In 1958, Harry Harlow took baby monkeys away from their mothers and gave them two fake substitutes. One "mother" was a bare wire cylinder that dispensed milk from a bottle. The other was the same cylinder wrapped in soft terrycloth — but it gave no food at all.
Every theory of the day said the babies should bond with the wire mother. Feed the infant, the thinking went, and love follows the food — attachment is just the warm afterglow of a full stomach. Freudians and behaviorists agreed on this, which almost never happens.
The monkeys disagreed. They clung to the cloth mother nearly around the clock, climbing over to the wire mother only to grab a quick drink before scrambling back to the soft one. When something frightening appeared, they ran to the cloth. The food source was not the safe base; the soft thing was.
That single result rewired how psychology understood love. Attachment, it turned out, isn't bought with calories. It's built from contact comfort — and that's where this lesson begins.
Before any specific finding, know the debates the whole field organizes itself around — the AP exam loves to ask which one a scenario illustrates.
The first is nature vs. nurture: how much of who you become comes from your genes (nature) versus your experiences and environment (nurture)? As in Lesson 1, the modern answer is interaction, not a winner — but developmental research is where you watch that interaction unfold in real time.
The second is continuity vs. stages: does development proceed gradually and continuously, like a dimmer switch slowly brightening, or in distinct qualitative stages, like climbing a staircase where each step is a different kind of thinking? Stage theorists (Piaget, Erikson, Kohlberg — coming in later lessons) argue for staircases. Others see smooth, cumulative change.
The third is stability vs. change: do our traits stay constant across the lifespan, or do we change as we age? Is the shy toddler destined to be the shy adult? The honest answer is "some of both" — temperament shows real stability, but people also change.
To study development you need to compare people of different ages — and there are two ways to do it, each with a fatal flaw.
A cross-sectional study compares different groups of people of different ages at the same time — testing 20-year-olds, 50-year-olds, and 80-year-olds this year and comparing them. It's fast and cheap, but it's haunted by the cohort effect: people born in different eras differ for reasons that have nothing to do with aging (the 80-year-olds had less schooling, different nutrition, different everything). So a "decline with age" might really be a generational difference.
A longitudinal study follows the same people over time, testing them at 20, then 50, then 80. This cleanly separates aging from cohort — but it's slow (you might wait 60 years), expensive, and plagued by attrition (participants drop out, move, or die, and the ones who stick around may be unusually healthy or motivated).
Mnemonic: Cross-sectional = a cross-section, one slice of time, many ages at once. Longitudinal = a long line through time, one group followed.
Development begins long before the first reflex. After conception, the zygote — the single fertilized egg cell — divides rapidly. From roughly two weeks to two months, it's an embryo, and the major organs begin to form. From about nine weeks until birth, it's a fetus. This zygote → embryo → fetus sequence is must-know vocabulary.
The danger is that the same period when organs form is the period when they're most vulnerable. A teratogen is any substance or agent that can cross the placenta and harm prenatal development — alcohol, certain viruses, nicotine, some medications, radiation. The classic example is alcohol: heavy prenatal alcohol exposure can cause fetal alcohol syndrome (FAS), marked by physical abnormalities (including distinctive facial features) and lifelong cognitive deficits. There is no established safe amount, which is why doctors advise against any drinking during pregnancy.
Try This. Why does timing matter so much for teratogens? A teratogen does the most damage to whatever structure is developing fastest at the moment of exposure. Exposure during the embryonic period (when organs are forming) tends to cause structural damage; the same exposure later in the fetal period more often affects growth and the nervous system. The "critical period" logic shows up here too — vulnerability is a window, not a constant.
A newborn looks helpless but ships with a surprising amount of working software. Reflexes are automatic, unlearned responses to specific stimuli — and several are survival tools you should know by name:
Newborns also arrive with sensory preferences — they prefer face-like patterns and the sound of their own mother's voice within days. The blank-slate newborn is a myth.
Much of early physical development isn't taught — it's maturation: the biologically driven sequence of growth that unfolds in a relatively fixed order, largely independent of experience. You don't train a baby to roll over before sitting before crawling before walking; the motor development sequence unfolds in that universal order because the nervous system matures from the top down and center outward. Experience can nudge the timing slightly, but not the order. A child raised in a culture that never places babies on their stomachs may crawl later or skip it — but the broad sequence holds. The signature of maturation: same order, everywhere, without instruction.
Some babies are mellow; some scream the house down. Temperament is a person's characteristic emotional reactivity and intensity, and it shows up early and is biologically based — a strong piece of evidence for the "stability" and "nature" sides of the debates. Thomas and Chess identified three classic temperament types: the easy child (regular routines, generally cheerful, adapts readily), the difficult child (irregular, intense, slow to adapt, easily upset), and the slow-to-warm-up child (mild, somewhat negative at first, warms gradually to new situations). Temperament is part of why "stability vs. change" doesn't have a clean answer — temperament is one of the most stable things about us.
Attachment is the deep emotional bond an infant forms with its primary caregiver. The big question — what creates it — is where the landmark studies live.
Harry Harlow's monkey experiments (1958) demolished the "cupboard theory" that infants love whoever feeds them. As the hook described, infant monkeys preferred a soft cloth surrogate over a wire one that provided milk, showing that contact comfort — the comfort of soft physical touch — matters more for attachment than nourishment. The cloth mother also served as a secure base: a frightened monkey would cling to it and then, reassured, venture out to explore.
Konrad Lorenz studied a different but related phenomenon in birds. Imprinting is the process by which certain animals (especially precocial birds like geese and ducks, which can move soon after hatching) form a rigid attachment to the first moving object they see during a brief critical period shortly after birth — normally the mother, but in Lorenz's famous case, Lorenz himself, whom the goslings then followed everywhere. Imprinting is fast, occurs only within a narrow window, and is essentially irreversible. Note: human infants do not imprint — that's a trap we'll hit in section (e).
John Bowlby built the broad theory: attachment is an evolved, adaptive system that keeps infants close to caregivers for protection, and the quality of early attachment shapes later relationships through an internal "working model" of how relationships work.
Mary Ainsworth turned Bowlby's theory into a measurement. In the Strange Situation, a structured lab procedure, a caregiver and infant enter an unfamiliar room; the caregiver leaves and returns, sometimes with a stranger present. What psychologists watch is the reunion — how the baby responds when the caregiver comes back. From this, Ainsworth identified attachment styles:
Two related fears emerge on schedule as attachment develops. Stranger anxiety — fear of unfamiliar people — appears around 8 months. Separation anxiety — distress when the attachment figure leaves — peaks around 13–15 months. Both are signs of a formed attachment, not problems.
Diana Baumrind identified parenting styles along two dimensions — warmth/responsiveness and demandingness/control:
The killer trap is authoritative vs. authoritarian — covered in (e). For now: authoritative parents authorize with reasons and warmth; authoritarian parents are autocrats — control without warmth.
Harlow's surrogate mother experiments (Harry Harlow, 1958).
Who & when: Harry Harlow, University of Wisconsin, published prominently in 1958 ("The Nature of Love").
Method: Harlow separated infant rhesus monkeys from their mothers and raised them with two inanimate surrogate "mothers." One was constructed of bare wire and held a feeding bottle; the other was wire wrapped in soft terrycloth and provided no food. He measured how much time the infants spent on each surrogate and which one they fled to when frightened (e.g., by a mechanical "monster" toy).
Finding: The monkeys spent the overwhelming majority of their time clinging to the soft cloth mother, going to the wire mother only to feed and then returning to the cloth. When frightened, they ran to the cloth mother and used it as a secure base before exploring. Contact comfort, not nourishment, drove the attachment.
Significance: Harlow overturned the dominant "cupboard theory" — that infants attach to whoever feeds them. It established that physical comfort and a secure base are foundational to attachment, profoundly influencing childcare, orphanage reform, and Bowlby's attachment theory. (Ethically, the maternal-deprivation procedures are now considered deeply troubling — important to note, since the same monkeys later showed severe social impairment, itself evidence of attachment's importance.)
Scenario 1. Researchers want to know whether vocabulary size changes across the lifespan. Team A tests 1,000 people aged 20, 40, and 60 this spring and compares their scores. Team B recruits 1,000 twenty-year-olds and tests them again at 40 and at 60.
Identify each design and one weakness of each. Team A ran a cross-sectional study — different ages compared at one time. Its weakness is the cohort effect: the 60-year-olds grew up in a different era (different schooling, media, language exposure), so any difference might reflect generation, not aging. Team B ran a longitudinal study — one group followed over time. Its weaknesses are attrition (dropout over 40 years) and sheer cost/time.
Scenario 2. A pediatrician observes a 9-month-old who plays happily while her father is in the room, cries when he steps out, but calms quickly and resumes playing the moment he returns and picks her up. A second 9-month-old barely reacts when his mother leaves and turns away from her when she returns.
Classify each infant's attachment. The first infant shows secure attachment — distressed at separation but readily comforted on reunion, using the caregiver as a secure base. The second shows insecure-avoidant attachment — minimal distress at separation and active avoidance on reunion. (The key diagnostic moment is always the reunion, per Ainsworth's Strange Situation.) The first infant's crying at separation is also normal separation anxiety, a sign of healthy attachment, not a red flag.
Scenario 3. Two parents respond to a broken curfew. Parent X says, "No phone for a week — and here's why the rule exists; let's talk about what happened," staying warm throughout. Parent Y says, "You broke the rule. No phone for a month. I don't owe you an explanation," and refuses to discuss it.
Name each parenting style. Parent X is authoritative — high demand (a real consequence) plus high warmth and explanation. Parent Y is authoritarian — high demand but low warmth, control without reasons. The behaviors look similar (both impose consequences); the difference is the warmth and explanation, which is exactly what Baumrind's two-dimensional model captures and what predicts better outcomes for authoritative parenting.
Cross-sectional vs. longitudinal. Both study change across age. Cross-sectional compares different people of different ages at once (fast, but vulnerable to the cohort effect). Longitudinal follows the same people over time (clean on cohort, but slow and prone to attrition). Mnemonic: a cross-section is one slice now; longitudinal runs a long line through time.
Imprinting vs. attachment. Imprinting (Lorenz) is rigid, near-instant, occurs in a narrow critical period, is essentially irreversible, and happens in precocial birds — not humans. Attachment (Harlow, Ainsworth, Bowlby) develops gradually over months in mammals including humans and is flexible. Do not say a human baby "imprints" on its mother — that's a classic miss.
Secure vs. insecure attachment types. Watch the reunion. Secure = distressed then easily comforted. Avoidant = indifferent, ignores caregiver. Anxious/ambivalent = distressed and resists comfort (clings AND pushes away). Disorganized = no coherent strategy. Students confuse avoidant ("doesn't care") with anxious ("can't be soothed") — opposite errors.
The four parenting styles (esp. authoritative vs. authoritarian). Map them on two axes — warmth and demand. Authoritative = high/high (best outcomes). Authoritarian = low warmth/high demand. Permissive = high warmth/low demand. Neglectful = low/low. The near-identical words authoritative and authoritarian are the trap: authoritative authorizes with warmth and reasons; authoritarian is an autocrat.
Four-choice MCQs in current AP format. Answers and explanations in section (h).
EBQ format: three summarized peer-reviewed sources on a shared topic. Write a response that (1) states a defensible claim, (2) supports it with specific evidence from at least two of the sources, and (3) provides reasoning that connects your evidence to your claim using course concepts. 7 points total: Claim (0–1) + Evidence (0–3) + Reasoning & Application (0–2).
Topic: Does the quality of early caregiving and attachment predict children's later social and emotional outcomes?
Source A
Introduction. Researchers examined whether infant attachment classification predicts social competence years later.
Method. In a longitudinal study, 120 infants were classified as securely or insecurely attached using Ainsworth's Strange Situation at 12–18 months. Teachers, blind to the infants' original classifications, rated the same children's peer social competence at age 5 on a standardized scale.
Results. Children classified as securely attached in infancy received significantly higher teacher ratings of peer social competence at age 5 (M = 7.8 on a 10-point scale) than children classified as insecurely attached (M = 5.1). The association held after controlling for family income.
Source B
Introduction. Researchers tested whether the responsiveness of early caregiving relates to attachment security.
Method. Trained observers visited 90 homes and rated each mother's caregiving sensitivity (how promptly and appropriately she responded to her infant's distress signals) over several months. Each infant was later assessed in the Strange Situation.
Results. Higher maternal sensitivity scores were strongly correlated with secure attachment classifications (r = +0.55). Infants of the least sensitive caregivers were disproportionately classified as insecure-avoidant or disorganized.
Source C
Introduction. Researchers asked whether early attachment effects are permanent or can change.
Method. 200 children initially classified as insecurely attached in infancy were followed for 10 years. Researchers recorded whether each child's family later experienced a major increase in caregiving stability (e.g., a stressed single parent gaining consistent support and resources).
Results. Among insecurely attached infants whose families gained caregiving stability, 46% were rated as securely functioning in relationships by age 11; among those whose family circumstances did not improve, only 19% were. Early insecurity predicted later difficulty, but the link was not fixed.
Claim. The quality of early caregiving and the attachment it produces meaningfully predict children's later social and emotional outcomes, but this early influence is a probabilistic tendency that later experience can modify rather than an unchangeable destiny. (Claim — 1 pt: defensible and responsive to the prompt)
Evidence & Reasoning. Source A provides direct evidence that early attachment predicts later social functioning: children classified as securely attached in infancy were rated by blind teachers as more socially competent with peers at age 5 (M = 7.8) than insecurely attached children (M = 5.1). (Evidence from Source A) This fits Bowlby's idea that early attachment forms an internal working model of relationships that the child carries into new social settings — a securely attached child expects others to be responsive and approaches peers accordingly. (Reasoning — applies course content)
Source B explains where secure attachment comes from: maternal caregiving sensitivity was strongly correlated with secure classification (r = +0.55), and the least sensitive caregivers had disproportionately insecure-avoidant or disorganized infants. (Evidence from Source B — a second source) This is exactly what Ainsworth found and what her Strange Situation was built to detect: sensitive, responsive caregiving lets the infant use the caregiver as a secure base, producing secure attachment, while inconsistent or unresponsive care produces insecure patterns. (Reasoning — applies course content)
Source C qualifies the claim: only 46% of insecurely attached infants in families that later gained caregiving stability were securely functioning by age 11, versus 19% in families that did not improve — early insecurity raised the odds of later difficulty but did not lock it in. (Evidence from Source C — a third source, exceeding the two-source minimum) This illustrates the stability-vs-change debate and the interaction of nature and nurture: attachment shows real continuity, yet a change in environmental input (more stable, responsive caregiving) can shift a child's developmental trajectory — consistent with Bowlby's view that working models can be revised. (Reasoning — connects multiple sources to the qualified claim)
(Evidence — 3 pts: specific data drawn from all three sources, well beyond the two-source minimum. Reasoning & Application — 2 pts: each piece of evidence is explicitly tied to the claim using accurate course concepts — working models, secure base, Strange Situation, stability vs. change, nature/nurture interaction.)
1. (C) zygote → embryo → fetus. Single fertilized cell (zygote) → organ formation (embryo) → ~9 weeks to birth (fetus). All other orders scramble the sequence.
2. (C). A teratogen is an external agent (alcohol, virus, drug, radiation) that crosses the placenta and harms development. (A) describes a genetic cause, not a teratogen; (B) describes a reflex; (D) is unrelated.
3. (B) rooting reflex. Cheek stroke → head turn + open mouth (searching to feed). (A) Moro is the startle/flailing response; (C) grasping is the palm-closing response; (D) sucking follows a touch to the roof of the mouth.
4. (C) contact comfort. The monkeys preferred the soft, foodless cloth mother, showing comfort of touch outweighs nourishment. (A) is the "cupboard theory" Harlow refuted; (B) imprinting is Lorenz and applies to birds, not these monkeys; (D) the feeding response did not drive the bond.
5. (B) Longitudinal. Longitudinal = same people over time. (A) cross-sectional compares different ages at once; (C) and (D) are not age-comparison designs.
6. (B) the cohort effect. Different age groups born in different eras differ for generational reasons, confounding apparent aging effects. (A) attrition is a longitudinal problem; (C) maturation is real development, not a methodological artifact; (D) is unrelated.
7. (C) when reunited with the caregiver after separation. Ainsworth classified attachment chiefly by reunion behavior — distressed-but-comforted (secure), avoidant, or resistant. The other moments are far less diagnostic.
8. (B) stranger anxiety. Fear of an unfamiliar person (the rarely-seen grandmother) emerging around 8 months is the textbook definition. (A) separation anxiety is distress when the attachment figure leaves — here the mother is present; (C) reaching for mother signals attachment, not avoidance; (D) is a newborn reflex.
9. (B) imprinting during a critical period. Precocial birds following the first moving object in a narrow window is imprinting (Lorenz). (A)/(C) are mammalian attachment concepts (Harlow); (D) is a temperament category.
10. (C) authoritative; better. High demand plus high warmth and explanation = authoritative, the style Baumrind linked to the best outcomes. (A) authoritarian lacks the warmth/explanation; (B) permissive lacks firm rules; (D) neglectful lacks both.
11. (C) easy. Regular, cheerful, adaptable = Thomas and Chess's easy temperament. (A) difficult is irregular/intense; (B) slow-to-warm-up warms gradually; (D) "disorganized" is an attachment type, not a temperament — a deliberate distractor.
12. (B) maturation. A universal, instruction-independent order of motor milestones is the hallmark of biological maturation. (A) reinforcement would predict cultural variation; (C) cohort effect is a research artifact; (D) contact comfort concerns attachment.
13. (B). 17.5 vs. 1.5 hours on the foodless cloth mother shows contact comfort beats the food source. (A) and (D) get the result backwards; (C) ignores the huge difference the data show.
14. (C) Anxious-ambivalent (12%). Distressed and resisting comfort — clinging while pushing away, never settling — is the anxious/ambivalent (resistant) pattern. (A) secure would be comforted; (B) avoidant would ignore the caregiver; (D) disorganized shows no coherent strategy rather than this specific approach-and-resist pattern.
15. (C) Stability vs. change. Whether an early trait (shyness) persists across the lifespan is precisely the stability-vs-change question. (A) concerns gradual vs. stage-like development; (B) concerns gene/environment sources; (D) is a methods distinction.
16. (B) fetal alcohol syndrome. Prenatal alcohol is a teratogen producing FAS (physical and cognitive deficits). (A) and (D) are attachment phenomena; (C) is a newborn reflex.
EBQ rubric (7 points)
- Claim (0–1): 1 pt for a defensible claim that directly answers whether early caregiving/attachment predicts later outcomes. (Best answers note the predict-but-not-destiny nuance, but a clear one-directional claim also earns the point.)
- Evidence (0–3): Up to 3 pts for specific, accurate evidence drawn from at least two sources (e.g., A's 7.8 vs. 5.1 competence ratings; B's r = +0.55 sensitivity–security correlation; C's 46% vs. 19% recovery rates). Evidence from only one source caps this component.
- Reasoning & Application (0–2): Up to 2 pts for connecting the cited evidence to the claim using accurate course concepts (working model, secure base, Strange Situation, caregiving sensitivity, stability vs. change, nature/nurture interaction, correlation ≠ causation). Listing evidence without linking it to the claim, or "reasoning" from everyday intuition, does not earn these points.
PsyIQ · Lesson 15 of 30 · Unit 3: Development and Learning. FRQ practice is an Evidence-Based Question (EBQ) — 3 summarized sources, modeled on the redesigned (2025+) AP Psychology exam. Not affiliated with the College Board. AP is a registered trademark of the College Board. Content pending external psychology QC.