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What and where pathways

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... two regions -- MT and VR. MT medial temporal motion ... MT -- recordings. stimuli. Neural. response. 15. V, M, Richards, University of Pennsylvania ... – PowerPoint PPT presentation

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Title: What and where pathways


1
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

2
Vision
  • Pathway to V1 (visual cortex)

3
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

4
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.

5
Fails if temporal cortex lesion
Fails if parietal lobe lesion
6
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.

7
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?

8
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

9
V2 three categories
  • Pale stripes
  • Wavelength sensitivity
  • Orientation sensitivity
  • Disparity sensitivity
  • Thin stripes
  • Wavelength sensitivity
  • Thick stripes
  • Motion sensitivity
  • Orientation sensitivity
  • Disparity sensitivity

10
One description
11
Where?
What?
Another description
12
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13
Consider two regions -- MT and VR
  • MT medial temporal motion recordings
  • Recordings
  • Stimulations
  • lesions
  • V4 color
  • recordings

14
MT -- recordings
stimuli
Neural response
15
V4 -- recordings
Stimuli light patches of different wavelengths
Neural response
16
Clinical Studies
  • Agnosia loss of knowledge
  • Motion agnosia brain damage to cortex around
    border of the occipital and temporal lobes

17
Motion Agnosia
18
Clinical Studies
  • Agnosia loss of knowledge
  • Prospagnosia inability to recognize faxes.
    Lesion in area of interior temporal cortex.

19
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20
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
21
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
22
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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