99% Invisible - 456- Full Spectrum

Episode Date: August 31, 2021

In 2015 the world was divided into two warring factions overnight. And at the center of this schism was a single photograph. Cecilia Bleasdale took a picture of a dress that she planned to wear to her daughter's wedding and that photo went beyond viral. Some saw it as blue with black trim; others as white with gold trim. For his part, Wired science writer Adam Rogers knew there was more to the story -- a reason different people looking at the same object could come to such radically divergent conclusions about something as simple as color.Rogers recently wrote a book titled Full Spectrum: How the Science of Color Made Us Modern. In this episode, Roman Mars talks with the author about how the pursuit to organize, understand, and create colors has been one of the driving forces shaping human history, starting with the story of this hotly debated piece of apparel from 2015 then winding back through built environments of global World's Fairs.Full Spectrum

This is 99% invisible. I'm Roman Mars. In 2015 the world was divided into two warring factions seemingly overnight and at the center of this schism was a single photograph. Social media is exploding this morning with a debate about one dress. The simple question is what colors do you see black and blue or white and gold? It's blue and black. It is white and gold. It's blue and black. I really see white and gold. It's blue and black. It's finally time for me to break my silence. I see white and gold.

If you've been living off the grid and under a rock, I'm here to tell you that once upon a time, a photo of a dress took over the internet. In 2015, Cecilia Blesdale took a picture of a dress that she planned to wear to her daughter's wedding, and that photo went so viral that it literally slowed down the internet. If you haven't seen it yet, Google it because depending on how your brain works, you either see it as blue with black trim or white with gold trim with absolutely no room in between for debate. But back in 2015, while the rest of us were a big ring over black versus white versus

blue versus gold, science writer Adam Rogers knew this story was way more than just a popular meme. You could tell that the biggest story in the country for the next eight hours was a science story, and it was a science of vision and neuropsychiatry and neurobiology and color. This is Adam, by the way, he was working as the science editor at Wired at the time. We just knew it had to be ours, and we also knew that everyone else would now be thinking of this as a science story, because the first story was the meme story. The first story was check out this dress that everybody thinks is two different colors, and immediately was the first thing that you say when that happens, the first thing you

say to yourself is why. Adam recently wrote a book called Full Spectrum, of a science of color made us modern. Today I'm going to be talking to him about how the pursuit to organize, understand, and create colors has been one of the driving forces shaping human history, starting with the dress. So could you tell me where you were and what you were up to the first time you saw a picture of the dress? It was the end of the day at Wired and this you know this meme came across everybody's desk I guess I should acknowledge upfront. I'm a little sugary to say I did not think much of it

In the picture first showed up. I thought huh. That's what I thought huh, but then a palamine That's what I thought. But then a palamine, a guy who was the executive editor, came and kind of plopped down next to me just to kibbit, as is the God-given right of all journalists. And we both kind of say, you see this dress thing? It's crazy, huh? This dress thing.

And it's like, yeah, that's crazy. And he just said, it's obviously white. And I went, Rob, it's blue, man. And he looked at me like I was insane. And I looked at him, like he was insane. And I'm not kidding, at that exact instant, the guy who edited the website at the time, Joe Brown, came running across from the other side of the building

where his desk was and like his mouth opened to make the first half of the word have to scream have you seen right and before he could even make the hat sound I yelled across the room were on it. So like optical illusions or even auditory illusions, they're all over the internet. The illusion where you see like two faces or a vase or that, the duck of the rabbit. Or you duck in a rabbit. What was it about the dress that stirred up so much debate? What, why did it slow down servers across the world?

How is it unique to this particular optical illusion? I have a hypothesis about what I think the most important thing was. And it's that the illusions that you just mentioned were all the illusions of form, even if they're bimodal, which is to say they look one way and then the other way. Our brains tend to flip in between them. They flip back and forth. You stare it for long enough and you see one and then the other and then one and then the other. But illusions of color, we don't. You're bringing kind of chose one and then locked in. And then when somebody else would say they saw the other

one, that just seemed insane. It was like somebody was saying, no, obviously people walk on the ceiling and then if they fall, they hit the floor. It's like, no, people walk on the floor. Or, you know, like it just, if somebody saw the way that you didn't, there was no, there was no crossing the gap. It was impenetrable. It was either you were correct or you are insane. And there was no middle ground between them, which is why great debates on the internet happen.

That's right. And also the stakes were so low. OK, so then let's get into it. What is happening here? Why does it seem like it's white and gold or blue and black to different people? Right. Well, so to get into that, you have to first understand that when we see colors, when we talk about colors, we're talking about two related but separate properties. Now,

obviously what we're talking about are photons or electromagnetic waves bouncing off of a thing and then bouncing into our eyes. So that's true. That's a thing that happens. That's physics. But surfaces will have a color, and then there's a color of illumination. There's light that's hitting those surfaces. And when we see colors, what are our eyes and our brains are doing a calculation essentially that combines those two things. And effectively tries to subtract the color of the illumination from the surface so that you can say what the surface color objectively is. That is an ability called color constancy. And so this, for example,

if I'm in a room with white walls and I know it's a room with white walls and I put a red light bulb in it, I don't think those are red walls. I think those are white walls, but they just look red to me because there's a red light bulb in the room. Yeah, that's exactly right. I would even invert it and say, if you see a picture of an egg,

but it's red, you don't go, oh, a red egg. You say, oh, an egg with a red light shining on it. Yeah, exactly. Now, the two examples that both of us just used there are two of the hypotheses for how the brain creates color constancy. The ability to see an object is having the same color under different illuminations. So that's what's going on. If your brain is trying to figure out what color is the light and what color is the object. Okay. The image taken on a phone, so with a sensor in 2015 that wasn't great, that wasn't really good at figuring out what the color of light was and what the color of the object is, seen on screens, so with light being emitted in two people's eyes

from the screens, not as a reflective surface as you would see on an absorbative surface as if you were looking at a photograph, let's say. And, and this is the key thing, what time of day was it? So because of the way the kind of the background of the photograph looked like it was lit, which was very brightly lit. Your brain could make a decision.

Unconsciously, your brain would decide, am I looking at a picture that was taken at high noon when the color of the light that's ambient light outside is bright yellowish white? Or am I looking at something that was taken in the afternoon? And so if you thought that the photograph was taken in mid-day, then the illuminance was white and the color of the dress was blue. But if you thought that the dress was in shadow,

or when the sun was lower in the sky, then you thought, that's a white dress in some sort of shadow, that what I'm seeing as blue is actually just the color of the light around it. So the mind makes that decision and sticks to it. With a lot of visual illusions, you either see the duck or the rabbit or the old woman or the young woman,

but there's no correct answer because it's both, like it's designed to be both. What's interesting about the dress is that half the people who say they saw white and gold were just wrong. I think we can agree that people who saw white were bad people. I think that's fairly clear to me. They're people who should be shunned, I think, broadly, but what you've identified there

is that the problem is that there really is a dress. There is a dress exists. That dress exists and it is blue. It was made to be blue. It's dyed blue. It's There is a dress exists. That dress exists and it is blue. It was made to be blue. It's dyed blue. It's made of a blue textile. It's made of a textile that has the properties of being blue. So it's a blue dress. But as soon as you were looking at a reproduction on a computer screen of an image taken with a digital camera and also honestly the color scientist really will say, look, ultimately, the color that you perceive is a function of the photons interacting with the

surface and then the way that your brain and eye process those colors. A bumblebee looking at the same object would see it as a different color because they have different photoreceptors. Their eyes work differently. Their brains work differently. So who's right? Is the bumblebee right or am I right? No, I mean, there's a color. If there's a thing, it has a color. It's a real thing.

If you stop believing that, then you're having a philosophical conversation. It's an important one, but it's a different one. But the question of how our brains and eyes make those colors for us, even when we do it the same way, even if you and I see the same color there, it's an interesting question of why we do it the same way. So the general public was very excited about this. You and all the folks at Wired were very

excited about this. What did the color scientists of the world think about this? What did they take from this? It was existential for them. So the scientists start trying all of the kinds of experiments that you would imagine that you would want to do. My favorite work was actually getting the dress, the real dress. So these researchers actually got the dress and set it up in a room with black walls, basically like a black box theater. And then set up the lighting in the room with tunable LED lights. One of the things that happens when human beings see light is that it can create, if there's combinations of wavelengths, you can create something called a metimer. So you can have one kind of light, you can have one

wavelength of light, but also a mixture of wavelengths that looks the same. And to our eye and our brain, they're indistinguishable. This is one of the key differences between seeing color and listening to music, let's say. When we listen to music, we hear all the individual wavelengths, we hear all the notes, and then they combine together in euphonias and harmonious ways, right? Like they've become chords, but that doesn't happen with light. It combines into one thing. And that can fool us into, so we're not sure what we're really looking at. So what they did in this room was you would think you were seeing the dress under white light.

And white light is equal amounts of every wavelength. But in fact, they would drop some wavelengths out, which alters the way that you perceive the object, but in an imperceptible way. And they found that they could control what color people reported, seeing on the dress, that they could force the card. They could make people see it as white or make people see it as blue or make people see it as really any color they wanted, which will keep you up at night if you're a color scientist.

I mean, you compare the dress and the book to the Rosetta Stone saying it may allow scientists to decrypt the corners of human perception and psychological color space. What do you mean by that? When we talk about color, we think we're talking about the color of an object. We have an object in our hand and it has some color that's intrinsic to it or intrinsic to its surface. And then if we really, if we think harder about that, we know we're also talking about something in physics, we're talking about something subatomic, photons are waves that are bouncing off of that thing and bouncing into our eyes.

And then if we think even harder about that, we know we're talking about, well, actually, we're talking about the way that these sensors built into our skulls process that information and transduce it into neuro-electrical signals that then goes into the meat that we think with and then gets re-translated into some vision of the world, literally a vision of the world that we have. And so that's the hardest anybody can think about this problem. But because it's happening inside our brains, because it's part of our, the process, our

creation of mind, it's influenced by who we are and how those brains developed, how the brain developed and how our specific brain developed. So there's these successive iterations of perception that if you can either take them all apart, figure out how they relate to each other, you can begin to understand culture, begin to understand the development of the brain, begin to understand how the brain works, and how the brain takes these signals from outside, takes what are objective signals from, I mean, there really are photons out there,

there really are electromagnetic waves, there really are objects, there really are those things, but we process them through our senses, and try to make sense of them. So understanding that, when you get an opportunity like the dress, that separates people into different categories, depending on how they do this,

you begin to understand, you can ideally begin to understand how all of those things work. The color white has been so impactful on human history that Adam devoted three whole chapters of his book to it, and we're going to spend the rest of the episode talking about one of those stories. The 1893 Brawlts Columbian Exposition, also known as the White City. Some of you might recognize it from Eric Larson's book called Devil in the White City, but

the whole serial killer part of the White City tends to overshadow the design aspect. Adam tells me about how this event was a powerful example of how color and architecture could be more than just aesthetic choices, but tools of asserting cultural dominance. The Chicago World's Fair, 1893 basically, the 2, 3, four. Really is this kind of picked over well, picked over fair for architecture, design fans, because the color and design of it are so much part of the story of American hegemony at the time. So by the time this world's fair happened, there had been several in Europe and they were grand successes. And especially one in Paris where they built this beautiful tower that people probably heard of or like the one in London where they built the Crystal Palace and their gorgeous exhibition halls and people would go all over the world they would show up and

they were, you know, these things were like educational and theme parks and also trade fairs all rolled into one thing and they really showed off the cities and the way that everybody always hopes like an Olympics will these days. And so in the US with the anniversary of Christopher Columbus arriving on the North American continent, or at least within ships through the North American continent, there was this desire in the US to celebrate that and also to celebrate what was seen

as this signal American achievement of having made it all the way across the continent of the fulfilling that the that manifest destiny that everybody thought was the right of the white people, the white men who were running the country at the time. So then the questions became, well, how do you celebrate that and where do you solve what do you do? And finally, after some competition, the city that really was kind of the center of American culture, physically really the center of American culture,

physically really, the center of American culture at the time, one was Chicago, which went out over these East Coast cities, there were the oldest cities, one out of New York and Boston, Philadelphia, whatever, mostly because it was the center of this vast rail network and the center of the American consumption of protein and a place where more people could come, but also because it was the, I mean, you could make the argument. It was the great city at that moment in the United States, partially because it was where the architects, famous architects were working on inventing the skyscraper.

This thing that we define cities all over the world by now is first being worked out in its most basic scheme by by specifically some architects, who then were the ones who got assigned to figure out the world's fair, this world's exposition. So you have these names of people who have a significant imprint on the American built environment, all working together in Chicago,

you have Daniel Burnham, who was the main exponent of the city, beautiful movement, to make no small plans, was the famous phrase always attributed to him, and his partner, John Root, and Frederick Law, Olmsted, Freshoff, his triumphant plans for parks, like the Amal Mechless in Boston, Central Park,

in New York, all coming together to figure out how are we gonna do this thing that's going to celebrate the American achievement? It's almost as if they were trying to design what uniquely American architecture should look like in the first place. Like, did they ever figure that out? I mean, what did they end up building? Well, they made a set of decisions that all, like, one sort of progressed from another,

but they made, the first decision they made was they said, we'll have this classic Olmsteadyen paths and hills and interaction between water and land. And in the center of it, there will be a court of architecture where we will celebrate the best of architecture that we have to offer. And all the other stuff, the fun stuff we're going to put off to the side. But in the middle part, they were going to have the court of honor, like the most, all the pavilions. And they decided that they didn't want the pavilions

to just look like the Crystal Palace had. They didn't want them to just be temporary looking metal and glass structures. They had to have solidity and they had to show permanence and they had to show dominance and control. They had to show that Americans had nailed it. Man, the Americans got it right. And the way that they were gonna show that was unclear

because there was so much work to do. And they finally had to like hire in all the other architects in the country, essentially, like the folks from McIntyne, Mead and White, which is the famous New York firm. And initially in the meetings, root especially, Burnham's partner did some drawings that were very fanciful and was kind of more

ish-influenced and red-brown brick. And then all the architects from the East Coast came out for a big meeting. It's a full and it's kind of moreish influenced and red brown brick. Then all the architects from the East Coast came out for a big meeting. In the beginning of that meeting, Rute wasn't feeling that well by the middle of that meeting, Rute had pneumonia. Before that meeting was over, over the course of about a week, Rute had died. And Burnham kind of lost it, but he just couldn't believe that they had come this close, together to like recreating the American built form together and then, you know,

it's snatched away from them. But Burnham did have something in common with these other architects who he brought in, which is they were all basically trained in this four, the Bozart's School of Architecture, which had come to emphasize a certain style inflected by what they believed the architecture of ancient Greece and Rome to have looked like. So, the fact that the capital building in Washington looks like a Greek temple, that's this. That is neoclassical architecture, totally.

But together, they decided that the way to convey this validity that they wanted to convey the permanence, the glory of Rome would be to go too hard and back to the glory of Rome, to the imperial architecture as a style. And they decided it would all match. They said everything on the court of honor would all have the same height. It would all be built and that style we're going to build. Everything that way, and I was all fake, it was all like, imagined-eared, because inside these buildings, they would look just like the crystal pearls.

They would just be metal and metal frames and glass. But on the outside, they would use this kind of plaster like stuff called staff, and they would make these forms that would look like they were carved out of the Tarato marble of Italy or whatever. But then they still had a decision to make, which was, okay, well, what are we going to, what's the surface going to, what's the surface treatment going to be? And they talked about stuff like a sort of kind of beige brown. They ignored a truth that I have convinced myself at least that they would have known at the time,

which is that those buildings, when they weren't neoclassical, but were in fact classical, when the Greeks and Romans built them, they were very colorful, highly chromatic. All the reds and yellows of the ochres and some blues and greens, the insides would have had harlequin and checkerboard patterns.

The archaeological evidence at the time that existed even showed that, and the Bowsarts people, the people who trained in the Bowsarts architectural school actually would travel to Athens and to Rome and paint these things. I've seen these images that they painted when they brought back for school assignments and they had all the colors on them. Some people still don't believe they're like, well, maybe that's just, you know, function of age. That's just like you know, function of age. That's just like liking or something growing on it.

There were arguments about it. So they went with what they ended up saying was like, okay, well, the court, everything that symbolizes, everything that is, they were gonna have all these exhibits at the fair of everything, all technology through history. So like the transportation building was gonna have, every mode of transportation that had ever been built, or the textile building, whatever,

every kind of loom ever, they would have everything ever and what they the guy who was doing the catalogs Came from the Smithsonian Describe this is being an object lesson everything would be an object lesson being object that would have a lesson to it It would have a catalog this would be like the card catalog like every item would be the real actual item and also be a lesson about the development of that item So the the design of the fair itself, of the Court of Honor, the architecture, that was its own object lesson. They were saying this is a country

that harkens the tradition of Rome and Greece, and in fact, it is the white men who run it. And it really is that direct, right? Like this idea of the cultural weight of whiteness and that all other color was sinful including pigments of skin and, you know, like it really, it's foregrounded. That I think that's something that I think much like the colorful, you know, facades of Greek classical architecture. I think people have a hard time recognizing how foregrounded the symbolism is to the whiteness.

I tend to have some insensitivity to this kind of symbolism. You know, when I read, I'm like, oh, that was the sled symbolizes a childhood. You know, like, I've missed that stuff. Here, it's so blatant. Yeah. They literally took everything of color and put it on the midway. There's one important exception, which is that every architect or architect's team

got assigned one of these buildings. And Burnham and Rute were rightly seen at the times being some of the parents of the idea of the skyscraper. The other parents, the skyscraper, one of them was an architect, and Louis Sullivan. Sullivan was another Chicago architect, and he came in and got assigned the transportation building. Sullivan had not been trained in the Bozart School. He'd been trained in a whole other school of architecture that grew out of a kind of weird romantic polychromatism

that had come out of Europe and textile work a couple hundred years before. And so he built this riot of color slightly off the court of honor of the transportation building. Mm-hmm. Sullivan's revolution, his chromatic revolution, I think is the one that actually obtained. It's the only building that really had it influence.

Everything else sort of faded away by the 20s. architectural critics were saying, whoa, we're thinking, we gotta try something else. It helps give rise to modernism in architecture is the rebellion against the same way that sort of punk in new wave, where, you know, rebelling against sort of the pop classism of disco in a weird way, like the architecture rebelled against that except for the transportation building, the public, the transportation building became much more of a touchstone. Yeah, because by the time you get to the 1901 World's Fair, it's all a celebration of polychromy. It's just like fashion and design and everything of the modernism is born and it is multi-gullar. Right, and two things happen. One of them is the cultural shift. One of them I think is an understanding,

like, well, look, this country is not going to just be monochromatic in its approach, in who the immigrants are, and who runs things. It's going to be more than that. By then, already, Chicago itself was the place where the Great Migration was going to be centered around. It was not just a white city.

It was an every-color city. And also the technology chain. So in addition to new pigments becoming available and becoming more available to designers and architects, the other thing that happened were electric light. And once electric light comes in, it becomes literally a whole different way of seeing the natural world outside. You start to see a whole different kind of colors projected onto surfaces. In fact, initially the Paris fair, that was the city of lights thing, it had been a gas

lamp thing, experience, but then becomes electrical. Chicago was heavily electrically lit. In the early decades of the 20th century, have things like Hoover Dam starting to provide electrical power to places on the west that can start to eliminate their streets. You get neon lights out there. You get a much more polychromatic experience that combines both the service pigment treatments and also the color of light shining on them at night. And people can see colors outside at night that they have never seen before. Yeah. Yeah.

I don't know why maybe I just have the wrong priors here, but when I think of all the sciences of the world, you know, I think of know why maybe I just have the wrong priors here, but when I think of all those sciences of the world, you know, I think of physics, I think of chemistry, the business of color doesn't seem like the preoccupation of serious people or something. I know I know this is wrong. I know it's totally wrong, but I had no idea how preoccupied people were with color. And, you know, as you describe it, it really is, in many ways, the first formal science. And not only that, but it's kind of human kinds first science at all because they're making ochre, zeta, dirt, and stone, and stuff like this. I mean, understanding how it really is fundamental to science.

It forces you to grapple. It forces scientists for the history of human science. It forces them to grapple with fundamental questions. It forces them to try to figure out, well, okay, we see these different colors, what are they made of? And they turn out to be made of the basic subsistix. If you're trying to apply colors to a surface, and you want to understand how to do that better,

that turns out to require you to understand the basics of chemistry. If you're trying to understand how the brain turns sense perceptions into mind, you turn to colors as the proxy to understand that because there are things that the brain does that it's not only a metaphor, it's an actual thing that gets turned into a perception and gets turned into a sense of the world. And so at every moment, to me, I could sort of go to every moment that were the beginnings of these multiple fields of basic science and find the person who got there by studying color. You get to, you know, James Clerk Maxwell

on the way to figuring out electromagnetism is working with color. John Dalton on the way to figuring out atomic theory for atoms, on the way there is trying to figure out color blindness and color. All the way back to this cave in South Africa, where archaeologists find 80,000 year old's workshop just for making paint. Because it's so important that there's a special place to do that that they preserve.

This episode was produced by Vivian Leigh. After the break, Adam Rodgers comes back to tell me what the world's first color wheel was made of. You're in for a cool story. So, one of the things that people were preoccupied with when it came to color was how to organize an order color. I'm intrigued by the earliest known example of a colored wheel and what it was made of and what it was made for. Can you describe that to me please? The very first physical color wheel.

People have been trying to put colors in order. It was a preoccupation of Aristotle and Plato and all of the Greek philosophers and then the early Arab philosophers tried to figure out what a color order is because you don't understand. There's all these colors. Are they a sequence?

How does one become the other? What is that transition like? Why is it different for light than for pigments? All these things are really hard questions. One of the very first ones, the earliest kind of known illustrated version of one of these is actually a line of glass vessels full of different shades of yellow liquid,

which are urine. It was doctors trying to diagnose ailments by the color of a person's urine. And so it would be like from clear to dark brown, or I guess blue if you have porphyry or something, but like blue to dark brown, like how what's could be wrong with this person? And you needed some kind of objective metric

to say like, oh, we're in the sort of dark yellow version that maybe too much of the wrong humor or something like that. So yes, it's just a diagram of P. The thing that I love about this though, I think it's super cool to me about this is that in order to make these Make the artwork of the drawing the the actual physical object were these flasks that, if you're in a lab today, you call it a boiling flask. It's like a sphere with a little stem at the top of it.

And being able to make those kind of accurately make a sphere out of glass, is it technical skill, glass blowing thing that people learned how to do. But before there were prisons, these glass globes, sort of goldfish-ball things, full of liquid, were an early optic technology. And it was looking at the way that light moved through these that allowed the Arab translators and scientists, like from the 300s to the 1100s, to understand correct and expand on the early optics work

of Aristotle and planning, folks like that. Because they were translating this work and it didn't make any sense and they were wrong about everything. So they did the experiments themselves and they used these glass spheres full of liquid to see how light moved and to understand what came to be refraction, to understand that that's that a rainbow could form by multiple refraction through drops, through raindrops, because these spheres, these same spheres that eventually would be, like in the 11 hundreds or whatever, were used to store urine and look at the color of it, were the thing that let them make a proxy for a single drop of water and figure out the movement of light.

It's not just a pee joke. It's not. That's okay. the pee joke. That's so good. Adam Rogers' book is called Full Spectrum of the Science of Color Made Us Modern. We only scratch the surface of what he covered in the book, so if you want to nerd out about color with atoms and more, and I highly recommend that you do that, you should definitely check it out.

99% Invisible was produced this week by Vivian Le, mixed in tech production by Jim Riggs, music by our director of Sound, John Rial. Dilling Hall is the executive producer, Kurt Coles, that is the digital director. The resident includes Chris Barube, Joe Rosenberg, Lachem Adon, Christopher Johnson, Emmith Fitzgerald, Sophia Klatsker, and me Roman Mars.

We are a part of the Stitcher and Serious XM Podcast family, now headquartered six blocks north in the Pandora building. In beautiful, uptown, Oakland, California. You can find the show and join discussions about the show on Facebook. You can tweet at me at Roman Mars and the show at 99PI or come on Instagram and write it to. You can find links to other Stitcher shows I love as well as every past episode of 99PI at 99PI dot org. T-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-t-