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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 [Music]
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