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How we learn new languages: songbirds offer insight

Vocal skills: Parakeets mimic our sounds and words, and “talk” human language.

Vocal skills: Parakeets mimic our sounds and words, and “talk” human language.   | Photo Credit: C.V.Subrahmanyam

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A recent study on zebra finches and owl finches shows a genetic link

We humans have used other animals as models to understand our own biological features and their mechanisms. The common fruit fly has been used for identifying several genes and how mutations in them are related to physiological and biochemical defects. Many of the genes in the transparent worm called C. elegans have functional counterparts in humans. Mice, rats and rabbits are somewhat “higher” animals and have offered us even greater insights. Such model organisms are easy to maintain and breed in the lab and can be studied right from their birth, adulthood and through their lifetime in short spans of time.

But when it comes to understanding the brain and the neurological basis of some actions, in particular, how we speak, sing, imitate and learn foreign words and languages, the above models are not the best. Some have tried using our closest ancestors, such as chimpanzees, in order to understand how they speak, sing or learn other words, but alas, with little success. Two psychologists (C & K Hayes) adopted a baby chimpanzee at their home, brought it up as a child and tried to teach this little girl chimp (called Viki) to speak human language. Alas, besides trying to say “mama”, “papa”, “up” and “cup”, Viki could do nothing more. The gradual shaping of her jaw and lips (as she tried hard) allowed her to utter these words, nothing more. It appears that the neural and physiological set up which she had, Viki could only utter chimp sound but not imitate humans. Likewise, another couple (the Gardners) had bred a chimp (called Washoe) at home, and she did a little better than Viki, in that she could do learn a ‘foreign’ language (not spoken but gestural), namely the American Sign Language (ASL), in which she could learn as many as 350 ASL signs and respond to some questions in this non-verbal language. It would thus appear that the necessary anatomical vocal ‘hardware’ is inadequate here, though the ‘software’ to learn is developed somewhat in chimps. We, their descendants, are blessed with the right hardware and software.

Animal models

Thus in looking for animal models for understanding how we speak, sing, imitate and learn ‘foreign languages”— and such brain-based activities — we need to go back in evolution and see which animals have been doing these activities, and which parts of their brains are involved in these, and look for similar features in the human brain. And the best animals models used so far are songbirds such as parrots, mynahs, finches, hummingbirds and such. For example, some of us keep parrots as pets at home and find that they not only utter their own words, calls and species songs, but also learn to mimic our sounds and words, and “talk” human language. This shows that, these songbirds have parts in their brain which play a key role not only in the normal vocal development which helps them in learning to speak/sing their own ‘species’ language (the normal genetically programmed ones from their parents), but also to imitate those of others. This has offered some insight and parallels with our own vocal development of learning to speak, sing and so forth.

An early summary, well worth reading, is from Peter Marler in the journal American Scientist; 1970:58:669-673, available online. While all animals, cats or chimps are programmed to learn and vocalise their own species language (grunts, gestures and such), learning and imitating is done by songbirds which arose 250 million years ago, and us humans, who came on earth only 2-3 million years ago.

How songbirds learn

Songbirds learn their species language, just like other animals do, by imitating the sounds of older members of their own species. This they do by modifying their voices such that they match what they have memorised. A newborn songbird starts with a babbling voice and sounds, which in a few weeks, turns to the language of the species; in other words, this “subsong” becomes the “song” of the species language. Note, too, how a newborn human infant babbles, which turns into human language — the language spoken at home by its parents and family members.

F. Nottlebohm, in his review article on the neural basis of birdsong (PLoS Biology, 2005; 3(5):759-761; e16) points out that there is a group of discrete brain areas (called nuclei) and their connecting pathways, referred to as the song system or song nuclei. In hummingbird brains (likewise in other songbirds, such as parrots) there are 7 discrete structures which are active during singing, showing that these are the anatomical and functional ‘vocal nuclei’. In such vocal learning birds, the brain’s forebrain region appears divided into two sub-pathways: in a vocal motor pathway used to produce learned vocalization, and the other, a loop, that allows the modification of these ‘songs’. We humans too have similar forebrain pathways (Davis, J. Ornithol. 2007; 148(1); 35-44).

An interesting work, in this connection, has appeared from a Japanese group in Hokkaido, this month (Wang et al., PLoS Biology 17(11): e3000476;htpps:doi.org/10.1371/journal.pbio.3000476). They studied the singing pattern of two finches — zebra finches (abbreviated as z) and owl finches (o), and studied the genes that are expressed in the song nuclei of each of them. There was about 10% difference in the expression of the genes, leading to different species songs that they sing. Next, they crossed the two species and produced two hybrids (zo, and oz, depending on which male crossed with which female), and recorded their songs. The zo hybrid sang both her parents’ species songs, the zebra finch song and also the owl finch song; likewise the hybrid oz sang the owl finch species song, plus the z song! More such inter-species hybrids would offer additional insights, though we cannot do so with humans (ethical considerations)!

dbala@lvpei.org

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Printable version | Dec 15, 2019 9:12:37 PM | https://www.thehindu.com/sci-tech/science/how-we-learn-new-languages-songbirds-offer-insight/article30062681.ece

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