W3: LGN & V1

Question 1

Describe the LGN structure and cell layer functions

Answer 1

4 Parvocellular Layers, 2 Magnocellular Layers Koniocellular layers between
Input from corresponding Ganglion Cells:
P: 70-80% small RFields, detect colour, don’t saturate at high contrast, fine details, sustained response
M: 10% large Rfields, can’t detect colour, saturate at high contrast, coarse details, transient response
K: 8% 1st site for critical yellow-blue comparisons
Only known cell to carry S cone signal

Question 2

What do convolutions form in the brain?

Answer 2

Gyri: Elevated regions
Sulci: Depressed regions

Question 3

Define retinotopy

Answer 3

Nearby cells in V1 represent nearby locations in the visual field

Question 4

Define cortical magnification
Where is it greater?

Answer 4

mm of cortical surface per degree of visual angle
Greater for foveal representation

Question 5

Describe the input/output relationship between LGN and V1

Answer 5

P (4A, 4Cbeta)
M (4Calpha)
K (2, 3)

Layers 2, 3, 6 project from V1 to extrastriate areas
Layer 5 projects to superior colliculus for eye movement

Question 6

Describe optic radiations

Answer 6

LGN fibres provide optic radiation projecting to V1

Question 7

Describe ocular dominance columns

Answer 7

adjacent columns in layer 4 of V1 thought to underpin stereopsis (depth perception)
arranged LE RE LE RE etc.
Blobs encode colour, slabs encode orientation of movement and length

Question 8

Describe the location role of:
Simple Cells
Complex Cells
Hyper-complex Cells (End-Stop)

Answer 8

Simple cells in L4/6 make orientation-selective Rfields for edge enhancement
Complex cells in L2/3/5 are multiple simple cells in same orientation to make RFields with overlapping On/Off response - detects movement
Hyper-complex in L2-4 respond maximally to defined length, if stimulus is longer response is inhibited

Question 9

Which 2 receptive field types are used for orientation?

Answer 9

Bar and edge detectors