PERCEPTUAL DEVELOPMENT

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PERCEPTUAL DEVELOPMENT

• Focus on visual perception because we know more
  than other areas of perception
• Also, a major source of new information is visual
• Most major changes occur in the first year of life

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PERCEPTUAL DEVELOPMENT

• We will discuss
• Methods
• Visual Acuity
• Color and Depth Perception
• Pattern and Object perception
• Selective Attention (?)

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Methods

• Infants do not talk so are not able to tell us
  what they see
• Must develop methods to assess what they are
  seeing

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Methods

• Looking Paradigms
• Preferential Looking
• Present two stimuli simultaneously
• Measure the infants preference for one or the
  other stimulus - percentage of total time looking
  at one or the other

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Methods

• Preferential Looking
• Requires a spontaneous preference on the part of
  the infant
• Example Visual Acuity

40
60
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Methods

• Looking
• If infant does not have a spontaneous preference
• Infant tends to look at a novel stimulus over a
  familiar

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Methods

• Habituation
• Familiarize to one stimulus and test with a
  different one
• Measure looking time to stimulus during
  habituation and test

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Methods

• Habituation
• If infant can discriminate test from familiar
  they should dishabituate

change stimulus
dishabituation
habituation
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Methods

• Novelty-Preference
• Has components of preferential looking and
  habituation
• Familiarize to initial stimulus like in
  habituation
• Test is similar to preferential looking

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Methods

• Habituation
• Familiarize to criterion - 50 decrease in
  looking
• 1 stimulus presented at test
• Compare test performance to pre-test performance
• Novelty-Preference
• Present number of familiarization trials
• 2 stimuli presented at test -- Novel Familiar
• Compare test performance of each stimulus to each
  other

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Methods

• Visual Scanning and Eye Movements
• Where the infant is looking
• How fast the infant looks

Salapatek (1968)
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Methods

• Reaching
• Mostly used in depth perception studies
• Infants will reach for the nearer of two objects
• Visual Evoked Potentials (VEP)
• Electrodes are placed on infants head
• First, present grey field
• Then present pattern
• Get response if can discriminate pattern

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Basic Visual Functioning Visual Acuity

• Tested with preferential looking and VEP
• VEP gives better acuity measures than looking
• Trend is the same, however

Preferential Looking
Adult
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Basic Visual Functioning Visual Acuity

• Tested with preferential looking and VEP
• VEP gives better acuity measures than looking
• Trend is the same, however

VEP
Adult
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Basic Visual CapacitiesVisual Acuity

• Acuity levels off after 6 mos. and reaches adult
  level by 1 year

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Basic Visual Functioning Acuity

• What accounts for their development?
• Cone density in fovea is 1/3 of adults
• Cone length is 1/10 of adults

1 mo cone density
6 mo cone density
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Color Perception

• Contrary to myth, newborns see color
• Preferential looking experiment with 1- to
  5-day-olds
• Colors were either red, green, yellow, or blue

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Color Perception

• Newborns could see red, yellow, and green
• Newborns could not see blue
• Adult-like color perception develops by 3 - 4
  months of age

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Depth Perception

• Binocular Cues
• Young infants have difficulty coordinating the
  two eyes early on
• Binocular Disparity
• Aslin - moved a target between a near (12 cm) and
  a far point (57 cm)
• Found that some binocular fixation occurs at 1
  and 2 months
• Reliable fixation does not occur before 3 months

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Depth Perception

• Richard Held measured infants preferential
  looking to one stimulus that had depth and one
  that did not.

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Depth Perception

• If infants can see the binocular disparity, then
  will look longer at stimulus on the left
• Found that infants do not use disparity until
  approximately 3.5 months

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Depth Perception

• Monocular Cues
• Interposition (or occlusion) One object is in
  front of another and occludes part of the one
  behind
• Size Objects that are closer appear larger

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Depth Perception

• Granrud Yonas
• Used a reaching paradigm and the stimuli
  interposed and not interposed
• If infants can use interposition, then should
  reach for interposed more than non-interposed

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Depth Perception

• Granrud Yonas
• Found that 7-month-olds but not 5-month-olds
  reached for the occluded display (a)

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Depth Perception

• Size - Granrud, Hoake, Yonas
• Used reaching
• The member of the test pair that is larger than
  in familiarization should be perceived as closer

Familiarize
Test
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Depth Perception

• Size - Granrud, Hoake, Yonas
• Used reaching
• Found that 7-month-olds but not 5-month-olds
  reached for the apparently closer object

Familiarize
Test
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Object Perception

• Illusory Contours

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Object Perception

• Bertenthal, Campos, and Haith - used habituation
• Found that 7-month-olds but not 5-month-olds
  dishabituated to a change between illusory and
  non-illusory

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Object Features and Feature Relations

• When do infants see a whole form?
• Salapatek measured infants visual scanning of
  triangles

1-month-old
2-month-old
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Pattern, Shape, Object Perception

• When do infants perceive whole forms?
• Cohen Younger (1984), using habituation, tested
  line orientation versus overall form
  discrimination

Change Orientation Test
Habituate
Change Form Test
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Pattern, Shape, Object Perception

• Found that 6-week-olds discriminate an
  orientation but not a form change
• 3-month-olds discriminate a form change

Change Orientation Test
Habituate
Change Form Test
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Object Perception

• Do infants perceive unitary objects?
• Kellman Spelke (1983)

Habituate
Unitary Object Test
Two Object Test
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Object Perception

• 4-month-olds perceive a unitary object, but only
  when the rod moved

Habituate
Unitary Object Test
Two Object Test
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Pattern, Shape and Object Perception

• Summary
• 2-month-olds could see the whole form
• 3-month-olds perceived a whole form
• 4-month-olds perceived a whole form even when
  they could not see the whole form