full transcript

From the Ted Talk by Colm Kelleher: How we see color

Unscramble the Blue Letters

You might have heard that light is a kind of wave and that the color of an object is raeletd to the frequency of light waves it reflects. High-frequency light waves look violet, low-frequency light waves look red, and in-between frequencies look yellow, green, orange, and so on. You might call this idea pahycisl color because it says that color is a physical property of light itself. It's not dependent on human perception. And, while this isn't wrong, it isn't quite the whole story either. For instance, you might have seen this picture before. As you can see, the region where the red and green lhtgis overlap is yellow. When you think about it, this is prttey weird. Because light is a wave, two different frequencies shouldn't interact with each other at all, they should just co-exist like singers sinigng in harmony. So, in this yellow looking region, two different kdnis of light waves are present: one with a red frequency, and one with a green fuencqery. There is no yellow light pseernt at all. So, how come this region, where the red and green lights mix, looks yellow to us? To unratesdnd this, you have to understand a little bit about biology, in particular, about how humans see color. Light perception happens in a paper-thin layer of cells, caleld the retina, that covers the back of your eyeball. In the retina, there are two different types of light-detecting cells: rods and cones. The rods are used for seeing in low-light ctondinios, and there is only one kind of those. The cones, however, are a different story. There three kinds of cone cells that roughly cnooersrpd to the colors red, green, and blue. When you see a coolr, each cone sends its own dtnsicit signal to your brain. For example, suosppe that yellow light, that is real yellow light, with a yellow frequency, is shining on your eye. You don't have a cone specifically for detecting yellow, but yellow is kind of close to green and also kind of colse to red, so both the red and green cones get activated, and each sends a signal to your barin saying so. Of course, there is another way to activate the red ceons and the green cones simultaneously: if both red light and green lhgit are present at the same time. The point is, your brain reeecivs the same sgianl, regardless of whether you see light that has the yellow frequency or light that is a mixture of the green and red frequencies. That's why, for light, red plus green equals yellow. And, how come you can't detect coorls when it's dark? Well, the rod clles in your retina take over in low-light conditions. You only have one kind of rod cell, and so there is one type of signal that can get sent to your brain: light or no light. Having only one kind of light detector doesn't leave any room for seeing color. There are infinitely many different physical colors, but, because we only have three kinds of cones, the brain can be trkceid into thinking it's seeing any color by carefully adding together the right combination of just three colors: red, geern, and blue. This property of human vision is really useful in the real world. For example, TV manufacturing. Instead of having to put infinitely many colors in your TV set to simulate the real world, TV manufacturers only have to put three: red, green, and blue, which is lucky for them, really.

Open Cloze

You might have heard that light is a kind of wave and that the color of an object is _______ to the frequency of light waves it reflects. High-frequency light waves look violet, low-frequency light waves look red, and in-between frequencies look yellow, green, orange, and so on. You might call this idea ________ color because it says that color is a physical property of light itself. It's not dependent on human perception. And, while this isn't wrong, it isn't quite the whole story either. For instance, you might have seen this picture before. As you can see, the region where the red and green ______ overlap is yellow. When you think about it, this is ______ weird. Because light is a wave, two different frequencies shouldn't interact with each other at all, they should just co-exist like singers _______ in harmony. So, in this yellow looking region, two different _____ of light waves are present: one with a red frequency, and one with a green _________. There is no yellow light _______ at all. So, how come this region, where the red and green lights mix, looks yellow to us? To __________ this, you have to understand a little bit about biology, in particular, about how humans see color. Light perception happens in a paper-thin layer of cells, ______ the retina, that covers the back of your eyeball. In the retina, there are two different types of light-detecting cells: rods and cones. The rods are used for seeing in low-light __________, and there is only one kind of those. The cones, however, are a different story. There three kinds of cone cells that roughly __________ to the colors red, green, and blue. When you see a _____, each cone sends its own ________ signal to your brain. For example, _______ that yellow light, that is real yellow light, with a yellow frequency, is shining on your eye. You don't have a cone specifically for detecting yellow, but yellow is kind of close to green and also kind of _____ to red, so both the red and green cones get activated, and each sends a signal to your _____ saying so. Of course, there is another way to activate the red _____ and the green cones simultaneously: if both red light and green _____ are present at the same time. The point is, your brain ________ the same ______, regardless of whether you see light that has the yellow frequency or light that is a mixture of the green and red frequencies. That's why, for light, red plus green equals yellow. And, how come you can't detect ______ when it's dark? Well, the rod _____ in your retina take over in low-light conditions. You only have one kind of rod cell, and so there is one type of signal that can get sent to your brain: light or no light. Having only one kind of light detector doesn't leave any room for seeing color. There are infinitely many different physical colors, but, because we only have three kinds of cones, the brain can be _______ into thinking it's seeing any color by carefully adding together the right combination of just three colors: red, _____, and blue. This property of human vision is really useful in the real world. For example, TV manufacturing. Instead of having to put infinitely many colors in your TV set to simulate the real world, TV manufacturers only have to put three: red, green, and blue, which is lucky for them, really.

Solution

  1. called
  2. kinds
  3. pretty
  4. singing
  5. cones
  6. frequency
  7. signal
  8. related
  9. suppose
  10. receives
  11. lights
  12. tricked
  13. close
  14. understand
  15. light
  16. distinct
  17. physical
  18. brain
  19. color
  20. present
  21. cells
  22. colors
  23. correspond
  24. green
  25. conditions

Original Text

You might have heard that light is a kind of wave and that the color of an object is related to the frequency of light waves it reflects. High-frequency light waves look violet, low-frequency light waves look red, and in-between frequencies look yellow, green, orange, and so on. You might call this idea physical color because it says that color is a physical property of light itself. It's not dependent on human perception. And, while this isn't wrong, it isn't quite the whole story either. For instance, you might have seen this picture before. As you can see, the region where the red and green lights overlap is yellow. When you think about it, this is pretty weird. Because light is a wave, two different frequencies shouldn't interact with each other at all, they should just co-exist like singers singing in harmony. So, in this yellow looking region, two different kinds of light waves are present: one with a red frequency, and one with a green frequency. There is no yellow light present at all. So, how come this region, where the red and green lights mix, looks yellow to us? To understand this, you have to understand a little bit about biology, in particular, about how humans see color. Light perception happens in a paper-thin layer of cells, called the retina, that covers the back of your eyeball. In the retina, there are two different types of light-detecting cells: rods and cones. The rods are used for seeing in low-light conditions, and there is only one kind of those. The cones, however, are a different story. There three kinds of cone cells that roughly correspond to the colors red, green, and blue. When you see a color, each cone sends its own distinct signal to your brain. For example, suppose that yellow light, that is real yellow light, with a yellow frequency, is shining on your eye. You don't have a cone specifically for detecting yellow, but yellow is kind of close to green and also kind of close to red, so both the red and green cones get activated, and each sends a signal to your brain saying so. Of course, there is another way to activate the red cones and the green cones simultaneously: if both red light and green light are present at the same time. The point is, your brain receives the same signal, regardless of whether you see light that has the yellow frequency or light that is a mixture of the green and red frequencies. That's why, for light, red plus green equals yellow. And, how come you can't detect colors when it's dark? Well, the rod cells in your retina take over in low-light conditions. You only have one kind of rod cell, and so there is one type of signal that can get sent to your brain: light or no light. Having only one kind of light detector doesn't leave any room for seeing color. There are infinitely many different physical colors, but, because we only have three kinds of cones, the brain can be tricked into thinking it's seeing any color by carefully adding together the right combination of just three colors: red, green, and blue. This property of human vision is really useful in the real world. For example, TV manufacturing. Instead of having to put infinitely many colors in your TV set to simulate the real world, TV manufacturers only have to put three: red, green, and blue, which is lucky for them, really.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
light waves 4
green lights 2
green cones 2

Important Words

  1. activate
  2. activated
  3. adding
  4. biology
  5. bit
  6. blue
  7. brain
  8. call
  9. called
  10. carefully
  11. cell
  12. cells
  13. close
  14. color
  15. colors
  16. combination
  17. conditions
  18. cone
  19. cones
  20. correspond
  21. covers
  22. dark
  23. dependent
  24. detect
  25. detecting
  26. detector
  27. distinct
  28. equals
  29. eye
  30. eyeball
  31. frequencies
  32. frequency
  33. green
  34. harmony
  35. heard
  36. human
  37. humans
  38. idea
  39. infinitely
  40. instance
  41. interact
  42. kind
  43. kinds
  44. layer
  45. leave
  46. light
  47. lights
  48. lucky
  49. manufacturers
  50. manufacturing
  51. mix
  52. mixture
  53. object
  54. orange
  55. overlap
  56. perception
  57. physical
  58. picture
  59. point
  60. present
  61. pretty
  62. property
  63. put
  64. real
  65. receives
  66. red
  67. reflects
  68. region
  69. related
  70. retina
  71. rod
  72. rods
  73. room
  74. roughly
  75. sends
  76. set
  77. shining
  78. signal
  79. simulate
  80. singers
  81. singing
  82. specifically
  83. story
  84. suppose
  85. thinking
  86. time
  87. tricked
  88. tv
  89. type
  90. types
  91. understand
  92. violet
  93. vision
  94. wave
  95. waves
  96. weird
  97. world
  98. wrong
  99. yellow