Linguists really want to know what's going on in the minds of babies. After all, a lot of our questions about what sorts of knowledge about language we're born with have to be heavily informed by what babies know when they come out. And it's also good to know what sorts of things they acquire when, and in what order. But we've got a big problem: infants and toddlers aren't exactly masters of verbal communication. Most of the techniques that we have require people to write or talk, and babies can't do either.
How do we get around this? By using different techniques, designed just for babies. We talk about three of the big ones: the High Amplitude Sucking Procedure, where we measure changes in how fast or hard babies suck on a pacifier to see whether they can tell the difference between sounds or words; the Head-Turn Preference Paradigm, where babies turn their heads to listen to various language stimuli, and we deduce things about their grammars from their biases from there; and the Preferential Looking Paradigm, where babies can choose to watch or listen to one video or another, based on what they just heard. From there, we can learn a lot about baby language, and we also talk about some of the discoveries made with these techniques, too.
There's another method to test infants that researchers have been using in recent years that's worth discussing, and that's event-related brain potentials, or ERPs. We touched on these in our episode on brains. Our brains are huge masses of electric pulses, winking away all the time, and the electric field that neural activity produces makes its way out faintly through our skulls. If we stick an electrode cap on someone and have them listen to some language, we can measure the changes that the different words or sentences they're hearing cause while they're listening.
Pulling off an infant ERP study has a high level of difficulty. Usually, you need the person you're testing to stay really still, to make sure that any electric changes we see are due to language and not to, say, squirming around or kicking. But if we put the baby on a familiar adult's lap and give him or her a lot of stimuli, we can hopefully get enough data before they get too bored or cranky. It doesn’t always work, but if you can get good data, reading a baby’s brain can give you solid info about what they're doing with language.
Fortunately, some brave researchers have pulled off just this kind of trick! For example, Adrian Garcia-Sierra and colleagues reported on a study in 2011 that looked at two groups of bilingual Spanish-English speaking babies: one between 6-9 months old and the other between 10-12 months old. The research group was interested in whether these double language babies had the ability to differentiate between the Spanish and English versions of /t/ and /d/, which differ somewhat in their pronunciation. (If you're curious about how they differ, it's a systematic variation in voice onset time, but you don't need to know about that to understand the rest of the experiment.)
Remember how, in the video, we said that there's a neurolinguistics testing method that works similarly to the High Amplitude Sucking Procedure, except without the pacifier? One that relies on your brain getting bored from hearing the same thing over and over again, and then perking up again if it hears something new? That's what Garcia-Sierra and his colleagues used here. It's known as Mismatch Negativity, or more generally a Mismatch Response, and it happens because your brain notices a change from something it's become used to.
Let's say you hear [ta]... [ta]... [ta]... [ta]... [ta]... and your brain gets super bored. Suddenly, you hear a [da], and your brain shoots up negative electric activity - new sounds! So exciting! But your brain only finds that invigorating if you actually notice that difference. You have to perceive that it's something new, or you’ll stay bored - just like with High Amplitude Sucking. And if it's not a difference that's important to your language, you don't hear it, as we talked about in our video on allophones. We can see this through Mismatch Negativity effects: monolingual English-speaking adults can tell the difference between the English [ta] and [da], but not the Spanish ones. Monolingual English babies of the same ages are the same - English differences are neurologically arousing, but Spanish differences are incomprehensible.
So how do the bilingual babies respond? Do their brains react the same way? It turns out they don't, exactly: it takes them longer to work out the relevant contrasts for each language. The younger group actually doesn't differentiate between either the Spanish or the English versions of [ta] and [da]; their brains stay bored through everything, because all the [t]'s and [d]'s sound the same to them. But by the time they get to the older group, infants can tell the difference between both the Spanish and English versions of the [t]/[d] contrast. That's pretty fast, considering the elder group is still just under a year old!
That sort of development fits with what we know already from non-neurolinguistic experiments on bilingual infants, like the Catalan-Spanish bilingual baby experiment we talked about in our bilingualism video. There, bilingual babies could differentiate Catalan vowels at 4 and 12 months, but not at 8 months. Here, we see they can't tell apart the English and Spanish sounds at 6-9 months, but they can at 10-12 months. And Garcia-Sierra and his colleagues also showed that their abilities increase with age, as well as with respect to how much exposure they get to the two languages. It takes bilingual babies a bit longer to work things out, but once they get there, they really get there! And the ERP results back this up.
This is just one infant ERP study, and ERP is a method of research that's getting increasingly popular for looking at baby linguistics. Here's another recent study by Angelika Becker, Ulrike Schild, and Claudia Friedrich, showing that German infants can predict what sounds are likely to be coming soon in a word, just like German adults do. But, unlike adults, the babies can't do the full prediction of what words are likely to be upcoming. Babies are amazing with language, but they still need time to get their words across!
So this is another very promising method of infant testing for language. When linguists cross baby research and brain research, a whole lot of science can happen, as long as you have the patience for the squirming.
So how about it? What do you all think? Let us know below, and we’ll be happy to talk with you about what little babies know about language and how we can test them. There’s a lot of interesting stuff to say, and we want to hear what interests you!