New study examines recursive thinking

Recursion, the computational ability to incorporate elements into elements of the same type, has been hailed as the intellectual cornerstone of language, tool use, and mathematics. A multi-agency team of researchers shows for the first time that this ability is shared across age, species and cultural groups in a new study published in the June 26 issue of the journal. Progress of science.

“Recursion is a way of organizing information that allows humans to see patterns in information that is rich and complex, and perhaps beyond what other species see,” said Jessica Cantlon, professor of developmental neuroscience Ronald J. and Mary Ann Zdrojkowski at CMU and lead author of the article. “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 and different from other species.”

The team organized a series of experiments with American adults, adults from an indigenous group in Bolivia that largely lacks formal education, American children, and nonhuman primates. After training on the task, the researchers provided each group with sequences to order. They studied how each group performed this task, either recursively or non-recursively (listed) and looked to see what order they naturally chose.

The researchers found that human participants of all ages and cultural groups spontaneously ordered the content from a recursive approach by building nested structures. Non-human primates most commonly used a simpler listing strategy but with additional exposure they began to use the recursive strategy, eventually ending up in the performance range of human children.

“This ability to represent recursive structures is present in children up to three years of age, suggesting that it is there even before they use it in language,” said Stephen Ferrigno, a postdoctoral fellow at Harvard University and first author of the Article. . “We also saw this ability in people from very different human cultures. Non-human primates also have the ability to represent recursive sequences, given the correct experience. These results dispel the traditional belief that only humans have the ability to use this rule.” .

The team found that working memory was an important factor affecting participants’ sequencing skills. There is a strong correlation between working memory and the use of hierarchical strategy.

“Some of the errors were due to working memory, because participants had to remember which objects came first and relate them to other objects later in the list,” said Ferrigno. “Children and non-human primates had more errors, which may be due to less working memory capacity.”

The authors note that this work offers a simplified version of a recursive task using visual cues. A more complex series of tasks may not produce the same results.

“There is something universal about being human that allows our brains to think this way spontaneously, but primates have the ability to learn it to some degree,” Cantlon said. “[This research] it really gives us an opportunity to work out evolutionary and developmental contributions to complex thinking. ”