So, the brain is generally what we're talking about and
here you have a picture, the overall view of the human brain.
A friend of mine, Jeremy Wolf, always said make sure you draw in the nose.
So, okay, so your nose is over there, your eyeballs here and then there
are all these various structures, the cerebellum in the back here.
Behind your head is where a lot of rapid motor control kinds of things take
effect, bunch a whole bunch of structures, all of this crinkly stuff up
here is the cortex and we'll talk about that a little bit later.
By the way these little things sticking out right here called the olfactory
bulbs, those are the things that actually go into your nasal cavity that
does sense of smell, that's actually a part of your brain that sticks out
into your into your nose.
And another part of your brain that sticks out is actually your retina and
we'll talk about that in a minute.
The parts of the brain I want to talk about today are, its, this lesson and
next, of course, are the parts that are involved with the human vision system.
And those are poorly drawn here on this schematic.
It's just ugly, but it's actually much clearer.
So, again, here we your two eyes.
Okay, okay now your nose is up here.
And, you notice that out, coming out of each eye is what's referred to as the,
an optic nerve, and they sort of cross in this funny way
at what's referred to as the apt, the optic chiasm.
They then make, a, a way stop.
They make a stop here, down in here in, lateral geniculate and
then the lateral ge, which we'll talk about, and the lateral geniculate
has projections up into something called the superior colliculus.
And the, most of it, a lot of it goes to what's called the visual cortex,
and we're going to talk about that.
By the way, we describe these things as if it's a flow of information going up.
And that's partially because as computationalists, we like to say, well,
first we do some low-level processing at the, at the, the detectors and
the retina and then it goes up to these weigh stations where various
kinds of things happen, and then up for higher level processing.
The reality is somewhere between 80 and 95% of the projections into,
for example, the lateral geniculate, are actually from the cortex back down.
So the engineers amongst you will say, oh,
that's gotta be feedback of some sort.
Well indeed it probably is,
and it's still stuff that we're just slowly getting a handle on.
So take what I'm about to say with a grain of salt.
In fact, well, take everything I ever say with a grain of salt.
But in particular, I'm only going to give you
a relatively simplistic view of what's going on in the vision system.
It's also a slightly dated view because while I'm
try to be pretty current about certain computer vision things,
there's a massive, massive field of neurophysiology and human vision.
So I'm just going to give you some of the highlights and it'll give you
a general overview and I encourage you to, to read more as we go forward.
One thing to say also before we continue forward is sort of the anatomy and
physiology of the brain really reflect the computational complexity of vision.
So to give you an example, you have auditory nerves that come from your,
cochlea that go into your brain and those nerves, there's two of them,
one for each ear, and those nerves have somewhere around 30,000 nerve fibers in,
in that bundle, okay?
The optic nerve, each one coming out of here, that has somewhere around
a million fibers, okay, 30,000 for hearing, a million for vision from each.
Likewise, and we'll talk more about this later.
We are going to talk about the visual cortex, this area back here.
So far, and that you can, again, you know, plus or minus,
somewhere around 30% of your cortex, right?
The cortex being the most recent part of the brain in terms
evolutionary structures.
We think of it as being sort of the human helmet.
Somewhere around 30% of the visual,
of the cortex is seen to have something to do with vision, as opposed to,
say, 3% for hearing and 8% for all somatic sensory touch.
So, again, the complexity of vision is not only showing up when you look at
your problem sets and how, and you say, how could this possibly work, but
it is also reflected in the detail structure of the human anatomy.