Perceiving is Believing: Crash Course Psychology #7

Summary

This script explores the fascinating world of perception, explaining how our brain organizes sensory data to create meaningful experiences. It discusses the influence of expectations, context, and cultural norms on our perceptions, highlighting the concept of perceptual set. Through examples like optical illusions and depth cues, the video illustrates how we interpret shapes, colors, motion, and depth. Ultimately, it underscores the brain's crucial role in constructing our reality, showing how perception helps us navigate and make sense of the world.

Takeaways

• 🌹 Not all roses have thorns, and various common sayings can be misleading.
• 👀 Perception is heavily influenced by expectations, experiences, moods, and cultural norms.
• 🧠 Our brain organizes and translates sensory data into meaningful perceptions.
• 👩‍👦 Without perception, familiar faces and scents would be meaningless shapes and smells.
• 🧩 Perceptual set theory explains how context, expectations, and emotions shape what we see.
• 🔄 The figure-ground relationship helps us distinguish objects from their backgrounds.
• 🏞️ Depth perception allows us to perceive the world in three dimensions using both eyes.
• 🎨 Monocular cues like relative size, linear perspective, and texture gradient help judge distance.
• 🏃 Motion perception lets us gauge speed and direction of moving objects.
• 🔍 Perceptual constancy helps us recognize objects despite changes in distance, angle, or lighting.

Q & A

Why is the statement 'Every rose has its thorn' not always true according to the script?

Because in reality, several varieties of roses do not have thorns.

What role does perception play in how we interpret sensory information?

Perception allows us to make meaning out of our senses and experience the world around us by organizing and translating sensory data into meaningful information.

How does the brain deal with upside-down faces, according to the script?

The brain struggles with upside-down faces because it is not used to them and tries to piece the data together, often resulting in a distorted perception.

What is 'perceptual set' and how does it influence our perception?

Perceptual set refers to the psychological factors that determine how we perceive our environment, influenced by expectations, experiences, moods, and cultural norms.

How does context affect our perception, as illustrated by the duck-bunny image?

Context affects perception by influencing which image we see based on surrounding cues, such as associating the image with Easter eggs making us see a bunny.

What is the 'figure-ground relationship' in form perception?

The figure-ground relationship is how we organize scenes into main objects (figures) and their backgrounds (ground), such as seeing either two faces or a vase in the classic illusion.

How do binocular cues contribute to depth perception?

Binocular cues use the slightly different images received by each eye (retinal disparity) to help judge the distance of objects.

What is 'retinal disparity' and how does it help in perceiving depth?

Retinal disparity is the difference between the images seen by each eye, which the brain uses to judge the distance of nearby objects.

What are some examples of monocular cues used in depth perception?

Monocular cues include relative size, linear perspective, texture gradient, and interposition, which help judge distances and scale of objects.

How does motion perception influence our understanding of moving objects?

Motion perception helps us infer the speed and direction of moving objects, using cues like shrinking objects appearing to retreat and enlarging objects seeming to approach.

Outlines

00:00

🌹 Perception and Reality

This paragraph explores how perception can differ from reality. Common sayings are challenged, emphasizing that our understanding is shaped by expectations, experiences, and cultural norms. The brain's role in interpreting sensory data is highlighted, illustrating how perception gives meaning to our experiences. The paragraph uses examples, like the upside-down face illusion, to demonstrate how our brains construct what we see, influencing our beliefs and experiences.

05:02

👥 Grouping and Depth Perception

This section discusses how the brain organizes sensory information using rules like proximity, continuity, and closure. It explains how we perceive groups based on these principles and the importance of depth perception in understanding the world in three dimensions. The text describes both binocular and monocular cues, such as retinal disparity and linear perspective, which help us judge distance and scale.

Keywords

💡Perception

Perception is the process by which the brain organizes and interprets sensory information to create meaningful experiences of the world. In the video, perception is highlighted as the brain's ability to interpret shapes, colors, sounds, and smells, transforming raw sensory data into recognizable and understandable forms, such as recognizing a mother's face or the smell of toast.

💡Perceptual Set

Perceptual set refers to the psychological factors that influence how we perceive our environment, including expectations, experiences, emotions, and cultural norms. The video illustrates this with the duck-rabbit image, where the viewer's expectations (based on cues like 'mammal' or 'bird') influence whether they see a duck or a rabbit.

💡Form Perception

Form perception is the ability to recognize objects and their shapes, organizing visual information into coherent forms. The video explains this concept using examples like the 'faces or vases' illusion, where the brain alternates between seeing two faces or a vase, depending on the figure-ground relationship.

💡Figure-Ground Relationship

The figure-ground relationship is a type of form perception where the brain differentiates an object (figure) from its background (ground). The video uses the example of the 'faces or vases' illusion to show how this relationship can flip, illustrating how our minds simplify visual scenes into main objects and their surroundings.

💡Depth Perception

Depth perception is the ability to perceive the world in three dimensions and judge the distance of objects. The video describes how depth perception uses both binocular cues (like retinal disparity) and monocular cues (like relative size and texture gradient) to help us navigate and understand the spatial relationship of objects around us.

💡Binocular Cues

Binocular cues are depth cues that require the use of both eyes, such as retinal disparity, where the slight difference between the images seen by each eye helps the brain judge distance. The video explains how these cues are particularly useful for perceiving objects that are close to us.

💡Monocular Cues

Monocular cues are depth cues that can be perceived with one eye, including relative size, linear perspective, texture gradient, and interposition. The video illustrates these cues with examples like judging the distance of a chihuahua in a room or the convergence of parallel lines in a perspective drawing.

💡Motion Perception

Motion perception is the process of inferring the speed and direction of moving objects. The video discusses how our brains gauge motion, such as interpreting shrinking objects as retreating and enlarging objects as approaching, and how large objects seem to move more slowly than smaller ones.

💡Perceptual Constancy

Perceptual constancy is the brain's ability to recognize objects as constant and unchanging despite changes in sensory input, such as distance, angle, or lighting. The video gives examples like recognizing a chihuahua regardless of how it appears under different conditions, illustrating how constancy helps maintain a stable perception of the world.

💡Optical Illusions

Optical illusions are visual phenomena that trick the brain into seeing something different from reality, often revealing how our perception works. The video uses examples like the table size illusion and the 'faces or vases' illusion to show how our brains can be misled by visual cues, highlighting the complexity of perceptual processes.

Highlights

Several varieties of roses do not have thorns, challenging common sayings.

Both the good and the bad can die young, debunking the phrase 'only the good die young.'

Fast and steady often beats slow and steady, contrary to the common belief.

Our perceptions are heavily influenced by expectations, experiences, moods, and cultural norms.

Perception allows us to make meaning out of our senses and experience the world around us.

The brain plays a critical role in perception, organizing raw sensory data into meaningful experiences.

Expectations and context can influence what we perceive, as shown with the duck-bunny illusion.

Perceptual set theory shows that believing can also lead to seeing.

Emotions and motivations also affect our perception, as demonstrated by the hill steepness example.

Form perception involves organizing visual stimuli into meaningful patterns using rules like proximity, continuity, and closure.

Depth perception helps us judge the distance and shape of objects using binocular and monocular cues.

Motion perception allows us to infer the speed and direction of moving objects.

Perceptual constancy helps us recognize objects regardless of changes in distance, angle, motion, or illumination.

The brain constructs our perceptions from sensory data, building a model of the world.

Understanding perception helps us comprehend how we navigate and interpret the world around us.

Transcripts

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.