Human infants and young birds ‘learn’ syllables in pairs

Early language — whether babbling or birdsong — is all about the ability to “arrange vocal elements in new sequences.” And popular assumption had it that babies begin to babble quite by instinct, much like how young birds start to sing. Now a study published recently in Nature counters this belief.

By comparing the young of these rather diverse species, the authors conclude that both birds and babies ‘learn’ to arrange syllables in different combinations at a very early age. In a surprising find, researchers, including psychologists, biologists, language acquisition researchers and musicologists found that cutting across species, vocal transitions occurred in a common, stepwise pattern.

First, young zebra finches and Bengalese finches were trained to imitate a certain song. The birds were then prompted to rearrange the syllables (eg. ABC-ABC, to ACB-ACB).

According to the authors, all the birds were able to solve the different rearrangement tasks in a “series of steps” by mastering the sequences pair by pair. The babbling of pre-lingual human infants showed a similar pattern. The researchers examined the development of babbling in babies who were nine to 28 months old. While classical studies identified a transition from repeated syllables (‘ba ba ba’) to a more diverse set of syllables (‘ba goo ga’), the authors say, the “infants’ large repertoire of syllable types is acquired gradually.” The developmental shift from repetitive to diverse sequence did not happen in one master stroke. Instead, it progressed in “multiple” shifts and at any given point of time, infants tended to produce a “mixture of newly acquired and old syllable types.”

According to them, results across species suggest that “new vocal transitions are acquired slowly during early stages of development.”

Of course, all three species have very different vocal capabilities and ranges: zebra finches generally sing in linear sequences; songs of Bengalese finches have more complex branching sequences; and pre-lingual human infants can transition between many syllables, “eventually allowing flexible imitation of a potentially infinite array of words.”

“However, what we found is that during vocal development, young birds and human infants struggle with similar difficulties, and go through a similar step-wise process of learning transitions between syllables (obviously, with human babies there are more steps, so the process takes much longer: 20-30 weeks versus 1-4 weeks in birds),”

Dina Lipkind, lead author and a psychologist at Hunter College in New York, said in an email to this correspondent. There are, however, surprisingly few animal groups that are vocal learners, she added. “For example, our closest relatives, apes and monkeys, lack the ability for vocal learning completely.

Besides humans and songbirds, vocal learning exists in parrots and hummingbirds, some marine mammals such as whales and dolphins, and maybe bats.”It would be very interesting to see whether the properties of the developmental process of learning transitions we found in infants can predict various speech disorders later on, Dr. Lipkind added.

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