Title: What and where pathways
1What 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
2Vision
- Pathway to V1 (visual cortex)
3Extrastriate 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
4Evidence 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.
5Fails if temporal cortex lesion
Fails if parietal lobe lesion
6Processing 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.
7Striate 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?
8Striate 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
9V2 three categories
- Pale stripes
- Wavelength sensitivity
- Orientation sensitivity
- Disparity sensitivity
- Thin stripes
- Wavelength sensitivity
- Thick stripes
- Motion sensitivity
- Orientation sensitivity
- Disparity sensitivity
10One description
11Where?
What?
Another description
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13Consider two regions -- MT and VR
- MT medial temporal motion recordings
- Recordings
- Stimulations
- lesions
- V4 color
- recordings
14MT -- recordings
stimuli
Neural response
15V4 -- recordings
Stimuli light patches of different wavelengths
Neural response
16Clinical Studies
- Agnosia loss of knowledge
- Motion agnosia brain damage to cortex around
border of the occipital and temporal lobes
17Motion Agnosia
18Clinical Studies
- Agnosia loss of knowledge
- Prospagnosia inability to recognize faxes.
Lesion in area of interior temporal cortex.
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20Equal-luminance projections
If there are color boarders, but no contrast
boarders, there is a loss of sense of depth,
motion, perception of complex patterns
21Equal-luminance projections
If there are color boarders, but no contrast
boarders, there is a loss of sense of depth,
motion, perception of complex patterns
22If 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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