1. Dorsal and Ventral Pathways

2. Dorsal and Ventral Pathways
Different visual cortex regions contain cells with different tuning properties represent different features in the visual field
V5/MT is selectively responsive to motion
V4 is selectively responsive to color

3. Dorsal and Ventral Pathways
V4 and V5 are doubly-dissociated in lesion literature: Achromatopsia and Akinetopsia, respectively

4. Dorsal and Ventral Pathways
V4 and V5 are key parts of two larger functional pathways:
Dorsal or “Where” pathway
Ventral or “What” pathway
Ungerleider and Mishkin (1982)
Magno and Parvo dichotomy arose at the retina and gives rise to two distinct cortical pathways

5. Dorsal and Ventral Pathways
Why “What” and “Where”?
monkey lesion experiments
human lesions
differences in tuning properties of cells
neuroimaging

6. Dorsal and Ventral Pathways
Pohl (1973) Early dissociations of Temporal and Parietal functions
Landmark task:
Monkeys trained to find reward in well near a landmark
once they get the task the contingency is switched
#errors until relearning indicates ability to use the spatial relationship information to perform task

7. Dorsal and Ventral Pathways
Pohl (1973) Early dissociations of Temporal and Parietal functions
Landmark task:
Dissociates Parietal and Temporal lobes
Parietal lesions impair relearning of landmark task

8. Dorsal and Ventral Pathways
Pohl (1973) Early dissociations of Temporal and Parietal functions
Object task:
Reward location is indicated by one of two objects
contingency is switched
# errors to relearn indicates ability to use object distinction to perform task

9. Dorsal and Ventral Pathways
Pohl (1973) Early dissociations of Temporal and Parietal functions
Object task:
Adding this task doubly dissociates Parietal and Temporal lesions
Temporal lesions impair object task

10. Dorsal and Ventral Pathways
Another dichotomy: conscious vs unconscious
do both of these pathways necessarily contribute their “contents” to visual awareness? V4

11. Agnosia V5
Lesions (especially in the left hemisphere) of the inferior temporal cortex lead to disorders of memory for people and things
recognition and identification are impaired
prosopagnosia is a specific kind of agnosia: inability to recognize faces
explicit (conscious) decisions about object features are disrupted V4

12. Agnosia Goodale and Milner – Patient DF
Patient could not indicate the orientation of a slot using her awareness
Patient could move her hand appropriately to interact with the slot
whether visually guided or guided by an internal representation in memory

13. Agnosia Single dissociation of action from conscious perception
Dorsal pathway remained intact while ventral pathway was impaired
Dorsal Pathway seems to guide motor actions, at least for ones that need spatial information
Activity within the Dorsal Pathway seems not to be sufficient for consciousness

14. Ataxia Ataxia is a discoordination of motor behaviour
a variety of different symptoms and causes
patients with ataxia due to lesions of parietal lobe in the dorsal pathway have difficulty operating and interacting with objects but they can identify them
doubly dissociates conscious perception in the ventral pathway from visually guided action in the dorsal pathway