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Sensation & Perception. -Discussion Section- Session 3 – Retina Cat Retina (Kuffler) Frog Retina...
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Transcript of Sensation & Perception. -Discussion Section- Session 3 – Retina Cat Retina (Kuffler) Frog Retina...
ΨΨSensation
&
Perception
ΨΨ-Discussion Section-
Session 3 – Retina
Cat Retina (Kuffler)
Frog Retina (Barlow)
Administrative stuff
Presentation 1: Discharge patterns and functional organization of mammalian retina (1951)
presented by Nick Wood
Presentation 2: Summation and Inhibition in the frog’s retina (1952)
presented by Joel Tan
BACKGROUND
Two giants of neuroscience
Stephen W. Kuffler Horace B. Barlow
1921-1913-1980
The Retina
Basic layer structure
Amacrine cell
Horizontal cell
PE Layer
PR Layer
BP Layer
GC Layer
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).
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.
Number of Ganglion cells
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.
Methods shape results
Sophisticated light measurements
Subthreshold summation
Light intensity
Firing
Threshold
= 500 Lux
Stimulus size
Firing
Threshold
100 Lux200 Lux400 Lux
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.
Subthreshold summation
=
Spatial integration - Ricco’s law (1877):
I x A = k
where I = Intensity, A = Area, k = constant
Spatial integration – Piper’s law (1903):
I x A0.5 = k
where I = Intensity, A = Area, k = constant