1. The Visual System: Higher Cortical Mechanisms
Lesson 19

2. Convergence of Visual Information
From retina  V1
parvocellular pathway
color
form ~
Retina
RGC
LGN V1

3. Divergence of Visual Information
Primary Visual Cortex (V1)
Secondary Visual Cortex (V2) V4
medial occipital lobe IT
inferotemporal cortex
V5 (MT)
middle temporal cortex
PPC
posterior parietal cortex ~ V1 V2 V5 V4 IT
PPC

4. Divergence of Color & Form
input to layer 4
Color  blob cells
Form  interblob cells ~

5. Color
LGN
Layer 4
Form V1

6. What and Where Pathways
Parallel Processing
Ventral Stream
What
V1  V2 V4  IT
Dorsal Stream
Where
V1  V2  V5  PPC ~ V1
Where
What

7. Form Perception Ventral stream - What Inferotemporal Cortex
complex stimuli
grandmother cells
Damage to IT
object recognition deficits
Visual Agnosia
Prosopagnosia ~

8. Posterior Parietal Cortex - PPC
Dorsal Stream - Where
Maps of body & space
spatial coordinates for behavior
Damage  problems organizing movements
Damage to right PPC
Contralateral (Spatial) neglect
Neglect left side of body & world
Including imagining scenes ~

9. Motion & Depth Perception
Temporal lobe
V5 (MT - middle temporal)
MST (medial superior temporal) ~ V5

10. Motion & Depth Perception
Magnocellular input
movement across visual field (retina)
also relative to background
Parvocellular input
depth & distance
retinal disparity
Damage  akinetopsia
no perception of motion
Perception without motion ? ~

11. What do we see?
Objects in visual awareness are not things in the real world...
but rather representations of those things
Constructed image
Interpreted by the brain ~