Development & Personality

Development

Part 1 of 4 — Piaget's Stages & the Growing Mind

The Starting Equipment: Reflexes & Milestones

Newborns arrive with diagnostic reflexes — rooting (turn toward cheek touch), sucking, Moro (startle-embrace), grasping, Babinski (toes fan to sole stroke; its persistence past ~2 years signals neurological problems). Motor milestones follow a cephalocaudal (head-down) and proximodistal (center-out) sequence: roll → sit (~6 mo) → crawl → stand → walk (~12 mo). Order is far more universal than exact timing.

Piaget's Engine: Schemas, Assimilation, Accommodation

• Schema: an organized pattern of thought or action
• Assimilation: fit new information into an existing schema (calls a whale a "fish")
• Accommodation: modify the schema when the fit fails (creates a "mammals that swim" category)
• Development alternates between the two, driven by equilibration — discomfort when predictions fail

The Four Stages (know the marquee ability and marquee failure of each)

Conservation is the star demonstration: water poured from a short wide glass into a tall thin one is judged "more" by the preoperational child, who centers on height and cannot mentally reverse the pouring.

The Critiques (where modern items live)

• Underestimation: violation-of-expectation looking-time studies show infants register object permanence months before Piaget's manual-search criterion — search tasks demand motor planning the infant lacks, not just the concept
• Continuity vs. stages: abilities emerge gradually and unevenly across domains (conservation of number before volume), straining the idea of unified stage shifts

• Piaget's own term for this within-stage unevenness is horizontal decalage.

• Culture and schooling shift stage timing, and formal operations depend heavily on domain experience
• Still, the SEQUENCE replicates broadly — the MCAT tests Piaget both as framework and as target of these critiques

Worked Example — A Conservation-and-Critique Passage, Fully Read

Passage. Researchers test 120 children (ages 4-9) on conservation of liquid. Standard procedure: equal beakers, pour one into a tall cylinder, ask "same or more?" Percent conserving: age 4 — 8%; age 6 — 41%; age 8 — 87%. In Condition 2, a "naughty teddy" appears to knock the liquid over accidentally into the cylinder before the question is asked; conservation answers at age 5 nearly double relative to the standard procedure. In Condition 3, infants aged 5 months watch a screen rotate through the space where a hidden block sits; they look far longer when the screen passes through the block's location than when it stops against it.

Step 1 — read the developmental gradient. The age trend in the standard task is the expected preoperational-to-concrete transition: centration and irreversibility fade as operations consolidate. So far, pure Piaget.

Step 2 — interpret the naughty-teddy result. When the transformation looks accidental, the child is less likely to infer that the adult's deliberate action plus repeated question SIGNALS that the answer should change (a pragmatic, conversational demand). Improved performance under incidental transformation suggests the standard task overestimates conceptual failure by adding social-interpretive load — competence was masked by performance factors.

Step 3 — interpret the looking-time result. Five-month-olds look longer at the IMPOSSIBLE event (screen passing through a hidden solid), implying they represented the unseen block — object permanence knowledge well before the 8-month search benchmark. Violation-of-expectation logic: longer looking = detected anomaly = the infant held an expectation.

Step 4 — the synthesis item. "Which conclusion do Conditions 2 and 3 jointly support?" Piaget's SEQUENCE stands, but his METHODS conflated competence with task demands (motor search, conversational pragmatics), so his age norms run late. That measured, both-things-true conclusion is the MCAT's favorite correct answer; extreme options ("Piaget was wrong about stages existing") overshoot the data.

Piagetian Development 🎯

Key Takeaways — Part 1

• Newborn kit: rooting, Moro, grasping, Babinski reflexes; milestones run cephalocaudal and proximodistal with universal order, variable timing
• Engine: assimilation fits input to a schema, accommodation rebuilds the schema, equilibration drives the alternation
• Stage anchors: sensorimotor = object permanence; preoperational = egocentrism, centration, failed conservation; concrete = conservation and reversibility on real objects; formal = abstract hypothetico-deductive reasoning (pendulum task)
• Conservation failure = centration + irreversibility; the pour never changes amount
• Critiques: looking-time studies push competence earlier (methods confound concept with motor/pragmatic demands); development is more continuous and domain-uneven than strict stages — but the sequence itself replicates

• Low-yield extras: Piaget called within-stage unevenness across domains (number conserved before volume) horizontal decalage

Development

Part 2 of 4 — Attachment, Temperament, Parenting & Vygotsky

Attachment: The Experimental Foundations

• Harlow's monkeys: infant rhesus monkeys separated from mothers overwhelmingly clung to a soft cloth surrogate over a wire surrogate that provided milk — attachment is built on contact comfort, not feeding (a direct refutation of the behaviorist "cupboard love" account). The cloth mother also served as a secure base for exploring frightening novelty.
• Lorenz's imprinting: precocial birds attach to the first moving object in a critical period — evidence for biologically prepared, time-windowed bonding (do not overextend to humans, where attachment forms gradually).
• Bowlby: attachment is an evolved system keeping the infant near a protector; stranger anxiety (~8 mo) and separation anxiety (peaking ~12-18 mo) are its normal signatures.

Ainsworth's Strange Situation (classify by the REUNION, not the separation)

• Typical base rates in middle-class U.S. samples: secure ~60-65%, avoidant ~20%, ambivalent/resistant ~10-15%, disorganized a small remainder.

Secure attachment tracks sensitive, responsive caregiving and predicts later social competence — as a probabilistic correlate, not destiny.

Temperament: The Child's Own Contribution

Thomas & Chess: easy, difficult, and slow-to-warm-up profiles, visible in infancy, biologically based, moderately stable (Kagan's behaviorally inhibited infants show lasting reactivity differences). Development runs on goodness of fit between temperament and caregiving — and the child's temperament also evokes particular parenting (bidirectionality: correlations between parenting and child outcome are not automatically parent-caused).

• In Thomas & Chess's sample, roughly 40% of infants were easy, 10% difficult, and 15% slow-to-warm-up; the rest fit no single profile.

Parenting Styles (Baumrind: two axes — demandingness × responsiveness)

• Authoritative (high/high): firm limits, warmth, explanation → best average outcomes (competence, self-regulation)
• Authoritarian (high demand, low response): obedience-focused, punitive → anxiety, lower autonomy
• Permissive (low demand, high response): warm, few limits → impulse-control problems
• Neglectful/uninvolved (low/low): worst outcomes Outcomes vary somewhat by culture and are correlational — the same caution as above.

Vygotsky vs. Piaget (the guaranteed contrast)

• Vygotsky: cognition develops socially first — skills appear between child and a more knowledgeable other, then are internalized. Key tools: zone of proximal development (what the child can do with help but not alone), scaffolding (calibrated, fading support), and language/private speech as the vehicle of thought.
• Piaget: the solo child-as-scientist constructing knowledge through action; development precedes and constrains learning.
• Discriminator: if the vignette's gains come through guided interaction, cultural tools, or instruction inside the ZPD → Vygotsky. If through independent exploration and stage-limited readiness → Piaget.

Worked Example — An Attachment-Methods Passage, Fully Read

Passage. In a longitudinal study, 200 infants complete the Strange Situation at 12 months. At reunion, Infant J ignores his returning mother and continues playing with his back turned; Infant K alternates between reaching to be held and arching away in anger, and cannot be soothed. At age 5, teachers blind to classification rate former secure infants higher in peer competence (d = 0.4). A second sample studied in a culture emphasizing early independence training shows nearly double the avoidant rate, and a third sample in which infants are almost never apart from their mothers shows elevated resistant classifications. Finally, temperament assessed at 3 months (irritability) predicts later resistant classification even after controlling for maternal sensitivity.

Step 1 — classify from the reunion. J: exploration plus reunion avoidance = insecure-avoidant. K: clingy-angry, comfort-resistant distress = insecure-ambivalent/resistant. The separations themselves are not diagnostic — many secure infants cry at separation; the REUNION response carries the classification.

Step 2 — treat the age-5 result correctly. Blind ratings remove expectancy bias, and d = 0.4 is a modest effect: attachment security is a probabilistic predictor, not a determinant. Answers phrased as "secure attachment causes later competence" overreach a correlational, self-selected design — sensitive parents may differ in many ways.

Step 3 — read the cross-cultural rates. Systematically shifted distributions suggest the Strange Situation's behaviors carry different meanings under different caregiving norms (independence training makes reunion indifference normative; constant proximity care makes brief separation exceptionally alarming). The measured conclusion: the procedure's VALIDITY is partly culture-bound, not that most infants in those cultures are disordered.

Step 4 — use the temperament finding. Early irritability predicting resistant attachment independent of maternal sensitivity supports a child-driven contribution — the bidirectional model. The strongest wrong answer will attribute classification entirely to parenting; the data given explicitly block that inference.

Attachment, Temperament & Guided Learning 🎯

Key Takeaways — Part 2

• Harlow: contact comfort beats feeding (cloth vs wire unconfounds them); Lorenz: imprinting shows time-windowed prepared bonding; Bowlby: attachment as evolved proximity system with normative stranger and separation anxiety
• Strange Situation classifies by REUNION: secure (settles, greets), avoidant (ignores), resistant (clings and rages, inconsolable), disorganized (contradictory/frozen); cross-cultural rate shifts question the measure, not the children
• Temperament (easy/difficult/slow-to-warm) is early, biological, moderately stable; goodness of fit and child-to-parent effects make parenting correlations bidirectional
• Baumrind grid: demandingness x responsiveness — authoritative (high/high) best on average; authoritarian, permissive, neglectful each miss one or both
• Vygotsky vs Piaget: guided interaction, ZPD, scaffolding, private speech = Vygotsky; solo construction gated by stage readiness = Piaget — pick by the vignette's mechanism of gain

• Low-yield extras: Strange Situation base rates (secure ~60-65%, avoidant ~20%, resistant ~10-15%, disorganized a small remainder); Thomas & Chess temperament percentages (easy ~40%, difficult ~10%, slow-to-warm-up ~15%)

Development

Part 3 of 4 — Erikson, Kohlberg & Identity Across the Lifespan

Erikson's Eight Psychosocial Crises (each age has a conflict; both outcomes matter)

• Erikson named a "virtue" for each favorable resolution, in order: hope, will, purpose, competence, fidelity, love, care, wisdom.

MCAT tactic: identify the character's approximate age AND the described struggle; distractors offer the adjacent stages.

Kohlberg's Moral Reasoning (score the REASONING, never the verdict)

Heinz dilemma responses are staged by their justification:

• Preconventional (self-interest): Stage 1 — avoid punishment; Stage 2 — instrumental exchange ("what's in it for me")
• Conventional (social order): Stage 3 — approval, good-boy/good-girl; Stage 4 — law and order, duty upholds society
• Postconventional (principle): Stage 5 — social contract, laws are revisable agreements; Stage 6 — universal ethical principles that can override law

Either verdict ("steal" or "don't steal") can be argued at ANY stage — items that classify by conclusion are traps. Gilligan's critique: the scheme privileges a justice orientation; an ethic of care is an alternative moral voice, not a lower stage.

Adolescence: Identity Work

• Marcia's identity statuses (two axes: exploration × commitment):
  • Diffusion — no exploration, no commitment
  • Foreclosure — commitment WITHOUT exploration (adopting parents' plan wholesale)
  • Moratorium — active exploration, commitment pending
  • Achievement — commitment following genuine exploration
• Adolescent egocentrism (Elkind): imaginary audience (everyone is watching me) and personal fable (my experience is unique; risks don't apply to me — the invulnerability belief behind risk-taking, compounded by still-maturing prefrontal control against an earlier-maturing reward system)

Adulthood & Aging (the positive-picture findings)

• Socioemotional selectivity (Carstensen): as perceived time horizons shrink, motivation shifts from information-seeking to emotionally meaningful ties — networks get smaller and more satisfying by choice, not by social failure
• The positivity effect: older adults preferentially attend to and remember positive material
• Cognitive aging recap (from the cognition lesson): fluid abilities and recall decline; crystallized knowledge and recognition hold — normal aging is NOT dementia
• Erikson's final crises (generativity, then integrity) frame midlife mentoring and late-life life review

Worked Example — A Moral-Reasoning Study, Fully Read

Passage. Researchers present the Heinz dilemma to 90 participants (ages 10, 16, 30). Four sample responses are recorded: (A) "He shouldn't steal — he'll be jailed." (B) "He should steal — a good husband is expected to protect his family, and people would think badly of him otherwise." (C) "He shouldn't steal — if everyone broke laws whenever they had a reason, society couldn't function." (D) "He should steal — the right to life is a universal principle that outranks property law, though he should accept the legal consequences." Stage distribution shifts upward with age, but many 30-year-olds remain at Stage 4, and cross-cultural replications find Stage 5-6 responses rare outside formally schooled populations. Female participants more often justify choices by relationship preservation, which the original scoring places at Stage 3.

Step 1 — score each response by its justification. A = Stage 1 (punishment avoidance, preconventional). B = Stage 3 (role approval, conventional) — note it REACHES the opposite verdict from A, proving verdicts don't carry stage information. C = Stage 4 (law-and-order, conventional). D = Stage 5/6 (principle over law, postconventional) — accepting punishment while violating the law is the postconventional tell.

Step 2 — read the age data with the theory's own claims. Upward drift supports an invariant SEQUENCE; adults plateauing at Stage 4 shows the top stages are not universal endpoints — Kohlberg himself conceded Stage 6 is rare. Sequence claims and universality claims are separable; the data support the first more than the second.

Step 3 — handle the cultural and gender findings. Rarity of postconventional scores in unschooled populations may mean the scoring privileges Western, verbal, principle-citing argument styles (a measurement-validity issue) rather than that whole cultures reason "lower." The gender finding is Gilligan's exact objection: care-based justifications get filed at Stage 3 by a scheme built on justice reasoning — a scoring-orientation bias, not a female deficit.

Step 4 — the anticipated item. "A participant argues Heinz should NOT steal because his wife's care network would collapse if he were imprisoned. Under Kohlberg vs. Gilligan..." — Kohlberg's scheme scores the relational content conventionally; Gilligan reads it as a mature ethic of care. Recognizing that the SAME response scores differently under the two frameworks is the passage's payoff.

Psychosocial Stages, Moral Reasoning & Identity 🎯

Key Takeaways — Part 3

• Erikson ladder: trust → autonomy → initiative → industry → identity → intimacy → generativity → integrity; match age plus struggle, and remember intimacy presupposes identity
• Kohlberg: score justifications only — punishment/exchange (preconventional), approval/law-and-order (conventional), social contract/universal principle (postconventional); sequence is better supported than universality
• Gilligan: care-based reasoning is an alternative orientation the justice-based scoring undervalues, not a lower stage
• Marcia grid: exploration x commitment → diffusion, foreclosure (commitment without exploration), moratorium, achievement
• Adolescent egocentrism: imaginary audience + personal fable (invulnerability → risk); aging brings socioemotional selectivity and the positivity effect — smaller, warmer networks by choice

• Low-yield extras: Erikson's named virtues for the eight favorable resolutions (hope, will, purpose, competence, fidelity, love, care, wisdom)

Development — Deep Dive

Part 4 of 4 — MCAT Integration: Nature-Nurture Designs & Reading Developmental Studies

The Genetically Informative Designs (what each one isolates)

• Concordance: probability both members of a pair show the trait
• Caveats the MCAT loves: MZ twins are also treated more alike (the equal-environments assumption); adoptive homes are range-restricted (screened, above-average); prenatal environment is shared in both twin types

Heritability — the Most Misread Statistic on the Exam

• Heritability = proportion of trait variance within a population attributable to genetic variance — a POPULATION statistic, never a statement about one person ("80% heritable" does not mean 80% of your IQ is genetic)
• It is environment-dependent: equalize environments and heritability RISES (remaining differences are mostly genetic); impoverish some environments and it falls
• Within-group heritability says NOTHING about between-group differences (the plant-in-two-soils analogy)
• Gene-environment interaction: a genotype's effect depends on the environment (a risk allele mattering only under stress exposure). Gene-environment correlation: genotypes and environments arrive together — passive (parents supply both), evocative (the child's traits elicit responses), active (niche-picking)

Prenatal Development & Teratogens

• Germinal (0-2 wk: zygote → implantation) → embryonic (3-8 wk: organogenesis — peak teratogen vulnerability) → fetal (9 wk+: growth, brain maturation continues throughout)
• Teratogens: alcohol (fetal alcohol syndrome — leading preventable intellectual disability; no established safe dose), tobacco (growth restriction), certain drugs, infections (rubella), radiation. Damage depends on TIMING (which system is forming), dose, and genotype — the same exposure harms different structures in different weeks
• The brain remains vulnerable across all trimesters (long organogenesis window)

Reading Developmental Methods (the recurring question set)

• Cross-sectional design: different ages tested once — fast, but confounds age with cohort (a 70-year-old and a 20-year-old differ in generation, schooling, tech exposure — not just age)
• Longitudinal: same people over time — isolates true change, but suffers attrition (selective dropout biases late waves toward the healthy/motivated), practice effects, cost
• Sequential designs mix both to separate age, cohort, and time-of-measurement
• Infant dependent measures: habituation/dishabituation looking time, preferential looking, violation-of-expectation — all infer cognition from attention recovery

• High-amplitude sucking applies the same habituation logic to newborns: sucking rate on a sensor-fitted pacifier drops as a stimulus grows familiar and rebounds when a new one is detected.

• Standard causal traps: parenting-outcome correlations (child effects, passive rGE), "critical period" claims needing deprivation evidence, and cohort-driven "decline" findings

Worked Example — A Nature-Nurture Passage, Fully Read

Passage. A study of cognitive ability reports: MZ-together correlation 0.86; MZ-apart 0.74; DZ-together 0.59; adoptive siblings (unrelated, same home) 0.28 in childhood, falling to near 0.04 by adulthood; adopted children's IQ correlates more with biological than adoptive parents by adolescence. The authors estimate heritability at ~0.5 in childhood, rising toward ~0.7 in adulthood. A commentator objects: "If IQ is 70% genetic, early-childhood enrichment programs are pointless, and the average difference between two neighborhoods' test scores must be genetic."

Step 1 — extract the design logic. MZ-apart (0.74) approaching MZ-together (0.86) shows strong similarity WITHOUT a shared home → genetic contribution plus a modest shared-environment effect (the 0.12 gap). Adoptive-sibling correlations fading to ~0 by adulthood is the classic finding that shared family environment's influence on IQ wanes as people select their own environments (active gene-environment correlation — niche-picking).

Step 2 — explain heritability RISING with age. Counterintuitive but standard: as individuals increasingly choose environments matching their genotypes, genetic differences amplify; and adult environments (self-selected) vary less arbitrarily than childhood ones. Rising heritability is evidence of gene-environment correlation at work, not of genes "switching on" alone.

Step 3 — dismantle the commentator, claim by claim. (a) Population heritability does not bound what a NEW environment can do — heritability is computed over existing environments; enrichment adds one that wasn't in the data (height is highly heritable, yet mean height rose across a century of better nutrition). (b) Within-group heritability licenses no inference about between-group gaps: two neighborhoods can differ entirely for environmental reasons while heritability within each is high — identical seed, different soil. Both errors are named, canonical, and heavily tested.

Step 4 — the design-extension item. "Which additional group would best isolate shared-environment effects?" Unrelated adoptive siblings already do — their entire similarity (0.28 in childhood) IS shared environment, since they share no genes. Recognizing which correlation carries which variance component is the skill the passage is built to test.

Twin Logic, Teratogens & Method Traps 🎯

Key Takeaways — Part 4

• Design logic: MZ-DZ concordance gap = genes; adoptee-biological resemblance = genes; adoptive-sibling similarity = shared environment; MZ concordance under 100% = environment and chance are real
• Heritability is a population variance statistic: not individual, not fixed, not intervention-proof, and never a bridge from within-group to between-group differences
• Gene-environment: interaction (allele effect depends on exposure) vs correlation (passive, evocative, active/niche-picking — the reason heritability rises with age)
• Teratogens strike by timing: embryonic weeks 3-8 = organogenesis peak; brain vulnerable all pregnancy; FAS = leading preventable intellectual disability
• Methods: cross-sectional confounds age with cohort; longitudinal fights attrition and practice effects; sequential separates them; infant cognition is read from looking-time recovery

• Low-yield extras: high-amplitude sucking, the newborn version of habituation-dishabituation (sucking rate rebounds when a new stimulus is detected)