MCB 161 Lec 8 Central Vision I: LGN, V1

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  1. Is perception and reality the same?
    Nope
  2. Why do we rely on vision way more somatosensation?
    • Can see from far away (predators)
    • Colors (ripeness of fruits)
    • Recognizing form
  3. Image UploadWhat is this illusion showing us?
    • Brain inference
    • Brain fills in info it thinks is there even when it's not
  4. Give an example that shows the importance of inference
    Might see bits and pieces of fruits hidden behind branches and such, but know it's a full fruit
  5. Why does the visual system make inferences about stimuli?
    To generate perceptions
  6. Describe contour saliency
    • Visual system looks for subtle contours
    • Higher part of cortex looks for shapes, thinking it's looking for something
  7. What's object segmentation?
    Brain can separate objects b/c of contrast and other cues
  8. Where is the LGN located?
    In the thalamus
  9. What does LGN stand for?
    Lateral geniculate nucleus
  10. Image UploadReady? Go!
    Image Upload
  11. Image UploadYee yee
    Image Upload
  12. What happens at the optic chiasm?
    Neurons/fibers decide whether or not to cross here
  13. What happens at LGN (and cortex)?
    • Get a lot of info
    • For 3D
  14. How is the LGN structured?
    Laminated (layered) structure
  15. How many layers does the LGN have?
    6
  16. How is info projected into the LGN?
    Projected into the layers but not mixed
  17. What do the LGN neuron receptive fields resemble?
    • RGC receptive fields
    • Center-surround RF
  18. Why is the LGN/thalamus considered largely a 'relay center'?
    There is no transformation of information
  19. How do the different layers of the LGN receive input from the eyes?
    • Receive input from either the left or right eye
    • Not both eyes
    • Info remains segregated in
  20. How is info from either eye organized in the LGN? In the cortex?
    • Information from either eye remains segregated in the LGN
    • Begins to mix in the cortex
  21. What is another name for the primary visual cortex?
    • V1
    • Striate cortex
  22. Where does the "action begin" and visual info start to combine?
    Primary visual cortex
  23. Where does visual info mostly come from?
    Center-surround receptive field
  24. What kind of map exists in the visual cortex?
    Precise spatial map of the visual world
  25. What is the spatial map in the visual cortex called?
    "Retinotopic" map
  26. How is info projected on the cortex?
    In a topographic formation
  27. Is the info projected identically on the cortex?
    No, not uniform
  28. Why is there a retinotopic map?
    Don't want info all over the place from different neurons
  29. What is the center of your visual field?
    Fovea
  30. Which part of the visual field is highly magnified/has more representation in V1?
    The center of the visual field from the fovea
  31. Why is there cortical magnification of the center of the visual field?
    • More density of photoreceptors (cones) in the fovea
    • High acuity
    • High number of cortical neurons to represent image
  32. What does receptive field size/cortical magnification vary with?
    RF size and cortical magnification varies systematically with eccentricity
  33. How are V1 selective?
    • Orientation selective
    • Directionally selective
  34. What does it mean to be orientation selective?
    Different responses at different orientations
  35. How is it possible for V1 neurons to be orientation selective?
    Asymmetric RF
  36. Are RGC's orientation selective?
    • No, there's no asymmetry in RGC's
    • Circles
  37. What kind of asymmetry causes orientation selectivity?
    • Simplest asymmetry
    • rectangle
  38. Describe (draw?) the receptive field of V1 neurons. (compared to rgcs?)
    ±±±±±

    •    -
    • - + - 
    •    -

    You get the point
  39. Image UploadWut dis
    The Hubel and Wiesel model for the generation of orientation selectivity
  40. What does it mean to be directionally selective?
    Different firing depending on the direction from which the object passes the eye
  41. What's a possible reason for the direction selectivity of V1 neurons?
    Probably have a delay line to cause asymmetry in direction or something
  42. What is the architecture of orientation-selective neurons in V1?
    Columnar architecture
  43. When is orientation selectivity constant?
    Along the vertical axis (column) of the cortex
  44. Image UploadWhat's going on with the two things?
    • The first one was inserted vertically (perpendicular) and all neurons in that column are selective for the same orientation
    • The second isn't perpendicular so the neurons it hits prefer different orientations
  45. Image UploadWut dis?
    • Colors represent specific orientation preference
    • Neurons that lie on top of each other prefer same orientation
    • Random but still somewhat organized?
  46. 'Computation module' in V1??
    Orientation tuning columns stacked on top of each other??
  47. What order do the maps stack on top of each other?
    • Most fundamental = spatial map
    • All other maps on top
  48. What kind of information do LGN neurons relay to V1?
    Retinal information about contrast and color
  49. What kind of map does V1 have?
    Retinotopic map of the visual world
  50. How do V1 neurons become orientation selective?
    By integrating across LGN neurons in a precise fashion
  51. How are orientated neurons in V1 arranged?
    In columns

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Mursizzle
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315971
Filename:
MCB 161 Lec 8 Central Vision I: LGN, V1
Updated:
2016-02-18 18:48:36
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MCB 161 Lec Central Vision LGN V1
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MCB 161 Lec 8 Central Vision I: LGN, V1
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