Human development in infancy

Infancy is defined as
First 2 years of life
Development from a tiny
and seemingly helpless
being into a small,
achieving child.

Brain Growth

How mature is the
human brain at birth?
The human newborn arrives in the world with a brain which is developed enough in some respects but relatively undeveloped in others.
Developed: brain systems and networks involved in the infant’s ability to perceive many aspects of the sensory world ? competencies to learn and store information.
Immature: brain regions that control movement and produce language competence ? require months or years to develop.
WHY? This allows the infant to explore and learn about the world without being limited to rigid patterns of behavior.

Some characteristics
of neonatal brain.
Similarities:
Weight – a quarter of an adult brain.
Looks – like an adult brain
Main structures – are present with all of the 100 billion neurons (no more neurons will be formed across the human lifetime)

How brains grow
Birth:
– 100-200 billion
Neurons
– Relatively few
neuron-to-neuron
connections
During first two
years:– Billions of new connections
established and become more complex

Differences:
1. Synaptogenesis. Massive overproduction of synapses (connections amongst the neurons). Newborn – 1/6 of the number of an adult brain. 1 year old – twice as many as an adult.
2. Myelinisation. An increase in the number of neurons that have a coating of myelin (a fatty sheath that makes the impulse travel faster along the neuron and helps the brain to function more efficiently)

Use it or lose it
Synaptic pruning
Unused neurons are eliminated
Allows established neurons to build more elaborate communication networks with other neurons
Development of nervous system proceeds most effectively through loss of cells
But also note the importance of myelin

Brain functioning
Lateralization of brain function begins after birth. Left hemisphere: speech perception and control of some movement. Right hemisphere: response to the spatial configuration of facial patterns.
Communication between these two continues to develop in the childhood.
Maturation: the growth and the use of the brain are tightly intertwined. Example: genes have been found that directly affect the growth of dendrites, but also experience promotes growth and strengthening of dendrites.

Don’t shake the baby!
Shaken Baby Syndrome
Brain sensitive to injury
Shaking can lead to brain rotation within
skull
Blood vessels tear - severe medical
problems, long-term disabilities, and
sometimes death

Growth in the body
Growth occurs because of increases in both the number of body cells and size of existing cells.
Height and weight
Girls are taller and heavier than boys.

Changes in Proportions
of the body.
Head:
Infant app ¼ of the body length
1 year old app 1/5 of the body length
Adult app 1/8 of the body length
Legs:
Infant app ¼
Adult app ½ (contributing to the balance

Changes in the
muscle –to-fat- ratio of the body.
Muscles grow gradually across childhood.
However, newborns have a high % of body fat and this continues to accumulate until app 9 months.
Then, children become slimmer until middle childhood (though girls have slightly higher body fat ratio).
Both nature and nurture influence the process of growth. For example identical twins show similar weights and heights across childhood.

Reflexes
Neonates are born with a number of reflexes that help them to adapt to their environment:
The rooting reflex occurs when you touch a baby’s cheek and he turns his head to search for the source (adaptive for survival)
The sucking reflex – when you touch the baby’s lips, he immediately begins to show it.
The swallowing reflex occurs automatically when something is in the baby’s mouth.
The Moro reflex (startle reflex) occurs when something in the environment changes quickly (loud noise? extends both arms and brings the feet close to the body)
The Babinski reflex – when the bottom of the baby’s foot is stroked (spreads out the toes and then curls them)

Sensory abilities
Characteristics:
Hearing. After birth ear canals are filled with amniotic fluid, but in a few days hearing is fairly normal. Prefer mother’s voice to other sounds; turn their heads toward all sounds.
Visual sense. Neonates are nearsighted and see best at about 9 inches. They perceive objects in motion and prefer complex visual stimuli, especially when they resemble a human face.
Taste : Neonates can discriminate different tastes and odors. Reaction to sweet solutions – smile, and suck, whereas to bitter solutions – spit.
Smell sense- prefer the smell of their mother’s milk, underarm odor (leading to attachment formation), whereas they wrinkle their noses and stick out their tongues when given a substance with rotten eggs odor under their noses.

Sensory Capabilities:
Experiencing the World
Seeing
Visual acuity not fully developed but can see to some extent
Attend to visual field highest in information and brightness
Possess some sense of size constancy
Distinguish and show preference for different colors

Auditory Perception: The World of Sound
Infants
– Are more sensitive to certain frequencies
– Reach adult accuracy in sound localization by age 1
– Can discriminate groups of different sounds
– React to changes in musical key and rhythm
– Can discriminate many language related sounds

Sensory-perceptual development.

Inter-modal perception
Adults expect different sensory impressions from the same object to be synchronous or coordinated.
So, do infants and children!
For example, four-month-olds prefer to look at synchronized puppet displays (where the puppets were jumping in rhythm with a sound track) than those that were out of synch. The same was observed with faces of people speaking (matching lips and sounds) rather than the mismatch.

5 main sensory – perceptual systems
Visual
Auditory (hearing)
Tactile- haptic (touch)
Olfactory (smell)
Gustatory (taste)
Perception is coherent because it provides structure to the flow of stimulation from outside world. It does this by keeping different sensations separate from each other but also binding them together where necessary.

Habituation and Familiarization.
These methods involve repeatedly presenting infants with a stimulus and then observing any change in response (fixation duration) when a novel stimulus is presented. Increase in fixation to the novel stimulus is taken as indicative of discrimination of the old and new stimuli.
These approaches have been used for over 30 years to assess whether infant perception works in a coherent way – that’s if infants can distinguish between different perceptual features as well as being able to bind these together when needed.

Habituation/ Dishabituation
- Habituation: baby’s response will decrease to “new” stimuli over time
Can use variety of stimuli types and use baby’s ability to discriminate to
infer learning/ perception
- Dishabituation: recovery in responses
infant can discriminate between “old” and “new” stimuli

High Amplitude Sucking
? - Infant sucking
brings about sound
stimuli
? - When bored
(habituated), they
slow sucking
? - Experimenter
changes sound, baby
becomes interested
again (dishabituates)
and increases
sucking speed

Motor Development

Motor Development in Infancy

Nutrition in Infancy
Fueling Motor Development
Without proper nutrition, infants cannot
reach physical potential and may suffer
cognitive and social consequences
Slower growth rate / Chronically malnourished during infancy = later lower IQ score
Infants differ in growth rates, body
composition, metabolism, and activity levels
If are allowed consume as much they seem to want, and not pressured to eat more, they will be healthy