Data compression

Question 1

Why?

Answer 1

130 mil photo receptors and only 1 mil nerve fibers in the optic nerve

It has to be compressed to 1 mil, without too much loss of information.

Question 2

1. Contrast coding

Answer 2

ON and OFF center surrounds RG cells. When the light hits receptors, hyperpolarization occurs (Na+ channel closes). Darkness depolarizes by closing NA+ channels); Graded potential signal

Hyperpolarizing: Sign conserving synaps -> OFF bipolar cell

Depolarization; sign inverting synapse -> ON bipolar cell

Ganglion creates action potential (bipolar only change membrane potential)

Question 3

Horizontal cells

Answer 3

Receive signal from widespread region of receptors. They accumulate and invert this, providing negative feedback on the central receptors.

Meaning it’s sensitive to light in the center and dark in the surround.

Because of that, Ganglions response to CONTRAST and not to luminance

Question 4

2. Rod signals

Answer 4

Connect to bipolar cell, but not directly to RGC. The do pass through the same RGC’s as cone signals. Rods mostly connect to Rod bipolar cells, and connect to cone driven bipolar cells via the amacrine cells.

Question 5

3. Color coding

Answer 5

Continuous spectrue but color opponent of RGCs, either Red and Green, Green and Red or Blue and Yellow. Which is why after overloading, you see opponent afterimage.

So; also colors are coded as contrast.

Question 6

4. Parallel pathways

Answer 6

RGC projection to the brain;

Midget cells transmit to Parvocellular layers (4 smaller cell layers) of the LGN

Parasol cells transmit to Magnocellular layers (2 larger layers) of the LGN

Similar properties (reaction, tranience color etc)

M-typs (Y-RGCs) arrive first (global precedence)