Language and Sound – A Baby’s Sophisticated Brain

I recently had the pleasure of listening to a seminar entitled “Learning Language,” which was about many different aspects of how babies and children acquire language skills. It was given by Dr. Patricia Kuhl, Professor of Speech and Hearing Sciences at the University of Washington’s Institute for Brain and Learning Sciences. Dr. Kuhl is internationally renowned for her research on brain development and language acquisition in infants and young children, and is one of the leading experts in the world. This was one of the more interesting seminars I’ve ever sat through – and believe me, I’ve sat through many seminars during my years as a scientist! Before this seminar, I had never really thought about the science behind how we learn language. But now that I know a little bit about it, it’s a fascinating topic.

To begin, let me tell you a story. I had a Chinese-American roommate fluent in both English and Mandarin. She once told me a popular Chinese children’s rhyme, which was in Mandarin. It was the strangest sounding children’s rhyme I’d ever heard! To me, it sounded like the same word, repeated over and over. To her, however, the words were different – distinguished by tonal differences in each word that her ears could detect. (If you’ve ever had experience with Asian languages, this may sound familiar to you!) The reverse is also true. Native Japanese speakers, for example, often cannot hear sound differences in the English language, such as the difference between “ra” and “la.”

Have you ever wondered why this is? I mean, it’s just sounds, right? I can hear pretty well – so why can’t I hear the tonal differences associated with Mandarin Chinese? Why can’t a native Japanese speaker distinguish an “L” from an “R?” It’s not just that we can’t pronounce them right – we can’t even hear them.

One possible answer is something called the “Native Language Magnet/Neural Commitment Theory.” Babies are born with the ability to recognize a vast range of differences in sounds, and studies have shown that they can distinguish differences in sounds from languages all over the world. However, once they’ve reached a year of age, their ability to distinguish sounds from foreign languages is greatly diminished. An example showed by Dr. Kuhl concerns the ability of Japanese and American babies to distinguish “ra” from “la.” Both sets of babies can distinguish “ra” from “la” very efficiently at 6-8 months of age. However, at 12 months, Japanese babies are only half as likely the be able to hear the difference as American babies; their discernment gets worse as they get older.

According to the Native Language Magnet/Neural Commitment Theory, the brains of babies are constantly listening to the world around them. And the sounds that they hear most often are the ones that their brains hone in on. An American baby, for example, will hear “ra” and “la” quite often in the speech of those around her. So her brain recognizes that the difference must be important! Therefore, it puts special effort into remembering the difference between the sounds. A Japanese baby, on the other hand, will likely never hear the sound “ra” - it doesn’t exist in the Japanese language. His brain will therefore have no reason to make an effort to remember the difference between the sounds. Instead, his brain will focus on important tonal sounds in the Japanese language.

In this theory, the infant brain passes through 4 phases. Phase 1 is the initial state, in which infants can discern phonetic differences of a wide variety. Phase 2 is the neural commitment state. Auditory processing results in the classification of vowels and consonants into “bins,” or distinguishable groups. When 2 different sounds are put into the same bin, the brain loses the ability to distinguish between them. A Japanese infant will group “la” and “ra” in the same bin – and thus, to them, it becomes the same sound. Phase 3 is really an enhancement of phase 2, in which these phonetic groupings get reinforced. And in phase 4, this neural commitment is stable. The infant brain has now developed in such a way that it can distinguish between the sounds of its native language, but not of other languages.

One interesting ramification of this work is that the sounds a baby hears is really important! He may not know the words you use, but he can use the sounds you make to build his foundation for understanding the language as a whole. It’s the sounds that matter. This means that baby talk is actually really, really important.

In baby talk (also known as “mother-ese” or “infant directed language”), adults exaggerate the phonetic sounds they make. The vowels are stretched, the pitch changes are exaggerated, and the words are slowed down. The end result is to make the sounds even easier for babies to hear and distinguish. Babies find this kind of talk immensely appealing – studies have repeatedly shown that baby talk holds an infant’s attention better and longer than does regular speech. And in terms of the neural commitment theory, baby talk makes it clear to infants what sounds are important for their native language. So evidence indicates that baby talk actually helps infants in the early stages of language acquisition.

There are vast reams of research on language acquisition and skills that I haven’t even hinted at here. It’s an immensely complicated subject, studied by neurobiologists, behavioral psychologists, and linguists, to name a few. But once again, I am amazed at how well our brains handle such an enormously complex thing – especially when we’re as young as 6 months old.