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Perception: Maastricht University > Task 4: On Columns & Pathways > Flashcards

Task 4: On Columns & Pathways Flashcards

1
Q

What is the optic nerve composed of?

A

the axons of retinal ganglion cells

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2
Q

Where do the axons of the retinal ganglion cells cross?

A

partly at the optic chiasm

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3
Q

What forms the optic tract?

A

optic nerve

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4
Q

Where is the optic tract found?

A

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

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5
Q

Where do LGN axons go?

A

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

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6
Q

Where do axons in the optic tract terminate?

A

most terminate in the LGN and some in the superior colliculus

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7
Q

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?

A

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

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8
Q

Define LGN

A

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

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9
Q

What does each cerebral hemisphere act as?

A

relay stations on the way from retina to cortex

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10
Q

What kind of receptive fields do LGN neurons have?

A

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

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11
Q

LGN neurons respond to

a) both eyes
b) one eye

A

b

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12
Q

Why does the LGN have 6 layers?

A

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

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13
Q

What are koniocellular cells/layers?

A

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

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14
Q

Define magnocellular layer

A
  • 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
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15
Q

Define parvocellular layers

A
  • 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
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16
Q

Topographical mapping

A

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

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

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17
Q

Give 2 alternative names of topographical mapping

A
  1. electronic map

2. retinotopic map

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18
Q

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

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

A

left, right

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19
Q

Define contralateral

A

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

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20
Q

Define ipsilateral

A

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

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21
Q

Define contralateral neglect

A

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

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22
Q

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

True or false?

A

true

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23
Q

Give 2 alternative names for V1

A
  1. striate cortex

2. primary visual cortex

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24
Q

Define V1

A

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

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25
Q

Explain topographical mapping in relation to the visual cortex

A

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

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26
Q

Explain magnification in relation to the visual cortex

A

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

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27
Q

Define cortical magnification and its consequence

A

amount of cortical area devoted to specific region in visual field

consequence - acuity declines in orderly fashion with eccentricity (distance from fovea)

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28
Q

Why is foveal representation in cortex so magnified?

A

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

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29
Q

Define the receptive field of a neuron

A

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

30
Q

Describe the receptive field of striate cortex neruons

A

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

31
Q

Discuss how selective responsiveness is a property of receptive fields

A

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

32
Q

Define orientation tuning

A

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

33
Q

Explain how striate cortex neurons are “filters”

A

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

34
Q

Discuss cortical cells and spatial frequencies

A

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

35
Q

Define ocular dominance

A

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

36
Q

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

A
  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

37
Q

Define simple cortical cell

A

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

38
Q

What is meant by simple cells being phase-sensitive?

A

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

39
Q

Discuss simple cells and edge detectors

A

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

40
Q

Discuss stripe detectors and simple cells

A

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

41
Q

Define complex cell

A

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

42
Q

What is meant by complex cells being phase-insensitive?

A

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

43
Q

Both simple and complex cells show ___ preference

A

ocular

44
Q

Define column

A

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

45
Q

How is the striate cortex organised?

A

in location and orientation columns

46
Q

Define location column

A

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

47
Q

Define orientation column

A

each column contains cells that respond best to a particular orientation

48
Q

Whats another name for end stopped cells?

A

hypercomplex cells

49
Q

Define hypercolumn

A

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)

50
Q

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

A

cortical magnification

51
Q

What is the hypothesized function of blobs in striate cortex?

A

they do something with colour and movement

52
Q

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

A

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

53
Q

What is a result of lesions to the inferotemporal cortex?

A

disrupt circuit specialized for identifying objects (visual agnosia)

54
Q

Describe the neurons of the ventral stream

A

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

55
Q

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

A

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

56
Q

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

A

interfere with neural mechanisms underlying spatial perception (optic agnosia)

57
Q

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

A

there are connections between them

58
Q

Do signals in both pathways

a) flow up
b) flow back
c) both

A

c

59
Q

Why are the pathways also connected to the frontal cortex?

A

because sometimes our lower order thinking cannot identify

60
Q

Define double dissociation

A

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

61
Q

Define single dissociation

A

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

62
Q

Define module

A

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

63
Q

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

A

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

64
Q

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

A

parahippocampal place area, located in inferior temporal cortex

65
Q

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

A

extrastriate body area, located in inferior temporal cortex

66
Q

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

A

lateral occipital complex, location from lateral to ventral cortex

67
Q

What area is responsible for identifying words?

A

visual word form area

68
Q

Define visual agnosia

A

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)

69
Q

Define optic ataxia

A

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

70
Q

Define Balint’s syndrome

A

disorders of spatial attention, gaze and visually guided reaching

-> damage to bilateral parietal region

Perception: Maastricht University (8 decks)

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