granted. This tiny spot - which covers an area of our visual field no
bigger than the moon in the sky - feeds your visual system almost all of its raw
information.

To build up a big picture, your eyes constantly dart about, fixating for a
fraction of a second and then moving on. These jerky movements between fixations
are called saccades, and we make about three per second, each lasting between 20
and 200 microseconds.

The curious thing about saccades is that while they are happening we are
effectively blind. The brain doesn't bother to process information picked up
during a saccade because the eyes move too rapidly to capture anything useful.
All in all, your visual system works like a man blundering around in the dark
waving around a flickering torch with a very narrow beam.

Despite the fact that you don't normally notice saccades, you can catch them in
action. Look at your eyes close-up in the mirror and flick your focus back and
forth from one pupil to another. However hard you try you cannot see your eyes
move - even though somebody watching you can. That's because the motion is a
saccade, and your brain isn't paying attention. Now pick two spots in the
corners of your visual field and flick your gaze from one to the other and back
again. If you're lucky you'll notice, just barely, a brief flash of darkness.
This is your visual cortex clocking off.

So how does your brain weave such fragmentary information into a seamless movie?
This remains something of a mystery. The best explanation, according to Andrew
Hollingworth of the University of Iowa in Iowa City, is that your short-term and
long-term visual memories retain information from previous fixations and
integrate them into a here-and-now visual experience (Visual Cognition, vol 14,
p 781).

There is also some guesswork going on. You can get a feel for this from the
frozen-time illusion - the sensation that you sometimes get when you look at a
clock and the second hand appears to freeze momentarily before tick-tocking back
into action.

This happens because of saccades. To compensate for the temporary shut-down of
vision, your brain makes a guess at what it would have seen, but it does so
retrospectively. So the 100 or so milliseconds of blindness gets back-filled
with the image that appears after the saccade is over. If your eyes happen to
alight on the clock just after the second hand has moved, your brain assumes
that the hand was in that location for the duration of the saccade too. The
"second" then lasts about 10 per cent longer than normal, which is enough for
you to notice.

The weirdness isn't confined to vision. Your auditory system is also full of
gaps and glitches that the brain cleans up so we can make sense of the world.
This is especially true of speech.

In everyday life we encounter lots of situations that obscure or distort
people's voices, yet most of the time we understand effortlessly. This is
because our brain pastes in the missing sounds, a phenomenon called phonemic
restoration. It is so effective that it is sometimes hard to tell that the
missing sounds are not there.

A good demonstration of this effect was published last year by Makio Kashino of
NTT Communication Science Laboratories in Atsugi, Japan. He recorded a voice
saying "Do you understand what I'm trying to say?" then removed short chunks and
replaced them with silence. This made the sentence virtually unintelligible. But
when he filled the gaps with loud white noise, the sentence miraculously becomes
understandable (Acoustic Science and Technology, vol 27, p 318).

"The sounds we hear are not copies of physical sounds," Kashino says. "The brain
fills in the gaps, based on the information in the remaining speech signal." The
effect is so powerful that you can even record a sentence, chop it into
50-millisecond slices, reverse every single slice and play it back - and it is
perfectly intelligible. You can listen to Kashino's sound files at
http://asj.gr.jp/2006/data/kashi/index.html.

“The sounds we hear are not copies of physical sounds”Another demonstration of
the brain's ability to extract meaning from distorted signals is a form of
synthesised speech called sine-wave speech. When you first hear a sentence in
sine-wave speech it sounds alien and unintelligible, somewhat reminiscent of
whistling or birdsong. But if you listen to the same sentence in normal speech
and then return to the sine-wave version, it suddenly snaps into auditory focus.
Try as you might, you cannot "unhear" the words that you didn't even realise
were words the first time you heard them (listen to demos at
www.mrc-cbu.cam.ac.uk/~mattd/sine-wave-speech and
www.lifesci.sussex.ac.uk/home/Chris_Darwin/SWS).

According to Matt Davis of the UK Medical Research Council's Cognition and Brain
Sciences Unit in Cambridge, this happens because the brain has circuits that
respond to speech, but doesn't switch them on unless it detects spoken language
(Hearing Research, vol 229, p 132). Sine-wave speech isn't speech-like enough to
trigger the circuits, but once you know it is speech they spring into action.
"It's an example of top-down influence," says Davis. "What you know about what
you're hearing changes the way you hear it."

Given the tricks that your visual and auditory systems play, it probably comes
as no surprise that when they get together, fights can break out. A good
demonstration of this is the McGurk effect, in which listening to a series of
identical syllables such as "ba ba ba ba" while watching somebody mouth "ba da
la va" makes you hear "ba da la va". Try it for yourself at
www.faculty.ucr.edu/~rosenblu/lab-index.html.

Until recently, psychologists believed that the visual system always trumps the
other senses, but in 2000 a team of psychologists at the California Institute of
Technology in Pasadena proved that this isn't the case. They showed volunteers a
single flash on a computer screen. If they accompanied the flash with two very
short beeps, the volunteers saw two flashes - in other words, this time the
auditory system wins (Nature, vol 408, p 788). See the illusion at
www.cns.atr.jp/~kmtn/soundInducedIllusoryFlash2/index.html.

2 This is not my nose
YOU may know the crossed-hands illusion. Hold your arms out in front of you and
cross them over, rotate your hands so your palms face each other, then mesh your
fingers together. Now slowly rotate your hands up between your arms so you're
staring at your knuckles. Ask someone to point to one of your index fingers,
then attempt to move it. Did you move the wrong one?

If so, you've just experienced a minor failure of your body schema - your mental
representation of the location, position and boundaries of your body. Your brain
builds this up by drawing on data from vision, touch and a body-wide network of
proprioceptive sensors that monitor position. Your body schema is a critical
part of self-awareness, which is why it feels so odd when it goes wrong.

In the crossed-hands illusion, the schema fails because of a confusing visual
input. You don't normally see your hands in this convoluted position; the finger
you move is the one that is pointing in the direction that the correct one would
be pointing if you had simply clasped your hands as if in prayer.

An even odder way of disturbing your body schema is an illusion that taps
straight into your sense of body ownership. Known as the rubber-hand illusion,
it fools you into thinking a rubber hand - or even a piece of wood, or a table -
is part of your body.

To experience the illusion, get hold of a model hand (it doesn't have to be very
realistic) and put it on the table in front of you. If it is a left hand, put
your actual left hand somewhere you can't see it, in the same pose as the rubber
hand. Now get someone to touch and stroke your unseen hand and the rubber hand
with identical movements. If you concentrate on the rubber hand, you will
probably get the uncanny feeling that it is your own. (See a video of the rubber
hand illusion here)

What this illusion shows is that your sense of body ownership is less anchored
in reality than you think. Your brain will happily override information from
proprioception to conjure up an incorrect yet coherent body schema based on
vision and touch.

In fact, your mental body map is an absolute sucker for visual information. This
year Frank Durgin of Swarthmore College in Pennsylvania set up the illusion as
described above but instead of touching the rubber hand he merely "stroked" it
with light from a laser pointer, leaving the unseen hand alone. Two-thirds of
220 subjects reported a sense of ownership of the rubber hand and said they had
the sensation of heat and even touch from the laser pointer (Psychological
Science, vol 18, p 152). "It's obvious the hand is rubber - no one is fooled at
all," says Durgin. "But if your brain decides it's your hand, all the conscious
awareness in the world won't change it."

If you can't get hold of a fake hand, there are other (though less reliable)
ways to experience the illusion. Some people can be fooled into believing a
piece of wood has replaced their hand. Around half of people can even be made to
feel a table top is part of their body. Sit at a table and put your hand out of
sight underneath. Get someone to tap and stroke this hand while doing exactly
the same to the table top directly above. If you watch the table top, you may
experience the illusion that the table has become part of your body.

Proprioception may be the junior partner to vision and touch in creating your
body schema, but it still plays a key role. You can demonstrate this with an
illusion that taps into proprioception alone. This Pinocchio illusion is hard to
do without a specialist piece of equipment called a physiotherapy vibrator, but
if you can get hold of one, try this. Close your eyes, touch the tip of your
nose and then get somebody to apply the vibrator at about 100 hertz to skin at
the very top of your bicep. This creates the strong sensation that you are
straightening your elbow, and that your nose is simultaneously growing longer
and longer, like Pinocchio's.

Vibrating the skin above a tendon excites stretch receptors in the muscle,
creating a powerful sensation that the muscle is stretching and the joint is
extending. This confuses your proprioceptors, which revise your body schema
accordingly. The result is rather like having a phantom limb: the sensed
position of your arm in space doesn't correspond to its actual position.

If you're touching your nose at the same time, this leads to a weird sensation
that it is growing. Your brain integrates the touch sensation from your fingers
with the "movement" of your arm and comes to the erroneous conclusion that your
nose must be growing to fill the gap.

The Pinocchio illusion is an important tool for understanding how the brain
calculates the size and shape of our bodies. This isn't just an academic
question. When it goes wrong, such as in body dysmorphic disorder, anorexia and
phantom limb, the results can be devastating (PLoS Biology, vol 3, p e412).

3 A brain of two halves
WOULD you consider yourself to be logical and analytical or creative and
empathic? According to popular psychology you're one or the other, and it's all
down to which half of your brain you use the most: the rational and calculating
left or the intuitive, artistic right.

It's a myth, of course, but like all good ones it contains a grain of truth.
Your cerebral cortex - the outer layer of your brain that deals with higher
functions - is indeed split into two halves. They are connected by a flat bundle
of nerve fibres called the corpus callosum, but work in subtly different ways -
and these differences occasionally flicker into your conscious awareness.

The left-brain/right-brain myth arose from experiments done in the early 1970s
on people who had had their corpus callosum cut as a last-ditch treatment for
epilepsy. These "split-brain" patients showed some strikingly odd responses to
information that was preferentially sent to one side of the brain or the other
by presenting it to the extreme left or right of their visual field. This works
because the right visual field is monitored by the right eye, which routes
straight into the left brain, and vice versa.

For example, when a word or picture is presented to their right brain,
split-brain patients are often unable to read or recognise it. This and similar
experiments led to the idea that the left side of the brain deals with logic and
facts while the right side is more intuitive and interpretive. We now know that
this dichotomy is too simplistic, but its essence holds true. The latest view is
that the two hemispheres have subtly different styles of information processing:
the left has a bias towards detail, the right a more holistic outlook. You can
watch a video of a split-brain experiment at
www.youtube.com/watch?v=ZMLzP1VCANo&mode=related&search=.

“Split-brain patients often can't read words sent to the brain's right side”Most
people, of course, have a functional corpus callosum that shunts information
between the hemispheres. Even so, subtle left-right differences exist. One task
where the hemispheres operate differently is face recognition. When most of us
see a face, our right cerebral hemisphere does the lion's share of the work
recognising its gender and decoding its expression. And because the right
hemisphere is fed by the left visual field, that means we have a notable
left-sided bias in our judgement of faces.

Look at this pair of faces (left). Which appears happier? Chances are you chose
the bottom one. The two faces are, however, identical apart from being mirror
images of one another. The picture is called a chimeric face and is made by
taking two pictures of the same face, one with a neutral expression and the
other smiling, chopping the pictures in half and joining the two mismatched
pieces. Our general bias towards the left side of the face (as we look at it)
makes us see the faces as different even though they are essentially equivalent.

It isn't just visual processing that is lateralised. There is some evidence that
emotion is too, with the right side of the brain more specialised for negative
emotions and the left for positive ones. Amazingly, simply activating one or
other hemisphere by moving parts of your body can noticeably change your
emotional state.

You can experience this by repeating an experiment first done in 1989 by Bernard
Schiff and Mary Lamon of the University of Toronto in Canada (Neuropsychologia,
vol 27, p 923). They asked 12 volunteers to perform a "half smile", lifting one
corner of their mouths and holding it for a minute. Left-smilers reported
feeling sadder afterwards, while right-smilers felt more positive.

Other researchers have reproduced the effect simply by getting people to
contract the muscles of their left or right hand a few times. More recent
research has suggested that motivation is similarly affected: people who
performed right-sided muscle contractions became more assertive and spent longer
trying to crack an impossible maths puzzle.

Unsurprisingly, these claims are controversial, with some teams failing to
replicate the results. Last year, however, Eddie Harmon-Jones of Texas A&M
University in College Station used EEG to confirm that flexing the hand muscles
produces changes in emotion, but only when it is preceded by activation of the
opposite cortex (Psychophysiology, vol 43, p 598). The left-brain/right-brain
legend, it appears, is alive and well.

4 Probe your subconscious
IT WAS a ground-breaking investigation into the nature of consciousness and free
will. In 1983, psychologist Benjamin Libet of the University of California, San
Francisco, hooked five volunteers up to an EEG machine and asked them to make
voluntary movements, such as lifting a finger, whenever they felt like it.
Watching the electrical activity in their brains, he discovered that his
subjects only became consciously aware of their intention to act a few hundred
milliseconds after their brain had initiated the movement. Libet was forced to
conclude that what feels like a conscious decision may in fact be nothing of the
sort (Brain, vol 106, p 623).

This experiment was the first demonstration of what is now an established theory
in neuroscience: a major proportion of your thoughts and actions - even things
you believe you are in conscious control of - actually take place in your
unconscious. Most of the time you are essentially flying on autopilot.

Libet's experiment involved equipment that you're unlikely to have at home, but
you can tap into a similar phenomenon using what is known as the "ideomotor
effect". Make a pendulum out of a paper clip and a piece of thread and dangle it
over a cross drawn on a piece of paper. Ask yourself a simple yes/no question,
such as "am I at home?" or "do I have a cat?", and tell yourself that if the
pendulum swings clockwise, the answer is yes, while anticlockwise means no.
Spookily, the pendulum will generally start rotating in the direction of the
correct answer.

It looks supernatural, but it's not. The reason it works is that, as soon as you
ask the question, your unconscious brain fires up motor preparation circuits in
anticipation of the answer it expects to see. These circuits initiate subtle
muscle movements that you are not normally aware of - except when they are
amplified by a pendulum (or dowsing stick or Ouija board). This is your
unconscious brain in action.

A different aspect of your mental underworld is reflected in your "implicit
assumptions". Your subconscious mind isn't just planning and executing actions,
it also spends a great deal of time analysing the world, looking for patterns
and relationships that can help you navigate through life. The conclusions it
comes to are called implicit assumptions - subtle prejudices about people and
events. For example, if you hear on the radio that a teenage boy has been shot
dead in a car park near his home, it's almost impossible not to make assumptions
about his family background and the area where he lived.

"Everybody has implicit assumptions," says Brian Nosek, a psychologist at the
University of Virginia in Charlottesville who played a big part in their
discovery. "They're a necessary part of how the brain operates and they
generally serve us very well."

But not always. Nosek and colleagues argue that because we are not in control of
our implicit assumptions, and are seldom aware of them, it is possible to
develop unconscious prejudices that your conscious mind would find unappealing
or even abhorrent - such as associating men with science and women with the
arts, preferring thin people to fat people or assuming that blonde women are
stupid. "You may think you're egalitarian, yet your associations are often quite
different," says Nosek.

Nosek and colleagues have devised a way to access these implicit assumptions
(take the test at https://implicit.harvard.edu/implicit). The tests are based on
the idea that people find it easier to recognise pairs of stimuli that fit their
unconscious assumptions - white people and positive words or black people and
negative words, for example. People often find the results of their tests
"provocative", says Nosek. "The most common implicit associations are race and
age - they're quite profound."

Maybe sometimes it is better to ignore your unconscious mind.

5 Pay attention!
IMAGINE you are walking down the street and a passer-by asks you for directions.
As you talk to him, two workmen rudely barge between you carrying a door. Then
something weird happens: in the brief moment that the passer-by is behind the
door, he switches places with one of the workmen. You are left giving directions
to a different person who is taller, wearing different clothes and has a
different voice. Do you think you would notice?

Of course you would, right? Wrong. When researchers at Harvard University played
this trick on 15 unsuspecting people, eight of them failed to spot the change.

What this demonstrates is a phenomenon called "change blindness". It happens
because of a chronic shortage of a crucial mental resource: attention. You are
blithely unaware of most of what is going on around you, to the point where you
can fail to notice "obvious" changes in your surroundings.

Attention is not well understood, but whatever it is, we have a limited amount.
Of all the information entering or being generated by your brain at any one time
- sights, sounds, memories, ideas and so on - only a tiny fraction enters your
consciousness. Object-tracking studies suggest that the maximum number of items
we can attend to at any one time is around five or six (see demos at
http://ruccs.rutgers.edu/finstlab/demos.htm).

Scientists studying attention spend a lot of time playing with change blindness
because it provides direct access to the attentional system. In the door
experiment, the subjects fail to see the change because their attention is
elsewhere and the door conceals what would otherwise be attention-grabbing
motion.

You can experience the same thing by watching "flicker images". These consist of
two consecutive images that differ only in one key feature - two cowboys who
swap heads, say. If the images are flashed up in quick succession with a brief
blank screen between them (which acts like the door), most people take an
astonishingly long time to spot the difference (see demos at
www.psych.ubc.ca/~rensink/flicker/download, or try flicking your attention
between the two images in the diagram below).

Similarly, we often fail to notice blatant continuity errors when films cut from
one scene to another. We also usually fail to detect gradual changes to a static
scene, such as the addition of a large building (see demos at
http://viscog.beckman.uiuc.edu/djs_lab/demos.html and
http://nivea.psycho.univ-paris5.fr/Slow%%20changes%%20bis/intro.html).

"Basically, the explanation is that attention is needed to see change," says
psychologist Ronald Rensink of the University of British Columbia in Vancouver,
Canada. "Attention is drawn automatically to the motion signals that accompany a
change. But if these are swamped, then the observer can't rely on automatic
control, but needs to hunt around with their attention."

A similar phenomenon is motion-induced blindness, in which concentrating on a
moving pattern causes what should be very prominent static objects - such as
bright yellow dots - to disappear (see demos at
http://pantheon.yale.edu/%%7Ebs265/demos/MIB-percScotoma.html). Motion-induced
blindness was only discovered in 2001 and it is still unclear why it happens,
but most researchers think it has something to do with attentional resources.

There is a related and even more counter-intuitive demonstration of our limited
capacity for attention. If you are deliberately concentrating on something, it
can render you oblivious to other events that you would normally have no trouble
noticing. This "inattention blindness" is probably the reason why motorists
sometimes collide with objects such as pedestrians and buses that they simply
"didn't see".

The most famous demonstration of inattention blindness was staged in 1999 by
Daniel Simons and Christopher Chabris of the University of Illinois at
Urbana-Champaign. It involves a game of basketball. Chances are you've seen it
or read about it before. If not, have a look at
http://viscog.beckman.uiuc.edu/grafs/demos/15.html. The task is to count the
number of passes made by the team in white. You won't believe your brain.

6 Made-up m emories
A FEW years ago, the actor Alan Alda visited a group of memory researchers at
the University of California, Irvine, for a TV show he was making. During a
picnic lunch, one of the scientists offered Alda a hard-boiled egg. He turned it
down, explaining that as a child he had made himself sick eating too many eggs.

In fact, this had never happened, yet Alda believed it was real. How so? The egg
incident was a false memory planted by one of UC Irvine's researchers, Elizabeth
Loftus.

Before the visit, Loftus had sent Alda a questionnaire about his food
preferences and personality. She later told him that a computer analysis of his
answers had revealed some facts about his childhood, including that he once made
himself sick eating too many eggs. There was no such analysis but it was enough
to convince Alda.

Your memory may feel like a reliable record of the past, but it is not. Loftus
has spent the past 30 years studying the ease with which we can form "memories"
of nonexistent events. She has convinced countless people that they have seen or
done things when they haven't - even quite extreme events such as being attacked
by animals or almost drowning. Her work has revealed much about how our brains
form and retain memories.

While we wouldn't want to plant a memory of a nonexistent childhood trauma in
your own brain, there is a less dramatic demonstration of how easy it is to form
a false memory called the Deese-Roediger-McDermott paradigm. Read the first two
lists of words and pause for a few minutes. Then read list 3 and put a tick
against the words that were in the first two. Now go back and check your
answers...

“List 1

apple, vegetable, orange, kiwi, citrus, ripe, pear, banana, berry, cherry,
basket, juice, salad, bowl, cocktail”“List 2

web, insect, bug, fright, fly, arachnid, crawl, tarantula, poison, bite, creepy,
animal, ugly, feelers, small

(Now wait a few minutes)”“List 3

happy, woman, winter, circus, spider, feather, citrus, ugly, robber, piano,
goat, ground, cherry, bitter, insect, fruit, suburb, kiwi, quick, mouse, pile,
fish”From issue 2622 of New Scientist magazine, 19 September 2007, page 34-41