Test is Friday Nov 20

Review session today after class

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

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

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

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

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

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?

V4

V5

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

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

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

Blindsight

Lesions of Retinostriate Pathway

• Lesions (usually due to stroke) cause a region of blindness called a scotoma

• Identified using perimetry• note macular sparing

X

Retinocollicular Pathway independently mediates orienting

• Rafal et al. (1990)

• subjects move eyes to fixate a peripheral target in two different conditions:– target alone

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

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)

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?