Sensation

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Author:
faulkebr
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104991
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Sensation
Updated:
2011-09-29 18:12:29
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Test 2
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  1. The human eye is made up of;
    eyelid - cornea/schlera-aqueous humor-iris-pupil-lens-vitreous humore-retina-fovea-choroid
  2. Refraction
    • Necessary to focus light
    • Function of the lens
  3. Accomodation
    process of using muscles to change the shape of the lens so that objects come into focus
  4. Lens is ____ when focusing on distant objects
    thin
  5. Lens is ____ when focusing on near objects
    fat
  6. Refractory Errors-
    • Emmetropia
    • Presbyobia
    • Hyperopia
    • Myopia
    • Astigmatism
  7. Emmetropia
    • No refractive error
    • Can see right on point
    • Refracts light perfectly
  8. Presbyopia
    • (old eyes)
    • the lens harden
    • near point increases, ass you age, that point get further and further away
    • Doesnt get to one precise point in th eretina
  9. Hyperobia
    • farsightedness
    • Problems seeing neer objects clearly
    • Focus light on retina by using a convex lens
  10. Myopia
    • nearsightedness
    • problems seeing distant objects
    • focus light on retina by using a concave lens
    • (could be because lens is too long; retina is normal)
  11. Theories for refractive errors
    • we watch things too closely
    • raising child with nightlight when sleeping
  12. Astigmatism
    if the cornea isnt spherical, then light isnt refracted properly
  13. back surface of an eyeball
    Fondus
  14. Example of brain lying to you
    the black dot test. Blind spot
  15. Scotoma
    not usually in both eyes. Photo receptors just dies for some reason
  16. Retina
    • Contains several layers of cells
    • Photyoreceptors change light energy into a neural energy (tansduction)
  17. Two kinds of photoreceptors
    • Rods
    • Cones
  18. Rods
    Everywhere else outside the fovea
  19. Cones
    in fovea
  20. Rods are for
    motion
  21. Cones are for
    • color; because you only have cones in the fovea. Everything in your peripheral is black and white
    • (if you see color in your peripheral then it is your brain tricking you)
  22. No convergence =
    photoreceptors speak directly to the bipolar cell. No information gets lost
  23. Convergence=
    • A whole bunch of rods share a bipolar cell.
    • Perception is that there is one black dot out there - lose some information
    • Lost information(lack of detail
  24. Acuity
    Ability to see small detail
  25. Sensitivity
    • Ability to see very dim things
    • Example: going to the bathroom in the middle of the night
  26. ....In Cones
    • there is very little convergence; there is very little spatial summation (averaging)
    • Detail is preserved=the less everaging, the more detail you will have
  27. Problem with cones
    • Cones cant detect low levels of light
    • But you do have detail (looking at stars)
  28. ....In rods
    • lots of convergence, therefore there is alot of spatial summation (all kinds of information is lost)
    • Detail is not preserved

    Rods can detect/see dim light
  29. Retinal Information Processing:

    2 types of ganglion cells
    • P cells
    • M cells
  30. P cells
    • part of the parvocellular pathway (cones)
    • small receptor field
  31. M cells
    • part of the magnocellular pathway (rods)
    • large receptor field
  32. Mach bands
  33. the ocean appears darker closer to the horizon (border)
    the egzagerated darker line when looking at shadows is the mach band
  34. Lateral inhibition
    • a process that enhances our ability to detect borders.
    • Increases contrast; results in a sharpening od vision (happens in horizontal cells)
  35. Lateral inhibition produces;
    mach bands
  36. Light activates a cell and causes it to;
    inhibit a neighboring cell
  37. Amount of inhibition a cell can produce depends on;
    intensity of the stimulus (assume 10%)
  38. Hermann Grid
    See gray spots at intersection because there is more inhibition there
  39. Cells fire when we;
    see different things
  40. Receptive Field
    the region in which stimuli will activate a neuron

    the further you go from the fovea, the receptor field gets bigger and bigger

    smaller in finger - the smaller the field the more detail.
  41. Centre
    • Surrounds receptive field in ganglion cells
    • 3rd layer of processing(ganglion cells)
  42. Pupils expand when;
    • arousal
    • alcohol/drugs
    • lying
  43. Photopic Vision
    • uses cones (fovea)
    • works best in daylight
    • high acuity, poor sensitivity
  44. Scotopic Vision
    • uses rods (peripheral vision)
    • Works best in nighttime, levels of lumination
    • Poor acuity, high sensitivity
  45. Dark Adaptation
    Process of adjusting to more dimly lit rooms

    • Coming out of movie theater in afternoon
    • Waking up to bright light
    • takes 20 minutes for eyes to adapt fully to the dark
  46. Macular Degeneration in the eyes (macula, fovea)
    • Cones start to fade out
    • Visual field becomes less and less clear
    • Comes with age and fatness

    Example: looking at someones face, blurry
  47. Retinitus Pigmentosa
    • Lose retina, half of the visual field is gone
    • Can see some in the middle, black frame around it (keeps moving in-tunnel vision)
  48. Usher's Syndrome
    People born deaf, and then they lose their vision in middle ages. Genetic
  49. Luminance
    Difference between dark and light bars
  50. Contrast sensitivity function:
    Shows how our sensitivity changes due to high/low contrast objects
  51. High spatial frequencies and low contrast =
    cant see
  52. We are less sensitive to;
    very low and very high spatial frequencies
  53. Most sensitive =
    less contrast

    • medium size objects-faces
    • larger objects are harder to see, will see person before car
  54. Selective Adaptation
    • The psychologists electrode
    • Our visual system contains neurons selective for spatial frequency
  55. The size of our receptive fields of our cones determines;
    What we can see. Determines the smallest thing that we can see
  56. Retinal ganglion cells/stripes

    Wide Stripes
    maximum excitation + maximum inhibition

    Produces a small response
  57. Retinal ganglion cells/stripes

    Thin stripes
    • Minimum excitation + minimum inhibition
    • Produces small response
  58. Retinal ganglion cells/stripes

    Medium stripes
    Maximum excitation + moderate inhibition

    Produces strongest response
  59. Deficits in contrast sensitivy
    • Unthoff's symptom
    • Night blindness
    • Glare sensitivity
    • Side effect of Lasik surgery
  60. Deficit in contrast sensitivity

    1. Unthoff's Symptom
    • Excercise or emotional strain impairs vision for several minutes
    • Retain acuity, but world appears washed out
    • Sensitivity to contrast decreases
  61. Deficit in contrast sensitivity

    2. Night blindness
    Causes: cataracts, retinitus pigmentosa, vit A deficiency, drugs...
  62. Deficit in contrast sensitivity

    3. Glare sensitivity
    associated with degenerative retinal disease
  63. Deficit in contrast sensitivity

    4. Side effect of Lasik Surgery
    • A change in sensitivity to contrast
    • Things inside are darkened, not enough light/but sunlight is way too bright.
  64. Pelli-Robson Charts
    • tests from contrast sensitivity problems
    • letters fade out gradually
  65. The development of spatial vision

    Infant visual acuity
    Foced choice preferential -looking paradigm (babies under 6m can tell difference in limas) lose this skill as the age
  66. Young children are not very sensitive to;
    high spatial frequency
  67. Strabismus
    eyes are not properly alligned
  68. Amblyopia
    reduced visual acuity in one eye, will cause problems with depth perception
  69. The secondary visual pathway is used to;
    orient you/ alert you
  70. 2 important features of striate cortex
    • cortical magnification
    • topographical mapping
  71. Cortical magnification
    more cells processing information coming from fovea than other areas of vidual fields
  72. Topographical mapping
    • Orderly
    • Information is split in optic chiasm-left visual fiels is blue, right visual field is red
  73. If the information stays on the same side and doesnt cross it is called-
    • Ipsilateral
    • temporal stuff
  74. Contralateral
    when information crosses hemispheres
  75. Receptive fields in V1
    • cells respond best to bars of light, not spots of light
    • gets information from all of the 4 cirlces
  76. Orientation Tuning
    • Neurons respond more to bars of certain orientations and less to others (V1)
    • Tuning curves
  77. Simple cells
    • very specific
    • respond to straight lines, edges
    • location specific
    • Orientation specific(angle of edge has to be just right)
  78. Complex Cells
    • more relaxed than simple cells
    • straight lines
    • orientation specific
  79. End Stopping
    Some cells prefer bars of light of a certain length

    Weisal thought that these were called hyper-complex, this is where they went wrong
  80. Ocular Dominence Columns
    • Each cell in V1 has preffered eye
    • But they respond to input from both eyes
  81. Orientation columns
    Within each column, all neurons have the same orientation tuning
  82. Hypercolumn
    Orientation column + ocular dominance column

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