Sensation & Perception. -Discussion Section- Session 3 – Retina Cat Retina (Kuffler) Frog Retina (Barlow)

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Presentation transcript:

Sensation & Perception

-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. KufflerHorace B. Barlow

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 Worked on the retina of crabs and frogs. Shared a Nobel prize for his findings in 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 Lux 200 Lux 400 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 A 0.5 = k where I = Intensity, A = Area, k = constant