Thirtysomethings flex their number sense

Insight into quantities maxes out in adulthood and may influence math achievement

Even 6-month-old babies can rapidly estimate approximate numbers of items without counting. But surprisingly, an apparently inborn sense for numbers doesn’t top out until around age 30.

Number sense precision gradually declines after that, generally falling to preteen levels by about age 70, say psychologist Justin Halberda of Johns Hopkins University in Baltimore and his colleagues. They report the findings, based on Internet testing of more than 10,000 volunteers ages 11 to 85, online the week of June 25 in the Proceedings of the National Academy of Sciences.

“I expected to see some improvement in number sense into preschool or maybe early elementary school, but not up to age 30,” Halberda says.

Evidence of critical mental abilities peaking after young adulthood is rare but has been reported for face memory (SN: 1/1/11, p. 16).

Participants in the new study completed a game that tested the precision of their number sense, or how accurately they could assess quantities. Volunteers saw a series of images showing mixes of blue and yellow dots and judged which color dot was more numerous. Each dot array appeared for a fraction of a second.

In some dot arrays, one color greatly outnumbered the other. In other arrays, one color slightly outnumbered the other.

Test-takers of the same age showed large differences in how accurately they could assess the dots, with the highest average scores coming around age 30, the researchers report. Teens and adults with a robust number sense reported doing moderately better at math in school and on the math portion of the SAT than those with a weak number sense.

Everyday activities, such as quickly deciding which of several supermarket check-out lines is shortest, may strengthen a person’s number sense, Halberda says. His team is devising an action video game containing number-related decisions that will aim to boost children’s number sense precision.

“Training to make numerosity discriminations could improve mathematics learning, whether it turns out that the ability to estimate quantities is the foundation for learning about numbers or just improves math confidence,” says cognitive neuropsychologist Brian Butterworth of University College London. 

Previous research had linked a keen number sense to superior math achievement in elementary school (SN: 9/27/08, p. 10).

Number sense is one of many influences on math performance in school and throughout life, Halberda says. A long-term study of U.S. and British youngsters published online June 14 in Psychological Science finds, for instance, that students who grasp fractions and division in grade school do particularly well in all forms of high school math.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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