Change Blindness 1. Intentional Search for Change

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Visual Development
How does the visual system work?
Look at how it develops over time
- what do neonate babies see?
- at what age do various abilities appear?
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Visual systems
Basis for conscious vision -relatively late to
develop (2-3 years) -relatively late to evolve
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Development of area V1 - synaptic connections
- age 0-8 months increasing connectivity
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Development of area V1 - synaptic connections
- age 8 months - 12 years neuronal pruning
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Development of area V1 - synaptic connections
- age 12-30 years stable connectivity
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Development of area V1 - synaptic connections
- age 30 years gradual loss (aging)
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Measuring performance of babies
Need a way to measure responses to stimuli -
how can babies communicate what they see?
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A second visual system
Basis for eye movements -relatively early to
develop (2-3 months) -relatively early to
evolve
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Measuring performance of babies
Can use eye movements - developed by 2-3
months - tell us what baby is interested in
Various techniques based on this
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1. Habituation/Dishabituation
- babies get bored quickly (habituate) - stop
looking when bored - start looking again
(dishabituate) when something new is
encountered
E.g., colour categories are adult-like at 2-4
months
How do we know?
a. Show baby something blue
b. Wait until they stop looking
c. Show baby something in a different colour
d. See if they start looking again
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2. Preferential Looking - babies look most at
what they find interesting
E.g., colour categories are adult-like at 2-4
months
How do we know?

• Show baby something blue, and at the
• same time a similar item, but in yellow

b. See if baby looks at one item more
c. If so, then baby can distinguish the colours
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3. Surprise (startle) - babies get startled
(sometimes frightened) when something
unexpected happens
E.g., colour categories are adult-like at 2-4
months
How do we know?

1. Show baby something blue (in a picture)

b. Suddenly change its colour to yellow
c. If baby startles, then must have seen a
difference in the colours
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Stages of increasing neural connectivity
At birth
brightness perception red-green color
vision motion objects moving around looming
objects getting nearer
At 1.5 months
depth via accommodation collision avoidance
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At 2 months
perception of blue (tritanopia ends)
perception of familiar objects (face
recognition) - prefer coherent faces over
scrambled ones (same parts, different
arrangements)
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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
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At 6 months
Gestalt grouping size constancy
At 7 months
familiar size shading cues
-gt Most processes in operation at 8 months of age
-gt Subsequent development (neuronal
pruning) leads to refinement of visual abilities
- better control of visual attention?
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Nature vs. Nuture
What governs the development of vision?
Possibility 1 Innate mechanisms
- people are born with a fixed program
- 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
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Test 1 Raise observer in deprived visual
environment
Blakemore raise kittens in environment
with vertical stripes only
What happens when kittens are in normal
environment?
-gt Good at seeing vertical stripes
-gt Bad at seeing horizontal stripes
edge detectors in striate cortex
developed only for vertical lines, not
horizontal ones
Need to interact with environment to develop
visual abilities
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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 -gt
e.g., astigmatism
- focusing of astigmatic lens is imperfect -gt
some orientations not perceived well
Correction must be done in infancy - child
will not recover if done later
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What about higher-level activities? (e.g.,
object perception)
Gregory S.B. - vision in early childhood
blind afterwards - given corneal transplant in
adult life
Could S.B. recognize objects by sight?
-gt No
-gt Needed extensive interaction with objects
before he could recognize them visually
(could always recognize them by touch)
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Test 2 change the visual environment
Stratton goggles invert incoming image (i.e.,
flip it upside down)
Can observer learn to adapt to this switch?
-gt Yes!
-gt Although it can take several days
Need to interact with environment to get
correct adaptation
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Note 1 Animals do not adapt so easily -
amphibia, chickens never adapt - only humans
and monkeys?
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)

Development of visual system involves both
innate (genetic) and environmental factors