L5 (perceptual) Flashcards
Sensation
the processing of the external world through receptors in the sense organs
Perception
organizing and interpreting sensory information
Empiricist view
infants have poor perception and experience is vital for sense development
Nativist view
perceptual development progresses through biological maturation, not experience
What’s the least developed sense at birth?
vision
“instinct blindness”
Vision grade at birth
20/200 (from VEPs) or 20/400 (from Teller tasks)
VEPs are visual evoked potentials; What newborns can see at 20ft, adults can see at 200ft
Vision grade at 8 months, 10 months, and 6 years
20/100 by 8 months, 20/50 by 10 months, 20/20 by age 6
difference in acuity between newborns and adults decreases with age
When do babies’ abilities reach near-adult levels?
8 months
e.g. smooth pursuit (or predictive ability) can’t be done until 4 months; scanning ability is limited (newborns tend to focus on high contrast areas)
How is the ability for smooth pursuit developed?
biological maturation, not experience
preterm infants do it much later after birth than full-term babies do
Color vision of young infants
not present at birth; young infants are only sensitive to bright colors and large patches of color (based on VEP studies)
What does it mean that humans are trichromatic?
we see color by comparing how different cones, which rapidly develop, respond to light
3 types of foveal cones: short/blue, medium/green, long/red
What causes color blindness?
one or more absent cones, or a weak response in cones of a certain type
Color perception is an example of
Categorical perception
perceiving clusters of likeness that does not necessarily transfer to physical likeness
color is determined via wavelength (a continous variable) but perception is categorical
How do linguistic differences impact color perception?
little to no impact; cultures without color words or with fewer color words perceive the same categorical boundaries of color
suggests that the categorical perception of color is innate
Evidence for categorical perception of color in preverbal infants
in a habituation task, 4-month-olds look longer at a change in color (categorical) than a change in tone of the same color
confirmed with fNIRS and suggests that categorical perception of color is innate
2 real-life applications for the role of experience in color experience
Hint: involves humans and monkeys
- humans born above the arctic circle are less sensitive to color, especially in the fall
- monkeys raised with only monochromatic light (not full wavelengths) do not categorize color the same way humans/typical monkeys do (have more than 3 clusters)
3 types of depth cues
binocular cues (requires 2 eyes), monocular/pictorial cues (requires only 1 eye and exists in 2D pictures), dynamic cues (moving objects)
Binocular disparity
retinal image of each eye is slightly different but our visual system fuses the two so that we don’t see double
closer objects have more disparity
Convergence
eye muscles are more tense when looking at closer objects
Stereopsis
using binocular cues to see depth
Nativist view of stereopsis
according to Descartes
we are endowed with innate computational systems to convert binocular information into depth perception
stereopsis is not necessarily innate (i.e. present at birth) but relies on biological maturation and the properties of the visual system
Berkeley’s theory of the development of depth perception (i.e. stereopsis)
empiricist view
babies learn to associate binocular cues with depth by building associations between convergence (i.e. amount of eye strain) and length of reach over time
How are binocular cues tested in infancy?
stereograms
artificially generated images that can only be seen when they are fused by the two eyes
When do infants’ eye movements begin to follow the movements of stereograms?
3-4 months
however, babies do not reach reliably for objects at 3-4 months so stereopsis couldn’t be from built-up experience with stereograms
Strabismus or amblyopia
eyes are misaligned
usually fixes itself by ~2 months but 4% of children have it beyond this period and the brain eventually suppresses input from the less clear eye
Effect of strabismus on stereopsis
stereopsis is worse if strabismus is not surgically fixed by age 2
How is stereopsis tested in kittens?
- kittens are made to wear alternating eye patches (no binocular input)
- binocular neurons are pruned away and no amount of later experience can resurrect them
3 kinds of pictorial cues in 2D images
aid with monocular depth perception
interposition, convergence in the distance, texture gradients
- interposition: overlapping shapes in front
- convergence in the distance: parallel lines meet at the horizon
- texture gradients: repeating patterns get smaller when farther away
How is pictorial depth tested in babies?
ames window
- present a flat stimulus (e.g. window) where it appears like the texture gradient shifted in depth
- with one eye covered, baby should systematically reach for the longer side if they have pictorial depth
Findings on pictorial depth from the ames window study
7-month-olds, but not 5-month-olds, reach to the long side of the window
this suggests that pictorial cues develop at ~6 months
2 kinds of dynamic cues
motion parallax and optical expansion
Motion parallax
dynamic cue
relative movement of near and far objects to the motion of the eye
when you turn your head to the left, near object moves faster and further toward the right than the far object
Optical expansion
retinal image of objects expand in size as they get nearer to you and the nearer object expands more quickly
a 1-month old blinks at expanding images (looming objects) but premies don’t avoid (blink) loooming objects until later, suggesting that dynamic cues are innate and emerge due to maturation
When do dynamic cues, binocular cues, and pictorial cues develop?
Remember the visual cliff/looming objects, Berkeley, and ames window studies
1 month (dynamic cues), 4 months (binocular cues), 7 months (pictorial cues)
- dynamic cues are almost never misleading (stable input from both eyes)
- binocular cues need good acuity and require both eyes to be aligned (no strabismus)
- pictorial cues are constantly misleading and are often illusions
Size constancy
i.e. perceptual constancy
an object is perceived as maintaining its size despite changes in its distance from us (and thus, changes in its retinal image size)
near objects occupy more of the retinal space
How is size constancy in infants tested?
is size constancy innate?
- Habituation: show newborns one object placed at varying distances (thus, varying retinal image sizes)
- Test: show the old object and a larger identical one that is farther away with their retinal image sizes equated
- Result: newborns looked toward the new object, suggesting that they habituated from the old object and that they have size constancy
newborns saw the old object as one repeated object despite changes in retinal size
Object segregation
the perception of separate objects in the visual array
newborns understand that a gap between objects means that they are separate
Common motion
motion cue to object segregation
elements that move together are likely part of the same object
Example: if someone picks up a cup and the saucer stays behind, they are probably two separate objects
How are motion cues tested in infancy?
Kellman & Spelke task
- No baseline preference for the broken rod relative to the solid rod
- Induce a negative preference to an occluded moving rod (just the solid rod moving back and forth behind a box)
- Baby still looks toward the broken rod, suggesting that they were able to use motion cues to fill in the blanks (i.e. could infer that the moving rod was solid)
suggests that motion cues are innate because, although newborns fail at the task (2-month-olds succeeed), newborns succeed in studies using strobe motion
Error babies make in perceiving pictures
distinguishing 2D from 3D
newborns can recognize 2D versions of 3D objects (i.e. understand that pictures are stand-ins for 3D objects) but try to pick up objects in a picture
error stops by 19 months but can be prolonged in babies raised in cultures that have no pictures
4 inherently appealing characteristics of faces to newborns
symmetry, high contrast, movement, top heavy (not humanness)
newborns show the same preference for other top-heavy configurations and are not able to distiguish faces from them
What kinds of faces do newborns prefer?
faces that are interacting with them (e.g. direct gaze, happy, attractive)
- newborns also prefer their mom’s face within 4-6 waking hours after birth
- younger siblings of autistic children who are at high risk of developing autism themselves have different social stimuli preferences (e.g. inverted face, averted gaze)
2 systems view of infant face preference
an initial crude face perception system (e.g. orienting to top-heavy stimuli) gets replaced by a more sophisticated one (e.g. learns about specific faces)
- face tracking goes away by 1-2 months then comes back and is improved dramatically by 3-4 months
- trough of the u-shaped curve is when systems are competing over dominance
How does face scanning develop over 8 months?
- mainly high-contrast areas first
- focus on eyes and a bit on the mouth by 2 months
- increase in mouth attention by 8 months (possibly reflects language learning)
HR infants later diagnosed with autism don’t show these developmental patterns
What is driving the development in face scanning?
change before and after 4 months
amount of face experience
* before 4 months, faces activate the FFA bilaterally and infants view faces 1/4 of the time awake
* after 4 months, infants begin to show right hemisphere lateralization (like adults)
focus decreases with age as the brain becomes more specialized
Developmental changes in face perception
based on the visual-paired comparison task
by 9 months (but not 6 months), infants are better at distinguishing different human faces than different monkey faces
Perceptual narrowing
babies’ face discrimination abilities narrow based on the faces they experience
e.g. tendency to prefer faces they’re most used to seeing like those of the same species (humans)
Gender preferences in face discrimination
- if raised primarily by a female caregiver, prefer and can better discriminate female faces by 3 months
- if raised primarily by a male caregiver, prefer and can better discriminate male faces by 3 months
some studies show that the effect in males is less strong
Do newborns show a face preference for their own race?
i.e. other-race effect
- no significant difference in white newborns’ looking time to own and other race faces
- white 3-month-olds look longer to Caucasian faces rather than other races
same pattern found in Chinese infants
Can experience influence the other-race effect in infants?
infants exposed to a diverse environment (e.g. lab or family) showed no bias for faces of their own race
Perceptual narrowing from the other-race effect
before and after 9 months
- before 9 months, infants are equally capable of distinguishing between 2 faces of any race
- from 9 months, they have trouble discriminating between 2 faces of any other race vs 2 faces of their own race
9-month-olds group faces of all other races into one category
What do 12-month-olds associate racial in-group vs out-group faces with?
positive valence (e.g. music); negative valence
Newborn preferences in terms of motion and interaction
- newborns prefer biological motion (e.g. right-side up hen) to scrambled motion (e.g. random motion and upside-down hen)
- female newborns prefer face-to-face interactive point-light walking hens than back-to-back
male chickens are pretty antisocial and highly polygynous
Sound preferences of newborns at birth
- own mom’s voice to other moms’ voices
- language sounds to non-language sounds
- own language to a foreign one
- familiar nursery rhyme (with familiar words) their mom read to them during last weeks of pregnancy
- detect big changes in pitch and loudness
How do cochlear implants work?
they bypass sensory regions and directly stimulate auditory areas in deaf children
Is there a critical period for hearing?
cochlear implants work better the earlier they’re used (before age 2) because brain auditory areas haven’t reorganized yet to deal with other sensory input
implanted adults can hear but don’t do as well at perceived, particularly language sounds
Music preferences of infants
- infant-directed singing over adult-directed singing, and singing over speech
- consonance over dissonance even at birth and even if their mother is deaf (similar pattern found in chicks and monkeys), suggesting adult-like music perception
preference measured in looking time toward source of sound
Infant preferences in Western music
- equally likely to notice within-key and out-of-key note changes
- Western infants more likely to detect complex rhythm changes than Western adults (but Balkan adults do well)
suggests perceptual narrowing
What factors influence the manual exploration of infants?
for haptic perception
position (e.g. sitting, lying down), age (e.g. motor development), and SES (in North America)
infant exploration via touch (especially with mouths) peaks at 6-7 months
What differences do infants notice in “holding time” habituation tasks?
for haptic perception
- newborns notice differences in shape (they dishabituate to a new shape)
- from 2-12 months, infants notice differences in hardness, temperature, and weight
Taste perception of newborns
- make adult-like expressions to sweet, sour, and bitter tastes
- sucrose (e.g. in breast milk) is soothing to very young infants
- taste still acquired (e.g. aversion to bitter milk lessens if given occasionally)
reflects prenatal experience of taste/smell through their mother
Intermodal perception
the ability to integrate information taken in by multiple sensory modalities into one coherent experience
Empiricist view of intermodal perception
William James
young infants can’t integrate multisensory information as it takes repeated associations
“baby feels it all as one great blooming, buzzing confusion”
Constructivist view of intermodal perception
Jean Piaget
infants’ conception of their mother comprises of several bits of sensory info and they actively construct whole mom over time and experience
e.g. seen mom, heard mom, smelled mom, tasted mom
Amodal sensory information
invariant features that cut across modalities (e.g. tempo and rhythm are seen, heard, and felt)
4-month-olds attend to amodal matches
Intercessory redundancy
information presented redundantly across two or more modalities facilitates learning
helps babies focus on most relevant (redundant) information
Evidence for nativist view of interodmodal perception
Clue: pacifier
Meltzoff & Barton
- 1-month-olds are made to suck on “smooth” and “nubby” pacifiers without seeing them
- afterwards, they are shown both pacifiers and accurately match their textures
newborns succeed too, suggesting that intermodal perception is innate
Mcgurk effect
auditory-visual illusion that shows change in auditory perception induced by incongruent lip movement
- what you see overrides what you hear
- from 2 months, babies look to the correct face depending on the sounds they hear
Perceptual narrowing in intermodal speech perception
evidence from Mcgurk effect
young infants detect sound-face movement matches for non-native speech sounds and monkey sounds while older infants cannot
