Optical illusions have a storied history in neuroscience, pointing out insights into how the brain works. A visual test now finds impaired abilities to see large motions in high-IQ folks.


High IQ folks' brains focus on the details and dispense with less relevant matters, an optical illusion study suggests Thursday, pointing to mental focus as the key to higher scores on intelligence tests.

Smarts are seen as the keys to success in modern society and scoring well on IQ (intelligence quotient) tests is one widely regarded measure of raw intelligence. In a visual motion test, however, high IQ scorers seemed almost impaired at noticing big motions. And that may be a key to intelligence, suggest the study authors.

"Rather than raw processing power, the ability to focus on relevant details is what we see in really efficient brains," says neuroscientist Duje Tadin of the University of Rochester (N.Y.), who headed the team reporting the motion test results in the journal Current Biology. "It's a little like opening up your e-mail every day and zooming in on the important message and focusing on that task to succeed."

In the study, Tadin and colleagues performed two series of tests on 67 people with an average IQ score of 100 (the volunteers took one of two forms of the IQ test), which is normal. The volunteers watched a visual test where they were shown movies of circular grids, large and small, that appeared to move to the left or right. Test takers were asked how many frames of the movie they needed to see to detect the motion.

The effect was particularly linked to the verbal intelligence portion of the IQ test, which Tadin suggests is because that provides the most general measure of smarts over logic, memory and math parts of IQ. That is a sign, he says, that this tendency of high IQ folks to spot the important tree in a forest of irrelevant details is a key to what we call intelligence.

"We don't think this will work with every visual effect," Tadin says. "I suspect that if we found a visual test where noticing the large motion was important, then the high IQ scorers would notice that first."

Rather than the test-takers with higher IQ noting motions any faster, the test revealed a larger gap between the number of frames needed to detect the motion on the small grid and their later perception of motion on the large one. "The brain is suppressing automatically the irrelevant larger motion, but zooming in on the small ones," Tadin says.

Neuroscientist Steven Rose of the United Kingdom's Gresham College London expressed caution about taking the visual test results too far. "Suppose that IQ isn't about intelligence at all but is simply a test which draws on focused sensory discrimination," Rose says, by e-mail. "That would be great. Then we could stop talking about IQ as if it were some absolute measure of 'intelligence' but instead as a way of measuring how sensorily focused people were — surely a useful attribute, but nothing so grand as general intelligence."

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