Receptors and neural processing

Question 1

What is meant by duplex retina

Answer 1

Rods and cones - scotopic and photopic vision

Question 2

Scotopic vision

Answer 2

rod dominated, sensitive in dim light, 510nm wavelength, poor acuity and no colour

Question 3

Photopic vision

Answer 3

cone dominated, insensitive in dim light, 555nm, good acuity and colour

Question 4

Cells of the retina

Answer 4

120million rods (high convergence), 6 million cones (low convergence peak in fovea) 1 million ganglion cells. Receptor - bipolar - ganglion cell

Question 5

Ganglion cells

Answer 5

convergence - receive input from 120 rods but only 6 cones. Greater summation = better sensitivity but poorer acuity

Question 6

Peripheral activity

Answer 6

low in periphery - magnification due to distance from fovea. More receptors per ganglion, more convergence

Question 7

Hartline, Ratcliff and Wagner 1956

Answer 7

work on limulus ommatidium. Each ommatidium feeds into single nerve fibre. High luminance = high fire rate. Interference from neighbouring cells via lateral connections. Lateral inhibition.

Question 8

Lateral inhibition in mammalian retina

Answer 8

Kuffler - identified centre surround organisation. Made from excitatory and inhibitory connections from different neurons (bipolar, amacrine (between ganglion) and horizontal (between receptor)). Enhances edges

Question 9

Mach band illusion

Answer 9

The Mach Band illusion refers to the apparent enhanced contrast that is typically seen at the edges (between bright and dark patterns). Result of lateral inhibition

Question 10

Herman grid

Answer 10

In the center of the receptive field the individual photoreceptorsexcitethe ganglion cell when they detect increased luminance. The photoreceptors in the surrounding areainhibitthe ganglion cell. Thus, since a point at an intersection is surrounded by more intensity than a point at the middle of a line, the intersection appears darker due to the increased inhibition