Ch6 - Vision

Question 1

Anatomy

Answer 1

Orbits (bony packets in front of skull suspending eye) → 6 extraocular muscles attached to sclera (white outer coat, vs transparent cornea in front) & conjunctiva (mucous membranes that line eyelid & fold back to attach to eye

Shape of lens (onion slices) altered by contraction of ciliary muscles → accommodation

Vitreous humor = clear gelatinous substance

Question 2

Visual pathway

Answer 2

Optic nerves→ optic chiasm → dorsal lateral geniculate nucleus (LGN) → (through optic radiations) primary visual cortex (V1, striate cortex)→visual association cortex (V2, extrastriate cortex) & additional cortical areas

Question 3

Transduction

Answer 3

1 human rod consists of 10 million photopigments → are embedded in lamellae (thin plates of membrane that make up outer segment of photoreceptors - outer & inner (contains cell nucleus) connected by cilium, break down when hit by light)

Photopigment molecules - 2 parts: opsin (protein, rhodopsin in rods) & retinal (lipid)

Question 4

LGN - 6 layers

Answer 4

1,2 - magnocellular layers - larger cell bodies
3-6 - parvocellular layers
K1 - K6 (ventral to each) - koniocellular sublayers
1,4,6 - opposite eye
2,3,5 - ipsilateral eye

Question 5

Striate cortex 6 layers

Answer 5

Inputs:
Top - orientation sensitive
Blobs (columbs) - 1,2,3, 5,6 - color processing 
4 - magnocellular input
4C beta - parvocellular 
2 - koniocellular

Outputs:
2,3,4B → other cortical areas
5 - superior colliculus & pons
6 - back to LGN

Question 6

Extrastriate cortex pathways

Answer 6

Dorsal stream - “where”, location - speed & direction - MT & MST (motion processing) → parietal lobe

Ventral stream - “what” - V4 & IT (color…)→ temporal lobe

Question 7

Extrastriate cortex info categorization/transmission color

Answer 7

(conveys striate info along ventral stream of inferior temporal lobe)

Parvocellular - high spatial low temporal (movement) resolution
Koniocellular - no fine details
Magnocellular - colourblind, high sensitivity to contrast, low spatial, fast temporal

Question 8

Striate cortex color

Answer 8

parvocellular system receives info from only red & green cones, blue is transmitted through koniocellular system

Question 9

Opponent-process coding

Answer 9

Neurons respond to opposing pairs of primary colors

Retina contains 2 kinds of color sensitive ganglion cells: red-green & yellow-blue

Other ganglion cells are black & white detectors

Question 10

Cerebral achromatopsia

Answer 10

colourblind from lesion of a restricted region of extrastriate cortex

Question 11

Form pathway

Answer 11

Neurons in striate sensitive to orientation & spatial frequency → V2 → ventral stream

Question 12

Lateral occipital complex (LOC)

Answer 12

relatively large region of ventral stream of V2 responding to wide variety of objects & shapes

Question 13

Visual agnosia

Answer 13

Damage to extrastriate cortex - unable to recognize objects by sight

Question 14

Prosopagnosia

Answer 14

FFA, fusiform face area altered in ppl w autism & williams syndrome

Or born with smaller anterior fusiform gyrus→ congenital prosopagnosia → decreased connectivity within occipito-temporal cortex

Fusiform face area enlarged with williams syndrome

Question 15

Spatial location

Answer 15

3D - stereopsis - binocular - depth

Neurons respond to retinal disparity - time & location of both eyes - in dorsal strem

Dorsal stream of V2 terminates in posterior parietal cortex

Question 16

Orientation & movement

Answer 16

Striate cortex: neurons responding to diff orientations

Extrastriate:
V5 (MT, medial temporal) neurons respond to movement/orientation
For 1 orientation: simple (specific region), complex, hypercomplex
MST (superior, adjacent to V5) neurons respond to complex patterns of movement (ex spiral) - MSTd = analysis of optic flow

Question 17

Motion

Answer 17

Motion-sensitive area V5 located within inferior temporal sulcus or lateral occipital cortex
Akinetopsia = bilateral damage to area V5
Form from motion - dots - processed in a different regions in extrastriate