So let’s talk about dilemmas. Sometimes, there’s no clear path to the heart of a
question. And when the question is how to understand what’s going on in the mind of
a baby, it's extra hard, especially if you can't
understand what the crying means. But we need to get in there if we want to find out what
our littlest humans know about language. And fortunately, we’ve worked out a few tricks
for working out what's going on in those tiny minds. So, let’s let you in on our secrets! I’m Moti Lieberman,
and this is The Ling Space.
So linguists have developed a lot of different types of experiments to help us figure out what people
do with language. Most of these, though, can’t help us at all when it comes to babies. Babies
can’t fill out questionnaires; they can’t check off boxes; they can’t tell stories
or press buttons or lie around calmly in MRI machines. They’re just impervious to most
of the things we can throw at them.
But a lot of the biggest questions in linguistics have to do with what we know when we’re
born, and how quickly we start acquiring things. So we’re really motivated to work out what
exactly babies know, and when they know it. To do that, we take a look at the reflexes
that babies naturally have, and the little actions they do when they’re curious or paying
special attention to things, to get at what's going on underneath.
Let’s start with the reflexes. You might know that infants will automatically try to
suck anything you put in their mouths - it’s an important part of their eating
abilities. But you might not know that the rate at which babies will suck actually changes
depending on how interested and alert the baby is at the time. Babies who
are bored suck at a lower rate than those who are bright-eyed and curious.
And that’s the kind of thing that linguists can make use of. Specifically, we make use
of the High Amplitude Sucking Procedure - and yes, I know, but that is the name of the thing.
Using this technique, we can tell whether babies can hear the differences between sounds.
It works like this: first, we give the baby a pacifier that’s hooked up to an
electrode and that electrode measures how often the baby sucks on it. Then we just measure for
a bit, to see what the usual rate of sucking is for that baby, and establish a baseline.
Next, we play the baby the same sound over and over again: something like, “Gus”.
At first, this sound is super interesting! But then, the baby hears it over and over.
“Gus. Gus. Gus. Gus. Gus.” So they get used to it; they habituate. It’s soooo boring.
They don’t care, and then their sucking rate goes way down.
But now what happens? Suddenly, a new sound comes up: “Bus”. Intriguing! If you suddenly
heard [bʌs] instead of [gʌs], you’d probably get excited, too. And what do you do when you
get excited, if you're a baby? You start sucking faster or harder again. It’s only if the baby notices the sound
change that they get excited, though. If they can’t hear the difference - if they hear
[bʌs] and just think it’s just [gʌs] all over again - then they’ll stay bored, and their
sucking rate will just stay low.
So that means that using this, we can tell whether or not babies can hear the difference
between language sounds. And this can be used on the tiniest of babies! They don’t have
to do anything other than listen and suck, and so this technique is safe to be used with babies
under 3 months old. So even at these really early stages, we can still tell what’s
going on with them. That’s what lets us know, for example, that these little bitty babies can
hear the difference between the vowels [i] and [a].
Once babies get a bit older, say from 6-12 months, the array of tools we can use to see
what they're doing with their language increases, too. Like, let’s take a look
at the head-turn preference procedure. This one makes use of another reflex: babies like
to turn their head to look at where stimuli are coming from. So we throw a whole bunch
of lights and sounds at them to see what they like most, language-wise.
Let’s run through an example here to show how this works: first, we put a baby in a quiet room,
on their parent’s lap. Then we put a green light on up at the front of the room, to catch
that baby's attention. That means every time, the baby starts the same exact way.
Then, a red light starts flashing! Shock! The baby turns to look, and when it does,
the light goes off, but some speech starts playing from a speaker underneath. If the baby
finds it interesting, they’ll keep looking at that source - where is this magical language
coming from, and why is it so cool? But after a while, the effect of these spell-binding
sounds goes away, and the baby gets bored and looks somewhere else. Once that happens for a couple of seconds,
the green light comes back on, and we start all over.
So what’s being measured here is what keeps babies interested for the longest - like what
they're more fascinated by. This test has been used pretty widely to look at how babies
like their words and sentences. For example, babies prefer to listen to well-formed sentences,
rather than bad ones. Or that they like to hear their own native language, rather than
some different one, so an Dutch-speaking baby will listen longer to Dutch than to English.
Or that they prefer to listen to frequent words in their language, like “baby” or
“kitty,” over weird rare ones, like “funky ”or “bones”.
It can be used for looking at how babies deal with sounds, too. Like, for example, it lets
us see that babies use information about English sound patterns
to decide whether they’re still within a single word or not.
Like, [ŋk] is more common as a combination
of sounds within a word, and [ŋt] is more common between them. That means if a baby is presented
with some fake word candidates, they'll probably think that [suŋ.kʌdʒ] is going to be one word, and [suŋ.tʌdʒ]
is probably two. You can learn a whole lot from where a baby looks,
and for how long.
And, that’s the basis for the last of the procedures we’re going to be talking about today,
too: the preferential looking paradigm. Here, we start with the idea that babies want to
stare at things that match what they’re hearing, and not things that are wrong.
But that only works if they understand what they’re hearing! So if they’re making
sense of the sentences, they’ll turn their head to watch the one that makes sense for longer; if
they don’t get it, then they’ll just be random little know-nothing babies.
So this one starts off pretty similar to the previous one: a baby sitting on their
parent’s lap, with a light on in front of them. In this one, though, there are two TV
screens. So what happens? As the light goes off, an audio cue starts playing: let’s
say it’s the sentence, “Look! Hazel is kissing Gus. Find Hazel kissing Gus!” And
on one screen, a video plays, showing Hazel kissing Gus; and on the other screen, a video plays showing Gus kissing Hazel.
If the baby understands the sentence, they should hone in on the one that matches what
they just heard. And once they’ve got tired of looking, everything resets.
This technique’s very versatile, and it’s been used to find results for babies who can’t
talk yet across all of linguistics, from phonology, to morphology and syntax, to semantics.
It’s been used to show that kids with as few as two words they can say out loud
still can understand word order in a sentence, so they can tell Hazel kissing Gus from Gus
kissing Hazel. Or that they pay attention to correct pronunciation, so they prefer
listening to “baby” rather than “vaby”. Or that they have sophisticated knowledge
of questions. So let’s say that you show some 15-month-old babies a video of a
book sliding into some keys. Then you show a new pair of videos, one with the
book and one with the keys, and you ask, “What hit the keys?” Those kids will
look at the book! Even though you didn’t say “book”. because they understood what
the question was. We can work out all of this, just from where babies are looking.
So we can learn a lot about what babies know about language, way before they can tell
us anything with their own cute little faces. We just measure how they react to things:
what they prefer to listen to or what they want to look at. From there, we can draw conclusions
about what our tiniest humans know about their linguistic world. No dilemmas left there.
So we’ve reached the end of the Ling Space for this week. If you preferred to turn your
head my way, you learned that we can use the High Amplitude Sucking Procedure to see
which sounds babies differentiate between; that we can test older babies using the Head
Turn Preference paradigm to see what they pay more attention to; and that we can
see what knowledge babies have about syntax, sounds, and words based on how they match
videos to speech in the Preferential Looking technique.
The Ling Space is produced by me, Moti Lieberman. It’s directed by Adèle-Élise Prévost,
and it’s written by both of us. Our production assistant is Georges Coulombe, our music and
sound design is by Shane Turner, and our graphics team is atelierMUSE. We’re down in the comments
below, or you can bring the discussion back over to our website, where we have some more material
on this topic. Check us out on Tumblr, Twitter and Facebook, and if you want to keep expanding
your own personal Ling Space, please subscribe. And we’ll see you next Wednesday. Uvidensya!