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News Release

December 13, 2006

Lefties Aren't So Different After All, Finds U of G Prof

This research is featured in the Globe and Mail and the Toronto Star.

Contrary to popular scientific belief, left-handedness is not linked to dyslexia, poorer spatial ability, homosexuality, asthma and hyperactivity, a University of Guelph psychology professor has found.

“We’ve shown on a number of tasks that there’s no difference between right- and left-handedness,” said Michael Peters, whose study of a quarter of a million people is published in the current issue of Brain and Cognition with co-authors Stian Reimers and John Manning.

The study did show, however, that individuals who didn’t favour either hand for writing had significantly poorer spatial performance in a mental rotation task and significantly higher prevalence of homosexuality, bisexuality, hyperactivity, dyslexia and asthma than individuals who had clear left- or right-hand preferences, said Peters.

The survey was hosted on the BBC Science and Nature website for a number of weeks. It included more than 150 questions about demographics, personality, sexuality, social attitudes and behaviours, as well as spatial and verbal tasks.

To have data on a 255,000 people is extremely significant in the study of handedness, said Peters. “Because only 10 per cent of the population is left-handed, you need a huge study group to draw any sensible conclusions.”

The researchers were cautious about their study results because of the lack of control over an Internet survey, but when they cross-checked the results, “we were impressed by how similar the prevalence figures we observed were to the figures obtained under more controlled conditions in the lab,” said Peters.

Instead of asking people if they were left- or right-handed, the survey asked subjects to indicate hand preference for writing on a scale from one (left) to five (right). Participants who chose “three” were comfortable writing with either hand. This mixed group made up less than one per cent of the participants, but they produced the most interesting results.

“Normally the mixed group is so small in laboratory studies that you can’t draw any conclusions from it,” said Peters.

The survey also asked participants to self-identify their sexual orientation as heterosexual, homosexual and bisexual. There was no significant difference in sexual orientation between the left- and right-handed respondents, but both males and females who said they used “either hand” to write were overrepresented in the non-heterosexual categories, especially the bisexual category.

There has been some evidence that the spatial ability between right- and left- handed is quite different, said Peters. “But we just didn’t find that in this study. We did find, however, that mixed-handedness definitely seems to be a factor in spatial ability.” Respondents who chose the “either hand” option performed worse on the spatial tasks.

The researchers included health categories and developmental problems in their study because there’s a general underlying rationale that left-handedness is a marker for “something not quite right,” said Peters. The lefties didn’t differ statistically from the right-handed participants in the number of asthmatics, dyslexics or cases of hyperactivity, but individuals in the mixed-hand category had the highest prevalence of these traits.

“Our study shows that much greater attention has to be paid to the definition of handedness,” he said.
Peters stressed that just because someone can write with either hand doesn’t mean the person is homosexual, bisexual or dyslexic. “Individuals who are unclear about their handedness make up a disproportionately higher number of dyslexics, but since there are so few dyslexics in the first place, the majority of people with mixed-handedness aren’t dyslexic. Similarly, there are a disproportionate number of homosexual males with mixed-handedness, but the largest number of mixed-handed males aren’t homosexual.”