03 Higher-level Vision

Question 1

The Visual Pathway

Answer 1

Optic Nerve -> Optic Chiasm (Contralateralization) -> Optic Tract -> Lateral Geniculate Nucles (LGN, in Thalamus) -> Optic Radiation -> V1
- LGN also projects to pulvinar nucleus (visual attention, saliency), superior colliculus (eye movement control) and extrastriate ares

Question 2

LGN - Layers

Answer 2

inner
- layer 1: magnocellular, contralateral eye
- layer 2: magnocellular, ipsilateral eye
- layer 3: parvocellular, ipsilateral eye
- layer 4: parvocellular, contralateral eye
- layer 5: parvocellular, ipsilateral eye
- layer 6: parvocellular, contralateral eye
outer

Question 3

LGN - retinal M, P & b/y cells

Answer 3

• retinal M cells: magnocellular, sensitive to dark levels of light and movement, rods, periphery, center-surround, larger receptive fields
• retinal P cells: parvocellular, sensitive to colour, information only from M- and L-cones, cones, fovea, red-center green-surround and vice versa, medium & high levels of light, color, detail, smaller receptive fields
• b/y cells: koniocellular

Question 4

Simple Cells in V1

Answer 4

• neurons that are tuned to certain orientations, edges, directions etc.
• information from multiple center-surround cells in LGN
• linearity

Question 5

What is a Gabor Filter?

Answer 5

• model of simple cells in V1
• constitutes a sinusoid multiplied with a Gaussian window

Question 6

Complex Cells

Answer 6

• neurons in V1, V2 & V3
• also tuned to certain (combination of) features
• spatial invariance (no linearity)
• end-stopped cells: decreasing firing rate with increasing length of stimulus beyond their receptive fields
• not end-stopped cells: increase firing rate
• allows for lateral inhibition

Question 7

The Icecube Model in V1

Answer 7

• orientation column: cells firing for a given orientation are grouped together
• ocular dominance column: cells for the same eye are grouped togehter
• blobs: colour coding

Question 8

Mapping in V1

Answer 8

• retinotopic mapping: image still inverted
• fovea is overrepresented: 0.01% of retina, but 8-10% of V1

Question 9

Mapping beyond V1

Answer 9

• mirror symmetry with quarter fields
• polar coordinate system

Question 10

V4/V8

Answer 10

• colour perception
• hemi-achromatopsia

Question 11

V5/MT

Answer 11

• movement, direction & speed
  cerebral akinetopsia: inability to perceive (fast) movement