Notes on The First Two Years: Body and Mind

Body Size
- Average Weight
- At birth: 7 pounds (3.2 kilograms)
- At 24 months: 28 pounds (13 kilograms)
- Average Length
- At birth: 20 inches
- At 24 months: 34 inches
- These numbers represent norms or average measurements; also related to the concept of failure to thrive.
Sleep Patterns
- Sleep specifics vary due to biological, caregiving, and cultural factors.
- Newborns sleep: 15–17 hours a day.
- By 12 months, norm is: 12 to 13 hours daily.
- Newborns primarily experience active sleep.
- Factors disrupting sleep include pain (colic, hunger).
Sleeping Environment
- Cultural differences exist in sleeping arrangements for infants.
- In the U.S., middle-class infants primarily sleep separated from parents; however, trends may be shifting.
- Co-sleeping or bed-sharing decisions influenced by:
- Culture
- Infant's age
- Mother's educational level
- Mental health (depression)
- Father's involvement
- Regions where co-sleeping is common include Asian, African, and Latin American cultures.
- Sudden Infant Death Syndrome (SIDS) is a critical concern connected to sleeping arrangements.

Prenatal and Postnatal Brain Growth
- Measured by head circumference, crucial for future cognitive ability.
- Head-sparing: A biological mechanism protecting the brain during malnutrition; brain is the last body part to suffer damage from malnutrition.
Brain Development Mechanisms
- Infants experience both exuberance (rapid dendrite growth) and pruning (whittling away unused dendrites).
- Growth affected more by experience than by genetic makeup.
Neurological Vocabulary
- Neuron: Nerve cell within the central nervous system.
- Axon: Fiber extending from a neuron, transmitting impulses to other neurons.
- Dendrite: Fiber receiving impulses from other neurons.
- Synapse: Junction between axons and dendrites of neurons.
- Neurotransmitter: Brain chemical relaying information between neurons.
- Cortex: Brain's outer layer where thinking, feeling, and sensing occur.

Brain Structures Related to Emotions
- Prefrontal Cortex: Responsible for anticipation, planning, impulse control.
- Limbic System: Interacts to produce emotions (includes amygdala, hypothalamus, hippocampus).
- Amygdala: Key in registering fear and anxiety.
- Hippocampus: Central processor of memory, especially for spatial awareness.
Stress Responses
- Cortisol: Primary stress hormone, fluctuating levels affect emotions.
- Pituitary Gland: Produces hormones controlling growth and gland functions (adrenal, sex glands).

Hearing
- Fully develops during the last trimester of pregnancy; most advanced sense at birth.
- Speech perception: Present by four months after birth.
Seeing
- Least mature sense at birth; can focus on objects 4 to 30 inches away.
- Binocular vision develops between 2 and 4 months.
Touch
- Extremely acute in infants; preference for specific touches develops over time.
- Pain and temperature sensations exist but are less intense than in adults.

Gross Motor Skills
- Develop sequentially during the first two years, following cephalocaudal (head-down) and proximodistal (center-out) patterns:
- Sitting unsupported
- Standing while holding on
- Crawling (creeping)
- Standing without holding on
- Walking well
- Walking backward
- Running
- Jumping up
- Average toddler takes about 2,400 steps per hour of play, travels significant distances, and frequently falls.
Fine Motor Skills
- Involves small movements, especially of hands and fingers (e.g., drawing, picking objects).
- Development shaped by culture and opportunity:
- Sequence includes skills like grasping, reaching, and stacking blocks.

Infant Learning
- Infants are born with a readiness to learn; they engage in gaze-following and exhibit innate logic.
- Implicit Memory: evident by 3 months and stabilizes by 9 months; long-lasting.
- Explicit Memory: develops later and is language-dependent.
Piaget's Sensorimotor Intelligence
- Cognitive development through interaction with the environment occurs in six stages:
- Primary Circular Reactions: Reflexes and acquired adaptations.
- Secondary Circular Reactions: Interaction with others.
- Tertiary Circular Reactions: Experimentation leading to purposeful learning.

Universal Sequence
- Infants globally follow the same sequence of language development.
- Language acquisition begins at birth, with understanding occurring before verbal expression.
Babbling and Gestures
- Babbling (extended repetition of syllables) starts between 6-9 months.
- Gestures serve as powerful early communication tools; baby signing can enhance responsiveness in communication.
Cultural Differences in Language
- Variability in exposure to child-directed speech and the number of words spoken influences language acquisition.
Naming Explosion
- Rapid increase in vocabulary occurs once infants have about 50 words.
Theoretical Perspectives on Language
- Skinner's Theory: Language is taught through reinforcement.
- Social Interactionist Theory: Social impulses drive language development.
- Chomsky's Theory: Language is an innate ability that doesn’t require explicit teaching.