Lecture 11: Vision 2

Question 1

What are the ganglion cells?

Answer 1

output neurons of the retina

Question 2

What are the characteristics of M (parasol) ganglion cells?

Answer 2

magnocellular = large
large receptive fields
motion detection, flicker and analysis of gross features

Question 3

What are the characteristics of P (midget) ganglion cells?

Answer 3

parvocellular = small
more numerous
visual acuity and colour vision

Question 4

What are the output targets of ganglion cells?

Answer 4

many brain regions

majority target the lateral geniculate nucleus (thalamus)

Question 5

What is the sequence of the visual pathway?

Answer 5

retina -> optic nerve -> lateral geniculate nucleus -> optic radiations -> visual cortex (V1)

Question 6

What is the optic chiasm formed by?

Answer 6

combination of the fibres from right and left optic nerves

the optic chiasm is where these fibres cross

Question 7

Where does the optic chiasm lie?

Answer 7

at the base of the brain, anterior to the pituitary

Question 8

What is the right visual hemifield “viewed” by?

Answer 8

the left hemisphere of the brain

Question 9

What is the left visual hemifield “viewed” by?

Answer 9

the right hemisphere of the brain

Question 10

What is a visual hemifield?

Answer 10

one half of the visual field, usually divided vertically through the fovea into the left or the right visual field

Question 11

What is the lateral geniculate nucleus and what is its role?

Answer 11

LGN is part of the thalamus and its role is to receive functional streams of information

Question 12

Which cells are contained within the LGN? What is their role?

Answer 12

magnocellular cells in layers 1,2 and parvocellular cells in layers 3-6
magnocellular cells receive input from M (parasol) ganglion cells and parvocellular cells receive input from P (midget) ganglion cells

Question 13

How many layers are in the lateral geniculate nucleus?

Answer 13

six layers (numbered 1-6)

Question 14

Where is the primary visual cortex?

Answer 14

in the occipital lobe at the back of the brain

Question 15

What is the role of the back of the calcerine fissure?

Answer 15

represents the location of interpretation of central vision

Question 16

Where is input from the LGN received?

Answer 16

layer 4C

Question 17

How are cells arranged in cortex V1?

Answer 17

cells are arranged vertically in columns and comprise a functional unit

Question 18

What are ocular dominance columns?

Answer 18

refers to the function of neurons in layer 4C

two LGNs-receive input from each eye (but segregated into different layers)

Question 19

What do neurons respond best to in orientation columns?

Answer 19

neurons respond best to a bar of light at a specific orientation

Question 20

What do layer 4C neurons respond to?

Answer 20

bars of light of different orientation and from a specific eye

Question 21

How is information coming from both eyes segregated?

Answer 21

segregation of information from different types of LGN cells
M type GC/LGN input to layer 4Cɑ
P type GC/LGN input to layer 4Cβ

Question 22

How is information coming from both eyes integrated?

Answer 22

mixing of information from each eye occurs in layers IVB and layer III

Question 23

What are the two large cortical streams of visual processing?

Answer 23

dorsal and ventral

Question 24

What is the role of the middle temporal lobe?

Answer 24

an area of the brain specialised for processing object motion

Question 25

What is the role of area V4?

Answer 25

receives input from the blob and interblob regions of the primary visual cortex via V2

Question 26

What are the receptive fields of neurons in V4 selective for?

Answer 26

orientation and colour

therefore, these neurons are important for perception of shape and colour

Question 27

What is the role of the inferior temporal area?

Answer 27

a major output of area V4

important for visual memory, perception and perception of faces