Dorsal and Ventral Pathways
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
Dorsal and Ventral Pathways
• V4 and V5 are doubly-dissociated in lesion literature:
Achromatopsia and Akinetopsia, respectively
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
• Why “What” and “Where”?
– monkey lesion experiments
– human lesions
– differences in tuning
properties of cells
– neuroimaging
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
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
– # 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
V5
• Another dichotomy:
conscious vs unconscious
V4
– do both of these pathways
necessarily contribute their
“contents” to visual
awareness?
Agnosia
• Lesions (especially in the left
hemisphere) of the inferior
temporal cortex lead to
disorders of memory for
people and things
V5
• 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
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
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
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