Chapter 5: The First Two Years: Biosocial Development

What facts indicate that infants grow rapidly in the first year?

A newborn's weight doubles by 4 months, and triples by a year. A typical baby grows approximately 10 inches in a year, measuring around 30 inches total.

What is universal and what is cultural in the development of gross motor skills in infancy.

All healthy infants develop skills in the same sequence, but they vary in age of acquisition. Studies of U.S. infants whom were grouped by ethnicity showed that African American babies were ahead of Latino babies when it came to walking, and in turn, Latinos were ahead of those of European decent. Internationally, the earliest walkers were in Africa, where healthy and well-nourished babies generally begin walking at around 10 months. The latest walkers are found in rural China, where infants are bundled up against the cold. In some cultures, babies are discouraged from walking, especially if hazards are nearby.

Why is hearing more acute than vision in the early weeks?

An infant's hearing develops during the last trimester of pregnancy- by contrast, an infant's vision is immature at birth. Because the fetus does not have much to see, newborns are legally blind; they focus only on things between 4 and 30 inches away.

Why do caregivers vary in which motor skills they encourage?

Caregivers influence every infant move, and every caregiver reflects their own culture.

Why are pediatricians not troubled when an infant is consistently small, say at the 20th percentile in height and weight?

Consistency is key. If a newborn is in the 20th percentile for height and weight, then they should be relatively that around six months of age as well. Pediatricians say that anything between the 10th and 90th percentile- as long as it's consistent- is considered normal. If an infant goes from the 50th percentile to the 20th percentile, it could indicate malnutrition, while an increase in percentile could indicate overfeeding.

How can pruning increase brain potential?

During the infant's first two years of life, transient exuberance occurs: meaning there is a dramatic increase of dendrites that develop in an infant's brain. TE is followed by pruning, which is the process in which unused connections in the brain atrophy and die. As the textbook says, "Just as a gardener might prune a rose bush by cutting away some growth to enable more (or more beautiful) roses to bloom, unused brain connections atrophy and die to make room for used brain connections."

What is the difference between experience-expectant and experience-dependent growth?

Experience-expectant growth is when certain functions require basic experiences in order to develop, and experience-dependent growth is when certain functions are not essential- they MIGHT happen, and because of this, one brain differs to another, even though both are developing normal. Experience-expectant events make all people similar, yet everyone is unique because each person undergoes particular experience-dependent growth. Experience-expectant growth MUST happen for normal brain development.

How do sleep patterns change from birth to 18 months?

In the first two months, newborns sleep up to 14 1/2 hours a day. 3-6 month olds sleep about 13 1/4 hours per day, while 6-17 month olds sleep 12 3/4 hours per day. The amount of sleep needed decreases as the infant matures.

What is the effect of stress or social deprivation on early development?

Infant brains do not develop well if they do not have the basic experiences that all humans need- therefore, severe lack of stimulation stunts brain growth. If the brain produces an overabundance of cortisol (the stress hormone) early in life, it can make the brain react to stress poorly lifelong, and as a result, years later that child may become hypervigilant or emotionally flat.

What particular sounds and patterns do infants pay attention to?

Infants show a preference to their mother's voice. Sudden voices startle and scare them, making them cry, while rhythmic sounds- such as a heartbeat- calm and soothe them.

What is the relationship between motor skills and the senses?

Motor skills emerge directly from reflexes and proceed in a cephalocaudal (head down) and proximodistal (center-out) direction. Infants first control their heads, lifting them up to look around. They then control their upper bodies, their arms, and finally their legs and feet. An example of head down and center out direction mastery is crawling.

What is known and unknown about infant pain?

Scientists are not certain about infant pain- some experiences that are painful to adults are much less so to newborns, although that does not mean that newborns never feel pain. Some people imagine that even the fetus feels pain; others say that sense of pain does not mature until much later. Physiological measures such as hormones, heartbeat, and brain waves are studied to measure infant pain, but the conclusions are mixed.

Why do some babies prefer certain tastes and smells that others dislike?

Tastes and smells rapidly develop depending on the social context of the infant. Babies appreciate what their mother's eat: prenatally, through amniotic fluid, then through breast milk, and finally through smells and spoonfuls of the family dinner. As babies learn to recognize each person's scent, they prefer to sleep next to their caregivers, and they nuzzle into their chests.

What are the arguments for and against bed-sharing?

The main benefit of bed-sharing is bonding with the infant and breastfeeding. Breastfeeding is more common with infants who bed-share, however, so is the chance of SIDS, or sudden infant death syndrome occuring. It can be dangerous for an infant to share the bed of an adult, especially because the chances of overlying (the adult rolling over on the infant) are higher.

What should caregivers remember about brain development when an infant cries?

The prefrontal cortex on an infant has not yet developed, therefore telling an infant to stop crying is pointless, because they cannot decide to stop crying. Caregivers to an infant should remember that although it is frustrating when an infant is consistently crying, that the response of the caregiver handling a crying infant should be to either comfort or walk away. NEVER shake the baby. Shaking a baby could lead to Shaken Baby Syndrome- a life-threatening injury that occurs when an infant is forcefully shaken back and forth, a motion that ruptures blood vessels in the brain and causes breaks in neural connections.

How does an infant's vision change over the first year?

When a baby is born, they are legally blind- because the eyes have not had things to see to help their eyes develop. They can only see things between four and thirty inches away. By two months old, infants not only stare at faces but also, with perception and cognition, smile. At 3 months old, an infant looks closely at the eyes and mouth, and they prefer photos of faces with features. At about 14 weeks, brain mechanisms are activated, allowing binocular vision, where both eyes can now focus on a single object.