Lecture 1: Visual Development

Question 1

What do babies see?

Answer 1

• Until a few decades ago, it was assumed that infants’ vision was almost non-existent and barely functional
• This is wrong
  *From birth, babies visually scan environment and pause to look at stuff
• Sowhat exactly can they see?
  *Can’t ask babies so have to get creative

Question 2

What are the 2 main methods in infant research?

Answer 2

1) Preferential looking paradigm
2) Habituation paradigm

Question 3

Preferential Looking Paradigm

Answer 3

• Assesses infants’ preference for one stimulus over another
• Present the baby with 2 stimuli beside each other at the same time
• If the baby looks longer at one stimulus than the other, it means that:
  
  1. they can distinguish between the two
  2. have a preference for one over the other

Since kids cannot point until 6 month - how do they assess where they are looking? Eye tracking device

Question 4

What is interesting to infants?

Answer 4

*Infants prefer to look at stimuli that are:
*More complex (details), more saturated (brighter) in colour
*Familiar

Question 5

Habituation Paradigm

Answer 5

• Paradigm takes advantage of babies’ natural preference for novelty
• Assesses infants’ ability to discriminate between stimuli
• Habituation phase: repeatedly present infant with a stimulus until they habituate to it
  - Reduced or stopped response to a stimulus
  - e.g., looks at it less
  - Wait for infant to get bored

Question 6

Habituation phase test

Answer 6

Test: Present habituated, “old” stimulus with a new stimulus:
* Dishabituation: If the baby shows greater interest in/looks longer at the new stimulus, they can tell the difference between the two
* If the baby looks at stimuli equally, they can’t tell the difference between stimuli

Question 7

Familiarity vs Novelty

Answer 7

• In general, infants show a preference for familiar stimuli
• But, Prolonged/ repeated exposure to a stimulus will cause infants to shift their preference to a novel stimulus (prefers novelty, ONLY if it gets bored of something first)

Question 8

Summary of the 2 methods in infant research

Answer 8

**Preferential-looking paradigm: **
*2 stimuli presented side-by-side
*Assesses an infants’ preference for one stimulus over another
*Prefer familiar and/or complex stimuli

**Habituation paradigm: **
*Infant presented with a stimulus many times until they get bored of it (habituation) and on the test trial, presented with this old stimulus beside a new, different stimulus
*Assesses an infants’ ability to distinguish between 2 stimuli
*Prefer novel stimuli as indicated by greater looking time (dishabituation)

Question 9

Visual Acuity

Answer 9

• Sharpness of visual discrimination
• Assessed by using preferential looking paradigm
• Infants presented with a succession of paddles with increasingly narrower stripes and narrower gaps between them until infant can no longer distinguish between stripped paddle and plain gray one.

Starts with thickest stripes vs grey…pass…move on to thinner stripes vs grey…until baby no longer can tell the difference between grey paddle and stripped one.

Question 10

Visual acuity at birth

Answer 10

*At birth, infants have poor visual acuity
- prefer to look at patterns with high visual contrast
- don’t discriminate between stimuli with lower contrast sensitivities

8-10 inches of distance they can see (same distance of baby - mother when breast feeding).

Question 11

Why do infants have poor visual acuity?

Answer 11

*Due to immaturity of cone cells in infants’ retinas
*Cone cells: light sensitive neurons involved in seeing fine details and colours (underdeveloped)
*8 months: adult-like visual acuity

Question 12

Colour Perception

Answer 12

• At birth: infants see in gray scale
• 2 months: colour vision appears (red is the first colour an infant can see)
• 5 months: adult-like colour perception
  * Due to maturity of cones and visual cortex (maturity of visual cortex plays a role)
  * Can discriminate between colour categories and between hues of the same colour

Question 13

Visual Scanning

Answer 13

• From birth: infants scan their visual environment and pause to look at something
  *BUT trouble tracking moving stimuli because eye movements are jerky
  *4 months: able to smoothly track moving objects if moving slowly
• 8 months: adult-like visual scanning; can smoothly follow objects
  *Improved visual scanning due to brain maturation
  *The ability to visually scan is important because one of the few ways that infants have control over what they observe and learn

Visual sense is the least developed at birth.

Question 14

Face Perception

Answer 14

• Babies often choose to look at faces (they love faces)
• Faces are also important for language (looking at mouth)
• Newborns show a preference for faces or face-like stimuli vs. non-face like stimuli

Question 15

Why are infants drawn to faces? (2 hypothesis)

Answer 15

• Special innate face perception mechanism?
• Hypothesis #1:
  
  • already born with innate, highly specialized area (Fusiform Face Area) that is preprogrammed to look at faces.
• Hypothesis #2: Infants have a general bias for stimuli that are more “top heavy” vs. “bottom-heavy”
  *Preferential looking paradigm to test this hypothesis
  *Showed babies:
  -regular faces
  -upside-down faces
  -scrambled, top-heavy faces
  -scrambled, bottom heavy face

Question 16

Why are infants drawn to faces? Testing the hypothesis

Answer 16

*If faces are special, babies should always prefer to look at upright face
*If general bias for top-heavy stimuli, babies should prefer upright face AND scrambled top-heavy faces

Question 17

Why are infants drawn to faces? Results

Answer 17

*Preference for upright face over upside-down face
*Preference for top heavy scrambled face vs. bottom heavy scrambled face
*Suggests that preference for faces simply result of general preference for stimuli that are “top-heavy” rather than “bottom-heavy

Question 18

Why are infants drawn to faces? Best out of the 3 tests

Answer 18

Best test: the 3rd example is the best test because both examples are top-heavy.
- if baby prefers face, it suggests hypothesis #1
- if baby shows no preference, it suggests hypothesis #2

Suggests that preference for faces simply result of general preference for stimuli that are “top-heavy” rather than “bottom-heavy

Question 19

Seeing Mom’s Face

Answer 19

• Infants very quickly learn to recognize and prefer their own mother’s face
• Just a few days after birth, babies prefer their mother’s face compared to another woman’s face
• Other ways of knowing its their mom:
  - sense of smell (more developed than vision)
  - voice (because was in eutero for so long, recognizes voice).
  - Infants spend lots of time in mom’s arms/with mom.

Question 20

When do infants become a Face Specialist

Answer 20

• Over 1st year of life, infants’ become face specialists
  *Better at distinguishing between faces that are frequently experienced in their environment
  *Worse at distinguishing between faces that they encounter less frequently

Question 21

Other-Race-Effect in Infants

Answer 21

• Other-race-effect: People find it easier to distinguish between faces of individuals from their own racial group than between faces from other racial groups (considered an exposure effect)

Also evident in infants:
* Researchers recruited Caucasian, Black, and Chinese infants
* Habituated infants to:
- Face from their own race OR
- Face from another race
* Then presented habituated face with a new face from the same race
* Can infants distinguish between the two faces?

Question 22

Other-Race-Effect in Infants (results)

Answer 22

Results:
*3 month olds: easily distinguish between faces of all races
*9 month olds: better at distinguishing between faces of own race
(up to a certain age, no problem distinguishing)

*Not innate, but rather exposure effect:
* During the first few months of life, 96% of faces that babies are exposed to are females from their own race (Sugdenet al., 2014)
* If infant is equally exposed to faces of different races, will not show other-race-effect
* Initially, babies have an easier time distinguishing between female faces rather than males due to exposure effect.

Question 23

Perceptual Narrowing

Answer 23

*Tuning of perceptual mechanisms to the specific sensory inputs that infants encounter in their daily life
*Improves perception of stimuli encountered often (females, races)
*Decline in the ability to distinguish stimuli that are not present in the infant’s environment
*Present for several perceptual domains
*Result of synaptic pruning

Question 24

Synaptic Pruning

Answer 24

Elimination of synapses to increase the efficiency of neural communication
* Follows “use it or lose it” principl

Question 25

Synaptogenesis

Answer 25

Formation of synapses between neurons
* Rapid synaptogenesis right after birth
* Results in hyper-connectivity in the brain
* Some synapses MUST be pruned for development to move forward

Question 26

Synaptic Pruning across Domains

Answer 26

Timeline for synaptogenesis and synaptic pruning varies for different parts of the brain.

Question 27

Face perception in children with ASD

Answer 27

*People with autism spectrum disorders (ASD) often have difficulty with face perception, e.g., prefer to not look at eyes
*Toddlers with ASD preferred looking at geometric shapes over pictures of people
* Opposite for typically developing kids (preference for people rather than geometrical shapes)

*Infants’ preference for non-faces could be an early indicator that the infant will later be diagnosed with ASD
* early markers for autism disorder: struggling with face perception

Question 28

Summary of Face Perception

Answer 28

• From birth, infants have a preference forfaces, especially their mother’s face
• Face preference is not innate but rather a result of general preference for top-heavy stimuli
• 9 months: Infants become face specialists as a result ofperceptual narrowing
  - Other-race effect in infants

Question 29

Perceptual Constancy

Answer 29

• The perception of objects as being constant in size, shape, colour. etc in spite of physical differences in the retinal image of the object
• Smaller retinal image is smaller but we understand that it is not shrinking (we know its just dept changing)

Question 30

Perceptual Constancy in infants

Answer 30

Study: Is perceptual constancy present from birth?
* Habituation paradigm with newborns:
* Habituation: Repeatedly show infant a small cube
- Cube shown at different distances on each trial (black + white cube over and over again - each trial show cube at varying distance).
- i.e., retinal image changed from trial to trial
- Do infants perceive these as the same object or as different objects?
* Test: Show infant the original, small cube and an identical larger cube
* Larger cube farther away so that both cubes projected the same-size retinal image

- Does it prefer to look at new cube = understand it is different cube - Should be creating same size retinal issue

Question 31

Perceptual constancy in infants: results

Answer 31

Results:
* Infants looked longer at the larger but further away cube
* Indicates that they see it as different in size from the original, smaller cube
* Means that infants saw the repeated presentations of the original, small cube as a single object of a constant size, even though the retinal image varied

• Suggests that perceptual constancy is present from birth

Question 32

Object Segregation

Answer 32

• The ability to identify that objects are separate from each other (by using colours, or movement)
• Movement is an important cue
  - Separate objects move independently of each other

Question 33

Object segregation in infants

Answer 33

• Habituation paradigm with newborns and 4 month olds
• Habituation: Repeatedly watched video of a rod moving side-to-side behind a box
  
  • Do infants see the rod as a single rod or as 2 separate short rods?
• Test: Shown 2 rod stimuli moving side-to-side
  *One rod vs. a broken rod

Question 34

Object segregation in infants. Results?

Answer 34

Results:
*4 month olds: Preferred to look at the broken rod
* Indicates that they understood that the rod behind the box is one object

*Newborns: Looked the same amount of time at broken rod and single rod
* Indicates that did not understand that rod behind the box was a single object
* However, newborns have a hard time tracking moving objects at this time (still not developed): so this might be why they struggled.

*Suggests that object segregation is not innate, has to be learned with experience
* Also relies on improvements in visual scanning
* Not innate, relies on experience.

Question 35

Depth Perception

Answer 35

*Binocular disparity: Difference between the retinal image of an object in each eye that results in two slightly different signals being sent to the brain
* Visual cortex combines the differing neural signals caused by binocular disparity
* Depth perception relying on binocular disparity is present at 4 months old (before this infants have a poor understanding of depth)

Question 36

Sensitive Period for Binocular Vision

Answer 36

Sensitive period: a biological period during which certain kinds of experiences are necessary for an ability to develop normally
Sensitive period for binocular vision: From birth to age 3
* Depth perception from cue of binocular disparity is a natural result of brain maturation as long asthe infant receives normal visual input from both eyes
* If infants do not receive normal binocular visual input until age 3, they may fail to develop normal binocular vision and have life-long difficulties with depth perception
* Visual input from both eyes constantly = develop normally

Question 37

Depth Perception

Answer 37

*Monocular depth cues: depth cues perceived with one eye
* e.g., relative size or overlap
* Perceived at 6 months old
* Assessed using visual cliff
- 6 month olds will not crawl over visual cliff but younger children will
* Suggests that this aspect of depth perception needs to be developed through experience
* Also relies on improvements + maturity in visual acuity

Question 38

Visual Cliff

Answer 38

• Table (one side painted, one side clear and look like a drop)
• Do they show fear? not when young, not aware of the cliff
• After a month after crawling, will not crawl.

Question 39

Visual Development Timeline

Answer 39

• At birth: rudimentary visual scanning, poor acuity, preference for high contrast, gray scale, preference for faces vs. non-faces, perceptual constancy
• 2 months: colour vision appears
• 4 months: object segregation and binocular depth perception appear
• 5 months: adult-like colour perception
• 6 months: face generalists, monocular depth perception appears
• 8 months: adult-like visual scanning and visual acuity
• 9 months: face specialists through perceptual narrowing
• Some visual abilities are native but refined and specialized with experience

Question 40

The Nature and Nurture of Visual Development

Answer 40

Innate: Perceptual constancy and preference for top-heavy stimuli
Improve with brain maturation: visual acuity, colour perception, and visual scanning
Experience dependent processes:
* Object segregation
* Face perception (perceptual narrowing)
* Depth perception (sensitive period of binocular vision)