Birds grasp basic rule of grammar, study finds

The European starling—long known as a virtuoso songbird and expert mimic—may also soon win a reputation as something of a grammatician, researchers say: the little bird can learn language patterns formerly thought to be unique to humans. Researchers led by Timothy Q. Gentner, a psychologist at the University of California, San Diego, have found that starlings can understand a key feature of grammar. This feature, called recursive center-embedding, is what lets speakers make new sentences by inserting words and clauses within other sentences.

Thus, for example, “Oedipus ruled Thebes” can become “Oedipus, who killed his father, ruled Thebes” or “Oedipus, who killed his father, whom he met on the road from Delphi, ruled Thebes.” This can theoretically go on without limit. Some researchers, including followers of the highly influential U.S. linguist Noam Chomsky, have held that this is a universal feature of human language, unique to humans, and which forms the logical core of our language. The new findings challenge that view, Gentner said. “If birds can learn these patterning rules, then their use does not explain the uniqueness of human language.”

The finding also “re-invigorates the search” for the evolutionary roots of language among animals, said Daniel Margoliash, a coauthor along with Gentner of a paper describing the findings. The study appears in the April 27 issue of the research journal Nature. The scientists created artificial starling songs that followed two different rules. One allowed a sound to be inserted in the middle of a series of sounds, the simplest form of recursive center-embedding. The other allowed for sounds to be added only at the beginning or end of a string.

The researchers used recordings of eight different “warbles” and eight different “rattles” produced by the same male starling to build 16 songs. Eight of these followed the first patterning rule, and eight the second. They then taught 11 adult birds to distinguish the two sets of songs. The birds received a food reward for pecking at a button when they heard songs from the first group, and for not pecking when they heard songs from the second set. Nine starlings eventually learned to distinguish the patterns, although it took months and a few tens of thousands of trials, the researchers reported.

When tested with different combinations of rattles and warbles that followed the same rules, the starlings performed well above “chance” levels, the researchers said. That suggests the birds had learned the abstract patterns and not just memorized specific songs, they added. The researchers also checked whether the birds responded to “ungrammatical” strings, that violated the established rules. The starlings treated these differently, they reported.

The experimenters then studied whether the birds could grasp a key feature of human grammars: Could they extrapolate these rules to distinguish among longer strings of sounds? Remarkably, Gentner said, they could. The finding that starlings can grasp even simple grammatical rules, Gentner said, suggests humans and other animals share pattern recognition skills and possibly other cognitive abilities. “There might be no single property or processing capacity,” the researchers wrote, “that marks the many ways in which the complexity and detail of human language differs from non-human communication systems.” More generally, Gentner said, “The more closely we understand what nonhuman animals are capable of, the richer our world becomes. Fifty years ago, it was taboo to even talk about animal cognition,” he continued. Now, “no one doubts that animals have complex and vibrant mental lives.”

World Science
May 23, 2006

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