How do our cognitive abilities change throughout our lives? Does the popular notion that babies' brains are little sponges and that older adults' minds are "all washed up" really hold water? Until now, it has been difficult to see, scientifically, how cognitive systems change over the grand time scale of an entire life.
In a recent article published in The Proceedings of the National Academy of Sciences (PNAS), we addressed this challenge for the gut number sense, a foundational cognitive system that supports numerical thinking. This so-called "approximate number system," or ANS, is present in children and adults from mathematically fluent cultures (such as our own) but also in tribes of people in the Amazon whose language reveals that they have very few words for numbers. Have you ever tried to guess how many jellybeans are in a jar, or tried to estimate the number of items in shoppers' carts at supermarket checkout lines before trying to pick the shortest (and fastest) line?
Animals, from monkeys and cats to birds and rats, have an ANS, too. Scientists contend that number sense probably evolved very early, to help animals and our prehuman ancestors survive in the wild.
In an effort to learn how the ANS fares over the human lifespan, we posted a very simple video game on the Web and invited people from all walks of life to play in order to find out about the precision of their number sense. Over the course of three months, more than 10,000 people between 11 and 85 years of age freely navigated to the site to test their own abilities. (Readers, if you want to find out how your number sense stacks up to other people your age, log on for yourself.)
Two patterns emerged. First, population trends suggest that the precision of one's number sense improves throughout the school-age years, peaking quite late, at approximately 30 years of age. And, second, despite this gradual developmental improvement, we found very large individual differences in number sense precision among people of the same age where a person's number sense precision related to how well they did in school mathematics classes. For example, one adult in eight appears to have a gut number sense that is less precise than that of a typical 11-year-old child's. These differences in gut number sense related to people's school mathematical performance throughout adolescence and in their adult years -- a relationship that continued all the way up into people's 80s. In other words, those whom the test revealed as having better number sense also generally reported being more successful in academic mathematics classes (in school and on the SAT, for instance) than did those whom the test revealed as having less accurate number sense. The relationship is a small but consistent one, and many scientists are currently busy trying to figure out how our gut senses and our academic abilities affect each other across development.
These results suggest that not all cognitive abilities are at their best when we are young, and furthermore, they reveal that number sense is malleable. Number sense, we hope, is something that can be improved, with "exercise" and practice.
The biggest open question is what is the most effective way to improve on this ability. That is the challenge we are starting to address in our current work.
The large individual differences we found, and the prolonged development of number sense, paired with its consistent and specific link to mathematics ability across the age span, hold promise for providing educational interventions that target the number sense.
Understanding how mental abilities change over the course of an entire life is a formidable challenge. One important approach has been to examine change longitudinally, following an individual person through maturation and changes in experience. However, the labor required for such studies is nearly prohibitive if one wishes to characterize change over the course of a full 70-year lifespan, for instance. Measuring abilities in tens of thousands of people, across various ages throughout development, is an alternative approach, and access to the enormous and varied population that uses the Internet holds great promise.