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Psychophysics H > Normal visual development > Flashcards

Normal visual development Flashcards

1
Q

what key aspects of vision improve during post-natal life & over what time-scales?

A

every aspect of vision improves, some slower/faster than others

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2
Q

why is it hard to accurately assess visual abilities of pre-verbal infants & early literate children

A

because we cannot ask them to do things, and they cannot respond to us by speaking

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3
Q

what are the 2 methods of examining pre-verbal infants

A
  • behaviour: forced choice preferential looking

- physiology: visually evoked potentials (by putting electrodes on scalp)

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4
Q

what method will you use to examine older literate children and what will this assess

A

subjective methods: picture matching/naming & letter reading to assess visual acuity

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5
Q

what general problems can you have with the subject with monitoring vision in young children

A
  • attention (short attention span so cannot do long tests)
  • co-operativity
  • variability
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6
Q

what general problems can you have with the method, when monitoring vision in young children

A

different stimuli - different responses from the same individual

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7
Q

what is usually the visual stimulus of a forced choice preferential looking test

A

gratings of high contrast and of a particular spatial frequency

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8
Q

what can you change in a forced choice preferential test grating to work out the visual acuity of a pre verbal infant

A

changing the spatial acuity & contrast acuity of the gratings

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9
Q

how does the observer see which grating the pre verbal infant looks towards, in a forced choice preferential looking test

A

a hole in the middle is where the observer looks to see which direction the child looks i.e. whats their attention attracted by

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10
Q

what will the child most likely look at in a forced choice preferential looking test

A

the grating that stands out more

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11
Q

what is used and where with a visually evoked potential method of examining pre-verbal infants

A

electrodes placed on the baby’s head

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12
Q

what stimulus is used and how is it used during the visually evoked potential method of examining a pre-verbal infant

A

high contrast patterns which are turned on and off or you can change the spatial phase

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13
Q

what happens when changing the spatial phase of a stimulus during visually evoked potential test

A

it becomes a contrast reverse called pattern reversal, and this will activate a lot of neurons

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14
Q

list 3 different tools used for subjective methods of examining vision as a child gets older

A
  • cardiff acuity cards
  • kay pictures
  • lea symbols (cards used as a substitute for Logmar chart)
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15
Q

what state is spatial vision of a human at birth

A

i.e. acuity, is poor

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16
Q

what is a humans visual acuity (spatial vision) equivalent to at birth

A

6/180 at best

more commonly 6/240

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17
Q

what is a humans grating resolution (spatial vision) equivalent to at birth

A

very low ~/

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18
Q

what is the state of a humans binocular depth vision at birth

A

it is absent i.e. no stereo acuity

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19
Q

what is the result of a humans having no binocular depth vision at birth

A
  • eyes not aligned (exo-deviation)
    &
  • eye movements are uncoordinated (vergence is not present/no orthotropia)
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20
Q

for what 2 reasons is a humans contour & object perception limited at birth

A
  • ‘cardinal’ horizontal & vertical axes present but obliques are not (takes about 6 months to develop and become visible)
  • large refractive errors is associated with image blur
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21
Q

describe how neonates view other humans

A

a blurred 2D image with no spatial detail (e.g. to the face) and no appreciation to depth

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22
Q

which aspects of vision improve markedly and how quick, from birth

A
  • spatial acuity
  • binocular depth perception
  • object vision
    all improve during 1st year of post-natal life
    but further improvements continue for many years after, maybe into early teens before visual system is adult like & mature
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23
Q

what is the average powers of the cornea and lens at birth

A

55D & 34D

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24
Q

what is the average powers of the cornea and lens at 1 years old

A

44D & 28D

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25
Q

what is the average powers of the cornea and lens at 5 years old

A

43D & 25D

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26
Q

what is the average axial length at birth

A

17mm

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27
Q

what is the average axial length at 1 years old

A

20mm

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28
Q

what is the average axial length at 5 years old

A

23mm

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29
Q

what is the average refractive error and mean ± standard deviation at birth

A

+2.5D ±2.75 standard deviation

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30
Q

what is the range of refractive error with a 95% confidence limit at birth

A

-6 - +8 D 95% confidence interval that a baby will have a range of 14D or refractive error at birth

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31
Q

what does the reduction in power of the cornea and lens, years following birth indicate

A

that refractive error reduces and becomes close to adult levels by the age of 5

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32
Q

by how much does astigmatism reduce from birth up till 1 years old

A

reduces from 20 - 30% at birth to 10% at 1 year

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33
Q

what is the average refractive error and mean ±SD at 1 years old

A

+1.5D ±2.0 SD

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34
Q

what is the average refractive error and mean ± SD at 5 years old

A

+1D ±1.6 SD

35
Q

which type of refractive error is more bias towards at birth

A

long-sightedness

36
Q

what type of range is the refractive error for a new born

A

wide range from -6D to +9D and a peak of +2D to +3D

37
Q

what does the result of CSF for babies ages 1,2&3 months old show from a 2AFC preferential looking test

A

at 1 month = 0.5 cpd and cut off of 2 cpd (low spatial frequencies) which dont get much better at 2 or 3 months old, so only low spatial frequencies at high contrast is visible at these ages

38
Q

what is the average grating acuity (visual acuity) of a 6 month old infant and what range is their grating acuity with a 95% confidence limit

A

average grating acuity = 6 cpd ~6/36 snellen equivalent

range = 6/120 - 6/24 from 95% confidence limit = large range

39
Q

on average how long does it take for a child to reach adult like acuity

A

till 8/9 years old

40
Q

explain how you can set up a test using forced choice preferential looking to assess the development of binocular depth perception & stereo acuity

A
  • done by TNO test (red & green filters used)
  • give patient a random stereogram with red & green dots
  • put items of left and right side of the screen either side of the hole
  • whilst practitioner is looking through hole
  • one image has disparity and other doesn’t
  • if disparity is crossed = child is able to detect it i.e. the image on the screen will appear nearer to them
41
Q

in comparison to what other type of acuity, is the development of stereo acuity much quicker than

A

visual acuity

42
Q

by what age does it take for a 100% of this population group to develop binocularity: fusion & stereo acuity

A

50%

43
Q

by what age does it take for a 100% of this population group to develop binocularity: fusion & stereo acuity

A

6 months

44
Q

how much % of 3-4 month year olds develop adult like binocularity: fusion & stereo acuity

A

50%

45
Q

what is the criterion of adult like stereopsis

A

1 min or 60 sec of arc (so to detect a disparity of 60 sec of arc)

46
Q

although it is normal for a 4 month year old to have adult like stereo acuity, what else is normal and why

A

for a 4 month old baby to have no stereo vision as stereo vision can be rapidly developed up to adult stereo within a few weeks, so if one baby of the same age has adult like stereo acuity and another baby does not, it is only a matter of weeks that that baby can develop adult like stereo acuity = there is a big range

47
Q

what is improved stereo acuity associated with

A

improved depth perception in real world 3D situations

48
Q

what is a behavioural test for testing depth perception in real world 3D situations on babies called

A

visual cliff, using disparity & texture grating to work out stereo & depth of things

49
Q

what does forced choice preferential looking studies show about faces with new born babies and what does this mean

A

images of what looks like a human face are ‘preferred’ stimuli compared to simple geometric form or other complex objects, however there is little preference for real verses schematic face (e.g. scrambled version of human face) stimuli even at 6 months of age, so tendency for parents to believe their baby recognises their face is wishful thinking, face recognition is a slow process

50
Q

up to what age does the foveal pit appear and mature

A

age 4-5 years

51
Q

how does the foveal pit form from birth up till the age of 4/5 years

A

inner cells migrate out: pushing inner retinal layers aside

52
Q

where do the cones migrate whilst the retina forms from birth whilst neural development in the visual system and what happens to the cones as a consequence

A

cones migrate in: increasing density & segment length

53
Q

what happens to the primary visual pathways as neural development in the visual system and up to which age does this fully develop

A

axon myelination, up to 2 years old

54
Q

what happens to the primary visual pathways as neural development in the visual system and up to which age does this fully develop

A

axon myelination, up to 2 years old

55
Q

what does the development of axon myelination improve

A

impulse conduction & reliability

56
Q

list 3 things that occur as part of neural development in the visual system in the LGN & primary visual cortex, and state up till what age it is fully developed

A
  • cell growth & synaptic connectivity - age 8 years+
  • geniculo-cortical connections by ~6 months
  • intra-cortical connectivity more prolonged refinements
57
Q

as a result of an undeveloped foveal pit in neonates, what things are present and not present at the fovea as a result of this

A
  • not many foveal cones
  • cells of the INL present
  • bipolar, amacrine and horizontal cells present
  • inner 5 layers yet to be pushed aside
  • RGCs still present, yet to be pushed aside
    all these result in light scatter at the fovea
58
Q

where do the cones migrate whilst the retina forms from birth whilst neural development in the visual system and what happens to the cones as a consequence

A

cones migrate in (towards foveal pit): increasing density & segment length

59
Q

what aspect of the cones does not change from birth, throughout life

A

average width of cones

60
Q

what 3 aspects of cones do change from birth, throughout life and state by how much

A
  • cone outer segment length increases from: 3um (at birth) to 45um (5 years old) by a factor of x15
  • inter-cone spacing decreases from: every 2.1 mins arc (at birth) to 0.3 mins arc (5 years old) by a factor of x-7
  • cone density increases from: 36,000 per mm2 (at birth) to 108,000 per mm2 (at 5 years old) by a factor of x3
61
Q

as a result of an undeveloped foveal pit in neonates, what things are present and not present at the fovea as a result of this

A
  • not many foveal cones
  • cells of the INL present
  • bipolar, amacrine and horizontal cells present
  • inner 5 layers yet to be pushed aside
  • RGCs still present, yet to be pushed aside
    all these result in reduced light scatter at the fovea
62
Q

what improvement is made as a consequence of increasing cone outer segment length

A

means more discs and more rhodopsin, so this increases light sensitivity

63
Q

what improvements are made as a result of decreased inter-cone spacing and increased cone density

A

increased image sampling & acuity

64
Q

what impact does loads of cones packed together & hardly any space between them have on fine grain spatial details

A

if you stick a high spatial frequency grating over the fovea, there will be a cone somewhere to pick up the difference between light & dark region of the sine wave, results in high resolution acuity found in adults

65
Q

what impact does fewer cones and larger gaps between them have on fine grain spatial details

A

if you stick a high spatial frequency grating over the fovea, bits of the grating are going to fall into spaces in-between the cones, so no cones can detect it & it become invisible, results in low resolution acuity found in infants

66
Q

upto which age is va’s predicted from the foveal development worse than expected and why

A

upto 2 years

because the visual cortex is still immature to receive & interpret signals

67
Q

unto which age is va’s predicted from foveal development better than expected any why

A

upto 4 years onwards

because cortical factors also contribute to see fine detail as we have hyper acuity hence va’s improve

68
Q

what anatomical changes occur during visual cortex development

A
  • inputs from the LGN to layer 4c are present from birth but an increased myelination and hence impulse conduction speed & reliability
  • as we increase in age, dendritic growth & synaptic numbers increase (x2-3) to a maximum at ~6 months, then decrease as they are functionally refined (get killed off) till 8 years old where adult density is acquired
69
Q

what does the amount of refinement, i.e. killing off of density of dendrites & synaptic numbers in the visual cortex depend on

A

visual experience i.e. vision drives the synapses that you want to keep e.g. development of binocular stereo vision parallels with increasing synaptic input in v1 = strong correlation (but no evidence they’re related)

70
Q

list the 3 functional changes from vep recordings occur during visual cortex development

A
  • latency of early LGN-dependent (P1) wave reduces by ~1 msec/day, until ~6 months
  • later positive (P2) & negative (N1) waves, which depend on intra-cortical processing appear
  • latencies reduce, amplitudes increase as synaptic activity becomes more reliable & synchronised
71
Q

what anatomical changes occur during visual cortex development

A
  • inputs from the LGN to layer 4c are present from birth but an increased myelination and hence impulse conduction speed & reliability
  • as we increase in age, dendritic growth & synaptic numbers increase (x2-3) to a maximum at ~6 months, then decrease as they are functionally refined (get killed off) till 8 years old where adult density is acquired
  • at the dendrites is where synaptic input of neurons is applied, so the number of synapses goes up the more dendrites there are
72
Q

what is the P1 wave in vep recordings called, and where is it believed to be generated from

A

positive first wave

generated from geniculo-cortical input i.e. axons that go to layer 4c

73
Q

what is the P2 wave in vep recordings called, and where is it believed to be generated from

A

later positive wave

generated from intra-cortical processing (what happens after the geniculo cortical input)

74
Q

what is the N1 wave in vep recordings called, and where is it believed to be generated from

A

negative wave

generated from intra-cortical processing (what happens after the geniculo cortical input)

75
Q

what is present in a vep recording for a child of up to 3 months old

A

p1 wave is the only component to the vep

76
Q

at what latency is the p1 wave in the vep recordings of a child of up to 3 months old and why

A
  • long latency of 150-200 msec post stimulus,

- as myelination hasn’t been completed so impulse conduction is not quick

77
Q

what does the peak/amplitude of a wave e.g. p1 in a vep recording depend on

A

synchronous activity = if can get all the neurons to fire at once, this results in a big wave, and if hey fire at different times, then the amplitude is flat

78
Q

what does the peak/amplitude of a wave e.g. p1 in a vep recording depend on

A

synchronous activity = if can get all the neurons to fire at once, this results in a big wave, and if hey fire at different times, then the amplitude is flat

79
Q

what changes occur in a vep recording of a human from 3 months onwards

A
  • p1 latency continues reducing now becomes 100 msec post stimulus
  • later n1 & p2 waves appear
80
Q

what 2 things does the development of a reduced p1 latency and the addition of n1 and p2 waves improvement result in

A
  • good for disparity detection &

- orientation selectivity

81
Q

what is present in a vep recording for a child of up to 3 months old and what does this mean

A

p1 wave is the only component to the vep so it only has a +ve flowing deflection which means input from the LGN to v1 cortex is working

82
Q

what 2 things does the development of a reduced p1 latency and the addition of n1 and p2 waves improvement result in for humans 3 months onwards

A
  • good for disparity detection &

- orientation selectivity

83
Q

what does the ‘nature’ mechanism of normal development mean

A

the brain & behaviour are products of our genes & the proteins they express (nativists)
- that is we’re hard wired depending on our genetic background e.g. gene mutation in albinism

84
Q

what does the ‘nurture’ mechanism of normal development mean

A

the brain & behaviour are products of the environment to which we are exposed (empiricists)
e.g. experience of the visual world

Psychophysics H (11 decks)

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