Speaker 1: Today's episode is part two about color and the brain.
Speaker 1: Why did royals wear purple? It's not accidental And if
Speaker 1: you rewound history ten thousand years and ran it again,
Speaker 1: you'd find exactly the same outcome. So what's going on?
Speaker 1: And how do we see colors that our recent ancestors
Speaker 1: never saw in their lives? Why can't you imagine a
Speaker 1: new color? Are there, in fact new colors that you
Speaker 1: could see? Yes, and I'm going to show you how
Speaker 1: to do that. Can you lose your color vision? And
Speaker 1: what does any of this have to do with language
Speaker 1: or culture? Or why the military likes color blind people
Speaker 1: for a particular task, and why I suggest that the
Speaker 1: cultural history of Thailand was influenced by one single, unknown neurodivergent.
Speaker 1: Welcome to Dinner Cosmos with me David Eagleman. I'm a
Speaker 1: neuroscientist and author at Stanford and in these episodes we
Speaker 1: look at the world inside us and around us to
Speaker 1: understand why and how our lives look the way they do.
Speaker 1: Today's episode is part two about the absolutely amazing and
Speaker 1: often underappreciated topic of color. And if I do my
Speaker 1: job right, this is going to allow you to see
Speaker 1: the world with totally fresh eyes. So we're going to
Speaker 1: start with a quick catch up from last week so
Speaker 1: we can continue this incredible story about color and the brain.
Speaker 1: Last week, we talked about the fact that color is
Speaker 1: not a property of the physical world, but it's a
Speaker 1: creation of the brain. Color doesn't exist in light itself.
Speaker 1: Light is just electromagnetic radiation of various wavelengths, and our
Speaker 1: brains interpret those wavelengths by constructing the experience of color.
Speaker 1: This private interpretation of color begins in the retina with
Speaker 1: a special type of photoreceptor cones, which detect wavelengths and
Speaker 1: come in three flavors sensitive to short, medium, and long wavelengths,
Speaker 1: which corresponds approximately to red, green, and blue. The brain
Speaker 1: then processes patterns of activation across these cells to produce
Speaker 1: the experience of color, and last week we talked about
Speaker 1: color constancy, which allows us to perceive colors as stable
Speaker 1: despite the changing lighting conditions, something that we see all
Speaker 1: the time in visual illusions. We also talked about evolution.
Speaker 1: For example, we humans have three types of giving us
Speaker 1: trichromatic vision, but this is a rare trait among mammals,
Speaker 1: most of whom are dichromatic, meaning they have two types
Speaker 1: of cones, and this is likely because of a nocturnal
Speaker 1: bottleneck where during the age of dinosaurs, the ancestors of
Speaker 1: mammals how to avoid getting stomped on and eaten, and
Speaker 1: so they scampered around at night and got better night vision,
Speaker 1: but lost some of their color vision. Now humans and
Speaker 1: some other primates reevolved trichromatic vision, possibly not just for
Speaker 1: spotting ripe fruit, but for social reasons, detecting subtle changes
Speaker 1: in skin coloration due to emotions. But in any case,
Speaker 1: lots of our neighbors in the mammalian kingdom can't see
Speaker 1: red and orange, which is why deer hunters wear orange vests,
Speaker 1: because that allows the hunters to see each other clearly,
Speaker 1: but the deer just can't see them. And finally we
Speaker 1: saw how other species like bees and snakes and manta
Speaker 1: shrimp they presumably perceive the world very differently because their
Speaker 1: eyes pick up on ultraviolet light or infrared light or
Speaker 1: polarized light. And if you tune into last week's episode,
Speaker 1: you'll hear lots of other stories about how color serves
Speaker 1: many functions like camouflage or warning or mating signals or
Speaker 1: deception or emotional communication. Now we're ready to continue our
Speaker 1: story this week. So let's start with something that I
Speaker 1: think is amazing, which is that we see so many
Speaker 1: more colors than even our recent ancestors did. This is
Speaker 1: not because of a change in our biology. It's because
Speaker 1: our current collection of technologies can generate so much more.
Speaker 1: For example, your great great grandparents never saw a lot
Speaker 1: of neon, or the bright ultra red of attack esla,
Speaker 1: or the blaze orange of a caution sign on the road.
Speaker 1: But we see these colors all the time. Now I
Speaker 1: want you to try this. Imagine a new color. Go ahead, Okay,
Speaker 1: you can't do it. The fact that you can't do
Speaker 1: it is very revealing, and it's very important because it
Speaker 1: illustrates for us the fence lines of our perceptions, beyond
Speaker 1: which we just can't walk. And by the way, if
Speaker 1: you could envision a new color, you wouldn't be able
Speaker 1: to explain the sensation of it to another person. For example,
Speaker 1: you have to experience purple to know what purple is.
Speaker 1: There's no amount of description on a podcast or in
Speaker 1: a textbook that's ever going to allow a totally color
Speaker 1: blind person to understand purpleness. Here's an analogy, just to
Speaker 1: make this clear, try explaining vision to a friend of
Speaker 1: yours who is born blind. You can try all you want,
Speaker 1: and your blind friend might even pretend to understan what
Speaker 1: you're talking about, but it is a fruitless attempt because
Speaker 1: to understand vision requires experiencing vision. And that's the same
Speaker 1: with experiencing purple or canary yellow or cobalt blue. You
Speaker 1: have to experience it to know it. There's no way
Speaker 1: to describe it. Language is just a way of tagging
Speaker 1: shared experiences, and if it's not shared in some way,
Speaker 1: no amount of language will do the trick. Okay, so
Speaker 1: let's come back to the idea of whether you will
Speaker 1: ever have the chance to see a new color. Well,
Speaker 1: it seems pretty clear that the answer is no, because
Speaker 1: the space of possible colors that humans can see are
Speaker 1: pretty well represented in our world, but under special circumstances
Speaker 1: you can see new ones. So first, let's start with
Speaker 1: what are known as impossible colors. These are colors that
Speaker 1: are outside what our cones can put together. For example,
Speaker 1: you can't have a reddish green or a yellowish blue.
Speaker 1: These are combinations that the visual system just isn't wired
Speaker 1: to perceive simultaneously. But under certain conditions. Using tricks in
Speaker 1: the laboratory, some people do report glimpsing these colors. These
Speaker 1: perceptions are fleeting, but they hint at the boundaries and
Speaker 1: the flexibility of color perception. So here's something that you
Speaker 1: can try easily. Let's say that you stare at a
Speaker 1: square that is cyan in color, and you just stare
Speaker 1: at that for twenty or thirty seconds. Then if you
Speaker 1: look over to a white piece of paper, you'll see
Speaker 1: an orange after image. Okay, fine, but now after staring
Speaker 1: at the cyan, try looking over at an orange piece
Speaker 1: of paper, and you will see what we call hyperbolic orange,
Speaker 1: which is an orange so orange that you never can
Speaker 1: normally see that. Now, there are a bunch of ways
Speaker 1: to see impossible colors. Here's one. Stare at a yellow
Speaker 1: square for a while, and then look at a piece
Speaker 1: of paper that's black. You'll see what is called stygian blue,
Speaker 1: which is a blue that is darker than black. Or
Speaker 1: stare at a green square for a while and then
Speaker 1: look at a white background and you'll see what's called
Speaker 1: self luminous red, a red that is brighter than white.
Speaker 1: These are some ways to see outside the normal fence
Speaker 1: lines of color, and I'll put demos of these on
Speaker 1: the show notes at Eagleman dot com. Now, there are
Speaker 1: other ways to see new colors that require doing so
Speaker 1: in the laboratory, and I'm going to come back to
Speaker 1: that near the end of the episode when I'm going
Speaker 1: to talk about the future of seeing color. But for now,
Speaker 1: I want to mention something else, which is the issue
Speaker 1: of seeing data outside the normal visual spectrum that we
Speaker 1: can see. For example, it might sound impossible to see
Speaker 1: in the altar for violet range, but it turns out
Speaker 1: your photoreceptors can do that. It's just that the lens
Speaker 1: of your eye blocks out UV light. But then something
Speaker 1: was accidentally discovered in the last couple of decades. A
Speaker 1: lot of people go in for cataract surgery and they
Speaker 1: get their lens exchanged for a synthetic replacement. Your natural
Speaker 1: lens blocks UV, but the replacement lens does not, So
Speaker 1: patients found themselves tapping into ranges of the electromagnetic spectrum
Speaker 1: that they couldn't see before. I wrote about one guy
Speaker 1: in my book Live Wire. His name is Alec, and
Speaker 1: he got a lens replacement for his cataracts, and he
Speaker 1: now describes a lot of things that he looks at
Speaker 1: as having a blue violet glow that other people just
Speaker 1: don't see. He noticed this the day after his cataract
Speaker 1: surgery when he was looking at his son's Colorado Rockies shorts.
Speaker 1: Everyone else saw the shorts as black, but he saw
Speaker 1: them with a blue violet sheen. When he put a
Speaker 1: UV filter over his eye to block out the UV,
Speaker 1: he saw them like everyone else. Here's another example. When
Speaker 1: you look at what's called a black light that's turned on,
Speaker 1: you don't see anything, but Alec sees a bright purple glow.
Speaker 1: So this gives him a new superpower, seeing past the
Speaker 1: normal spectrum of colors. Alec has different kinds of experiences
Speaker 1: than we do when he looks at sunsets, or gas
Speaker 1: stoves or flowers. Now I want to flip the question
Speaker 1: to examine the other side. Could you lose your color vision. Yes,
Speaker 1: it's rare, but it happens, and it's called a chromatopsia.
Speaker 1: People with this condition see the world entirely in shades
Speaker 1: of gray, as if life were filmed through the lens
Speaker 1: of an old black and white movie. It's not just
Speaker 1: muted color or red green confusion. It's the complete absence
Speaker 1: of color perception. Just imagine this, The vibrant world that
Speaker 1: we all take for granted gets rendered by your brain
Speaker 1: in a perpetual gray scale, where even a rainbow is
Speaker 1: just a smooth gradient of light and dark. Now, the
Speaker 1: thing I want to note is that achromatopsia results from
Speaker 1: brain damage, specifically to a region called area V four
Speaker 1: in the visual cortex. Because color vision doesn't happen in
Speaker 1: your eyes alone. While the cone cells in your retina
Speaker 1: detects different wavelengths of light, the experience of color is
Speaker 1: assembled in the brain, and one of the key regions
Speaker 1: responsible for putting those wavelengths together into color perception is
Speaker 1: this area of V four, located in what's known as
Speaker 1: the ventral visual pathway in the brain. The point is,
Speaker 1: if this area is damaged from a stroke, from head trauma,
Speaker 1: from a brain tumor, the person gets this cortical color blindness.
Speaker 1: The eyes are perfectly healthy, but the brain can't interpret
Speaker 1: color signals anymore, so the person experiences the world in grayscale.
Speaker 1: So this once again illustrates the simple but critical point
Speaker 1: that color is a construction of the brain, and you
Speaker 1: have to have all the right pieces and parts running
Speaker 1: or else. You can see just fine, but you can't
Speaker 1: see color. Now. Some people, of course, are born color blind,
Speaker 1: but not because of brain damage, but instead because they
Speaker 1: don't have some of the types of cones in their eye.
Speaker 1: As a reminder, most people are born with three different
Speaker 1: types of cones color photo receptors, but some people are
Speaker 1: born with only two types, or one type or none,
Speaker 1: giving them a diminished or no ability to distinguish between colors. Now,
Speaker 1: the military excludes colorblind soldiers from certain jobs, but they
Speaker 1: have come to realize that colorblind people do have a
Speaker 1: secret superpower. They can spot enemy camouflage better than people
Speaker 1: with normal color vision. Why because they're better at distinguishing
Speaker 1: between shades of gray. This is because they have the
Speaker 1: same amount of visual cortex at the back of their brain,
Speaker 1: but fewer color dimensions to worry about. So they're using
Speaker 1: the same cortical territory, but for a simpler task, just
Speaker 1: gray scale instead of color, and this gives them improved
Speaker 1: performance in distinguishing very subtle differences in brightness. So although
Speaker 1: it would be a real bummer to be colorblind, there
Speaker 1: are some advantages as well. So now let's return to color.
Speaker 1: Everything we've talked about so far as a reminder that
Speaker 1: color is not just about the electromagnetic radiation hitting the eye,
Speaker 1: but about what happens in the brain. And one very
Speaker 1: good example of that is something I've talked about before, synesthesia.
Speaker 1: This is a brain phenomenon in which color blurs with
Speaker 1: different concept a typical citisteit will perceive letters or numbers
Speaker 1: as having fixed colors, like a is always red, or
Speaker 1: the number seven is ce foam green, and it can
Speaker 1: commonly be with weekdays or months like Wednesday is indigo
Speaker 1: blue or August is yellow. Now it's not a hallucination,
Speaker 1: but to the person, it's just self evidently true that
Speaker 1: that's what that letter or number or weekday or month is.
Speaker 1: Of course it's purple or yellow or green. So I've
Speaker 1: studied synesthesia in my lab for many years because it's
Speaker 1: such a good inroad into conscious experience and also the
Speaker 1: differences between one person's experience and another's, and the difference
Speaker 1: is between people's experiences on the inside when they're perceiving
Speaker 1: the world. If you're interested in synesthesia, please listen to
Speaker 1: episode four. But for now, I want to zoom in
Speaker 1: on the issue of colored weekdays, which is a common form.
Speaker 1: The thing I want to emphasize is that the color
Speaker 1: palette ends up being different for each cynisthees. So one
Speaker 1: person might say, oh, Monday is clearly green and Tuesday
Speaker 1: is purple, and Wednesday is yellow, and a different cinisthee
Speaker 1: has a different color palette. Now, I've studied literally thousands
Speaker 1: of such cynthtes, but here's something I just learned that
Speaker 1: really surprised me. I learned that in Thailand there's an
Speaker 1: ancient tradition in which each day of the week has
Speaker 1: a corresponding color, rooted in Hindu based astrology. So Monday
Speaker 1: is yellow, Tuesday is pink, Wednesday is green, and so on.
Speaker 1: Apparently these colors are tied to planetary deities like Mars,
Speaker 1: for Tuesday is associated with pink, Mercury, for Wednesday is green,
Speaker 1: and so on, and traditionally it was believed to bring
Speaker 1: luck if you wore that color or use color on
Speaker 1: the corresponding day. This apparently used to be very common
Speaker 1: in Thailand to wear the right color every single day.
Speaker 1: Today it's a little less common. Now. You can probably
Speaker 1: guess what I'm wondering about, which is where did this
Speaker 1: colored weekday idea come from Well, if you consult any
Speaker 1: Taie book on this, they'll say it comes from the
Speaker 1: colors of their deities. But of course gods don't really exist,
Speaker 1: and if they did, it's not obvious they would have colors,
Speaker 1: or that anyone would have seen those colors. So my
Speaker 1: suspicion is that if we really did get to the
Speaker 1: bottom of this very ancient history, we'd find a very
Speaker 1: influential Cinistheite at bottom, someone who said, well, of course
Speaker 1: Tuesday is pink and Wednesday is green and so on,
Speaker 1: and because of some cult of personality, it stuck, and
Speaker 1: millennia later, kids are still told that this deity is
Speaker 1: this color, so that day is the color and you
Speaker 1: should wear that shirt. And so, like all stories with
Speaker 1: cultural momentum, people accept it. Why because everyone else accepts
Speaker 1: it and for thousands of years, So there must be
Speaker 1: something to it. But that's something I suggest is a
Speaker 1: single influential Cynistheide whose quirky neural network determined what everyone
Speaker 1: wore for hundreds of generations. So if you ever think
Speaker 1: neuroscience doesn't affect culture, take that. And on that topic
Speaker 1: of the intersection between neuroscience and culture, I want to
Speaker 1: zoom the camera out to see what happens when lots
Speaker 1: of humans start talking together about color. So we're going
Speaker 1: to turn now to language. For most listeners of this podcast,
Speaker 1: we look at a rainbow and divide it into red, orange, yellow, green, blue, indigo, violet.
Speaker 1: But not every culture divides the spectrum the same way
Speaker 1: or sees the same number of colors. In some languages,
Speaker 1: there is no distinct word for blue. In other languages,
Speaker 1: green and blue are considered shades of the same color.
Speaker 1: As an example of the kinds of differences here, the
Speaker 1: Himba people of Namibia group colors differently from English speakers.
Speaker 1: They have multiple words for what we call green and
Speaker 1: none for what we call blue. Even ancient texts reveal
Speaker 1: this difference in color vocabularies, So in Homer's Odyssey, the
Speaker 1: sea is never described as blue, but it's described as
Speaker 1: wine dark. Scholars have long puzzled over this poetic phrase.
Speaker 1: Was it a metaphor or was it that the ancient
Speaker 1: Greeks didn't categorize blue the way that we do. Blue
Speaker 1: appears almost nowhere in ancient Greek language, and where it
Speaker 1: does is often ambiguous. Why while in ancient Greece there
Speaker 1: were few blue dyes or paints, and by the way,
Speaker 1: blue animals are extraordinarily rare in nature. So while the
Speaker 1: Egyptians used a synthetic pigment, which we call Egyptian blue,
Speaker 1: the Greeks didn't use or produce blue. So it meant
Speaker 1: that blue was less present in their daily life, or
Speaker 1: in their clothing or in their art, and the thought
Speaker 1: goes that it was therefore less common in the language,
Speaker 1: in the same way that cultures on the equator have
Speaker 1: fewer words for distinguishing types of snow than do northern cultures.
Speaker 1: Now zooming out a moment, there were two researchers, Berlin
Speaker 1: and k who proposed that even though language might have
Speaker 1: different color terms, they all follow a predictable order in
Speaker 1: the development of these terms. In other words, the first
Speaker 1: two terms to appear historically in any language are always
Speaker 1: black and white or dark and light. Then comes red.
Speaker 1: Then when cultures get more culture as they introduce green
Speaker 1: or yellow. Only later do you get things like blue
Speaker 1: and brown and more nuanced shades like pink or orange.
Speaker 1: The hypothesis is that this progression matches the salience of
Speaker 1: colors in the environment. The contrast of light and dark
Speaker 1: is really important, the presence of blood, the ripeness of fruit,
Speaker 1: the necessity of distinguishing between plants. So it's only when
Speaker 1: society has become more complex and encounter more dyes and
Speaker 1: materials and artistic traditions then you get new color terms emerging.
Speaker 1: So different languages have different color terms, and one idea
Speaker 1: that has emerged is called linguistic relativity, which is this
Speaker 1: notion that the language that you speak shapes how you
Speaker 1: perceive the world. The idea is that although all people
Speaker 1: can see blue, if your language doesn't label it distinctly,
Speaker 1: you might not really pay attention to it as a
Speaker 1: separate category. And this is indeed what a lot of
Speaker 1: cognitive science studies have found. Your language shapes at least
Speaker 1: a little bit your color distinctions. For example, the Russian
Speaker 1: language has distinct words for light blue and dark blue,
Speaker 1: and when Russians are tested on their ability to distinguish
Speaker 1: shades of blue, they're faster at spotting the difference between
Speaker 1: light and dark blues than English speakers, who use one
Speaker 1: word for both blue. In other words, Russian speaking brains
Speaker 1: process the difference more quickly, suggesting that having a word
Speaker 1: for something helps you see it. If your language has
Speaker 1: more precise blue terms, like Russian, you can distinguish shades
Speaker 1: faster than languages that don't, like English, and you can
Speaker 1: see the same story in babies. Infants can see color
Speaker 1: long before they learn to speak, but once they acquire
Speaker 1: the words for specific colors, their ability to distinguish them improves.
Speaker 1: Language tunes the brain to attend to specific aspects of
Speaker 1: the scene. So if the Greeks didn't have a strong
Speaker 1: word for blue, they might have grouped it with other
Speaker 1: colors like green or gray and not really noticed it
Speaker 1: as blue. The Greeks didn't lack the ability to see blue,
Speaker 1: but in their culture they didn't isolate it with language,
Speaker 1: likely because blue was rare in their environment and their
Speaker 1: language hadn't evolved to distinguish it clearly. So when Homer
Speaker 1: describes the sea as wine dark, it's not because he
Speaker 1: was colorblind. It's because the way his culture saw and
Speaker 1: named colors was a little different from ours. And by
Speaker 1: the way this issue about the Greeks and blue, the
Speaker 1: same is true of many ancient languages, including Hebrew and
Speaker 1: Chinese and Japanese, and in modern studies we can look
Speaker 1: at the Himba people who as I mentioned have multiple
Speaker 1: words for green and none for blue. In experiments, they
Speaker 1: can easily distinguish green shades that we Westerners struggle to
Speaker 1: tell apart, but they find it difficult to pick out
Speaker 1: a blue square from a field of green. Now we've
Speaker 1: been talking about biology and language, but what's fascinating is
Speaker 1: how this private phenomenon of color takes on cultural meaning.
Speaker 1: A million examples of this. I'll just do a quick whistlestop, TORP.
Speaker 1: So just look at the way we organize our world
Speaker 1: through color. We have red states and blue states. We
Speaker 1: have green energy, we have black markets, we have white lies.
Speaker 1: Color becomes shorthand for complex social and political ideas. Even
Speaker 1: our moral frameworks become color coded. You've got the white
Speaker 1: hat and the black hat, and the old Westerns. You've
Speaker 1: got the white dove of peace, you have the red
Speaker 1: devil of temptation. And colors very commonly come to signal
Speaker 1: identity and allegiance. You have teams and uniforms that define
Speaker 1: us versus them by color. Movements adopt symbolic palettes. So
Speaker 1: the Suffragettes wore white and green and violet. AIDS awareness
Speaker 1: uses red, environmental causes green. You see rainbow flags and
Speaker 1: pride parades. You see orange worn by anti gun violence advocates.
Speaker 1: So in this way, when we look around, we see
Speaker 1: that color comes to serve as a quick symbol flag. Now,
Speaker 1: not surprisingly, there's nothing fundamental about these associations and therefore
Speaker 1: they aren't static. So in the eighteen hundreds, pink was
Speaker 1: considered a strong masculine color related to red. Blue was
Speaker 1: seen as delicate and feminine. These meanings flipped in the
Speaker 1: twentieth century, and it had to do with shifts in
Speaker 1: fashion and marketing and cultural signaling. Color, like language, evolves
Speaker 1: and political colors vary. So you've got red for the
Speaker 1: left in Europe, blue for conservatives in the UK, and
Speaker 1: it's reversed in the United States. What I recently read
Speaker 1: is that the colors in the United States blue for
Speaker 1: liberals and red for conservatives. This got nailed down just
Speaker 1: around the year two thousand, when the major television networks
Speaker 1: started using this as a visual shorthand for liberal and conservative,
Speaker 1: and that's how it got crystallized into public consciousness. I
Speaker 1: don't really know the history of this, but I suspect
Speaker 1: then in the day decades of black and white newspapers,
Speaker 1: it was easier to use a donkey and an elephant
Speaker 1: to distinguish the parties. And only when color television became
Speaker 1: ubiquitous did it make sense to introduce a quick color flag. Okay, So,
Speaker 1: now coming back to cultural messages, what is conveyed by
Speaker 1: a color depends on your local context. In Western traditions,
Speaker 1: white is associated with purity and innocence and weddings, but
Speaker 1: in many Eastern cultures, white symbolizes death and is worn
Speaker 1: by mourners. In South Africa, red can be a color
Speaker 1: of mourning. In Brazil, purple is reserved for funerals. I'll
Speaker 1: give you another example. Red, which in the West can
Speaker 1: symbolize danger or passion, is associated in China with celebration
Speaker 1: and joy and luck. A bride in India might wear
Speaker 1: a bright red sorry, while a Western bride walks down
Speaker 1: the aisle in white. So the point here is that
Speaker 1: cultural colors symbols are learned. They're not innate. They are
Speaker 1: built from shared stories and traditions and rituals. Now, despite
Speaker 1: this variation, as far as what color means what sometimes,
Speaker 1: there is a logic to it. Now, one thing I've
Speaker 1: always found fascinating is that purple is always associated with royalty.
Speaker 1: Why purple, why not orange or yellow or something else. Well,
Speaker 1: it turns out that started in ancient Rome with a
Speaker 1: die called Tyrian purple. This was a deep hue and
Speaker 1: it was unlike any other dye that was available at
Speaker 1: the time, and the color became irreversibly associated in their
Speaker 1: society with nobility and wealth and the divine aura of emperors.
Speaker 1: But what was so special about it? While Tyrian purple
Speaker 1: was made from the mucus of a specific sea snail,
Speaker 1: so producing just one gram of dye required thousands of
Speaker 1: snails and days of labor. In other words, the die
Speaker 1: was extremely labor intensive and therefore very expensive. Only the
Speaker 1: wealthiest could afford it, and so that's how a particular
Speaker 1: color came to represent something. What's interesting is that it
Speaker 1: started off as an economic issue, but by the Roman
Speaker 1: imperial era, the association between purple and power was codified
Speaker 1: in the law. So you weren't allowed to wear garments
Speaker 1: dyed in Tyrian purple unless you were an emperor or
Speaker 1: a high ranking official. Apparently you could be sighted with
Speaker 1: treason if you did this. So purple started out as expensive,
Speaker 1: but it eventually became politically exclusive and By the way,
Speaker 1: this wasn't just Rome. In various societies you find these
Speaker 1: laws called sumptuary laws, which are like dress codes backed
Speaker 1: by law, and these are there to restrict which people
Speaker 1: can wear which colors. For example, you find the same
Speaker 1: kind of sumptuary law in Elizabethan, England, where only royalty
Speaker 1: and nobility were allowed to wear certain dies. The idea
Speaker 1: with these laws is that they're designed to visibly maintain
Speaker 1: the social order. So again, colors become a shorthand label
Speaker 1: for larger concepts. Okay, so we've talked about this terrific
Speaker 1: history of colors where certain colors came to have particular meaning.
Speaker 1: But then what happened was the invention of synthetic dyes
Speaker 1: in the nineteenth century, and suddenly you had this explosion
Speaker 1: of vibrant hues that became accessible to the masses. The
Speaker 1: first synthetic dye was mauve, and that was discovered accidentally
Speaker 1: in eighteen fifty six, and that sparked a fashion because
Speaker 1: what followed was an explosion of new hues, artificial magentas
Speaker 1: and bright greens and vivid blues and optimistic yellow and
Speaker 1: eventually drunk tank pink and ultramarine and atomic tangerine and
Speaker 1: Nato green and millennial pink and safety orange and on
Speaker 1: and on. So the world in a very short period
Speaker 1: of time became much more colorful. So that's the recent
Speaker 1: history of color. But I'm also interested in the flip
Speaker 1: side question, which is what is the future of color,
Speaker 1: because we're beginning to enter an era where color doesn't
Speaker 1: have to be limited to what the ie evolved to
Speaker 1: see or the dyes that we're able to make. First
Speaker 1: of all, we're well beyond dies now because our modern
Speaker 1: technology has changed how we see color. We have digital
Speaker 1: screens that use RGB red, green, blue, and they mix
Speaker 1: light instead of pigment, and any typical screen now displays
Speaker 1: over sixteen million different colors. But the future of color
Speaker 1: is going to go way further than that. As a
Speaker 1: simple example, we've talked about how color can be used
Speaker 1: to label information, so we can use augmented reality glasses
Speaker 1: to map colors on the fly. Imagine that you are
Speaker 1: in a factory where some machines are hot and some
Speaker 1: are cold, and you just map the temperature data onto
Speaker 1: red or blue so that you can see the temperature
Speaker 1: at a distance. And of course it doesn't have to
Speaker 1: be temperature. It could be anything like how full the
Speaker 1: tanks are, or how many cycles per second are running
Speaker 1: on the chips, or whatever information you need to carry.
Speaker 1: You can encode that in color. But it gets better
Speaker 1: than that, because new technologies are actually expanding the colors
Speaker 1: that you can see. You can zap particular photoreceptors and
Speaker 1: not others to see more saturated colors than you've ever
Speaker 1: seen before. So at Berkeley, my colleagues have pulled off
Speaker 1: a new project where a bypass your eyes normal machinery
Speaker 1: and paint directly on your retina with light. And what
Speaker 1: they can create is a brand new color, a literally
Speaker 1: never before seen Hugh, a supersaturated blue green that the
Speaker 1: research team calls ololo. What does olo look like? So
Speaker 1: picture the most saturated peel that you can imagine, then
Speaker 1: crank it up past anything nature offers. The green of
Speaker 1: a laser pointer feels dull in comparison. Here's how it works.
Speaker 1: Using very tiny doses of laser light, they individually target
Speaker 1: photoreceptors in your eye. They don't just hit one photoreceptor,
Speaker 1: but an entire constellation of about one thousand cones. It's
Speaker 1: like they're painting on a tiny movie screen the size
Speaker 1: of your fingernail. They're painting with light directly on your retina.
Speaker 1: The key is that normally, each one of your cone
Speaker 1: cells responds to different wavelengths short, medium, or long. But
Speaker 1: there's so much overlap in the green and the red
Speaker 1: cones that has been impossible to isolate just the green
Speaker 1: cones the medium wavelength cones. But using this technique, that's
Speaker 1: what they can do. So when only the medium cones
Speaker 1: are stimulated, the result is Olo, a color that doesn't
Speaker 1: exist anywhere in the natural world. Now, if the laser
Speaker 1: jitters accidentally so that it activates nearby cones, the illusion
Speaker 1: collapses in your back to just plain green, and that
Speaker 1: shows how fragile this new color really is. So this
Speaker 1: is how we can unlock entirely new sensory experiences. Your
Speaker 1: brain is seeing something it never evolved to see, and
Speaker 1: that brings us back to a deep question in neuroscience.
Speaker 1: What happens when you feed the brain new information it's
Speaker 1: never had before, And we see that the brain just
Speaker 1: makes up a new color Olo, which is not born
Speaker 1: of the saun or of nature, but of precise cellular
Speaker 1: targeting in the lab. And so the possibility is there
Speaker 1: that maybe we're just at the beginning of what human
Speaker 1: perception is capable of. What amazes me is that we
Speaker 1: can't imagine new colors, but once we've seen them, then
Speaker 1: it's part of what we can imagine. And this tells
Speaker 1: us that there's always more beyond the fence lines of
Speaker 1: our internal models, which is what my next book is on,
Speaker 1: which will hopefully come out next year. Okay, now I
Speaker 1: want to get back to how science is going to
Speaker 1: expand our perception. I think it's inevitable that genetic tools
Speaker 1: are going to make it possible someday to modify our
Speaker 1: eyes to detect new parts of the spectrum. So, for example,
Speaker 1: will someday genetically give humans new flavors of photoreceptor cells?
Speaker 1: Could you add a fourth type of cone to the retina?
Speaker 1: I told you last week about tetrachromacy, in which a
Speaker 1: tiny fraction of women see hundreds of millions of colors
Speaker 1: rather than let's say a million, which is what most
Speaker 1: of us can see. And this is because they have
Speaker 1: a genetic mutation that gives them a fourth cone type.
Speaker 1: So you could genetically engineer tetrachromacy like this. But you
Speaker 1: could also engineer a fourth cone type to see beyond
Speaker 1: the current limits of visible light. Imagine your great grandkids
Speaker 1: being able to see magnetic fields like soft glows of color,
Speaker 1: or to see other things that are totally invisible to you,
Speaker 1: like infrared or ultraviolet, like snakes or bees do This
Speaker 1: would just be an extension of the way that our
Speaker 1: brains use colors as a way of tagging information in
Speaker 1: the world. But now we'll be extending our perception beyond
Speaker 1: its biological history. So let's wrap up. Color feels like
Speaker 1: one of the most real and immediate and obvious aspects
Speaker 1: of our experience. We fall in love with somebody's eyes,
Speaker 1: we remember the yellow walls of a child bedroom. We
Speaker 1: mourn in black, we celebrate in white or red or gold.
Speaker 1: But what we've seen in this episode, in the last
Speaker 1: is that color isn't fundamentally a property of the outside world.
Speaker 1: It's a creation of the brain. There's no color in
Speaker 1: a photon, there's just energy, just wavelength, and your retina
Speaker 1: receives that input, and your brain compares and contrasts it
Speaker 1: with other inputs, and out of this massive internal computation,
Speaker 1: you experience something radiant and vivid, and by the way.
Speaker 1: It's quite personal, which is why a blue and black
Speaker 1: dress can divide the Internet. So the next time you
Speaker 1: admire a sunset, or choose a shirt, or linger over
Speaker 1: a painting, remember that you're translating physics into a subjective interpretation.
Speaker 1: Color is a collaboration between the external world and your
Speaker 1: internal model of it. It's where physics color lies with perception. Finally,
Speaker 1: I just want to revisit how crazy I think it
Speaker 1: is that we see colors every day that Julius Caesar
Speaker 1: never did, and not just Caesar, but Shakespeare and Pocahontas
Speaker 1: and Abraham Lincoln everyone. Until the proliferation of synthetic dies
Speaker 1: and eventually digital screens, the world before us just didn't
Speaker 1: see that many colors, colors that we get to see
Speaker 1: every day, and typically don't even consider the size of
Speaker 1: the palette that we get to appreciate. So spend a
Speaker 1: few minutes today just looking around and thinking about the
Speaker 1: millions of hues that you're looking at. Look at the
Speaker 1: fashion around you, the clothing, the car colors, the paints,
Speaker 1: even the annoying stuff like the advertising posters and the
Speaker 1: road signs, even these are quite extraordinary when you look
Speaker 1: at them. Through a new lens of appreciation, and I'm
Speaker 1: really fascinated in thinking about how iotech will reach into
Speaker 1: new color territories that we can't currently imagine. I told
Speaker 1: you about the new color olo made by zapping specific
Speaker 1: photoreceptors and not others in the lab. Just imagine what
Speaker 1: things are going to look like in a century. Our
Speaker 1: descendants might feel as sorry for us and our pitiful
Speaker 1: little spectrum as we feel for our distant ancestors. Go
Speaker 1: to eagleman dot com slash podcast for more information and
Speaker 1: to find further reading. Join the weekly discussions on my substack,
Speaker 1: and check out and subscribe to Inner Cosmos on YouTube
Speaker 1: for videos of each episode and to leave comments Until
Speaker 1: next time. I'm David Eagleman, and this is Inner Cosmos.