I have five siblings, all boys. My brothers range from 11 to 21 years younger than me. (I bet that’s not where you thought that sentence was going!) As you can imagine, I am very familiar with the high-pitched, singsong way parents speak to their children. This style of speech, called Motherese (or Parentese), was used so frequently in my household that my mother sometimes accidentally directed it at me. For example, last year when I told her on the phone that I’d found a new apartment, she said, in excited motherly tones, “Did you?” to which I replied, “Yes, I did. And I’m 23.”
Although Motherese can be deeply annoying for older siblings and the general public, it’s important for children’s development of speech. Last Wednesday, I attended a lecture (part of Columbia’s Mind Brain Behavior Initiative and sponsored by the Dana Foundation) where the speaker, Dr. Sarah Woolley, told us that parents’ speech shapes infants’ auditory perception.
When adults use Motherese, they subconsciously enunciate differences between phonemes, the smallest units of speech sound (for example /f/ as in fade). At six months, babies can discriminate between all phonemes of all languages, but by one year, they can only differentiate between the phonemes of their native language(s). For example, Japanese speakers often have difficulty distinguishing between /l/ (as in lay) and /r/ (as in ray) when learning English, because these sounds do not exist as two distinct phonemes in their native language.
Additionally, if you don’t learn any language by the time you’ve gone through puberty, phonemes are the least of your problems. Language has a critical period, meaning that if you don’t learn a first language by adolescence, you probably never will. Second languages are different—it’s much easier to learn another language before the age of seven (as opposed to, say, struggling through three semesters of Italian in college), but you can still learn it later in life.
The intricacies of language development introduce a slew of questions being addressed by researchers like Dr. Woolley. However, because it’s unethical to isolate a child from language and see what happens in the brain, she first had to find an appropriate animal model of human language. Dr. Woolley uses songbirds in her lab, and not just because they’re supremely adorable. Bird song, it turns out, is the closest thing to speech in non-human animals, and birds learn song similar to the way humans learn speech. Little songbirds have their own version of infant babble; they absorb adult song the way babies absorb adult speech, and then they practice it by song-babbling. Within a species, each bird sings unique but species-specific songs, but Dr. Woolley has demonstrated that cross-species song tutoring is also possible. Furthermore, like in humans, if a songbird is isolated and doesn’t learn song before the end of the critical period, it can never learn to sing normally.
Now that she has demonstrated that songbirds are a good model for human language development, she and her colleagues are using birds to study the neural underpinnings of vocal learning and how their brains process things like song versus other complicated sounds. Understanding how language works in the brain may improve approaches to the many mental disorders in which language is affected.
In the meantime, I will leave you with a video, shared by Dr. Woolley at the lecture, of my new favorite animal, the lyrebird: