A new “brain test” floating around online shows a spinning dancer andasks whether you see the image rotating clockwise or counterclockwise.If it spins clockwise, you supposedly use more of your right brain.Counterclockwise, and you’re more of a left brain person. The test thenlists functions associated with each side of the brain – the left sideincludes “uses logic” and “facts rule,” while the right side includes“uses feeling” and “imagination rules.”

A good friend complained thatthe test told her she was a left brain person, even when she knewherself to not be into left brain associations such as “math andscience.” A similar discrepancy was discerned by one of the authors ofthe Freakonomics blog,when he conducted a quick, nonscientific survey of blog readers, whichcross referenced college majors and spinning dancer test results.

If the test sounds flawed,that’s not just because one shouldn’t use spinning dancers tocharacterize their brain strengths. Rather, the test is coming upinaccurate because it provides a crude view of the “lateralization ofbrain function,” or the concept that each side of the human brainspecializes in certain mental activities.

The concept was born in the 1960s, when Roger Sperry studied epilepsy patients whohad had a nerve connection between their hemispheres surgically cut. Hefound that the left brain hemisphere seemed to possess “speech and arational, intellectual style,” while the right side was “inarticulate,but blessed with special spatial abilities.”

Modern neuroscience studies using brain imaging technology such as fMRI –which shows active areas of the brain while a person is trying toperform a task – have further suggested that language ability tends tobe localized in the left hemisphere, while spatial ability tends to bein the right hemisphere.

However, neuroscience-minded blogs like Neurophilosophy pointout that doing any complex mental activity requires cooperation fromboth sides of the brain, although certain processing tasks required forthat activity may be concentrated on one side or the other. In otherwords, saying that “math and science are left brain functions” is anover-generalized statement.

“It’s not that you have aspecial math module somewhere in your brain, but rather that thebrain’s particular functional organization…predisposes it towards theuse of high-level imagery and spatial skills, which in turn just happento be very useful when it comes to doing math reasoning,” said MichaelO’Boyle, a psychologist at the University of Melbourne, Australia, in apublic statement through the American Psychological Association.

In fact, the best math students don’t even seem to settle for being “left brain” people. A study undertaken by O’Boyle found mathematically gifted students did better thanaverage students on tests that required both halves of the brain tocooperate. This demonstrated that, while the typical person might leanmore heavily on one hemisphere or the other to do mental tasksnecessary for math calculation, the brightest among us can more fullyintegrate both hemispheres of the brain.

The idea that emotionprocessing only occurs in the right brain hemisphere and factprocessing in the left is also misleading. Brain imaging studies haveshowed that people processed emotion using small parts of both brainhemispheres.

“The popular notion of an‘emotional’ right hemisphere that contrasts sharply with a ‘rational’left hemisphere is like a crude pencil sketch made before a full-colorpainting,” noted a 2005 Scientific American Mind article.

Believing in left brain orright brain people also fails to account for the human brain’smysterious flexibility and plasticity. People who had half their brain removed encountersome problems – like not being able to move or see from one side oftheir body – but largely retained or relearned mental abilities such aslanguage in their remaining brain hemisphere. All this research clearlypoints out that while Nobel winner Sperry was onto something with hislateralization research, trying to fully compartmentalize mentalactivity by brain hemisphere is imprecise.

So what does the spinning dancer tell us? The whole test is more of an optical illusion than anything else, according to Steven Novella,an academic clinical neurologist at Yale University School of Medicinewho blogs on NeuroLogica. When our brains process visual images to makesome order or sense of the world, they have to make assumptions. Thedancer is just a two dimensional image switching back and forth, butour brains process it as a three dimensional spinning object.

Depending on the assumptions made and visual cues picked up, your brain can make the dancer spin either way. Whenmy friend first sent the test to me, I saw it go clockwise…then switchto counterclockwise as I was staring at the screen. What this tells meabout my personality and mental abilities is hardly a no-brainer – thebrain test connection to our mental strengths and weaknesses isnonexistent.