1. Review session today after class
Test is Friday Nov 20
Review session today after class

2. 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

3. 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 – monkey must find well opposite to the landmark
#errors until relearning indicates ability to use the spatial relationship information to perform task

4. 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

5. 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 – monkey must use other object
# errors to relearn indicates ability to use object distinction to perform task

6. 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

7. Dorsal and Ventral Pathways
Different kinds of information are represented in the two visual pathways
do both of these pathways equally contribute their “contents” to visual awareness? V5 V4

8. Agnosia
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

9. Agnosia Goodale and Milner – Patient DF
Patient could not indicate the orientation of a slot using conscious information
Patient could move her hand appropriately to interact with the slot

10. 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

11. Blindsight

12. Lesions of Retinostriate Pathway
Lesions (usually due to stroke) cause a region of blindness called a scotoma
Identified using perimetry
note macular sparing X

13. Retinocollicular Pathway independently mediates orienting
Rafal et al. (1990)
subjects move eyes to fixate a peripheral target in two different conditions:
target alone

14. Retinocollicular Pathway independently mediates orienting
Rafal et al. (1990)
subjects move eyes to fixate a peripheral target in two different conditions:
target alone
accompanied by distractor

15. Retinocollicular Pathway independently mediates orienting
Rafal et al. (1990) result
Subjects were slower when presented with a distracting stimulus in the scotoma (359 ms vs. 500 ms)

16. Retinocollicular Pathway independently mediates orienting
Blindsight patients have been shown to posses a surprising range of “residual” visual abilities
better than chance at detection and discrimination of some visual features such as direction of motion
These go beyond simple orienting - how can this be?