Action Potential

# Monkeys master mental math

Everyone has had that awkward moment at a cocktail party or at the lunch table:

You: Congratulations on the little one; she’s beautiful! When was she born?

New mother: Thank you, thank you. Well, let’s see, I’ve kind of lost track, but with today being January 14 and her birthday being December 17…

You: Oh, so she’s already 5 weeks old then. Wow!

New Mother: Uhh…no. She is exactly 28 days old.

Although mistaken mental math has embarrassed us all, we humans still reign supreme in the nonverbal representation of numerical values, right? A new study in PLoS aimed to find out by directly comparing rhesus monkeys and college students on the same arithmetic task.

Many studies have previously established that other animals use a similar cognitive process as humans to nonverbally represent numerical values, but have only tested for the ability to order values according to the amount, as opposed to adding them together, which would require a mental transformation of the value.

Here, the authors directly compared the nonverbal arithmetic abilities of monkeys and adult humans using the same task and stimuli. Macaques and college students were presented with two sets of dots on a touch screen monitor, separated by a delay. Subjects were then required to choose between two new arrays: one with a number of dots equal to the sum of the first two sets, and a second, which contained a different number of dots. Monkeys could not only adequately perform this task (completing a wide range of addition problems), but with enough practice, could also correctly solve novel problems that were never used during training.

Based on modeling results and correlation analyses of the data, the authors determined that both human and nonhuman primates seem to use a primitive mathematical function that utilizes an analog representation of numerical values, with performance in both species limited by the ratio between the numerical values of the choice stimuli.

From the authors:

Numerical addition is a component of the primitive, language-independent set of numerical capacities that has a common evolutionary origin among primates, including humans. More broadly, our data demonstrate that the ability to combine mental representations, which is a characteristic of sophisticated aspects of human cognition, is a capacity that nonhuman animals use within the numerical domain.

So what was the result of the competition? Well, the college students outperformed the macaques, earning an “A” with a 94% accuracy rate, while the monkeys only managed a “C” (76% accurate). But the monkeys shouldn’t feel too bad about losing; after all, they were competing against students at Duke.

Cantlon, J., & Brannon, E. (2007). Basic Math in Monkeys and College Students PLoS Biology, 5 (12) DOI: 10.1371/journal.pbio.0050328