Transcript Last Lecture http://www.umich.edu/~psycours/345/

Last Lecture
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Maps
Plasticity of maps
Retinotopic map
Today’s Outline
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More: Retinotopic Map
Parallel Visual Pathways
Blindsight
Visual world onto the retina
LVF
Left Nasal retina
Right Temporal retina
Retinotopic Map
RVF
Left Temporal retina
Right Nasal retina
Left Eye’s View
Retinotopic Map
Right Eye’s view
Retinotopic Map
Perimetric testing to Diagnose
field defects
View from above
Retinotopic Map
Each eye’s field of
View (visual field)
is mapped out
Can light be detected
throughout the
visual field?
Retinotopic Map
VF Left Eye
VF Right Eye
Right
Combined Visual Field
Left
Retinotopic Map
VF Left Eye
VF Right Eye
Right
Combined Visual Field
Left
Retinotopic Map
Function: Perimetric Map shows blindness in
lower right quadrant of…
Left Eye
Right Eye
Where is the damage?
Retinotopic Map
On the retinae?
Retinotopic Map
From Retina to Brain
Geniculo-Striate Pathway
 Optic nerve carries
signals from retina.
• Decussation at optic
chiasm (optic tract)
• Synapse at Thalamus:
Lateral Geniculate
Nucleus (LGN)
• Optic radiations to
• AREA 17; Striate
Cortex, Primary visual
cortex
Retinotopic Map
Visual World Mapped onto Cortex
(via the retina) >> retinotopic map
Retinotopic Map
Upper Bank
CALCARINE FISSURE
Lower Bank
Deficit in 1/2 VF
(homonymous: both
eyes)
Retinotopic Map
Function: Perimetric Map shows blindness in
lower right quadrant of…
Left Eye
Right Eye
Where is the damage?
Retinotopic Map
defect affects
1/4 VF
Retinotopic Map
An area of visual loss
surrounded by relatively
well-preserved vision.
Size and shape vary.
Retinotopic Map
Gordon
Holmes
(1919)
Correlated
Visual Field
Defects with
lesion locus
to identify
the
Retinotopic
map.
Retinotopic Map
Sensitive areas are “magnified”
Field of View
Cortical Map of Visual Field
Retinotopic Map
Equi-visibility chart
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Objects in the
periphery must be
Physically larger
in order to be
as visible as
objects falling on
fovea
 Fovea is more
sensitive
 Cortical
Magnification
Anstis
Retinotopic Map
Fovea is a small portion of retina
Retinotopic Map
Cortical Magnification
• Area 17
neurons have
receptive
fields in the
retina
• More neurons
have foveal
receptive
fields
Retinotopic Map
Retinotopic map: Summary
Crossed organization
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Left 17 --> RVF
Right 17 --> LVF
Inverted organization
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Lower calcarine > Upper VF
Upper calcarine > Lower VF
Fovea: Disproportional
representation
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
cortical magnification
NOTE: Each visual cortex represents
a visual field NOT an eye.
Retinotopic Map
VF Left Eye
VF Right Eye
Right
Nasal
Combined Visual Field
Left
Retinotopic Map
VF Left Eye
VF Right Eye
Right
Nasal
Combined Visual Field
Left
Retinotopic Map
VF Left Eye
VF Right Eye
Right
Nasal
Combined Visual Field
Left
Retinotopic Map
For your review: the connections
LVF input to Rhem.
RVF input to LHem
Right Eye
Left Eye
Nasal hemiretina- RVF- projects
to left hemisphere
Temporal hemiretina- LVFprojects to right hemisphere
Nasal hemiretina- LVF- projects
to right hemisphere
Temporal hemiretina- RVFprojects to left hemisphere
RIGHT EYE’s
RETINA
LEFT EYE’s
RETINA
nasal
To cross at optic chiasm
uncrossed
uncrossed
Outline
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The Retinotopic Map
Parallel Visual Pathways
Blindsight
Parallel Pathways
From Retina
To primary
visual cortex
 To superior
colliculus
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Path to
SC
Parallel Pathways
Vision requires Area 17…or maybe not?
LORE of neurology until the early 70's...
LGN
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Reports of residual vision in Animals with striate
lesions (hamsters; monkeys):
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Recovery after experimental field defects (cortical ablations)
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Striate
extra
Striate
spared light/dark discrimination
spared localization abilities
Implication: Other pathways can compensate for
some geniculo-striate function.
Can this also be true in humans??
Parallel Pathways