Read Mind Hacks™: Tips & Tools for Using Your Brain Online
Authors: Tom Stafford,Matt Webb
Tags: #COMPUTERS / Social Aspects / Human-Computer Interaction
Mind Hacks™: Tips & Tools for Using Your Brain (34 page)
We all have a hand preference when undertaking manual tasks. But why is this so? And
do you always prefer the same hand, or does it vary with what you are doing? Does the way
people vary their hand preference differ between right- and left-handers?
The world is a right-handed one, as will be obvious to left-handers. Most tools are made
for right-handed people. Implements such as scissors, knives, coffee pots, and so on are all
constructed for the right-handed majority. In consequence, the accident rate for
left-handers is higher than for right — and not just in tool use; the rate of traffic
fatalities among left-handers is also greater than for right.
1
The word “sinister,” which now means “ill-omened,” originally meant “left-handed.” The
corresponding word for “right-handed” is “dexter,” from which we get the word
“dexterous.”
— T.S.
Nine out of 10 people are right-handed.
2
The proportion appears to have been stable over thousands of years and across
all cultures in which handedness has been examined. Anthropologists have been able to
determine the incidence of handedness in ancient cultures by examining artifacts, such as
the shape of flint axes. Based on evidence like this and other evidence such as writing
about handedness in antiquity, our species appears always to have been a predominantly
right-handed one.
But even right-handers vary in just how right-handed they are, and this variation may
have a link to how you use the different sides of your brain
[
Use Your Right Brain — and Your Left, Too
]
.
Have a go at the following tests to determine which is your dominant hand and just how
dominant it is. Do each test twice — once with each hand — and record your score, in seconds,
both times. You don’t have to do all of them; just see which you can do given the
equipment you have on hand.
Darts
- Throw three darts at a dartboard. (Be very careful when doing this with your
off-hand!) Add up the distances from the bull’s-eye.
Handwriting
- Measure the time that it takes to write the alphabet as one word, six times. Start
with the hand you normally write with and rest for 1 minute before starting with the
other hand.
Drawing
- Measure the time that it takes to draw a line between two of the lines of some
lined paper. Add a penalty of 2 seconds for each time your line touches one of the
ruled lines.
Picking up objects with tweezers
- Using tweezers, measure the time that it takes to pick up and transfer 12 pieces
of wire from one container to another.
Stoppering bottles
- Measure the time, in seconds, it takes to put the lids on five jars, the corks
back in five wine bottles, or the cap back on five beer bottles.
Here’s how to calculate your handedness quotient:
(Left-hand score – Right-hand score) / (Right-hand score + Left-hand score)
x 100
You can now see how the score differs for the different tasks and take an average to
see your average dominance. Positive numbers mean right-handedness, negative numbers mean
left-handedness. Bigger numbers mean greater dominance by one hand.
By doing the previous tests, you can see that you can still use your off-hand for some
things and that it is easier to use your off-hand for some things than for other things.
Most people have some things for which they use their dominant hand, some things they may
use both for, and some for which they use their off-hand.
So, in a sense, describing people as left-handed or right-handed is limiting because
it puts them into only one category and ignores the extent to which they may be in that
category — or in between the two. This is why, of course, we used behavioral measures to
work out the handedness quotient, rather than just asking people.
3
Handedness is only weakly genetic. The child of two left-handers has a 45–50% chance
of being left-handed, and thus handedness must partly be to do with how the child is
brought up as well, so we know that there is a large nongenetic influence on whether you
turn out to be a left-hander. Evidence also suggests that left-handedness may be
associated with neurological insult in the womb or during delivery.
4
If you try the test out on a few people, you will see that left-handed people more
easily use their right hand than right-handed people use their left hand. In part, this is
probably because our right-handed world forces left-handers to learn to use their right
more, and it could also be for deeper reasons to do with brain lateralization as
well.
Nine out of 10 people use their right hand predominantly, and at least 9 out of 10
people have their major functions on their left side.
5
This includes around two-thirds of left-handers. Everyone else, a
significant minority, either uses the right hemisphere for speech or uses both hemispheres.
6
One test of which half of the brain is dominant for language is the Wada
test. This involves a short-acting anesthetic (e.g., sodium amytal) being injected into
the carotid artery. This transiently anesthetizes the left hemisphere, thus testing the
functional capabilities of the affected half of the brain. People for whom the left
hemisphere is indeed dominant for language (i.e., most of us) will temporarily become
aphasic, losing the ability to comprehend or produce language. If counting at the time,
you’ll stop being able to do so for a few beats when injected with the
anesthetic.
The reason most people are still left-brainers for language may be due to how our
brain functions became lateralized
[
Use Your Right Brain — and Your Left, Too
]
before the evolution
of language, the brain lateralizing separately from the use of our hands.
It has been suggested that the speech areas of the brain developed near the motor
cortex because hand gestures were the principal form of communication before speech.
7
Studies show that, when a participant observes hand and mouth gestures,
parts of the motor cortex (F5) and Broca’s area (found in the left frontal lobe,
specifically involved in the production of language) are stimulated. It is argued that
before speech our ancestors used gestures to communicate, much as monkeys and apes do now
(i.e., lip smacks). And so the human speech circuit is a consequence of the precursor of
Broca’s area, which was endowed (before speech) with mechanisms to recognize action made
by others, from which speech developed.
It is plausible that only the one hand (the right) was used for a more efficient and
simple way of communicating. This would explain why language and hand dominance are on the
same side (remember, the left side of the brain controls the right side of the body, so
left-language dominance and right-hand dominance are both due to the left side of the
brain).
If this were the norm during evolution, it may help to explain why most left-handers
still have speech areas in the left hemisphere. However, this still doesn’t answer the
question of why the right hand was dominant in the beginning. At present, this can be only
speculation; the important point is that right- and left-handedness are distributed
differently — they are not mirror images of each other, which has implications for the
genetics of handedness and the laterality of other functions.
It has been argued that the original hand preferences evolved from a postural position
preference of the right hand and consequently a left preference for reaching in
arboreal
(tree-living) species.
8
So, with postural demands becoming less pronounced in ground-dwelling
species, the left hand remained the dominant one for highly stereotyped tasks like simple
reaching, whereas the right became the preferred one for more manipulative tasks or tasks
requiring some skill. In other words, we would hang on with the left hand and pick fruit
with the right.
Although this is an interesting theory for why the majority of the population is
right-handed, it does not give any indication as to why some people are left-handed. Are
left-handed people highly skilled in reaching? Are left-handed people as skilled in
manipulative tasks as their right-handed counterparts? Regretfully, these questions have
to wait for further research.
- Salive, M. E., Guralink, J. M., & Glynn, R. J. (1993).
Left-handedness and mortality.
American Journal of Public Health,
83
, 265–267. - Annet, M. (1972). The distribution of manual asymmetry.
The British Journal of Psychology, 63
, 343–358. - Hartlage, L. C., & Gage, R. (1997). Unimanual performance as
a measure of laterality.
Neuropsyhological Review, 7
(3),
143–156. - Bakan, P. (1971). Handedness and birth order.
Nature,
229
, 195. - Davidson, R. J., & Hugdahl, K (eds.) (1995).
Brain
Asymmetry
. Cambridge, MA: MIT Press. - Rasmussen, T., & Milner, B. (1977). The role of early
left-brain injury in determining lateralization of cerebral speech functions.
Annals of the New York Academy of Sciences
, 299,
355–369. - Rizzolatti, G., & Arbib, A. (1998). Language within our
grasp.
Trends in Neurosciences, 21
, 188–194. - MacNeilage, P. E. (1990). The “Postural Origins” theory of primate
neurobiological asymmetries. In N. A. Krasneger et al. (eds.),
Biological
and Behavioural Determinants of Language Development
, 165–168, Hillsdale,
NJ: Erlbaum.
- Laska, M. (1996). Manual laterality in spider monkeys (Ateles geoffroyi) solving
visually and tactually guided food-reaching tasks.
Cortex, 32
(4),
717–726.
— Karen Bunday
The logical left brain and intuitive right brain metaphor is popular, but the
real story of the difference between the two halves of your brain is more complex and more
interesting.
There’s a grain of truth in all the best myths, and this is true for the
left-brain/right-brain myth. Our cortex is divided into left and right hemispheres, and they
do seem to process information differently, but exactly how they do this isn’t like the
story normally told by management gurus and the self-help literature. As with many
scientific myths, the real story is less intuitive but more interesting.
Our brains follow the general pattern of the rest of our bodies: two of everything down
the sides and one of everything down the middle. With the brain, the two halves are joined
directly in the
subcortex
, but in the cortex the two halves, called
hemispheres
, have a gap between them. They are connected by a tight
bunch of some 250 million nerve fibers, called the
corpus callosum
,
which runs between the two hemispheres (it’s not the only way for information to cross the
hemispheres, but it’s the most important).
Each hemisphere is wired up to sense and act on the opposite side of the body. So
information from your right goes to the left side of the visual cortex, and signals from
your left motor cortex control your right hand. For higher functions, in which information
from both senses is combined, the two hemispheres seem to have different strengths and
weaknesses, so that for certain tasks one hemisphere or the other will be dominant.
The origins of the popular myth were studies of patients who had their corpus callosum
severed as part of a radical surgical intervention for epilepsy. These “split-brain”
patients could function seemingly normally on many tasks, but displayed some quirks when
asked to respond to the same material with different hands or when speaking (left brain)
rather than pointing with their left hand (right brain).
1
A simple distinction between a left brain specialized for language and cold logic and an
oppressed right brain that specializes in intuition grew into the myth we know today.
Similar to the 10% myth
[
Neuropsychology, the 10% Myth, and Why You Use All of Your Brain
]
, this led to the
further conclusion that most of us use only half of our brains. Although this distinction
may or may not be a useful metaphor in talking about styles of thinking, it is certainly not
a useful metaphor for conducting research nor for giving insight into the true differences
between the hemispheres.
Any real difference between the hemispheres may be the opposite of what people raised on
the left brain bad, right brain good myth would expect. Michael Gazzaniga, who was part of
the team that did the original split-brain
experiments and is now a very senior cognitive neuroscientist, recently wrote in
Scientific American
of an “inventive and interpreting” left brain, a
hemisphere for structure and meaning, and a “truthful, literal” right brain, limited by a
preoccupation with general surface features.
2
In his research, he found that the right hemisphere contained modules
specializing for computationally analyzing perceptions, in a very straightforward way, not
looking for any deeper meaning. It’s not good at smart search strategies, for example. The
left hemisphere is better at high-level associations and problem solving, including
language, looking for meaning, and patterns.
Many of the original demonstrations of hemispheric specialization involve showing an
image to just one
hemifield
of the eyes. Information from both eyes
is processed by both hemispheres of the brain, but in both eyes, the information to the
left of the focal point is processed by the right hemisphere and vice versa. By making
sure someone is looking straight ahead, you can control which hemisphere processes an
image by presenting it to the left or the right of his focal point — one hemifield. You have
to do it very quickly; as soon as an image appears before them, people will move their
eyes to look at it and thus feed the information to both hemispheres. Since this is
difficult to do with vision, here’s a nonvisual demo you can try at home.
3
The left hemisphere is better at processing rapidly occurring sounds and seems better
at keeping rhythm; it can hold fancier rhythms and keep them synchronized with a beat
better than the right hemisphere.
To show this in action, start tapping a regular beat with your left hand (1-2-3-4-
etc.) and then start tapping a fancy beat at the same time with the right hand (jazzy,
syncopated, like a melody line to accompany the regular beat). Now, try starting with the
regular beat on the right hand (1-2-3-4- etc.), and after a measure or two, start the
fancy beat on the left. See what happens. You should find it easier the first way round,
with your left hemisphere controlling the more difficult rhythm (your right hand).
Many left-handers actually get the same result as right-handers on this test, so it is
not just to do with mere handedness. It probably isn’t a coincidence that a piano keyboard
is organized with the lower notes, which are used for simpler rhythms, on the left side
where they can be delegated to the right hemisphere.
By comparing the performance of normal people on tasks that give information
to different hemispheres and by comparing responses controlled by different hemispheres,
cognitive neuroscientists have uncovered a number of functions that are done differently
by the different hemispheres, and some patterns are beginning to appear in the
data.
The most obvious specialized function is language. Speech is controlled by the left
brain, and understanding the literal meaning of words and sentence grammar is supported by
the left brain in most people (but not all). But that doesn’t mean that the right brain
has no role in language processing. Studies of people with right-brain damage, along with
other evidence, have suggested that the right brain may support analyzing global features
of language such as mood and implication. If I say, “Can you close the window?” I’m not
asking if you are able, I’m asking if you will. A step more complex is to say, “It’s cold
in here,” which is the same request, but more oblique (but maybe not as oblique as “Why
are you so selfish?”). It is this kind of pragmatic reasoning in language that some
researchers think is supported by the right brain.
The left-brain specialization for language carries over to an advantage in sequential
ordering and symbolic, logical reasoning.
The right brain seems specialized for visual and spatial processing, such as mental
rotation or remembering maps and faces, dealing with the appearance of things, and with
understanding the overall pattern. We have a bias whereby we judge faces by their left side.
4
You can see a demonstration of this at
http://perception.st-and.ac.uk/hemispheric/explanation.html
. The web site shows two faces, one looking more female than the other (see
Figure 6-8
). In fact, the faces are both
equally male and female, but the one that looks female has the more female half on the
left side (right-hemisphere processing) and the male half on the right side, where it
doesn’t affect your judgment of gender. Test this now by covering the left sides of the
faces in
Figure 6-8
and looking again; you
can now see that the face you first judged as female is half-male and the face you judged
as male is half-female.
dominates the perception of gender in faces, so you see one as more male and the other
as more female
5
Like perceiving gender and moods, musical appreciation also appears to mostly involve
right-brain-dominant processes (although, as we’ve seen, for keeping complex rhythms, the
left brain is dominant).
Brain imaging studies have suggested that these kind of results can be understood by
thinking of the hemispheres as specialized for different kinds of processing, not as
specialized for processing different kinds of things. One study
6
involved showing subjects letters made up of lots of little letters (e.g.,
the letter
A
made up of lots of little
S
s). The
left brain responded to the detail (the small letters) and the right brain to the global
picture (the large letter constructed out of small letters). Subsequent work has shown
that the story isn’t as clear as this study suggests. It seems you can get the
left-detail/right-global pattern to reverse with the correct kinds of stimulus-task
combination — but it has confirmed that the hemispheric dominance is due to the demands of
the task, not due to the nature of the information being processed.
7
This gives some tentative legitimacy to the idea that there are left-brain
and right-brain styles of processing.
But the important thing is how the two hemispheres combine, not how they perform in
artificial situations like those of the split-brain patients. Brain imaging studies of
normal people are based on the average results across many brains, and this tends to play
down the large variation between different individuals in how the functions are
distributed across the brain. Ultimately, however people’s brains are wired, they will be
using both sides to deal with situations they encounter — so it isn’t too helpful to become
preoccupied with which half does what and whether they are processing with their left or
their right.
- Some even claimed the two hemispheres of a patient’s split brain were
conscious in different ways. - Gazzaniga, M. S. (1998). The split brain revisited.
Scientific American, 279
(1), 50–55. (reprinted and updated
2002). - This demo is from the book
The Lopsided Ape
by
Michael C. Corballis (Oxford University Press, paperback, 1991), p.267. Many thanks to
Michael Parker (
http://www.michaelparker.com
) for bringing it to our attention. - At least we judge
holistic
features of faces
(like gender or mood) by their left side, using our right hemisphere. Neuroimaging
research shows left hemisphere involvement in analyzing the
parts
of faces. Rossion, B. et al. (2000). Hemispheric asymmetries for whole-based and
part-based face processing in the human fusiform gyrus.
Journal of Cognitive
Neuroscience, 12
, 793–802. - © Michael Burt, Perception Lab,
http://perception.st-and.ac.uk
. - Fink, G. R., Halligan, P. W., Marshall, J. C., et al. (1996). Where
in the brain does visual attention select the forest and the trees?
Nature
382
(6592), 626–628. There is a great discussion of this article by John
McCrone in
New Scientist
(13 July 1999), reprinted online (
http://www.dichotomistic.com/mind_readings_left%20vs%20right%20brain.html
). - Stephan, K. E., Marshall, J. C., Friston, K. J., Rowe, J. B., Ritzl,
A., Zilles, K., et al. (2003). Lateralized cognitive processes and lateralized task
control in the human brain.
Science, 301
(5631), 384–386.
- Other good starting points for reading about the neuroscience between the right
and left brain story are ABC’s “All in the Mind” (
http://www.abc.net.au/rn/science/mind/stories/s1137394.htm
), “Hemispheres” at Neuroscience for Kids (
http://faculty.washington.edu/chudler/split.html
), and “Workings of Split Brain Challenge Notions of How Language Evolved,”
article by Sandra Blakeslee archived on the New York Times website (
http://topics.nytimes.com/top/reference/timestopics/people/b/sandra_blakeslee/index.html
).