This course explores the brain bases of bilingualism by discussing literature relevant to differences in age of initial learning, proficiency, and control in the nonverbal, single language and dual-language literature. Participants will learn about the latest research related to how humans learn one or two languages and other cognitive skills.
2-2 AoA and Sensitive Periods
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From the course by University of Houston System
The Bilingual Brain
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From the lesson
Week 2
Meet the Instructors
Arturo E. HernandezProfessor
Psychology
[SOUND] Now there's
a related idea between age of acquisition one that's often been considered
in the literature called either a critical period or a sensitive period.
Now, the AOA to critical or sensitive periods, right?
There's an interesting literature,
one that's been developed mostly with work with animals.
We know this, essentially the effects of visual deprivation because of work by
Hubel and Wiesel.
Right. Hubel and
Wiesel won the Nobel Prize for their work and
they had worked in a laboratory looking at the neurophysiological affects of vision.
Essentially, looking at ways to measure what happens in
the visual system because of neurophysiology.
So they would essentially put electrodes inside single cells, right.
And then they would take, they would then present images.
Right?
To a cat and look at which cells fired for which types of images.
Now, they had already looked at and
seen in their lab work what's essentially the property of
very early stages of visual processing, which is called Center Surround.
There seem to be some cells, some neurons that are sensitive to
processing a very specific part of the visual field and
then other surrounding areas from the very specific part of the visual field,
they're sensitive and then surrounding areas they're not.
And Hubel and Wiesel had the idea that this was a very simple type of processing,
so what they envisioned was that cells in the occipital cortex or
higher up in the visual system would actually be
involved in detecting more complex types of things.
They spent several weeks presenting objects to animals.
Looking to see which neurons would fire to which types of objects.
So they presented object, after object, after object.
At the time they used these slide projectors, right?
These very old school things.
You'd put these slides in the projector.
And, and, you know, they would rotate and show different slides on a screen,
it's way be, way before PowerPoint and they did this for weeks.
They found nothing, no effects.
You wonder how did they get the Nobel Prize for nothing?
Well, they did find something eventually.
So one day they were presenting slides, they tried all different types of objects.
And finally, one day for some reason, they heard the cell firing.
So what they generally do in these studies is they,
they hook up this electrode to an actually amplifier that produces a sound, so
they can hear this this neuron firing.
And what they found was that suddenly a neuron fired.
Now, they had no idea why.
They said, why is, why is this neuron firing?
I, I, they hadn't presented anything different than they had before, so
it was the same objects they used.
What they figured out was and this used to happen quite often for
anybody who might remember using these slide projectors is that.
You know, these slides would pop out.
And those were real pain.
I mean, you, people would be presenting these slides and
then this, this thing would get jammed and you'd have to go and
work on the slides and get them to work right.
And then the apparatus would work again.
That was a physical slide projector, right?
So the slide had popped out and created an edge.
And in fact, what the brain cells were responding to was this edge,
the difference between light and
dark caused by this this edge of the actual slide popping out.
An interesting lesson for
those of, of us who always want to find exactly what we expect to find.
In this case, it was some mistake the actual popping out of this slide that led
them to discover and then eventually, discover these edge detectors, right.
And eventually, led to a Nobel Prize.
So it's interesting that, that would happen by chance.
And so what they did then was they began to look at what would happen if
they did different forms of visual deprivation.
If they covered up an eye for some period of time or
if they had a cat that was raised in essentially like a stroboscopic light and
then the kind that makes people look like they're moving in slow motion.
Maybe you've seen that at a, at a club.
Right?
And so they had cats either have visual deprivation of an eye input or
brought up in strobo, stroboscopic light.
And they found that there were certain periods which if the eye was covered or
the light was less than ideal, there would be permanent affects in vision.
Right.
These are called sensitive periods, right?
And, and, and the case of the visual system, their seem to be
these critical periods where visual stimulation is very important.
Otherwise, what happens is visual development never ever
seems to occur naturally.
The sensitive or critical periods have been seen in many different types of
animals, in many different types of domains involved you know,
auditory processing, visual processing.
Even in motor processing, there are sensitive periods.
So for example, if there is deprivation or there is binocu binocular vision.
Right. So we see right, essentially two
2D images that are slightly off and, and that creates a 3D image.
If that's slightly off, right?
Such that we can't see these images as clearly as infants and
that's why this needs to be corrected very early in children.
What'll happen is that children who don't have this corrected early enough,
will actually lose the ability to pursue or
to follow objects in the environment smoothly.
So again a problem early in life with some kind of motor vision
can lead to problems with smooth pursuit for the entire person's life.
That's why these need to be corrected so early.
Another place where people have started to look at this effect is in birdsong.
So interestingly, birdsong has is very complex complex enough
that we know now that people have suggested that some parts of
grammar that are very complex are actually present in birdsong.
Of course, with with song and not with words.
But the interesting thing about birdsong is it has different stages of development.
So an early stage of development of birdsong involves simply hearing, right?
The model songs.
So a young bird will hear a song from an adult and
that will serve as a basis for developing song later.
In a second stage, they'll start to produce.
It's what's called a sensory motor stage.
They start to product or mimic that song.
And then finally, in a crystallized stage, the song will be essentially fixed.
Right?
So that song will be mature and usable, right?
For the rest of that bird's life.
Interestingly, if the bird is not exposed to a good model early in life, right.
Then we can see the same types of issues with development of that bird song, right?
So if the model is not a good model, then the bird does not develop song as well.
If the bird is not allowed to imitate a song, then again,
song will not develop as well.
But deprivation of song in the crystallized phase.
So in the phase where the song is already developed
when there's deprivation such that the bird can no longer hear, right?
There will still be the correct type of song.
So this suggests again that bird song shows these types of sensory,
sensorimotor and then crystallized develop stage.
That we see again in visual domains and in auditory domains and in motor domains.
So the effect of sensitive period is also been seen
in non-linguistic domains for humans.
So let's take one example.
What's called perfect pitch or absolute pitch, right?
The ability to detect a single note and know what that note is in isolation.
This is considered quite rare.
It has perhaps a genetic component to it.
And the development of perfect or absolute pitch fall is a pretty strict timeline.
Essentially, by age five if somebody has not developed a perfect pitch,
they won't ever develop it.
Except if someone speaks a tonal language like Chinese or Thai, right?
A language that has tone in it and uses tone to communicate information.
And in those languages that can be pulled up to Age 10.
So there seems to be some effect of experience on widening this window, right?
But it closes pretty early.
Now, perfect pitch is not a necessity to be a well known musician,
a successful musician.
Lots of musicians use what's called relative pitch, right?
They hear two tones and know the difference between them.
And this idea of absolute pitch is, is again something that's interesting, but
not necessary for musical development.
Within musicians, we can also ask are there effects of musical training
on the brain and on the behavior that are due roughly to age.
So, one study found in fact that if you look at the corpus callosum.
The corpus callosum is one the tracks that connects the two hemispheres.
And if you look at musicians that are expert versus non-expert musicians,
the thickness of that corpus callosum differs.
Right? Those who receive musical training and
are better, more expert musicians show a thicker or show differences in this
corpus callosum relative to those who learned it music later in life.
And, and interestingly, it seems to not just track with expertise, but
actually it tracks also with when that's learned.
So that suggests that there's some neuroanatomical differences that occur in
those who learn music earlier in life versus those who learn it later in life.
Another interesting study that was done by a group in Montreal Canada was
to look at a group of musicians matching a flashing square to a motor response.
They had to press a button and match the, the pace of this flashing square.
This is not a musical task and yet,
musicians who learned earlier in life did better, right?
At matching the pace of this with their modem responses.
Suggesting again,
that musical training has an affect on how people are able to process information.
Right? With
early learning musicians being different than late learning musicians.
Now, we'll talk about this in later sections, the idea of expertise.
It's a, it's a big literature.
It's an interesting literature, looking at what makes the difference between someone
who is an expert and someone who's a novice.
Both the brain basis and, and also the behavior of experts and
novices has been studied.
As I alluded to right now, when I was talking about musicians.
And interestingly when we
think about these types of expert versus novice effects.
It also pops up in sports, right?
We can ask the question about athletes.
What's the differences between an expert and a novice athlete?
And Andrews Erickson has done an incredible amount of work looking at
cross all these different domains.
Music chess players athletes across these different
domains to look at the difference between experts and non-experts.
One idea, of course, that's emerged from this is the 10,000 hour rule,
which was coined by Gladwell.
But actually, discovered by Erickson and, and what Erickson suggested was
after 10,000 hours of doing something, somebody would become and expert.
Right. So, 10,000 hours led to expertise.
Now, the question I wanted to ask was,
well, what happens to people who learn a sport early or later in life.
Does that play a role?
And to do this I collaborated with Sian Beilock and
the idea Sian does very interesting study looking at golf putting.
So in these studies and, and we'll pick these up again when we
talk about the expertise literature later in, in the course.
In these studies, she'd asked experts and
novices to putt, basically to putt a golf ball under different conditions.
So, the cond, and there were various studies that were done.
But essentially, there was, what's called a simple putt.
So you just have to putt the ball and
she would measure things like, you know, how far was it from the target.
You know, an error measurement how often it hit,
it went in, it hit the target or not.
You could get sort of a correct incorrect type of
measurement and what she found was, was quite interesting.
When you look at experts, right?
Expert golf players who are putting.
They do better than novices at simple putting.
Not surprising.
But if we add a second task on it, so we can add actually a different type of task.
We could ask these golf players, right?
To tell us, you know, what their elbow is doing.
So for example, she'd play a tone and
she'd say, tell me where your elbow is when you hear this tone.
And similar types of studies, for example, a soccer players.
What part of your foot hit the ball?
Right. It's a very conscious type of task.
A second task or different task that was used by Beilock was well let's,
I'm going to play a bunch of words for you and
while you're doing this putting task, I want you to tell me afterwards.
What the words were that you heard?
So each player was asked or each participant was
asked later to tell back to the experimenter as many words as possible.
And of course, when there was no task, experts were better than novices.
Not surprising.
They're experts.
They should putt better.
But when this task that involved the body part was used.
In fact, experts did worse than novices.
And it suggests that experts somehow, because they're putting and
it's automatic,
they actually under-perform when they think about you know, their body parts.
And there's been a lot written by Beilock and
other researchers looking at the effects of,
you know, experts focusing too much on their body parts, under pressure.
So Beilock has a very interesting book called Choke,
which describes lots of these different types of effects that happen under stress.
And this was a stressor that actually affected the experts more than
the novices.
Now in the condition where people had to say back all the words they heard,
there they found that in fact the novices did worse than the experts.
Suggesting that experts were happy putting and
they could do this other word task quite well.
Novices were so busy putting,
they couldn't really do very well at this word task and putt at the same time.
So it suggests again that there might be a tradeoff between the types of
stressors that affect experts and those that affect novices.
So the question I had for Beilock was well, what about age of acquisition?
What about when someone learns to play a sport, would that have an effect?
And so we, we discussed possible, you know, brain experiments of those sorts and
one of her graduate students at the time,
Robert Redding came up with an idea to do this behaviorally.
The idea is that we would take early and
late learners of golf that were matched on their PGA handicap.
So the idea is that neither of these two groups differed on how well they
played golf, but one golf had learned to play golf before the age of ten and
the other group had learned to play golf after the age of ten.
So we're looking again at the idea that would learning, right?
And the age at which they first began to play golf affect
the types of processing that occurred during a golf putting task.
So again, we use the three conditions.
Right. Simple putt.
The early and late learners had to putt a golf ball.
A second, a dual task where they had to tend to a body part.
And a third task where they had to monitor for words, right?
So they had to hear these words while they were putting and
then we compared their ability to hear these words.
So not surprisingly,
there were no differences between the groups in Simple Putting.
They were matched again on their golf ability.
Right. Like how well they could play golf.
And so there was no difference when they were just putting.
And there was no difference when they had to monitor for words.
Both groups could do that equally well.
But the group that learned to play golf earlier in life,
actually had a more difficult time.
They made more errors and
they were off the mark more when they had to focus on a body part.
And those who learned golf later in life,
were not affected by focusing on the body part.
Right? So this suggests again that when we
look at early and late learning and
we look in this case, at the acquisition of a motor skill, golf putting.
That the early learners seem to have more of
we would call this an embodied representation.
Right? And
it's actually embodied, but it's actually in a chunk.
So if you ask someone who learns to play golf early in life to tell you
what their elbow is doing, you're asking them to actually pull apart a chunk.
And what happens is their behavior is affected more than someone who learns it
later in life,
where they actually might have learned in a slightly more conscious manner.
And they don't struggle as much with pulling apart this chunk, right?
And telling you what their body part is doing.
And again, this suggests that the effect of age of acquisition
occurs within a motor skill, right?
Outside of language.
And what we've considered so
far is when we think about this is that this age of acquisition or
this sensitive period occurs within sensory motor types of domains.
Right?
Within vision.
Within birdsong.
Within smooth pursuit.
Within music.
Right? Listening to music, absolute pitch.
Tracking when a flashing square is on the screen.
And in the case of sports having to putt a golf ball, right?
All of these are sensory motor types of processing outside of language and
they are sensitive to when the learning took place.
In other words, learning early and late in life for sensory motor skills differs.
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