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Monkeys Understand Basic Counting Skills

March 30, 2011

A team of researchers studying Old World monkeys have found that the primates have better numerical skills than previously believed, BBC News reports.

They found, using a basic numeracy test, that long-tail macaques were able to determine which of two plates had more raisins. However, in strange fashion, the macaques only excelled in the basic test if they were not allowed to eat the raisins used in the experiment.

The results of the experiments show that the animals have the ability to understand the concept of relative quantities.

The researchers, from the German Primate Center in Goettingen, Germany, first tested the macaques by showing them two different amounts of raisins. The primates were then fed the raisins that they pointed to. But the researchers noted that in this test, the monkeys usually got it wrong — choosing the smaller pile of raisins.

Vanessa Schmidt, lead researcher on the study, said that instead of thinking about the quantities, the monkeys were thinking more about how much they wanted to eat the raisins.

“This impulsiveness impaired their judgment,” Schmidt told BBC News. “But when we repeated the test, this time showing them two plates of inedible objects – pebbles – they did much better.”

To find out if the monkeys could actually distinguish quantities, the team decided to try another experiment.

“We wanted to know if they could simultaneously maintain two mental representations of the food items, first as choice, and second as food reward,” said Schmidt.

In the new experiment, which was a little more complex than the original, the macaques were shown plates of raisins, but the reward for pointing to the correct plate was to be fed raisins that were actually hidden underneath.

“They perform as well in this task as they do when choosing the pebbles,” said Schmidt. “This seems to show that they see the raisins as signifiers – representations of the food rewards they’re going to receive.”

Professor Julia Fischer, the study’s co-researcher, said that young children displayed the same difficulty in suppressing their impulses. “There’s a well-known experiment called the reverse reward paradigm,” she said.

“You have two heaps of candies – one big, and one small. The child obviously points at the big heap – which is then given to another child, while the [first] child itself gets the small heap,” Fischer explained.

“Young children have trouble comprehending that they should point at the small heap to get the big one, but if you replace the candies with numerals or other symbols, they can do it,” she added.

Other studies of primates in the past, that have used food to test numeracy skills, may have had inconclusive results because of this effect, and therefore didn’t really understand the real abilities of these types of animals.

The study is published in the journal Nature Communications.

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