News in Science

Number instinct peaks at 30-something

Math mind The instinct that help us chose the fastest-moving supermarket queue keeps developing well into adulthood, much longer than many had suspected, US scientists have found.

Their research provides the first ever glimpse into how a core component of human cognition develops over the course of a lifetime. It also raises tantalising questions about how we might improve other mental faculties.

Cognitive scientist Justin Halberda of Johns Hopkins University in Baltimore, and colleagues, wanted to study our gut animal sense for numbers, known as the 'approximate number system'.

"We use this sense every day without even knowing we are doing mathematics," says Halberda, who is lead author of the study which appears in the Proceedings of the National Academy of Sciences.

"For instance, when you are trying to estimate which checkout line at the market might move the fastest, you are estimating the numbers of items in people's carts, the numbers of folks in line, how fast the checkout person is working."

But studying how our cognitive systems change over the scale of a lifetime has proven a real challenge for normal scientific methods.

"Measuring those changes is a nearly insurmountable challenge for traditional science done in the lab," Halberda says, "because we simply can't measure enough folks from enough different ages in order to determine how our abilities change over the grand timescale of an entire life."

So he and his colleagues turned to the internet.

Spot the dots

They set up a website that allowed people to test their own approximate number systems using a test that asked them to determine whether there were more yellow or blue dots in an image flashed quickly onto their computer screens.

Over a three month period, more than 10,000 people did the test, each undertaking 300 trials of the number system dots test in about 8 minutes. The ages of the participants ranged from 11 to 85, allowing Halberda's team to see how this instinctive ability varied between people and how it changed with age.

"Initially, we expected that basic cognitive abilities might improve rapidly during early childhood but that they would be fairly stable after childhood," he says.

"But we found that the precision of a person's approximate number system appears to improve ... and that optimal precision is attained for most folks at around age 30."

Later in life, this number sense declined.

"This continuous improvement into the 30's runs counter to what much of our popular culture might lead us to expect, where we tend to hear that being younger is better," says Halberda. "I expect that there may be many cognitive abilities that continue to improve up into our 30's."

Linked to school

While the researchers found very clear population trend, they also noted huge differences between individuals. Some adults struggled on the dots task and performed no better than a typical 11-year old, while others did exceptionally well.

When the researchers asked participants about how good they were at school maths, they found a correlation with their results on the dot test.

"We found that some people have a very precise sense for numbers while others struggle, and that a more precise number sense is linked to being better at school mathematics during the school-age years and at every age thereafter throughout one's life," says Halberda.

The fact that number sense improves as we age - at least until our 30s - means we may be able to develop ways of improving it, he says.

"Finding out that our basic numerical intuitions continue to improve up into our 30's is edifying for all of us who want to practice and continue to grow and improve."

"I think one of the most important goals right now is for the public to support science's search for tools that are optimal for helping us grow and maintain healthy cognitive functioning."