Even education does not completely wipe out innate number sense, common in children and uneducated adults, a study has found.
Educated adults generally understand numbers 'linearly' based on the familiar number line from 0 to infinity.
On the other hand, children and uneducated adults understand numbers 'logarithmically' - in terms of what percentage one number is of another.
Now a team of researchers from France and Israel have discovered that educated adults continue to retain traces of their childhood, or innate number sense.
"We were surprised when we saw that people never completely stop thinking about numbers as they did when they were children," said Dror Dotan, a doctoral student at Tel Aviv University in Israel.
"The innate human number sense has an impact, even on thinking about double-digit numbers," he said.
To analyse how educated adults process numbers in real time, the researchers asked the participants in their study to place numbers on a number line displayed on an iPad using a finger.
Their analysis showed that the participants placed the numbers on the number line in a linear way, as expected.
But surprisingly - for only a few hundred milliseconds - they appeared to be influenced by their innate number sense.
In the case of 20, for example, the participants drifted slightly rightward with their finger - toward where 20 would belong in a ratio-based number line - and then quickly corrected course.
"It really looks like the two systems in the brain compete with each other," said Dotan.
The research showed that the innate number sense is capable of handling the complexity of two-digit numbers as well.
The results provide some of the most direct evidence to date that the innate number sense remains active, even if largely dormant, in educated adults.
The findings provide new insight into in understanding how people process numbers. This could also contribute to the development of methods to more effectively educate or treat children with learning disabilities and people with brain injuries.