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