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 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.

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

Handwriting

Drawing

Picking up objects with tweezers

Stoppering bottles

Here’s how to calculate your handedness quotient:

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

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.

— 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.

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.

Figure 6-8. Both faces are equally male and female, but on different sides; your right brain
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.