Color vision

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Color vision

  1. 1. Science of the Eye Professional Development Workshop Ishara Mills-Henry, Ph.D. MIT www.scienceoftheeye.org
  2. 2. Workshop Outline <ul><li>I. Color Vision </li></ul><ul><ul><li>How do we see? </li></ul></ul><ul><ul><li>Where’s Waldo? </li></ul></ul><ul><li>Intro into the Retina </li></ul><ul><ul><li>What can you see in the dark? </li></ul></ul><ul><ul><li>Acting it Out – Phototransduction </li></ul></ul><ul><ul><li>Central versus peripheral vision </li></ul></ul><ul><ul><li>Colorblindness </li></ul></ul><ul><li>Retinal Processing </li></ul><ul><ul><li>Colored Shadows (the color wheel, mixing color versus reflecting color) </li></ul></ul><ul><ul><li>What a weird American flag! </li></ul></ul><ul><ul><li>The “Bionic” Eye </li></ul></ul><ul><li>Group Discussion </li></ul>
  3. 3. Outline Cont’d <ul><li>II. Vision and the Brain (if time and you’re not exhausted) </li></ul><ul><li>Visual Centers of the Brain (basic overview) </li></ul><ul><ul><li>Blind Spot </li></ul></ul><ul><ul><li>3-D Magic </li></ul></ul><ul><ul><li>Let’s FACE IT – Face Recognition </li></ul></ul><ul><ul><li>Fun Illusions and explanation </li></ul></ul><ul><li>Group Discussion </li></ul><ul><li>III. Surveys and Feedback </li></ul>
  4. 4. Workshop Concepts <ul><li>Rod Photoreceptors respond primarily in dim light/ Cones respond to colors and are important for acuity </li></ul><ul><li>Photoreceptors convert light into electrical signals (Phototransduction) </li></ul>Rods = Dim Light Cones = Color
  5. 5. Workshop Concepts <ul><li>Most cones are in the macula, leading to high quality of central vision compared to peripheral vision </li></ul><ul><li>Retinal processing involves integration of signals from cones and rods. </li></ul><ul><li>The retina is complex but can be compared to a web of information that is processed and sent to the brain in several channels of information </li></ul><ul><li>Most visual processing takes place in the brain </li></ul>
  6. 6. Things about vision science to communicate to students <ul><li>Vision is fun!! </li></ul><ul><li>Ways to teach complex concepts and perhaps address student’s misconceptions about vision </li></ul><ul><li>Relate vision to our everyday lives </li></ul><ul><li>Science is not static and knowledge is added all the time </li></ul>
  7. 7. If a mirror is mounted flat against the wall, how big does it have to be in order for you to see your entire body? <ul><li> What are your predictions? </li></ul><ul><li>Most MIT graduates and high school students were asked this question and gave similar answers! </li></ul>
  8. 8. How do we see? Indirect light
  9. 9. How big does the mirror have to be?
  10. 10. Introducing the eye <ul><li>What is a digital camera? </li></ul><ul><li>  </li></ul><ul><li>How do you think it works? </li></ul><ul><li>  </li></ul><ul><li>What do you need to make a digital camera? </li></ul>
  11. 11. Digital Camera and the Eye
  12. 12. Observe parts of camera <ul><li>Lenses – focuses light onto the sensor </li></ul><ul><li>Sensor (e.g. CCD) –pixels (photosensors) capture light (color and intensity) and convert it to an electrical signal and digital signal   </li></ul><ul><li>Image Processing Unit - processes the information, and creates an image (e.g. jpeg) </li></ul>LENSES SENSOR IMAGE PROCESSOR Convert Electrical signal to Digital Storage
  13. 13. Label parts of the eye that are analogous to camera
  14. 14. In Living Color: Constructing color vision <ul><li>What are your favorite colors? </li></ul><ul><li>What is light and how is it useful? </li></ul><ul><li>Compare these two photos: </li></ul>
  15. 15. Visible Light Spectrum Blu-Ray laser – 405 nm Standard DVD laser – 650nm Visible Light Spectrum
  16. 16. <ul><li>Marsh Marigold Flower </li></ul><ul><li>A. Visible Light (how humans see the flower) </li></ul><ul><li>UV light (how bees see the flower) </li></ul><ul><li>(Image from http://www.eso.org/~rfosbury/home/natural_colour/biochromes/UV_flowers/nc_bio_flower_uv.html </li></ul>Some animals have UV cones
  17. 17. Activity: Introducing Color Vision <ul><li>Where’s Waldo? </li></ul>
  18. 18. Signals Everywhere!! <ul><li>Give an example of a signal. How do we use this signal? </li></ul><ul><li>Name one example of how signals are important in your everyday life. </li></ul><ul><li>What are some examples of signals in the cell or human body? </li></ul>
  19. 19. Sending Messages <ul><li>Imagine you want to pass a note (without a cell phone) how would you do it…. </li></ul><ul><li>Signals indicate warn direct command or act. Electrical quantity or effect that can be varied in such a way as to convey a message </li></ul>Will you go out with me? Yes ___ No ____ Maybe ____
  20. 20. The Retina From www.howstuffworks.com
  21. 21. Retina <ul><ul><li>Humans are considered trichromats – </li></ul></ul><ul><ul><li>Blue, Red, and Green Cone Photorecpetors </li></ul></ul><ul><ul><li>Rod photoreceptors – are important for vision in dim light </li></ul></ul>
  22. 22. Photoreceptors respond to different wavelengths
  23. 23. Photoreceptors Compare the sizes of the photoreceptors outer segments, which one is bigger? Three Main Parts: a. Outer Segments b. Cell body c. Synaptic terminal Outer segments
  24. 24. Photosensitive Proteins <ul><li>Rhodopsin (the rod opsin) and cone opsins are situated in the membrane of the disk structures </li></ul>Rhodopsin
  25. 25. What do you see in the dark? <ul><li>When you walk into a dark room, can you immediately see objects around you? </li></ul><ul><li>Are you able to distinguish colors in dim light? </li></ul><ul><li>Do you think that you can see certain colors in the dark? If so, which colors? </li></ul>
  26. 26. Activity: What can you see in the dark? (groups of four) <ul><li>Three types of colored balls </li></ul><ul><li>Test colors by using cups of water with varying amounts of food coloring </li></ul><ul><li>or colorful magazine pictures. </li></ul><ul><li>Test variables, i.e. light </li></ul><ul><li>Light Adaption: What is the minimum amount of light that is necessary for cones to respond? </li></ul>
  27. 27. Pirates of the Caribbean <ul><li>Separate by color </li></ul><ul><li>Left Center Right </li></ul><ul><li>Blue Yellow Orange </li></ul><ul><li>Separate Easter Eggs by number </li></ul><ul><li>Left Right </li></ul><ul><li>1 2 </li></ul>
  28. 28. Count the number of errors <ul><li>Three sets of Data </li></ul><ul><li>In the light </li></ul><ul><li>Immediately after light is turned off </li></ul><ul><li>With “pirate eye” </li></ul><ul><li>Questions to ponder: </li></ul><ul><li>What are your predictions? </li></ul>
  29. 29. How photoreceptors respond <ul><li>In the dark, photoreceptors are constantly releasing neurotransmitters. They have a starting negative membrane potential. Photoreceptors respond to light through the rhodopsin and cone opsins </li></ul><ul><li>Absorption of light initiates change in protein setting off cascade of events making photoreceptor more negative </li></ul><ul><li>Change in membrane potential stops release of a signal (neurotransmitter) from terminal (faucet gets turned down) </li></ul>
  30. 30. Phototransduction = converting light into electrical signal Outer Segment (Rod) Na + /Ca ++ Channels
  31. 31. Activity: Acting it out <ul><li>Phototransduction </li></ul><ul><ul><li>Light (Light bulbs, electric personality) </li></ul></ul><ul><ul><li>Na+ (salt shaker, a good chef) </li></ul></ul><ul><ul><li>Membrane (disks, self-identified introverts) </li></ul></ul><ul><ul><li>Opsins (good dancers) </li></ul></ul><ul><ul><li>Ion Channel (2 people, difficult to separate in class) </li></ul></ul><ul><ul><li>cGMP (dynamic personality) </li></ul></ul><ul><ul><li>Neurotransmitter (free spirit) </li></ul></ul>
  32. 32. Activity: Central versus Peripheral Vision
  33. 34. Measuring your Central Vision <ul><li>Basically created a Giant Protractor </li></ul><ul><li>Predict what you think you can see “out the corner of your eye”. </li></ul><ul><li>Focus on the pushpin while another person moves the colored shapes toward the center of the protractor </li></ul><ul><li>When you see color or shape, notify recorder </li></ul><ul><li>Use protractor and ruler to measure the angle </li></ul>
  34. 35. The macula is responsible for central vision Macula <ul><li>Small sensitive region in the center of the retina </li></ul><ul><li>All cones and no rods </li></ul><ul><li>The majority of cones are present in the macula </li></ul>Light Retinal Layers Retina Fovea
  35. 36. Types of Color Blindness Monochromacy Rod or Cone – very rare, All rods or all cones are missing Dichromacy – Two types of photoreceptors are present Protanopia – red cones are missing Deuteranopia – green cones are missing Tritanopia – blue cones are missing Anomalous Trichromacy - All three photoreceptors are present but there is a spectral shift Protanomaly- spectral sensitivity of red cones are shifted Deuteranomaly – spectral sensitivity of green cones are shifted Tritanomaly – spectral sensitivity of blue cones are shifted
  36. 37. NORMAL CONE SENSITIVITY CURVES (TRICHROMAT) B R G 437 nm 564 nm 533 nm NORMAL CONE SENSITIVITY CURVES (TRICHROMAT) Activity: Color blindness
  37. 38. B R 437 nm 564 nm Deuteranopia (no green cones; only red and blue) 1% of Males
  38. 39. B G 437 nm 533 nm Protanopia (no red cones; only green and blue) 1% of Males
  39. 40. R G 564 nm 533 nm Tritanopia (no blue cones; only green and red) Very rare
  40. 41. B R 437 nm 564 nm Most common Deuteranomaly (green shifted toward red) 5% of Males G
  41. 42. Color Blindness Left Right
  42. 43. Results
  43. 44. Pedigree What is the mode of inheritance?
  44. 45. Gene Therapy for color blind monkeys All male squirrel monkeys are born only able to see mostly yellows and blues. It is difficult for them to distinguish reds from greens. Female squirrel monkeys can see the whole spectrum. What photoreceptor(s) do you think they lack? What advantage does color provide for these animals? Credit: Neitz Laboratory
  45. 46. Colored Shadows Activity <ul><li>What color do you get when you mix all colors together? </li></ul><ul><li>Remind students about subtractive and additive color mixing </li></ul>
  46. 47. Colored Shadows <ul><li>How many colors do you see? </li></ul><ul><li>What are the color of the shadows? </li></ul><ul><li>What are the colors of the shadows when they overlap? </li></ul><ul><li>When you block one of bulbs or turn it off, what color shadows do you see (do this for all 3)? </li></ul>
  47. 48. How can you make a thousand colors out of three types of cone photoreceptors? <ul><li>If you mix equal amounts of red, green, and blue light, you will get white color </li></ul><ul><li>Other colors are perceived by mixing the proper ratio of red, green, and blue </li></ul>
  48. 50. Flow of Information <ul><li>Vertical flow of information – direct – photoreceptors to bipolar to ganglion cells </li></ul><ul><li>Lateral flow of information –indirect - input from horizontal and amacrine cells </li></ul>
  49. 51. Stare at the white cross for 30 seconds
  50. 52. The theory of Color Opponency <ul><li>Ever notice that some colors do not exist, Red – Green or Blue - Yellow </li></ul><ul><li>Some ganglion cells sort color information into three different channels before sending signal to the brain </li></ul><ul><li>The three channels (like TV) are </li></ul><ul><li>Red/Green = Sports </li></ul><ul><li>Blue/Yellow = News </li></ul><ul><li>Light Intensity (Degree of whiteness or blackness) = Reality TV </li></ul>
  51. 53. <ul><li>You = Red, Opponent = Green </li></ul><ul><li>You are stronger – RED wins </li></ul><ul><li>Opponent is stronger – GREEN Wins </li></ul><ul><li>You and Opponent have same strength – no one wins </li></ul>
  52. 54. More Afterimages
  53. 55. Activity: Research Focus <ul><li>The “bionic” eye </li></ul><ul><li>What would happen if you no longer had functional photoreceptors? </li></ul>
  54. 56. Retinal Diseases Describe how the vision of an individual with Retinitis Pigmentosa is affected? Describe how the vision of an individual with Age-related Macular Degeneration is affected?
  55. 57. How it works <ul><li>Do you think that individuals with the “Bionic” eye implant will be able to perceive images immediately? </li></ul><ul><li>Do you think that the “Bionic” eye implant, individuals will be able to see colors? </li></ul>
  56. 58. Bionic Eye Video <ul><li>Artifical Retina </li></ul><ul><li>http://www.cnn.com/2009/HEALTH/12/11/bionic.eye/ </li></ul>
  57. 59. Group Discussion
  58. 60. Vision and the Brain
  59. 61. Optical or Visual Illusions
  60. 62. Where’s my blind spot?
  61. 63. Why is it so hard to find? Right Eye Left Eye
  62. 64. 3-D Magic
  63. 65. Face IT!! From: http://www.youramazingbrain.org.uk/supersenses/hollow.htm
  64. 66. Other Illusions and Explanations
  65. 67. Which table is longer?
  66. 68. Rotating Wheels
  67. 69. Group Discussion
  68. 70. I hope today wasn’t like this MIT’s Stata Center It is said that MIT’s education is like drinking from a firehouse…….
  69. 71. Check out our Website and Summer Program <ul><li>www.scienceoftheeye.org </li></ul><ul><li>Summer Program </li></ul>
  70. 72. Surveys/Feedback
  71. 73. Thank you <ul><li>Comments/Questions </li></ul><ul><li>www.scienceoftheeye.org </li></ul>

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