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ABBY NOYCE: So we've been talking this week
about perception of language, how
you take all of this information that's coming in,
sort it out, figure out the structure to it.
We're going to talk today about a slightly smaller subject,
or something that has been studied
in less depth than comprehension has,
which is how you produce language.
You can do the same thing in reverse.
You can go from this kind of non-semantic idea of something
that you want to convey to your listeners.
So that's this kind of message level,
where you've got an idea and from there,
you select the words you're going to use to convey it
and you put together a sentence structure for it.
And from there, once you have words in a sentence structure,
then you need to pull up the phonological information
about the sentence, about all of the words that
are going into it.
And finally, you pass all of this information onto the motor
control centers so that you can actually
articulate your sentence.
So this is a fairly standard--
This model shows that there are four different levels
of processing, and these don't necessarily
happen sequentially, like you do all
of your grammatical encoding before any
of your phonological encoding.
There's some reasonably good evidence
that they interact a bit.
And likewise, with phonological encoding and articulation.
But first, just to get our brains working,
we're going to have a moment of design an experiment.
So you're a cognitive neuroscientist, or
psycholinguist, perhaps, and you believe
that there are distinct levels involved
in the production of language.
So when somebody produces a sentence,
they have to go through different kinds of processing
to do that.
How might you prove or disprove-- how
might you test this hypothesis that there are distinct
phases in language production?
Think about it.
You can talk to your classmates.
Things in your brain that are involved in language.
So we talked earlier this week about,
remember Wernicke had had this idea that there were
auditory images in Wernicke's area and motor images
and Broca's area.
And so Wernicke's aphasia versus Broca's aphasia,
the difference was which of these centers was harmed.
And there's a lot of flaws in that model.
And this guy named Marsel Mesulam modified
it a little bit and said that all language, again,
depends on circuits, on activities
between different language areas.
And Mesulam was one of the first ideas
to point out that different kinds of language production
require different kinds of processing.
And then the example he used is that if I
ask you to do something like name
all the months in the year.
Ready?
Go.
Come on.
January, February, March, April, May, June, July, August,
September, October, November, December.
So this is something that requires
a lot less planning and a lot less
structuring than actually producing
a well-formed sentence does.
And Mesulam hypothesized that just
rote motor connection like this, or recite the alphabet,
or recite your times tables, or any of these things
that you learned by heart as a little kid, really
only requires premotor and motor areas up
here in the frontal lobe.
So we have our primary motor cortex
is this strip right along here, and premotor is the blue stuff
next to it.
He pointed out, though, when you're hearing words,
this activates primarily auditory cortex down here
in the frontal lobe in auditory association areas.
Unimodal, so auditory alone versus these kind
of crossmodal representations, when you're actually thinking
about what you're hearing.
If I say the word, I don't know, baseball,
you probably come up with not just an auditory response
to that, but all of these other associations.
You might have visual memories that you associate
with that or auditory memories that
aren't just the sound of the word
that you associate with that.
So that would be like a crossmodal association.
But Mesulam says that when you're just listening to words
but not acting on them, then most of what's activated
is just auditory cortex.
And Mesulam says when you're producing words,
then you end up seeing activity all over the brain.
You get motor stuff.
You get word knowledge stuff.
All of these different pieces are involved.
So here's an example of--
this is some old-ish, at this point, data--
a PET scan.
So these are participants doing four different tasks.
So they're looking at a computer screen.
And in the first case, they would just
show a word on the screen, and the participants
didn't have to do anything but look at the word.
And as you can see, most of what's
most active in that condition is occipital.
It's all that visual cortex.
You can see there's a little bit in the frontal lobes,
a little bit in the temporal lobes,
but the areas that are most active
are the visual cortex in the back of the brain there.
The second case was pretty similar,
except instead of looking at words, this was auditory.
So you'd have headphones on and look at the screen
and you would hear words being played into the headphones.
And in this case, it's mostly, as you
might expect, temporal lobe stuff that's most active.
It's auditory cortex on the sides of your head
there in the temporal lobe.
And one of the things that's moderately
interesting about that-- and I don't have a good story for why
this is-- is that a lot of the frontal lobe activation you
see in the looking-at-words case goes away in the auditory case.
AUDIENCE: [INAUDIBLE]?
ABBY NOYCE: They were just looking at a blank screen.
I think it had like a fixation point on it.
"Keep looking at the little dot on the screen."
In the third case, they showed them a word on the screen
and participants had to read the word aloud.
They had to pronounce it.
And as you can see, at this point, a lot of the activity
is suddenly in the motor cortex.
I'm sure you all are shocked.
So this is one piece of evidence that articulation requires
a different kind of activity than simply understanding
or perceiving words, that you do,
in fact, need motor activation.
So this is that strip between the frontal lobe
and the parietal lobe, where motor cortex is.
And finally, they asked them to do a word generation task.
So they would show them one word on a screen
and ask the participant to say a word that was related.
So if the word that was shown to them was "bike,"
they might say "ride" or they might say "helmet"
or they might say "Cambridge."
If the word on the screen was "boat,"
they might say "sail" and so on.
So trying to find a word that's associated
with the word on the screen.
So this suddenly requires participants to actually use
the semantics of the word in a way that they didn't have to
on any of the previous levels.
If you're just reading it or just hearing it or just reading
it aloud, you don't really have to think about what it means.
Whereas if you're trying to come up with a related word,
you've got to tap into all of your semantic knowledge
about what that word represents.
And what's interesting about this is that you get,
again, some motor activation, and you
get some auditory activation, but you
get a whole bunch of stuff going on kind of in that premotor
area, that area that kind of coordinates and plans--
utterances and other motor things, but in this case,
utterances.
So this kind of imaging scan of participants
on tasks that require them to think
about language on different levels
is one piece of evidence showing that there probably are
different phases of processing.
Another piece of evidence that shows
that there are different stages in processing
are the kinds of mistakes that people make when they talk.
We all got used to making fun of President Bush
because his command of English language
can be a little weak at times, but the fact of the matter
is that, if you followed anybody,
no matter how articulate they are, around with microphones
and wrote down everything they said,
you'd find tons of errors.
We all make speech errors anytime
you're talking and not just reading
aloud, and sometimes even then.
So one of the most common types of speech errors
are what are called exchange errors,
and you'll see these when people are talking fast all the time.
And you'll get both word exchange errors
like, "I wrote a mother to my letter,"
and you'll also see sound exchange errors,
phoneme exchange errors, and these are called spoonerisms
in honor of Archibald Spooner, who
was a professor at one of the colleges in New York
in like the early 20th century and was
notorious for doing this.
And there are many statements, such as the one there,
that have been attributed to Monsieur Spooner,
and he has given his name to this kind of sound exchange
error.
"You've hissed all my mystery lectures."
"You have tasted the whole worm."
AUDIENCE: What's it supposed to really be?
AUDIENCE: Yeah.
"Wasted the whole term."
AUDIENCE: Oh.
ABBY NOYCE: There you go.
So sound exchange errors are pretty common.
I mean, I remember my eighth grade earth science
teacher sent the entire class of us
into about five minutes of uncontrollable giggling.
We were talking about volcanoes, and he
talked about how volcanoes would release clouds of gash and ass.
And of course, this is eighth grade,
and [GASPS] he said "ass."
And there was much giggling.
And it's just a straight up sound exchange error
like people make all the time.
So let's look at some of these different levels of processing
that have to happen in order to produce
an utterance of some sort.
So the message level is probably pretty straightforward.
You have some piece of information, some idea,
that you want to convey to the people around you.
How you move on from there is a little bit harder.
So one of the things that happens
is that there's this word selection stage.
So you're going from this raw meaning idea
and trying to find the words that
are necessary to represent it.
Most likely, if we look at the sort of models
that we've been looking at throughout this course, where
you've got competing activations,
you can think of this as like the meaning that you
want to get across then is going to activate different word
representations depending on how strongly related to the meaning
they are.
So if we think of the cortical interconnections that we've
considered all along.
And sometimes, every once in a while, you'll
get errors that are a blend of two different words.
So sometimes when you have two words that
are both strongly activated for a particular position
in your sentence, you'll try to say both of them at once
and get all tangled up.
The example in the reading is, if you dropped
a pen under somebody in front of you's chair
and you're trying to ask them to pick it up for you
and you've got both the word "chair" and the word "seat"--
you know, "My pen is under your chair.
My pen is under your seat.
Can you get it for me?"
But the "chair" and the "seat" are both
competing for that noun slot in the middle there.
And if they're both equally strongly activated,
they can both get passed down to the phonological stage
and you can end up trying to pronounce both.
And you'll say things like "My pen is under your cheat--
under your sair-- under--
under your chair.
Can I have it, please?"
And I don't know if anyone here has ever
experienced that kind of tangled up language production,
but it's fairly common if you start listening for this stuff.
The other step in grammatical encoding
that's happening kind of at the same time
as you're trying to find the words you need
is you're trying to understand how
the syntax is put together-- what guides sentence syntax.
And this is, at least immediately,
hard to think about because all that you get to see of it
is the output.
It's what sentences finally come up.
You don't get to see any of the intermediate processes.
And so somebody did a kind of clever study.
They told participants they were doing a memory experiment.
And so they showed them a string of simple images
and said, hey, in order for you to remember these better,
we want you to say one sentence about each image
as it's presented to you.
These were simple scenes.
So you might have--
I don't know if I showed you.
Here's a house and a tree.
And so for this sentence, you could say either,
the house is next to the tree, or you could say,
the tree is next to the house.
And what these guys did is, before each picture was
presented, they just put up a word
and told subjects just to read it out loud.
And so for a scene like this, they might put up a word like,
oh, I don't know, "building" versus a word like "pine."
And what they were hypothesizing was
that, if your priming word was a word that
was related to the house part, then
when you tried to develop a sentence about this picture,
your ideas about houses are going
to be faster to activate because they've
been primed by the word than your ideas about trees.
And so you would expect to see people
say sentences that were like, the house is next to the tree.
They'd pull up the house part first and then
fill the rest of it in later.
Whereas if the priming sentence was something
like pine or maple, then your tree representations
would be more active and easier and faster to be pulled up.
And so you would start developing a sentence
structure that let the tree part go first
and fill in later with the other half
of the image with the house, so that you would see people say,
the tree is next to the house, if they
were primed with one of those tree-related words.
And pretty much what they found is
that the part of the scene that was primed generally
came first in the sentences people spoke.
And the part of the scene that was not related to the priming
word came second.
So you'd see people putting things
into active versus passive voice depending on which
part of the scene was first--
not so much for this image, but an image that shows one
object acting on another object.
So this idea that word selection and sentence structure
happen kind of at the same time and how fast you can pull up
the words you want is going to affect how
you structure your sentences.
If you can get one word right away,
then you're going to build the rest of the sentence
to accommodate putting that word at the beginning
and filling in later with the other words that are
a little bit slower to come up.
So back to these ideas about stages
that are involved in language production.
We talked about grammatical encoding earlier.
Let's talk about this next stage down,
this phonological encoding.
When people are speaking fluently,
they usually produce about three words every second.
And so for each of these words, the speaker's
got to be able to pull up the phonological information
about it-- the information about what pattern of phonemes,
what pattern of sounds, makes up that word, how you stress them,
how it maybe changes when it's next to other words
in a particular order, all of that information.
And one thing that you tend to see happening when people fail
at pulling up this phonological information
is what's call a "tip of the tongue" state.
When somebody maybe reads you a definition and asks you,
what's that word?
And you know it.
You know it's a word you know, and the word just
won't come to you, or the name.
Who's that person?
Oh, I know them.
They are-- and you just can't get it.
Anyone ever have this happen to them?
AUDIENCE: All the time.
ABBY NOYCE: Right.
So it's a "tip of the tongue" state.
And in this model, this "tip of the tongue" scenario
is explained by when you know all of the semantic stuff
about the word.
If it's a name that you can't get,
you know which person you're talking about.
You can tell somebody all sorts of things about them,
like if they were in your history class last semester
or whatever, but you can't come up with the name.
And this is generally believed that when
the connection between the semantic representation
and the phonological information is blocked for whatever reason,
that you can't go from the semantic step
to the phonological step.
"Tip of the tongue" states are more common for moderately
uncommon words.
So for really common, everyday, short words,
"tip of the tongue" states are pretty rare.
For longer, more precise words, words
that you don't see so often, they're more common.
Usually when you have a "what's that word?"
it's for a word that's not one of the most
common in the language.
And there have been a few cases of patients,
usually following some kind of brain injury, brain trauma,
where they have this "tip of the tongue" phenomenon
all the time.
They have a great deal of difficulty.
For every word they try and come up with, they just can't--
they know what they want to say.
They've got the semantic representation right there,
and they just can't find the phonological representation
for it.
Yeah, tip of the tongue.
So this is another kind of example
of a stage where the sentence construction
stage, the grammatical encoding stage, of producing language
is working OK, and then this later phonological encoding is
not working.
So another piece of evidence that these might, in fact,
be separate phases in language processing, language creation,
language production, something.
So do these things ever interact with each other?
The easiest way of looking at this model
is saying that sentences start out as abstract meanings, which
then are passed to this grammatical encoding
level, which finds words and builds a structure, which then
passes them to the phonological level, which
finds sounds, which then passes them to this articulation
machine.
But it turns out there's actually
at least some feedback going on between the levels,
or it seems to be.
And the best evidence for this at the moment
is that we talked about word exchange errors.
"I wrote a mother to my letter."
And these occur-- if there was no interaction
between the grammatical levels and the phonological levels,
then you'd expect to see that word exchange errors happen
equally often between pairs of words,
disregarding whether they have any phonological similarity.
If you actually document what kinds of word exchange errors
people tend to make, this isn't true.
The word exchange errors people make occur more often
in words that have some kind of similar phoneme pattern.
So "mother" and "letter" both have a stressed first syllable,
and then that last syllable with just the E-R on it
that's unstressed.
And patterns like that are what you tend to see.
So there's some amount of feedback going on
between these levels.
Articulation, of course, this last stage.
Articulation is mostly just a matter of motor control.
It's saying, OK, I've got a phonological representation.
How do I turn that into actual, specific movements
of my mouth, my tongue, my lips, all of this stuff that's
actually articulating it?
So here's our good old brain diagram.
Again, primary motor cortex here.
And it's been really well documented
at this point that is kind of laid out
over a strip along motor cortex are regions that
respond to different things.
So toes, ankles, hip, knee, trunk, arm.
Notice there's a lot of cortex devoted to your hands.
That's probably not too shocking.
Fine control over hands is really important for humans.
It's important for a lot of things that we do.
There's also a lot of it connected to, like, lips
and jaw and tongue.
Again, this ability to have really fine and precise control
over these things is important.
I'm always kind of startled at just how much motor cortex goes
to the swallowing and throat control, which makes sense,
but it's not something that we think
of as requiring a lot of control.
So motor cortex happening right up there.
Remember, if we go back to--
what was his name?
The guy we were talking about at the beginning of class
who had a model of how language depends
on different parts of the motor cortex.
And I'm totally blanking on his name.
"Tip of the tongue" moment.
Starts with an M. What was it?
AUDIENCE: Mesulam.
ABBY NOYCE: Mesulam, OK.
Yeah, him.
And he was saying that, depending on what you're doing,
some kinds of articulation basically just require
motor control.
Others have to be kind of coordinated from further up.
So we've got our motor cortex.
So the primary motor cortex, the strip
that's right along the sulcus there,
right up against the parietal lobe,
controls mostly fine motor coordination,
very fine control of movement.
There's actually nerve fibers that go from primary cortex
all the way out to the muscles.
This is like direct muscular control for fine motion.
And then next to it is this kind of premotor area.
And the premotor area seems to be most involved in setting up
sequences of actions, especially in response
to perceptual information.
So for example, if I was to toss something
across the room to a student.
Sarah, catch.
And Sarah is-- very nice.
So Sarah is taking in all of this perceptual information,
where she sees the pen coming towards her,
and coordinating this plan that involves moving her hands up
at the right time and in the right place
in order to be able to catch the pen when it gets to her.
And that's coordinated in part--
setting up that sequence is coordinated
through the premotor area and the cerebellum.
The cerebellum has a lot to do with getting
this kind of smooth coordination so that our muscles are all
working at the right time relative to one another
so that we aren't moving all jerkily.
And then there's this kind of supplementary motor
area that is involved in more self-directed action planning.
So premotor is really working with responding
to your immediate environment, taking that perception
and building a sequence from there.
Supplementary motor area is involved
in longer-term planning.
If I was like, I have a motor goal
of getting to that window, that would
be coordinated by the supplementary motor area.
And then that premotor area would
be more involved in helping me walk around obstacles
and make sure I don't walk into anything
on my way of getting there.
So all of these are going to be involved in articulation.
Someone did a study in monkeys, training them to--
no, what am I thinking of?
Yeah, this was a study in monkeys,
but it wasn't a directly articulation-related one.
Someone did a study in monkeys--
because monkeys don't have language--
where they had either trained them
to push a set of three buttons in a certain pattern
or train them to look at how the buttons lit up and then
repeat the pattern by pushing the buttons.
So one of these was a task where the monkey had
to know the plan in advance.
One of these was a task where the monkey
had to respond to environmental input
to perceptual information.
And this is one of the really solid pieces of evidence
for the difference between supplementary motor
and premotor in terms of what they do.
When the monkeys were working entirely from memory,
then it was mostly their supplementary motor area
that was active.
When they were working in response
to what was shown to them right then, it was mostly premotor.
One other thing about articulation before we move on
is just that, because our face is right up
here close to the brain, a lot of the nerves that
control the muscles that are involved in articulation
don't run through the spinal cord the way a lot of them
do for, say, controlling your hands.
A lot of it is these direct cranial nerves
that come right from the brain.
They don't go out and through the spinal cord and back.
So the way that the circuit works for controlling
facial stuff is different than for controlling
a lot of the rest of your body.
Moving on very quickly.
The other context in which we tend to produce language
is writing things.
How we produce spoken language is not well understood.
How we produce written language is even less well understood.
But there are some key differences
between producing written language
and between speaking language that I just wanted
to highlight for you guys.
Unlike when you talk-- you're usually talking to people,
with people, with people immediately around you--
when you're writing, it's usually just you, usually just
your stream of language that's being put down.
You aren't building it into like a conversation or anything
like that.
If you analyze the syntax that's used
in people's writings versus a syntax that's
used when they are speaking, it's more complex.
You'll see more recursion, more subordinate clauses, more
nested phrases, all of that.
And this seems to be easier to follow when reading, too.
So this make sense on both sides.
And when you're writing, you get to futz with it
and change it after you can write it down and be like, no,
that doesn't make sense.
Let me go back.
You don't get to do that when you're talking.
If you say something that doesn't make sense,
you're kind of stuck with it being out there.