Duke Research: Creating Knowledge. Serving Society

Elizabeth Brannon is an assistant professor of psychology and neuroscience at Duke who studies how human adults, infants and monkeys think about numbers. This is abstract thought that doesn’t necessarily require language. She’s looking for the brain systems that support thinking about numbers with an eye toward figuring out how this skill may have evolved.

Q - I’m pretty sure I saw my pre-verbal toddler do some quick math when I snuck two of his four pacifiers out of the crib at bedtime. He seemed to notice the difference and let me know! Is that even possible?

In fact it is! Many studies show that babies even in the first year of life can tell the difference between quantities. For example, if you show a baby all sorts of pictures that have the same number of objects in them they will become bored rapidly and attend less and less to additional pictures. Then if you present the baby with a new picture that has a different number of objects they will get more interested. This suggests that they actually noticed the change in number! But this only works if the change represents a sufficient ratio change. For a 6 month-old baby we would need to double or half the number of objects in the pictures for them to notice. So yes, your toddler may certainly have noticed a reduction of 4 to 2 pacifiers!

Q - In your study about the monkeys and college students doing quick sums without words, how do you know the college kids weren’t counting? (see news release)

If the Duke students were counting, I would hope they would do a little better than they did! We instructed the students not to count and to respond as quickly as they could while still getting a majority of problems correct. Other studies have required adults to recite poems while doing number tasks to make sure they were not counting, but in our case it didn’t seem necessary. The fact that the college students performed so similarly to monkeys shows us they were not using language.

Q - Why would primates need to count anything?

There are all sorts of reasons why number would be useful for nonhuman animals in the wild. In foraging situations animals need to make decisions about how long to stay in a given patch of food and when to move on. This likely involved calculating the rate of return in a given patch of food and comparing it to the average return in the area. Thus animals may make calculations such as the number of food items they have gathered per unit of time they have searched. Another situation where numbers may be important is for territorial animals that need to assess the number of individuals in their own group relative to competing groups to decide whether to stand ground or retreat.

Q - A while ago, I read about a tribe of people in South America who don’t have words or concepts for any quantities but “one or a few” and “many.” If our math ability is a feature of the brain that has evolved, where do these people fit in?

Yes there are two different Brazilian groups, the Munduruku and the Piraha, that don’t use number words in a formal counting series. When these people are tested with nonverbal tasks like the ones we use in my lab they perform just like Western adults who are not verbally counting and just like monkeys. Certainly if we transported an infant Munduruku to Durham NC and raised the child with the English count list, the child would learn symbolic math just as readily as you or I. However, without a language for numbers the Munduruku and Piraha are unable to appreciate precise numerical differences such as 2006 vs. 2007 and instead are limited to the approximate number sense that we all share with nonhuman animals and babies.

Q - Would your findings have any bearing on how we teach pre-schoolers about numbers and counting?

We are just starting to explore how the nonverbal number sense that we study in babies eventually transforms into the symbolic system for counting and mathematics learned in school. If the nonverbal number sense is really providing a critical foundation for math achievement then this will suggest teaching methods that provide more grounding in the nonverbal quantity system.

NEXT MONTH

Engineering new heart muscle with Nenad Bursac. He’s an engineer who works with stem cells to find a way to patch and repair the damage created by a heart attack. Ask Dr. Bursac your own questions about stem cells, tissue engineering and biomaterials.