Chapter 5 Key Questions How do the human body and nervous system develop? Does the environment affect the pattern of development? What developmental tasks must infants accomplish in this period? How does nutrition affect physical development? What sensory capabilities do infants possess?
Physical Growth: The Rapid Advances of Infancy Infants grow at a rapid pace over the first 2 years of their lives. By the age of 5 months, the average infant’s birthweight has doubled to around 15 pounds. By the first birthday, the baby’s weight has tripled to about 22 pounds. The weight gains of infancy are matched by increased length. By the end of the 1st year, the typical baby grows almost a foot and is about 30 inches tall.
Four Principles of Growth Cephalocaudal principle The principle that growth follows a pattern that begins with the head and upper body parts and then proceeds down to the rest of the body The cephalocaudal growth principle means that we develop visual abilities (located in the head) well before we master the ability to walk.
Four Principles of Growth Three other principles help explain the patterns by which growth occurs: Proximodistal principle The principle that development proceeds from the center of the body outward Principle of hierarchical integration The principle that simple skills typically develop separately and independently but are later integrated into more complex skills Principle of the independence of systems The principle that different body systems grow at different rates
The Nervous System and Brain: The Foundations of Development Neuron The basic nerve cell of the nervous system Neurons can communicate with other cells, using a cluster of fibers called dendrites at one end. Dendrites receive messages from other cells.
The Nervous System and Brain: The Foundations of Development At their opposite end, neurons have a long extension called an axon , the part of the neuron that carries messages destined for other neurons. Synapse The gap at the connection between neurons, through which neurons chemically communicate with one another
Synaptic Pruning Babies are actually born with many more neurons than they need. In addition, although synapses are formed throughout life, based on our changing experiences, the billions of new synapses infants form during the first 2 years are more numerous than necessary.
Synaptic Pruning After birth, neurons continue to increase in size. In addition to growth in dendrites, the axons of neurons become coated with myelin Myelin A fatty substance that helps insulate neurons and speeds the transmission of nerve impulses
Synaptic Pruning The neurons also reposition themselves as they grow, becoming arranged by function. Some move into the cerebral cortex, the upper layer of the brain, while others move to subcortical levels , which are below the cerebral cortex.
Synaptic Pruning The subcortical levels, which regulate such fundamental activities as breathing and heart rate, are the most fully developed at birth.
Environmental Influences on Brain Development Brain development, much of which unfolds automatically because of genetically predetermined patterns, is also strongly susceptible to environmental influences. Plasticity The degree to which a developing behavior or physical structure is modifiable
Environmental Influences on Brain Development Compared with those brought up in more enriched environments, infants raised in severely restricted settings are likely to show differences in the brain’s structure and weight Sensitive period A specific time when organisms are particularly susceptible to certain kinds of stimuli in their environment A sensitive period may be associated with a behavior—such as the development of full vision—or with the development of a structure of the body, such as the configuration of the brain.
Environmental Influences on Brain Development Developmentalists suggest that there are many simple ways parents and caregivers can provide a stimulating environment that will encourage healthy brain growth.
Integrating the Bodily Systems: The Life Cycles of Infancy In the first days of life, infants’ body rhythms govern the infant’s behavior, often at seemingly random times. Rhythms Repetitive, cyclical patterns of behavior State The degree of awareness an infant displays to both internal and external stimulation
Integrating the Bodily Systems: The Life Cycles of Infancy Some of the different states that infants experience produce changes in electrical activity in the brain. These changes are reflected in different patterns of electrical brain waves , which can be measured by a device called an electroencephalogram (EEG) .
Sleep: Perchance to Dream? At the beginning of infancy, the major state that occupies a baby’s time is sleep. On average, newborn infants sleep some 16 to 17 hours a day. However, there are wide variations. Rapid eye movement (REM) sleep The period of sleep that is found in older children and adults and is associated with dreaming
SIDS: The Unanticipated Killer Sudden infant death syndrome (SIDS) The unexplained death of a seemingly healthy baby SIDS strikes about 1 in 1,000 infants in the United States each year. Although it seems to occur when the normal patterns of breathing during sleep are interrupted, scientists have been unable to discover why that might happen.
SIDS: The Unanticipated Killer Although no reliable means for preventing the syndrome has been found, the American Academy of Pediatrics now suggests that babies sleep on their backs rather than on their sides or stomachs—called the back-to-sleep guideline. The number of deaths from SIDS has decreased significantly since these guidelines were developed.
Motor Development The shape and proportions of newborn babies are simply not conducive to easy mobility. Their heads are so large and heavy that young infants lack the strength to raise them. Because their limbs are short in relation to the rest of the body, their movements are further impeded.
Motor Development Furthermore, their bodies are mainly fat, with a limited amount of muscle; the result is that they lack strength. Fortunately, it doesn’t take too long before infants begin to develop a remarkable amount of mobility.
Reflexes: Our Inborn Physical Skills Reflexes Unlearned, organized involuntary responses that occur automatically in the presence of certain stimuli Newborns enter the world with a repertoire of reflexive behavioral patterns that help them adapt to their new surroundings and serve to protect them.
Ethnic and Cultural Differences and Similarities in Reflexes Although reflexes are, by definition, genetically determined and universal throughout all infants, there are actually some cultural variations in the ways they are displayed. In some cases, reflexes can serve as helpful diagnostic tools for pediatricians.
Ethnic and Cultural Differences and Similarities in Reflexes Because reflexes emerge and disappear on a regular timetable, their absence—or presence—at a given point of infancy can provide a clue that something may be amiss in an infant’s development.
Gross Motor Skills The motor skills of newborn infants are unsophisticated; still, young infants are able to accomplish some kinds of movement. As their strength increases, they are able to push hard enough against the surface on which they are resting to propel their bodies in different directions.
Gross Motor Skills Crawling appears typically between 8 and 10 months. Walking comes later; half of all infants can walk well by the end of 12 months.
Fine Motor Skills By the age of 3 months, infants show some ability to coordinate the movements of their limbs. The sophistication of fine motor skills continues to grow. By the age of 11 months, infants are able to pick up objects as small as marbles. Grasping, like other motor advances, follows a sequential developmental pattern in which simple skills are combined with more sophisticated ones.
Dynamic Systems Theory: How Motor Development Is Coordinated Each skill (such as a baby’s ability to pick up a spoon and guide it to her lips) advances in the context of other motor abilities (such as the ability to reach out and lift the spoon in the first place).
Dynamic Systems Theory: How Motor Development Is Coordinated Furthermore, as motor skills are developing, so also are nonmotoric skills such as visual capabilities. Dynamic systems theory A theory of how motor skills develop and are coordinated
Developmental Norms: Comparing the Individual to the Group Norms The average performance of a large sample of children of a given age Brazelton Neonatal Behavioral Assessment Scale (NBAS) A measure designed to determine infants’ neurological and behavioral responses to their environment
Developmental Norms: Comparing the Individual to the Group Although the norms provided by scales such as the NBAS are useful in making broad generalizations about the timing of various behaviors and skills, they must be interpreted with caution. Because norms are averages, they mask substantial individual differences in the times when children attain various achievements.
Nutrition in Infancy: Fueling Motor Development The rapid physical growth that occurs during infancy is fueled by the nutrients that infants receive. Without proper nutrition, infants cannot reach their physical potential, and they may suffer cognitive and social consequences as well. Infants should consume about 50 calories per day for each pound they weigh—an allotment that is twice the suggested caloric intake for adults.
Malnutrition Malnutrition , the condition of having an improper amount and balance of nutrients, produces several results, none good. Children who have been chronically malnourished during infancy later score lower on IQ tests and tend to do less well in school. Children in the United States rarely become severely malnourished, but children living in poverty remain susceptible to undernutrition , in which there is some deficiency in diet.
Malnutrition Malnutrition during the 1st year can produce marasmus , a disease in which infants stop growing. Older children are susceptible to kwashiorkor , a disease in which a child’s stomach, limbs, and face swell with water.
Malnutrition In some cases, infants who receive sufficient nutrition behave as if they have been deprived of food. The real cause, though, is emotional. This is known as nonorganic failure to thrive . Nonorganic failure to thrive A disorder in which infants stop growing due to a lack of stimulation and attention as the result of inadequate parenting
Obesity Obesity is defined as weight greater than 20% above the average for a given height. Although the evidence linking infant obesity to adult obesity is inconclusive, what is apparent is that the societal view that “a fat baby is a healthy baby” is not necessarily correct. Given the lack of clarity regarding infant obesity, parents should concentrate less on their baby’s weight and more on providing appropriate nutrition.
Breast or Bottle? For the first 12 months of life, there is no better food for an infant than breast milk. Breast milk not only contains all the nutrients necessary for growth, but it also seems to offer some degree of immunity to a variety of childhood diseases.
Breast or Bottle? Breast milk is more easily digested than cow’s milk or formula, and it is sterile, warm, and convenient for the mother to dispense. There is even some evidence that breast milk may enhance cognitive growth, leading to high adult intelligence. Breast-feeding also offers significant emotional advantages for both mother and child, and may even be advantageous to mothers’ health.
Social Patterns in Breast-feeding Although it has several advantages, only about 70% of all new mothers in the United States employ breast-feeding. Issues of age, social status, and race influence the decision whether to breast-feed. The rates of breast-feeding are highest among women who are older, have better education, are of higher socioeconomic status, and have social or cultural support.
Introducing Solid Foods: When and What? The American Academy of Pediatrics and the American Academy of Family Physicians suggest that babies can start solids at around 6 months, although they aren’t needed until 9 to 12 months of age. Solid foods should be introduced into an infant’s diet gradually, one at a time, to allow awareness of the child’s preferences and allergies. The timing of weaning , the gradual cessation of breast or bottle-feeding, varies greatly.
The Development of the Senses The infant’s world grows increasingly comprehensible as its ability to sense and perceive the environment develops. Babies appear to thrive in an environment enriched by pleasing sensations. Sensation The physical stimulation of the sense organs Perception The sorting out, interpretation, analysis, and integration of stimuli involving the sense organs and brain
Visual Perception: Seeing the World The vision of newborns provides the same degree of distance acuity as the uncorrected vision of many adults who wear eyeglasses or contact lenses. Other visual abilities grow rapidly. For instance, binocular vision , the ability to combine the images coming to each eye to see depth and motion, is achieved at around 14 weeks. Research has shown that infants reliably prefer to look at stimuli that include patterns than to look at simpler stimuli.
Auditory Perception: The World of Sound Even in the womb, the fetus responds to sounds outside of its mother. Furthermore, infants are born with preferences for particular sound combinations. Infants can discriminate groups of different sounds, in terms of their patterns and other acoustical characteristics quite well. Even more intriguingly, young infants are able to discriminate one language from another.
Smell and Taste The sense of smell is so well developed, even among very young infants, that at least some 12- to 18-day-old babies can distinguish their mothers on the basis of smell alone. Infants also develop taste preferences based on what their mothers drank while they were in the womb.
Contemporary Views on Infant Pain Infants are born with the capacity to experience pain. Pain produces distress in infants. Their heartbeat increases, they sweat, show facial expressions of discomfort, and change the intensity and tone of crying when they are hurt. Medical experts now endorse the use of anesthesia and painkillers during surgery for even the youngest infants.
Responding to Touch Touch is one of the most highly developed sensory systems in a newborn, and it is also one of the first to develop; there is evidence that by 32 weeks after conception, the entire body is sensitive to touch. Furthermore, several of the basic reflexes present at birth, such as the rooting reflex, require touch sensitivity to operate. Infants’ abilities in the realm of touch are particularly helpful in their efforts to explore the world.
Multimodal Perception: Combining Individual Sensory Inputs Multimodal approach to perception The approach that considers how information that is collected by various individual sensory systems is integrated and coordinated Infants’ abilities at multimodal perception showcase the sophisticated perceptual abilities of infants, which continue to grow throughout the period of infancy. Affordances The action possibilities that a given situation or stimulus provides