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Last Updated: Monday, 7 February, 2005, 10:26 GMT
Left-handers have different view
Hands
Left handers may be more prone to accidents
Left-handed and right-handed people view the world differently, scientists have shown.

Psychologists found they use opposite sides of their brains when looking at, and making sense of, an image.

It is already known that handedness is associated with differences in the way we make sense of language, and possibly in spatial orientation.

Details of the study, by the University of Birmingham, are published in Nature Neuroscience.

Not only our language function, but even the way we see the world can depend on our handedness
Professor Glyn Humphreys
The researchers showed right-handed people use the right hemisphere of their brain to focus on the whole of an image - for example a forest.

But when it comes to focusing on the detail within an image - for instance individual trees in a forest - then they use their left hemisphere.

For left-handers the opposite is true.

Disrupted activity

The researchers used a technique called Transcranial Magnetic Stimulation (TMS) which momentarily disrupts brain activity.

The researchers applied TMS over either the left or right parietal lobe at the back of the brain while volunteers concentrated on the details of a visual stimulus.

Stimulation of the left side of the brain made it harder for right-handers to attend to detail, whilst stimulation of the right side had this effect on left-handers.

Professor Glyn Humphreys from the University's School of Psychology said: "In right-handed people the right hemisphere sees the whole picture, whereas the left hemisphere attends to the details.

"However, we have found that in left-handed people, this is completely reversed.

"Not only our language function, but even the way we see the world can depend on our handedness."

Professor Humphreys told the BBC News website the findings suggested that brain damage would affect left and right-handers ability to make sense of detail in different ways.

It was also possible that reading skills - which require making sense of a lot of close detail - may development in different ways.

Dr Stephen Williams, a chartered psychologist based in Colchester, was doubtful that the perception of images was quite so starkly different between left and right handed people.

It had been thought that the left half of the brain was responsible for language processing in right handed people, while the right hemisphere played the same role for left handed people, he said.

But subsequent research had found that while 95% of right handed people did indeed process language in the left hemisphere, so did 70% of left handed people - and half of the rest used both hemispheres.

Research has suggested that left-handed people are more susceptible to a range of problems, including allergies, auto-immune diseases, depression, drug abuse, epilepsy, schizophrenia and sleeping disorders.

Left-handers are thought to have poorer spatial skills, and thus to be more vulnerable to car crashes and other serious accidents.

However, a study published by The Lancet suggested there was no truth in the theory that left-handers are more likely to die prematurely.




SEE ALSO:
Left-handers 'better in fights'
08 Dec 04 |  Health
Left-handedness common in Ice Age
13 Feb 04 |  Science/Nature


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