Every rose has it’s 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 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.