Study shows rhesus monkeys able to add numbers together for a reward

Apr 22, 2014 by Bob Yirka report
A rhesus macaque monkey chooses between two letters that represent different sized rewards. Credit: Margaret S. Livingstone

( —A team of researchers working at Harvard Medical School has found that it is possible to teach rhesus monkeys to perform simple addition. In their paper published in Proceedings of the National Academy of Sciences, the group describes studies they undertook to teach lab monkeys to add symbols together in order to receive a reward, the results of which have shown that other primates besides humans are capable of performing simple math.

Scientists know that many animals are capable of making numerical estimates—they can tell if they are being invaded by a few predators or many, for example. They also know that some primates have shown a rudimentary ability to add numbers together—to understand that multiple that hold value hold more when combined, for example. In this new effort, the researchers have found that at least one primate—rhesus —can actually add values together to form a result which can be used for comparison with another value.

To learn about the monkey's abilities, the researchers taught several of them to memorize values associated with the digits 0-9, along with 16 letters, and then to assign value to each of them (by giving them a treat if the picked the one with higher value). Then, to find out if they could add, the researchers presented two previously associated characters alongside another single one. To receive a treat a monkey had to add the value of the two symbols then compare the result against the value of the single character and then choose which had the greatest value. The researchers report that the monkeys were able to choose correctly approximately 90 percent of the time.

Of course, the team realized the monkeys may have simply memorized the value of all possible pairings, instead of actually adding, so they introduced a whole new set of characters. Once the monkeys had been trained to associate values with them, they immediately, on their own, applied the math skills they had learned on the first experiment, proving that they were in fact adding the values together to reach a sum, which had a value all its own.

A rhesus macaque monkey is about to touch the symbol 8, worth eight drops of reward, rather than 4, worth four drops of reward. Credit: Margaret S. Livingstone

The researchers noted that that the monkeys did less well when the values of two symbols were closer together, suggesting that at least part of their were based on making estimates—a finding that could prove useful to researchers looking to understand how it is we humans are able to make mathematical calculations.

Explore further: What bee-killing mites can teach us about parasite evolution

More information: Symbol addition by monkeys provides evidence for normalized quantity coding, Margaret S. Livingstone, PNAS, 2014. DOI: 10.1073/pnas.1404208111

Weber's law can be explained either by a compressive scaling of sensory response with stimulus magnitude or by a proportional scaling of response variability. These two mechanisms can be distinguished by asking how quantities are added or subtracted. We trained Rhesus monkeys to associate 26 distinct symbols with 0–25 drops of reward, and then tested how they combine, or add, symbolically represented reward magnitude. We found that they could combine symbolically represented magnitudes, and they transferred this ability to a novel symbol set, indicating that they were performing a calculation, not just memorizing the value of each combination. The way they combined pairs of symbols indicated neither a linear nor a compressed scale, but rather a dynamically shifting, relative scaling.

Related Stories

Monkeys can point to objects they do not report seeing

Nov 19, 2013

Are monkeys, like humans, able to ascertain where objects are located without much more than a sideways glance? Quite likely, says Lau Andersen of the Aarhus University in Denmark, lead author of a study ...

Primates too can move in unison

Jan 28, 2013

Japanese researchers show for the first time that primates modify their body movements to be in tune with others, just like humans do. Humans unconsciously modify their movements to be in synchrony with their peers. For example, ...

Recommended for you

The math of shark skin

57 minutes ago

"Sharks are almost perfectly evolved animals. We can learn a lot from studying them," says Emory mathematician Alessandro Veneziani.

Seafaring spiders depend on their 'sails' and 'anchors'

6 hours ago

Spiders travel across water like ships, using their legs as sails and their silk as an anchor, according to research published in the open access journal BMC Evolutionary Biology. The study helps explain how sp ...

Why the seahorse's tail is square

17 hours ago

Why is the seahorse's tail square? An international team of researchers has found the answer and it could lead to building better robots and medical devices. In a nutshell, a tail made of square, overlapping ...

User comments : 6

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Apr 22, 2014
Not only Reward; Add Mild Electric Shock as Punishment too in case of errors; That will speed up the process of learning!
1 / 5 (1) Apr 22, 2014
Not only Reward; Add Mild Electric Shock as Punishment too in case of errors; That will speed up the process of learning!

Monkeys should pay for this NUISANCE Research!
1 / 5 (1) Apr 22, 2014
This kind of research should be in the domain of kids as a hobby. Nothing more!
1 / 5 (2) Apr 22, 2014
People with Brain Size of a Monkey do this kind of B.S Research!
1 / 5 (1) Apr 22, 2014
Ripley's Believe it or Not presented a film of a dog which supposedly could do multiplication and bark out the answer.
not rated yet Apr 22, 2014
Maybe they are training them to work at McDonalds.....

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.