Week 6: Vision Part II Central Processing

Question 1

What is the optic nerve composed of?

Answer 1

Composed of axons of retinal ganglion cells, which exit the eye through the optic disc. Eventually enters the brain.

Question 2

Where is the suprachiasmatic nucleus located?

Answer 2

Hypothalamus

Question 3

How much axons does the suprachiasmatic nucleus receive from the retina

Answer 3

A small number

Question 4

What is the suprachiasmatic nucleus involved in?

Answer 4

Controlling circadian rhythms

Question 5

What does the pretactal nuclei consist of? And where is it located?

Answer 5

Cluster of small nuclei

Midbrain

Question 6

What is the pretactal nuclei involved in?

Answer 6

Controls visual reflexes

Question 7

What are the 3 types of visual reflexes controlled by the pretactal nuclei?

Answer 7

1) optokinetic nystagmus - observed when a repetitive visual stimulus moves fast in 1 direction
2) pupilary light reflex - pupil becomes larger or smaller in response to intensity of light reaching the eye. More light, pupil contracts, allowing less light to enter. Dark, pupil relaxes (larger), allowing more light to enter.
3) Vestibule-ocular reflex

Question 8

Where is the superior colliculus located?

Answer 8

Midbrain

Question 9

How much axons does the superior colliculus receive from the retina?

Answer 9

Large number

Question 10

What is the superior colliculus essential for? What could it be involved in?

Answer 10

Visuomotor transformations (eg. fixing on a visual item)
May play a role in visual processing. Believed to underlie newborns' visual capacities. Primary target of retina in many mammals.

Question 11

Where is the lateral geniculate nucleus (LGN) located?

Answer 11

Thalamus

Question 12

_____ is the primary retinal target in primates.

Answer 12

Lateral Geniculate Nucleus (LGN)

Question 13

What is the LGN essential for?

Answer 13

Conscious vision

It is the primary input to the visual cortex

Question 14

There are 6 layers in the LGN.
Layers 1-2 are the _____ layers.
Layers 3-6 are the _____ layers.

Answer 14

Magno

Parvo

Question 15

Where do the parvocellular layers of the LGN receive input from?

Answer 15

Midget cells in the retina

Question 16

What are midget cells characterised by?

Answer 16

• very small dendritic trees
• largest population of retinal ganglion cells
• small receptive fields
• slow at propagating action potentials

Question 17

Where do magnocellular layers of the retina receive input from?

Answer 17

Parasol cells in the retina

Question 18

What are parasol cells characterised by?

Answer 18

• large dendritic trees
• larger receptive fields
• small proportion of retinal ganglion cells
• fast transmission of information, action potentials move faster down axons

Question 19

What does fixating on an object mean?

Answer 19

Positioning both eyes such that the object is located right in the center of your fovea.

Question 20

Why does the fovea have the highest resolution for vision?

Answer 20

It has the highest density of photoreceptors

Question 21

Light from the right visual field falls on the ___ side of the left eye and ___ side of the right eye.

Answer 21

temporal; nasal

Question 22

Light from the left visual field falls on the ___ side of the left eye and ___ side of the right eye.

Answer 22

nasal; temporal

Question 23

What is the optic chiasm?

Answer 23

The point where fibres in the optic nerve cross over the other hemisphere of the brain.
right hemifield –> left thalamus (LGN)
left hemifield –> right thalamus (LGN)

Question 24

Layers 1, 4, 6 of the LGN receive _____ projections.

Layers 2, 3, 5 of the LGN receive ______ projections.

Answer 24

contralateral (left eye, right thalamus etc.)

ipsilateral (left eye, left thalamus etc.)

Question 25

LGN is often considered a relay station between ___ and ____?

Answer 25

retina ; visual cortex

Question 26

Why is the LGN often considered a relay station between retina and visual cortex?

Answer 26

Because the response properties of its neurons are similar to those found in the eye.

Question 27

The LGN projects to V1, where they are processed in different "columns", what are they called?

Answer 27

Ocular dominance columns

Question 28

What is the difference between an orientation selective complex cell vs simple cell?

Answer 28

Complex cell has no inhibitory cell unlike the simple cell. Complex cells also tend to have larger receptive fields.

Question 29

What will evoke an activity in a complex cell?

Answer 29

A bar located anywhere in the receptive field in the right orientation will evoke an activity

Question 30

simple cells and complex cells are neurons found in ____?

Answer 30

V1

Question 31

Besides orientation selectivity, what other property do complex cells possibly have?

Answer 31

direction-selectivity

Question 32

The dorsal (where) /magnocellular pathway spans which part of the brain?

Answer 32

posterior parietal cortex

Question 33

The ventral (what) / parvocellular pathway spans which part of the brain?

Answer 33

temporal lobe

Question 34

What is the magnocellular pathway involved in?

Answer 34

involved in processing spatial information (where things are)

Question 35

What is the parvocellular pathway involved in?

Answer 35

Involved in processing object identity (what they are)

Question 36

What is the input to magnocellular layers in the magnocellular pathway?

Answer 36

parasol cells, characterised by very fast transmission speed | dorsal pathway processes motion, which require very fast responses

Question 37

What is the input to parvocellular layers in the parvocellular pathway?

Answer 37

midget cells. characterised by smaller receptive fields, which is important for shape perception, since we need high resolution to determine identity of objects.

Question 38

Where does the neurons in the dorsal pathway project to?

Answer 38

Area MT (middle temporal area)

Question 39

What do neurons in the dorsal pathway consist of?

Answer 39

complex direction-selective cells with very large receptive fields

Question 40

What condition arises from the damage of MT area?

Answer 40

Akinetopsia -- the inability to perceive motion. person only sees flashes of stationary stimuli, very disturbing since motion is an important dimension of vision.

Question 41

What condition results from damage to dorsal parietal visual areas?

Answer 41

visuospatial neglect -- inability to pay attention to a part of space when another competing stimulus is present on the other hemisphere. right parietal damage --> hemineglect of left visual field vice versa

Question 42

Which two conditions can arise from damage to the inferior temporal area?

Answer 42

1) agnosia -- inability to recognise objects | 2) prosopagnosia -- inability to recognise faces

Question 43

What is agnosia characterised by?

Answer 43

Can recognise borders and maybe shape, but unable to link these visual features with the identity of objects he has learned throughout his life. can recognise faces!

Question 44

What is prosopagnosia characterised by?

Answer 44

inability to recognise faces, including own face :( | can learn to cope by using other visual cues, like smile, hair colour etc.