PowerPointPrsentation

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Sensation Perception
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-Discussion Section- Session 3 Retina Cat
Retina (Kuffler) Frog Retina (Barlow)
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Administrative stuff
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Presentation 1 Discharge patterns and
functional organization of mammalian retina
(1951)presented by Nick Wood

Presentation 2 Summation and Inhibition in
the frogs retina (1952)presented by Joel Tan
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BACKGROUND
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Two giants of neuroscience
1921-
1913-1980
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The Retina
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Basic layer structure
GC Layer
BP Layer
PR Layer
PE Layer
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Basic facts

• Humans have roughly 120m Rods, 1m Cones and 1m
  Ganglion cells.
• Frogs have roughly 1m PRs, 30k Ganglion cells
• Primates have a fovea and a blind spot
• A lot of animals have no fovea, including cats.
• Up to 70 different types of Amacrine cells, 12
  different types of horizontal cells.
• 3 types of cones (l,m,s), 1 type of rod, at least
  3 types of Ganglion cells (M, P, PR).

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Basic heuristic

• The more advanced the animal, the more
  sophisticated functions are outsourced from the
  retina to the brain.
• The lower the animal, the more stuff is done in
  the retina, for example motion and feature
  detection.

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Number of Ganglion cells
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Pioneer Haldan Keffer Hartline

• 1903-1983
• Worked on the retina of crabs and frogs.
• Shared a Nobel prize for his findings in 1967.
• Found evidence for electrical image processing in
  the retina.
• Results qualitative.
• Plagued by technical troubles.
• Both papers today extend findings substantially,
  in different directions.

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Methods shape results
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Sophisticated light measurements
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Subthreshold summation
100 Lux
200 Lux
400 Lux
Threshold 500 Lux
Threshold
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Subthreshold summation

• Neuron fires if a stimulus is brighter than a
  certain light intensity.
• Neuron ALSO fires if a stimulus is not as bright,
  but has a larger spatial extent.
• ? Subthreshold spatial summation.

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Subthreshold summation

Spatial integration - Riccos law (1877) I x
A k where I Intensity, A Area, k
constant
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Spatial integration Pipers law (1903) I x
A0.5 k where I Intensity, A Area, k
constant