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Hack 68. Test Your Handedness
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 rightand 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 [Hack #69] . In Action Have a go at the following tests to determine which is your dominant hand and just how dominant it is. Do each test twiceonce with each handand 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. Negative numbers mean right-handedness, positive numbers mean left-handedness. Bigger numbers mean greater dominance by one hand. How It Works 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 categoryor 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 [Hack #69] 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 differentlythey 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. End Notes 1. Salive, M. E., Guralink, J. M., & Glynn, R. J. (1993). Left-handedness and mortality. American Journal of Public Health, 83, 265-267. 2. Annet, M. (1972). The distribution of manual asymmetry. The British Journal of Psychology, 63, 343-358. 3. Hartlage, L. C., & Gage, R. (1997). Unimanual performance as a measure of laterality. Neuropsyhological Review, 7(3), 143-156. 4. Bakan, P. (1971). Handedness and birth order. Nature, 229, 195. 5. Davidson, R. J., & Hugdahl, K (eds.) (1995). Brain Asymmetry. Cambridge, MA: MIT Press. 6. Rasmussen, T., & Milner, B. (1977). The role of early left-brain injury in determining lateralization of cerebral speech functions. Annuls of the New York Academy of Sciences, 299, 355-369. 7. Rizzolatti, G., & Arbib, A. (1998). Language within our grasp. Trends in Neurosciences, 21, 188-194. 8. 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. See Also · 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 |
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Hack 69. Use Your Right Brainand Your Left, Too
 
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 [Hack #6], 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.
6.9.1. In Action
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 pointone 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.
6.9.2. How It Works
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 female5
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 study6 involved showing subjects letters made up of lots of little letters (e.g., the letter A made of up lots of little Ss). 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 combinationbut 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 encounterso it isn't too helpful to become preoccupied with which half does what and whether they are processing with their left or their right.
6.9.3. End Notes
1. It was even claimed the two hemispheres of a patient's split brain were conscious in different ways (http://www.macalester.edu/~psych/whathap/UBNRP/Split_Brain/Split_Brain_Consciousness.html).
2. Gazzaniga, M. S. (1998). The split brain revisited. Scientific American, 279(1), 50-55. (reprinted and updated 2002).
3. 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.
4. 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.
5. © Michael Burt, Perception Lab, http://perception.st-and.ac.uk.
6. 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://web.archive.org/web/*/http://www.btinternet.com/~neuronaut/webtwo_features_leftbrain.html).
7. 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.
6.9.4. See Also
· 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 "New Theories of Expression Focus on Brain's Two Sides," article by Sandra Blakeslee (http://members.aol.com/sakrug/dualbrain.html; reprinted from the New York Times).
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| Chapter 7. Reasoning
Section 7.1. Hacks 70-74
Hack 70. Use Numbers Carefully
Hack 71. Think About Frequencies Rather than Probabilities
Hack 72. Detect Cheaters
Hack 73. Fool Others into Feeling Better
Hack 74. Maintain the Status Quo
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| 7.1. Hacks 70-74
We consider ourselves pretty rational animals, and we can indeed be pretty logical when we put our minds to it. But you only have to scratch the surface to find out how easily we're misled by numbers [Hack #70], and it's well-known that statistics are really hard to understand [Hack #71] . So how good are we at being rational? It depends: our logic skills aren't too hot, for instance, until we need to catch people who might be cheating on us [Hack #72] instead of just logically solving sums. And that's the point. We have a very pragmatic kind of rationality, solving complex problems as long as they're real-life situations.
Pure rationality is overrated anyway. Figuring out logic is slow going when we can have gut feelings instead, and that's a strategy that works. Well, the placebo effect [Hack #73] works at leastbelief is indeed a powerful thing. And we have a strong bias toward keeping the status quo [Hack #74] too. It's not rational, that's for sure, but don't worry; the "If it ain't broke, don't fix it" policy is a pragmatic one, at least.
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Hack 70. Use Numbers Carefully
Our brains haven't evolved to think about numbers. Funny things happen to them as they go into our heads.
Although we can instantly appreciate how many items comprise small groups (small meaning four or fewer [Hack #35] ), reasoning about bigger numbers requires counting, and counting requires training. Some cultures get by with no specific numbers higher than 3, and even numerate cultures took a while to invent something as fundamental as zero.1
So we don't have a natural faculty to deal with numbers explicitly; that's a cultural invention that's hitched onto natural faculties we do have. The difficulty we have when thinking about numbers is most apparent when you ask people to deal with very large numbers, with very small numbers, or with probabilities [Hack #71] .
This hack shows where some specific difficulties with numbers come from and gives you some tests you can try on yourself or your friends to demonstrate them.
The biases discussed here and, in some of the other hacks in this chapter, don't affect everyone all the time. Think of them as forces, like gravity or tides. All things being equal, they will tend to push and pull your judgments, especially if you aren't giving your full attention to what you are thinking about.
7.2.1. In Action
How big is:
9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1
How about:
1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9
Since you've got both in front of you, you can easily see that they are equivalent and so must therefore equal the same number. But try this: ask someone the first version. Tell her to estimate, not to calculatehave her give her answer within 5 seconds. Now find another person and ask him to estimate the answer for the second version. Even if he sees the pattern and thinks to himself "ah, 9 factorial," unless he has the answer stored in his head, he will be influenced by the way the sum is presented.
Probably the second person you asked gave a smaller answer, and both people gave figures well below the real answer (which is a surprisingly large 362,880).
7.2.2. How It Works
When estimating numbers, most people start with a number that comes easily to mindan "anchor"and adjust up or down from that initial base. The initial number that comes to mind is really just your first guess, and there are two problems. First, people often fail to adjust sufficiently away from the first guess. Second, the guess can be easily influenced by circumstances. And the initial circumstance, in this case, is the number at the beginning of the sum.
In the previous calculations, anchors people tend to use are higher or lower depending on the first digit of the multiplication (which we read left to right). The anchors then unduly influence the estimate people make of the answer to the calculation. We start with a higher anchor for the first series than for the second. When psychologists carried out an experimental test of these two questions, the average estimate for the first series was 4200, compared to only 500 for the second.
Both estimates are well below the correct answer. Because the series as a whole is made up of small numbers, the anchor in both cases is relatively low, which biases the estimate most people make to far below the true answer.
In fact, you can give people an anchor that has nothing to do with the task you've set for them, and it still biases their reasoning. Try this experiment, which is discussed in Edward Russo and Paul Schoemaker's book Decision Traps.2
Find someonepreferably not a history majorand ask her for the last three digits of her phone number. Add 400 to this number then ask "Do you think Attila the Hun was defeated in Europe before or after X," where X is the year you got by the addition of 400 to the telephone number. Don't say whether she got it right (the correct answer is A.D. 451) and then ask "In what year would you guess Attila the Hun was defeated?" The answers you get will vary depending on the initial figure you gave, even though it is based on something completely irrelevant to the questionher own phone number!
When Russo and Schoemaker performed this experiment on a group of 500 Cornell University MBA students, they found that the number derived from the phone digits acted as a strong anchor, biasing the placing of the year of Attila the Hun's defeat. The difference between the highest and lowest anchors corresponded to a difference in the average estimate of more than 300 years.
7.2.3. In Real Life
You can see charities using this anchoring and adjustment hack when they send you their literature. Take a look at the "make a donation" section on the back of a typical leaflet. Usually this will ask you for something like "$50, $20, $10, $5, or an amount of your choice." The reason they suggest $50, $20, $10, then $5 rather than $5, $10, $20, then $50 is to create a higher anchor in your mind. Maybe there isn't ever much chance you'll give $50, but the "amount of your choice" will be higher because $50 is the first number they suggest.
Maybe anchoring explains why it is common to price things at a cent below a round number, such as at $9.99. Although it is only 1 cent different from $10, it feels (if you don't think about it much) closer to $9 because that's the anchor first established in your mind by the price tag.
Irrelevant anchoring and insufficient adjustment are just two examples of difficulties we have when thinking about numbers. ( [Hack #71] discusses extra difficulties we have when thinking about a particularly common kind of number: probabilities.)
The difficulty we have with numbers is one of the reasons people so often try to con you with them. I'm pretty sure in many debates many of us just listen to the numbers without thinking about them. Because numbers are hard, they lend an air of authority to an argument and can often be completely misleading or contradictory. For instance, "83% of statistics are completely fictitious" is a sentence that could sound convincing if you weren't paying attentionso watch out! It shows just how unintuitive this kind of reasoning is, that we still experience such biases despite most of us having done a decade or so of math classes, which have, as a major goal, to teach us to think carefully about numbers.
The lesson for communicating is that you shouldn't use numbers unless you have to. If you have to, then provide good illustrations, but beware that people's first response will be to judge by appearance rather than by the numbers. Most people won't have an automatic response to really think about the figures you give unless they are motivated, either by themselves or by you and the discussion you give of the figures.
7.2.4. End Notes
1. The MacTutor History of Mathematics Archive: a History of Zero (http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Zero.html).
2. Russo, J. E., and Schoemaker, P. J. H. (1989). Decision Traps. New York: Doubleday.
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Date: 2015-12-11; view: 689
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