Left-handed DNA found – and it changes brain structure

By James Gallagher Health and science correspondent, BBC News

Scientists have found the first genetic instructions hardwired into human DNA that are linked to being left-handed.

The instructions also seem to be heavily involved in the structure and function of the brain – particularly the parts involved in language.

The team at the University of Oxford say left-handed people may have better verbal skills as a result.

But many mysteries remain regarding the connection between brain development and the dominant hand.

What does this tell us?

About one in 10 people is left handed.

Studies on twins have already revealed genetics – the DNA inherited from parents – has some role to play.

However, the specifics are only now being revealed.

The research team turned to the UK Biobank – a study of about 400,000 people who had the full sequence of their genetic code, their DNA, recorded.

Just over 38,000 were left-handed.

And the scientists played a giant game of spot-the-difference to find the regions of their DNA that influenced left-handedness.

The study, published in the journal Brain, found four hotspots.

“It tells us for the first time that handedness has a genetic component,” Prof Gwenaëlle Douaud, one of the researchers, told BBC News.

But how does it work?

The mutations were in instructions for the intricate “scaffolding” that organises the inside of the body’s cells, called the cytoskeleton.

Similar mutations that change the cytoskeleton in snails have been shown to lead to the molluscs having an anticlockwise or “lefty” shell.

(Remember the quest to find Jeremy the garden snail a mate because, in the snail world, righties and lefties can’t have sex as their genitals are in the wrong place as far as the other is concerned?)

Image copyright University of Nottingham Image caption Jeremy the “lefty” snail and one of his right-spiralling-shell offspring

Scans of participants in the UK Biobank project showed the cytoskeleton was changing the structure of the white matter in the brain.

“For the first time in humans, we have been able to establish that these handedness-associated cytoskeletal differences are actually visible in the brain,” Prof Douaud, who is herself left handed, said.

In the left-handed participants, the two halves of the brain – the left and right hemispheres – were better connected and more co-ordinated in regions involved in language.

The researchers speculate left-handed people may have better verbal skills, although they do not have the data from this study to prove it.

The study also showed slightly higher risks of schizophrenia, and slightly lower risks of Parkinson’s disease, in left-handed people.

Does this change what it means to be left-handed?

Being left-handed has often led to a raw deal.

“In many cultures being left handed is seen as being unlucky or malicious and that is reflected in language,” said Prof Dominic Furniss, a hand surgeon and author on the report.

In French, “gauche” can mean “left” or “clumsy”. In English, “right” also means “to be right”.

“What this study shows is that being left-handed is just a consequence of the developmental biology of the brain, it has nothing to do with luck or maliciousness,” Prof Furniss said.

“And it is driven at least in part by genetic variants we’ve discovered.

“This adds to the understanding of what makes us human.”

Is this the end of the story?

Far from it.

The best guess is handedness is 25% genetic and 75% down to the environment (anything that’s not in the genes).

Yet this study has found only the first 1% of that genetic component and only in a British population.

So, much more work is needed to understand the genetic component of handedness in people across the globe, never mind what the huge environmental effects are, and then piece together how those elements result in people being either left or right handed.

Visitado em 23/04/2020

Raising a Left-Handed Child

By Fritz Lenneman

Eleven percent of the population is born left-handed, and if they seem different, it’s because they are! Learn six tips for raising a left-handed child.

Step 1: Is she a lefty? Congratulate—or blame—yourself.

The question of whether left-handedness could be inherited was answered in 2007 when scientist Clyde Francks announced the isolation of a gene—called LRRTM1—that contributes to left-handedness. Francks’ research suggests the gene is inherited on the father’s side.

Parents can monitor their child’s handedness by keeping tabs on which hand reaches for toys and food or by noting which direction a child stirs with a spoon. Righties tend to stir clockwise, while lefties stir counterclockwise.

Babies usually start showing a hand preference at about 7 to 9 months old, but they may not make a final distinction until they start school. “Doodling and eating are not fine motor skills requiring premium dexterity, which is why many babies and toddlers, under the influence of rapidly developing brains, switch between using the left and right hands, often masking underlying handedness and leading parents to conclude falsely that their children are ambidextrous,” David Wolman writes in A Left-Hand Turn Around the World. “This is a common error among people who associate ambidextrousness with high intellect.”

Step 2: Remember that she is different.

Lefties think differently. The left side of the brain—which controls the right hand—is in charge of speech, language, writing, logic, math and science. The right side—which controls the left hand—is responsible for music, art, perception and emotion. The right side handles abstract, big picture ideas; the left side thinks in straight lines.

Right-handers’ brain organization is usually quite rigid. The right side only handles language and logic; the left side only handles emotion and perception.

Meanwhile, left-handers’ brains tend to be more flexible—understanding of music could be on the left side or math could be on the right. As a result, the corpus callosum, the part of the brain that allows the two hemispheres of the brain to communicate with each other, can be 11 percent larger in left-handed brains than right-handed ones.

Some think left-handers’ brain structures may be the product of living in a right-handed world. “Growing up surrounded by right-handed equipment, instruments, appliances and tools, lefties give their nondominant side more exercise than the average righty,” Melissa Roth wrote in The Left Stuff. “Biomechanic research has revealed that training the nondominant side of the body actually enhances the dominant side—something known as the cross-training effect—since the body’s neural network is integrated on both sides.”

Step 3: Get her public speaking lessons.

After all, she’s going to need to be a good speaker when she’s president.

Four of the past seven presidents have been certifiably left-handed. A fifth, Ronald Reagan, was rumored to be ambidextrous. Many people assume this means the Gipper was born a lefty, but was forced to switch by schoolteachers—a common practice all over the world until the late 20th century.

And it’s not only the presidential election winners who are left-handed. Both candidates in 2008—Barack Obama and John McCain—write with their left hands. In 1992, the left-handed Ross Perot mounted one of the strongest third-party presidential campaigns in American history against his fellow southpaws George H.W. Bush and Bill Clinton.

Is this just some fluke? According to economist and co-author of the best-selling book Freakonomics, Steven Levitt, it probably isn’t. “Ten to 15 percent of men are left handed,” he wrote in his blog for The New York Times, “which means, according to my calculations, that this many recent left-handed presidents would only happen by chance one time in 1,000.”

Step 4: Buy school and art supplies.

Some of the greatest artists in history have been lefties, including M.C. Escher, Leonardo da Vinci, Michelangelo and Rembrandt. Contrary to some reports, Pablo Picasso wasn’t left-handed—despite this handicap, he turned out to be a pretty talented artist anyway.

Painting isn’t the only profession that favors lefties. Studies have shown large numbers of left-handed students and professors in schools of architecture, music and math.

However, this doesn’t mean that all creative subjects are easy for left-handed children. Using equipment designed for right-handers can end in frustration. Prevent the problems by investing in good left-handed scissors and smudge-free pencils and pens. Parents also can relatively easily switch the settings on computers to make a mouse or cursor more lefty-friendly.

Step 5: Buy sports equipment.

Polo and field hockey are probably out of the question since both require participants to play right-handed, but many of other sports actually allow significant advantages for lefties. Left-handed fencers routinely win medals in top competitions. Left-handed boxers pose serious problems for their opponents. And playing tennis left-handed has not hampered the careers of superstars like John McEnroe, Martina Navratilova or Rafael Nadal.

In baseball, left-handed pitchers have been highly sought after since the sport’s earliest days. Since most pitchers are right-handed, batters tend to have trouble clearly seeing a ball thrown by a lefty. The advantage for left-handed pitchers is even more pronounced against left-handed batters. In the 1980s, baseball managers began capitalizing on that dominance by relying on the “left-handed specialist”—a left-handed pitcher who comes into the game to face just one left-handed batter in late innings. The left-handed specialist’s average workday could consist of as throwing as few as a five or six pitches—and then hitting the shower before breaking a sweat.

One of the greatest left-handed specialists in baseball history was Jesse Orosco, who played for nine teams in 24 seasons. When he retired in 2003 at age 46, Orosco had set the record for most ever games played by a pitcher at 1,252. He also earned around $1 million a year starting in 1988—not bad for a few minutes of work a day.

Step 6: Pay for the school supplies and sports equipment you just bought.

If you need a loan to pay for those expensive new school supplies and sports equipment, start with your left-handed relatives—they might have some extra cash lying around.

Economists at Johns Hopkins and Lafayette College investigated whether handedness affects earnings, with expectation that if it did, it would not turn out well for the lefties. “If left-handedness is associated with poorer health, higher accident rates and lower average cognitive skills, it is natural to expect that these result in lower labor productivity and thereby lower earnings,” they wrote. “Left-handed people may be less productive in those occupations which use tools, machines and systems that are designed for right-handers.” Somewhat surprisingly, they found that lefties with college educations earned 15 percent more than their fellow right-handed alumni.

On the other hand, the news isn’t all good. This left-handed wage boost did not exist for left-handed women. A different study by economists at University College Dublin and University of Warwick found that left-handed women born in 1958 actually earned 5 percent less than right-handed women.

Keep Reading

Visitado em 29/02/2020

https://www.oprah.com/relationships/6-tips-for-raising-a-left-handed-child/all

Help left-handers get it right

Around 10 per cent of the population is left-handed. Left-handedness is not considered to be a special educational need in itself, but it is widely accepted that left-handed children may need extra support

You can help them to adapt to a right-handed environment by familiarising yourself with some of the potential pitfalls for left-handers. There is also a wealth of resources and equipment available to help left-handed children, their teachers and their parents.

If you don’t know what it feels like to be left-handed in a right-handed world, attempt to write your signature with your non-writing hand. Better still, go online to the Left-Handers in Society website and click on ‘basic problems’ (this can work well as a topic for students to explore as well).

Left or right? Developing handedness

It is generally agreed that hand-preference is established early on: between 18 months and three years of age. But it can continue to develop until the age of nine. There are varying degrees of left-handedness: some children write with their left hand but use their right for other tasks. Until the 1940s children who showed a preference for their left hand routinely had their left hands tied behind their backs at school. This was to force them to use their right hand. Psychologists nowadays stress the importance of allowing children to develop hand-preference in their own time.

* With younger children who are developing hand-preference, it is essential to make sure that objects such as pens or pencils are presented to them in the middle of their body. Do not push writing objects into either their left or right hand.

The write stuff

Many children, not just left-handers, experience difficulties in producing clear and legible handwriting. Left-handers may be more likely to slip into mirror-writing (flowing from right to left on the page) or to smudge their work. Some left-handers may write more slowly than others. This can be especially problematic for exams and tests.

The good news is that much of the equipment designed for left-handers is geared towards writing. Mainstream shops, such as the Early Learning Centre, stock useful products. Specialist pens with left-handed nibs, pencils and pencil-grips are widely available (see ‘resources’ below).

Softer lead pencils are recommended for left-handers.

Children who struggle with drawing lines neatly may benefit from a left-handed ruler (with a zero on the right and numbers running towards the left).

Left-handers are likely to find it easier to write leaning on pads and books, rather than on single sheets of paper.

Specific guidance for teachers on helping left-handers with writing is given in the Left-Handers Handbook and training video (see ‘resources’).

Whiteboards with wipeable pens can pose a challenge. Left-handers have a tendency to wipe off what they have just written as they go along. Tilting the board to the right may help (for left-handed teachers as well!).

Left-handers are actually at an advantage with the normal QUERTY keyboard as 57 per cent of typing is done with the left hand. However, the position of the numeric keypad on the right may cause problems for some. Specialist keyboards are available.

More commonly, left-handers experience difficulties with a right-handed mouse. Either supply an ergonomic left-handed mouse, or ensure that one mouse is set up for left-handers.

Children who experience real difficulties in writing and drawing may benefit from a sloping board. Handwriting experts suggest a sheet of hardboard to help promote good positioning for writing.

Positioning matters: of the child, of the hand, of the pen, of the desk.

If a left-hander is seated to the right of a right-handed person they will bump elbows. This is particularly problematic where space is limited. Keep left-handers to the left of a double desk. Ideally, they should not have a wall to their left.

Make sure they have enough room. Left-handers may need more space as they will be working at a different angle to right-handers.

Left-handers write into their bodies and may develop an awkward writing posture. This is usually to avoid smudging their work, or so that they can see what they are writing. Be sensitive to this when positioning them for activities.

Some workstations or conference-style desks with a right-handed rest will be impossible for left-handers to use.

Get a grip

Triangular pens, special nibs and certain pencil-grips can all prove problematic for left-handed children. But remember that everyday tools may also be harder for left-handed children to use. A survey of children for the Centre for Left Handed Studies found that 43 per cent had difficulty using potato peelers and 26 per cent could not master knitting or sewing skills. At an even simpler level:

Left-handed scissors are essential. Make sure there are enough pairs available and that they are easily identifiable. Mark left-handed equipment or keep in different-coloured wallets.

Many left-handed children struggle with compasses. Left-handed ones are produced and many children find these helpful.

Fun and games

If you are demonstrating an activity, such as craft or a sporting technique, it will help to face left-handers. This means that they can see a mirror-image of themselves. The exception to this method is writing, as it may induce mirror-writing.

Myth-busting

Diane Paul is the author of The Left-Handers Handbook (see ‘resources’). She warns that a wealth of mythology and misinformation surrounds left-handedness. ‘There is no proof that left-handers differ from right-handers in terms of educational attainment or IQ. They are not all geniuses or members of an elite group, any more than they are all disturbed, schizophrenic or low achievers’.

See this lesson plan to explore the perspective of left-handed people coping in a right-handed society. It also links to famous left-handers webpage.

Encourage left-handed children to join the Kids club at www.anythingleft-handed.co.uk

Leftie parents

Some parents may be concerned about their left-handed child, particularly if they do seem to write in an awkward fashion, or if their writing appears illegible. They can be directed to sites such as www.anythingleft-handed.co.uk which has practical advice for parents. It also lists equipment, school packs and educational games to help left-handed children achieve their potential.

fonte http://www.teachernet.gov.uk/teachingandlearning/library/lefthanders/

Visitado em 17/06/07

Handedness develops in the womb

Handedness develops in the womb

10:58 22 July 2004
Exclusive from New Scientist Print Edition
Laura Spinney, Lisbon

The hand you favour as a 10-week-old fetus is the hand you will favour for the rest of your life, suggests a new study.

The finding comes as a surprise because it had been thought that lifelong hand preferences did not develop until a child was three or four years old.

A team led by Peter Hepper of the Fetal Behaviour Research Centre at Queen’s University, Belfast in the UK reached this conclusion after studying ultrasound scans of 1000 fetuses.

In one study, nine out of 10 fetuses at 15 weeks’ gestation preferred to suck their right thumbs. Hepper’s team followed 75 of those fetuses after birth, and found that at 10 to 12 years old all 60 of the right thumb-suckers were right-handed, while 10 of the 15 left thumb-suckers were left-handed and the rest right-handed.

At 10 weeks old, even before they suck their thumbs, fetuses wave their arms about. A second study found that most prefer to wave their right arm, a preference that persisted until 24 weeks, after which the fetus is too cramped to move. Hepper reported the findings at the Forum of European Neuroscience in Lisbon, Portugal, earlier in July.

Reflex arc

Hepper is quick to point out that these observations do not show that the fetus can control its movements at such a young age. Nervous connections to the body from the brain are not thought to start developing until around 20 weeks’ gestation.

In addition, at the same stages of development fetuses that lack a brain cortex, a condition called anencephaly, move their limbs in a similar way, also favouring their right arm over the left.

“There is no evidence that the brain has any control over these movements at this stage,” says Hepper. “It’s most likely to be a local reflex arc involving the spinal cord.” He speculates that the fetus may have a preference for one side of its body simply because that side develops slightly faster.

The findings challenge the favourite theory of how handedness in humans develops. According to that theory, it is a side effect of brain lateralisation, in which one side of the brain predominantly handles certain functions, such as language. As the fetal scans show that handedness appears long before the brain has any control over limb movement, that theory cannot be correct.

Sensory connections

Instead, Hepper speculates that the reverse may be true: the fetus’s body movements

may somehow lead to the development of an asymmetrical brain. He points out that the sensory connections from the body to the brain develop before the connections that allow the brain to control the body’s movement.

But Stephen Wilson, a developmental biologist at University College London, is sceptical. “The movements you see in a fetus don’t have to be influencing brain asymmetries.”

It is more likely, he says, that in the early fetus there is already a difference in gene activation between the right and left sides of the brain and that this leads to lateralisation.

fonte http://www.newscientist.com/article.ns?id=dn6186

Visitado em 17/06/07

 

Gene for left-handedness is found

Scientists have discovered the first gene which appears to increase the odds of being left-handed.

 

The Oxford University-led team believe carrying the gene may also slightly raise the risk of developing psychotic mental illness such as schizophrenia.

 

The gene, LRRTM1, appears to play a key role in controlling which parts of the brain take control of specific functions, such as speech and emotion.

The study appears in the journal Molecular Psychiatry.

The brain is set up in an asymmetrical way.

In right-handed people the left side of the brain usually controls speech and language, and the right side controls emotions.

However, in left-handed people the opposite is often true, and the researchers believe the LRRTM1 gene is responsible for this flip.

They also believe people with the LRRTM1 gene may have a raised risk of schizophrenia, a condition often linked to unusual balances of brain function.

 

Further research

 

Lead researcher Dr Clyde Francks, from Oxford University’s Wellcome Trust Centre for Human Genetics, said the next step would be to probe the impact on the development of the brain further.

He said: “We hope this study’s findings will help us understand the development of asymmetry in the brain. “Asymmetry is a fundamental feature of the human brain that is disrupted in many psychiatric conditions.”

However, Dr Francks said left-handed people should not be worried by the links between handedness and schizophrenia.

He said: “There are many factors which make individuals more likely to develop schizophrenia and the vast majority of left-handers will never develop a problem.

“We don’t yet know the precise role of this gene.”

About 10% of people are left-handed.

 

Differences

 

There is evidence to suggest there are some significant differences between left and right-handed people.

Australian research published last year found left-handed people can think quicker when carrying out tasks such as playing computer games or playing sport.

And French researchers concluded that being left-handed could be an advantage in hand-to-hand combat.

However, being left-handed has also been linked to a greater risk of some diseases, and to having an accident.

Dr Fred Kavalier, a consultant geneticist at London’s Guy’s Hospital, said: “I don’t think left-handed people should be alarmed.

“Undoubtedly there are many, many other factors that contribute to schizophrenia. This may be a tiny little element in the big jigsaw.”

 

‘Devastating condition’

 

Marjorie Wallace, of the mental health charity SANE, said scientists working in its research centre in Oxford were also looking at the link between brain asymmetry and schizophrenia.

She said: “We desperately need research into the origins of psychosis to better understand why some people are more vulnerable than others.

“Then the treatment could be more targeted and carry the potential to prevent this devastating condition which affects one in 100 people worldwide.”

Jane Harris, of the mental health charity Rethink, said: “No-one really understands what causes schizophrenia yet.

“It is probably a combination of factors, including genetics, problems in childbirth, viral infections, drug use, poverty and urbanisation.”

 

fonte: http://news.bbc.co.uk/2/hi/health/6923577.stm

 

visitado em 01/08/2009

Creation of the Sinister: Biological Contributions to Left-handedness

by Monica Watkins

We live in a right-handed world. Left-handedness has been, and in some cases still is, considered an inconvenience, a bad habit, or a symbol of the “sinister”. Studies still attempt to link left-handers with socially undesirable behaviors, such as psychosis or criminal activity. The social implications of these stigmas are immense. “Left-handers may be one of the last unorganized minorities in our society, with no collective power and no real sense of common identity,” says Stanley Coren (1992).

Past research has emphasized the physical, mental, and social consequences of being left-handed. However, scientists are now beginning to focus on the biological basis for this “sinister” preference. The Geschwind-Behan-Galaburda (GBG) Theory of Left-Handedness was presented in 1987 (Geschwind and Galaburda, 1987a; Geschwind and Galaburda, 1987b; Geschwind and Galaburda, 1987c). The GBG Theory proposes that right-handed children have developed normally; they exhibit leftward symmetries in language areas. In contrast, left-handed children have suffered complications, which have led to anomalous cerebral dominance. Subsequently, motor coordination shifts to the left side in these children. Though comprehensive alternative has been advanced, the GBG Theory has been a subject of much debate.

The GBG Theory holds that genetics is a minor factor in the determination of left-handedness. Influences outside a strict genetic program exert the most control over determination. Studies have shown that injury to the developing brain at specific developmental stages can cause significant changes. It is possible that variations in the chemical environment of the fetus may cause such changes, and lead to a certain cerebral dominance. These chemical variations also influence the development of the immune system. Later in life, the effects of these chemical influences may manifest themselves as immune disorders and abnormal brain structures.

According to the GBG Theory, the chemical variation and its effects account for the following: why left-handedness is more common in men (Oldfield, 1971), why language disorders are more prevalent in men (Heceaen, 1984), why left-handedness is linked with developmental disorders of childhood (Porac and Coren, 1981), and why immune disorders and other diseases are more common in left-handers (Geschwind and Behan, 1982, 1984). In other words, left-handedness is the common thread among problems thought to be unrelated.

Definition of Left-Handedness

Basic to any analysis of left-handedness is a working definition of handedness. Left-handedness and right-handedness must be defined in standard terms. The layperson tends to focus upon handedness as the sole factor of sidedness. It is important to realize that left-eyedness, left-footedness, and left-earedness exist. Therefore, sidedness is a function of all these factors, and scientists use questionnaires that measure sidedness. For example, one question might be: which eye would you use to look through a keyhole? Research on the validity of these questionnaires suggests that the accuracy of the questionnaire depends on how the question is phrased. The most widely used test is the Edinburgh, Oldfield, Handedness Inventory. The test is concise set of 10 to 15 questions that concern handedness exclusively. One limitation of these questionnaires is that they do not address social forces that may have influenced left-handedness. The only way to guarantee validity is to combine standardized questionnaires, behavioral tests, and interviews regarding social influences.

The Road to the GBG Theory: Incomplete Genetic Continuance and Developmental Orchestration

There are many areas of research that led to the GBG Theory. The inability to show direct genetic linkage of left-handedness between parent and child or between identical twins was the most influential precursor to the theory. Porac (1976 as reviewed in Coren 1992) completed a three year study of 459 Canadian families. Results were similar to eleven former studies ranging from 1913 to 1982. If neither parent is left-handed or if only the father is left handed, the child has a 1:10 chance of being left-handed. However, if only the mother is left-handed, the ratio is 2:10. Finally, if both parents are left-handed, the chance rises to 4:10. Therefore, as Porac states, even under “genetically optimal” circumstances, the chance of right-handedness is still much greater than the chance of left handedness.

Twin studies provide a further complication to theories concerning the genetic basis of left-handedness. Identical twins have the identical genes. If left-handedness were determined completely from genetics, both twins would show the same handedness. Porac (1992) analyzed thirteen identical and fraternal twin studies, ranging from 1933 to 1985. The composite shows that only 76% of the expected 100% identical twins are both left-handed.

Incomplete genetic continuance for left-handedness has forced researchers to explore other biological causes of left-handedness If humans are genetically destined to be right-handed, then left-handedness is a failure to become right-handed. This would explain the small percentage of left-handers. The GBG Theory considers what type of developmental “mistake” has been made. Studies have shown that focal injury to the developing cortex can lead to reorganization of both the cortical architecture and the pattern of connectivity. This reorganization occurs not only in the area of damage, but also in distant, related regions (Goldman-Rakic and Rakic, 1984, as described in Geschwind and Galaburda, 1987a). These changes may produce enlargements in certain brain regions, and disrupt the natural asymmetry of the brain, making the brain more symmetric (LeMay, 1977). Thus, destruction of normal development in the left-brain causes a shift to the right-brain. The right-brain becomes more dominant ,and left-handedness results. Furthermore, the factors causing this developmental change are most likely chemical since a complex mix of hormones, including sex hormones, orchestrate brain development, (as reviewed in Geschwind and Galaburda, 1987a).

The GBG Theory suggests the possible factors that lead to developmental changes. Geschwind and Galaburda suggest that fluctuations in the chemical environment could provide the variability for the characteristic of left handedness (Geschwind and Galaburda, 1985 a, b, c). They observed the apparent difference between the number of male left-handers and female left-handers. Oldfield (1971 as reported in Geschwind & Behan, 1984), using the standard Edinburgh Handedness Inventory, reported that 90% of women are right-handed while 86% of men are right-handed. Oldfield claimed that the 4% difference is significant. Ellis, Ellis, and Marshall (1988) used the very same Edinburgh Inventory and failed to reach any significant sex difference. Their study suggested that any difference in left-handedness and the sexes must be smaller than 1.5%. However, the Ellis et al. study used only a few hundred subjects. Although few other studies have tested the sex difference, it is an important fuel for the GBG Theory. The Oldfield study remains well cited despite the controversy surrounding it.

If we accept that there are more male left-handers than female left-handers, it seems that the chemical which causes the shift to right-brain dominance is male-linked. The authors chose to study the influence of testosterone in high levels. Stress during pregnancy can cause fetal testosterone levels to rise in rats (Ward & Weisz, 1980 as reviewed in James, 1987). In the womb, both males and females share the same maternal and placental hormones. Once the testes develop, testosterone rises to high levels. An increase in testosterone in the womb, combined with the extra testosterone from the testes, could cause slow development in the left-hemisphere. This would explain why left-handedness would be more common in males. The strength of the link between testosterone and slow growth stems not from prenatal studies of hormone effects on cortical structure, but from postnatal studies. Hormones administered to the rat fetus after birth were able to alter asymmetries in the right brain and change tail posture, an indication of cerebral laterality (Diamond,1984 and Rosen et al, 1983 as review in Geschwind and Galaburda, 1987a). Scientists have not yet proved that prenatal testosterone causes abnormal development.

The Link with Developmental Disorders

A further principle of the GBG Theory concerns a possible connection between left-handedness and the following: dyslexia, attention deficit disorders, learning disabilities, and mental retardation. In 1860, Broca showed that language is usually lateralized to the left side of the brain. However, Goodglass, Quadfasel, and Zangwill (1954, 1960 as reported by Porac and Coren, 1978) confirmed that 50-67% of left-handers have right-brain dominance. GBG hypothesized that excessive delays in the speech controls of the left hemisphere would lead to problems. The normal lateralization of speech would come to a stop. The left-handed person could keep left-brain lateralization for speech, but learning disorders will result. However, the left-handed person might switch to right-brain speech lateralization.

In developmental dyslexic patients, Drake (1968 as reported by Geschwind and Galaburda, 1987c) found excessive neurons in the white matter of parietal region but did not specify any differences in laterality. Galaburda and Kemper (1979 as reported in Geschwind and Galaburda, 1987c) found several abnormalities in the left hemisphere of left-handed dyslexic patients. Neurons were clustered abnormally in patchy clumps., called ectopias. There was also evidence of dysplasia, the alteration of the number of neurons and neuronal architecture. Critics of the above studies state that only a few autopsied cases were used. In addition, Satz et al. (1985) found that dyslexics with hemisphere damage tend to be right-handed. Whereas, left-handers with developmental brain damage in the left-hemisphere are rarely dyslexic.

The link between left-handedness and dyslexia is stated most boldly by Geschwind and Behan (1982). The study reported that very strong left-handers were 11 times as likely to have dyslexia than very strong right-handers. The researches repeated the experiment two more times with different populations. Results similar to the first study were found. However, Satz (1986) points to many examples examining adult dyslexics that have failed to find an association between left-handedness and cognitive disability. In addition, Satz points to studies of children that have yielded no results. In contrast, Porac & Coren (1981) noted that difficulties due to lateral differences often do not become visible until high school or junior high school.

The Link Between Left-Handedness and Immunity

Based on the assumption that developmental speech disorders arise from testosterone induced brain abnormalities, Geschwind and Galaburda move to the final phase of their theory. High testosterone levels have been shown to inhibit the thymus both in utero and after birth in both rabbits and rats. (Frey-Wettstein and Craddock, 1970; Behan, 1987 as reviewed in Geschwind and Galaburda, 1987). The thymus is an important link in proper immune development. A faulty thymus will lead to defects in the immune system, which is crucial for the body’s defense against foreign substances. Lymphocytes recognize foreign substances and attack them. Many lymphocytes reside in the thymus. If the development of the thymus were hindered, the lymphocytes would also be hindered. Perhaps, they would be unable to recognize foreign matter. GBG suggest that the development of the immune system has been altered in left-handedness. Thus, immune disorders should be more prevalent in left-handers.

From the above assumption, the GBG Theory links immune disorders, language disorders, and left-handedness. Geschwind and Behan (1982) published the first study showing that people suffering from immune disorders and/ or dyslexia were more likely to be left-handed. Five hundred Oldfield Handedness Inventories were distributed to recruit subjects. Researches recruited applicants from a left-hander’s supply shop in London and from the general public around Glasgow. Only people with a perfect score of strong left-handedness or right-handedness were selected as subjects. In the first part of the study, the frequency of disease reported in left-handers was 2.7 times that of right-handers. This was especially true for thyroid and bowel disorders. In addition, left-handers reported learning disorder nine times more often than right-handers. A second part of the study handed the questionnaire to the general public. However, only those who had a hospital diagnosis for an immune disorder were chosen. For this study, the rate concerning left-handers and immune disorders was 2.3 times that of right-handers. Additional studies have been done to replicate these findings.

Discordance with the Autoimmune Theory

A study of the link between left-handedness and immune disease must examine criticisms and contradictions to the theory’s principles. An analysis from this viewpoint will show that more research and critical thinking are necessary to nullify questions of statistical reliability and theoretical rationale. Satz and Soper (1986) completed a complex analysis of Geschwind and Behan 1982 study. First, Satz and Soper object to the way that subjects were chosen. Satz and Soper object to the recruitment of subjects from a left-hander’s supply shop, since those subjects may be too “eager to please” in the questionnaire..

Satz and Soper also criticize the use of self-reports as evidence of disease. They claim that the first part of Geschwind’s and Behan’s 1982 study is faulty. It is possible that the subjects are misdiagnosing themselves. The second part of second study tried to correct for the self-reporting bias by choosing only patients whose diagnosis was received in a hospital. However, as Satz and Soper note, this is still self-reporting. Bentancur et al. (1990) eliminated self-reporting in their study. Patients were recruited from an allergy clinic. The control population was of the same sex and age distribution. Bentancur found no support for the GBG Theory.

Satz and Soper (1986) completed an analysis of the statistical tests used by Geschwind and Behan. The authors state that the results of the 1982 study are inconclusive. Other studies also report that the difference between left-handers and right-handers is insignificant Bryden et al. (1994) conducted a statistical analysis of thirty-one studies used to support the GBG link between immune disorder, developmental disorder, and left-handedness. Only 16 of these 31 studies were statistically significant.

Bryden (1991) decided to control for the type of test that would assess left-handedness. He determined left handedness by three following tests: the hand which one writes with, the Edinburgh Handedness Inventory (the same test that Geschwind and Behan used), and self reported left-handedness. For example, 637 said they were right-handed, 72 said they were left-handed, and 32 said they were ambidextrous. 668 wrote with their right hand, while 75 wrote with their left hand. The Edinburgh Test reported that 672 subjects right-handed while 70 were left-handed. No matter how handedness was assessed, there was no evidence of increased immune diseases in left-handedness.

Other Suggested Correlations Concerning the GBG Theory

One of the first offshoots of the GBG Theory is a supposed correlation between talent, left-handedness, and immune disorders. The left-hander is right-brain dominant. Thus, his or her strongest talents should be consistent with the functions of the right brain. The right brain is superior in visual- spatial; such abilities are useful in mathematics and architecture. Therefore, left-handers should be drawn to these fields. In addition, these left-handers would be more likely to have immune vulnerability. The elevated rates of males in mathematics (Benbow, 1986) are supported by the GBG Theory. In addition, Annet and Manning (1990) have shown a link between strong right-handedness and the lack of mathematical ability. Musical talent has also been linked with immune diseases (Hassler and Gupta, 1993).

Another offshoot to the GBG Theory concerns biological explanations of homosexuality. Coren (1992) reviews some of the biological theories. One theory suggests that homosexuality is the result of a hormonal imbalance. Homosexual males may have a deficiency of testosterone or a surplus of estrogen (the major female hormone). Homosexual females may have an excess of testosterone or a deficiency of estrogen. If the GBG Theory is valid, we would expect to see fewer left-handed homosexuals. Therefore, left-handedness and homosexuality would be directly linked. However, one study with a subject size of 94 homosexual men showed that left-handedness was much more common (Lindesay, 1987 as reported in Coren, 1992). The findings of this study were replicated with 38 homosexual men (McCormick et al., 1990). In addition, 32 homosexual women were studied and the same trend was found.

The GBG Theory has brought a new focus to the issue of AIDS susceptibility. If left-handers are more susceptible to immune diseases and more homosexual men are left-handed, left-handed homosexual men would be more defenseless against AIDS. Becker (1992), using the resources of the Multicenter AIDS Cohort Study (MACS), conducted the largest study of homosexual men. Left-handedness was judged using the Edinburgh Test and self reports. The results failed to show a greater preponderance of left-handed homosexual men with AIDS. This result was replicated by Satz et al (1991). Both studies seem to defeat the assumption that the GBG Theory applies to homosexuality and immune susceptibility.

A final application of the GBG Theory considers whether left-handed persons are more likely to die young. Coren & Halpern (1991) published a controversial article about the “Elimination Hypothesis,” stating that the percentage of left-handers decreases steadily. Thus, there are fewer left-hander’s in older age groups. This result has been replicated in various populations. Coren and Halpern suggest that left-handers are dying for one of two reasons. Left-handedness reduces their “survival fitness,” making them accident prone. The alternate theory states that the left-hander is prone to immune disease. Low resistance increases the probability of early death. A second theory, the “Modification Hypothesis,” states that changing social patterns force left-handers gradually to change to right-handedness.

Coren and Halpern tested the elimination hypothesis. The Baseball Encyclopedia provides information about baseball players from the year baseball was established as a national sport till 1975. Baseball was chosen because a single sex study could be conducted. The age at death was recorded for every player who had died before 1975. Results show that a right-handed baseball player is five times more likely than a left-handed baseball player to reach the age of 90. There seemed to be an equal risk of death for left-handers and right-handers before the age of thirty. A follow-up study was conducted using over 2,875 Californians as subjects. These subjects were asked to report the handedness and age of death of their kin. The study showed that the average age of death for right-handers was 75 years while the average age for left-handers was 66 years. Basically, right handers appear to live nine years longer. Coren (1992) states that the California results are more significant than the baseball study since baseball players do not represent the health of the average American. Although women were reported to live longer than men, right-handed women lived an average of five years longer than left-handed women. However, we must remember that the entire study is based on secondhand reports.

Evidence is accumulating against the early death hypothesis for left-hander. Fudin, Renninger, Lembessis, and Hirshon (1993 as reviewed in Coren & Halpern, 1993), repeated the Baseball Study and found that a longevity advantage was present for left-handers. However, this finding was insignificant under close statistical analysis. It is important to note that the baseball study does not tell us how strongly handed the players were.

Some studies support the modification hypothesis over the elimination hypothesis. The modification hypothesis claims that changing soical patters force left-hander’s to switch handedness. Hugdahl et al. (1993) showed that left-handedness was present in 15% of 21-31 year-olds. Left-handedness was present in 1.67% of all those 80 year-olds or older. However, there was corresponding increase in the number of subjects who switched to the right hand to write. Of the 21-31 year-olds, 2.69% had switched handedness. 6.75% percent of those over 80 had switched handedness. This suggests that left-handedness was discouraged decades ago.

Conclusion: Using Extreme Caution

The aim of this paper was to present enough opposing views to suggest that left-handedness is far to complicated to be ruled exclusively by a biological theory. One must keep in mind the classic nature-nurture controversy as it may apply to left-handedness. Certain characteristics of left-handedness are definitely influenced by the social environment. Every study has confirmed that left-handedness is not a simple genetic trait. Research concerning further genetic study is simply beyond our reach at this point, but not impossible. Current sudies are focused on lower organisms, where the search for genes is more simplistic.

Proposing one sweeping theory upon the characteristics of a group of people is hazardous. The GBG Theory ultimately suggests a decreased survival fitness for left-handers. Speaking from an evolutionary point of view, what possible purpose would this serve? A species evolves to adapt for better survival. Therefore, if left-handedness were less favorable, one would expect the amount of left-handers to decrease over time. This does not appear to be the case. Coren (1992) has addressed issues concerning the evolution of handedness. The author suspects that the ratio between left-hander and right-hander is a constant in human evolution. Thus, left-handedness would be a characteristic of Homo Sapiens. Coren searched university collections of art books from European, Asian, African, and American sources and found 10,000 works spanning the Stone Age to 1950. It is assumed that the artist tells us the handedness of the people around him or her by the way the objects are placed in the picture. Coren claims there has been the same distribution of right-handers for 50 generations. Additional studies have been done by anthropologists who analyzed tools used by man since the Stone Age. These studies report the same handedness distribution (Coren, 1992). It seems that left-handedness either has some benefit or is at least not harmful enough to be eliminated. In other words, there is room for both left-handers and right-handers to survive in our society.

The GBG Theory has been presented to the popular culture without complete confidence or overwhelming statistical significance It appears that we have come full circle in our beliefs about the diversity among humans. The dictionary defines left-handed as “clumsy, awkward, backhanded, or dubious.” In most cultures, left handedness was a sign of misforutne. Although these former beliefs may have been forgotten, the GBG Theory has unwillingly encouraged the resurgence of these prejudices. Perhaps, one day the theory will be proven correct. Until such time, restraint is the key to preventing any further discrimination towards the left-hander.

References

Aggleton, J.P., Kentridge, R.W., Neave, N.J.(1993). Evidence for Longevity Differences Between Left-Handed and Right-Handed Men-An Archival Study of Cricketers. Journal of Epidemiology and Community Health, 206-209.

Annet, M. Genetic and Nongenetic Influences on Handedness. (1978). Behavior Genetics, 8, 227-249.

Annet, M., & Manning, M. (1990). Reading and a balanced polymorphism for laterality and ability. Journal of Child Psychology and Psychiatry, 31, 511-529.

Bakan, P., Dibb, G., & Reed, P. (1973). Handedness and birth stress. Neuropsychologia, 11, 363-366.

Beaton, A. Left-handedness and life expectancy. (1992) British Medical Journal, 308, 408.

Becker, J et al. (1992). “Hand preference, immune system disorder and cognitive function among gay/bisexual men: the Multicenter AIDS cohort Study (MACS)., Neuropsychologia, 30

Benbow, C.P. (1986). Physiological correlates of extreme intellectual precocity. Neuropsychologia, 24, 719-725.

Betancur, C. Velez, A. Cabanieu, G., Le Moal, M. & Neveu, P.J. (1990). Association between left-handedness and allergy: a reappraisal. Neuropsychologia, 28, 223-227.

Bryden, M.P. McManus, I.C. & Bulman-Fleming, M.B. (1994). Evaluating the empirical support for the Geschwind-Behan-Galaburda model of cerebral lateralization. Brain and Cognition, 26, 1- 65.

Bryden, M.P, McManus, I.C., Steenhuis, R.E. (1991). Handedness is not related to self-reported disease incidence. Cortex, 27, 605-611.

Chavance, M., Dellatolas, G., Bousser, M.G., Amor, B., Grardel, B., Kahan, A., Kahn, M.F., LeFloch, J.P., & Tchobroutsky, G. (1990). Handedness, immune disorders and information bias. Neuropsychologia, 28, 429-441.

Corballis, M.C. (1991). The lopsided ape. New York: Oxford University Press.

Coren, Stanely. (1992). The Left-Hander syndrome- The Causes and Consequences of Left-Handedness. New York: Free Press

Coren, S and Halpern, D. (1993). A replay of the baseball data. Perceptual and Motor Skills, 76,403-406.

Coren, S. and Halpern, D.F. (1991) Left-Handedness: A marker for decreased survival fitness. Psychological Bulletin. 109, 90-106.

Coren, S., & Porac, C. (1978). The validity and reliability of self-report inventory to assess four types of lateral preference. Journal of Clinical Neuropsychology, 1, 55-64.

Dellatolas, G., Annesi, I. Jallon, P. (1990) Chavance M., Lellousch, J. An epidemiological reconsideration of the Geschwind-Galaburda theory of cerebral lateralization. Archives of Neurology. 47, 778-782.

Ellis, S.J., Ellis, P.J. (1988) Marshall, E. Hand preference in a normal population. Cortex, 14, 157-163.

Geschwind, N., & Behan, P. (1982). Left-handedness: Assoication with immune disease, migraine, and developmental learning disorder. Proceeding of the National Academy of Science, USA, 79, 5097-5100.

Geschwind, N., & Behan, P.O. (1984). Laterality, hormones, and immunity. In N. Geschwind & A.M. Galaburda (Eds.)., Cerebral Dominance. Cambridge, MA: Harvard Univ. Press, 211-224.

Geschwind, N., & Galaburda, A.M. (1985a or 1987a).

Cerebral lateralization: Biological mechanisms, associations, and pathology: I. A hypothesis and a program for research. Archives of Neurology, 42, 428-459.

Geschwind, N., & Galaburda, A.M. (1985b or 1987 b). Cerebral lateralization: Biological mechanisms, associations, and pathology: I. A hypothesis and a program for research. Archives of Neurology, 42, 564-578.

Geschwind, N., & Galaburda, A.M. (1985c or 1987 c).. Cerebral lateralization: Biological mechanisms, associations, and pathology: I. A hypothesis and a program for research. Archives of Neurology, 42, 634-654.

Harburg, E. (1981) Handedness and drinking-smoking types. Perceptual and Motor Skills, 52, 279-282.

Hassler, M., & Gupta, D. (1993). Function brain organization, handedness, and immune vulnerability in musicians and non-musicians. Neuropsychologia, 31, 655-660.

Hugdahl, K., Satz, P., Mitrushina, M., Miller, & E.N. (1993) Left-handedness and old age: Do left-handers die earlier? Neuropsychologia, 4, 325-333.

James, W. (1988). Testosterone Levels, Handedness and Sex Ratio at Birth. Journal of Theoretical Biology, 133, 261-266.

London, W.P. (1989). Left-handedness and life expectancy. Perceptual and Motor Skills, 68, 1040-102.

McCormick, C. Witelson, S., Kingstone, E. (1990). Left-handedness in homosexual men and women: neuroendocrine implications. Psychoneuroendocrinology, 15, 69-76.

McKeever, W. & Rich, D.(1990). an investigation of immune system disorder as a “marker” for anomalous dominance. Brain & Cognition, 12, 78-95.

Merckelbach, H , Murris, P., Kop, W.J. Handedness, symptom reporting, and accident susceptibility. Journal of Clinical ,Psychology, 50, 389-392.

Peters, M. & Perry, R. (1991). No link between left-handedness and maternal age and no elevated accident rate in left-handers. Neuropsychologia, 29, 1257-1259.

Peto, R. 1994. Left-Handedness and life expectancy- causal inferences cannot be trusted. British Medical Journal, 308, 403-404.

Porac, C., & Coren, S. (1981). Lateral preferences and human behavior. New York: Springer-Verlag.

Satz, P., Miller, E.N. Selnes, O., Van Gorp, W., D’Elia, L.F., & Visscher, B. (1991). Hand preference in homosexual men. Cortex, 27, 295-306.

Satz, P., Orsini, D.L., Saslow, E., & Henry, R. (1985). The pathological left-handedness syndrome. Brain and Cognition, 4, 27-46.

Satz, P. & Soper, H. (1986). Left-handedness, dyslexia, and autoimmune disorder: a critique. Journal of Clinical & Experimental Neuropsychology, 8, 453-458.

Smith, V. & Chayatee, C. (1983). Left-handed versus right-handed alcoholics: An examination of relapse patterns. Journal of Studies in Alcoholism, 44, 553-555.

Temple, C. (1990). Academic discipline, handedness and immune disorder. Neuropsychologia, 28, 303-308.

Tonnessen, F.E., Lokken, A., Hoien, T., & Lundberg, I. (1993). Dyslexia, left-handedness, and immune disorder. Archives of Neurology, 50, 411-416.

Van Strien, J. Bouma, A., & Bakker, D.J. (1987). Birth stress, autoimmune diseases, and handedness. Journal of Clinical and Experimental Neuropychology, 9, 775-780.

Wood, L.C. & Cooper, D.S. (1992). Autoimmune thyroid disease, left-handedness, and developmental dyslexia. Psychoneuroendocrinology, 17, 95-99.

Fonte: http://hcs.harvard.edu/~husn/BRAIN/vol2/left.html

Visitado em 17/06/07

Creation of the Sinister: Biological Contributions to Left-handedness

Breast cancer more likely in left-handers

By Duncan Gardham
(Filed: 26/09/2005)

Women who are left-handed are more than twice as likely to contract breast cancer before the menopause as right-handed women, research has found.

Scientists believe the cause may lie in the exposure to high levels of sex hormones before birth which can induce left-handedness as well as changes in breast tissue.

Epidemiologists in the Netherlands looked at more than 12,000 healthy middle-aged women as part of their research, published in the British Medical Journal today.

“Although the underlying mechanisms remain elusive, our results support the hypothesis that left-handedness is related to increased risk of breast cancer,” said the authors.

Risk factors such as social and economic status, smoking habits, family history and reproductive history were also recorded.

But the results showed that adjusting for risk factors made no difference to the increased chances of left-handed women contracting the disease.

The risk increased to 1.39 times that for right-handed women overall and 2.41 times for premenopausal cancer.

“This risk is compatible with left handedness being a marker of constitutional risk rather than of environmental risk as with postmenopausal breast cancer.”

The cause of left-handedness has previously been attributed to the hormone diethylstilbestrol and the authors suggest that this may also be responsible for the increased risk of breast cancer.

fonte

Visitado em 17/06/07

 

Biology determines handedness in chimps, study finds

What makes a chimpanzee left-handed–nature or environmental influences? Mostly nature, according to a recent study of chimp mothers and infants.

That result refutes past animal research, which suggested that behavioral reinforcement and other external factors largely determine animals’ hand–or paw–preferences. In contrast, this study from Emory University’s Yerkes Regional Primate Research Center found that a chimp’s preference for right or left stems mainly from birth order and genes.

To reach that conclusion, researchers Bill Hopkins, PhD, and Jeremy Dahl, PhD, investigated hand preference in a group of 134 mother-infant pairs and a group of 155 sibling pairs. In the first sample, the researchers placed first-born and sixth-born infants in one group at “high risk” for being left-handed. They placed the rest of the infants in a “low risk” group and determined the handedness of babies in both groups.

They theorized that the early- and late-born babies were more likely to favor their left hands due to hormonal fluctuations, birth trauma and other developmental instability associated with first and later pregnancies.

As expected, they found that more of the babies of right-handed mothers–86 percent–were right-handed in the low-risk group, while slightly more of the babies of right-handed mothers–54 percent–were left-handed in the high-risk group

“We found that left-handedness is atypical in chimps,” says Hopkins. “And the fact that chimpanzees’ socioeconomic status is identical indicates that the explanation for handedness is biological.”

To further probe for a biological basis of handedness, the researchers examined handedness among pairs of chimp siblings. That study also revealed that–independent of being first- or sixth-born and regardless of being reared together or apart–siblings tended to favor the same hand as one another, indicating “the genetics of their handedness is very strong,” says Hopkins.

What might these findings suggest about humans? Probably that biology plays a major role in human handedness too, but that culture has mediated that, says Hopkins. Where as more than a third of chimpanzees are left-handed, only about 10 to 20 percent of people are, likely because right-handedness is taught and valued in human society, he says.

“The point is that what we see in chimps is truly biological,” says Hopkins, whose findings are published in the current issue of Psychological Science (Vol. 12, No. 4). “What we see in humans is biology plus culture.”

–B. MURRAY

Visitado em 17/06/07

fonte

A guide to left-handed computing

Lefties can feel disadvantaged in the world of computing, but we’ve got some tips and tweaks to help them get ahead
Leo Waldock, Computeractive 12 Apr 2005

There are eight chances in nine that you are right-handed, and if you are, you will probably never have considered the problems faced by the one in nine of computer users who are left-handed.

So imagine that the vast majority of products you use with your computer, from the mouse and keyboard to the software, have been developed with somebody else in mind; a right-handed somebody else.

Take a quick look at the set-up of a typical PC and the problems faced by left-handed users become a little clearer.

The mouse may well be designed to fit comfortably in the palm of the right hand and the integrated number pad on the keyboard will almost certainly be situated on the right-hand side. The backspace and return buttons are also located in a position that will favour a right-handed user.

Most keyboards have the short cuts for Cut (Ctrl+C), Paste (Ctrl+V), Undo (Ctrl+Z) and the like set up for activation with the left hand. This means that the left-hander is likely to have to leave their left hand hovering over the keyboard while using the mouse with their right hand.

This is usually only a minor inconvenience until it’s time for a creative job such as drawing a picture, which will necessitate moving the mouse back to the left hand, particularly if you want to combine mouse navigation with shortcut activation simultaneously.

As for digital cameras, every model is a right-handed design. Suddenly, it becomes clear that the needs of the 11 per cent of women and 13 per cent of men in the UK who are left-handed are not being sufficiently catered for.

The shape of things
While this may seem like just an inconvenience, for left-handed users there are other implications. It is generally accepted that your PC should be set up in the most comfortable configuration possible. The set-up should promote ease of use in order to make your computing experience as pleasant as possible and to avoid putting unnecessary strain on hands and arms when using your computer for prolonged periods of time or performing repetitive movements such as typing.

Feedback from left-handed Computeractive readers highlights mouse usage as a particular problem for left-handers. “As a left-hander, I was disappointed with the mouse I recently bought, which is designed for a right-handed person in terms of its shape and the location of additional buttons on the side,” explains reader Anne Lloyd.

“When I first used this mouse I found it very uncomfortable and I kept pressing the buttons accidentally. As a result, I am an accidental trigger-happy killer of my comrades on Counter Strike 2. I haven’t seen anything that impresses me, as left-handed products are very hard to come by.”

Peripherals manufacturers, such as Logitech, acknowledge that there is a problem. Sylvain Sauvage, Logitech’s usability specialist, agrees that a product such as a mouse should fit with the user rather than the user having to adapt to the mouse.

“It is commonly estimated that around 10 per cent of people are left-handed. However, when it comes to mouse usage, surveys indicate that only two per cent of people use their mouse on the left side of the keyboard. Clearly a large proportion of left-handers are using their mouse as a right hander,” she explains.

This means that the vast majority of left-handed users are struggling to fit with the right-handed computer usage model. As we have discussed, having to use a mouse designed for a right-handed user will throw up a range of problems for the left-hander.

Hand to hand
One solution adopted by manufacturers such as Logitech is to create ambidextrous products that can be used by either a right- or left-handed user. The diNovo Cordless Desktop for Notebooks set from Logitech (£99) not only has an ambidextrous cordless optical mouse allowing the user to have it on either the right or left of the keyboard, but has a separate MediaPad, incorporating a number pad, which can be placed anywhere a user likes around the keyboard.

Microsoft adopts a similar approach to its product development. Mike Haigh, hardware product marketing manager for the Home and Retail Division at Microsoft, tells us: “Currently all our products are ambidextrous with the exception of the Intellimouse Explorer model which is right-handed only.

“Currently we have no left-hand specific products as we prefer most of our mice to be ambidextrous so they can be used by anyone. In our own studies we found that, although a significant proportion of the population is left-handed, a large proportion of these actually use the mouse with their right hand.”

He adds that given that only around a tenth of the potential market for Microsoft’s products is left-handed, the company has no plans to start developing products aimed specifically at the left-handed user.

While ambidextrous mouse designs will certainly alleviate many of the usability problems encountered by left-handed users, some issues still remain. In a basic two-button mouse design, the buttons can usually be remapped for left-handed users so that the left mouse button performs the functions usually performed by the right and vice versa (we’ll come on to how to do this in just a moment).

The optional supplementary buttons located in the sculpted area housing the thumb when you hold a mouse with your right hand are still effectively out of bounds for left-handed users, however.

Learn to adapt
The scope for adapting physical computing equipment such as a mouse may be limited, but the keyboard shortcuts in many popular programs can be changed to better suit the left-handed user. This is possible in Word and PowerPoint, although not in Excel.

To change keyboard shortcuts in Word, for example, select Customize from the Tools menu, choose the Commands tab and then click on the Keyboard button. The Categories box on the left of this dialogue box allows you to browse commands by type and you can select specific commands in the Commands box to the right of this.

To change the Paste (Ctrl+V) shortcut, for example, select Edit in the Categories box, then scroll down to the EditPaste option in the Commands box. The current shortcut will be displayed in the Current Keys box. To change it, click in the Press New Shortcut Key box and perform the shortcut you wish to assign to this function, now click on Assign.

Remapping the index and middle finger buttons of an ambidextrous mouse is pretty straightforward in Windows XP, even though the settings you need to alter are tucked away. Select Windows Control Panel from the Start menu. If Windows is set to Classic View, you’ll need to click on the Switch to Category View option to the left of the Control Panel window.

Now click on Themes and Appearances. Click on the Mouse Pointers option to the left of this window and select the Buttons tab, then check the box labelled Switch primary and secondary buttons. Then click on OK.

For some users, it may be better to dispense with the mouse altogether to perform certain tasks. Chris Boba, associate product manager at Corel UK tells us that Corel has a long-standing relationship with graphics tablet manufacturer Wacom as it feels that the best way to use its graphics packages is with a tablet, rather than a mouse. This is especially true for left-handed users who are struggling to use a mouse designed for a right-handed user.

The latest Wacom Intuos3 tablet (£358) has five buttons on the top left and the top right, and it is possible to remove your most common shortcuts in Painter IX (£296) from the keyboard and map them to the tablet. Chris tells us that it is no coincidence that the nine-fingered hand on the box of Corel Painter IX is a left hand.

The combined price of Corel’s Painter IX and Wacom’s graphics tablet represents a very expensive investment, though, and there are more affordable options that left-handed users can explore to make computing a more comfortable experience.

If you have the necessary £99 for a new Logitech diNovo desktop set, you’ll find the answers to some of your problems. The diNovo has a separate number pad which doubles up as a remote control for music playback, so the keyboard is a little more left-hand friendly than other designs and the mouse is an ambidextrous design which will better suit left-handers.

Other ambidextrous mice include Microsoft’s aesthetically pleasing Starck Optical Mouse (£40), Wireless Notebook Optical Mouse (£40) and Logitech’s Cordless Optical Mouse for Notebook (£30).

It is possible to buy a dedicated mouse developed specifically with left-handed users in mind, although these are admittedly relatively rare. The Anything Left Handed shop in London sells a left-handed keyboard and mouse on its website. These are tucked away in the Miscellaneous section of the site and cost £91 and £79 respectively.

Stay in the game
When it comes to PC games the left-hander will have to choose carefully. Many games use the mouse and keyboard simultaneously and we’ve already established that this presents a number of issues for the left-hander.

Flight simulators often use a joystick but these can also be a nightmare for the left-hander. While the basic joystick and thumb controls won’t be problematic for the left-handed gamer, the thumb button, throttle control and extra buttons are most likely to be placed on the left, exactly where the right-hander wants them but of little use to the left-hander.

A gamepad such as the Logitech Cordless Rumblepad2 (£30) is a better choice for left-handers. Although the eight-way directional control is on the left and the four buttons are on the right, most of the controls are quite symmetrical, and you’ll find that every control can be configured in the game set-up.

It’s no coincidence that the gamepad is used on every serious gaming console and a wireless model from Logitech does away with the annoying control cable.

The third type of gaming controller is the steering wheel, which is used, of course, for driving games. A decent design will be completely symmetrical, although there is likely to be a gear change lever on the right, which messes things up. Ironically, the right-hand-side gear change lever commonly included in gaming steering wheels is usually on the right, which is the wrong side for us Brits, so most games support the use of fingertip controls instead.

Left leaning
Life isn’t easy when you’re a left-handed computer user but by knowing where to buy the correct products and how best to set them up, it’s possible to make the experience of using a computer more efficient and more comfortable.

It would be unfair to say that left-handers are discriminated against by the PC industry today but neither are they given due consideration. Many left-handers have learned to adapt to using right-handed equipment in all walks of life, including the world of IT, but it doesn’t need to be that way.

Remember, we’re talking about a significant part of the population, so perhaps it’s time the manufacturers started marking their products with a left-hand-friendly logo.

Fonte: http://www.vnunet.com/features/1162410

Visitado em 17/06/07