Every rose has its thorn. Only the good die young.
Slow and steady wins the race. And what you see is what you get. Except that in reality, several varieties
of roses do not have thorns; both the good and the bad, on occasion, tragically
die young; fast and steady beats slow and steady every time; and what you see is, well...
Our perception, or how we order the cacophonous chaos of our environment, is heavily influenced,
biased even, by our expectations, experiences, moods, and even cultural norms. And we can be
pretty good at fooling ourselves. In the last two lessons, we've learned how we see shapes and
colors, hear sounds, and smell and taste the world's chemical concoctions, but our senses mean little without our
brain's ability to organize and translate that data
into meaningful perceptions. Without perception, your mother's face is just a combination of shapes. Without the ability to
interpret scent, we couldn't differentiate the smell of toast from a grease fire. Our perception
is the process that allows us to make meaning out of our senses and experience the world
around us. it's what makes life understandable, but also it means that sometimes what you
see is not actually what you get. [INTRO MUSIC] So that was awesome, right? Upside-down,
I look like me. Right-side-up, I look like some kind of terrifying monster. Your brain isn't
used to upside-down faces, so it's basically just doing its best to put the pieces together.
But it knows exactly what a right-side-up face should look like, and that is not it. Just one of
thousands of examples proving that your brain does all the work of perception, and your eyes
really are just feeding raw data. It's important data, but it isn't actually what we see. What we
see is the realm of the mind, not the eye. What kind of bird do you see right now? A duck,
right? But if I said, "What kind of mammal do you see?" a bunny probably would have popped out
at you. Now, you should be seeing both of them popping back and forth, but likely your brain
wants to perceive the image related to whichever cue you first heard, or whichever
image is more familiar to you. By cueing "mammal" or "bird," I influenced your expectations
and you saw what I wanted you to see. Pretty cool! Your expectations are just one factor in your
perceptual set: the psychological factors that determine how you perceive your environment.
Sometimes, seeing is believing, but perceptual set theory teaches us that believing is also
seeing. Context is another factor in your perceptual set. If the duck bunny thing was
pictured with easter eggs all around it, you'd think bunny right away -- which is
kind of weird, considering that of ducks and bunnies, one is actually much more likely
to be near an egg (it's not the bunny). And that's an example of how culture is also
an important part of our perceptual set. As much as our perceptions are affected
by context and expectations, they're also swayed by our emotions and motivations.
People will say a hill is more steep if they're listening to emo by themselves than if they're
listening to power pop and walking with a friend. Most of the time, your personal perceptual set
leads you to reasonable conclusions, but sets can also be misleading or even harmful. They're the basis of tons of
entertaining optical illusions. These two tables, for example, are the same size, but the positions of their
legs make that impossible for you to believe until I
lay them over each other. And while all the fooling of our visual perception can be fun, it also helps
us understand how it works. Our minds are given a tremendous amount of information, especially
through the eyes, and we need to make quick work of it. Turning marks on a paper into words; blobby lumps
into the face of a friend; seeing depth, color, movement, and contrast; being able to pick out an
object from all the other clutter around it seems so simple, but we've come to discover that it is quite
complicated. So complicated that we have a name for it:
form perception. Take a neat little dynamic called the
"figure-ground relationship." It's how we organize and simplify whatever scene we're looking at into the main objects or figures
and the surroundings or ground that they stand out against. The classic "faces or vases" illusion
is an example. Is it two faces against a white background, or a vase against a black background? If you look long enough, you'll
see that the relationship between the object and its surroundings flip back
and forth, continually reversing, sometimes white is the figure and black is
the ground. That figure-ground dynamic, though, is always
there. The concept applies to non-visual fields as
well. Say you're at a party, holding up the wall and creeping on your crush across the room, trying to
casually listen in on what they're saying. As the focus
of your attention, that voice becomes the figure, while all
the other voices jabbering about sports and beer pong
and Sherlock and everything that doesn't have to do with
that one beautiful person all becomes the ground. Now that your mind has distinguished figure from
ground, it has to perceive that form as something meaningful. Like for one, that large shape on the couch is a person, and further, that person isn't
just any person, but the specific unique person of your dreams. One way
our minds shuffle all of these stimuli into something coherent is by
following rules of grouping, like organizing things by
proximity, continuity, or closure. The rule of proximity, for
instance, simply states that we like to group nearby
figures together. So instead of seeing a random garble of partygoers, we tend to mentally connect people
standing next to each other. Like, there's the hockey team over there, and the
debate team over there, and then you've got the band geeks -- why are all these people at the same
party? We're also drawn to organize our world with attention to continuity,
perceiving smooth, continuous patterns, and often ignoring
broken ones. We also like closure -- and not just after
a breakup. Visually, we want to fill in gaps to create
whole objects. So here, we see an illusory triangle breaking
the completion of these circles on the left. But just
add the little lines, close up the circles, and you stop
seeing the triangle. Form perception is obviously crucial to making sense of the world, or, y'know, a
moderately interesting party. But imagine trying to navigate the world without depth perception. As you
gaze upon your one true love, the image hits your retina in
two dimensions. Yet somehow, you're still able to see
the full three-dimensional gloriousness of their form. You can thank your depth perception for that! Depth perception is
what helps us estimate an object's distance and full shape. In this case, a nice shape that is currently too far away from
you. It is at least partially innate -- even most babies
have it. We're able to perceive depth by using both binocular
and monocular visual cues. Binocular cues, as the name
gives away, require the use of both eyes. Because your eyes
are about 2.5 inches apart, your retinas receive
ever-so-slightly different images. You know, camera one, camera two. So when you're looking with both your eyes, your brain compares
the two images to help judge distance. The closer the object, the greater the difference between the
two images, also known as the retinal disparity. Retinal disparity is pretty
easy to see, you just hold your fingers up, and then you look past them, and suddenly you have four instead of two fingers.
Because those left and right images vary only slightly, retinal disparity doesn't help much
when it comes to judging far-off distances. For that, we look to monocular cues to help
us determine the scale and distance of an object. These are things like relative
size and height, linear perspective, texture gradient, and interposition. Relative size allows you to determine that your
crush is not supporting a tiny newborn chihuahua on their shoulder, but
rather, there's a full-grown chihuahua behind them in the back of the room. In the absence of a chihuahua
(or like object), you can also judge distances
using your linear perspective. If you've ever made a
perspective drawing in art class, you'll remember that parallel lines appear to meet as they move into the distance.
Just like the tiled floor, the sharper the angle of
convergence, and the closer the lines together, the
greater the distance will seem. And if you've ever looked out at a mountain range or a Bob Ross painting, you'll understand texture
gradient as the cue that makes the first ridge appear all rocky and textured, but as your eye
follows the ridges into the distance, they become less detailed. And finally,
our interposition, or overlap, cue tells us when one object, like this oaf here, blocks our view of something else, your crush,
we perceive it as being closer. And in this case, especially annoying. So all these perceptual
concepts can be demonstrated with a fixed image, but of course, life involves a lot of
movement. At least if you're doing it right. We use motion perception to infer speed
and direction of a moving object. Like, your brain gauges motion based partly
on the idea that shrinking objects are retreating and enlarging objects are
approaching. The thing is, your brain is easily tricked when it comes to motion.
For instance, large objects appear to move much more slowly than small ones going
the same speed. And in addition to organizing things by form, depth, and motion, our perception
of the world also requires consistency. Or as psychologists call it, constancy. Perceptual
constancy is what allows us to continue to recognize an object, regardless of its
distance, viewing angle, motion, or illumination, even as it might appear to change color, size,
shape, and brightness, depending on the conditions. Like, we know what a chihuahua
looks like, whether it looks like this this, this, or this. In the end, though, your perception isn't just about funky
optical illusions. It's about how you understand the world and your place
in it, both physically and psychologically. Your sensory organs pull in the world's raw data, which is disassembled into
little bits of information and then reassembled in your brain to form your
own model of the world. It's like your senses are just collecting a bunch
of Legos and your brain can build and rebuild whatever it perceives. A party, your crush, a duck, or a chihuahua.
In other words, your brain constructs your perceptions. And if you were correctly
constructing your perceptions this lesson, you learned what forms your perceptual set,
how form perception works, and the many visual cues that influence your depth perception.
Thank you for watching, especially to all of our Subbable subscribers who make this whole
channel possible. If you'd like to sponsor an episode of Crash Course Psychology, get a copy
of one of our Rorschach prints, and even be animated into an upcoming episode, just go
subbable.com/crashcourse. This episode was written by Kathleen Yale,
edited by Blake de Pastino and myself, and our consultant
is Dr. Ranjit Bhagwat. Our director and editor is Nicholas Jenkins, the
script supervisor is Michael Aranda who is also our sound designer, and the graphics team
is Thought Café.