Humans and monkeys ‘think in the same way’, study shows

What do indigenous people from the Amazon rainforest, American adults, pre-school children and macaque monkeys have in common?

Not a huge amount, you’d imagine – but it turns out that the way humans and monkeys deal with ideas is very, very similar, based on tests using symbols similar to language.

Not only that, but monkeys performed far better on the tests than researchers had imagined.

The findings could help us understand how language evolved, the researchers believe.

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“For the first time, we have strong empirical evidence about patterns of thinking that come naturally to probably all humans and, to a lesser extent, non-human primates,” said study co-author Steven Piantadosi, a UC Berkeley assistant professor of psychology.

The tests revolved around linguistic patterns found in speech, known as “recursion”, or “nested structures”.

One example is the nursery rhyme "the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built”.

"Our data suggest that, with sufficient training, monkeys can learn to represent a recursive process, meaning that this ability may not be as unique to humans as is commonly thought," said Sam Cheyette, a PhD student in Piantadosi's lab and co-author of the study.

Monkeys, American adults and indigenous Tsimane people in Bolivia's Amazon rainforest performed tests using touchscreens and index cards which mimicked “phrases within phrases” (known in linguistic terms as “nested structures”).

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Researchers tested the recursive skills of 10 US adults, 50 preschoolers and kindergarteners, 37 members of the Tsimane and three male macaque monkeys.

First, all participants were trained to memorise different sequences of symbols in a particular order.

Specifically, they learned sequences such as { ( ) } or { [ ] }, which are analogous to some linguistic nested structures.

Participants from the US and monkeys used a large touchscreen monitor to memorise the sequences. They heard a ding if they got a symbol in the right place, a buzzer if they got it wrong and a chime if the whole sequence was correct. The monkeys received snacks or juice as positive feedback.

Meanwhile, the Tsimane participants, who are less accustomed to interacting with computers, were tested with paper index cards and given verbal feedback.

To varying degrees, the participants all arranged their new lists in recursive structures, which is remarkable given that “Tsimane adults, preschool children and monkeys, who lack formal mathematics and reading training, had never been exposed to such stimuli before testing," the study noted.