PS222 Exam 2 F25

retinal ganglion cells RGC

• organize into into light-dark boundaries

• deemphasize uniformity

• emphasize boundaries

• behaviorally relevant units

receptive field size

determined by how many photoreceptors (?) converge at at retinal ganglion cell

• dendritic trees show single RGC gets signal from many bipolar cells

• NOT UNIFORM across retina

parasol RGCs

more convergence

→ lots of branches

→ signals from rods,  PERIPHERY

→ projects to M layers in LGN

small RGCs 

less convergence 

→ info from cones

→ M/L waves 

→ projects to P layers in LGN

small bistratisfied RGCs

moderate convergence

→ info from cones

→ S waves

→ projects to K layers in LGN

fovea

• high acuity/sharpness

• small RFs

• see more details

periphery

• high sensitivity

• larger RFs

• likely to detect faint stimuli

retinotopic mapping

next to each other in the retina/LGN (upside down, left-right reversed) means next to each other in the real world

right visual field

nasal right, temporal left

left visual field 

temp right, nasal left 

ipsilateral fibers

temporal side, stays on the same side

contralateral fibers

nasal side, crossover

optic tracts 

past crossover (optic chiasm), rep the same part of the visual field 

left side of the visual field →

right side of the brain

• axons from temporal leave eye and stay on same side of brain

aka TEMPORAL = SAME SIDE

superior colliculus (10% axons)

• deep in brain

• phylogenetically older so found in species we not closely related to

• where > what

• important for eye movement planning i.e tracking

• multisensory with RFs in many sensory areas (i.e moving and making sound)

lateral geniculate nucleus LGN (90% axons)

• RGC axons terminate in diff layers of lateral geniculate nucleus LGN 

• integrate info from 2 eyes, further organize

magnocellular layers

layers 1, 2

• parasol RGC

• periphery

• rods

parvocellular layers

layers 3, 4, 5, 6

• small RGC

• fovea

• cones

koniocelllular layers

between layers 3, 4, 5, 6

the pink between the brown layers

• small bistratisfied RGC

• fovea 

• cones

M-cells

strong opponency - LGN emphasizes light-dark boundaries

• detects fast change, motion, flicker

• bigger RFs

P-cells & K-cells

• color component cells

• smaller RFs