Focus on lefties, brain function and talents

Are left-handed people more gifted than others? Our study suggests it may hold true for maths, write Giovanni Sala and Fernand Gobet

THE belief that there is a link between talent and left-handedness has a long history. Leonardo da Vinci was lefthanded. 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. But is it really true that left-handers are more likely to be geniuses? Let’s take a look. It is estimated 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. Hand preference is a manifestation of brain function and is therefore related to cognition. Left-handers exhibit, on average, a more developed right brain hemisphere, which is specialised for processes such as spatial reasoning and the ability to rotate mental representations of objects. Also, the corpus callosum – the bundle of nerve cells connecting the two brain hemispheres – tends to be larger in left-handers. This suggests some lefthanders have an enhanced connectivity between the two hemispheres and hence superior information processing. Why that is, however, is unclear. But these peculiarities may be the reason that left-handers seem to have an edge in several professions and arts. For example, they are over-represented among musicians, creative artists, architects and chess players. Efficient information processing and superior spatial skills are essential in all these activities.

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 to be a predictor of mathematical precociousness. The study found that the rate of lefthandedness among students talented in mathematics was much greater than among the general population.

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.

For example, one study discovered that lefthanded children slightly underperformed in a series of developmental measures.

Also, a recent review reported that left-handers appeared to be slightly over-represented among people with intellectual disabilities.

Another large study found that left-handers performed more poorly in mathematical ability in a sample of children aged five to 14.

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 might be the cause of the mixed observed results.

To get more reliable results, we decided to carry out a whole series of experiments with more than 2 300 pupils in primary school and high school. These experiments varied in terms of type and difficulty of mathematical tasks.

To assure comparability, we used the same questionnaire – the Edinburgh Inventory – in all the experiments. This questionnaire asks people which hand they prefer for writing, drawing, throwing, etc. Importantly, it assesses the extent to which someone prefers their right or left – it’s a scale rather than a categorical left versus right assessment. This allowed us to build more reliable and powerful statistical models.

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 simple arithmetic, there was no difference between left- and right-handers.

We also discovered that extreme right-handers – individuals who said they preferred to use their right hand for all items on the handedness test – underperformed in all the experiments compared to moderate right-handers and lefthanders.

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 might represent a disadvantage for mathematics.

But handedness is just an indirect expression of brain function. For example, only a third of the people with a more developed right hemisphere are left-handed. So plenty of righthanded people will have a similar brain structure to 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. — this article first appeared in The Conversation; https://theconversation.com

● Giovanni Sala is a PhD candidate in cognitive psychology, at the University of Liverpool, UK and Fernand Gobet is a Professor of decision making and expertise, also at the University of Liverpool