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
died young fast and steady beats slow
and steady every time and what you see
is well how our perception or how we
ordered the cacophonous chaos of our
environment is heavily influenced by ax
Steven by our expectations experiences
moods and even cultural norms and we
could 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 a 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
[Music]
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 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 eye 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
see context is another factor in your
perceptual set if the duck bunny thing
was pictured with Easter eggs all around
it you 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 sense 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 leaves 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 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
lobbie lumps into the face of a friend
seeing depth color movement in contrast
being able to pick out an object from
all the other clutter around it seems so
simple we've come to discover that it is
quite complicated so complicated that we
have a name for it form perception
taking a 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 are 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 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 and 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 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 the same party we're all so 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 or perception is obviously
crucial to making sense of the world or
you 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 an eight 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 1 camera 2
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 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 and
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 about 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 inter position or overlap cue tells
us when one object like this off 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 and the end-of-year 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 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
are 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
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go to subbable.com slash crash course
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 cafe
you