in this slide we include the normal development of human vision step by step with advancing age, visual system process, synaptic connections development with age,Measuring performance of babies with various technique,

1. Visual
Development
-Anurag shukla
Fellow optom.
Dr. shroff charity eye hospital ,delhi
1

2. 2
How does the visual system work?
Look at how it develops over time
- what do neonate babies see?
Visual Development
- at what age do various abilities appear?

3. 3
Visual systems:
Basis for conscious vision
-relatively late to develop (2-3 years)
-relatively late to evolve
EyeObject
Lat eral
geniculat e
nucleus
( LGN)
St riat e
cort ex
Geniculo-striate pathway

4. 4
Development of area V1 - synaptic connections
- age 0-8 months: increasing connectivity
.
4
8
12
16
20
0
SynapsesinV1(x1011)
0 3 6 9 12
months
2 7 12
years
30 70
years
inf ancy childhood adult hood

5. 5
Development of area V1 - synaptic connections
- age 8 months - 12 years: neuronal pruning
.
4
8
12
16
20
0
SynapsesinV1(x1011)
0 3 6 9 12
months
2 7 12
years
30 70
years
inf ancy childhood adult hood

6. 6
Development of area V1 - synaptic connections
- age 12-30 years: stable connectivity

7. 7
Development of area V1 - synaptic connections
- age 30+ years: gradual loss (aging)
4
8
12
16
20
0
SynapsesinV1(x1011)
0 3 6 9 12
months
2 7 12
years
30 70
years
inf ancy childhood adult hood

8. 8
Need a way to measure responses to stimuli
- how can babies communicate what they see?
Measuring performance of babies

9. 9
A second visual system:
Basis for eye movements
-relatively early to develop (2-3 months)
-relatively early to evolve
EyeObject
St riat e
cort ex
Tecto-pulvinar pathway
Tect um
( superior
colliculus)
EyeObject
Pulvinar
St riat e
cort ex
Tecto-pulvinar pathway
Tect um
( superior
colliculus)
EyeObject
Pulvinar
St riat e
cort ex
Tecto-pulvinar pathway
Tect um
( superior
colliculus)
Ext ra-
st riat e
cort ex
EyeObject
Pulvinar
St riat e
cort ex
Tecto-pulvinar pathway
Tect um
( superior
colliculus)
Ext ra-
st riat e
cort ex
Frontal eye
fields (FEF)

10. 10
Can use eye movements
- developed by 2-3 months
- tell us what baby is interested in
Measuring performance of babies
Various techniques based on this…

11. 11
1. Habituation/Dishabituation
a. Show baby something blue
c. Show baby something in a different colour
b. Wait until they stop looking
E.g: colour categories are adult-like at 2-4 months
How do we know?
d. See if they start looking again
- babies get bored quickly (habituate)
- stop looking when bored
- start looking again (dishabituate)
when something new is encountered

12. 12
2. Preferential Looking
- babies look most at what they find interesting
a. Show baby something blue, and at the
same time a similar item, but in yellow
b. See if baby looks at one item more
E.g. colour categories are adult-like at 2-4 months
How do we know?
c. If so, then baby can distinguish the colours

13. 13
3. Surprise (startle)
- babies get startled (sometimes frightened)
when something unexpected happens
a. Show baby something blue (in a picture)
b. Suddenly change its colour to yellow
E.g.:colour categories are adult-like at 2-4 months
How do we know?
c. If baby startles, then must have seen
a difference in the colours

14. 14
At birth:
• brightness perception
• red-green color vision
• motion — objects moving around
• looming — objects getting nearer
Stages of increasing neural connectivity
At 1.5 months
• depth via accommodation
• collision avoidance

15. 15
At 2 months:
• perception of familiar objects (face recognition)
- prefer coherent faces over scrambled ones
(same parts, different arrangements)
• perception of blue (tritanopia ends)

16. 16
At 3 months:
• depth via binocular disparity
• depth via vergence
At 4 months:
• depth via motion (kinetic depth)
• biological motion perception
At 5 months:
• depth via pictorial cues (T-junctions)
• relative size

17. 17
At 6 months:
• Gestalt grouping
• size constancy
At 7 months:
• familiar size
• shading cues
-> Most processes in operation at 8 months of age
-> Subsequent development (neuronal pruning)
leads to refinement of visual abilities
- better control of visual attention?

18. 18
What governs the development of vision?
Possibility 1: Innate mechanisms
- people are born with a fixed program
Nature vs. Nuture
- this program unfolds regardless of environment
- cf. Rationalist (Nativist) philosophers
Possibility 2: Environmental influences
- people born only with general ability to learn
- vision results via interaction with environment
- cf. Empiricist philosophers

19. 19
Blakemore — raise kittens in environment with
vertical stripes only
Test 1: Raise observer in deprived visual environment
-> Good at seeing vertical stripes
• edge detectors in striate cortex developed
only for vertical lines, not horizontal ones
What happens when kittens are in normal environment?
-> Bad at seeing horizontal stripes
Need to interact with environment
to develop visual abilities

20. 20
Note 1: For normal development, must have exposure
to environment during critical period
Cannot recover ability later.
Note 2: This can happen to humans, too
-> e.g., astigmatism
- focusing of astigmatic lens is imperfect
-> some orientations not perceived well
Correction must be done in infancy
- child will not recover if done later

21. 21
Gregory — S.B.
- vision in early childhood; blind afterwards
- given corneal transplant in adult life
What about higher-level activities?
(e.g., object perception)
-> No
Could S.B. recognize objects by sight?
-> Needed extensive interaction
with objects before he could
recognize them visually
(could always recognize them by touch)

22. 22
Stratton — goggles invert incoming image
(i.e., flip it upside down)
Test 2: change the visual environment
-> Yes!
Can observer learn to adapt to this switch?
-> Although it can take several days…
Need to interact with environment
to get correct adaptation

23. 23
Note 1: Animals do not adapt so easily
- amphibia, chickens never adapt
- only humans and monkeys?
Development of visual system involves both
innate (genetic) and environmental factors
Note 2: Limits to human adaptation
- good (but not perfect) adaptation to
shifts, inversions, rotations
- unable to adapt to time delays
-unable to adapt to remappings of colour
(e.g., photographic negative)

24. Thank you !
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