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NEUR3006 > Visual System > Flashcards

Visual System Flashcards

1
Q

What is the purpose of the parallel visual pathways?

A

• Parallel visual pathways- enable us to process colour, form and motion of objects in the visual world

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2
Q

What is a general outline of the conscious vision optic pathway?

A

• Conscious vision optic pathway: Retina-> optic nerve-> decussation at optic chiasm-> lateral geniculate nucleus of the thalamus-> Primary visual cortex
o Cells of nasal retina decussate to contralateral side
o Cells in temporal half of the retina remain on ipsilateral side

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3
Q

What is the optic disk?

A

• Optic disk- point where ganglion cell axons lave the eye to form the optic nerve

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4
Q

What is eccentricity?

A

distance from centre of fovea

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5
Q

Describe the dendritic trees of midget cells

A

o Midget cells-
 Small dendritic trees
• As move away from fovea, dendritic tree size increases

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6
Q

Describe the dendritic trees of parasol cells

A

 Big dendritic trees

• As move away from fovea, dendritic tree size increases

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7
Q

Compare the size of midget cells and parasol cells at any eccentricity

A

o At any eccentricity, midget cells are smaller than parasol cells

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8
Q

How do ganglion cells cover the surface of the retina?

A

• Each ganglion cell type forms ordered mosaic which covers the surface of retina in most efficient way
o Any point in the retina is being covered by dendrites of at least one ganglion cell

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9
Q

What is the purpose of wide-field ganglion cells?

A

o Chromatically selective (important for colour vision)

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10
Q

What is an example of wide-field cells?

A

o Example of wild field cells are small bistratified cells

 In general, these cells have low spatial density but large dendritic trees compared to midget and parasol cells

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11
Q

What are the three main divisions of the lateral geniculate nucleus?

A

• Three main divisions-
o Top 4 layers- parvocellular
o Lower 2 layers- magnocellular
o Intermediate layers between parvocellular and magnocellular- koniocellular

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12
Q

Compare the parvocellular lateral geniculate nucleus layer to the magnocellular lateral geniculate nucleus in terms of:

  • Cell size
  • Response time course and identity
  • Input
  • Function
  • Receptive field size
  • Type of contrast sensitivity
  • What part of the visual image each layer is the best at detecting
A

Parvocellular layer:

  • Small cells
  • Sustained response
  • Input from midget ganglion cells
  • Responsible for high acuity vision
  • On type response
  • Small receptive fields
  • Sensitivity at high contrast
  • Better at detecting higher spatial frequencies

Magnocellular layer:

  • Large cells
  • Transient response
  • Input from parasol ganglion cells
  • Responsible for motion perception
  • On type response
  • Large receptive fields
  • Sensitivity at low contrasts
  • Better at detecting contrast sensitivity
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13
Q

Compare the sizes of koniocells, parvocells and magnocells

A

koniocells are smaller than parvocells, which are smaller than magnocells

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14
Q

Describe the response timecourse of parvocells

A

 Response timecourse
• Responds quickly to stimulus changes
• Reaches maximum quickly but falls slowly
• Sustained type of response

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15
Q

Describe the response timecourse of magnocells

A

 Response timecourse
• Responds quickly to stimulus changes
• Reaches maximum quickly and falls quickly
• Transient type of response

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16
Q

What cells do parvocells get input from?

A

 Get input from midget ganglion cells

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17
Q

What cells do magnocells get input from?

A

 Get input from parasol ganglion cells

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18
Q

What is the function of parvocells?

A

 Responsible for high acuity vision

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19
Q

What is the function for magnocells?

A

 Responsible for motion perception

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20
Q

What is the optic axis?

A

o Optic axis-direction that the eye is pointing when it is fixated on an object in the real world

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21
Q

What is the fovea? Describe structure and function

A

o Diameter less than a mm
o Point in which our visual acuity is highest
 Over half the fibres in the optic nerve contain ascending signals from the fovea
 Blood vessels are curled around the fovea but do not enter the fovea
o If lose function, become functionally blind as this is the area in which photoreceptors are most tightly packed
o Photoreceptor cell bodies are most dense at the centre of the fovea but post-receptor layers are most dense in the periphery
 This is to reduce light scatter when light reaches fovea
 Structural connectivity remains the same

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22
Q

Describe the convergence at the fovea

A

o Each bipolar cell is driving by a single photoreceptor and ganglion cells are driven by a single bipolar cell (low convergence)
o Characterised by low post-receptoral convergence

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23
Q

What is coverage?

A

• Coverage- the extent to which something is covered

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24
Q

What is visual submodality?

A

• Visual submodality- Distinction of the visual modality

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25
Q

What is contrast sensitivity?

A

• Contrast sensitivity-Ability to distinguish an object from its background

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26
Q

What is spatial frequency?

A

• Spatial frequency-change in intensity as a function of space

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27
Q

What is low spatial frequency?

A

o Low spatial frequency: slow change in intensity as a function of space

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28
Q

At what spatial frequency do parvocells exhibit the higher amplitude at and why? (in doing so, describe its activity at other spatial frequencies

A

o Parvocells exhibit highest amplitude response at intermediate spatial frequency
o At low spatial frequency, off-surround antagonises the centre as it is also at a brighter phase of the grading- low response
o At intermediate spatial frequency, on-centre is activated and not antagonised by off-centre-high response
o At high spatial frequency, both on and off surround cancel each other out- no response

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29
Q

What is contrast modulation transfer function and when is it highest?

A

• Contrast modulation transfer function-how your sensitivity to contrast is modulated by spatial frequency
o Low frequencies, threshold is higher than at intermediate and higher frequency

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30
Q

What is the nyquist limit?

A

• Nyquist limit-the highest frequency that can be coded at a given sampling rate in order to be able to fully reconstruct the signal

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31
Q

What is the human nyquist limit for the visual system and what cell achieves this?

A

o At this limit (about 60 cycles/degree in humans), the parvocells are the ones activated
 Parvocells can detect higher spatial frequencies than magnocells

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32
Q

How do on-centre cells respond to contrast?

A

• On-centre cells respond to positive contrast
o The greater the contrast between stimulus and background, the greater the response of on-centre cells
o Negative contrast is inhibitory for the on-centre cell

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33
Q

How do off-centre cells respond to contrast?

A

• Off-centre cells respond to negative contrast

o The greater the negative contrast, the greater the response

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34
Q

What is Michelson contrast?

A

• Michelson contrast= (max phase-min phase)/(max+min)

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35
Q

Describe the relative response of magnocells and parvocells to increasing contrast

A

o Neuron activity increases linearly as contrast increases
o Magnocells show much greater contrast sensitivity than parvocells
 At about 50% contrast magnocells response is saturated
• Good for low contrast
 Parvocells can signal higher contrasts
• Good for high contrast

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36
Q

What is degree of spatial antagonism set by?

A

o Degree of spatial antagonism is set by the relative strength and relative size of centre and surround

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37
Q

What are the advantages of colour vision?

A
  • Identifying objects in the world based on spectral reflectance
  • Important linking feature to analyse visual scenes
  • Colour signals used by organisms to attract/repel certain other organisms
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38
Q

What determines the colour that the object appears?

A

• White light can be broken up into a spectrum
• Objects appear the colour of the wavelengths that they reflect most strongly
o Each receptor sends its own level of activation to the brain
o Brain interprets relative activation of receptors as colour

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39
Q

What is the principle of univariance for colour vision?

A

• For a single receptor system, if the integral of photon catch by a receptor is identical then the message it sends to the brain will be identical
o Receptor is colour-blind and univariant-
 The principle of univariance states that all absorbed photons generate the same response independently of wavelength (that is, any photon that is absorbed by photopigments generates the same response in the photoreceptor)

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40
Q

What is the trichromatic theory and who developed it?

A

• Trichromatic theory (Young and Helmholtz)-
o Different colour experiences are due to the differential activation of just 3 receptor types
 Long wavelength- red
 Medium wavelength-green
 Short wavelength-blue

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41
Q

What is the trichromatic theory based on the observation of?

A

o Based on observation that could generate all possible colours if mix light of just three different wavelengths

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42
Q

What wavelength does the red cone absorb and what percentage of total cones does it makeup?

A
  • Readily absorbs 564nm light

* About 40% of total cones

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43
Q

What wavelength does the green cone absorb and what percentage of total cones does it makeup?

A
  • Readily absorbs 534nm light

* About 40% of total cones

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44
Q

What wavelength does the blue cone absorb and what percentage of total cones does it makeup?

A
  • Readily absorbs 420nm light

* About 10-25% of total cones

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45
Q

How does photoreceptor adaptation occur and what happens during photoreceptor adaptation?

A

o Photoreceptor adaptation-
 When stare at colour, adapt to colour
• Excessive firing of particular receptors makes them reach threshold
 When neutral colour is added, cone that has not been firing fires more than other cones, who have reached their firing threshold and hence don’t fire much anymore
• The excessive firing of the cones used when staring at the colour skews towards opponent colour

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46
Q

What does amino acid sequence in cones determine? Describe

A

• The amino acid sequence determines spectral tuning
• S cone is non-homologous to M and L cones
o M and L cones have a homologous structure (only 12 amino acid difference)

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47
Q

What determines isomerisation probability in cones?

A

• Isomerisation probability is determined by the local environment-> determined by local amino acid residues of opsin-encoding genes within region of protein

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48
Q

Describe how the different cones (short, medium, long wavelength) communicate to their respective ganglion cels

A

• Dendrites of bipolar neurons reach out across the retina to make contact with all cones of one type in range of their dendrites
o System for selective preservation of signals for one of the 3 cone types in the array
• Blue cone transmits signal to blue cone bipolar cell which transmits signal to on dendrites of small bistratified ganglion cell
o Off dendrite gets input from medium and long cones through diffuse bipolar cell
• Long wave/medium wave cone preserved through tight link between midget system and long wave/medium wave signals
o The density of bipolar and ganglion cells is so high that each cone can connect to an off-type and on-type midget type bipolar cell and in turn transmit that signal to an on-type and an off-type midget ganglion cell
• Different types of cells are excited by some wavelengths of light and inhibited by other specific wavelengths of light
• Cells have an opponent signature

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49
Q

Does change in overall density of stimulus change what wavelength cones responds to?

A

• Change in overall density of stimulus doesn’t change what wavelength cell responds to

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50
Q

Describe the evolutionary history of human colour vision and the implications of it

A

• All diurnal mammals showed dichromatic vision
o S cone gene- on chromosome 7
o L cone gene- on X chromosome
• At 50 million years ago, South American monkeys emerged allelic variations in the genes encoding L and M cone genes on the X chromosome
o Only females expressed trichromatic colour vision
• About 30 million years ago, there was a gene duplication event where both the L and M cone genes were situated on the same X chromosome-> means that every X chromosome encodes for both cones
o Males can show trichromatic colour vision
 As there can be errors in transcription due to binding errors, the L or M cone gene can be untranscribed on that specific X chromosome
 It is hence more likely that males will be colour vision deficient than females as females have a spare X chromosome

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51
Q

Describe the basis of the common inherited colour vision deficiency

A
  • Colour vision deficiencies depend on lack of normal (3) cone number for humans
  • As there can be errors in transcription due to binding errors, the L or M cone gene can be untranscribed on that specific X chromosome and one of these genes can be missed
  • It is hence more likely that males will be colour vision deficient than females as females have a spare X chromosome
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52
Q

What is colour consistency?

A

• Colour constancy- the ability to maintain relatively uniform colour perception under different lighting conditions
o Means by which the average colour of illumination falling on a scene can be effectively measured or discovered

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53
Q

What is the supposed explanation for colour constancy?

A

• High level association cortex phenomenon

o Transformation between cells that detect wavelength and cells that react to perceived colours

54
Q

What information do signals that leave the retina contain?

A

• The signal that leaves the retina contains information concerning brightness, colour, movement, direction of movement and other features

55
Q

Where do axons leaving the retina go to?

A

o 10% of retinal output goes to the hypothalamus (rhythms)
o 10% of midbrain, superior colliculus (some eye movements)
o 80% go to the layered lateral geniculate nucleus

56
Q

From what cells does the lateral geniculate nucleus recieve input from, what is this input and what layers does this input project to?

A

 Input from midget cells-
• Carry information about colour and shape
• Project to the parvocellular layers
 Input from parasol cells-
• Carry information about movement and brightness
• Project to the magnocellular layers

57
Q

From what visual field does the visual cortex receive information from?

A

o Visual cortex will receive information from contralateral visual field

58
Q

When do retinal ganglion axons become myelinated?

A

• The optic nerve within the eye is composed of axons that arise from retinal ganglion cells
o In most mammals, most of these axons only become myelinated when they are bundled together at the level of the optic disk to form the optic nerve

59
Q

Is the visual field covered by both eyes entirely separate or entirely overlapping? Why?

A

• The visual fields covered by both eyes overlap extensively, which is essential for depth perception
o However, the visual fields are not identical, as some visual fields can only be seen by one eye because they are too far in the periphery to be seen by the contralateral eye

60
Q

What is the binocular visual field?

A

o The section of the visual field that can be seen by both eyes is called the binocular visual field

61
Q

What are the three major steps to the conscious visual pathway?

A
  • Partial decussation of the optic nerve at the optic chiasm
  • Retinofugal projection to the lateral geniculate nucleus: segregation of inputs according to eye of origin
  • Lateral geniculate projects to the primary visual cortex and terminate in layer 4 (the stria of Gennari)
62
Q

Describe the partial decussation of the optic nerve and why this occurs

A

• Partial decussation of the optic nerve
o Nasal retina of the eye looks at the ipsilateral visual field
 Fibres decussate at the optic chiasm
o Temporal retina of the eye looks at the contralateral visual field
 Fibres remain ipsilateral at the optic chiasm

63
Q

What layers of the lateral geniculate nucleus do inputs from ipsilateral fibres terminate in?

A

o Inputs from ipsilateral fibres project to layers 2, 3 and 5

64
Q

What layers of the lateral geniculate nucleus do inputs from contralateral fibres terminate in?

A

o Inputs from the contralateral fibres project to layers 1,4 and 6

65
Q

Do neurons in the lateral geniculate nucleus possess different or similar receptive field properties to the neurons in the retina?

A

o Neurons in the lateral geniculate nucleus possess very similar receptive field properties to the neurons in the retina
 They have concentrically and antagonistically organised receptive fields

66
Q

Where is the primary visual cortex located?

A

o The primary visual cortex (V1, Brodmann area 17, striate cortex) is located in the occipital cortex surrounding the calcarine sulcus

67
Q

How many layers does the primary visual cortex have?

A

 Organised in 6 main (9 real) layers

68
Q

What layer of the primary visual cortex do lateral geniculate inputs from magnocellular cells target?

A

o Lateral geniculate inputs from magnocellular cells target layer IVCalpha of the primary visual cortex

69
Q

What layer of the primary visual cortex do lateral geniculate inputs from parvocellular cells target?

A

o Lateral geniculate inputs from parvocellular layers target layer IVCbeta of the primary visual cortex

70
Q

What layer of the primary visual cortex do lateral geniculate inputs from koniocellular cells target? What is the functional consequence of this?

A

o Lateral geniculate inputs from koniocellular layers go to layers II and III of the primary visual cortex and target the blobs for colour analysis

71
Q

How were primary visual cortex blobs found?

A

revealed by cytochrome oxidase staining

72
Q

Describe the properties of cells found in layer IVCalpha of the primary visual cortex

A

• Simple cells have elongated receptive fields and their preferred stimulus is an elongated bar of a particular orientation
o Simple cells have an on centre and an off surround
• These are mostly monocular

73
Q

To what layer do neurons from the primary visual cortex layer IVCalpha project to and what is the functional consequence of this? What is the name of this channel?

A

 Neurons from layer IVCalpha project to layer IVB (M channel for motion detection)

74
Q

Describe the properties of neurons in layer IVB of the primary visual cortex

A

• Neurons in layer IVB have elongated receptive fields and are responsive to bars
• Neurons in layer IVB are direction selective (sensitive to direction of the bar)
o When bar moves from left to right- neuron fires action potentials
o When bar moves from right to left-neuron produces no change in action potentials
• Neurons in layer IVB are binocular and can be triggered by both eyes

75
Q

Describe the properties of neurons in layer IVCbeta of V1 (primary visual cortex)

A

 Neurons have small, circular and monocular receptive fields

76
Q

To what layers do neurons from layer IVCbeta of the primary visual cortex project to? What is the functional consequence of this?

A

 P channel interblob for shape analysis
• Neurons from layer IVCbeta project to the interblob area of layers II and III
 Blobs for colour analysis
• Neurons from layer IVCbeta project to the blobs in layer II and III of the primary visual cortex

77
Q

What are the properties of neurons in the interblob area of layers II and III of the primary visual cortex

A

o These neurons are complex cells with elongated receptive fields that respond to bars and the orientation of bars, but don’t have a centre-surround area
 They have a binocular response and are wavelength insensitive

78
Q

What are the properties of neurons in the blob area of layers II and III of the primary visual cortex?

A

o Neurons in the blobs of layer II and III have a small and circular receptive field
 Display colour opponent responses
 Wavelength sensitive and monocular responses

79
Q

How are the inputs from the right and left eyes mapped in the visual cortex?

A

o Right and left eyes input to adjacent cortical columns

 Inputs from each eye are separated in alternating columns

80
Q

Describe the layered structure of the visual cortex

A

• Most superficial layer is layer I whilst the deepest layer is layer VI
o Layer IV can be divided into layer IVA, IVB and IVC
 Layer IVC can be divided into alpha and beta layers

81
Q

What are the most common receptive fields in V1 and what are they sensitive to?

A

o V1 receptive fields are elongated and rectangular, and are extremely sensitive to direction of bars of light: different cells have different orientation preferences

82
Q

Describe the orientation-specific arrangement of cells in V1

A

 Orientation preference varies across primary visual cortex areas
• All different orientations were covered in a distance of 1 millimetre
• Cells preferring different orientations are found in columns
o Cells within a column have the same orientation preference to each other
o Cells within a row have different orientation preferences to each other

83
Q

Describe the stimulus activation of elongated receptive field cells in V1

A

 Stimulus activation of the neuron-
• Bars that are not in a preferred orientation will produce no firing rate for the neuron
• If the stimulus is in an angle close to the preferred orientation, a relatively weak response will be produced
• If the bar stimulus is in the preferred orientation, it will elicit a strong response

84
Q

Describe the Hubel and Wiesel model of how V1 elongated receptive fields are built from retinal circular receptive fields

A

o Hubel and Wiesel model of elongated receptive field
 If V1 cortical neurons receive converging input from three or more lateral geniculate nucleus neurons whose receptive fields are aligned on a line in the retina

85
Q

Do ocular dominance and orientation preference map on the same or different patch of cortex?

A

• Ocular dominance and orientation preference maps from same patch of cortex

86
Q

How is information segregated in the visual cortex (what is the location of the two streams of information)

A

o Visual information will flow from V1 to different extrastriate cortex via two streams
 Ventral stream-analysis of object form (what an object is)
 Dorsal stream- analysis of object location (where an object is)

87
Q

Describe the inputs and outputs of the ventral stream of visual information, and what happens when you damage this stream

A

• Receives mostly parvocellular and some magnocellular inputs
• Projects to extrastriate cortex (V2 and V4) and to inferior temporal cortex
o Damage produces difficulty in object perception

88
Q

Describe the inputs and outputs of the dorsal stream of visual information, and what happens when you damage this stream

A

 Dorsal stream- analysis of object location (where an object is)
• Receives mostly magnocellular input
• Projects to post parietal cortex via V2, V3, V3A, MT (V5), MST
• Damage can produce
o Problems in grasping an object
o Perception of motion problems

89
Q

How does selectivity of cells increase along the visual information flow? Provide examples

A

o After V1 there is segregation of processing-
 Selectivity of cells increases across the visual information flow: specialisation of functional properties along the route from V1 to V4 and MST
• MT- most cells are direction selective
• V4- most cells are responsive to wavelength and colour
 V4 seems specialised for colour whilst area MT seems more specialised for motion
 Intertemporal cortex (area IT) seems to be specialised for face recognition

90
Q

What implies serial processing in visual areas of the cortex?

A

o Different visual areas are arranged in a hierarchical manner
 Implies serial processing

91
Q

What is the fovea and the role of the fovea, as well as how it achieveshat role?

A

• Retina
o Fovea contains the highest density of cones connected in a very selective manner
 High spatial resolution and high visual acuity
• Limited to 1 degree of the visual field
 Low convergence

92
Q

What is the concept of retinal magnification and how is this achieved?

A

o Visual information arising from the fovea is highly represented in other visual areas- big areas devoted to foveal information
 Lateral geniculate nucleus and primary visual cortex are retinotopically organised
 Foveal information only occupies 1% of the retinal surface but 20% of the lateral geniculate nucleus and primary visual cortex
• Retinal magnification

93
Q

What moves the eye?

A

Extra-ocular muscles

94
Q

Are eye movements voluntary or involuntary?

A

Voluntary and involuntary

95
Q

What are the antagonist extra-ocular muscle pairs and what general movement are they responsible for?

A 
	Horizontal movement:
•	Medial rectus
•	Lateral rectus
	Mainly vertical movement:
•	Superior rectus
•	Inferior rectus
	Torsion movement
•	Superior oblique
•	Inferior oblique
96
Q

What is adduction?

A

o Adduction- moves towards the midline

97
Q

What is abduction?

A

o Abduction- moves away from the midline

98
Q

At what angle does the lateral rectus insert itself into the eye and what is the consequence of this?

A

o Inserts with an angle of 90 degrees- movement occurs in only one plane

99
Q

At what angle does the superior rectus insert itself into the eye and what is the consequence of this?

A

o Inserts to the eye with angle of 23 degrees- complex movement

100
Q

At what angle does the superior oblique insert itself into the eye and what is the consequence of this?

A

o Passes through the trochlea and inserts into the eye at an angle of approximately 50 degrees-complex movements

101
Q

How does the lateral rectus move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A 
Action: Moves eye laterally
Primary action: Abduction
Secondary action: None
Tertiary action: None
Controlling cranial nerve: Abducens (CNVI)
102
Q

How does the medial rectus move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A 
Action: Moves eye medially
Primary action: Adduction
Secondary action: None
Tertiary action: None
Controlling cranial nerve: Oculomotor (CNIII)
103
Q

How does the superior rectus move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A 
Action: Elevates eye
Primary action: Elevation
Secondary action: In(cyclo)torsion
Tertiary action: Adduction
Controlling cranial nerve: Oculomotor (CNIII)
104
Q

How does the inferior rectus move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A 
Action: Depresses eye 
Primary action: Depression
Secondary action: Ex(cyclo)torsion
Tertiary action: Adduction
Controlling cranial nerve: Oculomotor (CNIII)
105
Q

How does the inferior oblique move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A

Action: Elevates eye and turns it laterally
Primary action: Excyclotorsion
Secondary action: Elevation
Tertiary action: Abduction
Controlling cranial nerve: Oculomotor (CNIII)

106
Q

How does the superior oblique move the eye, what is its primary action, secondary action and tertiary action and by what cranial nerve is it controlled by?

A

Action: Depresses eye and turns it laterally
Primary action: Incyclotorsion
Secondary action: Depression
Tertiary action: Abduction
Controlling cranial nerve: Trochlear (CNIV)

107
Q

What are the different types of eye movements and their primary prupose?

A

• Gaze alignment (keep the fovea on a visual target)
o Saccades
o Smooth pursuit
o Vergence
• Gaze stabilisation (stabilize the eye when the head moves)
o Vestibulo-ocular reflex
o Optokinetic reflex (OKR)

108
Q

What is a saccade?

A

 Sacccade- A rapid, ballistic conjugate eye movements to bring new objects of interest onto the fovea

109
Q

Are saccades voluntary or involuntary?

A

• Eye movements towards a stimulus are voluntary or involuntary (sounds, tactile stimuli, verbal commands, memories of space)

110
Q

How big are saccades?

A

• Most saccades are 15 degrees in size

111
Q

Are saccades always accurate?

A

• Saccades can land on object accurately or overshoot/undershoot in which case a small corrective saccade is required

112
Q

What is the velocity of saccades?

A

• Can have a velocity of 700 degrees/second

113
Q

What is conjugate eye movement?

A

 Conjugate- both eyes move in the same direction

114
Q

What is saccadic suppression?

A

 Saccadic suppression-healthy humans do not perceive the motion of this saccade

115
Q

Describe the saccade refractory period

A

 After a saccade, there is a short refractory period of about 150 ms
• Limits number of saccades that can be done in a given period

116
Q

How long do fixation periods last?

A

200-300 ms

117
Q

Describe Yabus 1960 experiment and findings on saccades and fixation

A

• Fovea fixation
o Looked at saccades performed when a human face is displayed
o Humans tend to fixate on nose, eyes and mouth which are vital in human communication
 Fixation periods lasted from 200-300 ms and movements between fixation points were very rapid
• Saccades for inspecting and planning
o When people look at a painting/scene, people mostly focus on faces

118
Q

Describe the neuroanatomy of saccades

A

• Cell bodies of neurons that send axons to CN III, IV and VI are located in the midbrain and the pons (output)
o Midbrain and pons receive inputs from the superior colliculus, frontal eye fields (which are under the influence of the supplementary eye fields and posterior parietal cortex)

119
Q

What are smooth pursuits eye movement?

A

 Conjugate movements of eye in order to hold the image of a moving target on the fovea

120
Q

Are smooth pursuits eye movement voluntary or involuntary?

A

Involuntary (requires a moving visual stimulus)

121
Q

Are smooth pursuits eye movement ballistic or not ballistic?

A

 Not ballistic

122
Q

Describe the activation of muscles in smooth pursuit eye movement

A

 Both agonist and antagonist muscles are activated

123
Q

What is the velocity of smooth pursuit eye movement?

A

 Velocity of 40-50 degrees/second

124
Q

What is the neural pathway of smooth pursuit eye movement?

A

 Neural control of smooth pursuit movement

• Striate cortex -> MT and MST-> pontine nuclei-> cerebellum-> brainstem

125
Q

What is are vergence movements?

A

 Disconjugate eye movements to adjust for different viewing distances

126
Q

What are disconjugate eye movements?

A

 Disconjugate- both eyes move in opposite directions

127
Q

What are convergent eye movements and what muscles do they engage?

A

 Convergence- both eyes move towards midline, bilateral contraction of medial recti

128
Q

What are divergent eye movements and what muscles do they engage?

A

 Divergence- both eyes move away from midline, bilateral contraction of lateral recti

129
Q

What is the purpose of the vestibulo-ocular reflex and how does it achieve this purpose?

A

o Vestibulo-ocular reflex
 Compensates for rapid head movements
• Not sensitive to slow head movements
 Use vestibular input to hold images stable on the retina during brief or rapid head rotation
• Eyes move in opposite direction to head movement

130
Q

What is the purpose of the optokinetic reflex and how does it achieve this purpose?

A

 Eyes move to reduce image motion
 Sensitive to slow visual motion
 Use visual input to hold images stable on the retina during sustained or slow head rotation
• Repetitive manner- slow movement followed by a fast movement and etc.
o Slow phase is like a smooth pursuit movement
o Fast phase is the return of the eye to the centre of gaze

131
Q

In the LGN, describe which colour vision the parvocellular layer is responsible for

A

 Carries signals for red-green colour vision and for high acuity spatial vision

132
Q

In the LGN, describe which colour vision of the koniocellular layer is responsible for

A

 Adifferent to achromatic changes but strongly respond to short wave (B) sensitivity cone modulation – strong colour selectivity

NEUR3006 (5 decks)

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