We all know it takes a while to study the foreign language, but how does it happen? How come that the meaningless mumbling starts making sense? We are not born with the ability to understand an arbitrary language, but are able to learn it from the other humans. Using self-introspection we could hardly remember when we ourselves started to speak, yet by studying children, researchers could have a better sense of how it happens. Nonetheless, due to ethical reasons it is almost impossible to record the activity of single neurons in the baby brain. Therefore, our understanding is substantially limited.
To overcome this difficulty researchers use the animal models to study language acquisition. But which animals could have something comparable to the human speech? In the lab of Sarah Woolley at Columbia University researchers use zebra finches and their bird songs as a model for language acquisition. Undoubtedly human language is different from bird songs, yet they both share certain similarity when it comes to learning. In the experiments they wanted to know what determines the particular bird song structure, is it innate behaviour or is it learned? The bird song is very important to for them, especially for males. If the male bird does not sing it right, there will be no chance for him to make an offspring. The male chicks pick the song from their fathers. The female do not want to mate with the males that do not sing right, which could mean that something is wrong with their brain. This has created the selective pressure for the male birds that can only sing their songs right, i.e. the way the female like.
To answer the question about innate or learned behaviour, Sarah Woolley studied two similar species with different songs: zebra finches and long tail finches. After both bird couples laid eggs, researchers carefully exchanged them between zerba and long-tail finches in the same bird colony. Later on when the little chicks in both nests were maturating, they were exposed to the songs of their surrogate fathers as well as their biological ones since they lived in the same colony. Later, when the birds were matured in two nests, the scientists recorded the songs in these birds with surrogate families. Surprisingly, they found that little zebra finches learned the songs of long-tale finches, while the long-tail finches learned to sing like zebra finches. It is surprising because despite the fact that young birds listened to the songs of their own species, they learned their songs only from their surrogate fathers. In other words the bird song behaviour is learned and not hard-wired in the brain.
After analysing these songs researchers turned to the bird brain. Once again, they found that the activity in the auditory cortex was very similar between original zebra finches and long-take finches raised by zebra finches. This result confirmed the idea that the mechanisms of bird-song acquisition is substantially similar between two species, i.e. they are using the same neural mechanisms. It means that the experience, i. e. learning the songs from their fathers, determines what songs will be learned, not genetics.
What could these studies tell us about human language acquisition? The natural analogy comes to studying languages. If the child is exposed to the foreign language since he/she was born, it would become the mother tongue of this child. The brain learns language from the environment and it is not genetically hard-wired to study the particular one. Nonetheless the human brain is probably hard-wired to learn human language, but that is another big story.
Thus, by studying the animal models, like zebra finches we can increase our understanding how exactly the brain learns the language. Unlike human studies, we could get the insight into neural network mechanisms of language acquisition. Certain labs are also studying how the language is acquired by measuring activity in babies before they start to speak. Taken together, these studies would help us to fully understand how we learn language, so we could study new ones more efficiently.