2 The Nature of Learning

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En provenance du cours de University of Houston System

The Bilingual Brain

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University of Houston System

The Bilingual Brain

158 notes

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.

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Week 2

Office Hours 217:22

2 The Nature of Learning18:13

2-1 AOA In A Single Language12:47

2-2 AoA and Sensitive Periods20:37

2-3 AoA and Language4:28

2-4 Digging into the Depth of Language4:58

2-5 Building a Grammar6:15

2-6 The Sensorimotor Nature of AoA1:56

Rencontrer les enseignants

Arturo E. Hernandez
Professor
Psychology

[MUSIC]

In this next section of the course, we're going to discuss the nature of

learning and how it occurs across the lifespan.

If you recall what Rebeau proposed, he talked about early memories being

organic or deeply rooted, and later memories in life being more conscious,

you might use the word controlled in the psychological literature.

And in this section what were going to consider is how early and

late learning differ, and we’ll talk a lot about the nature of early learning and

its sensory motor basis.

To think about sensory motor nature of processing, I,

the best way to do this, to illustrate this, is to think about the brain.

We can divide the brain into different lobes.

In the back of the brain is the occipital lobe,

about here is the temporal lobe, right around my ear, right.

Up above and

slightly in the back part of my head is the post the parietal lobe, right.

And then the front part of the brain is, not surprisingly, called the frontal lobe.

And of course, the brain is divided into two hemispheres, right.

Left and right.

They're not identical.

They're slightly, what's called asymmetric, slightly different.

So some areas on the left are slightly larger than areas on the right,

especially in the adult brain.

But they are, for the most part, quite symmetrical with some asymmetries.

Now, the back part of the brain, the occipital lobe,

is devoted entirely, to vision.

So, what happens is that light, goes from the environment,

right, in through, the eye, right, through the lens.

Back, actually interestingly,

all through this very gucky kinds of stuff that's in our eye that's very good for

our eyem but not so good for light, because it actually breaks the light up.

And then hits the receptors, which are actually in the back of the eye.

So the light travels through all this junk, going through the eye, hits

the receptors in the back, right, to rods and cones, some devoted to color vision,

others devoted to night vision low, low light vision, that are black and white.

And after that, it travels down the optic nerve,

through some subcortical circuits and then back to the occipital lobe, right?

So the occipital lobe gets, essentially, a, a,

a picture, right, of, of the environment.

And from there, that information gets processed more and more in a more and

more complex manner, through parts of the temporal lobe,

right, and also up into the parietal lobe.

In general, these are two areas,

the temporal lobe is considered an area involved in recognizing what an object is,

right, and the parietal lobe, this sort of up, superior route,

is involved in figuring out where an object is located.

Right, so it's sort of a spatial reference.

And as you can see from this, right, the temporal lobe,

this bottom part of the temporal lobe involved in vision, and

the parietal lobe involved, again, in other parts of visual processing.

This whole back part of the brain is essentially involved in

sensory processing, or more complex sensory forms of processing.

The occipital lobe does lots of different types of computations, as well.

For example it determines motion.

There are areas in the occipital devo, devoted to motion.

There are areas in the occipital lobe devoted to color processing, so

there are patients who can have damage to their brain and not consciously see color.

It's not because they don't get the sig, the color signal from the receptors,

it's the fact that the brain itself, has damage to areas involved in color.

So you've got more and

more complex processing fanning out from this occipital lobe in the visual domain.

Now there are other senses, of course.

For example, auditory processing, that's involved.

There are areas in the temporal cortex that are involved in processing sounds.

And if we go on the parietal lobe, and we go just to the edge of the frontal lobe.

What you find is that those areas are devoted to sensation,

where it's called somatosensory processing, right?

Sensation of different body parts, are located essentially in

a pretty well organized strip, right on the edge of the frontal lobe.

And if we go to that, that's the parietal lobe.

If we go to the other side, just over to the frontal lobe, we have that same strip,

except now that strip is devoted to motor process.

So you can see right at the edge, between the parietal and

the frontal lobe is this sort of sensory motor divide.

And interestingly, these areas are the ones that develop the earliest,

these basic sensory and motor areas.

Sensory first, motor second.

These are the earliest developing areas of the brain.

So that's another interesting thing to think about as well.

Right, and then as we go through the frontal lobe, more and

more forward, you get more and more complex types of processing, right?

So you could think of those as loops upon loops upon loops

that create very complex type of processing.

Now, interestingly these areas are not egalitarian, right?

So and what I mean is that the size of whatever body part is

not actually represented exactly in that way in the brain.

So for example, if we were to take and make a picture of

this area what we would see is, we would see a person with very huge hands.

Why is that?

Well, there's more brain devoted to representation of the hands because,

in fact, we need lots of sensation, right?

Very fine sensation on our hands and

we also make very fine motor movements with our hands.

So our hands are generally highly represented relative to our

feet which are much smaller.

So you can have a relatively large part of the body being represented in

a smaller part of the brain and a much smaller part of the body represented in

a much larger chunk of brain.

Same with the, the head right, the face, all this area has lots of

intricate sensation, and similarly, it has intricate movement and so

you would basically see a huge head overlaid on top of the brain.

And huge hands with, with much smaller feet and legs.

So, it's not exactly the, it doesn't correspond exactly to our body size.

So, when we think about how the brain develops,

we see a similar type of pattern.

The early areas involved in sensory processing are developed the earliest.

And what I mean by that is that there are lots of changes that

the brain goes through across development.

One change that happens is in fact, early in

development there's an overproduction of brain cells, so we actually have,

when we're born, more brain cells than we do later in life and as an adult.

So, part of what happens is a reduction in the number of, brain cells, of neurons.

The second thing we have is we have an overproduction of

the actual connections between neurons, right?

Those are the ways in which the neurons communicate with each other.

Well they're actually, these are called synapses.

And there's actually an overproduction of these.

And what happens across development is, these connections between the neurons,

the synapses actually get pruned back, they get reduced.

And the third thing that changes across development is what's called myelination.

So, in fact, there's a sheath on, if you look at a neuron,

there's a receptive end of a neuron that gets information from other neurons,

and then there is a sort of a productive end, if you will.

A part that sends out signals to other neurons.

And so in-between that is what's called an axon,

and it actually transmits the signal electrically across the neurons.

Each signal that's sent between neurons is chemical.

That gets turned into an electrical signal that travels down this axon, and

then a second signal is produced at the other end, right,

a chemical signal, that again goes on to other neurons.

So you can think of the neuron as a, basically, kind of chip,

if you will, processor that's involved with chemical and electrical signals.

Now, the electrical signal that goes down the axon can travel quite slowly.

So, what's happened is there's this myelin sheath,

it's basically a sheath that serves as an insulator.

That helps to maintain that signal and

make sure that it travels down the axon more quickly.

And that's another thing that develops, right?

Myelination of the brain occurs across development.

So we can look at all these three types of measures, right,

the cell proliferation, the number of cells that are available.

The, the synaptic proliferation,

the production of these connections between the neurons and the myelination.

And by looking at that we can ask then, what happens across development

in these three different metrics of brain anatomy?

The other thing we can ask, is we can ask about how does the brain develop?

In the sense of, how does it mature?

And, one way that researchers have started to think about this,

is they can think of it as occurring in certain centers of the brain.

So we could think of visual development occurring at,

initially at a very center part, right in the center of the,

essentially the occipital cortex, and then fanning out over time.

This is called a primary to secondary to tertiary type of development.

Similar things are seen in auditory cortex with the primary to secondary to tertiary.

All right?

The other axis of development is from back to front, or posterior to anterior,

and the other axis of development is right to left specialization.

All right? So development across a human, right,

lifespan, involves, especially from childhood to adulthood,

essentially, more and more complex, from primary to secondary to tertiary,

from posterior to anterior,aAnd right to left specialization

that occurs as more complex processing is taking place.

And, you know, you might ask, and there's a lot that's been said,

I won't spend too much time talking about hemispheric differences, all right?

They're all over the literature and I do want to make one sort of

point that should be clear if you're talking about the brain scientifically.

I know a lot of people use the term right brain and left brain.

There is only one brain, right?

There is a right hemisphere and a left hemisphere.

So again, we'll talk about the right hemisphere and

left hemisphere as we go through this course.

But there is specialization.

It is the case that our brain takes on functions,

specifically language, for which it needs to, the brain needs to adapt and

do things a little differently than it does for other animal species.

What happens, because our brain has to adapt and

do things differently than it does for other animal species,

is that it needs to take on functions on the left, right, and functions

on the right that are slightly different than those seen in other animal species.

Specifically language has to be crowded into an areas all across the left that

are generally devoted to other processes in other species, and presumably,

if we didn't have language, would be devoted to other processes as well.

So you have this hemispheric specialization,

these differences across these hemispheres.

And we'll talk a little bit about that, it's a very interesting topic of research.

But again its something we should be mindful of.

We should know that in general when we talk about these right and

left differences we're talking about the left being more involved in language and

the right being more involved in what's thought of as visual-spatial processing.

But, again, these two hemispheres coordinate and

they work together in pretty much anything that we do.

It's not that just one hemisphere is acting in isolation, but

rather that they coordinate, and one may be more dominant.

So let's consider two different measures of brain development.

Think about myelination.

You know, when that sheath gets developed on the axons,

that serves to transmit that electrical signal across the neuron.

And we'll also talk about, synaptic pruning, right.

The pulling back of these connections between neurons.

You would think that across development we'd start to produce the right

connections for the right type of processing.

But rather than do that, the brain actually produces too many connections and

then prunes back the ones that are less adaptive.

It's an interesting process.

So let's think about that pruning.

Well, if we look, and

this is some work that's been done looking specifically at the brains, of course,

after autopsy, and this is very difficult work done by Huttenlocher many years ago.

Looking at, essentially the connections between,

these different neurons in different aged brains.

So this was all done atu, upon autopsy.

Of course, it's very difficult, laborious work.

And what was found was that the pruning

occurred earliest in sensory parts of the brain, right?

So the sensory parts of the brain were actually pruning back these connections

earlier then motor parts of the brain began to show pruning and, and

finally much, much later in frontal lobe areas.

Now subsequent work done by Elizabeth Sowell at UCLA along with Arthur Toga and

a group of very well known group that's done work with neuroanatomical MRI.

So in this newer work what they did is they took images across development.

And they looked at essentially,

the structural the properties of the brain, right?

Essentially a measure of myelination, how myelinated the brain was.

And what they found was that,

these metrics also showed a similar type of pattern, right?

Earlier development of sensory cortices, areas involved in vision,

auditory processing, later, later development of the frontal lobe.

And there's quite a bit of debate about that,

exactly when the frontal lobe has fully developed.

It's roughly between 18 and 25.

And what I always like to tell people is,

you know, probably the insurance companies have it just about right, you know?

About 25 is when they start to reduce insurance rates,

auto insurance in the US, rental cars are also available after 25.

So there's some, seems to be some real world correlate between the age of 25 and

the full development of the frontal lobes and

other types of more responsible action in the real world.

There's another area of the brain interestingly that develops even

later than the frontal lobe.

Somewhat surprising finding on the one hand because there's so

much talk about the frontal lobe and how late it develops.

but, in fact, the left temporal lobe,

so this posterior part of the left temporal lobe that's involved in language,

seems to show maturation up until age 40, which is interesting.

I mean, it suggests that language development is very, very protracted.

It takes a very, very long time to develop language.

And I think one thing that I can point out that I mentioned in the previous section

was that we can think of language as a collection of things.

And so what we see is, in fact, that areas involved in very complex

forms of language processing develop very, very late in life, relatively speaking.

Even to the frontal lobes which is at 25, we have language development going up

until the 40's, so that's, that's quite interesting, if you think aboutit.

And that's reflected in the actual brain anatomy when

we look across normally developing individuals.

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