Psychology 1100: Lifespan Development

Chapter 3: Infancy - Physical Development

Presenter: Bart Pulson

Sequence of Physical Development

• Age Range: From 2 months (fetus) to 16 years
• Change in Proportions: Head counts for half the size at 2 months

Development Patterns

1. Cephalocaudal Development
   • Head grows first
   • Essential since the brain regulates vital functions like heartbeat
2. Proximodistal Development
   • Growth from the trunk (torso) outward
   • Development of nerves from the spinal cord to limbs
   • Essential for life functions (e.g., breathing, heartbeat)
3. Differentiation
   • More specific physical reactions as children grow older
   • Example: Touching a hot stove, whole body reaction initially, localized reaction as they mature

Changes in Weight and Height

• Weight
  • Infants double birth weight in about 5 months
  • Triple it by the first birthday
• Height
  • Increases by about 50% in the first year
  • Newborns: Arms and legs equal in length (~ 1.5 times head length)
  • First birthday: Neck, arms, and legs elongate
  • Second birthday: Arms longer than legs

Failure to Thrive (FTT)

• Definition: Disorder impairing growth in infancy and early childhood
• Causes: Biological (organic) or non-biological (non-organic)
  • Core issue usually feeding problems
• Impact: Slow physical growth, cognitive, behavioral, and emotional problems
• Treatment: Addressing biological causes can lead to developmental catch-up

Nutrition: Breastfeeding vs. Bottle Feeding

Breastfeeding Advantages

• Less likely to upset infant's stomach
• Contains antibodies to ward off illnesses
• Protects against lymphoma
• Fewer digestive problems and allergic responses
• Decreased chance of obesity later in life

Breastfeeding Disadvantages

• Transmission of substances (e.g., alcohol, drugs, prescription medication)
• Transmission of diseases (e.g., HIV)
• Requires mother's adequate nourishment
• Physical demand on mother's body

Bottle Feeding

• Allows others to feed the baby
• More flexible feeding schedule
• Requires thorough exploration of both options

Brain and Nervous System Development

Neurons

• Basic unit of the nervous system
• Components: Cell body, dendrites, axon, and axon terminals
• Babies are born with ~100 billion neurons
• Myelination: Process of encasing axons in myelin sheath (fat)
  • Improves communication efficiency
  • Provides insulation to prevent cross-firing
• Continued myelination: Up to the second decade of life
  • Advances in working memory and language ability

Brain Growth

• Brain triples in weight by one year
• Growth in myelin and dendrite connections
• Infants gain control over movements over time
• Brain development influenced by biological maturation (nature) and stimulation/nutrition (nurture)

Motor Development

• Massive strides within the first year
• Initial: Unable to support their necks
• 6 Months: Begin grasping objects and rolling over
• 8-9 Months: Begin crawling
• 10 Months: Can stand
• 12-15 Months: Walking (toddlers)

Study by Wayne and Marena Dennis (1940)

• Native American Hopi children strapped to cradle boards in first year
• Little motor activity initially, but caught up quickly in walking ability

Sensory and Perceptual Development

Vision

• Nearsighted at birth, significant improvement by 6 months
• Peripheral vision improves to adult level by 6 months
• Respond to depth cues by 6-8 months (e.g., visual cliff)
• Develop size and shape constancy

Hearing

• Newborns can orient heads toward sound (if lying down)
• By 18 months, sound localization abilities match adults
• Gradual expansion of pitch range and ability to detect differences in pitch and loudness