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 own 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. So that was awesome, right? Upside down, I

look like me; right side up, I looked 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? 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 kinda 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 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 of 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 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 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 left. But just add the little lines to close-off the circles, and

you stop seeing the triangle.

Form perception obviously is 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 eyes, your

brain compares these two images to help judge distance. The closer the object, the greater

the difference between the two images, also known as their 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.

But because those left and right eye images vary only slightly, retinal disparity doesn’t

help much when it comes to judging far-off distances. For that we look to our 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 that 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 of 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 is 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. Thanks 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 our Rorschach prints, and even

be animated into an upcoming episode, just go to 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.