Scientists Have Discovered That Monkeys Can Add Up

A rhesus macaque monkey chooses between two letters that represent different sized rewards.Image: Margaret S. Livingstone.

Scientists have found that monkeys can add up, especially when there’s a reward at the end of it.

In a US study, rhesus macaque monkeys demonstrated the ability to not only differentiate between symbols but also to add the values of two symbols at a time.

Margaret S. Livingstone of the Department of Neurobiology, Harvard University Medical School, and colleagues trained the three monkeys to associate an alpha-numeric symbol set with different quantities of a reward.

Given the choice of two different symbols, the monkeys chose the symbol on the touch screen which represented the larger reward with up to 90% accuracy, suggesting that the monkeys had learned to assign specific values to the 26 distinct abstract symbols.

The authors then introduced pairs of symbols that carried a reward equal to the symbols’ additive value.

The monkeys learned to choose the larger value whether it was represented by a single symbol or two symbols which had to be added.

To confirm that the monkeys were performing addition rather than memorising the reward value of all possible symbol combinations, the authors trained the monkeys to recognise a second symbol set.

The monkeys immediately applied their ability to add symbol values to the new symbol set.

The research results are published in PNAS (Proceedings of the National Academy of Sciences).

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