What and where pathways

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What and where pathways

• Outline
• General layout of visual pathway
• What and where pathways
• Details of pathway convergence
• Evidence for distinct processing
• Animal research
• Human (clinical) research
• Attention

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Vision

• Pathway to V1 (visual cortex)

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Extrastriate pathways

• Ventral (What) Pathway
• From V1 to InferoTemporal region of cortex
• Perception of Form
• what has T for temporal
• Dorsal (Where) Pathway
• From V1 to Parietal cortex
• Perception of Movement

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Evidence for parallel where and what pathways

• Two problems (Ungerleider and Mishkin)
• Object perception
• Landmark discrimination
• Train monkey to run a task then examine impact
  of lesions to (a) parietal lobes, (b) temporal
  cortex.

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Fails if temporal cortex lesion
Fails if parietal lobe lesion
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Processing streams (2/3)--

• Ganglion cells (center-surround receptive field)
• P-cells
• Linear summation sustained firing, smaller
  receptive fields wavelength sensitive
• Project to Parvocellular layers of LGN
• M-cells
• Not linear transient firing, larger receptive
  files wavelength insensitive
• Projects to Magnocellular layers of LGN
• Magno and Parvocellular regions of the LGN have
  similar properties as M- and P-cells.

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Striate Cortex (V1)

• Many more dimensions in which receptive fields
  may be described or tuning
• Receptive field size
• Sensitivity to motion?
• Sensitivity to chages in wavelength?
• Orientation selectivity?
• Occular dominance?

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Striate Cortex (V1)

• Projection to V1 from magnocellular portion of V1
  
• Motion sensitivity (direction and velocity)
• Orientation sensitivity
• Disparity sensitivity
• Projection to V1 from parvocellular portion of V1
  
• Wavelength sensitivity
• Orientation sensitivity
• Disparity sensitivity

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V2 three categories

• Pale stripes
• Wavelength sensitivity
• Orientation sensitivity
• Disparity sensitivity
• Thin stripes
• Wavelength sensitivity
• Thick stripes
• Motion sensitivity
• Orientation sensitivity
• Disparity sensitivity

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One description
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Where?
What?
Another description
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Consider two regions -- MT and VR

• MT medial temporal motion recordings
• Recordings
• Stimulations
• lesions
• V4 color
• recordings

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MT -- recordings
stimuli
Neural response
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V4 -- recordings
Stimuli light patches of different wavelengths
Neural response
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Clinical Studies

• Agnosia loss of knowledge
• Motion agnosia brain damage to cortex around
  border of the occipital and temporal lobes

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Motion Agnosia
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Clinical Studies

• Agnosia loss of knowledge
• Prospagnosia inability to recognize faxes.
  Lesion in area of interior temporal cortex.

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Equal-luminance projections
If there are color boarders, but no contrast
boarders, there is a loss of sense of depth,
motion, perception of complex patterns
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Equal-luminance projections
If there are color boarders, but no contrast
boarders, there is a loss of sense of depth,
motion, perception of complex patterns
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If processing streams are parallel how are a
singles object perceived

• Possibly through attention
• Preattentive processing rapid detection of
  elementary properties such as brightness, color,
  orientation
• Attentive processing direct attention to
  specific region / allows combination of
  elementary objects (the glue that binds)

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