Okay, so now we're going to leave the retina and
we're going to get visual information into the cortex.
And of course, from retina we actually, before we can talk to cortex,
we have to go through thalamus.
Remember, thalamus is our translator.
So, what we're going to do here is just follow the pathway from retina to
primary visual cortex.
And this shows you the two visual fields.
This is a person who's foveating,
whose two foveas are fixated on this center spot.
And this is the right visual field, in red.
And, and in blue is the left visual field.
And what you can see because of the pathway that light takes,
this left visual field is going to hit this half of the right et,
retina and this half of the left retina.
Now you could memorize that this is the right temporal and the left nasal.
But, there's a much easier way to remember these pathways.
I've never memorized this, I just draw it out every time because the easy thing
to remember is that this left visual field has to end up on the right visual cortex.
So, if it already is on the right, it doesn't have to cross.
So information from this retina, this half of the retina which is getting
information from the other side's visual field,
it's just simply going to go to the thalamus on the same side, and
from the thalamus on the same side to the visual cortex on the same side.
On the other hand, this information from this half of the retina,
which is getting information from this half of the visual field,
it's on the wrong, it's on the opposite side from where it has to end up.
So where does visual information cross?
It all crosses at the optic chiasm.
That's this structure right here, the optic chiasm.
So it's going to go down, across, over into the thalamus,
and from there to the, to the visual cortex.
So there are a few points that we're going to make with this.
One is that if you, if you test visual fields you test one eye at a time.
So normally in the left eye, if you are looking at this
center point you can see the right half of the world, and the left half of the world.
Normally, if you are looking at the world with your right eye,
you can also see the left and right halves of the world.
What would happen if, let's just take a few, we're going to take a few cuts.
What would happen if there was some, something that prevented this