Chennai: Cognitive ability to represent recursive sequences occurs in humans and non-human primates across age, education, culture and species, according to a new study.
A multi-institutional team of researchers set up a series of experiments with US people, adults from an indigenous group in Bolivia that largely lacks formal education, US children and non-human primates.
After training on the task, the researchers provided each group with sequences to order. They studied how each group conducted this task, either in a recursive or non-recursive way (listing) and looked to see which order they naturally chose.
Recursion—the computational capacity to embed elements within elements of the same kind—has been lauded as the intellectual cornerstone of language, tool use and mathematics.
In the case of language, sentences are constituents that may contain smaller sentences.
According to Jessica Cantlon, the Ronald J and Mary Ann Zdrojkowski Professor of Developmental Neuroscience at CMU and senior author on the paper, “Recursion is a way to organise information that allows humans to see patterns in information that are rich and complex, and perhaps beyond what other species see.”
They added: “We try to trace the origins of our complex and rich intellectual activities to something in our evolutionary past to understand what makes our thinking similar to and distinct from other species.”
According to the scientists, the human participants from all age and cultural groups spontaneously ordered content from a recursive approach by building nested structures. The non-human primate subjects more commonly used a simpler listing strategy but with additional exposure began using the recursive strategy, eventually ending up in the range of performance of human children.
Stephen Ferrigno, a post-doctoral fellow at Harvard University and first author on the paper, said, “This ability to represent recursive structures is present in children as young as three years old, which suggests it is there even before they use it in language.”
He added: “We also saw this ability across people from widely different human cultures. Non-human primates also have the capacity to represent recursive sequences, given the right experience. These results dispel the long-held belief that only humans have the capacity to use this rule.”
The study published in the journal Science Advances found that working memory was an important factor affecting the sequencing abilities of participants. A strong correlation exists between working memory and the use of the hierarchical strategy.