Lecture 6, 7: From the retina to V1

Question 1

(p1)
What does the Retinex Theory say?

Answer 1

The retinex = retina & cortex.
The cortex compares information from different sections of the retina to determine the brightness and color of each segment –> it takes the context into account

Question 2

(p1)
What are the organizational rules of visual perception?

Answer 2

Look at experience and build in wiring (new experience).
- look for similarity, proximity, good continuation & contour saliency

NOTE: contour saliency is the ability to detect and prioritize continous edges/bounderies that stand out from the surrounding background

Question 3

(p1)
What is the state of rods their receptor, bipolar cell and ganglion cell when there is no light?

Answer 3

• Receptors are inhibitory and active
• Bipolar cells are excitatory and inactive
• No activity of ganglion cells to the brain

Question 4

(p1)
What is the state of rods their receptor, bipolar cell and ganglion cell when there is light?

Answer 4

• Light inhibits the receptor
• Receptors are inhibitory and become inactive
• Bipolar cells are excitatory and become active (disinhibition)
• Activity in ganglion cells to the brain

Question 5

(p1)
V1 is the primary visual cortex.

What are processing pathways from V1?

Answer 5

• Ventral stream (down): After processing in V1, information is sent through the ventral stream. Here the form and color of an object is analysed.
• object identification
  (WHAT?)
• Dorsal stream (up): Analysis of motion and spatial relations. (WHERE?)

Question 6

(p1)
Which brain structure is responsible for the connection between the ganglion and V1?

Answer 6

The lateral geniculate nucleus of the thalamus (retina via optic nerve)

Question 7

(p1)
What happen with receptive fields when higher visual areas are recorded?

Answer 7

Receptive fields become larger, since the complexity of the representation increases (higher visual area)

Question 8

(p1)
What is prospagnosia?

Answer 8

Facial blindness
(lesion in fusiform face area, but intact temporal cortex)

Question 9

(p2)
What are similarities and differences between the receptive fields of LGN and retinal ganglion cells?

Answer 9

Receptive fields both have a on/off receptive field that are tuned in dots.
Receptive field of LGN cells is larger.

-Both have mutual inhibition: no response when both center and surround are stimulated
- stopping the stimulus creates a ‘rebound’ in another part of the cell

Question 10

(p2)
What are the 3 basic types of ganglion cells and what are their characteristics?

Answer 10

• Parvocellular neurons: small receptive field, predominantly around the fovea, sensitive to color (input from cone), object pathway (ventral)
• Magnocellular neurons: large receptive field, in the entire retina, not sensitive to color, orientation pathway (dorsal)
• Koniocellular neurons: mix of both, can project to dorsal and ventral pathway

Question 11

(p2)
Where does visual perception mostly happen?

Answer 11

Via the thalamus to the visual cortex (90%). Optic nerve -> optic chiasm -> optic tract

Question 12

(p2)
Which areas also use visual information?
(So NOT to visual cortex)

Answer 12

• Hypothalamus: biological rhythm (day/night cycle)
• Pretectum: Reflex control of pupil and lens
• Superior colliculus: orienting the head & eyes in response to a stimulus (know where things are in space)

Question 13

(p2)
How does reflex control the pupils and lens?

Answer 13

Retina (to optic nerve) –> pretectum –> accessory oculomotor nucleus –> ciliary ganglion –> pupil muscles

Question 14

(p2)
Through which muscle and nerve system is pupil dilation and constriction controlled?

Answer 14

• Dilation: Dilator pupilea muscle via sympathic system (norepinephrine)
• Constriction: Sphincter pupilea muscle via parasympathic system (aCH)

Question 15

(p2)
How do the superior colliculus and basal ganglia contribute to reflex and voluntary movement of the head and eyes?

Answer 15

• Superior colliculus for reflex orientation to visual and auditory cues.
  Pathways: V1 –> SC (1), V1 –> posterior
  parietal cortex –> SC (2)
• Basal ganglia for voluntary movements through cognition. Visual cell dendrites in the SC detect info from visual system annd connects them to the motor circuit for movement.
  Pathway: Frontal cortex –> frontal eye
  field (FEF) –> basal ganglia (BG) –>
  substantia nigra (SN) –> SC (3)

NOTE: Fast -> slowest pathway = 3 - 1 - 2

Question 16

(p2)
What are critical structure in the reticular formation of the brain stem, which is involved in regulating voluntary movement and gaze control and help controlling the direction of the movement?
(eye movement coordination)

Answer 16

• Paramedian pontine reticular formation located in the pons: coordinates the eye muscles horizontally
• Rostral interstitial nucleus located in the midbrain in the medial longitudinal fasciculus: coordinates the eye muscles vertically

Question 17

(p2)
What is a visual field?

Answer 17

It’s what u see

Question 18

(p2)
Which cortical layer of the lateral geniculate nucleus gives the most input to V1?

Answer 18

Layer 4

Question 19

What is name of the cortex in which V1 lays in?

Answer 19

The striate cortex

Question 20

(p2)
What is the superior and inferior visual field?

Answer 20

• Superior: upper half of your visual field that is above your horizontal line of sight.
• Inferior: lower half of your visual field that is below your gaze

Question 21

(p2)
How is the superior and inferior visual field topographically mapped?

Answer 21

• Superior: info goes from inferior LGN to V1 (Meyers) loop, enter V1 ventral to calcarine sulcus
• Inferior: info goes from superior LGN to V1 loop, enter V1 dorsal to calcarine sulcus

Question 22

(p2)
Which layers of the visual cortex (6 layers) gives input and which output?

Answer 22

• layer 4 gives input, other are for output
• layer 6: output thalamus
• Layer 2 and 3 are within the visual cortex
• Layer 5 and 6 are outside the visual cortex

Question 23

(p2)
Which cortical layer is for monocular vision and which for binocular vision?

Answer 23

• Layer 4 is for monocular vision (separate left and right)
• Layer 3 is start of binocular representation

Question 24

(p2)
What is eccentricity?

Answer 24

Distance of a receptive field from the fovea

Question 25

(p2)
How is the receptive field of V1 simple cells constructed?

Answer 25

By combining the input from multiple LGN neurons with center-surround receptive fields. Through the spatial alignment of these inputs, simple cells develops sensivity to specific orientations of edges

NOTE: contributes to detection of shape, contour, patterns

Question 26

(p2)
How is the receptive field of V1 complex cells constructed?

Answer 26

Are constructed by pooling inputs from multiple simple cells that share the same orientation preference.
- This makes them detect edges/bars of a specific orientation and do they respond to these stimuli anywhere in their receptive field
- show direction selectivity

NOTE: crucial for higher-level tasks like oving edges, contours and textures in the visual field (motion)

Question 27

(p2)
What are orientation columns in V1?

Answer 27

Orientation selectivity in V1 is organized in columns. This organization minimizes the distance required for neurons with similar functional properties to communicate with each other.
–> resuls in minimal number of neurons and maximal processing time.

Question 28

(p2)
What are hypercolumns in V1?

Answer 28

• They’re elementary processing units of V1. Each row contains the complete neural machinary for the analysis of a small region of the visual field.
• all orientations, colors, etc. for both eyes

NOTE: collaterals of pyramidal cells link cells with similar orientation preference. They make excitatory connections and project to other pyramidal cells and inhibitory neurons.