Crows able to understand the concept of recursion

Hierarchical order of supporting stimuli. (A) Following identical procedures in Experiment 1, two new training lists were presented until the criterion was met. Again, transfer trials were introduced which consisted of a unique pair of carriers from each of the training lists. (B) Valid responses embedded in the center with the two pairs can be ordered in two different ways. In Experiment 1, there was no difference in order. In this experiment, the test pairs were composed of the outer pair from List 1 and the inner pair from List 2. Crows greatly preferred responding externally to internally when producing centrally embedded sequences. Credit: Scientists progress (2022). DOI: 10.1126/sciadv.abq3356

Researchers from the University of Tübingen have found through experimentation that crows are able to understand the concept of recursion. In their article published in the journal Scientists progressDiana Liao, Katharina Brecht, Melissa Johnston, and Andreas Nieder describe experiments they conducted with crows and what they learned.

For many years, scientists believed that humans were the only animals capable of understanding the concept of recursion, in which meaningful structures are embedded into other structures. An example would be “The rat that the cat chased ran.” In this example, the words “the cat chased” are embedded in another sentence. But two years ago, a team of researchers conducted experiments that showed that certain types of monkeys are able to understand the idea of ​​recursion in the same way as three- to four-year-old human children.

In this new effort, the research team conducted similar experiments with crows that show that they too have the cognitive ability to understand recursion.

The experiments conducted by the two teams involved training test subjects to choose pairs of parentheses in a sentence made up of symbols, choosing the parentheses in the sentence {()}, for example. Once the crows had the idea, the researchers then created longer sentences to see if the test subjects could still choose which ones were built in. As with the monkeys, the researchers found that the test subjects could select the embedded characters in greater numbers than chance would allow.

The researchers in this new effort, noting a problem with previous tests done with monkeys, added more complexity to ensure that test subjects weren’t simply memorizing the order in which the symbols were displayed. They added another character, allowing phrases like {[()]}. That didn’t slow the crows down; they were just as proficient as they had been with the original character set. The researchers noticed something else: the crows were able to spot the built-in characters without the extra training that most monkeys need.

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