A new “brain test” floating around online shows a spinning dancer and asks 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 then lists functions associated with each side of the brain – the left side includes “uses logic” and “facts rule,” while the right side includes “uses feeling” and “imagination rules.”

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

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

The concept was born in the 1960s, when Roger Sperry studied epilepsy patients who had had a nerve connection between their hemispheres surgically cut. He found that the left brain hemisphere seemed to possess “speech and a rational, 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 to perform a task – have further suggested that language ability tends to be localized in the left hemisphere, while spatial ability tends to be in the right hemisphere.

However, neuroscience-minded blogs like Neurophilosophy point out that doing any complex mental activity requires cooperation from both sides of the brain, although certain processing tasks required for that activity may be concentrated on one side or the other. In other words, saying that “math and science are left brain functions” is an over-generalized statement.

“It’s not that you have a special math module somewhere in your brain, but rather that the brain’s particular functional organization…predisposes it towards the use of high-level imagery and spatial skills, which in turn just happen to be very useful when it comes to doing math reasoning,” said Michael O’Boyle, a psychologist at the University of Melbourne, Australia, in a public 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 than average students on tests that required both halves of the brain to cooperate. This demonstrated that, while the typical person might lean more heavily on one hemisphere or the other to do mental tasks necessary for math calculation, the brightest among us can more fully integrate both hemispheres of the brain.

The idea that emotion processing only occurs in the right brain hemisphere and fact processing in the left is also misleading. Brain imaging studies have showed that people processed emotion using small parts of both brain hemispheres.

“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-color painting,” noted a 2005 Scientific American Mind article.

Believing in left brain or right brain people also fails to account for the human brain’s mysterious flexibility and plasticity. People who had half their brain removed encounter some problems – like not being able to move or see from one side of their body – but largely retained or relearned mental abilities such as language in their remaining brain hemisphere. All this research clearly points out that while Nobel winner Sperry was onto something with his lateralization research, trying to fully compartmentalize mental activity 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 Medicine who blogs on NeuroLogica. When our brains process visual images to make some order or sense of the world, they have to make assumptions. The dancer is just a two dimensional image switching back and forth, but our 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. When my friend first sent the test to me, I saw it go clockwise…then switch to counterclockwise as I was staring at the screen. What this tells me about my personality and mental abilities is hardly a no-brainer – the brain test connection to our mental strengths and weaknesses is nonexistent.