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					         Visual Pathway
          Visual area
          of the thalamus
                       Optic
                       nerve

                 Optic
                 chiasm
                               Optic
                                       Retina
                               tract



Visual
cortex
Information flow through the visual system
• Go to the Virtual lab
• Retina 
     Optic Nerve 
     Optic Chiasm  (after O.C. called Optic Tract)
                 Lateral Geniculate Nucleus (LGN; of
                       the Thalamus (90%)) 
                 or, Superior Colliculus (10%) 
                       Visual (Striate) Cortex
                            (multiple layers)
Lateral Geniculate
Nucleus (LGN)

Centre-Surround
Receptive Fields
  inhibition

        excitation
                            Retinotopic Map in LGN

Temporal     VISUAL FIELD      Temporal

       A B C D Nasal                      A   B
                                                  C
Left                           Right
                                                      D




                optic
                chiasm




       LGN               LGN
Ganglion cells =      approximately 1-million cells
LGN cells      =      approximately 1-million cells


Probably little in the way of convergence (compared to
  what happens with Rods & to a lesser extent Cones in
  the retina)

• LGN communicating with more than retinal Ganglion
  – to and from Cortex
  – other areas of Thalamus
Three types of Ganglion cells from the
         Retina to the LGN
• Parvocellular cells (“P-cells”)
  – Small cell bodies
  – Sustained firing patterns
  – Information about color, patterns/forms, depth
• Magnocellular cells (“M-cells”)
  – Large cell bodies
  – Fire in bursts
  – Information about movement
• Kinocellular cells (“K-cells”) – don’t know what the
  function of these cells are?!?
                   6
                  5    c    layers 1 and 2
                   i         - magnocellular
           4
                             layers 3-6
          3        c          - parvocellular
              i
         2i                layers 2, 3 and 5
                           - ipsilateral (same
     1   c
                           side) eye
                              layers 1, 4 and 6
                              - contralateral
                              (opposite side) eye


lateral geniculate nucleus (LGN) is a “bilateral
structure”: 1 in the right Hem. & 1 in left Hem.)
LEFT Eye in RIGHT LGN (contralateral)
         6

             5

         4

             3

             2

         1




RIGHT Eye in RIGHT LGN (ipsilateral)
Lesion



         Destruction of the parvocellular
         layers of the LGN results in
         deficits in color, form (pattern) &
         some depth perception
Destruction of the
magnocellular layers of the
LGN results in deficits of
movement perception
         Visual Pathway
          Visual area
          of the thalamus
                       Optic
                       nerve

                 Optic
                 chiasm
                               Optic
                                       Retina
                               tract



Visual
cortex
              Primary Visual Cortex




“W” is White matter – cells from LGN enter cortex here
White Matter is white because of color of myelin (axons)
Gray Matter is gray because of color of cell bodies
         Visual Pathway
          Visual area
          of the thalamus
                       Optic
                       nerve

                 Optic
                 chiasm
                               Optic
                                       Retina
                               tract



Visual
cortex
     Hubel & Weisel’s “accident”
• Measuring for cortical responses to spots of light
• Previously shown that “center-surround” firing
  existed in retina and LGN to spots of light
• Could not get a response from cortical cells in
  situations that Ganglion & LGN cells were firing
  wildly!
• “The accident” – changing slides in the projector
  resulted in firing of cortical cells to horizontal
  line stimulus moving down the screen
Hubel and Wiesel - cells of visual cortex
 Hubel & Weisel findings: 3 types of
  cortical cells in the visual system
• Simple Cells – respond to a particular orientation
  (“orientation selective”) and of specific size and
  stimuli that are static (i.e., non-moving).

• Complex Cells – responds to particular orientation
  in movement

• End-Stopped Cells – respond to moving lines of
  specific length; moving corners or angles
 Hubel and Wiesel - cells of visual cortex

simple cells -

respond to "bars" of light of a particular orientation
(orientation selective)

Similar to Center-Surround receptive fields, but they are
now “side-by-side” excitatory-inhibitory arrangement
Simple Cell Receptive Field

          - + -
          - + -
          - + -
            +
                                (15 spikes)
                     on   off


          - + -
          - + -
          - + -
            +                   (9 spikes)
                     on   off


          - + -
          - + -
          - + -
            +
                                (3 spikes)
                     on   off
How simple cells work together for “orientation tuning”
Orientation Tuning Curve

                                                             100 o
                                                                        11 spikes
   90 o    on     off
                        (15 spikes)


                                                             110 o
   80 o
                                                                        5 spikes
          12 spikes
                                     16

                                     14


   70 o                              12

          7 spikes                   10

                                      8

                                      6

                                      4

                                      2
                        (3 spikes)

  0 o     on    off
                                      0
                                          0   20   40   60   80   100    120   140   160

                                                   orientation (degrees)
Orientation Selective Simple Cells have different
sizes of receptive fields (for different sizes of
visual lines-bars)


     - + -
     - + -
     - + -
       +




     - + -    -   +   -     - +   -    - +-
     - + -    -   +   -     - +   -    - +-
     - + -    -   +   -     - +   -    - +-
       +          +           +          +
Hubel and Wiesel - cells of visual cortex

simple cells -

Similar to Center-Surround receptive fields, but they are
now “side-by-side” excitatory-inhibitory arrangement

Respond to "bars" (not “spots”) of light of a
particular orientation (orientation selective)


Respond to specific sizes of stimuli
Hubel and Wiesel - cells of visual cortex

simple cells - respond to "bars" of light of a
    particular orientation (orientation selective)

complex cells - respond to "bars" of light of a
    particular orientation, moving in particular
    direction (orientation and direction selective)
Complex Cell Receptive Field
           +++
        +++++++
        ++ +++ ++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
        ++ +++ ++     on   off
        +++++ ++
           +++




           +++
        +++++++
        ++ +++ ++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
        ++ +++ ++     on   off
        +++++ ++
           +++
Complex Cell Receptive Field
           +++
        +++++++
        ++ +++ ++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
        ++ +++ ++
        +++++ ++
           +++
                       on      off




           +++
        +++++++
        ++ +++ ++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
       +++ +++ +++
        ++ +++ ++
        +++++ ++
           +++
                       on      off
 Direction Tuning Curve

                                   25


                                   20

excitation   inhibition
                                   15



                          spikes
                                   10


                                    5


                                    0
                                        0   45    90   135   180   225   270   315
                                                 direction (degrees)
Hubel and Wiesel - cells of visual cortex
simple cells - respond to "bars" of light of a
    particular orientation (orientation selective)
complex cells - respond to "bars" of light of a
    particular orientation, moving in particular
    direction (orientation and direction selective)
end-stopped cells - respond to moving "bars" of
     light of a particular orientation and a particular
      length, or moving "corners“(orientation, direction
    & discontinuous selective)
End-stopped Cells
       --- --- ---
           ---
       --- ------
     ------ ------
     ------ ------
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
     ------ ------
     ------ ------
       --- ------
       --- --- ---
           ---
                     on   off




       --- --- ---
           ---
       --- ------
     ------ ------
     ------ ------
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
    +++ +++ +++
     ------ ------
     ------ ------
       --- ------
       --- --- ---
           ---       on    off

				
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posted:8/30/2011
language:English
pages:30