Notes: Physical and Cognitive Development in the First Two Years

Growth and Nutrition in Infants

Norms – average or standard for a particular population
Percentiles – ranking scale from $0$-$100$
Growth benchmarks:
- Infants usually double their birth weight by month $4$ and triple it by age $12$ months: $2 imes$ birth weight by $4$ months, $3 imes$ birth weight by $12$ months
Nutrition in the first year:
- First $6$ months = a liquid diet (breast milk or infant formula)
- Pros/cons? (discussion prompt in transcript)
- Research methods review: what kind of method would tell us whether human/breast milk is “better” than formula? What would we need to consider?
- Considerations for this research question:
- Study design (e.g., longitudinal vs. cross-sectional; randomized if ethical)
- Randomization feasibility and ethics; parental choice
- Confounding variables (e.g., socioeconomic status, healthcare access, maternal health, breastfeeding support)
- Outcome measures (growth metrics, health outcomes, cognitive/behavioral development, immune function)
- Duration and follow-up length
- Sample size and power calculations
- Measurement reliability and blinding where possible
- After $6$ months: slow introduction of solid foods, supplemented by formula/breast milk
- Why $6$ months? (transition point discussed in transcript)
Transition to solids and continued feeding practices are framed by growth norms and health considerations discussed above

At birth: many neurons but relatively few connections
Early development depends on maturation and experience
Synaptogenesis = process of creating new synapses
Synaptic pruning = elimination of unused connections
Brain growth patterns:
- Lots of growth in the cerebellum and cortex (movement and emotion regulation)
- Myelination increases the speed and efficiency of neural signaling
Brain function categories:
- Experience-Expectant brain functions – basic brain functions that require common, universal experiences to develop
- Experience-Dependent brain functions – functions that may or may not develop depending on individual experiences

Stress triggers cortisol and other hormones
Frequent or chronic stress can lead to either heightened or blunted stress responses across development
Implications: early environments shape long-term regulation and reactivity to stress

What kinds of experiences should a parent provide for a 4-month-old? (to support healthy brain development)
How to describe brain development in the first two years to a curious parent?

Newborn sleep cycles and circadian rhythms
Changes in sleep across infancy
High REM sleep early on
Factors to consider affecting sleep:
- Parents
- Culture
- Medical conditions
- Co-sleeping considerations

How might researchers determine what babies can sense (see, hear, taste, smell, feel)?
How can we get a sense of what babies know and don’t know?

Looking time / head turning
Preferential gaze / reaching
Habituation – decreased responsiveness to a stimulus after repeated presentations
- Dishabituation – recovery of a habituated response after a change in stimulation
High-amplitude sucking (HAS) paradigm
Example resources cited: video demonstrations and explanations

Hearing: develops during the last trimester; fairly acute at birth
Vision: least mature at birth
- Nearsighted; limited peripheral vision; little accommodation
- Underdeveloped cones ⇒ poor color vision at birth
Smell, Tasting, Touching (including pain)

Gross Motor Skills – large body movements (e.g., crawling, standing, walking)
Cephalocaudal development – head-to-toe progression
Proximodistal development – core control before extremities
Fine Motor Skills – small, precise movements (e.g., grasping, hand coordination)

Prompt from transcript: craft a multiple-choice or short-answer test question from the content covered thus far

The mind as a computer model: input, processing, connections, memory storage, output
Core components: Attention, memory, processing speed
Related teaching resource: explanatory video link in transcript

Habituation-based assessment of memory: infants prefer new things and look away from familiar stimuli
Implicit memory (skills, recognition of people) by around $3$ months
Explicit memory: more verbal, detailed, linked to time of learning
Role of hippocampus and language development in memory formation

Gopnik (Science, 2012) – infers population-level information from a sample
Xu and Garcia (2008) – referenced in the context of infant statistical reasoning

Recognizing language sounds: infants can distinguish phonemes from all languages early on; this ability declines after about $6$ months
Patricia Kuhl – linguistic foundations of babies and language acquisition (TED talk recommended in transcript)

Communication vs. Language: distinction explained
Sequence of vocalizations is similar across languages
Receptive vocabulary exceeds expressive vocabulary in early years
Fast mapping – learning a new word after a single exposure (typically around $18$ months)
Overextensions – applying a word too broadly (e.g., every wheeled vehicle as a truck)
Underextensions – restricting a word to a narrow context (e.g., only family cat is a cat)

Prompts reflection on how physical and cognitive development principles guide toy design and selection for infants

Research methods and findings discussed throughout (habituation, imitation, memory, language acquisition, etc.)
Links to further resources provided in transcript (YouTube videos and CDC reference)