When you're looking
at an object, it's necessary to break it down
into its component features in order to make sense of
what you're looking at. This is known as
feature detection. There are many components that
make up feature detection. So let's go into these. When you're looking
at a rose, not only do you have to look and decide,
OK, what color am I looking at, you also have to figure out,
OK, what shape is the rose. So you have to get a
little bit of information about the form of the rose. You also need to get
information about motion. So is the rose moving? Am I throwing it across a room? What's going on? So whenever we
look at any object, we need to get
information about color, we need to get information
about the form of the object, and information about motion. So let's go into each one
of these different features. So our ability to
sense color actually arises from the presence
of cones within our retina. Cones are extremely
important, because they're sensitive to various
types of light. So we have three
major types of cones. There are red
comes, which make up 60% of the cones in your eye. There are green
cones, which make up 30% of the cones in your eye. And there are blue cones,
which make up about 10% of the cones in your eye. Now, we divide them into
red, green, and blue cones because the red
cones are extremely sensitive to red light. So if we're looking
at this rose, the petals are actually
reflecting red light. And so this is red
light enters your eye. And if it happens
to hit a red cone, then the cone will
activate, and it will fire an action potential. And this action potential
will reach your brain, and your brain will
recognize that you're looking at something
that is red. So this basically
happens regardless of what we're looking at. And this has come to be known
as the trichromatic theory of color vision. So what other
features do we need to take into consideration when
we're looking at this rose? So aside from breaking the rose
down into the different colors, we also need to
figure out, OK, what are the boundaries of the rose,
so the boundaries of the stem, the boundaries of the leaf,
the boundaries of the petals, from the background. And this is also
really important, because not only do we need
to distinguish the boundaries, but we also need
to figure out, OK, what shape are the leaves,
what shape are the petals. And these are all
very important things that your brain ultimately
is able to break down. So in order for us to figure out
what the form of an object is, we use a very
specialized pathway that exists in our brain, which
is known as the parvo pathway. So the parvo pathway is
responsible for figuring out what the shape of an object is. So another way to say this
is that the parvo pathway is really good at
spatial resolution. Let me write that down. So spatial resolution. And what spatial
resolution means is that it's really
good at figuring out what the boundaries
of an object are, what the little details
that make up the object are. So if something isn't
moving, such as when you're looking at a picture or when
you're looking at a rose, you're able to
break down and look at the little tiny details. So you're able to look at the
little veins that make up the rose leaf. You're able to see all the
little nuances of the rose. And that's because you're
using the parvo pathway, which has a really high level
of spatial resolution. One negative aspect
of the parvo pathway is that it has really
poor temporal resolution. And what I mean by this is that
temporal resolution is motion. So if a rose is in motion, if
I throw it across the room, I can't really use the parvo
pathway to track the rose. The parvo pathway is used
for stationary objects to acquire high levels
of detail of the object. But as soon as that
object starts moving, you start losing your ability
to identify tiny little details in the object. And you've probably
noticed this. So when you're in a car,
you're driving along, and there's a little Volkswagen
Beetle driving right by you, it's going pretty slow. You can acquire a good number
of details about the car, about the driver. But if you look
down at the wheels, the wheels are spinning
really, really quickly. And so if you try
and look at the rims and figure out what
design are the rims, it's really hard
to figure that out. That's because the
wheels are spinning so fast that it's really
difficult to acquire any type of detail
about the shape of the rims, about
what they look like, and things like that. And finally, the
parvo pathway also allows us to see
things in color. So the parvo pathway
not only allows us to acquire fine details
about what we're looking at, but it also allows
us to see in color. So if something is moving, we
can't use the parvo pathway. But what we do use
is the magno pathway. So we use the magno
pathway in our brain. And the magno
pathway is basically a set of specialized
cells-- just like the parvo pathway-- that
allow us to encode motion. So it allows to encode motion. And what that means
is that it has really high temporal resolution. So as we've said,
the parvo pathway has really low
temporal resolution. The magno pathway has
high temporal resolution, which means that if
something is in motion we're able to track it, we're
able to see an object moving. And in contrast to
the parvo pathway, the magno pathway has very
poor spatial resolution. So one way to
think about this is that if I was looking at this
rose using the parvo pathway, it's stationary, and I'm able
to see all these fine details in the petals, all these
fine details in the leaves. But if I was looking at the
rose using the magno pathway, the rose would actually
look a little bit like this. It would look very blurry. You would only be
able to see this kind of blurry aspect of the rose. And when you're looking at
the stem and the petals, you only see this very
blurry vision of the rose. This is one way to imagine
the difference between parvo and magno. If you're looking at this
rose using your parvo pathway, you see all these details. If you're looking at the same
rose using the magno pathway, it's very blurry. But the benefit of
the magno pathway is that if this rose were to
be moving, you can see it move. Whereas if you're using
the parvo pathway and a rose is moving, you wouldn't
even be able to see it at all. These are kind of the pros
and cons of the two pathways. And finally, the magno pathway
does not encode any color. So it just simply would
encode its motion. So our ability to detect
these three different features whenever we're looking
at an object all happens at the same exact time. So when I'm looking at
a rose, I don't first focus on the color
and then the form and then whether
or not it's moving. I get all this information
at the same exact time. And our ability to see
all three things whenever we're looking at something
at the same exact time is known as parallel processing.