Crows that can understand the concept of recursion
Hierarchical order of bracket stimuli. (A) Following identical procedures from experiment 1, two new training lists were presented until the criterion was reached. Transfer trials were again introduced consisting of one unique pair of parentheses from each of the training lists. (B) Valid center-embedded answers with the two pairs can be ordered in two different ways. In experiment 1, there was no difference in the order. In this experiment, test pairs were composed of the outermost pair of lattice 1 and the innermost pair of lattice 2. The crows greatly preferred to react in an outside-in fashion when producing center-embedded sequences. Credit: scientific progress (2022). DOI: 10.1126/sciaadv.abq3356
Researchers at the University of Tübingen have discovered through experiments that crows are able to understand the concept of recursion. In their article published in the magazine scientific 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 within other structures. An example would be, “The rat that chased the cat ran away.” In this example, the words “the haunted cat” are embedded in another sentence. But two years ago, a team of researchers conducted experiments that showed that some species apes are able to understand the idea of recursion as in three- to four-year-old human children.
In this new effort, the research team conducted similar experiments on crows that show that they too have the cognitive ability to understand recursion.
Both teams’ experiments include training test subjects to choose parenthesis pairs in a sentence made up of symbols, for example by choosing the parentheses in the sentence {()}. Once the crows came up with the idea, the researchers made longer sentences to see if the subjects could still pick out the embedded sentences. As with the monkeys, the researchers found that the subjects could pick out the embedded characters in numbers larger than chance would allow.
Noting a problem with the earlier tests with the monkeys, the researchers of this new effort added more complexity to ensure that the subjects didn’t just memorize the order in which the symbols were shown. They added another one charactermaking sentences like {[()]}. This 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 could pick out the embedded characters without the extra training most monkeys needed.
More information:
Diana A. Liao et al, Recursive sequence generation in crows, scientific progress (2022). DOI: 10.1126/sciaadv.abq3356
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