After one million years of evolution, Duke students actually aren't so different from their primate relatives when it comes to on-the-fly mental math.
The information comes from a study by Jessica Cantlon, a researcher at Duke's Center for Cognitive Neuroscience and graduate student in psychology and neuroscience, who compared basic addition capabilities in rhesus macaques and college students. On average, Cantlon found that the students' accuracy was only slightly better than the monkeys'.
The study was published last month in the Public Library of Science Biology journal and suggested that a common evolutionary base gave rise to pre-verbal cognitive processes in both primate species.
"People think that language is the holy grail of human thought, but language might just help us build on abilities we've had for thousands of years, abilities we share with monkeys and other animals," Cantlon said.
In the experiment, each group was presented with two sets of dots on a computer screen, followed by several choices-one of which was the sum of the first two quantities. The human subjects were asked to touch the correct answer as quickly as possible without counting verbally. Response times were usually within a second.
"When college students do the same task very rapidly, they use the same process that monkeys use-this kind of fuzzy arithmetic where they don't know exactly how many there are, but have a rough idea," Cantlon said.
The students chose the correct total about 90 percent of the time, whereas the two monkeys-nicknamed Feinstein and Boxer after the California senators-trailed them by 10 percent. The primates' accuracy was high enough to rule out randomness as a factor.
The monkeys had previously been conditioned to choose the larger of two numbers on a touch-screen, Cantlon said. Nevertheless, she and Elizabeth Brannon, assistant professor of psychology and neuroscience and Cantlon's dissertation advisor, were surprised by how quickly the duo mastered the rules of addition.
"There was no way that they were simply memorizing the answers," Cantlon said. After a few weeks, the monkeys were able to add any two numbers between one and 17, although their performance decreased as the sums grew larger and closer together. For instance, "1 + 1 = 2" was considerably easier than "2 + 3 = 5."
The experiment demonstrates that primitive mathematical abilities evolved in primates before more complex forms of symbolic representation, such as language, Brannon said.
"We think that monkeys are keeping track of [quantity] because it's meaningful in their environment," she said. "When they're trying to form accurate representations of how possible patches of food for foraging are, or comparing the number of individuals in different groups, adding becomes important."
Cantlon remarked that certain Amazonian tribes without verbal counting systems showed the same patterns as the students in similar tests-evidence for a mathematical base extending beyond language or culture.
Warren Meck, professor of psychology and neuroscience, said ongoing research of basic abilities in monkeys and infants may shed light on the vast mathematical capability of the human brain.
"[Cantlon's study] is like putting a man on the moon... in that it's the first step to take in order to find out how the brain can do mathematics," he said.
The team is now researching the ability of primates to perform subtraction and probability, because it is unclear whether or not these functions require the use of language. As for addition, Cantlon cautioned against drawing too-drastic conclusions from the study's results.
"It's not the case that monkeys can take a college math exam," she said.
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