Crows are said to have abilities thought to be strange to humans

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Crows are known for their extreme intelligence, which is among the highest in the animal kingdom. Experimental studies have shown that they can create and use tools to solve a specific problem, and understand and use digital signals, among other skills. Researchers from the University of Tübingen, Germany, have discovered that they also understand the concept of recursion – which until now was considered a uniquely human skill.

Recursion refers to the cognitive ability to combine a structure of elements with other structures of the same type, with a certain hierarchy. The following sentence is an example: The mouse ran, chased by the cat » ; the phrase “cat chased” is embedded here in another sentence. The grammatical rules of the language use recursion to expand the variety and complexity of possible sentences. Thus, recursion is considered the key concept that distinguishes human language from all other forms of animal communication.

Its evolutionary origins are however controversial and few studies have been conducted to verify whether animals can understand and construct recursive sequences. In 2020, a team of researchers showed in an experimental study that some monkeys understand the idea of ​​recursion, at least three- to four-year-old children — suggesting that the concept is not unique to late to people.

An ability that non-human primates seem to have mastered

In this experiment, two pairs of symbols — together with ( ), [ ] and { } — were presented to human and animal subjects on a screen, in random order. Subjects are trained to rearrange them into a recursive sequence of the “central integration” type — such as { ( ) } or ( { } ) for example. If successful, the humans received verbal approval, while the monkeys received a reward in the form of food.

The researchers then showed their subjects an entirely new set of brackets and observed how often they laid them back and forth. In this task, monkeys proved to be as good as children; however, they need an additional training session. Inspired by the results of this research, animal physiologists from the University of Tübingen set out to conduct a similar experiment with crows.

These birds have repeatedly demonstrated complex cognition, through elaborate tool use, analogical reasoning, and numerical skills. ” As songbirds, their vocal communication abilities have interesting parallels with human speech, such as complex acoustic cues, sensitive learning periods, the need for auditory feedback, detailed abilities to voice production, and social learning. “, underlined the researchers in Advances in Science. All these characteristics make the crow a promising candidate for recursion comprehension research.

(A) Training procedure. (B) Symbol pairs used for training. (C) Major types of responses elicited. (D) Proportion of response types made by crows (in saturated colors) compared to American adults, Tsimane adults, American children, and monkeys as reported by Ferrigno et al., Advances in Science (2020). © D. Liao et al.

First, the birds are trained to order pairs of symbols in the form of a centered recursive sequence (pecking with their beaks at each symbol in the correct order). If successful, they will be rewarded; if unsuccessful, the screen flashes and a beep sounds. They were then tested on their ability to center nested structures against previously unseen symbol pairs.

Performance equivalent to that of human children

Crows are trained to master the structures { ( ) } and { [ ] }, until you get more than 70% success. Then, these are the pairs ( ) and [ ] — never shown together in practice — submitted to them. Result: the crows were able to produce recursive sequences in about 40% of the trials, a performance “significantly higher than chance”, underlined the team. The performance of crows is not much different from children, but higher than that of monkeys – especially since crows do not need additional training, unlike primates.

The team wanted to test whether the position of the training symbols affected the birds’ responses. In another experiment, they therefore arranged that one of the pairs used for training was either the inner pair or the outer pair. Therefore, the birds are trained with two sets of symbols: < [ ] > and [ ( ) ]. In the test, the pairs < > and ( ) are shown together. Result: Not only did the crows give fewer cross-type responses, but they almost always gave the structure: < ( ) >. ” This result suggests that crows may be sensitive to the bounded hierarchical structure of centered sequences. “, note the researchers.

Some experts remained skeptical of the results of the 2020 study, saying it was possible that the sequence of symbols during training had a significant influence on the monkeys’ responses. For example, if the training sequence is [ ( ) ], and then offered the pairs ( ) and { }, they tend to position the parentheses memorized the previous scheme. The same problem arises here, with crows. To dispel doubt, the researchers added a level of complexity, using training lists with three pairs of symbols, as described below.

Constructing recursive sequences from three pairs of symbols. © D. Liao et al.

With three pairs of symbols, the possibility of creating sequences without understanding the underlying concept of recursion becomes less. said Diana Liao, first author of the study. The Ravens performed as well as the previous experiment. ” The majority of responses were by far centric order, with proportions of 42.5 and 43.8% for crow 1 and crow 2, respectively. “, the team reports.

This discovery raises the question of why crows (and possibly other animals capable of recursion) can use this ability. ” They seem to lack elements similar to human language, so recursion may be useful for other cognitive functions. “, assumes Giorgio Vallortigara, professor of neurosciences at the University of Trento in Italy, who did not participate in this study. One hypothesis is that animals can use recursion to represent relationships within their social that group.

Source: DA Liao et al., Science Advances

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