Task 4: On Columns & Pathways

Question 1

What is the optic nerve composed of?

Answer 1

the axons of retinal ganglion cells

Question 2

Where do the axons of the retinal ganglion cells cross?

Answer 2

partly at the optic chiasm

Question 3

What forms the optic tract?

Answer 3

optic nerve

Question 4

Where is the optic tract found?

Answer 4

wrapped around the midbrain and axons then continue to the LGN in the thalamus where they synapse

Question 5

Where do LGN axons go?

Answer 5

expand via white matter as optic radiations (which carry information) where they travel to V1

Question 6

Where do axons in the optic tract terminate?

Answer 6

most terminate in the LGN and some in the superior colliculus

Question 7

The left primary visual cortex gets input from which eyes and which visual field?

The right primary visual cortex gets input from which eyes and which visual field?

Answer 7

The left primary visual cortex gets input from both eyes but only the right visual field

The right primary visual cortex gets input from both eyes but only the left visual field

Question 8

Define LGN

Answer 8

structure in thalamus, part of midbrain, receives input from retinal ganglion cells and has input and output connections to visual cortex

Question 9

What does each cerebral hemisphere act as?

Answer 9

relay stations on the way from retina to cortex

Question 10

What kind of receptive fields do LGN neurons have?

Answer 10

concentric receptive fields like retinal ganglion cells therefore respond to same patterns and provide input

Question 11

LGN neurons respond to

a) both eyes
b) one eye

Answer 11

b

Question 12

Why does the LGN have 6 layers?

Answer 12

the visual system splits input from image into different types of information

Question 13

What are koniocellular cells/layers?

Answer 13

split the layers of the LGN between magno and parvo cellular layers

-> each koniocellular layer is specialized e.g. one is for relaying signals from the S-cones

Question 14

Define magnocellular layer

Answer 14

• 2 bottom layers of LGN
• Cells are physically larger than those in parvocellular layers
• input from M retinal ganglion cells
• respond to large fast-moving objects

Question 15

Define parvocellular layers

Answer 15

• top 4 layers of LGN
• cells are physically smaller than those in the top 2 layers
• receives input from P retinal ganglion cells
• responsible for processing details of stationary targets

Question 16

Topographical mapping

Answer 16

the orderly mapping of the word in the LGN and visual cortex

-> provides a neural basis for knowing where things are in space

Question 17

Give 2 alternative names of topographical mapping

Answer 17

1. electronic map

2. retinotopic map

Question 18

Left LGN receives projections from ___ side of retina in both eyes

Right LGN receives projections from ___ side of retina in both eyes

Answer 18

left, right

Question 19

Define contralateral

Answer 19

layers 1, 4 and 6 of right LGN receive input from left eye

layers 1, 4 and 6 of left LGN receive input from right eye

Question 20

Define ipsilateral

Answer 20

layers 2, 3 and 5 of right LGN get input from right eye

layers 2, 3 and 5 of left LGN get input from left eye

Question 21

Define contralateral neglect

Answer 21

cannot see whats either on the left or right (draw numbers of a clock on half a clock)

Question 22

There are more feedback connections from visual cortex to LGN than vice-versa

True or false?

Answer 22

true

Question 23

Give 2 alternative names for V1

Answer 23

1. striate cortex

2. primary visual cortex

Question 24

Define V1

Answer 24

area of cerebral cortex that receives direct inputs from LGN and feedback from other brain areas

Question 25

Explain topographical mapping in relation to the visual cortex

Answer 25

image in our right is mapped onto regions corresponding to layer 3 and 4 in striate cortex that tells our visual system that image must be in positions 3 and 4 of visual field

Question 26

Explain magnification in relation to the visual cortex

Answer 26

information is scaled from different parts of visual field, thus, objects imaged near fovea are processed by neruons in large part of striate cortex and objects imaged in far right/left periphery are given tiny portion of it

Question 27

Define cortical magnification and its consequence

Answer 27

amount of cortical area devoted to specific region in visual field consequence - acuity declines in orderly fashion with eccentricity (distance from fovea)

Question 28

Why is foveal representation in cortex so magnified?

Answer 28

Since high resolution requires great number of resources, in order to see the entire visual field with such high resolution we would need larger eyes and brain. Therefore, we evolved a visual system that provides high resolution in center and lower resolution in periphery

Question 29

Define the receptive field of a neuron

Answer 29

the region in space in which the presence of a stimulus alters neuron's firing rate

Question 30

Describe the receptive field of striate cortex neruons

Answer 30

elongated therefore respond more vigorously to bars, lines, edges and gratings than to round spots of light

Question 31

Discuss how selective responsiveness is a property of receptive fields

Answer 31

individual neurons don't respond equivalently to any stripe in its receptive field

Question 32

Define orientation tuning

Answer 32

tendency of neurons (complex cells) in striate cortex to respond optimally to certain orientations and less to others -> more cells are responsive to horizontal and vertical orientations than to obliques= humans have lower visual acuity and contrast sensitivity for oblique targets than for horizontal and vertical ones

Question 33

Explain how striate cortex neurons are "filters"

Answer 33

for a portion of image that excites the cell, each striate cortex neuron functions as a filter - electrical, or optic neruon that allows the passage of some range of parameters and blocks the passage of others

Question 34

Discuss cortical cells and spatial frequencies

Answer 34

each cortical cell is tuned to a particular spatial frequency which corresponds to a particular line width -> cortical cells respond to a smaller range of spatial frequencies than retinal ganglion cells

Question 35

Define ocular dominance

Answer 35

property of receptive fields of striate cortex neurons by which they demonstrate a preference, responding more rapidly when stimulus is presented in one eye than when it is in other

Question 36

Name the 2 types of cortical neurons and explain what is meant by end stopped or not

Answer 36

1. simple 2. complex -> each one is end-stopped or not: process by which a cortical cell first increases its firing rate as bar length increases to fill up its receptive field and then decreases its firing rate as the bar is lengthened further, play a role in the ability to detect luminance boundaries and discontinuities

Question 37

Define simple cortical cell

Answer 37

cortical neuron whose receptive field has clearly defined excitatory a inhibitory regions

Question 38

What is meant by simple cells being phase-sensitive?

Answer 38

might respond only if stripe is presented in center of receptive field

Question 39

Discuss simple cells and edge detectors

Answer 39

highly excited when there is light on one side of its receptive field and darkness on the other

Question 40

Discuss stripe detectors and simple cells

Answer 40

responds best to line of light that has particular width surronded on both sides by darkness

Question 41

Define complex cell

Answer 41

cortical neuron whose receptive field does not have clearly defined excitatory and inhibitory regions

Question 42

What is meant by complex cells being phase-insensitive?

Answer 42

respond regardless of where the stripe is presented, as long as it is within cell's receptive field -> subunits of receptive fields give these cells spatial frequency and orientation tuning but complex pooling operation makes this cell insensitive to precise position of stimulus within its receptive field

Question 43

Both simple and complex cells show ___ preference

Answer 43

ocular

Question 44

Define column

Answer 44

neurons with similar receptive fields and orientation preferences arranged in columns that extend vertically through the cortex

Question 45

How is the striate cortex organised?

Answer 45

in location and orientation columns

Question 46

Define location column

Answer 46

perpendicular to cortex surface, all neurons within a location column have their receptive fields at the same location on retina

Question 47

Define orientation column

Answer 47

each column contains cells that respond best to a particular orientation

Question 48

Whats another name for end stopped cells?

Answer 48

hypercomplex cells

Question 49

Define hypercolumn

Answer 49

block of striate cortex containing 1 location and 1 orientation column, each covering every possible orientation (0-180 degrees) with one set preferring from the left eye and one set preferring input from the right eye (ocular dominance)

Question 50

Why don't all hypercolumns see the world at the same level of detail?

Answer 50

cortical magnification

Question 51

What is the hypothesized function of blobs in striate cortex?

Answer 51

they do something with colour and movement

Question 52

Define ventral pathway i.e. what pathway and magnocellular system

Answer 52

pathway reaching temporal lobe (inferotemporal cortex), responsible for determining object's identity

Question 53

What is a result of lesions to the inferotemporal cortex?

Answer 53

disrupt circuit specialized for identifying objects (visual agnosia)

Question 54

Describe the neurons of the ventral stream

Answer 54

they are very sensitive to form, pattern and colour - high resolution selectivity

Question 55

Define dorsal pathway i.e. where/how/action pathway and parvocellular system

Answer 55

pathway leading from striate cortex to parietal lobe (posterior parietal region) which is responsible for determining object's location, sensorimotor transformation for visually guided actions directed at objects

Question 56

What is a result of lesions to the posterior parietal region?

Answer 56

interfere with neural mechanisms underlying spatial perception (optic agnosia)

Question 57

Are the ventral and dorsal pathways entirely seperated or do they have connections?

Answer 57

there are connections between them

Question 58

Do signals in both pathways a) flow up b) flow back c) both

Answer 58

c

Question 59

Why are the pathways also connected to the frontal cortex?

Answer 59

because sometimes our lower order thinking cannot identify

Question 60

Define double dissociation

Answer 60

helps determine whether 2 functions operate independently from one another, involves 2 people: 1: damage to brain area causes function A to be absent while B is present 2: damage to another area of brain causes function B to be absent while A is present

Question 61

Define single dissociation

Answer 61

allows one to infer that function X and Y are independent of each other in some way, involves 1 person 1: person has lesion to structure A disrupting function X but not Y

Question 62

Define module

Answer 62

a structure specialized to process information about particular types of stimuli, areas for stimulus e.g. face, places, bodies go through ventral pathway

Question 63

What area is responsible for detecting faces and where is it located?

Answer 63

fusiform face area, located in fusiform gyrus on underside of brain, directly below inferior temporal cortex

Question 64

What area is responsible for places and where is it located?

Answer 64

parahippocampal place area, located in inferior temporal cortex

Question 65

What area is responsible for body and where is it located?

Answer 65

extrastriate body area, located in inferior temporal cortex

Question 66

What area is responsible for identifying contrasting object images with scrambled versions and where is it located?

Answer 66

lateral occipital complex, location from lateral to ventral cortex

Question 67

What area is responsible for identifying words?

Answer 67

visual word form area

Question 68

Define visual agnosia

Answer 68

unable to recognize or describe common objects, faces, pictures etc however can navigate through them everday -> brain damage to occipitotemporal region (mediates object but not spatial vision)

Question 69

Define optic ataxia

Answer 69

unable to reach accurately towards visual targets that they have no difficulty recognizing, cannot position hands when reaching toward objects oriented in different angles, cannot grasp -> damage to posterior parietal region

Question 70

Define Balint's syndrome

Answer 70

disorders of spatial attention, gaze and visually guided reaching -> damage to bilateral parietal region