So let’s talk about illusions. Sometimes, our minds play tricks on us, and we see or
hear things that just aren’t there. This isn’t superstition or pseudo-science, it’s
a fact about our brains. And some of our strategies in how we
process language can make our perceptions swerve away from reality.
So let’s take a listen and hear just what can go wrong. I’m Moti Lieberman, and this
is The Ling Space.
So like we’ve said before, just having a normal conversation is actually really hard.
Speech comes at you super fast, like often a couple of hundred words a minute. And beyond
that, the world is a noisy, noisy place. There are cars whizzing by and wind blowing around
and lots of other people having their own conversations that you don’t really
need to listen to. So just dealing with the background noise to your conversation is a real challenge.
But let’s forget about what’s happening around you, and just focus on the conversation
you’re trying to have. Even there, it’s no walk in the park.
First, you have to adjust to the way that your friendly conversation partner actually puts
their words out into the world. Even if they speak the same language as you -
even if they speak the same dialect! – there’s still going to be some variation in the way that they
talk. The melody of their sentences, the way they
craft their vowels, there’s always something to get used to, with everyone.
And even once you get used to the little peculiarities of the verbal cannon lobbing rapid-fire words
at you, there’s still variation within the way that we talk.
We don’t pronounce things exactly the same way every time that we get them out of our mouths.
There are always little differences one time to the next. Some of the variations follow
predictable patterns based on where the sound shows up - so like /k/ sounds different
when you pronounce it in [kʰi] or [skʷup].
But even when we try to make the exact same sound, we’re still not perfect. And when
we’re listening, we have to account for that. Now, we’re totally well-equipped for all
of this. Because we expect there to be all sorts of variation in what we’re hearing,
we have all sorts of strategies to deal with it. And we deploy them super quickly!
Like, take for example a 2004 study that looked at how native English speakers dealt with speech
from two different groups. They heard other native English speakers,
or second-language learners of English whose first language was either Spanish or Chinese.
The researchers found that, as you might expect, they had the easiest time with the native
English group. But! That advantage lasted for basically a minute.
Once they’d been listening to the non-native speech for only a minute, all the English got processed
about the same. So yeah. We get better quickly, even in situations that start out tough.
But here’s the thing. This all has to come at a cost.
If we’re going to be able to adapt so quickly to noisy environments, unfamiliar accents,
and the little wiggly bits in the way everyone pronounces everything, we’re going to need
some top-notch processing strategies. And if we have mental machinery powerful enough
to overcome all of these problems, once in a while, we're going to hear things that aren’t there, or
process things in a way that doesn’t match what actually happened.
Like, take for ezample something that we talked about a few episodes ago.
Sometimes, our brains can compensate for sounds that have been replaced by other sounds, or just
dropped out of words entirely. Not to pull the same trick twice, but did
you notice that earlier, I said “ezample” [əzæmpl] instead of "example" [əgzæmpl]?
Probably not, because when I said “take for ezample”, you knew what you were supposed
to hear, and that was the word [əgzæmpl], with some rock-solid [g] right in the middle.
So you just charitably filled it in for me. Thanks!
This illusion is known as phoneme restoration, and it’s more nuanced than it first appears.
Like, let’s take a sentence from a classic experiment that first looked at this neat
trick: “The state governors met with their respective
legislatures convening in the capital city.” In the original study, the [s] in the middle
of "legislatures" got replaced with a cough the exact same length as the [s].
But the participants in the study reported that they heard the full legislatures,
complete with [s]. Not only that, but they heard the cough, too. Except they said they heard it before or
after legislatures. So these people didn't just sub in a sound
that wasn’t there, they turned the cough to background noise and then kicked it out of the
word entirely. And lest you think, well, that’s just one
sound, we can replace one sound easy? Participants behaved the same way when the whole [dʒɪs]
syllable was replaced with a cough, too.
But even when we have only one word, we can use what we know about our language
to work out what was probably said. So I’m going to give you a bunch of sounds
here, like, basically a word, and I’m going to cover my mouth while I do it so you can’t
read my lips: [s_læʃ]. What did you hear? You probably heard splash, right? Well, maybe
this isn’t a surprise by now, but there wasn't actually any sound between the [s] and the [l].
But as we’ve talked about before, when you make stop sounds like [p], [t], and [k], the
air flow through the mouth gets totally blocked for a bit.
So they all sound the same when you make the consonants by themselves: like (silence).
So when you hear nothing, you figure it’s got to be one of those sounds.
So then why do you hear the word as splash? Well, you have three choices as an English
speaker for what that sound could be. But you also know how English syllables work,
and that lets you solve the problem. [stl] isn’t a good way to start a syllable
of English; like, we don’t have any word like [stlawt]. And while we do have [skl]
at the beginning of a word, it’s way less common than [spl]. So you fill in the silence
with a [p], and you get splash. Even though what I actually said was [sklæʃ]. Did I trick you?
Okay, so now that we’re done with being tricky, why does this work? Why don’t we
just listen to what people are saying and then get the right meanings? Well, of course,
we do that, too. Otherwise, we’d never be able to work out what people are trying to say in unpredictable
situations. Like this: “when I went to the beach, I brought my ferret.” Now, ferrets are
not things you bring to the beach normally. But you can work it out, even though you would
never have guessed I’m a ferret beacher.
That’s because we have two different systems for processing speech.
We have bottom-up processing, where we pay attention just to the sounds that we hear,
and match them up to things in our mental dictionary. That’s what lets you understand
unpredictable things. But the world is noisy, right? If you just relied
on hearing things correctly and then processing them, you’d be losing meanings all the time.
So we also have top-down processing. In top-down processing, we use our knowledge about language
and about the world to work out what’s likely being said.
And the thing is, we use both kinds of processing all the time. They’re both at work when
we hear speech. Without top-down, we’d need everything to
be perfectly silent. And perfect conversation partners saying everything perfectly.
But without bottom-up, we wouldn’t be able to work out words or meanings that were hard
to guess from the context. I mean, we wouldn’t even really be able
to interpret any of the things people were saying - you sort of need to translate sounds
into words for that.
And we really, really want to do that. We humans like language a whooole lot, and we
want to hear it even when it’s not, well, actually language. An interesting example
comes from the work of Austrian composer Peter Ablinger. He took a recording of human speech
and then broke it down into the component sounds that made it up - so like warbly clusters of frequencies, that
he interpreted as musical notes. Then, he linked up mechanical pistons,
which can move way faster than human fingers, to the 88 keys on a piano.
And when he programmed them to play the clusters of notes that he got from the speech recording,
what came out was something that really does sound like a talking piano, if you put your
mind to it. We’ve got a link down in the video description. If you just listen
to the piano by itself, you might not be able to hear the words. But once you're given captions,
and you know what the piano is supposed to be “saying”, everything changes.
This kind of combination of using your eyes and ears to work out what’s being said is
also behind another super-cool phonological illusion: the McGurk effect. The best way to introduce
this is to just show it to you, and it's got to be up close. So watch me as I speak.
What do you hear? You probably heard three [da]’s, right?
That’s because your mind is combining the visual of me saying [ga], with the audio of
me saying [ba]. And you average it out, and end up with the sound in between those two, so, [da].
Try going back and just listening to it without watching, or watching it without any
audio, and you can clearly tell what sound I'm making. But even if you know what I’m doing,
you still hear [da] if you watch and listen to it at the same time. Just, so cool!
So the tactics we’ve developed to deal with the harsh realities of language in a noisy,
imperfect world make our lives much easier. But they do get our minds tied up chasing
phantom sounds or inserting things that aren’t there some of the time. It’s a small price
to pay, though. And I don’t think life would be very interesting if we didn’t get to
keep some of our illusions.
So we’ve reached the end of the Ling Space for this week. If you filled in all my silences,
you learned that there’s a lot of noise and variability that we have to sift through to
understand speech; that we use two kinds of processing to deal
with these challenges, top-down and bottom-up; that because of this, we can get tricked into
hearing sounds and syllables that aren’t really there; and that we want to hear speech so
much, sometimes we even turn non-language things into words.
The Ling Space produced by me, Moti Lieberman. It’s directed by Adèle-Elise Prévost,
and it’s written by both of us. Our editor is Georges Coulombe, our production assistant
is Stephan Hurtubise, our music 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’ll have some extra 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. Tot ziens!