Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,
Speaker 1: Laura vogelbaumb here. Even at full function, our eyes don't
Speaker 1: provide us with a complete picture of the world around us.
Speaker 1: There are plenty of things we can't see under normal circumstances,
Speaker 1: like ultraviolet wavelengths or impossible colors like stiggy and blue.
Speaker 1: Sticky and blue if you're unfamiliar, is what's called a
Speaker 1: chimerical color. It's an after image. Specifically, it's the color
Speaker 1: you perceive when you stare at a bright yellow circle,
Speaker 1: say for several seconds, and then look at a black square,
Speaker 1: you'll see an after image of a deep blue circle,
Speaker 1: a blue that's just as dark as the black against
Speaker 1: the black square. The color is named after the underworld's
Speaker 1: river sticks. Of course, a blue that's as dark as
Speaker 1: black is impossible, but our weird brains nevertheless perceive it
Speaker 1: if it helps. There's actually no such thing as blue
Speaker 1: to begin with, or red or green or fusia. These
Speaker 1: are just words we have for particular sensory experiences. Color
Speaker 1: exists purely in our minds. A banana, for example, is
Speaker 1: not inherently yellow. To prove it is, stumble to your
Speaker 1: kitchen in the middle of the night and hold a
Speaker 1: banana in front of your face. What color is it then?
Speaker 1: Kind of a muddy grayish black, probably definitely not bright yellow.
Speaker 1: And that's because colors are not emitted from most objects.
Speaker 1: They are reflected. A banana is yellow because when visible
Speaker 1: light hits it, the wavelengths that we call yellow are
Speaker 1: what bounce back. We've talked about light and color before.
Speaker 1: A white light from the sun or a normal light
Speaker 1: bulb is composed of wavelengths spanning the entire visible spectrum.
Speaker 1: You know your basic ROYGBIV, going from the longest wavelengths
Speaker 1: to the shortest. That's red, orange, yellow, green, blue, indigo,
Speaker 1: and violet. But when white light shines on a banana peel,
Speaker 1: something frankly incredible happens. There's a natural pigment in the
Speaker 1: peel called xanthophyl that's chemically programmed to absorb certain wavelengths
Speaker 1: of light and reflect others. The dominant wavelength reflected by
Speaker 1: xanthophyl is yellow, but the yellow of that banana still
Speaker 1: doesn't exist as such. It only starts to exist when
Speaker 1: the reflected light from that peel is detected by millions
Speaker 1: of color sensing cells in your retinas called cones. Most
Speaker 1: humans have three types of cone cells, referred to as red, green,
Speaker 1: and blue cones, or more accurately as long, medium, and
Speaker 1: short cones, because each are more sensitive to wavelengths of
Speaker 1: light in those ranges. The cones send a multitude of
Speaker 1: electrical impulses to the brain that data is processed. Each
Speaker 1: cone can process one hundred or more different shades of color,
Speaker 1: giving your average human a range of a million to
Speaker 1: ten million perceivable colors. Some evolutionary biologists think that this
Speaker 1: trichromatic color vision evolved in primates to help us spot
Speaker 1: colorful berries amongst foliage. But we know that other animals
Speaker 1: perceive color differently because they evolved to have different numbers
Speaker 1: or types of cones. Dogs, for example, have just two
Speaker 1: types of cones, blue and yellow. They don't really perceive
Speaker 1: reds and greens. Most birds have four types of cones, red, green, blue,
Speaker 1: and ultraviolet, meaning that they can see colors we can't.
Speaker 1: Honeybees can see into the infrared part of the spectrum.
Speaker 1: Now ultraviolet and infrared light exist, we know they do.
Speaker 1: We can observe them in other ways, and we know
Speaker 1: that what we call yellow light exists. It's the part
Speaker 1: of the electromagnetic spectrum with wavelengths around five hundred and
Speaker 1: seventy two five hundred and eighty nanometers or thereabouts. But
Speaker 1: other colors that we perceive technically don't exist, like sticky
Speaker 1: and blue, or think about magenta. Magenta is what we
Speaker 1: see when our brains process a combination of red and
Speaker 1: blue light. But red and blue are on opposite ends
Speaker 1: of the visible spectrum. There is no wavelength for magenta.
Speaker 1: On the flip side of the coin, people with red
Speaker 1: green color deficiency might not be able to cite the
Speaker 1: difference between red and green apples. For them and for
Speaker 1: the best dog in your life, those colors don't exist.
Speaker 1: The moral of this color story is this, without our
Speaker 1: visual system and without our brains, no color really exists.
Speaker 1: It's all in the mind of the ball, which is
Speaker 1: enough to make you say dude, And it leads to
Speaker 1: a fascinating question. Are there colors within the visible spectrum
Speaker 1: that our cones and brains can't see? The so called
Speaker 1: impossible colors or forbidden colors break the biological rules of perception.
Speaker 1: We're going to get more into impossible colors, but first
Speaker 1: we're going to get into a quick break for a
Speaker 1: word from our sponsors, and we're back. Thank you sponsors. Okay,
Speaker 1: to talk about this, let's start by digging deeper into
Speaker 1: the science of color perception. Each of your eyes contains
Speaker 1: roughly six million cones concentrated in the center of the retina.
Speaker 1: These cones come in those three different varieties types that
Speaker 1: pick up on short, medium, or long wavelengths of visible light.
Speaker 1: When a cone receives a strong sign in its wavelength zone,
Speaker 1: it sends electrical impulses to the brain. The brain's jobs
Speaker 1: to combine the millions of electrical signals from each cone
Speaker 1: to recreate a composite image of the color that you're
Speaker 1: looking at. The brain, of course, is not a computer,
Speaker 1: but rather has a complex lump of highly specialized cells
Speaker 1: called visual cortex that's responsible for processing the electrical signals
Speaker 1: from the cones. We're still learning how these cells work
Speaker 1: and work together and with other regions of the brain
Speaker 1: to process input from the eyes. But basically the color
Speaker 1: related cells are called opponent neurons, and they traditionally have
Speaker 1: been separated into two basic types, red green opponent neurons
Speaker 1: and blue yellow opponent neurons. They're called opponents because they
Speaker 1: function in a binary way. The red green opponent neuron
Speaker 1: can signal either green or red, but not both simultaneou,
Speaker 1: and the blue yellow opponent neuron can signal either blue
Speaker 1: or yellow. I feel obligated to say here that recent
Speaker 1: research has indicated that this explanation is actually a culturally
Speaker 1: convenient oversimplification of what seems to be a three ish
Speaker 1: step brain process that more precisely involves lavender lime opponent
Speaker 1: neurons and salmon teele opponent neurons of five varying opponentcies
Speaker 1: that can combine to red versus green, and blue versus yellow.
Speaker 1: But since I'm not a neuroscientist, oh, let's stick with
Speaker 1: the convenient oversimplification for today. Okay, So, opponent neurons how
Speaker 1: they basically work is this. When you look at a
Speaker 1: pure yellow image, the yellow portion of the blue yellow
Speaker 1: opponent neuron is excited and the blue portion is inhibited.
Speaker 1: Switch to a pure blue image, and the blue portion
Speaker 1: of the opponent neuron is excited while the yellow is inhibited.
Speaker 1: And now imagine trying to see an image that's equally
Speaker 1: blue and yellow at the same time. The opponent neurons
Speaker 1: can't be both excited and inhibited simultaneously. That's why bluish
Speaker 1: yellow is an impossible color. The same is true for
Speaker 1: reddish green. You might be saying, I know what yellow
Speaker 1: and blue look like together. It's green and red and
Speaker 1: green make a kind of muddy brown. But that's the
Speaker 1: result of mixing two colors together, not of a single
Speaker 1: pigment that's equally blue yellow or red green. All the
Speaker 1: way back in eighteen oh one, long before scientists knew
Speaker 1: about cones and neurons, English physician Thomas Young theorized that
Speaker 1: the human eye has three types of color receptors, blue, green,
Speaker 1: and red. Young's trichromatic color theory was proven correctsh in
Speaker 1: the nineteen sixties, when cone cells, named for their shape,
Speaker 1: were to discovered to have special sensitivity to about those wavelengths.
Speaker 1: The opponent color theory of perception has been around since
Speaker 1: the eighteen seventies, when German physiologist Edvald Herring first postulated
Speaker 1: that our vision was ruled by opponent colors across from
Speaker 1: each other on the color wheel, with the corset being
Speaker 1: red versus green and blue versus yellow. This theory is
Speaker 1: simple and intuitive enough that it's still repeated in physiology textbooks,
Speaker 1: but in the past five to ten years, neural imaging
Speaker 1: has shown that what's going on in our brains is
Speaker 1: more complicated. Still, it's functional enough to roll with for today.
Speaker 1: So taken together, trichromatic theory and opponent theory argue that
Speaker 1: it is impossible for the human eye and mind to
Speaker 1: perceive certain colors described as red, green, or blue yellow. However,
Speaker 1: as Luigi wisely told us in the nineteen ninety three
Speaker 1: Super Mario Brothers Life live action film, nothing's impossible, improbable, unlikely,
Speaker 1: but never impossible. In that spirit, in the early nineteen eighties,
Speaker 1: visual scientists hewet Crane and Thomas Piantinada designed an experiment
Speaker 1: with the goal of tricking the brain into seeing impossible colors.
Speaker 1: In their experiment, subjects were instructed to stare at an
Speaker 1: image of a vertical red stripe adjacent to a vertical
Speaker 1: green stripe. The subject's heads were stabilized with a chin rest,
Speaker 1: and their eye movements were tracked by a camera. With
Speaker 1: every tiny twitch of a subject's eyes, the redd and
Speaker 1: green image was automatically adjusted so that the subject's gaze
Speaker 1: remained fixed on the opposing colors. It turned out that
Speaker 1: if people stared at adjacent opposing colors for long enough,
Speaker 1: the border between them would dissolve and new impossible colors
Speaker 1: would emerge. The resulting colors were so new that subjects
Speaker 1: had a hard time describing them. By stabilizing the image
Speaker 1: to track eye movements, the researchers theorized that different areas
Speaker 1: of the eye were being continuously bathed in different wavelengths
Speaker 1: of light, causing some opponent neurons to get excited and
Speaker 1: others to be inhibited at the same time. But after
Speaker 1: several other researchers failed to achieve the same dramatic results,
Speaker 1: this experiment was dismissed as a parlor trick. Subjects, instead
Speaker 1: of seeing brand new hues of greenish red or bluish yellow,
Speaker 1: usually described the blended color as mud brown. Others would
Speaker 1: see fields of green with pixelated red dots scattered across it.
Speaker 1: Impossible colors became a scientific joke. But then in twenty ten,
Speaker 1: biophysicists Vincent Bellick and Brian Zoe published results that they
Speaker 1: believed explained why Crane and Piontinita had succeeded where others
Speaker 1: had failed. They identified the combination of eye tracking and
Speaker 1: luminance or brightness as being key to tricking the brain
Speaker 1: into seeing impossible colors. They ran their own experiments in
Speaker 1: which subjects were again strapped to a chin rest and
Speaker 1: monitored by the latest retinal tracking technology, With the images
Speaker 1: stabilized to these subject's eye movements. The researchers played with
Speaker 1: the luminance of the two opposing color stripes. When there
Speaker 1: was a difference in brightness, the subject's experienced to the
Speaker 1: pixelated colors reported in earlier experiments. But when the two
Speaker 1: colors were exactly the same brightness, then six out of
Speaker 1: seven observers saw impossible colors. Even better, two of them
Speaker 1: could see the new colors in their minds for hours
Speaker 1: after the experiment was over. While few of us have
Speaker 1: a retinal stabilizer in the basement, there are some simpler
Speaker 1: exercises that can temporarily trick the brain into seeing the forbidden.
Speaker 1: Direct is to stare at an image of two opposing
Speaker 1: color squares side by side, each with a white plus
Speaker 1: sign in the middle. You can find examples of this online.
Speaker 1: What you do is relax and cross your eyes until
Speaker 1: the two plus signs merge into one. I tried this
Speaker 1: the blue, yellow one was weird, and the red green
Speaker 1: one made me laughably uncomfortable. Sort of makes you wonder
Speaker 1: what else is out there that we can't see yet.
Speaker 1: Today's episode is based on the article how impossible colors
Speaker 1: like Stiggy and Blue work on how stuffworks dot Com,
Speaker 1: written by Dave Ruse. Brain Stuff is production of iHeartRadio
Speaker 1: in partnership with how stuffworks dot Com and is produced
Speaker 1: by Tyler Klang. Four more podcasts from my heart Radio.
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