Okay. So now, we’re going to get
into the topic of perception.
How do you perceive things?
And this is a process that I think a lot
of us just take for granted, right?
We don’t ever think about, “How am
I going to perceive this image?”
Or “How am I going to
perceive the situation?”
It kind of just happens and
you just deal with it.
Let’s start with an image.
So take a look at this image.
What do you see?
Take a minute, think about it.
And you’re reaction
might be, “Oh, I see.”
So you might see two triangles
opposed to one another
with one on top of
the other, right?
How are you seeing that?
Because in reality what’s drawn
there are a couple of broken lines
and a couple of green Pac-Mans which
aren’t connected to anything.
But you’re still
seeing two triangles.
So you’re perceiving a complete picture
you’ve completed in your mind.
How does that happen?
Look at this one.
What are you seeing here?
Take a minute.
Get up close to your
Get up close to your computer screen.
Now, there's two possibilities here.
You have two Taylor Swift
looking ladies on either end
with a candelabra in the middle.
Or do you see two people?
Let’s go with a guy and a girl.
Maybe it’s two girls. Who knows?
About to kiss in the middle.
So what do you see?
Again, you could see either,
you could see both.
And if I’m directing your attention
to one versus the other,
you might see it that way but
you’re perceiving a picture
based on broken pieces
So theoretically, on paper,
this shouldn’t make sense.
How am I seeing a few odd things and
realizing that that’s a woman’s face?
How am I looking and
seeing two girls kissing
when really that’s not
what was drawn there.
Okay? And this comes
back down to perception.
So what we’re going to do
is we’re going to look
at two ways we can process
And the first one is going to look
at the information coming in.
So what are we sensing
So the info that’s coming in,
we’re going to take that and piece it
together and come up with a concept.
So let’s take a look at
these two diagrams here.
We have what looks like the letter
A, one kind of broken apart.
We have what looks like,
you know, some lines here.
What is that? I don’t know.
So using bottom-up processing,
we’re saying we’re taking
the sensory information
or information that’s coming in through
our senses, in this case, our eyes,
from the different receptors
and we’re going to take all those bits
and pieces of sensory information,
integrate that at the
brain, in the CNS,
which stands for central nervous system,
and come up with an idea
of what we think it is.
So this first one on the right, the one
on the right that you’re seeing here,
we see these lines, we’re saying, “That
could be, I don’t know, train tracks.”
And, you know, what is that?
I don’t know.
How about this one right here?
Here’s an example of you taking your
perception and coming up with an answer.
So, what’s around us?
This now might become
a train track.
And what you’ve done here
is you’ve added context.
You’ve added some surrounding information
to now change your perception
of what I’m seeing, okay?
So what was a couple of lines
now might be train tracks,
it might be a ladder that allows you
to climb the tree. I don’t know.
So another way of looking at
it is top-down processing.
And that’s where we’re using
experience and expectations
to interpret sensory
to interpret sensory information.
Your eyes are seeing the lines,
but your mind is saying, “In the past
I know that lines in that orientation
typically means train
tracks or a ladder
or it might be two girls kissing
or it might be, you know, a
triangle on top of another triangle
because I’ve seen that before.”
So you’re using previous experience and
your expectations of what that should be.
The lines weren’t actually
drawn together, weren’t closed,
but you saw two triangles,
you saw two girls.
So you’re making that leap
based on your previous experiences along
with looking at that sensory information.
So where top-down kind
of refers to mind down
versus bottom-up which is sensory
information coming in through the receptors
going up to your mind
to get processed.
So that kind of differentiates
bottom-up versus top-down.
So let’s walk through that
use the sensory information
from the receptors
and works up to integration at
the central nervous system.
So coming in the eyes, getting
integrated up at the brain,
and we make our idea of
what we think that is.
Top-down is the other way around.
We use the experiences that
we have saved in our mind
to take a look and figure
out what we just saw.
Now in reality, as humans, we
use a combination of both.
So you know that you saw
a couple of broken lines
and that gets integrated
in your mind as triangles
but you also know you’ve
seen a triangle before.
So what I’m trying to say to you is
I don’t think it’s so clear cut.
It’s not so black and white.
It’s not so we only use
bottom-up for this
or we only use top-down for this.
It’s actually a combination
of both which is good.
And it also allows our
perception to be quite fast.
So there’s a term that you need
to know for the MCAT and that’s,
I guess, a German term called
“gestalt” which means whole.
And that’s a principle that states
that humans perceive objects
rather than individual features.
So if I were to show you a triangle
that is not completely drawn together,
you would still know
that that’s a triangle
because in your mind,
you have saved
a gestalt of what a triangle
normally looks like.
When you see your mama’s face,
and you could be in a crowded room,
or you see her from a mile away
and you see your mama, you know
right away, “That’s my mama.”
You don’t have to sit there and
say, “I’ve seen that lady before.
I think she gave life to me.
Yeah, that’s my mom.”
Instead, you right away
know that’s mama, okay?
And this can apply to so
many different things.
It can apply to street signs.
It can apply to names.
It can apply to anything.
And the ideas in our mind, we have saved
these gestalts or these whole diagrams
of things that we know to be true,
instead of saving all the individual
features that we need to memorize
and know to realize what it is.
So the human mind forms a gestalt
and this has a reality of its own.
So again, we’re saving these
nuggets of information
and that allows us to be very,
very fast with our perceptions.
Which is why in a crowded room,
you can very quickly pull out
people and things that you know
as opposed to having to sit
there and wait for your mind
to get all that bottom-up,
top-down processing to happen.
So collectively, putting all these pieces
together, this explains how we, as humans,
use various facets and ways to process
to bring our perceptions together.