Five of the six figures shared some property. The participants had to guess which figure did not belong. (In their language the Mundurucú described it as "the ugly one.")
For example, one set included a pair of nonparallel lines amid five pairs of parallel lines. Another set had six triangles, only one of which had no right angle.
In the second test, each participant was given a map showing where to find an object hidden under one of three boxes.
The Mundurucú don't typically use maps, but they are adept at navigating their river valley home in the Brazilian state of Pará.
The boxes in the test were arranged in right triangles or isosceles triangles on the floor. The maps correctly reproduced these geometric relations. Stars on the maps marked the locations of the hidden objects.
Dehaene finds it significant that the U.S. and Mundurucú children had similar scores while U.S. adults outperformed Mundurucú adults.
The results suggest that "the concepts of geometry are grounded in extremely basic mechanisms in the human brain," he said, "whatever its culture and its education."
Brian Butterworth, a neuroscientist at Britain's University College London, agrees.
"We are born with a 'starter kit' of core concepts that helps us interpret our three-dimensional world, and this is refined by constant interaction with it," said Butterworth, who was not involved in the Mundurucú study.
"If the world has lots of straight lines, as the world of the [U.S.] subjects [in these experiments] does, then this may explain why, when they reach adulthood, they are somewhat better at dealing with problems involving straight lines," he said.
The research may also cast new light on an old conundrum: Does the brain learn concepts through wordspossibly in different ways for different languages? Or does abstract thinking somehow precede speech?
Rafael Núñez is a cognitive scientist at the University of California, San Diego. He believes that concepts can precede words, but he says the evidence in the new study does not constitute proof.
Although their language lacks certain words, the Mundurucú may be able to express the same concepts through metaphors.
"I could also say that in English we have few words to talk about the future," Núñez said, "because we use metaphors like 'the week ahead' and 'way back in the sixties,' which are spatial metaphors relative to front and back."
That's not the only difficulty in interpreting the data, according to Dehaene, the study's lead author. Some of the recognition may be taking place at the visual level, rather than at the level of abstract thought.
Peter Gordon, a behavioral scientist at New York's Columbia University, said that further tests would be needed for scienists to better understand the study results.
"Imagine if you did this task and had five transistors and a capacitor and had subjects pick the capacitor as being odd," he said. "Would this mean that they had concepts of electronic circuitry?"
Dehaene says the concern that the children's ability is largely visual doesn't seem to apply to the map-based test. That's because using a map requires "abstraction of geometrical information." In other words, the test subjects had to be able to understand that the shapes on the page corresponded to the boxes arranged on the floor.
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