Card Set Information

2010-09-22 20:45:01
vision neuroscience

Visual Processing
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  1. fovea
    a small central pit located in the macula region of the retina; composed of closely packed cones
  2. macula
    the retinal area responsible for fixed central vision during good light
  3. retina
    sensory part of the eye; transforms light into electrical impulses; found at the the inner surface of the eye
  4. optic nerve
    transmits visual information from the retina to the brain
  5. optic disk
    location in which retinal ganglion fibers exit the eye to form the optic nerve; no photoreceptors exist at this point; causes the blind spot
  6. foveola
    found in the center of the fovea; contains only cones and no rods
  7. photoreceptors
    specialized neurons that are capable of phototransduction; includes rods and cones
  8. pigment epithelium
    layer of cells found just outside the retina; responsible for maintaining retinal environment
  9. rods
    photoreceptors; first-order neurons; detect low levels of light (scotopic); low temporal resolution; exist in greater number than cones
  10. cones
    photoreceptors; first-order neurons; functional in high levels of light (photopic); high temporal resolution
  11. structure of rods
    short cone-shaped outer segment; inner segment; synaptic terminal
  12. structure of cones
    long cylindrical outer segment; inner segment; synaptic terminal
  13. rod and cone systems
    rod systems are highly convergent - many rods synapse on a single bipolar cell; cone systems are not convergent - one cone sypapses on one bipolar cell
  14. rhodopsin
    visual pigment that absorbs light for rods; composed of opsin and 11 -cis retinal molecules; captured light causes a conformational change to metarhodopsin
  15. phototransduction process
    light activates rhodopsin to metarhodopsin; metarhodopsin activates transducin (a G-protein); transducin activates cGMP phosphodiesterase; cGMP levels are reduced; the photoreceptor cell is hyperpolarized
  16. rod currents in dark and light
    cGMP is high in the dark; cells are depolarized and produce current in the dark; light closes potassium channels and prevents potassium from leaving the cell; light hyperpolarizes cells
  17. calcium-dependent adaptation
    light opens calcium channels; influx of calcium reduces cGMP; reduction in cGMP helps to shut down channels in bright light
  18. retinal ganglion receptive fields
    have center and antagonistic surround receptive fields
  19. on-center retinal ganglion cells
    cell is activated when the cell is stimulated in the center and deactivated when the cell is stimulated in the surround; good at recognizing increases in light
  20. off-center retinal ganglion cells
    cell is deactivated when the cell is stimulated in the center and activated when the cell is stimulated in the surround; good at recognizing decreases in light
  21. on-center bipolar cells
    hyperpolarized by glutamate; are depolarized following illumination; have metabotropic receptors
  22. off-center bipolar cells
    depolarized by glutamate; are hyperpolarized following illumination; have ionotropic receptors
  23. projection to hemiretinas
    right visual field is projected onto the left hemiretinas and vice versa; nasal hemiretinas cross at the optic chiasm while temporal hemiretinas follow an ipsilateral path
  24. subcortical targets of retinal ganglion cells
    90% project -> LGN of thalamus -> occipital lobe; others project to hypothalamus and tectum (among other areas)
  25. pupillary reflex
    pretectal neurons proceed to bilateral Edinger-Westphal nuclei -> production of bilateral pupil constriction
  26. direct response
    bright light shined in one eye will provoke the pupil of that eye to constrict
  27. consensual response
    bright light shined in one eye will provoke the pupil of the contralateral eye to constrict
  28. lateral geniculate nucleus
    found with the thalamus; important relay center; 6-layered structure; project via optic radiations to the occipital lobe
  29. cells of the LGN
    have on- and off-center receptive fields; are magnocellular (layers 1 & 2) or parvocellular (layers 3-6)
  30. retinotopy
    LGN and cortex are retinotopically organized; retina is topographically represented
  31. monocular vision
    results from damage to one optic nerve; complete loss of vision in one eye
  32. binocular hemianopsia
    results from splitting of the optic chiasm; bilateral loss of temporal vision
  33. homonymous hemanopsia
    results from damage to one optic chiasm; bilateral loss of vision in one half of the visual field
  34. quadrantanopsia
    results from damage to the optic projections; bilateral loss of vision in one-quarter of the visual field
  35. macular sparing
    foveal vision often is not lost when cortical visual damage occurs; may be spared due to extensive cortical representation
  36. cortical organization of visual information
    projections from the LGN enter in layer 4C of the cortex; ocular dominace columns are formed; L/R eye separation is maintained
  37. receptive field of visual cortical cells
    cells in the primary visual cortex are maximally receptive to specifically oriented bars of light
  38. organization in the primary visual cortex
    there is a columnar organization of orientation selective cells in the visual cortex
  39. blobs
    found in layers 2 and 3 of the primary visual cortex; respond selectively to color
  40. arrangement of ocular dominance columns
    cells with preferences for specific orientations of light are arranged in columns that show preference for input from one eye
  41. hypercolumns
    hypercolumns are groups of columns that possess a complete representation of visual input -- all orientations & blobs & both ocular dominance columns are represented
  42. color agnosia
    damage between the occipital and temporal lobe may lead to an inability to recognize color
  43. motion agnosia
    damage in the middle temporal region may lead to an inability to assess motion
  44. prosopagnosia
    damage to the inferior temporal area may lead to an inability to recognize faces
  45. 2 pathways for visual processing
    spatial vision pathway and object recognition pathway
  46. spatial vision pathway
    also called the dorsal pathway; involves projections from V1 -> V2 -> middle temporal region -> parietal lobe; involved in motion detection
  47. object recognition pathway
    also called the ventral pathway; involves projections from V1 -> V2 -> V4 -> temporal lobe; involved in identification of fine detail and color
  48. magnoceullular pathway
    M RGCs ->layers 1 & 2 of LGN -> layer 4-alpha of cortex; involved in analysis of gross features and movement
  49. parvocellular pathway
    P RGCs -> layers 3-6 of LGN -> layer 4-beta of cortex; involved in analysis of color and fine detail
  50. koniocellular pathway
    K RGCs -> areas in between LGN layers; analyze color information; primarily involved in ventral pathway
  51. M cells
    M RGCs and LGN cells = large; extensively branched; large receptive fields; respond optimally to large objects; high tempora resolution
  52. P cells
    P RGCs and LGN cells = small; small receptive fields; high spatial resolution
  53. monocular clues for depth perception
    familiar size; occlusion; linear perspective; size perspective; illumination; motion parallax
  54. binocular disparity
    differences in visual input between eyes helps brain to construct 3-D image (depth perception)
  55. reflectance function
    shows the reflectance/absorbance of different objects for light of different wavelengths
  56. types of cones
    S (blue) cones - most sensitive to short wavelengths; M (green) cones - most sensitive to middle wavelengths; L (red) cones - most sensitive to long wavelengths
  57. protanopia
    loss of L cone function
  58. deuteranopia
    loss of M cone function
  59. tritanopia
    loss of S cone function
  60. anomalous trichromacy
    colorblindness involving abnormal cone types
  61. protoanomaly
    replacement of L cone pigment with L/M hybrid
  62. deuteranomaly
    replacement of M cone pigment with L/M hybrid