so here's a straightforward question
what color are the strawberries in this
photograph the red right wrong those
strawberries are gray if you don't
believe me we look for one of the
reddest looking patches on this image
cut it out now what color is that it's
great right but when you put it back on
the image it's red again it's weird
right
this illusion was created by a Japanese
researcher named Akiyoshi Kitaoka and it
hinges on something called color
constancy it's an incredible visual
phenomenon by which the color of an
object appears to stay more or less the
same regardless of the lighting
conditions under which you see it or the
lighting conditions under which your
brain thinks you're seeing it to explain
how color constancy works we're gonna be
looking at a whole bunch of visual
illusions that mess with the way you
perceive color illusions like this one
can you tell which of the squares on the
left is the same color as a square on
the right it's probably not the ones you
think to help us out we called up David
Eagleman he's a neuroscientist at
Stanford and an expert in visual
illusions you might remember him from
our previous episode we invited him to
wires offices in San Francisco to spend
the day running some experiments what is
color constancy the brain wants to see
an object as a particular color all the
time irrespective of what the lighting
condition is light has a lot to do with
how you perceive color in large part
because light itself can be colored
tungsten light named for the filament
inside of incandescent bulbs is orange
and the color of daylight can vary
dramatically from bluish white at midday
to vibrant reds and yellows and oranges
at sunset so for example we were just
outside and I was holding a white coffee
cup but it looks white to you and now
inside with different lighting
conditions
it still looks white to you even though
what's actually hitting your eyes is
different in the lighting because of
what's called the
that comes and reflects off of this what
actually hits you is very different in
these cases and this would look white to
you if we were under tungsten or
fluorescent or incandescent bulb that's
what color constancy is so what's going
on with that picture of the strawberries
to find out we worked with an artist
named Reina Takahashi to create some
paper strawberries and put them under
different lights this looks kind of like
midday midday Sun it's this very very
bright clear kind of white color yeah
and this is a much more yellow this is
clearly just like a tungsten light so
what happens if we move these into the
light strands okay they look slightly
different but but they remain red even
though the what's called the illuminance
is is quite different on them now
there's something interesting going on
here you can rationally recognize that
these objects are different colors but
your brain still classifies both
groupings of strawberries as red which
brings us back to quito focus photo you
might have noticed it has a kind of
blue-green overlay to it
researchers think that your visual
system perceives that overlay as the
color of the light that's hitting the
strawberries and it corrects for that
light by subtracting it from the actual
physical gray color of the pixels in the
image and this causes you to perceive
the berries as red so check this out
we have some filters here that like the
overlay on the strawberry photo is
Bluegreen which is opposite red on the
color spectrum and that means that if
you use these filters to cover up our
camera lens it actually blocks red light
so if we now point our camera at these
red objects the pixels on your computer
screen are technically grey but to you
these objects probably still look red
that's what color constancy is is the
brain always trying to say what is that
actual what is that object actually in
the world so with that said you might
think that the reason these strawberries
look red to you is because you know
strawberries are supposed to be red and
while researchers think that might be
part of why this illusion is so
compelling it's not the whole story
and here's how we know that these
objects we just showed you unlike with
strawberries you have no prior memory
- what color this kind of object should
or shouldn't be and yet when we filter
our lens to block the red light they
still look red to you which when you
think about it is a pretty amazing
feature of human vision and in the brain
except there are also illusions that can
leverage that berry feature against you
okay so this is the painting that's by
an artist named James gurney we've seen
this yeah not that painting but this
sort of illusion okay so you're familiar
with the conceit my guess is that even
though it looks like this is under green
light that's in a red light that the
physical paint in one of these squares
one of these squares is the same and yet
they look totally different under these
two conditions right exactly and it's
interesting you say light because that's
the condition we're just coming from
identical object under slightly
different light and that is by
appearances what looks like what's going
on here you've got an identical cube
under what looks like a kind of greenish
light then under a kind of reddish light
but in fact it's actually entirely
different colors of paint but to the
brain maybe it doesn't matter yeah it
doesn't matter because it's just what
hits your retina and usually what hits
your retina your brain tries to figure
out what is the illuminant that's
hitting that and reflecting but it
doesn't matter you can just cheat it so
at the end it's all coming off and
hitting your retina this way right to
help us illustrate what's going on here
we wanted to bring the painting into the
real world and make it human size so our
team built this giant version out of
paper okay so we've done our best to
reproduce Kearney's painting in the real
world how's that you know good
instead of using paint what we've used
this construction paper and
interestingly one of the pieces of
construction paper there is exactly the
same color as one of the pieces here
okay and so when I look at this from
where I'm standing this upper right cube
looks the same color as that upper right
cube and this lower right cube looks the
same color as that lower right cube but
that's not the match yeah so the
matching squares are actually this one
on the lower right and this one on the
top here so let's go ahead and prove
that which we can't do in the painting
but we can do physically like this okay
so you can see that this is exactly the
same color of construction paper here
that is yeah that is 100% the same piece
of paper so if we put it back over there
the key is that because this side of the
world appears to be bathed in a green
illuminant and this is in a red
illuminant they end up looking quite
different because the way your brain
judges the color has to do with all the
surrounding colors as well as the
illuminant around and so what your brain
serves up to you can be completely
different than what is actually
physically hitting it retina okay so
here's my question is this happening in
my eye or is it happening in my brain ah
good question that has been debated in
the literature since the beginning of
these sorts of illusions and the answer
is it's both there's lots of stuff
happening at the level of the eye all
the way back to your brain making what
are called unconscious inferences about
the world in other words it's guesses
about the world based on its prior
assumptions and so there's things
happening at all these different levels
your brain takes into a into account the
context all around and then serves up
some story about what it thinks the
color is based on what is most useful
right because if your brain was a
complete literalist it would have no
problem telling that that's where and
that's where are the exact same color
yeah that's right
okay so for me this raises the
inevitable question that every college
student has you know postulated in their
dorm room which is like how do I know
that the color I see is the same color
you see right actually you you can't
know that we don't know that your mother
taught you to call this green and my
mother taught me to call this screen so
we can transact and negotiate in the
outside world and I can say past the
green thing and you can do it but our
internal experience we don't know if
it's the same thing on the inside or not
and in fact one of the things that's
been surfacing lately on the internet a
lot are allusions where we can actually
demonstrate that people are having
slightly different perceptions of what's
going on like the dress like the dress
you remember the dress right of course
you remember the dress everybody
remembers the dress the viral internet
sensation that divided the internet back
in 2015 some people saw it as blue and
black other people saw it as white and
gold still drives people up the wall so
which camp is right well the short
answer is
neither the actual pixels in the image
are blue and brown but the full answer
is a bit more complicated scientists
still aren't sure why two people can see
the dress so differently but a popular
hypothesis is that the colors you see
depend on how your brain interprets the
light hitting the dress if your brain
thinks the light falling on the dress is
blue it subtracts that color from the
pixels in the image and you're more
likely to see gold and white
conversely if your brain thinks the
light falling on the dress is more
yellow in hue it subtracts yellow from
the pixels and you're more likely to see
blue in black in other words the colors
you see depend on whether you attribute
the blue in the image to the dress or
the light falling on it and believe it
or not this isn't the only time the
Internet has been divided over the color
of a piece of clothing a couple years
after the dress this photo of a shoe
went viral for the same reason some
people see it as gray in teal while
others see it as pink and white okay so
then I feel like the really big question
then is do you think it would be
possible for us to physically reproduce
one of those ambiguous illusions I think
we could tweak the letting the
difficulty is knowing we'll see it in
just one way and the question is really
tested if we don't see it opposite ways
how do we know we've kept it well we'll
have to find some other people and ask
about people and if some people say it's
one way and symbols say the other way
then we've reproduced it right yeah
let's give a shot all right so we said
about applying everything we learned up
to that point we knew that our brains
would try to correct for the color of
light hitting the shoes and we also
hypothesized that the more ambiguous
that lighting was the more ambiguous the
color of the shoe would ultimately be we
tried using gels and different kinds of
lights and we tried mixing up what was
in the background of the image all to
make it harder for our brains to
determine what color light was falling
on the shoe but we couldn't quite get
the colors right straight out of the
camera so Juno took our picture into
Photoshop to shift the hues around and
it worked at least it did for us so to
see if lots of other people would see it
differently we asked folks around the
office yeah gran deal
it's pink and white obviously green teal
definitely it's pink and white those are
gray and I think it's gray and teal no
remember we called this an ambiguous
illusion well that's partly because
different people see it differently but
it's also in part because for some
people it switches back and forth okay
so now I see pink so the color changed
in the last like 20 like 15 seconds in a
sense it did if you don't believe us we
posted some links in the show notes
below that might help you see the other
colors the fact is there is a lot we
don't understand about color which might
seem strange because color is such a
fundamental part of our lives but it
wasn't just the internet that flipped
out over the dress in the shoe it was
scientists too before the dress
researchers had never observed such
stark differences of opinion over the
color of an object and there's still not
entirely sure why those differences
exist everybody's brain is a little bit
different so if you come to the table
with different expectations about what
you're seeing you'll see it differently
one of the theories about the dress is
that how you see it might have to do
with whether you're an early riser or a
night owl the idea is that people who
stay up late are more likely to perceive
the dress as blue because they spend
more time seeing things in artificial
yellow light whereas early risers are
more likely to perceive the dress as
white and gold because they spend more
time observing objects under natural
bluish light color adds this layer of
information to your perception of the
world allowing you to distinguish
between objects and react quickly in a
variety of situations most of the time
you don't even think about all the work
your visual system does to serve you
that information but every once in a
while an illusion like the dress or the
shoes or kita uka strawberries comes
along to remind you of all the things
your brain takes care of under the
which is pretty amazing right
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