Good

What two features define an experimental design?

Random assignment of participants to groups, and experimental control. Together they allow conclusions about cause and effect.

Control group vs. experimental group

Experimental group gets the experience of interest. Control group is treated identically but does not get it.

Independent variable (IV)

The experience the experimental group receives and the control group does not.

Dependent variable (DV)

The behaviour measured to see whether the IV had an effect.

Cross-sectional design

Compares children of different ages on a behaviour over a short period. Gives no information on stability or on how individual children change.

Longitudinal design

Studies the same children twice or more over a substantial time. Shows stability and change (e.g., Brendgen et al., 2001: popularity stable from age 7 to 12).

Four ethical principles from the slides

Maximize benefits and minimize harm to children; respect for dignity of persons and peoples; equity; scientific integrity.

What does WEIRD stand for, and why does it matter?

Western, Educated, Industrialized, Rich, Democratic. Most child research uses these samples, so findings may not be as universal as claimed.

Gamete

A reproductive cell (sperm or ovum) with half the genetic material of the donor.

How long is pregnancy, and when is it counted from?

40 weeks, counted from the start of menstruation, about 2 weeks before conception.

Zygote

The fertilized egg. Starts dividing within 12 hours, roughly doubling twice a day.

What happens by day 4 after conception?

The cells form a hollow sphere with an inner cell mass. If it implants in the uterine lining (before the end of week 2), the inner cell mass becomes the embryo.

Amniotic sac

Fluid-filled membrane that surrounds and protects the developing organism.

Placenta

Temporary organ with a semipermeable membrane that exchanges materials between parent and fetus. Linked to the fetus by the umbilical cord.

What passes from parent to fetus through the placenta, and what returns?

To fetus: oxygen, nutrients, minerals, some antibodies. Back: waste (carbon dioxide, urea).

Dizygotic (fraternal) twins

Two zygotes: two ova fertilized by two sperm. Share on average 50% of genotype.

Monozygotic (identical) twins

One zygote that splits. Close to 100% shared genotype.

How does the timing of the split affect MZ twins?

Before implantation: separate placentas and sacs. Early after implantation: shared placenta, separate sacs. Later: shared placenta and sac.

Name the four developmental processes that turn a zygote into a fetus

Mitosis (cell division), cell migration, cell differentiation, apoptosis (cell death).

Apoptosis: what is it and what is the example?

Programmed cell death. Cells between the ridges of the fetal hand plate must die so the fingers separate.

Embryo period

Weeks 3 to 8. Major systems and organs begin (not finish) developing: heart, limbs, sensory organs, brain.

Cephalocaudal development

Structures near the head develop before those farther away (head-to-tail).

What happens to the neural tube in week 4?

It begins to become the brain and spinal cord. It closes like a zipper from the centre outward; the top becomes the brain.

Fetal milestones at weeks 9, 16 and 28

9: all major organs present. 16: lower half develops, genitals may be visible. 28: lungs and heart developed enough that a premature baby could possibly survive without medical help.

Why does fetal movement matter?

Movement starts around 6 weeks, and fetal activity is associated with later self-regulation skills.

What does swallowing amniotic fluid do?

Promotes digestive system and palate development.

What visual preference do fetuses show?

They prefer top-heavy light patterns resembling correctly oriented faces.

Ustun et al. (2022)

Ultrasound of third-trimester fetuses: grimaced to bitter kale, smiled to sweet carrot. Fetuses can tell flavours apart.

Mennella et al. (2001)

Flavour experience before birth (carrot juice vs. water groups CW, WC, WW) affected later flavour preferences. Prenatal learning carries into infancy.

Cat in the Hat study: method and result

Parents read the book in the last 6 weeks of pregnancy. Newborns sucked a special pacifier in the pattern that played the familiar story. Evidence of prenatal hearing and learning.

Habituation vs. dishabituation

Habituation: decreased response to repeated stimulation (seen at 30 weeks gestation). Dishabituation: new stimulus revives interest.

Teratogen

A potentially harmful external agent that can damage prenatal development.

Sensitive period (in prenatal development)

The time when a developing organism is most affected by external factors. Different systems have different periods.

Dose-response relationship

Greater exposure to a teratogen generally means worse outcomes.

Alcohol and pregnancy

Leading cause of fetal brain injury and the most preventable. Linked to fetal alcohol spectrum disorder (FASD).

Why is marijuana hard to study as a teratogen?

Use often co-occurs with other teratogen exposure.

Tobacco and pregnancy

Nicotine lowers oxygen for parent and fetus. Linked to low birthweight, SIDS, cancer, ADHD, lower IQ. Includes secondhand smoke and e-cigarettes.

Thalidomide

1960s anti-nausea drug thought not to cross the placenta. Caused major limb deformities, but only when taken in weeks 4 to 6 (sensitive period).

Accutane

Acne medication with extreme prenatal risk. Users use multiple forms of birth control and get regular pregnancy tests.

Environmental pollutant examples

Mercury (Grassy Narrows and White Dog First Nation), lead (pipes, old paint, gasoline), pesticides, plastics. Nanoplastics are a future research direction.

Name two other prenatal risks beyond teratogens

Maternal age, nutrition and mental health.

Oxytocin

Hormone that causes uterine contractions. Synthetic oxytocin is used to induce labour.

Breech position

Fetus not head-down (3 to 4% of fetuses). Raises risks for parent and fetus.

How does being squeezed during birth help the baby?

Moves baby low in the canal (crowning), shrinks the head as skull plates overlap, triggers hormones that help withstand brief oxygen loss, forces fluid out of the lungs.

How much of newborn sleep is REM?

About 50%. Newborns sleep about twice as much as adults.

When does infant crying peak and decline?

Peaks around 6 to 8 weeks, decreases around 3 to 4 months.

Swaddling: what and why?

Wrapping a baby snugly. Mimics the womb: compression, heartbeat sound, parent's smell.

Colic

Excessive, inconsolable crying for no apparent reason. About 1 in 10 infants, ends around 3 months, no long-term effects on the infant.

Miscarriage: key facts

Usually due to genetic problems incompatible with life. About 15% of recognized pregnancies; 25% to maybe 50% of women have at least one; about 1% have recurrent miscarriage (3+).

Infant mortality, Canada 2020

4.5 deaths per 1000 births in the first year. Improving over time but rank vs. other countries is worsening. 2 to 3 times higher in Nunavut and NWT than in Nova Scotia and BC.

Multiple-risk model

Risks often co-occur and are cumulative: more risk factors, worse outcomes, across many domains. Poverty is a hazard because multiple risks link to low SES.

Structural racism

Behaviours and beliefs that harm specific racial and ethnic groups (segregation, uneven health care, incarceration). Affects fetal and newborn health.

Developmental resilience

Successful development despite multiple, seemingly overwhelming hazards. Helped by personal strengths and responsive care from someone.

Gene vs. allele

Gene: section of a chromosome coding for a trait. Allele: one of two or more versions of a gene.

Genotype vs. phenotype

Genotype: the genetic material inherited. Phenotype: its observable expression in body and behaviour.

Genome

The complete set of genes of an organism.

How many chromosomes do humans have?

23 pairs (46). Each parent gives one of each pair; each gamete has 23.

Two sources of genetic variation in gametes

Random assortment of chromosomes and crossing over (pairs swapping DNA sections).

Dominant vs. recessive alleles

Dominant is always expressed when present. Recessive is expressed only without a dominant allele.

Regulator genes

Genes that switch other genes on and off. The environment can influence them (e.g., thalidomide).

Polygenic

A trait determined by more than one gene. Most traits are.

MAO-A gene finding

Low-MAOA allele plus childhood maltreatment greatly raises antisocial behaviour. Without maltreatment, no difference. Gene-environment interaction.

Epigenetics

Stable, environment-driven changes in gene expression without changing the genotype. Can be passed across generations.

Family studies: logic and catch

More resemblance among closer relatives suggests genetic influence. Catch: families share environment.

Twin studies: logic

MZ more alike than DZ means genotype matters. About equal means environment matters more.

Twin studies: limits

Assumes similar environments. MZ twins may be treated more alike and share more prenatal environment.

Why do researchers care whether MZ twins share a placenta?

Greater similarity in twins who share one points to a bigger prenatal environment effect.

Adoption studies: logic

More like biological parents means stronger genetic influence. More like adoptive parents means stronger environmental influence.

Three directions of nature and nurture on the slides

Genotype to phenotype; environment to phenotype (and genotype via epigenetics); phenotype to environment (children shape their surroundings).

Neurogenesis

Neurons multiply through cell division, starting weeks after conception. They migrate, then grow and differentiate.

Synaptogenesis

Forming synapses: trillions of connections. Too many form.

Synaptic pruning

Eliminating rarely used synapses so only useful pathways stay. Timing varies by region.

Plasticity

The brain's capacity to be changed by experience.

Experience-expectant plasticity

Wiring from experiences the brain evolved to expect (language, vision).

Experience-dependent plasticity

Ongoing rewiring from your own unique life experiences.

Sensitive period (brain)

Window when the brain must receive certain stimulation to develop normally. Otherwise those systems may never develop typically (cataract and occipital lobe example).

Piaget's core view of children

Active learners from birth, little scientists who predict, test and conclude. Learn through play, intrinsically motivated. A constructivist view.

Why are Piaget's stages 'qualitative'?

Children at different stages think in different ways, not just know less (e.g., 4-year-old considers only own view; 8-year-old can consider others').

Assimilation

Interpreting new information with existing concepts (a pufferfish is still a fish).

Accommodation

Adjusting understanding in response to new information (dolphins are mammals, so update the concept of fish).

Equilibration, equilibrium, disequilibrium

Balancing assimilation and accommodation. Equilibrium: knowledge works. Disequilibrium: new information does not fit, motivating development.

List Piaget's four stages with ages

Sensorimotor (0 to 2), preoperational (2 to 7), concrete operational (7 to 12), formal operational (12 to adulthood).

Sensorimotor stage

Learning about the body and world through senses and actions (sensorimotor intelligence).

Object permanence

Understanding that objects still exist when out of sight. Piaget placed it at about 8 months.

A-not-B error

Object hidden at A and found; then hidden at B in view. 8-month-olds keep searching at A (perseverative error).

Preoperational stage

Children represent experience in language, imagery and symbols (pretend play, drawing shapes, vocabulary growth).

Symbolic representation

Using one thing to stand for another (pretend play, drawings, language).

Egocentrism

Only considering your own point of view (e.g., toddlers refer to things the listener does not know about).

Centration

Focusing on only one prominent feature of an object or event.

Conservation

Understanding that changing an object's appearance does not necessarily change its other key properties. Lacking in the preoperational stage.

Concrete operational stage

Logical reasoning about concrete objects and events, but struggles with hypothetical, abstract and systematic thinking.

Pendulum problem: concrete vs. formal

Concrete: random combinations, miss possibilities, faulty conclusions. Formal: test one variable at a time and conclude rope length matters.

Formal operational stage

Reasoning about hypotheticals, multiple perspectives, systematic thinking. Not everyone reaches it.

Counterfactual reasoning

Entertaining 'what if' questions that run counter to fact. Concrete operational children get stuck on the premise; formal operational can apply logic despite it.

Limitations of Piaget's theory

Describes but does not explain change; overlooks social learning; inconsistent stage descriptions; underestimated children at all ages.

Why is Piaget still important?

Introduced ideas others could test and refine; opened new questions about cognitive development.

Evidence against Piaget on object permanence

Eye-tracking shows infants can track objects they cannot see (under some conditions), though less consistently than adults.

Information-processing view of the child

Little computers: thinking broken into component processes in a hierarchy, with 'hardware and software updates' (capacity, speed, strategies).

Encoding

Taking in information and putting it in a form that can be stored. Requires selective attention.

Working memory

Actively attending to, maintaining and processing information. Limited capacity, improves across childhood. Formerly short-term memory.