Visual Development Flashcards
1- Why Focus on Infancy?
- Very rapid changes in the first 2 years of an infant’s life
- Changes in one area enable changes in other areas
- Methods for studying infants are different than methods for studying older children that can communicate more clearly with adults
- Sheds light on nature/nurture debate
2- What do babies see?
- 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 - So what exactly can they see?
-Can’t ask babies so have to get creative
3- Methods in Infant
Research: Preferencial looking paradigm
Preferential Looking Paradigm
* Paradigm takes advantage of infants’
preference to look at “interesting” things
* 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
* Assesses infants’ preference for stimuli
Eye movement scan (idk what it’s called)
What is interesting to infants?
Infants prefer to look at stimuli that are:
* More complex, more saturated in colour
* Familiar
- Natural familiarity: Stimuli infants experience often in their lives
- Lab-induced: Familiarize infant to a new stimulus by exposing them to for
some time
– Will then show a preference for the familiar stimulus when paired with a new
stimulus
4- Methods in Infant
Research: Habituation paradigm
Habituation Paradigm
* 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
* Test: Present habituated, “old” stimulus with a new stimulus:
-Dishabituation: If the baby shows greater interest in 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
Familiarity vs. Novelty
* In general, infants show a preference for familiar stimuli
* Prolonged/ repeated exposure to a stimulus will cause infants to shift
their preference to a novel stimulus
* In lab settings, length of exposure time determines whether an infant
will show a familiarity or novelty preference:
- Short exposure = familiarity preference
- Long/ repeated exposure = novelty preference
Implications
* Exposure time in lab-induced preference procedures need to be long enough for the baby to become familiar with the stimulus but short enough so that they don’t get bored (habituation)
- Usually only one familiarization trial that is brief
* Habituation paradigms need to repeat the presentation of a stimulus enough times to ensure that the infant is bored
- Many trials
5- Summary of Research methods
Summary
* 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
(habituate) and then presented with a different stimulus on a test trial
- Assesses an infants’ ability to distinguish between 2 stimuli
- Prefer novel stimuli
6- Visual Acuity
Visual Acuity
* 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
* 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
* Why?
- Due to immaturity of cone cells in infants’ retinas (light sensitive neurons involved in seeing fine details and colours)
* 8 months: adult-like visual acuity
7- Colour Perception
- At birth: infants see in gray scale
- 2 months: colour vision appears
- 5 months: adult-like colour perception
- Due to maturity of cones and visual cortex
- Can discriminate between colour categories and between hues of the
same colour
Using habituation paradigm
8- Visual Scanning
Visual Scanning
* 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
9- Face Perception
Face Perception
* Newborns show a preference for faces or face-like stimuli vs. non-face
like stimuli
Why are infants drawn to faces?
* Special face perception mechanism?
Like fusiform face area?
Or more general mechanism?
* Hypothesis: Infants have a general bias for stimuli that are more “top
heavy” vs. “bottom-heavy”
- Preferential looking paradigm
- Showed babies: * regular faces * upside faces * scrambled, top-heavy faces * scrambled, bottom heavy faces
* 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
Results:
* 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”
Seeing Mom’s Face
* 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
Becoming a Face Specialist
* Over 1st year of life, infants become face specialists
* better at distinguishing between faces that are frequently experienced
in their environment
* Evidence:
* 9-month-olds (and adults) can distinguish between 2 human faces but struggle to distinguish between 2
monkey faces specialist
* BUT 6-month-olds are equally good at distinguishing human AND monkey faces generalist
10- Face perception + Perceptual narrowing
Perceptual Narrowing
* Tuning of perceptual mechanisms to the specific sensory inputs that
infants encounter in their daily life
* Improves perception of stimuli encountered often
* Decline in the ability to distinguish stimuli that are not present in theinfant’s environment
* Present for several perceptual domains
* Result of synaptic pruning
Recap: Synaptic Pruning
* Synaptogenesis: Formation of synapses between neurons
- Rapid synaptogenesis right after birth
- Results in hyper-connectivity in the brain
* Synaptic pruning: Elimination of synapses to increase the efficiency
of neural communication
- Follows “use it or lose it” principle
(4 years old, 6 years old… see picture)
Synaptic pruning across domains: see pic
Perceptual Narrowing in Face Perception
* Evidence of perceptual narrowing in face perception:
- Infants becoming face specialists
- Infants demonstrate the other-race-effect
Other-Race-Effect in Infants
* 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
* Also evident in infants:
- Researchers recruited Caucasian 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?
Results:
* 3 month olds: distinguish between faces of all races
* 9 month olds: can only distinguish between faces of own race
* 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 (Sugden et al., 2014)
- If infant is equally exposed to faces of different races, will not show ORE
Face Perception in Children with ASD* 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
* Infants’ preference for non-faces could be
an early indicator that the infant will later
be diagnosed with ASD
Summary of Face Perception
* From birth, infants have a preference for faces, 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 of perceptual narrowing
* Human faces vs. monkey faces study
* Other-race effect in infants
11- Object perception: Perceptual Constancy
Perceptual Constancy
* The perception of objects as being constant in size, shape, colour. etc in spite of physical differences in the retinal image of the object
Perceptual Constancy in Infants
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 - 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
Results:
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
12- Object perception: Object segregation
- The ability to identify that objects are separate from each other
- Movement is an important cue
- Separate objects move independently of each other
Study: Is object segregation present from birth?
* 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
Results:
* 4 month olds: Preferred to look at the broken rod
- See the broken rod as novel
- 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 they did not understand that rod behind the box was a single object
* Object segregation is not innate, has to be learned with experience
13- Depth Perception
Depth Perception
* 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
- Perceived at 4 months old
Sensitive Period for Binocular Vision
* Sensitive period: a time period during which experience shapes the
development of an ability more than at other times
* 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 as the infant receives normal visual input
* If infants do not receive normal visual input until age 3, they may fail
to develop normal binocular vision and have life-long difficulties with
depth perception
- Monocular depth cues: depth cues perceived with one eye
- e.g., relative size or overlap
- Perceived at 6-7 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
14- Visual Development Timeline
Visual Development Timeline
* 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
15- The Nature and Nurture of Visual
Development
- 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)
