Prenatal Development: Stages and Fetal Learning

Page 1

Prenatal Development

Nature vs Nurture

Genotype (nature) + environment (nurture) = Phenotype (how DNA is expressed; like our characteristics and behavioral tendencies)

Stages of prenatal development

Zygote - when it is only cells and just beginning to form

Embryo - this has a similar structure across species

Fetus - 9 weeks to birth

Fetal Behavior

We begin to learn before we are even born but after viability

Viability occurs 24+ weeks

Fetus can remember auditory stimulus, learned to recognize it, and discriminate a novel stimulus

Do Fetuses have long term memories too?

Audition study - The Cat in the Hat

In this study pregnant moms had to read the cat in the hat allowed twice a day for 6 weeks

When the baby was born they gave them a special pacifier to suck on. They would play two stories, one being the cat in the hat and one a random story. The baby would adjust their sucking pattern in order to hear the familiar story

Newborns remembered patterns while still in the womb

Smell Study - Amniotic Fluid Study

In this study newborns were given a blanket that either had their amniotic fluid on it or another babies

They preferred the blanket with their own amniotic fluid on it

Newborns remembered smells that they encountered while they were still in the womb, and they should familiarity preferences

Taste study - Carrot Juice Study

Pregnant mom would drink carrot juice 4 days a week for their last 3 weeks of pregnancy

Once the child was 5.5 months old they gave the baby cereal prepared with carrot juice and cereal prepared with water

The babies “given” carrot juice before birth preferred the carrot juice cereal

Newborns remember tastes they were given in the womb, even 6 months later

Native Language Study

Newborns had their special pacifier and the experimenter played two sounds, one was of their native language and the other was of another language (french)

The baby adjusted their sucking to hear their native language

Newborns remember linguistic sounds that they heard while still in the womb

After viability the newborn shows both short-term and long-term memory

Brain Growth

Babies have few neurons at birth. They then gain a bunch of neurons over the next few years so that around the age of 7 there are the most neurons. Then as we get older we slowly lose those extra neurons.

Helps us to learn a bunch of new things when we are young

The way the brain grows and develops is due to both nature and nurture

Experience-Expectant Plasticity

According to this evolution expects that all individuals have certain common experiences (due to nature)

The idea is that the brain is wired to have these things already programed into it (such as vision)

Normally development will involve certain types of experiences that shape neural connectivity

These changes WILL NOT OCCUR without a particular experience during the right time period

Experience-Dependent Plasticity

Each individual has very different experiences throughout life

Normal experiences throughout lifespan shape cognition and behavior, resulting in different brains for different individuals

Brain Structure

Our brains are built to make up for if a critical input is missing (such as vision)

Our brain is hard-wired to organize information in a certain way, but it is able to reorganize if an unusual experience occurs

Teratogens

An environmental agent that can cause harm to a baby before it is born (while it is still in prenatal development)

4 Principles of degree of harm:

Age of fetus at time of exposure

sensitivity period: this is when a certain thing of the baby is developing most during a particular time. During this time that structure/ability is most vulnerable to damage

Example: when thalidomide was prescribed in the 1950s for morning sickness and babies had limb development issues

Dose Size

The greater the dose the greater the harm to the fetus

Example: Fetal Alcohol Syndrome

Heredity: Genetic makeup of mothers and fetus

Other negative influences (additional teratogens, lack of access to health care, etc.)

SIDS

Unexpected death of infant, no known cause

Associated with smoking (3.5x more likely)

What can be done?

Don’t smoke

Put baby on back to sleep

Firm mattress, no pillows, loose blanket, toys

Environmental Pollutants

Lead exposure, particularly in poor communities

Higher lead levels leads to higher risk of miscarriage, pre-term birth, later ADHD symptoms and lower academic performance

Maternal Factors

Age

Nutrition

Disease

Stress

Prematurity and Low Birth Weight

Prematurity = born at or before 35 weeks

Low birth weight = <5.5 lbs; very low = <3.3 lbs

Infant and Maternal Mortality

What can be done?

Increase access to healthcare

Combat systemic racism and appropriately train staff

Increase maternity leave and make it paid

Narrow the income gap

Perceptual Development 1

Perception

Organizing and interpreting sensory input (such as the light hitting the retina)

5 things involved in discrimination

Attend to some stimuli over others (discrimination)

Locate the source of the perceptual information

Identify perceptual information by comparing it to previous experiences

Integrate information across different sensory modalities (e.g., sound and sight)

Use that information to guide behavior

Taste and Smell

Infants can discriminate between taste/smell

They tend to prefer tastes that they have had before (Such as the carrot juice study)

Innately prefer sweeter tastes, they tend to dislike sour and bitter tastes

They prefer the scent of their own lactating mother to any other lactating woman

This requires discrimination, comparison to smells stored in memory

Audition

Infants tend to prefer listening to human speech over other sounds

Locating sounds

Infants reflexively turn their heads towards sounds

By 4 months, infants seem to “expect” something from the place where the sound came from

Complex sounds

Infants are able to distinguish between categorial sounds in speech in different languages

Vision

Infants were originally thought to be blind at birth, this is not true

However, babies vision is really bad when they are born and improves over time

Visual Acuity

Infants’ visual acuity measured via preferential looking

Assumptions:

Infants will prefer to look at the display that is more visually complex

If they infant shows any preference that means that they are able to discriminate between the two screens

Visual Acuity Study-1

In this study babies are shown two screens one with chunkier/larger black and white lines and another with smaller and thinner black and white lines

The infants eye gaze is then studied and they should look at the one that looks more visual complex to them (which should be the larger one)

As the lines get smaller, they may not be able to see a difference and the child would not show a preference for an image and get bored

Visual Acuity Study-2

Same idea can be done but you are showing the child paddles with the lines on them if the child puts in the effort to turn their head or gaze to look that means they can see the lines

Infants can see, and their vision improves drastically over the first year of life

Visual Acuity Study-3

Same study as 1, however the contrast is turned down from black to gray on the larger stripes

Babies do not react to low contrast

Color Perception

Newborns show color preferences

By 3-4 months, infants’ color perception is like adults’

Do infants innately perceive the same color categories as we do? Or do they learn color categories from us?

Visual Habituation Procedure

Babies will habituate to a light blue and then dishabituate when the color is changed to a dark blue

If they suddenly show the baby a green color, the baby will dishabituate even more

By just a few months, infants reliably discriminate different color categories

Some aspects of perception require maturation (e.g., visual acuity, color perception), but do not depend on learning

Intermodal Perception

Integrating at least 2 senses, this seems to be present in the first few months of life

Touch and smell

Touch and vision

Babies have either a smooth or bumpy pacifier in their mouth and they will look at the image of the one that they have in their mouth

Vision and audition

A noise is played and the baby will look at the video that would make that sound

Critical Periods

If a particular experience doesn’t occur at a particular time, there can be a dramatic impact on development/learning

Learning is easiest during a sensitive period

What happens when an input is missing?

(Vision) if repaired later in life, vision will somewhat recover, it will never reach full functioning

If one input is missing another one will attempt to make up for it

Perceptual Development 2

The Problem of Depth

Even after objects are identified, how do we know if they are near or far?

How do we ever know how far away objects are?

Cues:

Convergence (binocular cue)

The closer an object is to your face, the more your eyeballs will turn inwards (aka the more your eyeballs will converge)

The farther the object is from your face, the more your eyeballs will stay parallel

Example: when you slowly move your finger closer to your face the closer it gets the more your eyes cross/converge

Binocular Disparity (binocular cue)

The closer an object is to your face, the more different the image received by the left vs right eye will be

Abnormal depth perception: Strabismus

Example: when you put your finger up in front of your face and blink one eye at a time your finger will appear to move

Optical Expansion

Sudden increase in apparent object size that may signal to you that an object is approaching

Example: a ball flying at your face; it goes from looking tiny to a lot bigger as it approaches

Motion Parallax (motion cue)

Nearby objects appear to “pass by” at a faster rate than more distant objects

Example: when you are driving in a care and look ahead things look to be passing pretty slow but if you look out the window beside you things look to me flying by really fast

Interposition (monocular/pictorial cue)

Nearby objects usually look more “complete”; farther objects often occluded

Example: in a picture if a child is standing in front of their mother you don’t just assume that the lower half of the mother doesn’t exist because the child is blocking the view of it. You know the lower half exists even though you cannot see it

Texture Change (monocular/pictorial cue)

Objects that are father form a finer texture than nearby objects

Example: think of a picture of a crowd of people you are going to be able to pick out heads in the front of the picture but it is going to get harder and then impossible as you get father away in the “back” of the picture

Linear Perspective (monocular/pictorial cue)

Lines appear to converge with increasing distance

Example: if you look at a train track it will be clear to you that the rails under you are parallel but if you look far ahead it looks like the rains are slowly leaning into each other or converging as the distance increases

Do we have to learn depth?

Descartes says “No” ; Berkeley says “Yes”

Can infants use any of these cues to perceive depth?

We already know that 1 month olds respond defensively to looming objects

Eleanor Gibson’s visual cliff experiments (1950s)

In this experiment there is a table with a glass top. Under the glass top there is a checkered board pattern. One one side it appears to be right there under the glass, on the other side it appears on the floor so to the baby or animal on the table it looks like a ledge that they would “fall” off of if they went there

This study was done on babies

They would encourage the baby to crawl onto the “cliff” side and they wouldn’t do it

Did babies learn to perceive depth and avoid the deep side?

Possibility 1: A few weeks of crawling experience taught babies about depth and relative safety

To test this possibility they put pre-crawlers in a harness and lowered them onto the “cliff side” while measuring their heart rate

Their heart rate would increase

This indicated that infants perceived depth prior to crawling experience; Ruling out Possibility 1

Possibility 2: Babies learn from visual experiences, not motor experiences (crawling is not necessary)

This was tested by using animal models (rats)

They used light-reared rats (normal) and dark-reared rats (they have never seen anything before

Both the light and dark reared rats avoided the cliff

Cliff avoidance is independent of visual experience in rats; Ruling out Possibility 2

The study was then conducted with other animals that can walk right after birth and none would go on the side of the cliff

Conclusions

There is no necessary relationship between mechanisms of depth perception and cliff avoidance across species

Every animal that was tested was found to have unlearned mechanisms for perceiving depth and avoiding the cliff

Evolutionary argument

Face Perception

Infants prefer to look at faces over other stimuli

How do we know? What is it about faces?

Different types of faces study

Newborns were shown three different types of “faces” on paddles

One was a normal black and white schematic face

One was scrambled or upside down

One was 3 oriented blobs (that resembled a face)

The newborns tracked the normal and 3 blob faces equally, but tracked the scrambled face less

What is innate appears to be pretty simple

Face preferences

By a few hours old, an infant will prefer to look at their mother’s face over a strangers

By a few days old, an infant will prefer to look at female faces over male faces (as long as a female is the primary caregiver)

By 3 months old, infants will prefer looking at faces of their own race rather than faces of another race

Perceptual Narrowing

Until 6 months old, infants can discriminate between faces of various races

By 9 months infants lose this ability to discriminate between other race faces = this is perceptual narrowing

Motor Development

Reflexes

Definition = innate, fixed patterns that occur in response to particular types of stimulation

These are remnants from our revolutionary past

Many of our reflexes disappear after some time, while other persist throughout our life

Eye blink

Stimulation: Sudden light or noise

Response: Rapid closing of eyelids

Disappears: Never

Probable function: Protects from suddenly looming objects

Rooting

Stimulation: Stroke of face near mouth

Response: Head turns toward stimulus to suck

Disappears: 3 weeks

Probable Function: Locate nipple

Sucking and Swallowing

Stimulation: Object in infant’s mouth

Response: Rhythmic sucking and swallowing

Disappears: Never

Probable Function: Ingestion of nutrients

Moro

Stimulation: Sudden removal of support

Response: Arched back, extended legs, arms out then in

Disappears: 6 months

Probable Function: Clinging to parent

Palmer Grasp

Stimulation: Object pressed against palm

Response: Spontaneous tight grasp

Disappears: 3-4 months

Probable Function: Clinging to parent (evolutionary past); prepares for voluntary grasping

Stepping

Stimulation: Supported infants’ bare feet touch surface

Response: Alternating stepping response

Disappears: 2 months (comes back around one year)

Probable Function: Prepares for voluntary walking

Stepping - Why does it disappear?

Observation: after 2 months when upright, stepping disappears; when lying down, stepping reappears!

Hypothesis: Infants’ legs are too heavy to lift against gravity when upright

Experiment: Artificially alter the infants’ body weight to see if stepping is modulated

They put a baby over 2 months but not walking yet waist down in water and they would start stepping

They then put lead-weighted boots on the baby while they were in the water and they would no longer step

Result: Body weight influences stepping ability (and later on, once they get strong enough to lift their legs they begin stepping again)

Motor Milestones

Gross motor development

Lifting head

On stomach, can raise chest with arms

Rolls over

Sits on own

Stands

Walk along furniture

Walking

Fine motor skills

Palmer grasp

Raking grasp

Pincer grasp

Neat pincer grasp

Proximodistal trend: Motor control proceeds from torso out to fingers

Determinants of Motor Milestones

Some cultures actively promote motor development. How?

Back-sleeping, tummy time / rolling

Toys that help them cruise (walk with aid) and chairs that sit practically newborns straight up and down

Different cultures can shift motor milestone timing/onset, but children universally develop similar skills in roughly similar order

Motor Learning

Question: What do babies learn from experience in these different postures?

Answer: Learn about physical properties of bodies, and interactions between their bodies and surfaces in the world

Karen Adolph Studies

Placed two raised “tables” and put a baby on one table then a gap and then a toy at the other

If the baby didn’t recognize the situation as dangerous if they reached, they would reach for the toy and “fall” into the gap

If they recognized the situation as dangerous they would not reach for the toy, and therefore not “fall”

First they had babies sit, then crawl, then walk

What they found is that the baby had to be experienced in each of these tasks (sit, crawl, and walk) in order to be able to judge the situation correctly

Infants learning appears to be posture-specific:

Learn about changing body (taller, stronger, more slender,

Learn about limitations of body in different positions

Learn about limitations of body on different surfaces

This job continues throughout the lifespan

Motor development is partially due to nature (innate reflexes, inherited body proportions) and partially a result of nurture (culture values, learning about what your body can/can’t do in different postures, on different surfaces)

Understanding the Physical World

Jean Pieaget

empiricism/constructivism view

Believes that nearly everything must be learned; only physical growth and ability to learn from experience are innate

Believed that children are actively constructing knowledge about the world

Believed that children passes through qualitatively different knowledge states on the way to final state of mature knowledge (discontinuous change)

Discontinuous change

Stages are qualitatively different from one another

Children go through brief transitions when passing through one stage onto the next

Stages are broadly applicable, capturing children’s thinking about many different types of problems

All children pass through all stages in an invariant sequence

What did Piaget think infants start with?

Stage 1: Sensorimotor

Piaget: infants begin without any knowledge; they must learn everything by experiencing the environment

Newborns: “bundle of reflexes” which are fine-tuned with experience

Months 1-4: slowly organize reflexes into coordinated actions (e.g., bring hand to mouth to suck on)

Months 4-9: become interested in objects and people, but discover relationships by change

Months 9-12: understand relationships between sights, sounds, etc.

Throughout all of this, Piaget thought infants have a very different understanding of the world than adults do

Object Permanence

Piaget: infants see the world very differently than adults do

Thus, believed that infants don’t have object permanence

Object permanence test

Put down two towels, showed the baby a toy (for example) and would then in front of them put the toy under the towel and the baby would look confused like they didn’t know where it went

Once the baby got older (8-10) they would lift up the towel to find the toy

Or they put a toy in front of them them but then put a wall blocking between them blocking the babies view of the toy

Came to believe that “for infants, objects only exist when visible”; and that infants don’t have object permanence

Piaget:

Infants initially perceive objects as loose collections of color and shapes

Over time and experience, infants begin to accidentally interact with objects

This teaches them about how to interact with objects (“if I reach for an object, I usually get it”)

With more experience (not until a year), they develop more complex rules of interaction (“If I reach for an object the last place I saw it, I usually get it”)

“Knowledge is hard-won, but built slowly using action experience”

But was Piaget right??

Possibilities

Concepts (like “object”) themselves change over time

Example: when the toy is in front of them “wow look at that toy” then when the wall is put between “poof! Nothing there!”

Concepts remain constant; Memory changes

Example: when the toy is in front of them “ooh, a toy!” then when the wall is put between “was something there? I forgot”

Concepts remain constant: Action abilities change

Example: when the toy is in front of them it is easy for them to get to, then when the wall is put there they know it is too difficult for them to get to so they don’t even try

Competence-Performance Distinction = a subject’s ability to demonstrate knowledge may be masked by demands of the task, unrelated to the knowledge itself

The trick: To get infants’ knowledge, make the task easier!

Baillargeons’s rotating barrier experiment (4 months)

Baby watches a screen rotate back and forth 180 degrees

Possible event: Then as a test trial they but an object behind the screen and once the screen hits it it stops at 120 degrees

Impossible event: They “put the object” behind the screen but the screen does not stop it goes the whole 180 degrees

Make the task easier, infants succeed

Infants even represent that an object cannot pass through another object

So why do infants fail with Piaget’s version of the task?

Possibility 1: Infants’ memory is too short to allow them to remember the occluded object

Study: they tested this by doing the test where they have the toy under a towel.

At 9 months old with a long delay the baby did not “find” the toy.

At 9 months old with a short delay the baby found the toy

Possibility 2: Infants still remember the toy, but representation of the cloth overwhelms the weaker toy representation

Study: they did the cloth study but did it in the light and in the complete dark

At 7 months in the light the baby was not able to find the toy

At 7 months in the dark the baby was able to find the toy

Possibility 3: Means-end problem: Infants have trouble coordinating series of behaviors needed to get the toy

Easy: the toy is right in front of the infant with nothing blocking it

Harder: the toy is in front of the baby but in a box

Hardest: the toy is in a box that is flipped on its side where the baby is not able to see the toy

All 3 of these factors/possibilities probably affect infants’ “failures

Infants progress through stages in their competence in their behavior toward objects

Piaget thought this reflected infants’ changing concept of “object”

Newer research suggests that Piaget underestimated infants’ knowledge

Many factors affect how infants will behave in a task (memory, other interesting representations, means-ends demands)

All of these combine to reflect changes in object COGNITION

Liz Spelke’s Core Knowledge Hypothesis

Nativism / core knowledge hypothesis view

Infants come into the world with knowledge about a small number of core demains

What does babies’ core knowledge of objects consist of?

Spelke: infants are born with principles for reasoning about objects, including: Continuity, Solidity, Cohesion, Contact, and Support

Continuity: objects continue to exist, even when hidden (entails object permanence, plus more)

Baby knows objects don’t magically disappear

Baby knows objects don’t magically appear

Question: is this knowledge innate?

Demonstrated in 3 month old babies

Demonstrated in newborn animals

Imprinting: newborn chicks will imprint on the first mid-sized object they see (usually mom)

Test: Will a newborn chick imprint on a triangle. If the triangle is blocked by something, will baby chicks know it is still there and follow it?

Chicks follow the triangle mom behind the screen that is blocking it. Showing that they must know she still exists even though the chick cannot see it. They know this even though it is the first time they have seen an object blocked by something else

It is innate not learned

Question: Are infants representing that “some object” will continue to exist? Or are they representing that particular object?

Carrot Study - do 3.5 month olds remember the height of a hidden object

First they habituate the babies by having the carrot go behind a normal block and the come out the same side as the same size

Next they do a possible test trial where the block has a cut out and the carrot goes behind it but you still wouldn’t be able to see the carrot through the cut out because it is too short

Then they do an impossible test trail where block has a cut out and the carrot goes behind it but this time the carrot is taller so you would see it through the cut out, but you don’t see it

Conclusion: longer looking to impossible trials

Infants represent object properties, and use these to reason about how an object should (and shouldn’t) behave

Solidity: objects cannot pass through one another

Bailargeon’s drawbridge study: Do babies actually understand solidity?

Do infants detect other solidity violations?

Toy car going into or through wall study

They had a car go down a ramp into a wall sometimes it would stop at the wall other times it would end up on the other side of the wall

Infants as young as 2 months reliably look longer at the “impossible” trials across a variety of experiments

Infants understand object solidity

Cohesion: Objects move as unified wholes (if you pick up an object the whole thing will move not just part of it will come off)

Contact: No action at a distance

Example: if you slide one object into another and it makes contact it will make the other object move. If they don’t make contact the other object will not move

Support: Unsupported objects will fall

Bailargeon support studies

Has one block on a surface and does a possible support test where the block stays on the surface. Then does an impossible support test where the block is pushed off the surface and it floats.

Spelke’s Claim: This knowledge stays with us throughout our lifespans, and is probably evolutionarily ancient (present in chicks, dogs, primates)

Question: Does that mean knowledge of objects doesn’t change at all over time, or with experience?

No! Object knowledge does change, but it gets REFINED, not overturned

Bailargeon shows that infants’ knowledge of support gets refined over the first year

3 months: initial concept: contact vs no contact

4.5 months: which surfaces are in contact

6.5 months: amount of contact

12.5 months: Proportional distribution

Core Knowledge does not equal Anti-learning

Stahl and Feigenson (2015) solidity and support studies

Solidity: had a toy car go down a ramp and it either ran into a wall or “went through” the wall

Support: toy car on raised surface and it was either pushed on the surface or pushed off the surface and floated

All infants who saw violation to core object knowledge learned better about that object: they played with it in specific ways to see if there was anything special about the object

Solidity: repeatedly banged the object on solid surface (to see if it would magically go through an object again)

Support: repeatedly dropped the object (too see if it would magically float again)

Babies come into the world with innate expectations about objects (Spelke, Baillargeon), and they can use that knowledge guide what to learn about and explore in the future (nature and nurture)

Summary: Core Knowledge of Objects

Conceptual knowledge about what objects can/can’t do (continuity, solidity, cohesion, support, etc.)

Present in babies and newborn animals, at least to some extent

A fundamental set of expectations about the world which remains constant through life

This knowledge gets refined or added to, with experience

In some cases (e.g., object permanence), early knowledge gets masked by other deficits

Numeral Cognition

Number Knowledge

How can young infants determine how many objects there are?

Number = case of innate, core knowledge, and genuine qualitative (discontinuous) change

Do you children know anything about numbers?

Kids seem to be able to count really young, however kids don’t actually know how to count until age 3 ½

When they count up to then they are really just mocking what they have heard they don’t understand what it truly means to count

Just reciting the count list is not actually counting

Counting involves many abilities:

One-to-one correspondence (each object in the set should only be counted once)

Stable order (counting in correct number order)

Order irrelevance (it doesn’t matter what order you count the objects in)

Abstract nature of number (anything that can be counted can be quantified)

Cardinal world principle (idea that the last word that you say when you are counting is the answer to how many there are of that thing)

What kinds actually learn about counting by each age:

1.5-2 years: understands “one” (=”a”); all other number words synonymous with “some”

For 6-8 months, when asked for sets >1 (e.g., “two” or “five”), kids grab any random set larger than one

They do not actually count to create the set and often violate counting principles when checking

They do not fix it correctly when asked (70% of wrong answers are not adjusted, or adjusted in the wrong direction

2-2.5 years: master meaning of “two”; all words except “one” and “two” taken to mean “some”

Children learn what “two” means, give 2 without counting, but grab randomly when asked for “three” or more

This persists for 6 months

2.5-3 years: Master meaning of “three”; all words except “one”, “two”, or “three” taken to mean “some”

Children learn what “three” means, give 3 without counting, but grab randomly when asked for “four” or more

This persists for a few months

3.5-4 years: master meaning of “four”

Once they master “four”, they usually understand the meaning of all other words in their count list

A major induction is made: “the next word in my count list refers to the set created by adding one more object”

Learning to count is hard and takes nearly 2 years to master

Could young children show a simpler, non-verbal sensitivity to numbers?

Large, approximate number system

Adults (and kids) can represent approximate number, independent of counting

Dot study

Performance shows 2 important “signatures”:

Mean increases with target number

Error increases with target number

Performance follows Weber’s Law

The ability to discriminate 2 numbers depends on their ratio, not the absolute difference between them

What about infants?

Xu and Spelke (2000): Habituate 6 month olds to either 8 or 16 dots

They would habituate babies to 8 dots until they seemed to get bored and then would show them 16 dots and they would be intrigued again

Test with old number vs new number

6 months old can determine a 1:2 ratio

Yes! Infants have approximate, non-linguistic number representations that are sensitive to numerical ratio (Weber’s Law)

In infancy

Other ways to test approximate number discrimination

Numerical change detection

Intermodal matching (makes a certain number of sounds then baby has to look at which picture has that many objects)

Present in newborns too

Newborns can discriminate a 1:3 ratio

By 6 months, infants discriminate a 1:2 ratio

By 9 months, infants discriminate a 2:3 ratio

By adulthood, we can discriminate a 10:11 ratio

Like the case of visual acuity, approximate number representations present early on

Like visual acuity, these representations sharpen over development (continuity throughout the lifespan)

Manipulating quantities

5+5= about 10

5+5 does not = about 5

Infants can mentally manipulate large quantities (addition and subtraction) approximately

Beyond Infancy

Children’s ability to approximate large number quantities in infancy is related to their preschool math abilities several years later

Children’s ability to approximate large number quantities in childhood is related to their math SAT scores many years later

Small, exact number system

Can infants keep track of precise numerical quantities?

YES, but we find out in cracker study that the ability is limited

Wynn (1992): 5 month olds do simple “addition” and “subtraction”

An object is placed on a stage and then a screen comes up

Another object is added, and the baby watches the hand leave empty

The possible outcome: screen drops leaving 2 objects

The impossible outcome: screen drops revealing 1 object

Baby looks confused when the impossible outcome of 1 object is revealed

Also shows object permanence

Feigenson, Carey, and Hauser (2002): Cracker choice task (10-12 months

They show the baby a certain amount of crackers and places one amount in one cup and another amount in a different cup

Then see what cup the baby goes to

Their performance falls to chance (50%) when >3 crackers presented in the location

Babies can precisely track and compare quantities of objects

But can only do so for 1, 2, or 3; more than 3 and they fall apart!

Performance determined by absolute number of objects shown, not by ratio between quantities

Very different performance “signature” implicates different representational system for that used for large, approximate number

Adults are fast and accurate at recognizing arrays for 1, 2, or 3

Adults too use one system for representing 1, 2, and 3, and a different system for approximating larger quantities

Large Approximate vs Small Exact

Large approximate number system

For large quantities

Imprexise

Estimations get less accurate as number increases

Ratio-dependent

Small exact number system

For small quantities

Highly precise

Limited to absolute number of items (3-4)

Not ratio-dependent

Number Summary

Humans endowed from birth with 2 core systems for representing number:

Large, approximate system

Small, exact system

These two systems are in place throughout the lifespan, and are present in other animal species - continuity!

But only humans develop ability to represent exact, large numbers (e.g., “17”, “12,823”)

This ability seems to involve language, and learning to count