Unit 3.2: Physical Development Across the Lifespan
AP Psychology | Unit 3: Development and Learning
🎯 Exam Focus
Physical development encompasses bodily changes from conception through death. Master prenatal influences (teratogens, genetics, maternal health), infant reflexes (rooting, sucking, grasping), motor development patterns (cephalocaudal, proximodistal), depth perception (visual cliff), critical and sensitive periods, adolescent changes (puberty, brain development), and adulthood decline (sensory changes, menopause, reaction time). This content appears frequently on both multiple-choice and FRQ sections. NOTE: Specific prenatal stages (zygote, embryo, fetus) are NOT tested on the AP exam.
📚 Introduction to Physical Development
Physical development refers to the biological changes in body structure, function, and abilities that occur throughout the human lifespan from conception to old age.
These physical changes profoundly influence behavior and mental processes. Motor skills enable exploration and learning, brain development supports cognitive abilities, and sensory changes affect how we perceive and interact with the world.
Understanding physical development helps explain age-related capabilities, limitations, and the biological foundations of psychological experiences across the lifespan.
👶 Physical Development Before Birth
⚠️ IMPORTANT EXCLUSION NOTE
The specific stages of prenatal development (zygote, embryo, fetus) will NOT be tested on the AP Psychology exam. Focus instead on the factors that influence prenatal development.
Teratogens
Teratogens are environmental agents (substances, diseases, conditions) that can harm the developing fetus and cause birth defects or developmental abnormalities.
Common Teratogens:
- Alcohol: Causes Fetal Alcohol Spectrum Disorders (FASD) with facial abnormalities, growth problems, cognitive deficits, and behavioral issues
- Tobacco/Nicotine: Low birth weight, premature birth, respiratory problems, increased SIDS risk
- Recreational drugs: Cocaine, heroin, marijuana — developmental delays, withdrawal symptoms, behavioral problems
- Prescription medications: Some anticonvulsants, isotretinoin (Accutane), certain antibiotics
- Environmental toxins: Lead, mercury, radiation, pesticides
- Maternal infections: Rubella, Zika virus, toxoplasmosis, cytomegalovirus
Critical Timing:
The severity of teratogenic effects depends on WHEN exposure occurs. Early pregnancy is especially vulnerable because organs and major body structures are forming. The same teratogen can have different effects depending on the timing of exposure.
Additional Prenatal Influences
Genetic Factors:
- Inherited mutations from parents
- Spontaneous mutations during cell division
- Chromosomal abnormalities (Down syndrome, Turner syndrome)
- Single-gene disorders (sickle cell anemia, cystic fibrosis)
Maternal Health Conditions:
- Chronic conditions (diabetes, hypertension)
- Maternal fever and severe stress
- Infections crossing the placental barrier
- Nutritional deficiencies (especially folate/folic acid)
Hormonal Environment:
- Maternal hormone imbalances (thyroid, cortisol)
- Endocrine-disrupting chemicals
- Hormones influencing sexual differentiation and brain development
📏 Principles of Physical Development
Developmental Patterns
Physical development follows predictable, orderly patterns that reflect nervous system and muscle maturation:
Cephalocaudal Pattern (Head-to-Toe)
Physical development and motor control proceed from the head downward to the lower body.
Example: Babies gain head control → then trunk control → then leg control. They can lift their heads before they can sit, and sit before they can walk.
Proximodistal Pattern (Center-to-Periphery)
Development proceeds from the center of the body outward to the extremities.
Example: Babies gain control of torso and shoulders → then arms → then hands → then fingers. They can reach for objects before they can grasp them precisely.
🏃 Motor Development in Infancy and Childhood
Gross Motor Skills
Large movements using whole body or major muscle groups
Examples:
- Rolling over
- Sitting
- Crawling
- Walking
- Running
- Jumping
Fine Motor Skills
Small, precise movements using hands and fingers
Examples:
- Grasping objects
- Pincer grasp (thumb+finger)
- Using utensils
- Stacking blocks
- Drawing/writing
- Buttoning clothes
📊 Typical Motor Development Milestones
Important Note: While the SEQUENCE is universal and predictable, the TIMING varies significantly between children due to genetics, nutrition, health, and environmental stimulation.
🍼 Infant Reflexes
What are Reflexes?
Reflexes are automatic, involuntary responses to specific stimuli that are present at birth. They indicate healthy neurological development and help infants survive.
Key Survival Reflexes:
1. Rooting Reflex
When a baby's cheek is stroked, they turn their head toward the touch and open their mouth. Helps locate food source (breast/bottle).
2. Sucking Reflex
Automatic sucking when something touches the roof of the mouth. Essential for feeding.
3. Palmar Grasp Reflex
Automatically grasps fingers or objects placed in the palm. Evolutionary remnant of clinging to caregiver.
4. Moro Reflex (Startle Reflex)
Throws arms outward and then brings them back to the body when startled or head drops back. Protective response.
Developmental Significance: These reflexes typically disappear on a predictable timeline as voluntary motor control develops. Persistence beyond expected ages may indicate neurological concerns.
👁️ Depth Perception Development
The Visual Cliff Experiment (Gibson & Walk)
The visual cliff is a classic experiment designed to test depth perception in infants using a transparent surface that creates the illusion of a drop-off.
Experimental Setup:
- Glass table with a checkered pattern underneath
- One side appears shallow (pattern directly under glass)
- Other side appears deep (pattern several feet below glass)
- Infant placed on shallow side; mother calls from deep side
Key Findings:
- Most 6-8 month old infants refuse to crawl over the "deep" side
- They can perceive depth even before they can crawl
- Depth perception is partially innate but refined through experience
- Infants use visual information to guide protective behavior
Significance: This research revolutionized understanding of infant perception, showing that babies actively process environmental information and use it to guide behavior far earlier than previously thought.
⏰ Critical and Sensitive Periods
Critical Periods
Critical periods are specific, limited timeframes when certain experiences MUST occur for normal development. If the experience doesn't happen during this window, development may be permanently impaired.
Examples:
- Visual system development: Requires appropriate visual stimulation in first months; deprivation can cause permanent vision loss
- Language acquisition: Most efficient before puberty; children not exposed to language early may never fully develop normal language abilities
- Attachment formation: Critical period during first two years for forming secure bonds
Sensitive Periods
Sensitive periods are optimal timeframes when development occurs most easily and efficiently. Learning can still happen outside these windows, but requires more effort and may be less complete.
Examples:
- Second language learning: Easier and more native-like before puberty, but still possible in adulthood
- Musical training: Starting young leads to better skill development, but adults can learn
- Motor skills: Some complex motor patterns easier to acquire in childhood
Imprinting (Non-Human Example)
Imprinting is a rapid form of learning during a critical period in some animals (especially birds) where they form an attachment to the first moving object they see, usually their mother.
- Demonstrated by Konrad Lorenz with goslings
- Occurs within hours after hatching
- Once formed, extremely difficult to reverse
- Evolutionary survival mechanism ensuring offspring stay near caregiver
Note: Humans do NOT imprint in this way. Human attachment develops gradually over months through repeated caregiver interactions.
🌱 Physical Development in Adolescence
Puberty and the Adolescent Growth Spurt
Puberty is the period of rapid physical maturation during which the body becomes capable of sexual reproduction. It's triggered by hormonal changes and brings dramatic physical transformation.
Timing:
- Females: Typically begins ages 10-12; growth spurt peaks around 11-12
- Males: Typically begins ages 12-14; growth spurt peaks around 13-15
- Individual variation is normal and influenced by genetics, nutrition, health, and environment
Primary Sex Characteristics:
Body structures directly involved in reproduction:
- Females: Ovaries, uterus, vagina mature; Menarche (first menstruation) typically ages 12-13
- Males: Testes, penis, prostate mature; Spermarche (first ejaculation) typically ages 13-14
Secondary Sex Characteristics:
Physical changes not directly involved in reproduction:
- Both sexes: Pubic and underarm hair, increased oil/sweat gland activity (acne), height increase, muscle development
- Females: Breast development, widening of hips, fat redistribution
- Males: Facial and body hair, voice deepening, muscle mass increase, broadening of shoulders
Adolescent Brain Development
The adolescent brain undergoes significant structural and functional changes that affect behavior, emotions, and decision-making.
Key Brain Changes:
- Synaptic pruning: Unused neural connections are eliminated; frequently used connections strengthen
- Myelination: Fatty myelin sheath increases on neurons, speeding neural transmission
- Limbic system: Emotional centers mature early, leading to heightened emotions and reward sensitivity
- Prefrontal cortex: Responsible for planning, impulse control, and judgment; develops LAST (not fully mature until mid-20s)
Behavioral Impact: The limbic system maturing before the prefrontal cortex explains why teenagers can be emotionally intense, impulsive, risk-taking, and peer-focused. Emotions drive behavior before rational thinking fully develops.
👴 Physical Development in Adulthood
Early Adulthood (20s-30s): Peak Physical Function
- Peak physical strength, speed, and stamina
- Optimal sensory functioning (vision, hearing, taste, smell)
- Maximum reproductive capability
- Fastest reaction times
- Completed brain development (prefrontal cortex fully mature by mid-20s)
Middle Adulthood (40s-50s): Gradual Decline Begins
Physical Changes:
- Gradual decrease in muscle mass and strength
- Slower metabolism; weight distribution changes
- Decreased flexibility and joint mobility
- Mild sensory declines (presbyopia — farsightedness around age 40-50)
- Slower reaction times
Reproductive Changes:
Menopause (Females): End of menstruation and fertility, typically ages 45-55
- Decreased estrogen and progesterone production
- Physical symptoms: hot flashes, night sweats, sleep disruption
- Long-term effects: decreased bone density (osteoporosis risk), cardiovascular changes
- Psychological impacts: mood changes, potential depression or anxiety (varies widely)
Male Changes: Gradual decline, not abrupt cessation
- Gradual testosterone decline
- Decreased sperm production and motility
- Reduced fertility (though can remain fertile into advanced age)
Later Adulthood (60s+): Accelerated Decline
Physical Changes:
- Strength and mobility: Significant decreases in muscle mass, strength, flexibility, balance
- Reaction time: Noticeably slowed processing speed and motor responses
- Recovery: Longer recovery time after physical exertion or illness
- Bone health: Decreased bone density (especially in women)
- Cardiovascular: Reduced heart efficiency, increased blood pressure risk
Sensory Changes:
- Vision: Decreased acuity, reduced color discrimination, need for more light
- Hearing: Presbycusis (age-related hearing loss), especially high frequencies
- Taste and smell: Diminished sensitivity
- Touch: Decreased sensitivity to temperature and pain
Impact on Behavior and Mental Processes: Sensory declines increase cognitive load (brain works harder to decode input), slower processing affects decision-making, and mobility limits reduce social engagement opportunities.
📝 AP Exam Strategy
Multiple Choice Tips
- Know teratogens: Alcohol (FASD), drugs, infections, environmental toxins and their effects
- Master infant reflexes: Rooting, sucking, grasping, Moro — know what they are and when they disappear
- Understand motor development: Gross (whole body) vs. fine (hands/fingers); sequence is universal, timing varies
- Remember developmental patterns: Cephalocaudal (head-to-toe), proximodistal (center-to-periphery)
- Visual cliff: Tests depth perception in infants; shows perception develops before locomotion
- Critical vs. sensitive periods: Critical = must happen; sensitive = optimal but flexible
- Puberty: Primary (reproductive organs) vs. secondary (other physical changes) sex characteristics
- Brain development: Limbic system (emotions) matures before prefrontal cortex (judgment)
- Adulthood: Peak in 20s-30s, gradual decline in 40s-50s, accelerated decline 60s+
Free Response Question (FRQ) Tips
- Explain behavioral impacts: Don't just list physical changes — explain HOW they affect behavior and mental processes
- Use precise terminology: Say "cephalocaudal pattern" not "top-down development"
- Provide specific examples: For teratogens, name specific substances and their effects
- Connect concepts: Link motor development to exploration and cognitive growth
- Distinguish age periods: Clearly differentiate prenatal, infancy, childhood, adolescence, adulthood
- Apply to scenarios: If given a case study, identify which physical changes explain observed behaviors
✨ Quick Review Summary
🔑 The Big Picture
Physical development across the lifespan is influenced by prenatal factors (teratogens like alcohol/drugs, maternal health, genetics, hormones) that can cause developmental abnormalities. NOTE: Prenatal stages (zygote, embryo, fetus) are NOT tested. Motor development follows predictable patterns: cephalocaudal (head-to-toe) and proximodistal (center-to-periphery). Gross motor skills (whole body) and fine motor skills (hands/fingers) develop in sequence, though timing varies. Infant reflexes (rooting, sucking, grasping, Moro) indicate healthy development. Visual cliff experiments show depth perception emerges by 6-8 months. Critical periods require specific experiences for normal development (language, vision); sensitive periods are optimal windows but flexible. Adolescence brings puberty (primary sex characteristics: reproductive organs; secondary: body changes), growth spurts (females 10-12, males 12-14), and brain development (limbic system matures before prefrontal cortex, explaining impulsivity). Adulthood peaks in 20s-30s, declines gradually in 40s-50s (menopause, sensory changes), and accelerates decline 60s+ (reduced mobility, flexibility, reaction time, sensory acuity).
💡 Essential Concepts
- Teratogens
- Fetal Alcohol Spectrum Disorders
- Cephalocaudal pattern
- Proximodistal pattern
- Gross motor skills
- Fine motor skills
- Rooting reflex
- Sucking reflex
- Palmar grasp reflex
- Moro (startle) reflex
- Visual cliff
- Depth perception
- Critical periods
- Sensitive periods
- Imprinting
- Puberty
- Primary sex characteristics
- Secondary sex characteristics
- Menarche
- Spermarche
- Adolescent growth spurt
- Prefrontal cortex
- Limbic system
- Synaptic pruning
- Myelination
- Menopause
- Presbyopia
- Presbycusis
📚 AP Psychology Unit 3.2 Study Notes | Physical Development Across the Lifespan
Master physical development from prenatal to old age for exam success!