Visual circuits

Question 1

What are the visible wavelengths of light

Answer 1

400-700nm

Question 2

Identify the two synaptic pathways of the primary visual cortex [2]

Answer 2

lateral gesticulate nucleus
primary visual cortex

Question 3

Describe the flow of information in the visual pathway [4]

Answer 3

• retina sends visual signals
• through optic tract
• to lateral genticulate nucleus
• the LGN sends info to primary visual cortex

Question 4

Lambeth the cells of the retina [5]

Answer 4

see diagram

Question 5

What is opsin

Answer 5

light sensitive photopigment in outer segment o photoreceptor

Question 6

What is retinal and what is its function [3]

Answer 6

• chromophore that changes shape (cis to trans) with light
• activates opsin
• which hyper polarises photoreceptor

Question 7

Where is rhodopsin found

Answer 7

rods

Question 8

Identify 3 different opsins found in cones and the type of wavelength they detect

Answer 8

• S-cones: short wavelength (blue)
• M cones (medium wavelengths: green)
• L cones (long wavelengths: red)

Question 9

What is dichromatic vision [2]

Answer 9

• only has two cones
• aka colour blindness

Question 10

Define the term receptive fields

Answer 10

area of retina where light stimulation induces changes in membrane potential of cell

Question 11

Define the term centre-surround organisation [2]

Answer 11

• light stimulation of centre and surround has antagonistic effects
  -enhances response to spatial contrasts

Question 12

What is meant by the term ON-OFF cells

Answer 12

cells are depolarised (ON) or hyperpolarised by light (OFF)

Question 13

What is the role of M cells in the retina [2]

Answer 13

• detect orientation and position of objects in space
• more sensitive to low contrast stimuli

Question 14

What is the role of the P cell

Answer 14

• Convey info about colour

Question 15

12. Label the cells [9]

Answer 15

see diagram

Question 16

What are amacrine cells [2]

Answer 16

• inhibitory cells
• carry signals to rod cells

Question 17

Describe the visual field [3]

Answer 17

• region of space seen by both eyes
• visual hemifield: overlapped
• binocular field: non overlapped

Question 18

Describe the renitropy in the visual field [3]

Answer 18

• neighbouring cells in retina project to neighbouring in LGN and V1
• point to point representation of visual field in visual system
• central retina (fovea) more represented than peripheral retina (less inneravetd)

Question 19

Describe the structure of the LGN [4]

Answer 19

• 6 layers
• info segregated
• axonal projections from ipsilateral eye arrive at layers 2,3 and 5
• axial projections from contralateral eye arrive at layers 1, 4 and 6

Question 20

Where are ocular dominant columns found?

Answer 20

Layer IV of V1

Question 21

What is meant by binocularity [4]

Answer 21

• In upper layers of V1
• projections from ocular columns converge from both eyes
• responses still dominated by one eye
• underpins ability to see in 3D

Question 22

Identify the similarities between simple and complex cells [2]

Answer 22

• elongated receptor fields
• found in V1

Question 23

Identify 3 difference between simple and complex cells

Answer 23

• receives convergence inputs from IV cells/ from simple cells
• receptive fields have centre (surround antagonism/ no centre
• ON/OFF areas spatial segregated/ ON/OFF areas randomly distributed across receptive fields

Question 24

Identify the neurones involved in orientation and and direction selectivity [2]

Answer 24

• orientation selective neurones: analyse object shape
• direction selective neurones: analysis of object motion

Question 25

Describe the experiment by Hubel and Wiesel

Answer 25

- single cell recording (micro electrode) in V1 of cats - hooked up microphones to click when neurone fired - bar of light shown to cat at different areas of visual fields - in some areas neon fires when light is in (ON neurones) - others fire when neurones fire when light is off (OFF cells) - areas of periphery neurones fire fire less than when light in centre of visual field - preferred orientation for some neurones (orientation selective) - complex cells highly orientation specific

Question 26

Describe the functions of the dorsal pathway in the extra striate visual areas [3]

Answer 26

- location of objects - analysis of motion - orientation

Question 27

Where is the dorsal pathway predominantly located

Answer 27

parietal lobe

Question 28

Describe the function of the ventral pathway [2]

Answer 28

- what objects are - colour identification

Question 29

Where is the ventral pathway predominantly located

Answer 29

temporal lobe

Question 30

Identify 3 connectivity patterns

Answer 30

- feedforward - feedback - horizontal

Question 31

Define feedforward [2]

Answer 31

- lower to higher areas - transmission of info

Question 32

Define feedback [2]

Answer 32

- higher to lower areas - modulatory role

Question 33

Define horizontal

Answer 33

- across the same area - intrinsic computation

Question 34

5. Label the diagram with connectivity patterns

Answer 34

see diagram

Question 35

Describe the role of association areas in sight [3]

Answer 35

- establish elaborate connections between association areas - eventually generate mental representation of what we are looking at - requires extraction of visual primitives

Question 36

Which layers are blobs found in the V1 [3]

Answer 36

- outside layer IV - layer II - layer III

Question 37

Describe blobs and their function [3]

Answer 37

- monocular - non orientation selective - analysis of object colour

Question 38

Describe the cortical module [4]

Answer 38

- 2x2mm chunk of cortex - contains all the machinery to analyse image in point of space - input from both eyes - orientation and colour

Question 39

Why are visual pathways described as parallel [2]

Answer 39

- different features of visual info sent to V1 - segregated and parallel manner

Question 40

What is the first step for shape analysis [4]

Answer 40

- neurones in visual cortex - lines segments that are aligned with orientation of receptive fields - if at orientation matching that of neurone: increased firing - to determine orientation

Question 41

Define the term binocular disparity [1]

Answer 41

- difference in which each eye perceives same image - allows for depth perception

Question 42

Describe how we see in 3D and have depth perception [4]

Answer 42

- images on the plane of fixation have corresponding representation on both retinas - images at in front or behind area of fixation have different representation on each retina - neurones in V1 preferentially respond to each of these situations (different planes) - allows for depth perception and 3D sight

Question 43

What is the aperture problem [2]

Answer 43

- receptive fields of neurones are small - only detects fraction of moving object

Question 44

Describe how motion is perceived and processed [3]

Answer 44

- visual system intergretaes local motion signals to determine direction of motion - often assumes direction of movement perpendicular to orientation - some neurones in mid temporal lobe responds to overall directions of movement

Question 45

What area of the brain processing colours

Answer 45

V4

Question 46

Define the colour constancy

Answer 46

- colour of objects remain the same under different levels of illumination - and under different wavelengths of light