tag:theconversation.com,2011:/ca/topics/handedness-26051/articlesHandedness – The Conversation2021-03-29T19:04:24Ztag:theconversation.com,2011:article/1555482021-03-29T19:04:24Z2021-03-29T19:04:24ZCurious Kids: why are some kids left-handed and others are right-handed?<figure><img src="https://images.theconversation.com/files/392148/original/file-20210329-17-bw9avh.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4288%2C2848&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><strong>Why are some kids left-handed and others are right-handed? — Sofia, aged 8</strong></p>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Hi Sofia, thanks for your great question!</p>
<p>For a lot of human history, lefties have been seen as a little odd, and unfortunately some have even been treated very badly. For example, the word “sinister” <a href="https://www.merriam-webster.com/dictionary/sinister">comes from</a> the Latin for “left” or “left hand”.</p>
<p>Luckily, some cultures have been more kind. The Inca, an old civilisation from South America, thought left-handed people had <a href="https://www.independent.co.uk/voices/comment/why-are-left-handed-people-so-brilliant-8919135.html">special spiritual powers</a>. Also, it was good luck to be left-handed <a href="https://www.independent.co.uk/voices/comment/why-are-left-handed-people-so-brilliant-8919135.html">among the North American Zuni peoples</a>. To be clear — there’s nothing wrong with being left-handed!</p>
<p>This preference for a particular hand is known as “handedness” and can be seen across many parts of the world.</p>
<p>Interestingly, only around <a href="https://psycnet.apa.org/record/2020-23033-001">one in ten</a> people are left-handed. This means there are probably two or three kids in your class who will use their left hand to throw a ball or draw a picture.</p>
<p>It seems humans throughout history have preferred to use our right hand instead of our left. <a href="https://pubmed.ncbi.nlm.nih.gov/30097196/">Evidence suggests</a> our ancestors tended to use their right hand for tasks, perhaps like throwing rocks or picking berries, as far back as seven million years ago!</p>
<h2>Why do we prefer one hand over another?</h2>
<p>Sticking to one hand while writing a letter, drawing a picture, or throwing a ball <a href="https://journals.sagepub.com/doi/abs/10.2466/pms.1977.45.3f.1041">helps</a> make you better at performing those tasks.</p>
<p>Constantly swapping hands may mean the brain takes longer to learn how to do those things, so your brain tells you to favour a particular hand.</p>
<p>It’s also the reason why you probably prefer using a particular foot when kicking a ball. Remember, the more you kick with that foot, the better you become at kicking.</p>
<p>But it’s not just our hands and feet that we prefer one side over another when performing a task — even our brain does this!</p>
<figure class="align-center ">
<img alt="An illustration of the human brain" src="https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392149/original/file-20210329-13-1k2b0a7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The human brain has two big parts. One on the left, and one on the right! Certain abilities are linked with one side of the brain.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>For example, your abilities to speak, do maths, and paint a picture prefer to sit on one side of the brain compared to the other.</p>
<p>Amazingly, the hand you use to write or throw a ball is often related to the side of the brain you use to speak. For example, if you use the left side of the brain to speak, you will likely be right-handed and the opposite is also true.</p>
<p>This relationship between brain function and handedness seems to be the reason why some people are left-handed, and some are right-handed. </p>
<h2>When do we become left-handed or right-handed?</h2>
<p>Which hand you use is not a choice. Rather, it’s a mixture of your genes which you get from your parents, and also your life experience. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-are-cells-made-out-of-142728">Curious Kids: what are cells made out of?</a>
</strong>
</em>
</p>
<hr>
<p>Interestingly, identical twins, who share exactly the same genes, don’t always share the same handedness.</p>
<p>Most parents can begin to tell which hand their kid prefers <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1467-7687.2009.00850.x">by around two years of age</a>. </p>
<p>However, scientists can accurately predict whether you will be left or right-handed <a href="https://pubmed.ncbi.nlm.nih.gov/9705063/">before you</a> <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/dev.21119">are even born</a>! By measuring which arm moves the most in babies still living in their mum’s womb, they can determine which hand you will prefer when you are born.</p>
<p>For now, even though lefties make up around 10% of the population, there are reasons to celebrate: August 13 is officially Left-handers Day! So, who’s got the upper hand now?</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p><img src="https://counter.theconversation.com/content/155548/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It’s a mixture of your genes which you get from your parents, and also your life experience.Matthew Barton, Senior lecturer, School of Nursing and Midwifery, Griffith UniversityMichael Todorovic, Senior Lecturer, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1467652020-09-28T19:59:08Z2020-09-28T19:59:08ZThere’s no single gene for left-handedness. At least 41 regions of DNA are involved<figure><img src="https://images.theconversation.com/files/360180/original/file-20200928-22-12vzevi.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4288%2C2843&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Most people consistently use the same hand to do tasks that require skill and control such as writing or threading a needle. We know genetics plays a big part in which hand a person prefers, but it has been difficult to identify the exact genes responsible. </p>
<p>To find out more, we <a href="https://doi.org/10.1038/s41562-020-00956-y">analysed</a> the DNA of more than 1.7 million people and discovered 41 regions of the genome associated with being left handed and another seven associated with being ambidextrous.</p>
<h2>What makes people left-handed?</h2>
<p>About 88% of people prefer to use their right hand for complex tasks, around 10% prefer their left hand, and the other 2% report they do not have a preference and can use either hand. Hand preference develops so early that it can be seen <a href="https://www.sciencedirect.com/science/article/abs/pii/S0028393204002428">in the womb</a>. </p>
<p>Handedness tends to stabilise around the time children are learning to draw. In the absence of injury or training it remains constant throughout life. Evidence from historic human populations suggests it has been this way for <a href="https://www.tandfonline.com/doi/abs/10.1080/1357650X.2010.529451">hundreds of thousands of years</a>.</p>
<p>Research examining patterns of handedness in twins and families shows most of the variation is down to non-genetic factors, such as training and the environment in which we gain early motor skills. However, genetics does play <a href="https://www.sciencedirect.com/science/article/abs/pii/S0028393208003722">a significant role</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ive-always-wondered-can-animals-be-left-and-right-pawed-83716">I've always wondered: can animals be left- and right-pawed?</a>
</strong>
</em>
</p>
<hr>
<h2>There is no single gene for handedness</h2>
<p>Since the mid-1980s more than 100 journal articles have explored the idea that a single gene might influence handedness. These <a href="https://books.google.com.au/books/about/Left_Right_Hand_and_Brain.html?id=3Y4oAAAAYAAJ&redir_esc=y">theories</a> suggested one variant of the gene would bias an individual towards right-handedness, while the alternate variant led to handedness being randomly determined.</p>
<p>While there have been many theories attempting to explain different human characteristics via single genes, in recent years we have discovered that the reality is often much more complicated. More recent research uses <a href="https://www.genome.gov/about-genomics/fact-sheets/Genome-Wide-Association-Studies-Fact-Sheet">genome-wide association studies</a> (GWAS) to look for a relationship between a trait of interest and the number of copies of a genetic variant someone has. These analyses are run for millions of variants located across the genome. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-much-junk-is-in-our-dna-53929">How much ‘junk’ is in our DNA?</a>
</strong>
</em>
</p>
<hr>
<p>These genome-wide studies have shown that almost all human traits are influenced by many hundreds or thousands of genetic variants. Often these variants are located between genes whose purpose is not clearly identifiable, in what used to be called “junk DNA”. </p>
<p>GWAS has also shown most traits are influenced by large numbers of genes which each contribute a very small effect, rather than a single gene which has a large effect. To track these small effects, large collaborative studies with many participants are required in order to identify the individual genetic variants involved.</p>
<h2>What GWAS reveals about handedness</h2>
<p>In 2009 we started a project involving researchers from around the world to hunt for genetic variants that influence handedness using GWAS. We did not recruit participants based on their handedness, so the number of left-handed people was relatively small. As a result, we have only recently gathered enough to undertake robust analyses.</p>
<p>Our <a href="https://doi.org/10.1038/s41562-020-00956-y">study</a> brought together analyses of data from 1,766,671 people. Of these people, 194,198 were left-handed and 37,637 were ambidextrous. We found 41 regions of the genome associated with left-handedness and seven regions associated with ambidexterity. </p>
<p>Many of the regions of the genome associated with left-handedness contained genes that code for microtubule proteins. These proteins play important roles during development in the migration of neurons and in the ability of the brain to adapt to changes in the environment. </p>
<figure class="align-center ">
<img alt="A young girl writing on a blackboard with both hands at the same time." src="https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=475&fit=crop&dpr=1 600w, https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=475&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=475&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=597&fit=crop&dpr=1 754w, https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=597&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/360210/original/file-20200928-18-wngw1n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=597&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Only around 2% of people are ambidextrous, and it may be caused by completely different genes than those responsible for left-handedness.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Interestingly, genes that influence <a href="https://www.theguardian.com/science/blog/2016/sep/08/situs-inversus-and-my-through-the-looking-glass-body">other asymmetries</a> in the body, such as <a href="https://rarediseases.info.nih.gov/diseases/6268/dextrocardia-with-situs-inversus">which side</a> of the body <a href="https://rarediseases.info.nih.gov/diseases/4883/situs-inversus">the heart</a> is located on, were not associated with handedness in our study.</p>
<p>Another important finding was that there was little overlap between the regions of the genome associated with left-handedness and those associated with ambidexterity. This suggests that ambidexterity is more complicated than we previously thought. The mechanisms that influence the <em>direction</em> of hand preference might be different from those that influence the <em>degree</em> of hand preference. </p>
<p>These findings give us promising new leads but more work is needed to identify further genetic variants that influence handedness. There is also a long way to go before we understand how these variants play a role in someone becoming right-handed, left-handed or ambidextrous.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-there-life-through-the-looking-glass-the-riddle-of-lifes-single-handedness-48819">Is there life through the looking-glass? The riddle of life's single-handedness</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/146765/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Evans receives funding from the National Health and Medical Research Council of Australia and the Wellcome Trust. </span></em></p><p class="fine-print"><em><span>Sarah Medland receives funding from the Australian National Health and Medical Research Council and the Medical Research Future Fund. </span></em></p>A study of more than 1.7 million people has revealed 41 distinct genetic regions associated with left-handedness, and another 7 tied to ambidexterity.David Evans, Professor of Statistical Genetics, The University of QueenslandSarah Medland, Cordinator Mental Health Research Program, QIMR Berghofer Medical Research InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1217112019-08-12T14:55:19Z2019-08-12T14:55:19ZBeing left-handed doesn’t mean you are right-brained – so what does it mean?<figure><img src="https://images.theconversation.com/files/287689/original/file-20190812-71909-1c4xhk5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/left-handed-man-writing-on-notebook-1463607707">Wachiwit/Shutterstock</a></span></figcaption></figure><p>There have been plenty of claims about what being left-handed means, and whether it changes the type of person someone is – but the truth is something of an enigma. Myths about handedness appear year after year, but researchers have yet to uncover all of what it means to be left-handed.</p>
<p>So why are people left-handed? The truth is we don’t fully know that either. What we do know is that only <a href="https://www.livescience.com/19968-study-reveals-lefties-rare.html">around 10% of people</a> across the world are left-handed – but this isn’t split equally between the sexes. About 12% of men are left-handed but <a href="https://psycnet.apa.org/record/2008-11487-004?doi=1">only about 8% of women</a>. Some people get very excited about the 90:10 split and wonder why we aren’t all right-handed. </p>
<p>But the interesting question is, why isn’t our handedness based on chance? Why isn’t it a 50:50 split? It is not due to handwriting direction, as left-handedness would be dominant in countries where their languages are written right to left, which it is not the case. Even the genetics are odd – only about <a href="https://theconversation.com/how-childrens-brains-develop-to-make-them-right-or-left-handed-55272">25% of children</a> who have <a href="https://psycnet.apa.org/record/1993-98645-005">two left-handed parents</a> will also be left-handed.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-childrens-brains-develop-to-make-them-right-or-left-handed-55272">How children's brains develop to make them right or left handed</a>
</strong>
</em>
</p>
<hr>
<p>Being left-handed has been linked with all sorts of bad things. Poor health and early death are often associated, for example – but neither are exactly true. The latter is explained by many people in older generations being <a href="https://www.sciencedirect.com/science/article/pii/002839329390156T">forced to switch</a> and use their right hands. This makes it look like there are less left-handers at older ages. The former, despite being an appealing headline, <a href="https://journals.sagepub.com/doi/full/10.1177/2398212818820513">is just wrong</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TGLYcYCm2FM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Positive myths are also abound. People say that left-handers are more creative, as most of them use their “right brain”. This is perhaps one of the more persistent myths about handedness and the brain. But no matter how appealing (and perhaps to the disappointment of those lefties still waiting to wake up one day with the <a href="https://www.sciencedirect.com/science/article/pii/S0278262604000612">talents of Leonardo da Vinci</a>), the general idea that any of us use a “dominant brain side” that defines our personality and decision making <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0071275">is also wrong</a>.</p>
<h2>Brain lateralisation and handedness</h2>
<p>It is true, however, that the brain’s <a href="https://courses.lumenlearning.com/waymaker-psychology/chapter/the-brain-and-spinal-cord/">right hemisphere controls the left side of the body</a>, and the left hemisphere the right side – and that the hemispheres do actually have specialities. For example, language is usually processed a little bit more within the left hemisphere, and recognition of faces a little bit more within the right hemisphere. This idea that each hemisphere is specialised for some skills is known as brain lateralisation. However, the halves do not work in isolation, as a thick band of nerve fibres – called the corpus callosum – connects the two sides.</p>
<p>Interestingly, there are some known differences in these specialities between right-handers and left-handers. For example, it is often cited that around 95% of right-handers are “left hemisphere dominant”. This is not the same as the “left brain” claim above, it actually refers to <a href="https://www.tandfonline.com/doi/abs/10.1080/09647049609525672">the early finding</a> that most right-handers depend more on the left hemisphere for speech and language. It was assumed that the opposite would be true for lefties. But this is not the case. In fact, <a href="https://www.frontiersin.org/articles/10.3389/fpsyg.2014.01128/full">70% of left-handers</a> also process language more in the left hemisphere. Why this number is lower, rather than reversed, is as yet unknown.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-is-life-left-handed-the-answer-is-in-the-stars-44862">Why is life left-handed? The answer is in the stars</a>
</strong>
</em>
</p>
<hr>
<p>Researchers have found many other brain specialities, or “asymmetries” in addition to language. Many of these are specialised in the right hemisphere – in most right-handers at least – and include things such as face processing, spatial skills and perception of emotions. But these are understudied, perhaps because scientists have incorrectly assumed that they all depend on being in the hemisphere that isn’t dominant for language in each person. </p>
<p>In fact, this assumption, plus the recognition that a small number of left-handers have unusual right hemisphere brain dominance for language, means left-handers are either ignored – or worse, actively avoided – <a href="https://www.nature.com/articles/nrn3679">in many studies of the brain</a>, because researchers assume that, as with language, all other asymmetries will be reduced.</p>
<p>How some of these functions are lateralised (specialised) in the brain can actually influence how we perceive things and so can be studied using simple perception tests. For example, in my research group’s <a href="https://doi.org/10.1080/1357650X.2019.1652308">recent study</a>, we presented pictures of faces that were constructed so that one half of the face shows one emotion, while the other half shows a different emotion, to a large number of right-handers and left-handers. </p>
<p>Usually, people see the emotion shown on the left side of the face, and this is believed to reflect specialisation in the right hemisphere. This is linked to the fact that visual fields are processed in such a way there is a bias to the left side of space. This is thought to represent right hemisphere processing while a bias to the right side of space is thought to represent left hemisphere processing. We also presented different types of pictures and sounds, to examine several other specialisations. </p>
<p>Our findings suggest that some types of specialisations, including processing of faces, do seem to follow the interesting pattern seen for language (that is, more of the left-handers seemed to have a preference for the emotion shown on the right side of the face). But in another task that looked at biases in what we pay attention to, we found no differences in the brain-processing patterns for right-handers and left-handers. This result suggests that while there are relationships between handedness and some of the brain’s specialisations, there aren’t for others.</p>
<p>Left-handers are absolutely central to new experiments like this, but not just because they can help us understand what makes this minority different. Learning what makes left-handers different could also help us finally solve many of the long-standing neuropsychological mysteries of the brain.</p><img src="https://counter.theconversation.com/content/121711/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emma Karlsson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>10% of people are left-handed but we still haven’t uncovered how this changes the way their brains work.Emma Karlsson, Postdoctoral researcher in Cognitive Neuroscience, Bangor UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/879482017-11-29T20:37:00Z2017-11-29T20:37:00ZUnderstanding children’s mirror writing<figure><img src="https://images.theconversation.com/files/195797/original/file-20171122-6055-tk1mv6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">file ubn</span> <span class="attribution"><a class="source" href="https://visualhunt.com/f2/photo/1059067259/cd6aca5fb5/">Marin Dacos/VisualHunt</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>In recent studies we have been investigating mirror writing by typical 4- to 6-year-old children. The term is used because the characters – numbers and capital letters – are reversed, yet are correct when looked at in a mirror. In the case of standard writing, the mirror must be placed to the right or to the left, perpendicular to the horizontal plane of writing. There can also be vertical mirror writing, which look correct if we look at them in a mirror placed below or above.</p>
<p>At first one might think that children, who often sit face-to-face in kindergarten, reverse the characters because they see them on the sheet of the child who faces them. But this is not so because such an origin of reversal would lead children to double mirror writing – reversed both horizontally and vertically (see Figure 1).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=278&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=278&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=278&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=349&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=349&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195798/original/file-20171122-6061-1ez630m.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=349&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Figure 1: Mirror-written French-style numbers digits (except 0 and 8).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The origin of the horizontal mirror writings – particularly impressive when the letters are in cursive and thus attached, see the writing of Joséphine in Figure 2 – has long remained a mystery. But it can be slightly disconcerting as well because children spontaneously produce writings they have never seen before and certainly didn’t learn. The American linguist <a href="https://en.wikipedia.org/wiki/Noam_Chomsky">Noam Chomsky</a> has essentially used such an argument – that children make sentences they have never heard (nor read, of course) – to support the notion that language is <a href="https://en.wikipedia.org/wiki/Innateness_hypothesis">innate</a>. On the contrary, we will see here how the horizontal mirror writing of the characters is explained by the culture, within the constraints imposed by the cerebral processing.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=65&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=65&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=65&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=81&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=81&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195799/original/file-20171122-6039-100ac87.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=81&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mirror writing of their name by two right-handed children, aged 5 years, 5 months and 5 years, 7 months (spontaneously, but under some spatial constraints).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Mirror writing entered the scientific literature with an article of the German neurologist Alfred Buchwald in 1878 (in German, mirror writing is called <em>Spiegelschrift</em>), but over the following 125 years the explanations for the phenomenon were not only insufficient but also often wrong. One of the main reasons for the explanations’ failure is that they often involved a “culprit” – writing with the left hand. For a long time, this dominant discourse was supported by the observation of left-handed children writing reverse characters, their names or even whole words and sentences. Thus throughout the 20th century, scientific journals have published mirror writing almost exclusively produced by left-handed children. Even today, left-handedness is often the favourite explanation of teachers when children produce mirror writing.</p>
<h2>Cerebral and behavioural components</h2>
<p>The explanation we find for the phenomenon of mirror writing of characters works on two successive levels, the first cerebral and the second behavioural. The cerebral level was long been limited to the simplistic 1925 theory by <a href="https://en.wikipedia.org/wiki/Samuel_Orton">Samuel Orton</a> that one of the cerebral hemispheres (usually the left) would correctly represent the letters while the other would represent them in mirror. More recently, however, it has been shown that the brain eliminates orientation (left or right) when storing images, a process called <a href="http://www.jle.com/fr/revues/nrp/e-docs/la_magie_computationnelle_de_la_voie_ventrale_a_href_xref_note_fn1_name_xref_cite_fn1_1_est_elle_a_lorigine_de_linversion_des_lettres_et_des_chiffres_chez_lenfant_de_cinq_a_six_ans__303540/article.phtml">symmetrisation</a> or <a href="http://readinginthebrain.pagesperso-orange.fr/figures">mirror generalization</a>. This mirror-generalization process, which can be very useful – for example, to recognise a face by both its left and right profiles – leads children aged 5 to know, from memory, the shape of the characters, but not their left/right orientation. Given the features of the process – horizontal mirror in the visual modality – it is important to note that the initial implicit learning of the form of the characters by the children is mainly visual, and that the children produce almost exclusively horizontal mirror writing.</p>
<p>At the behavioural level, when children write the characters from memory, they must give them an orientation. In countries whose primary languages are written in Latin characters – written from left to right – children most often point them toward the right. This leads them to reverse mainly the left-oriented characters: J, Z, 1, 2, 3, 7, and 9 will be considerably more reversed than other characters (see Figure 3). However, when spatial constraints cause them to write from right to left, the children instead reverse the right-oriented letters (see the E, N, and C of <em>MAXENCE</em> in Figure 2). This suggests that children usually orient characters in the direction of their writing.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=81&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=81&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=81&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=102&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=102&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195800/original/file-20171122-6055-135dcb5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=102&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Figure 3: Writing of a series of characters by a right-handed child, 6 years and 2 months old.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Since this explanation has nothing to do with the handedness of the children, it can be predicted that right-handed children will reverse characters almost often as left-handed children, and that – left-handed or right-handed – children will primarily reverse left-oriented characters in Western culture. This prediction was confirmed in a <a href="https://www.ncbi.nlm.nih.gov/pubmed/26333384">2016 study</a>, as was another subtle <a href="https://www.sciencedirect.com/science/article/pii/S0885201416300119">prediction</a>: children who reverse left-oriented characters the most are also those who reverse the right-oriented characters the least. This because they strictly orient the characters in the direction of writing.</p>
<p>Our explanation is supported by an analysis of tens of thousands writing samples from more than a thousand children that was published in different journals, notably in the <a href="http://psycnet.apa.org/doiLanding?doi=10.1037%2Fa0025735"><em>Journal of Educational Psychology</em></a>. The <a href="https://link.springer.com/article/10.1007/s11145-016-9688-y">theory</a> remains relatively unknown, perhaps due to its recency, and some parents continue to wonder if mirror writing by their children might be the precursor of a disorder such as dyslexia. And some paediatricians or occupational therapists today still have no answer other that suggest thwarted left-handedness or a bad lateralization in the child, neither of which are supported by our research on typical developing children.</p><img src="https://counter.theconversation.com/content/87948/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jean-Paul Fischer ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Spontaneous mirror writing by both left- and right-handed children has long remained a mystery. Recent studies of brain processing and writing have led to an unexpected explanation.Jean-Paul Fischer, Professeur émérite de psychologie, Université de LorraineLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/837162017-09-24T20:03:21Z2017-09-24T20:03:21ZI’ve always wondered: can animals be left- and right-pawed?<figure><img src="https://images.theconversation.com/files/186153/original/file-20170915-16298-1p6agw1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Southpaws seem to be more common among cats and dogs than humans.</span> <span class="attribution"><span class="source">Eric Isselee/Shutterstock.com</span></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
<hr>
<blockquote>
<p><strong>While watching my cat engaging in yet another battle with my shoelace, I noticed that he seemed mainly to use his left front paw. Do animals have a more dextrous side that they favour for particular tasks, just like humans? – Mike, Perth.</strong></p>
</blockquote>
<hr>
<p>The short answer is: yes they do! Like humans, many animals tend to use one side of the body more than the other. This innate handedness (or footedness) is called behavioural or motor laterality. </p>
<p>The term laterality also refers to the primary use of the left or right hemispheres of the brain. The two halves of the animal brain are <a href="http://www.rightleftrightwrong.com/brain.html">not exactly alike</a>, and each hemisphere differs in function and anatomy. In general terms, the left hemisphere controls the right side of the body and the right hemisphere controls the left side. </p>
<p>Laterality is an ancient inherited characteristic and is widespread in the animal kingdom, in both vertebrates and invertebrates. Many <a href="http://www.rightleftrightwrong.com/theories.html">competing theories</a> (neurological, biological, genetic, ecological, social and environmental) have been proposed to explain how the phenomenon developed, but it remains largely a mystery. </p>
<h2>Animal ‘handedness’</h2>
<p>Humans tend to be right-handed. Lefties or “southpaws” make up <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3927078/">only about 10% of the human population</a>, and <a href="http://psycnet.apa.org/doiLanding?doi=10.1037/a0012814">more males than females are left-handed</a>.</p>
<p>Great apes show <a href="http://www.sciencedirect.com/science/article/pii/S0166432812006237?via%3Dihub">similar handedness patterns</a> to humans. Most chimps, for instance, <a href="http://video.nationalgeographic.com/video/news/chimps-right-hand-vin?source=relatedvideo">seem to be right-handed</a>. But not many studies have looked at laterality in non-primate animals. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-are-most-people-right-handed-the-answer-may-be-in-the-mouths-of-our-ancestors-69712">Why are most people right handed? The answer may be in the mouths of our ancestors</a>
</strong>
</em>
</p>
<hr>
<p>There is some evidence to suggest that <a href="http://www.sciencedirect.com/science/article/pii/S0376635702001614?via%3Dihub">dogs</a> and <a href="https://www.ncbi.nlm.nih.gov/pubmed/2265897">cats</a> can be right- or left-pawed, although the ratio seems to be more evenly split than in humans, and it is unclear whether there are sex differences. </p>
<p>If you’re a pet owner you can <a href="http://www.dailymail.co.uk/news/article-2195039/Is-pet-right-left-handed-The-test-uses-cheese-sofas-backdoor-out.html">do an experiment for yourself</a>. Which paw does your cat or dog lead with when reaching out for something, or to tap open a pet door?</p>
<p>To test your pet dog, you can place a treat-filled <a href="https://www.kongcompany.com/en-au/kong-101/kong-101/">Kong toy</a> directly in front of your dog and see which paw he or she uses to hold it to get the food out. A dog may use either paw or both paws.</p>
<p>To test your pet cat, you can set a “food puzzle” by putting a treat inside a glass jar and watching to see which paw your cat uses. Don’t forget to repeat it lots of times and take notes to see whether the effect is real or just random chance!</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ykb46flx47c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Don’t forget to repeat the experiment lots of times.</span></figcaption>
</figure>
<p>Horses also seem to <a href="http://www.equinescienceupdate.co.uk/mslat.htm">prefer to circle in one direction rather than the other</a>. Meanwhile, one study suggests that <a href="http://news.nationalgeographic.com/2015/06/150618-kangaroos-evolution-animals-science/">kangaroos are almost exclusively lefties</a>, although the neural basis for this is unknown. </p>
<h2>Lateralisation and brain function</h2>
<p>In humans, the left hemisphere is mainly associated with <a href="https://www.sciencedaily.com/releases/2014/07/140704134633.htm">analytical processes and language</a> and the right hemisphere with orientation, awareness and musical abilities, although this dichotomy is simplistic at best.</p>
<p>Is there evidence of lateralised brain function in non-human animals too? A team of Italian researchers think so. They found that dogs <a href="http://www.cell.com/current-biology/pdf/S0960-9822%2807%2900949-9.pdf">wag their tails to the right</a> when they see something they want to approach, and to the left when confronted with something they would rather avoid. This suggests that, just as for people, the right and left halves of the brain do different jobs in controlling emotions.</p>
<p>Laterality is also connected to the direction in which hair grows (so-called stuctural laterality), or even to the senses (sensory laterality). Many animals use they left eye and left ear (indicating right brain activation) more often than the right ones when <a href="http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0184933&type=printable">investigating objects that are potentially frightening</a>. However, asymmetries in olfactory processing (nostril use) are less well understood. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Research suggests most kangaroos are southpaws.</span>
<span class="attribution"><span class="source">Ester Inbar/Wikimedia Commons</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The left or right bias in sensory laterality is separate from that of motor laterality (or handedness). However, some researchers think that side preference is linked to the direction of hair whorls (“cow licks”), which can grow in a clockwise or anticlockwise direction. More right-handed people have a <a href="https://www.ncbi.nlm.nih.gov/pubmed/14504234">clockwise hair pattern</a>, although it is <a href="http://doctorbarkman.blogspot.com.au/2013/10/can-canine-hair-whorls-predict.html">unclear if this is true of other animals</a>. </p>
<p>The direction of hair growth and handedness are also related to temperament. Left-handed people might be <a href="http://onlinelibrary.wiley.com/doi/10.1002/jts.20222/pdf">more vulnerable to stress</a>, as are <a href="https://www.ncbi.nlm.nih.gov/pubmed/16893254">left-pawed dogs</a> and many other animals. In general, many animals, including humans, that have a clockwise hair whorl are less stress-prone than those with anticlockwise hair growth. The position of the hair whorl also matters; cattle and horses with hair whorls directly above the eyes are <a href="http://www.j-evs.com/article/S0737-0806%2815%2930055-1/pdf">more typically difficult to handle than those with whorls lower down on the face</a>. </p>
<p>Elsewhere in the animal kingdom, snails also have a form of laterality, despite having a very different nervous system to vertebrates like us. Their shells spiral in either a “right-handed” or “left-handed” direction – a form of physical asymmetry called “chirality”. This chirality is <a href="https://phys.org/news/2009-11-rightleft-handedness-snails-lab.html">inherited</a> – snails <a href="http://jeb.biologists.org/content/213/5/v.2">can only mate with matching snails</a>.</p>
<p>Chirality is <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692985/">even seen in plants</a>, depending on the asymmetry of their leaves, and the direction in which they grow.</p>
<p>As an aside, left-handedness has been discriminated against in many cultures for centuries. The Latin word <em>sinistra</em> originally meant “left” but its English descendant “sinister” has taken on meanings of evil or malevolence. The word “right”, meanwhile, connotes correctness, suitability and propriety. Many everyday objects, from scissors to notebooks to <a href="https://plus.google.com/+Vi0letAshes/posts/88cRFZbqZX4">can-openers</a>, are designed for right-handed people, and the Latin word for right, <em>dexter</em>, has given us the modern word “dextrous”.</p>
<h2>Why is the brain lateralised?</h2>
<p>One adaptive advantage of lateralisation is that individuals can perform two tasks at the same time if those tasks are governed by opposite brain hemispheres. Another advantage might be resistance to disease – hand preference in animals is associated with differences in immune function, with <a href="https://www.ncbi.nlm.nih.gov/pubmed/15265650">right-handed animals mounting a better immune response</a>.</p>
<p>Does it matter if your cat, dog, horse or cow favours one paw (or hoof) over another? Determining laterality – or which side of the brain dominates the other – could change the way domestic animals are bred, raised, <a href="http://www.abc.net.au/catalyst/stories/3465535.htm">trained and used</a>, including predicting which puppies will make the best <a href="http://www.sciencedirect.com/science/article/pii/S1090023311003649?via%3Dihub">service dogs</a>, and which racehorses will <a href="http://www.equinescienceupdate.co.uk/mslat.htm">race better on left- or right-curving tracks</a>. </p>
<p>And even if your dog or cat never clutches a pen, or uses one limb more than the other, just be grateful that they haven’t yet developed opposable thumbs!</p>
<hr>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em>This article is dedicated to the memory of Bollo the cat, who inspired this question but has since passed away.</em></p><img src="https://counter.theconversation.com/content/83716/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The animal kingdom is full of lefties and righties, although rarely is the ratio skewed as much as it is in humans. If you’re wondering about your own pet, you can find out with a simple experiment.Janice Lloyd, Senior Lecturer in Veterinary Behaviour, Welfare & Ethics, James Cook UniversityRichard Squires, Associate Professor of Companion Animal Medicine, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/790592017-06-14T09:33:07Z2017-06-14T09:33:07ZAre left-handed people more gifted than others? Our study suggests it may hold true for maths<figure><img src="https://images.theconversation.com/files/173409/original/file-20170612-9404-1m749h.jpg?ixlib=rb-1.1.0&rect=7%2C33%2C1583%2C845&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Barack Obama signs at his desk</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Barack_Obama_signs_at_his_desk2.jpg">Pete Souza</a></span></figcaption></figure><p>The belief that there is a link between talent and left-handedness has a long history. Leonardo da Vinci was left-handed. So were Mark Twain, Mozart, Marie Curie, Nicola Tesla and Aristotle. It’s no different today – former US president Barack Obama is a left-hander, as is business leader Bill Gates and footballer Lionel Messi. </p>
<p>But is it really true that left-handers are <a href="http://www.independent.co.uk/voices/comment/why-are-left-handed-people-so-brilliant-8919135.html">more likely to be geniuses</a>? Let’s take a look at the latest evidence – including <a href="http://journal.frontiersin.org/article/10.3389/fpsyg.2017.00948/full">our new study</a> on handedness and mathematical ability.</p>
<p>It is <a href="http://www.sciencedirect.com/science/article/pii/002839329290065T">estimated</a> that between 10% and 13.5% of the population are not right-handed. While a few of these people are equally comfortable using either hand, the vast majority are left-handed.</p>
<p>Hand preference is a manifestation of brain function and is therefore related to <a href="http://www.tandfonline.com/doi/abs/10.1080/13803395.2013.778231?journalCode=ncen20">cognition</a>. Left-handers exhibit, on average, <a href="http://www.rightleftrightwrong.com/brain.html">a more developed right brain hemisphere</a>, which is specialised for processes such as <a href="http://psychology.jrank.org/pages/545/Right-Brain-Hemisphere.html">spatial reasoning</a> and the ability to rotate <a href="https://en.wikipedia.org/wiki/Mental_rotation">mental representations</a> of objects. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=341&fit=crop&dpr=1 600w, https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=341&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=341&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=429&fit=crop&dpr=1 754w, https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=429&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/173420/original/file-20170612-9404-1diev1t.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=429&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The corpus callosum.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Corpus_callosum.png">Life Science Databases(LSDB)/wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Also, the corpus callosum – the bundle of nerve cells connecting the two brain hemispheres – tends to be <a href="http://science.sciencemag.org/content/229/4714/665.long">larger in left-handers</a>. This suggests that some left-handers have an enhanced connectivity between the two hemispheres and hence superior information processing. Why that is, however, is unclear. One theory argues that living in a world designed for right-handers could be forcing left-handers to use both hands – thereby increasing connectivity. This opens up the possibility that we could all achieve enhanced connectivity by training ourselves to use both hands.</p>
<p>These peculiarities may be the reason why left-handers seem to have an edge in several professions and arts. For example, they are over-represented among <a href="http://musicweb.hmtm-hannover.de/sightreading/Kopiez-etal(2006)NP-Laterality.pdf">musicians</a>, <a href="http://journals.lww.com/jonmd/Abstract/2007/10000/Creativity_and_Psychopathology__Higher_Rates_of.6.aspx">creative artists</a>, <a href="http://journals.sagepub.com/doi/abs/10.2466/pms.1977.45.3f.1216">architects</a> and <a href="https://www.researchgate.net/publication/6598587_The_role_of_domain-specific_practice_handedness_and_starting_age_in_chess">chess players</a>. Needless to say, efficient information processing and superior spatial skills are essential in all these activities.</p>
<h2>Handedness and mathematics</h2>
<p>But what about the link between left-handedness and mathematical skill? Unsurprisingly, the role played by handedness in mathematics has long been a matter of interest. More than 30 years ago, a seminal study claimed left-handedness <a href="http://www.sciencedirect.com.liverpool.idm.oclc.org/science/article/pii/0028393286900114">to be a predictor of mathematical precociousness</a>. The study found that the rate of left-handedness among students talented in mathematics was much greater than among the general population.</p>
<p>However, the idea that left-handedness is a predictor of superior intellectual ability has been challenged recently. Several scholars have claimed that left-handedness is not related to any advantage in cognitive skills, and may even exert detrimental effects on general cognitive function and, hence, academic achievement.</p>
<p>For example, one study discovered that left-handed children <a href="https://link.springer.com/article/10.1353/dem.0.0053">slightly under-performed</a> in a series of developmental measures. Also, a recent review <a href="http://www.sciencedirect.com/science/article/pii/S0149763415001712">reported</a> that left-handers appear to be slightly over-represented among people with intellectual disabilities. Another large study found that left-handers <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1467-985X.2012.01074.x/abstract">performed more poorly</a> in mathematical ability in a sample of children aged five to 14.</p>
<h2>Carefully designed experiment</h2>
<p>Interestingly, these past studies, just like many others, differed from each other in how handedness was measured and how participants were categorised – some of them simply asked people what their hand preference was in general. And, most importantly, they had different approaches to measuring mathematical ability – ranging from simple arithmetic to complex problem solving. These discrepancies in the experimental design may be the cause of the mixed observed results.</p>
<p>To get more reliable results, we decided to carry out a whole <a href="http://journal.frontiersin.org/article/10.3389/fpsyg.2017.00948/full">series of experiments</a> including more than 2,300 students (in primary school and high school). These experiments varied in terms of type and difficulty of mathematical tasks.</p>
<p>To assure comparability, we used the same questionnaire – <a href="http://www.sciencedirect.com/science/article/pii/0028393271900674">the Edinburgh Inventory</a> – to assess handedness in all the experiments. This questionnaire asks people which hand they prefer for writing, drawing, throwing, brushing and other things. It assesses to what extent someone prefers their right or left – it’s a scale rather than a categorical left versus right assessment. This specific feature allowed us to build more reliable and powerful statistical models. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/173426/original/file-20170612-10249-1nmc0gj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Could training to use both hands boost mathematical ability?</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Math_class_in_Da_Ji_Junior_High_School_2006-12-1.jpg">enixii/flickr</a></span>
</figcaption>
</figure>
<p>The results, published in Frontiers, show that left-handers outperformed the rest of the sample when the tasks involved difficult problem-solving, such as associating mathematical functions to a given set of data. This pattern of results was particularly clear in male adolescents. By contrast, when the task was not so demanding, such as when doing simple arithmetic, there was no difference between left- and right-handers. We also discovered that extreme right-handers – individuals who said they prefer to use their right hand for all items on the handedness test – under-performed in all the experiments compared to moderate right-handers and left-handers.</p>
<p>Left-handers seem to have, on average, an edge when solving demanding mathematical tasks – at least during primary school and high school. Also, being strongly right-handed may represent a disadvantage for mathematics. Taken together, these findings show that handedness, as an indicator of connectivity between brain hemispheres, does influence cognition to some extent.</p>
<p>That said, handedness is just an indirect expression of brain function. For example, only <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3258574/">a third</a> of the people with a more developed right hemisphere are left-handed. So plenty of right-handed people will have a similar brain structure as left-handers. Consequently, we need to be cautious in interpreting people’s hand preference – whether we see it as a sign of genius or a marker for cognitive impairment.</p><img src="https://counter.theconversation.com/content/79059/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Giovanni Sala receives funding from the University of Liverpool.</span></em></p><p class="fine-print"><em><span>Fernand Gobet receives funding from the University of Liverpool and is Research Associate at the Centre for Philosophy of Natural & Social Science, London School of Economics. He gets royalties from a number of books on expertise and talent.</span></em></p>People who have an extreme preference for using their right hand may be worse at maths, according to new research.Giovanni Sala, PhD Candidate - Cognitive Psychology, University of LiverpoolFernand Gobet, Professor of Decision Making and Expertise, University of LiverpoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/697122017-01-10T19:35:10Z2017-01-10T19:35:10ZWhy are most people right handed? The answer may be in the mouths of our ancestors<figure><img src="https://images.theconversation.com/files/152078/original/image-20170109-23468-nfbyxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How our ancestors ate could explain why today's humans are mostly right-handed. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/hugomartinsoliveira/14693903652/">Flickr/Hugo Martins</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Roughly <a href="https://www.scientificamerican.com/article/why-are-more-people-right/">90% of humans are right-handed</a> and this is one of the traits that separates us from most other primates who don’t really show any overall preference for left or right handedness.</p>
<p>It’s believed that handedness played an important role in human evolution, with a <a href="http://www.sciencedirect.com/science/article/pii/S0047248416300719">recent study</a> on the earliest evidence of right-handedness in the fossil record shedding light on when and why this trait arose. Interestingly, the clues were found not in our ancient hands, but in our ancient teeth.</p>
<p>We have long known that the human brain is composed of two roughly similar halves. The left hemisphere controls language and motor abilities, whereas the right hemisphere is responsible for visual-spatial attention.</p>
<p>It is less well known that brain lateralisation, or the dominance of some cognitive processes in one side of the brain, is a distinctive feature of humans, and one associated with <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767540/">improved cognitive ability</a>.</p>
<p>Could handedness have played a role in brain lateralisation? Ancient stone tools made and used by our earliest ancestors reveal some clues. </p>
<h2>Use of tools</h2>
<p>The earliest stone tools date to <a href="http://www.nature.com/nature/journal/v521/n7552/full/nature14464.html">3.3 million years ago</a> and were found in modern day Kenya, Africa. Early stone tool making would have required a high level of dexterity. We know from <a href="https://scholarblogs.emory.edu/stoutlab/files/2013/07/Stout-et-al-2000.pdf">experiments</a> that have replicated tool-making processes that the brain’s left hemisphere, which is responsible for planning and execution, is active during this process.</p>
<p>At the same time, humans are overwhelmingly <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.1995.tb00362.x/abstract">right-handed</a> when it comes to tool making compared to other species. This is most likely because the left and right hemispheres control motor action on the <a href="https://theconversation.com/how-childrens-brains-develop-to-make-them-right-or-left-handed-55272">opposite sides</a> of the body. </p>
<p>While this relationship is <a href="https://www.scientificamerican.com/article/why-are-more-people-right/">not straightforward</a>, it would appear that, in most cases, handedness and brain lateralisation go hand in hand (pun intended).</p>
<p>So why use teeth to investigate handedness? The answer lies in the scarcity of matching left and right arm bones in the fossil record, particularly those belonging to our earliest ancestors. </p>
<p>Without matching left and right sets, it is impossible to examine differences in size and shape to determine which hand an individual favoured when completing manual tasks.</p>
<p>Teeth, on the other hand, tend to <a href="http://anthro.palomar.edu/time/time_1.htm">survive relatively well</a> in the fossil record and can preserve scratches, or “striations”, that establish handedness.</p>
<p>In an <a href="http://www.sciencedirect.com/science/article/pii/0047248488900292">earlier study</a>, researchers noted striations on the front side of teeth belonging to European Neanderthals. They hypothesised that these marks were made when material was held in one hand and gripped between the front teeth and worked by the other hand with a stone tool, with the stone tool occasionally striking these teeth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=368&fit=crop&dpr=1 600w, https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=368&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=368&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=462&fit=crop&dpr=1 754w, https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=462&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/152077/original/image-20170109-23477-16z32g9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=462&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Study finds striations on teeth of a <em>Homo habilis</em> fossil 1.8 million years old moved from left to right, indicating the earliest evidence in the fossil record for right-handedness.</span>
<span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/pub/125005.php">David Frayer</a></span>
</figcaption>
</figure>
<p>These actions were replicated during experiments in which participants wore mouthguards. The results indicated that right-slanting striations are made on teeth when material is pulled with the left hand and struck with the right hand. Right-slanting striations are therefore a good indicator of right handedness.</p>
<p>The subject of the <a href="http://www.sciencedirect.com/science/article/pii/S0047248416300719">new study</a> – an ancient upper jawbone – provides the oldest evidence for right-handedness known in our genus <em>Homo</em>.</p>
<p>The jawbone belonged to one of our earliest human ancestors, <a href="http://australianmuseum.net.au/homo-habilis"><em>Homo habilis</em></a> (literally, the “handy man”), who roamed Tanzania in Africa around 1.8 million years ago. The jaw was identified at Olduvai Gorge in the Serengeti Plain, which has yielded some of the <a href="http://science.sciencemag.org/content/299/5610/1217">earliest archaeological traces</a> in the world. </p>
<h2>Marks on teeth</h2>
<p>The authors of the study noted a number of striations on the front side of the teeth. They used high-powered microscopes and digital cameras to investigate these striations, particularly patterning in their direction. </p>
<p>Interestingly, nearly half of all striations were right-slanting. Right-slanting striations were particularly dominant on four of the front teeth (left and right central incisors, right second incisor and right canine).</p>
<p>This led the authors to argue that most marks were made with the individual’s right hand. They also suggested that the four front teeth with many right-slanting striations were the focus of most processing activities.</p>
<p>The <em>Homo habilis</em> jaw is important as it provides the oldest evidence for right-handedness in the fossil record. But it is also significant as it suggests that a major level of brain organisation had occurred in humans by at least 1.8 million years ago.</p>
<p>This brain development enabled us to master crucial early skills such as <a href="http://www.nature.com/scientificamerican/journal/v314/n4/full/scientificamerican0416-28.html">stone tool making</a> and potentially also paved the way for <a href="http://www.sciencemag.org/news/2013/08/striking-patterns-skill-forming-tools-and-words-evolved-together">language development</a>. Right-handedness therefore means a lot more to us than simply a preference for using the right hand.</p>
<p>Just some food for thought next time you are brushing your teeth, sending a text message or high-fiving someone.</p><img src="https://counter.theconversation.com/content/69712/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Caroline Spry has previously received funding from the Australian Government and La Trobe University.</span></em></p>The way early humans learned to handle food could explain why the majority of people today are right handed.Caroline Spry, Honorary Associate, PhD, La Trobe UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/552722016-04-06T10:24:01Z2016-04-06T10:24:01ZHow children’s brains develop to make them right or left handed<figure><img src="https://images.theconversation.com/files/117317/original/image-20160404-27145-tsvago.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Left-handedness is no longer seen as an abnormality. </span> <span class="attribution"><span class="source">Aleksei Potov/www.shutterstock.com</span></span></figcaption></figure><p>As children grow older, they tend to favour one hand over the other for certain tasks, particularly for writing or drawing. A child’s “handedness” is generally categorised as right, left or mixed, and <a href="http://www.ncbi.nlm.nih.gov/pubmed/8284160">tends to settle</a> around the same time they acquire language – about four-years-old. It remains a persistent characteristic throughout our life. </p>
<p>We now know that a child’s handedness says something about the organisation and function of their brain. </p>
<p>The left and right hemispheres of the brain control motor action on the opposite sides of the body. Yet, the left and right halves of the brain are not equal in their control of different types of behaviours, which results in a bias of one hand over the other for certain tasks. The dominance of one hemisphere over the other for certain behaviours is called <a href="https://www.researchgate.net/publication/26319337_Origins_of_the_Left_Right_Brain">cerebral lateralisation</a>. </p>
<p>Scientists think that there are clear reasons for the evolution of cerebral lateralisation. First of all, having one hemisphere take control of a process lowers the chance of both hemispheres competing to control a response. It also allows for different processes such as language and attention to operate in parallel across the two hemispheres. </p>
<p>For the vast majority of people, the left hemisphere of the brain is the dominant one used for speech. And the same region of the left hemisphere that <a href="http://physiologyonline.physiology.org/content/20/1/60">controls speech also controls hand actions</a>. </p>
<p>As a result, the majority of the human population (about 90%) is <a href="http://www.hup.harvard.edu/catalog.php?isbn=9780674016132">right-handed</a> when they use tools, such as pens, and when they make gestures. Evolutionary psychologists speculate that tool use and hand gestures played an important role in the evolution of human speech. One theory suggests that because vision is our primary sense, human communication <a href="http://www.americanscientist.org/issues/pub/the-gestural-origins-of-language/1">first emerged as hand gestures</a>. As we became sophisticated tool users, it was more efficient to keep our hands free for tool use and our communication transferred to speech. The structured sequences of hand actions required to make and use tools may also have <a href="http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7252168&fileId=S0140525X00071235">prepared the brain for language syntax</a>. </p>
<p>In order to acquire complex skills like language, children must first development basic sensory and motor abilities. Developmental psychologists argue that fine motor capabilities like manipulating objects and gesturing <a href="https://www.pearsonhighered.com/program/Carlson-Psychology-The-Science-of-Behavior-7th-Edition/PGM294565.html">sets the stage for acquiring systems</a> required for the subsequent development of language. </p>
<h2>Left, right or both?</h2>
<p>Early to mid-20th century scientists considered left-handedness to be a developmental abnormality. It was associated with a range of developmental dysfunctions ranging from <a href="http://www.ncbi.nlm.nih.gov/pubmed/3722117">language deficits to mental health disorders</a>. In fact, many left-handed children of this era were forced to write with their right hands in an effort to “<a href="http://www.sciencedirect.com/science/article/pii/S0140673611608544">retrain</a>” them. </p>
<p>Today, we understand that handedness is not a binary characteristic (left or right), but rather, it exists along a gradient that ranges from strongly left-handed to strongly right-handed. </p>
<p>As they start to develop their motor skills, children may use both the left and right hands equally for simple actions such as reaching for objects. This is because both hands can accomplish the task with ease. Yet, for the majority of the population, more complex tasks require the specialised processing properties of the left hemisphere of the brain. For example, the majority of children choose their right hand for writing. </p>
<p>The skill develops over time and becomes consistently right-handed as children progress from using a “fisted” grip, to make their first marks on a page, to the delicate “<a href="http://www.ot-mom-learning-activities.com/pencil-grasp-development.html#FistedGrasp">tripod</a>” grip required for fine motor actions like forming and joining letters. Observing a child’s handedness for fine motor activities, such as writing, can give us an indication of how well the two hemispheres have developed their specialised processing capabilities.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116264/original/image-20160323-28176-nnl91e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Both hands.</span>
<span class="attribution"><span class="source">Anelina/www.shutterstock.com</span></span>
</figcaption>
</figure>
<p>Recent research suggests that children who are strongly left or right handed also have good cerebral lateralisation and <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.7.2218&rep=rep1&type=pdf">typical language production</a>. On the other hand, <a href="https://peerj.com/articles/507/">mixed-handedness</a> (not developing a dominant hand) has been linked with atypical development of motor and language abilities.</p>
<p>Ambidextrous individuals make up about 3–4% of the general population. This figure rises to between 17% and 47% in populations of children with autistic spectrum disorders (<a href="https://www.researchgate.net/publication/236643528_Atypicalities_in_Cortical_Structure_Handedness_and_Functional_Lateralization_for_Language_in_Autism_Spectrum_Disorders">ASDs</a>). Children with ASDs also show motor abnormalities as early as <a href="http://docs.autismresearchcentre.com/papers/2014_Leonard_EuropeanJournalDevelopmentalPsychology_Early_and_persistent_motor_difficulties.pdf">seven months</a> of age. This suggests that ASDs are likely to be present and observable early in a child’s development, and are likely to have “knock on” effects to the development of higher cognitive functions like language. </p>
<h2>How can handedness be useful?</h2>
<p>New <a href="https://www.westminster.ac.uk/news-and-events/news/2014/gillian-s-forrester-senior-lecturer-in-psychology-features-in-bbc-science-programme-dissected-the-incredible-human-hand">research</a> that I’m working on is considering how infant handedness can be used as a marker of a child’s risk of developing language disorders. Current diagnoses of ASDs tend to occur relatively late, when children fail to produce and understand basic language. Late diagnoses can limit benefits that may come from early interventions and therapies. Infant brains are incredibly flexible and the right kinds of early intervention may improve later cognitive development and mental health. </p>
<p>Handedness is not the only bias of our motor skills that comes from cerebral lateralisation. A majority of the population has a right hemisphere of the brain that is dominant for responding to danger. This means that we are faster at recognising threatening faces and expressions when they appear to our left side (in the left visual field) compared to our right side. This has been demonstrated in a range of classic psychology laboratory studies where adults are faster to judge pictures of faces expressing <a href="http://psycnet.apa.org/journals/psp/58/2/330/">negative emotions</a> presented to their left compared to those presented to their right. </p>
<p>Mapping the developmental paths of motor biases and cognitive abilities in children provides a novel way for us to better understand the relationship between brain organisation, brain function and behaviour.</p><img src="https://counter.theconversation.com/content/55272/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gillian Forrester does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The development of ‘handedness’ and language are closely linked.Gillian Forrester, Senior Lecturer in Psychology, University of WestminsterLicensed as Creative Commons – attribution, no derivatives.