Chapter 5: The First Two Years – Biosocial Development
I. Body Changes
● Birth weight doubles by 4 months, triples by 1 year
● Height increases by ~10 inches in the first year
● Growth slows after first year but remains rapid
● Head-sparing: brain is last part to be affected by malnutrition
II. Brain Development
● Neurons: ~100 billion at birth
● Synaptogenesis: rapid creation of synapses
● Pruning: unused connections atrophy and die
● Myelination: speeds up neural transmission
● Experience-Expectant vs. Experience-Dependent growth
● Plasticity: adaptability of the brain in early years
III. Sleep
● Newborns sleep ~15-17 hours/day, gradually decreases
● REM sleep high in infancy, crucial for brain development
● Co-sleeping: cultural differences in sleeping arrangements
IV. Sensory & Perceptual Development
● Hearing: Develops during prenatal life, well-developed at birth, preference for mother's
voice
○ At birth, sounds trigger reflexes, even without perception
○ Soon, infants turn their heads to see the source of a voice
● Vision: Least developed sense at birth, improves rapidly
○ Newborns focus between 4 and 30 inches away
○ Binocular vision by 2-4 months
○ Depth perception by 3 months (visual cliff experiment)
○ By 12 months, infants are more attracted to people's faces than other salient
objects
● Touch: Sense of touch is acute in infants, essential for bonding and comfort
○ Gentle touch is effective even for newborns
● Pain: Pain and temperature are connected to touch
○ Sugar and breastfeeding relieve pain
○ Newborn pain perception differs from adults
● Taste & Smell: Preferences develop early, influenced by prenatal exposure
V. Motor Skills
I. Body Changes
● Birth weight doubles by 4 months, triples by 1 year
● Height increases by ~10 inches in the first year
● Growth slows after first year but remains rapid
● Head-sparing: brain is last part to be affected by malnutrition
II. Brain Development
● Neurons: ~100 billion at birth
● Synaptogenesis: rapid creation of synapses
● Pruning: unused connections atrophy and die
● Myelination: speeds up neural transmission
● Experience-Expectant vs. Experience-Dependent growth
● Plasticity: adaptability of the brain in early years
III. Sleep
● Newborns sleep ~15-17 hours/day, gradually decreases
● REM sleep high in infancy, crucial for brain development
● Co-sleeping: cultural differences in sleeping arrangements
IV. Sensory & Perceptual Development
● Hearing: Develops during prenatal life, well-developed at birth, preference for mother's
voice
○ At birth, sounds trigger reflexes, even without perception
○ Soon, infants turn their heads to see the source of a voice
● Vision: Least developed sense at birth, improves rapidly
○ Newborns focus between 4 and 30 inches away
○ Binocular vision by 2-4 months
○ Depth perception by 3 months (visual cliff experiment)
○ By 12 months, infants are more attracted to people's faces than other salient
objects
● Touch: Sense of touch is acute in infants, essential for bonding and comfort
○ Gentle touch is effective even for newborns
● Pain: Pain and temperature are connected to touch
○ Sugar and breastfeeding relieve pain
○ Newborn pain perception differs from adults
● Taste & Smell: Preferences develop early, influenced by prenatal exposure
V. Motor Skills
