chpt 3 body and mind

Early dendrite growth is called transient exuberance: exuberant because it is rapid and transient because some is temporary. Expansive growth is followed by pruning. 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 disappear to enable children to connect the neurons needed in their culture.

As one expert explains it, there is an exuberant overproduction of cells and connections, followed by a several-year sculpting of pathways by massive elimination of much of the neural architecture. [Insel, 2014, p. 1727] Notice the word sculpting, as if an artist created an intricate sculpture from raw marble or wood. Human infants are gifted sculptors, designing their brains for whatever family, culture, or society they happen to be born into, discarding the excess in order to think more clearly.

OLDER INFANTS

At 12 months, more improvement is evident. One-year-olds learn from parents and strangers, from other babies and older siblings, from picture books and family photographs, from their own walking and talking (Hayne & Simcock, 2009). Dendrites grow to reflect remembered experiences. Every day of their young lives, infants are processing information and storing conclusions. Indeed, if you saw a photo of a grandmother who cared for you every day when you were an infant and who died when you were 2, your brain would still react, even though you thought she was forgotten. Information-processing research finds evidence of early memories, with visual memories particularly strong (Leung et al., 2016; Gao et al., 2016).

STAGES THREE AND FOUR

By 4 months (stage three), reactions are no longer confined to the infant's body; they are an interaction between the baby and something — or someone — else. At first babies are merely responsive to what happens: Stage three is also called the stage of "making interesting sights last." By stage four (between 8 and 12 months), babies initiate actions to get what they want. Seeing a parent putting on a coat, they might drag over their own jackets to signal that they want to go along. If the caregivers have been using sign language, among the first signs learned are "eat" and "more." Even without parental signing, babies this age begin displaying some universal signs — pointing, pushing, and reaching up to be held. Piaget thought that, at about 8 months, babies first understand object permanence— the realization that objects or people continue to exist when they are no longer in sight. As Piaget discovered, not until about 8 months do infants search for toys that have fallen from the crib, rolled under a couch, or disappeared under a blanket. Babies with visual impairment also acquire object permanence toward the end of their first year, reaching for an object that they hear nearby (Fazzi et al., 2011).

seeing

By about 4 months, when her auditory cortex is rapidly creating dendrites, the repeated word Emily is perceived as well as sensed, especially because that sound emanates from interactions with the people she often sees, smells, and touches. By 6 months, Emily opens her eyes and smiles when her name is called, perhaps babbling in response. This rapid development of hearing is the reason newborn hearing is tested. If necessary, remediation begins in infancy. By age 5, deaf children who got cochlear implants before age 2 are much better at understanding and expressing language than those with identical losses but whose implants came later (Tobey et al., 2013).

Motor Skills

Every motor skill (any movement ability), from the newborn's head-lifting to the toddler's stair-climbing, develops over the first two years. motor skill The learned abilities to move some part of the body, in actions ranging from a large leap to a flicker of the eyelid. (The word motor here refers to movement of muscles.) Reflexes become skills if they are practiced and encouraged. As you saw in the chapter's beginning, Mrs. Todd set the foundation for my fourth child's walking when Sarah was only a few months old by encouraging her stepping reflex. Similarly, some 1-year-olds can swim — if adults have built on the swimming reflex by having the infants paddle in water in the early weeks.

This excerpt describes Piaget's classic experiment to measure object permanence: An adult shows an infant an interesting toy, covers it with a lightweight cloth, and observes the response. The results:

Infants younger than 8 months do not search for the object by removing the cloth. At about 8 months infants search, removing the cloth immediately after the object is covered but not if they have to wait a few seconds. At 18 months, they search quite well, even after a wait, but not if they have seen the object put first in one place and then moved to another. They search in the first place, not the second, a mistake called the A-not-B error. Thus, they search where they remember seeing it put (A), somehow not understanding that they saw it moved (to B). By 2 years, children fully understand object permanence, progressing through several stages of ever-advanced cognition (Piaget, 1954/2013a). This sequence has intrigued scientists as well as parents for decades, as it clearly indicates cognition, maturation, and motivation together. However, as you will see later, Piaget misestimated the age of object permanence, because he did not take into account the brain activity of the infant.

As a recent statement of this phenomenon explains:

Many parents in our typical American middle-class households have tried out Piaget's experiment in situ: Take an adorable, drooling 7-month-old baby, show her a toy she loves to play with, then cover it with a piece of cloth right in front of her eyes. What do you observe next? The baby does not know what to do to get the toy! She looks around, oblivious to the object's continuing existence under the cloth cover, and turns her attention to something else interesting in her environment. A few months later, the same baby will readily reach out and yank away the cloth cover to retrieve the highly desirable toy. This experiment has been done thousands of times and the phenomenon remains one of the most compelling in all of developmental psychology.

LISTENING AND RESPONDING

Newborns prefer to listen to the language their mother spoke when they were in the womb. They do not understand the words, of course, but they like the familiar rhythm, sounds, and cadence. Surprisingly, newborns of bilingual mothers differentiate between the languages (Byers-Heinlein et al., 2010). Data were collected on 94 newborns (age 0 to 5 days) in a large hospital in Vancouver, Canada. Half were born to mothers who spoke both English and Tagalog (a language native to the Philippines), one-third to mothers who spoke only English, and one-sixth to mothers who spoke English and Chinese. The infants in all three groups sucked on a pacifier connected to a recording of 10 minutes of English and 10 minutes of Tagalog. The two languages were matched for pitch, duration, and number of syllables. As evident in their sucking, most of the infants with bilingual mothers preferred Tagalog. For the Filipino babies, this was probably because their mothers spoke English in formal settings but not when with family and friends, so Tagalog was associated with more relaxed and animated talk. Those babies with English-only mothers preferred English (Byers-Heinlein et al., 2010). Curiously, the Chinese bilingual babies, who had never heard Tagalog, nonetheless preferred it to English. The researchers believe that they liked Tagalog because the rhythm of that language is similar to Chinese (Byers-Heinlein et al., 2010). Infants improve in their ability to distinguish sounds in whatever language they hear, whereas their ability to hear sounds never spoken in their native language (such as another way to pronounce "r" or "l") deteriorates (Narayan et al., 2010). If parents want a child to speak two languages, they should speak both of them to their baby from birth on. By 12 months, analysis of brain waves finds that babies attend to sounds of their native language; unlike 6-month-olds, their brains seem indifferent to sounds of languages they never hear. The brains of bilingual 1-year-olds respond to both languages (Ramírez et al., 2017). In every language, adults use higher pitch, simpler words, repetition, varied speed, and exaggerated emotional tone when talking to infants. Babies respond with attention and emotion. By 7 months, they begin to recognize words that are highly distinctive (Singh, 2008): Bottle, doggie, and mama, for instance, might be differentiated, but not baby, Bobbie, and Barbie. Infants also like alliteration, rhymes, repetition, melody, rhythm, and varied pitch. Think of your favorite lullaby (itself an alliterative word); obviously, babies prefer sounds over content and singing over talking (Tsang et al., 2017). Early listening abilities and preferences are the result of brain function.

THEORY ONE: INFANTS NEED TO BE TAUGHT

One idea arises from behaviorism. The essential idea is that learning is acquired, step by step, through association and reinforcement. B. F. Skinner (1957) noticed that spontaneous babbling is usually reinforced. Typically, when a baby says "ma-ma-ma-ma," a grinning mother appears, repeating the sound and showering the baby with attention, praise, and perhaps food. Repetition strengthens associations, so infants learn language faster if parents speak to them often. Few parents know this theory, but many use behaviorist techniques. They may praise and respond to the toddler's simple, mispronounced speech, thus teaching language. Behaviorists note that some 3-year-olds converse in elaborate sentences; others just barely put one simple word with another. Such variations correlate with the amount of language each child has heard. Parents of the most verbal children teach language throughout infancy — singing, explaining, listening, responding, and reading to their children every day, long before the first spoken word (Forget-Dubois et al., 2009) (see Figure 3.3).

Sensorimotor Intelligence

Piaget called cognition in the first two years sensorimotor intelligence. He subdivided this period into six stages (see Table 3.1). [Life-Span Link: Piaget's theory of cognitive development is introduced in Chapter 1.] sensorimotor intelligence Piaget's term for the way infants think—by using their senses and motor skills—during the first period of cognitive development. TABLE 3.1 The Six Stages of Sensorimotor Intelligence For an overview of the stages of sensorimotor thought, it helps to group the six stages into pairs. Primary Circular Reactions The first two stages involve infants' responses to their own bodies. Stage One (birth to 1 month) Reflexes: sucking, grasping, staring, listening Example: sucking anything that touches the lips or cheek Stage Two (1-4 months) The first acquired adaptations: accommodation and coordination of reflexes Examples: sucking a pacifier differently from a nipple; attempting to hold a bottle to suck it Secondary Circular Reactions The next two stages involve infants' responses to objects and people. Stage Three (4-8 months) Making interesting sights last: responding to people and objects Example: clapping hands when mother says "patty-cake" Stage Four (8-12 months) New adaptation and anticipation: becoming more deliberate and purposeful in responding to people and objects Example: putting mother's hands together in order to make her start playing patty-cake Tertiary Circular Reactions The last two stages are the most creative, first with action and then with ideas. Stage Five (12-18 months) New means through active experimentation: experimentation and creativity in the actions of the "little scientist" Example: putting a teddy bear in the toilet and flushing it Stage Six (18-24 months) New means through mental combinations: thinking before doing, new ways of achieving a goal without resorting to trial and error Example: before flushing the teddy bear again, hesitating because of the memory of the toilet overflowing and mother's anger

Information Processing

Piaget's emphasis on senses and motor abilities limited his understanding of infant cognition. He missed many early cognitive accomplishments, now apparent from brain scans, heart rate, muscle tension, and gaze. As explained in Chapter 1, Piaget's sweeping overview of cognition contrasts with information-processing theory, which breaks down cognition into hundreds of small steps between input and output. Computer analysis measures cognition long before the baby can demonstrate understanding. information-processing theory The idea that human cognition and comprehension occurs step by step, similar to the way that input, analysis, and output occur via computer. information-processing research has found that signs of attention may be a critical indication of cognition. Babies who focus intently on new stimuli and then turn away are more intelligent than babies who stare aimlessly (Bornstein & Colombo, 2012). Smart babies like novelty and try to understand it (Schulz, 2015).

Malnutrition

Protein-calorie malnutrition occurs when a person does not consume enough food to sustain normal growth. This form of malnutrition affects roughly one-third of children in developing nations (World Health Organization, 2014). Some experience stunting (being short for their age), because chronic malnutrition kept them from growing. Severe stunting is defined as 3 standard deviations from typical height. Less than 1 percent of children are genetically that short, but in many nations 35 percent are that short because they are chronically underfed (see Figure 3.7). Even worse is wasting, when children are severely underweight for their age and height (3 or more standard deviations below average). Many nations, especially in East Asia, Latin America, and central Europe, have seen improvement in child nutrition in the past decades, with an accompanying decrease in wasting and stunting. India is one such nation (Dasgupta et al., 2016). However, much more is necessary. In India in 2014, 17 percent of young children were severely stunted and 5 percent were severely wasted (UNICEF, 2015). wasting The tendency for children to be severely underweight for their age and height as a result of malnutrition. In other nations, primarily in Africa, wasting is increasing. Most adults who were severely malnourished as infants have lower IQs throughout life, even if they eat enough later on (Waber et al., 2014). Some of this is directly related to brain growth, but in addition, severely malnourished infants have less energy and reduced curiosity. Young children naturally want to do whatever they can: A child with no energy is a child who is not learning.

FROM SENSING TO THINKING

Sensation occurs when a sensory system detects a stimulus, as when the inner ear reverberates with sound or the eye's retina and pupil intercept light. Thus, sensations begin when an outer organ (eye, ear, nose, tongue, or skin) meets anything that can be seen, heard, smelled, tasted, or touched. sensation The response of a sensory organ (eyes, ears, skin, tongue, nose) when it detects a stimulus. Perception occurs when the brain processes a sensation. This happens in the cortex, usually as the result of a message from one of the sensing organs, such as from the eye to the visual cortex. perception The mental processing of sensory information when the brain interprets a sensation. The sight of a bottle, for instance, is conveyed from the retina to the optic nerve to the visual cortex, but it has no meaning unless the infant has been repeatedly bottle-fed. Similarly, a scrap of paper means nothing to adults unless they are searching for something written on just such a scrap or are trying to clean up the floor, the room, the sidewalk. Perceptions require experience and motivation, not just sensation. Without them, the bottle or paper is unnoticed, not really seen. Thus, perception follows sensation, when sensory stimuli are interpreted in the brain. Then cognition follows perception, when people think about what they have perceived. The baby might reach out for the bottle; the adult might pick up the paper, look at it, and discard it. The sequence from sensation to perception to cognition requires first that the sense organs function. No wonder the parts of the cortex dedicated to hearing, seeing, and so on develop rapidly: Thinking begins there.

FINE MOTOR SKILLS

Small body movements are called fine motor skills. The most valued fine motor skills are finger movements, enabling writing, drawing, typing, tying, and so on. Movements of the tongue, jaw, lips, teeth, and toes are fine movements, too. fine motor skills Physical abilities involving small body movements, especially of the hands and fingers, such as drawing or picking up a coin. (The word fine here means "small.") Actually, mouth skills precede hand skills by many months (newborns can suck; chewing precedes drawing by a year or more). Since every culture encourages finger dexterity, children practice finger movements, and adults give toddlers spoons, or chopsticks, or markers. By contrast, mouth skills such as spitting or biting are not praised. (Only other children admire blowing bubbles with gum.) The Macmillan logo is shown. VIDEO: Fine Motor Skills in Infancy and Toddlerhood shows the sequence in which babies and toddlers acquire fine motor skills. Regarding hand skills, newborns have a strong reflexive grasp but lack control. During their first 2 months, babies excitedly stare and wave their arms at objects dangling within reach. By 3 months they can usually touch such objects, but because of limited eye-hand coordination they cannot yet grab and hold on unless an object is placed in their hands. By 4 months, infants sometimes grab, but their timing is off: They close their hands too early or too late. Finally, by 6 months, with a concentrated, deliberate stare, most babies can reach, grab, and grasp. Some can even transfer an object from one hand to the other. Almost all can hold a bottle, shake a rattle, or yank a sister's braids. Toward the end of the first year and throughout the second, finger skills improve as babies master the pincer movement (using thumb and forefinger to pick up tiny objects) and self-feeding (first with hands, then fingers, then utensils) (Ho, 2010). (See At About This Time on page 95.) As with gross motor skills, fine motor skills are shaped by practice, which is relentless from the third month of prenatal development throughout childhood. Practice is especially obvious in the first year, when "infants flap their arms, rotate their hands, and wiggle their fingers, and exhibit bouts of rhythmical waving, rubbing, and banging while holding objects" (Adolph & Franchak, 2017).

THE NAMING EXPLOSION

Spoken vocabulary builds rapidly once the first 50 words are mastered, with 21-month-olds typically saying twice as many words as 18-month-olds (Adamson & Bakeman, 2006). This language spurt is called the naming explosion because many early words are nouns, that is, names of persons, places, or things. naming explosion A sudden increase in an infant's vocabulary, especially in the number of nouns, that begins at about 18 months of age. Before the explosion, nouns are already favored. Infants learn the names of each significant caregiver (often dada, mama, nana, papa, baba, tata) and sibling (and sometimes each pet). (See Visualizing Development on page 107.) Other frequently uttered words refer to the child's favorite foods (nana can mean "banana" as well as "grandma") and to elimination (pee-pee, wee-wee, poo-poo, ka-ka, doo-doo). Notice that all of these words have two identical syllables, a consonant followed by a vowel. Many words follow that pattern — not just baba but also bobo, bebe, bubu, bibi. Other early words are only slightly more complicated — ma-me, ama, and so on. The meaning of these words varies by language, but every baby says such words, and every culture assigns meaning to them. Such words are easier in the naming explosion as well: That's why rabbits are "bunnies" and stomachs are "tummies."

BREAST MILK

The best defense against malnutrition is one that humans have relied on for 400,000 years, breast milk. The World Health Organization now recommends exclusive (no formula, juice, cereal, or water) breast-feeding for the first six months of life (see Table 3.2). That stunning endorsement of breast milk is based on extensive research from all nations of the world. The specific fats and sugars in breast milk make it more digestible and better for the brain than any substitute (Drover et al., 2009; Wambach & Riordan, 2014). Ideally, nutrition starts with colostrum, a thick, high-calorie fluid secreted by the mother's breasts at birth. This benefit is not understood in some cultures, where mothers are forbidden to breast-feed until their milk "comes in" two or three days after birth. (Sometimes other women nurse the newborn; sometimes herbal tea is given.) This is one time when culture is harmful: Colostrum saves infant lives, especially if the infant is preterm (Moles et al., 2015; Andreas et al., 2015). Breast-feeding mothers should be well nourished and hydrated; then their bodies will make the perfect food for their babies. Formula is preferable only in unusual cases, such as when the mother is HIV-positive, or uses toxic or addictive drugs. Even then, however, exclusive breast-feeding may be best. In some nations, the infants' risk of catching HIV from their HIV-positive mothers is lower than the risk of dying from infections, diarrhea, or malnutrition as a result of bottle-feeding (A. Williams et al., 2016). In China, a study of more than a thousand babies in eight cities compared three groups of babies: those exclusively breast-fed (by their own mothers or wet nurses), those fed no breast milk, and those fed a combination of foods, formula, and breast milk. Based on all of the data, the researchers suggest that the WHO recommendation for exclusive breast-feeding for the first six months "should be reinforced in China" (Ma et al., 2014, p. 290). The more research is done, the better breast milk seems. For instance, the composition of breast milk adjusts to the age of the baby, with milk for premature babies distinct from that for older infants. Quantity increases to meet the demand: Twins and even triplets can be exclusively breast-fed for months. Each generation of scientists, and consequently each generation of mothers, knows more about breast milk (see A Case to Study on page 120).

SURPRISE AND THE BRAIN

The conclusion that surprise indicates object permanence is accepted by most scientists. Other scientists are less convinced (Mareschal & Kaufman, 2012). They may interpret object permanence differently (Marcovitch et al., 2016), noticing the fragility of the concept in early infancy (Bremner et al., 2015) or suggesting other measures of surprise (Dunn & Bremner, 2017). But, everyone agrees that waiting until babies can physically uncover an object is waiting too long: Babies are thinking before bodies can demonstrate cognition. Cognition can be measured via surprise, by gaze, by movement of arms and legs. Caregivers notice that babies look around and seem intently interested in what is happening. Adults also have better ways to interpret what they see. Instead of noticing children's many "faults or shortcomings relative to an adult standard," we need to appreciate that children remember what they need to remember (Bjorklund & Sellers, 2014, p. 142). Infants remember who their caregivers are, and soon remember what those caregivers do and say. Repeated sensations and brain maturation are required in order to process and recall whatever happens. That is true later in life as well (Bauer et al., 2010). Everyone's memory fades with time, especially if that memory was never encoded into language, never compared with similar events, never discussed with a friend.

HEARING

The fetus hears during the last trimester of pregnancy; loud sounds trigger reflexes even without conscious perception. Familiar, rhythmic sounds such as a heartbeat are soothing: That's why newborns may stop crying if they are held with an ear on the mother's chest. Because of early maturation of the language areas of the cortex, even 4-month-olds attend to voices, developing expectations of the rhythm, segmentation, and cadence of spoken words long before comprehension (Minagawa-Kawai et al., 2011). Soon, sensitive hearing combines with the maturing brain to distinguish patterns of sounds and syllables. That is why hearing is crucial: Ear infections, for instance, need to be treated promptly. By about 4 months, when her auditory cortex is rapidly creating dendrites, the repeated word Emily is perceived as well as sensed, especially because that sound emanates from interactions with the people she often sees, smells, and touches. By 6 months, Emily opens her eyes and smiles when her name is called, perhaps babbling in response. This rapid development of hearing is the reason newborn hearing is tested. If necessary, remediation begins in infancy. By age 5, deaf children who got cochlear implants before age 2 are much better at understanding and expressing language than those with identical losses but whose implants came later (Tobey et al., 2013).

Better Days Ahead

The first month is the most hazardous. Now almost all newborns who survive the first month live to adulthood. Some nations have seen dramatic improvement. Chile's rate of infant mortality, for instance, was almost four times higher than the rate in the United States in 1970; now both nations have improved, and their rates are virtually identical (see Figure 3.4). As more children survive, parents focus more effort and income on each child, having fewer children overall. Worldwide, the average woman had five (4.96) births in 1950; she now has two or three (2.52) (United Nations, 2017). Infant survival and maternal education are the two main reasons the world's fertility rate is half the 1950 rate. This is found in data from numerous nations, especially developing ones, where educated women have far fewer children than those who are uneducated (de la Croix, 2013). That advances the national economy, allowing for better schools and health care — and fewer infant deaths.

Theories of Language Learning

The first theory says that infants are directly taught, the second that social impulses propel infants to communicate, and the third that infants understand language because of brain advances that began several millennia ago.

REMIND ME!

The most dramatic proof of very early memory comes from a series of innovative experiments in which 3-month-olds learned to move a mobile by kicking their legs (Rovee-Collier, 1987, 1990). The infants lay on their backs connected to a mobile by means of a ribbon tied to one foot. Virtually all of the babies realized that kicking made the mobile move. They then kicked more vigorously and frequently, sometimes laughing at their accomplishment. So far, this is no surprise — observing self-activated movement is highly reinforcing to infants. When infants as young as 3 months had the mobile-and-ribbon apparatus reinstalled and reconnected one week later, most started to kick immediately, proof that they remembered their previous experience. But when other 3-month-old infants were retested two weeks later, they kicked randomly. Had they forgotten? It seemed so. But then the lead researcher, Carolyn Rovee-Collier, two weeks after the initial training, allowed some infants to watch the mobile move when they were not connected to it. The next day, when a ribbon again tied their leg to the mobile, they kicked almost immediately. Apparently, watching the mobile the previous day reminded them about what they had previously experienced. Other research similarly finds that reminders are powerful. If Daddy routinely plays with a 3-month-old, goes on a long trip, and the mother shows Daddy's picture and says his name on the day before his return, the baby might grin broadly when he reappears.

Infant Cognition

The rapid development of sensory and motor skills just described is impressive, but the intellectual growth that uses those sensorimotor skills is even more awesome. Recognition of this was one of Piaget's insights.

THEORY TWO: SOCIAL IMPULSES FOSTER INFANT LANGUAGE

The second theory arises from the sociocultural reason for language: communication. According to this perspective, infants communicate because humans are social beings, dependent on one another for survival and joy. All human infants (and no chimpanzees) seek to master words and grammar in order to join the social world (Tomasello & Herrmann, 2010). According to this perspective, it is the social function of speech, not the words, that undergirds early language. This theory challenges child-directed videos, CDs, and MP3 downloads named to appeal to parents (Baby Einstein, Brainy Baby, and Mozart for Mommies and Daddies — Jumpstart your Newborn's I.Q.). Since early language development is impressive, even explosive, some parents who allow infants to watch such programs believe that the rapid language learning is aided by video. Commercial apps for tablets and smartphones, such as Shapes Game HD and VocabuLarry, have joined the market. However, developmental research finds that screen time during infancy may be harmful. One recent study found that toddlers could learn a word from either a book or a video but that only book-learning, not video-learning, enabled children to use the new word in another context (Strouse & Ganea, 2017). Another study focused particularly on teaching "baby signs," 18 hand gestures that refer to particular objects (Dayanim & Namy, 2015). The babies in this study were 15 months old, an age at which all babies use gestures and are poised to learn object names. The 18 signs referred to common early words, such as baby, ball, banana, bird, cat, and dog. In this study, the toddlers were divided into four groups: video only, video with parent watching and reinforcing, book instruction with parent reading and reinforcing, and no instruction. Not surprisingly, the no-instruction group learned words (as every normal toddler does) but not signs, and the other three groups learned some signs. The two groups with parent instruction learned most, with the book-reading group remembering signs better than either video group. Why? The crucial factor seemed to be parent interaction. When parents watch a video with their infants, they talk less than when they read a book or play with toys (Anderson & Hanson, 2016). Since adult input is essential for language learning, cognitive development is reduced by video time. Infants are most likely to understand and apply what they have learned when they learn directly from another person (R. Barr, 2103). Screen time cannot "substitute for responsive, loving face-to-face relationships" (Lemish & Kolucki, 2013, p. 335). Direct social interaction is pivotal for language, according to theory two.

MEMORY IN THE FIRST YEAR

We focus now on one specific ability that Piaget underestimated and that information processing reveals: memory (Schneider, 2015). One crucial insight from information-processing theory is that the infant brain is a very active organ, ready from birth to take in experiences and remember repeated ones (Aslin, 2017). Within the first days after birth, infants recognize their caregivers by face, voice, and smell. Innovative ways to measure cognition have been crucial to the research that finds that Piaget did not realize that the idea of object permanence can emerge before 8 months. The best-known example is a series of studies by Renee Baillargeon which proved that 3-month-old infants grasp object permanence, long before 8 months, when Piaget thought it began. They remember what they saw! Baillargeon devised clever experiments that entailed showing infants an object, then covering it with a screen, and then removing the screen. If the object vanished behind the screen, the babies' brain waves, heart rate, or focused eyes showed surprise. That meant they expected the object to still be present — i.e., that an object's existence was permanent (Baillargeon & DeVos, 1991; Spelke, 1993).

body size

Weight gain is dramatic. Newborns lose weight in the first three days and then gain an ounce a day for several months. Birthweight typically doubles by 4 months and triples by a year. An average 7-pound newborn will be 21 pounds at 12 months (9,525 grams, up from 3,175 grams at birth). Physical growth in the second year is slower but still rapid. By 24 months, most children weigh almost 28 pounds (13 kilograms). They have added more than a foot in height — from about 20 inches at birth to about 34 inches at age 2 (from 51 to 86 centimeters). This makes them about half their adult height and about one-fifth their adult weight, four times heavier than they were at birth (see Figure 3.1). Each of these numbers is a norm, which is a standard for a particular population. The "particular population" for the norms just cited is North American infants. Remember, however, genetic diversity: Some perfectly healthy, well-fed babies are smaller or larger than these norms. Each child follows his or her own trajectory.' At each checkup, growth is compared to that baby's previous numbers. Measurements are expressed as a percentile, from 0 to 100, comparing each infant to others the same age. For example, if a 1-month-old weighs at the 30th percentile, then 29 percent of 1-month-olds weigh less, and 69 percent weigh more. If a baby's percentile changes markedly, either up or down, that is a signal that something might be amiss. If a baby moves down from, say, the 30th to the 10th percentile, that might be failure to thrive. Pediatricians consider it "outmoded" to blame parents, but the biological or social cause of failure to thrive must be discovered and remedied (Jaffe, 2011, p. 100). Similarly, if weight moves up from the 30th to the 70th percentile, especially if height still is close to the 30th percentile, overfeeding might be a problem.

THEORY THREE: INFANTS TEACH THEMSELVES

A third theory holds that language learning is genetically programmed. Adults need not teach it (theory one), nor is it a by-product of social interaction (theory two). Instead, it arises from a particular gene (FOXP2), brain maturation, and the overall human impulse to imitate. For example, English articles (the, an, and a) signal that the next word will be the name of an object, and since babies have "an innate base" that primes them to learn, articles facilitate learning nouns (Shi, 2014, p. 9). Articles prove to be a useful clue for infants learning English but are frustrating for anyone who learns English as an adult. Adults may be highly intelligent and motivated, but their language-learning genes are past the sensitive learning time. Our ancestors were genetically programmed to imitate for survival, but until a few millennia ago, no one needed to learn languages other than their own. Thus, human genes allow experience-dependent language learning, pruning the connections that our particular language does not need. If they are needed by another language that we want to learn in adulthood, our brains cannot resurrect them. The prime spokesman for this perspective was Noam Chomsky (1968, 1980). Although behaviorists focus on variations among children in vocabulary size, Chomsky focused on similarities in language acquisition — the evolutionary universals, not the differences. Noting that all young children master basic grammar according to a schedule, Chomsky hypothesized that children are born with a brain structure he called a language acquisition device (LAD), which allows children, as their brains develop, to derive the rules of grammar quickly and effectively from the speech they hear every day. For example, everywhere, a raised tone indicates a question, and infants prefer questions to declarative statements (Soderstrom et al., 2011). This suggests that infants are wired to talk, and caregivers universally ask them questions long before they can answer back. According to theory three, language is experience-expectant, as the developing brain quickly and efficiently connects neurons to support whichever language the infant hears. Because of this experience-expectancy, the various languages of the world are all logical, coherent, and systematic. Then some experience-dependent learning occurs as each brain adjusts to a particular language. The LAD works for deaf infants as well. All 6-month-olds, hearing or not, prefer to look at sign language over nonlinguistic pantomime. For hearing infants, this preference disappears by 10 months, but deaf infants begin signing at that time, which is their particular expression of the universal LAD.

TASTING AND SMELLING

As with vision and hearing, smell and taste function at birth and rapidly adapt to the social world. Infants learn to appreciate what their mothers eat, first through breast milk and then through smells and bits of the family dinner. The foods of a culture may aid survival: For example, bitter foods provide some defense against malaria, hot spices help preserve food and may prevent food poisoning, and so on (Krebs, 2009). Thus, for 1-year-olds, enjoying the taste of their family cuisine not only joins them to their community, it may save their lives. Notice once again how early experiences sculpt the brain. Taste preferences endure when a person migrates to another culture or when a particular food that was once protective is no longer so. Immigrants may pay high prices to buy the foods that were cheap in their native land because early on they developed an experience-dependent preference. Similarly, in communities threatened with starvation, people sought high-calorie foods. Now many of their descendants like French fries, whipped cream, and bacon, preferences that jeopardize their health. Adaptation also occurs for the sense of smell. When breast-feeding mothers used a chamomile balm to ease cracked nipples, their babies preferred that smell almost two years later, unlike babies whose mothers used an odorless ointment (Delaunay-El Allam et al., 2010). The smell of bread baking, or garlic frying, or sour pickles brings happy memories to some people because of childhood moments. As babies learn to recognize each person's scent, they prefer to sleep next to their caregivers, and they nuzzle into their caregivers' chests — especially when the adults are shirtless. One way to help infants who are frightened of the bath (some love bathing, some hate it) is for the parent to join the baby in the tub. The familiar smells of the adult's body and the soap, as well as the touch, sight, and voice of the caregiver, make the entire experience a pleasant one.

Nutrition

As already explained, infant mortality worldwide has plummeted for several reasons: fewer sudden infant deaths, advances in prenatal and newborn care, clean water, and, as you just read, immunization. One more measure is making a huge difference: better nutrition. Worldwide, about half of all childhood deaths occur because malnutrition makes a childhood disease lethal, not only the leading causes of childhood deaths — diarrhea and pneumonia — but also milder diseases such as measles (Walker et al., 2013; Roberts, 2017). Some diseases result directly from malnutrition — including both marasmus during the first year, when body tissues waste away, and kwashiorkor after age 1, when growth slows down, hair becomes thin, skin becomes splotchy, and the face, legs, and abdomen swell with fluid (edema).

STAGES FIVE AND SIX

At about 12 months, Piaget found that infants begin to actively experiment. At first they do not think before acting, as when they squeeze all of the toothpaste out of the tube, draw on the wall, or uncover an anthill. Piaget called 1-year-olds "little scientists" who "experiment in order to see." Their devotion to discovery is familiar to every adult scientist — and to every parent. Finally, toward the end of the second year, toddlers think about what they are doing before they do it, hesitating a moment before yanking the cat's tail or dropping a raw egg on the floor. Of course, the urge to explore may overtake caution: Things that are truly dangerous (cleaning fluids, swimming pools, open windows) need to be locked and gated. Image Especially for Parents One parent wants to put all breakable or dangerous objects away because the toddler is able to move around independently. The other parent says that the baby should learn not to touch certain things. Who is right? (see response, page 123) The ability to combine thoughts and actions allows toddlers to pretend. For instance, they know that a doll is not a real baby, but they can strap it into a stroller and take it for a walk. At 22 months, my grandson gave me imaginary "shoe ice cream" and laughed when I pretended to eat it. They also watch other people carefully and draw conclusions about what they see. Deferred imitation occurs when infants copy behavior that they noticed hours or even days earlier (Piaget, 1962/2013c). Piaget described his daughter, Jacqueline, who observed another child who got into a terrible temper. He screamed as he tried to get out of a playpen and pushed it backwards, stamping his feet. J. stood watching him in amazement, never having witnessed such a scene before. The next day, she herself screamed in her playpen and tried to move it, stamping her foot lightly several times in succession. [Piaget, 1962/2013c, p. 63] These words illustrate Piaget's genius: He observed children carefully, noticing how they thought at each stage. Scientists were awed by Piaget's recognition that babies "learn so fast and so well" (Xu & Kushnir, 2013, p. 28). However, he underestimated the age at which various accomplishments occurred. You already saw this with object permanence; the same is true for deferred imitation.

BABBLING AND GESTURING

Between 6 and 9 months, babies repeat certain syllables (ma-ma-ma, da-da-da, ba-ba-ba), a vocalization called babbling because of the way it sounds. Babbling is experience-expectant; all babies babble and caregivers usually encourage those noises. Babbling predicts later vocabulary, even more than the other major influence — the education of the mother (McGillion et al., 2017). babbling An infant's repetition of certain syllables, such as ba-ba-ba, that begins when babies are between 6 and 9 months old. Expectations appear early. Before uttering their first word, infants notice patterns of speech, such as which sounds are commonly spoken together. A baby who often hears that something is "pretty" expects the sound of prit to be followed by tee (MacWhinney, 2015) and is startled if someone says "prit-if." Infants also learn the relationship between mouth movements and sound. In one study, 8-month-olds watched a film of someone speaking, with the audio a fraction of a second ahead of the video. Even when the actor spoke an unknown language, babies noticed the mistiming (Pons & Lewkowicz, 2014). Some caregivers, recognizing the power of gestures, teach "baby signs" to their 6- to 12-month-olds. Then babies use hand signs months before they move their tongues, lips, and jaws to make words. There is no evidence that baby signing accelerates talking (as had been claimed), but it may make parents more responsive, which itself is an advantage (Kirk et al., 2013). For deaf babies, sign language is crucial in the first year: It not only predicts later ability to communicate with signs but also advances crucial cognitive development (Hall et al., 2017). Even without adult signing, gestures become a powerful means of communication (Goldin-Meadow, 2015). One early gesture is pointing and responding to pointing from someone else. The latter requires something quite sophisticated — understanding another person's perspective. Most animals cannot interpret pointing; most 10-month-old humans can. They look at where someone else points and already point with their tiny index fingers. Pointing is well developed by 12 months, especially when the person who is pointing also speaks (e.g., "look at that") (Daum et al., 2013).

Brain Basics

Communication within the central nervous system (CNS)—the brain and spinal cord—begins with nerve cells, called neurons. At birth, the human brain has an estimated 86 billion neurons, far more than any other primate. Especially in the cortex (the brain's six outer layers where most thinking, feeling, and sensing occur), humans have more neurons than other mammals ( The cortex includes regions dedicated to particular aspects of brain function—the visual cortex, auditory cortex, and so on, all evident in newborns. The last part of the brain to mature is the prefrontal cortex, the area behind the forehead that is crucial for anticipation, planning, and impulse control. The prefrontal cortex is inactive in early infancy and gradually becomes more efficient in childhood, adolescence, and adulthood, with marked variation from one person to another (Walhovd et al., 2014). Neurons connect to other neurons via intricate networks of nerve fibers called axons and dendrites. Each neuron typically has a single axon and numerous dendrites, which spread out like the branches of a tree. The axon of each neuron reaches toward the dendrites of other neurons at intersections called synapses, which are critical communication links within the brain. Axons and dendrites do not touch at synapses. Instead, electrical impulses in axons cause the release of chemicals called neurotransmitters, which carry information from the axon of the sending neuron to the dendrites of the receiving neuron. During the first months and years, rapid growth and refinement in axons, dendrites, and synapses occur, especially in the cortex. Dendrite growth is the main reason that brain weight triples from birth to age 2 (M. H. Johnson, 2011). An estimated fivefold increase in dendrites in the cortex occurs in the 24 months after birth, with about 100 trillion synapses present at age 2. According to one expert, "40,000 new synapses are formed every second in the infant's brain" (Schore & McIntosh, 2011, p. 502). Those synapses develop in every part of the brain, but during infancy this seems especially apparent in the limbic system, a cluster of brain areas deep in the forebrain that is heavily involved in emotions and motivation. Three crucial parts of the limbic system are the amygdala, the hypothalamus, and the hippocampus. These three develop early in life and are crucial for fear, depression, and anxiety lifelong (Ng et al., 2017; Qiu et al., 2015; Braun, 2011). The amygdala is a tiny structure, about the same shape and size as an almond. It registers strong emotions, both positive and negative—especially fear. The amygdala is present in infancy, growing with experience. Frightening a baby is likely to increase amygdala activity, causing terrifying nightmares or sudden terrors later on. amygdala A tiny brain structure that registers emotions, particularly fear and anxiety. Another structure in the emotional network is the hippocampus, located next to the amygdala. A central processor of memory, especially memory for locations, the hippocampus responds to the amygdala by summoning memory. Some places feel comforting (perhaps a childhood room) and others evoke fear (perhaps a doctor's office). Those emotions may continue even when the experiences that originated those emotions are long gone. The size of the hippocampus is markedly affected by maternal emotions during pregnancy and by cortisol―the hormone produced by stress. Sometimes considered part of the limbic system is the hypothalamus, which responds to signals from the amygdala and to memories from the hippocampus by producing hormones, especially cortisol. [Life-Span Link: Many other hormones are discussed in Chapter 9, because puberty is caused, enhanced, and bedeviled by rising hormones.] hypothalamus A brain area that responds to the amygdala and the hippocampus to produce hormones that activate other parts of the brain and body.

GROSS MOTOR SKILLS

Deliberate actions that use many parts of the body, producing large movements, are called gross motor skills. These skills emerge directly from reflexes and proceed in a cephalocaudal (head-down) and proximodistal (center-out) direction. gross motor skills Physical abilities involving large body movements, such as walking and jumping. (The word gross here means "big.") Infants first control their heads, lifting them up to look around, an early example of cephalocaudal maturation. Then control moves downward — upper bodies, arms, and finally legs and feet. (See At About This Time, which shows age norms for gross motor skills based on a large, representative, multiethnic sample of U.S. infants.) age norms are affected by culture and cohort. The first five norms are based on babies from five continents [Brazil, Ghana, Norway, United States, Oman, and India] (World Health Organization, 2006). The next three are from a U.S.-only source [Coovadia & Wittenberg, 2004; based on Denver II (Frankenburg et al., 1992)]. Mastering skills a few weeks earlier or later does not indicate health or intelligence. Being very late, however, is a cause for concern. Sitting requires muscles to steady the torso, no simple feat. By 3 months, most babies can sit propped up in a lap. By 6 months, they can usually sit unsupported, but "novice sitting and standing infants lose balance just from turning their heads or lifting their arms" (Adolph & Franchak, 2017). Babies who are never propped up (as in some institutions for orphaned children) sit much later, as do blind babies who cannot use vision to adjust their balance. Crawling is another example of the head-down and center-out direction of skill mastery, as well as of the importance of practice. When placed on their stomachs, many newborns reflexively try to lift their heads and move their arms as if they were swimming. As they gain muscle strength, infants wiggle, attempting to move forward by pushing their arms, shoulders, and upper bodies against the floor. Usually by 5 months, infants add their legs to this effort, inching forward (or backward) on their bellies. Exactly when this occurs depends partly on how much "tummy time" infants have had to develop their muscles, and that, of course, is affected by the caregiver's culture (Zachry & Kitzmann, 2011). Most 8- to 10-month-olds can lift their midsections and crawl (or creep, as the British call it) on "all fours," coordinating the movements of their hands and knees. Crawling depends on experience, not just maturation. Some normal babies never do it, especially if the floor is cold, hot, or rough, or if they always lie on their backs. It is not true that babies must crawl to develop normally. All babies find a way to move (inching, bear-walking, scooting, creeping, or crawling) before they walk, but many resist being placed on their stomachs. Heavier babies master gross motor skills later than leaner ones because practice and balance is harder when the body is heavy (Slining et al., 2010). As soon as they are able, babies stand and then take some independent steps, falling frequently at first, about 32 times per hour. They persevere because walking is much quicker than crawling, and it has other advantages — better sight lines and free hands (Adolph & Tamis-LeMonda, 2014). A photo shows a child walking towards the mother. Bossa Nova Baby? This girl in Brazil demonstrates her joy at acquiring the gross motor skill of walking, which may quickly become dancing whenever music plays. Once toddlers can walk by themselves, they practice obsessively, barefoot or not, at home or in stores, on sidewalks or streets, on lawns or in mud. Some caregivers offer many opportunities, holding infants to walk in the bath, after diapering, around the house, on the sidewalk. Indeed, "practice, not merely maturation, underlies improvements . . . in 1 hour of free play, the average toddler takes about 2400 steps, travels the length of about 8 U.S. football fields, and falls 17 times" (Adolph & Franchak, 2017).

CULTURAL DIFFERENCES

Early communication transcends culture. In one study, 102 adults listened to 40 recorded infant sounds and were asked which of five possibilities (pointing, giving, protesting, action request, food request) was the reason for each cry, grunt, or whatever. Half of the sounds, and about half of the adults, were from Scotland and the other half from Uganda. Adults in both cultures scored significantly better than chance (although no group or individual got everything right). It did not matter much whether the sounds came from Scottish or Ugandan infants, or whether the adults were parents or not (Kersken et al., 2017).

EXPECTED OR DEPENDENT? expected

Every child's experiences sculpt the brain (Kolb et al., 2017). Some sculpting is called experience-expectant and some is called experience-dependent (Greenough et al., 1987). experience-expectant Brain functions that require certain basic common experiences (which an infant can be expected to have) in order to develop normally. experience-dependent Brain functions that depend on particular, variable experiences and therefore may or may not develop in a particular infant. Brain development is experience-expectant when it is necessary for normal brain maturation. In deserts and in the Arctic, on isolated farms and in crowded cities, almost all babies have things to see, objects to manipulate, and people to love them. Without such expected experiences, dendrites and specific regions within the brain do not grow.

The Senses

Every sense functions at birth. Newborns have open eyes, sensitive ears, and responsive noses, tongues, and skin. Very young babies use all of their senses to attend to everything, especially to people (Zeifman, 2013). Meanwhile, adults also have an innate fondness of infant "cuteness," the sight, sounds, touch, and smell of the infant. Thus, from the very beginning, a mutual, multifaceted, sensory connection between infant and caregiver is apparent (Kringelbach et al., 2016). Infants are born with the ability to experience sensations, with a drive to perceive, and, as seen years later when they are adults, with an emotional impulse to care for the next generation.

FORGET ABOUT INFANT AMNESIA!

Piaget, Freud, and other early developmentalists described infant amnesia, the idea that people forget everything that happened to them before age 3. However, although adults do not remember what happened at age 1, they evidently do remember many simple things — especially when emotion is involved. An insight regarding infant amnesia begins with the distinction between implicit and explicit memory. Implicit memory is not verbal; it is memory for movement or thoughts that are not put into words. Implicit memory begins by 3 months, is stable by 9 months, continues to improve for the first two years, and varies from one infant to another (Vöhringer et al., 2017). Explicit memory takes longer to emerge, as it depends on language. Thus, when people say "I don't remember," they mean "I cannot recall it," because it is not in explicit memory. Unconsciously and implicitly, a memory might be present. A person might have an irrational fear of doctors or hospitals, for instance, because of terrifying and painful experiences in the first year — experiences they do not consciously recall.

Brain Development

Prenatal and postnatal brain growth is crucial for later cognition (Gilles & Nelson, 2012). From two weeks after conception to two years after birth, the brain grows more rapidly than any other organ, being about 25 percent of adult weight at birth and almost 75 percent at age 2. Over the same two years, brain circumference increases from about 14 inches to 19 inches. If teething or a stuffy nose temporarily slows weight gain, nature protects the brain, a phenomenon called head-sparing. (As discussed later, head-sparing cannot overcome prolonged malnutrition.)

EXPECTED OR DEPENDENT? dependent

In contrast, certain facets of brain development are experience-dependent: They result from experiences that differ from one infant to another, resulting in brains that also differ. What specific language is heard, whose faces are seen, or how emotions are expressed — from slight pursing of the lips to throwing oneself on the ground — vary from one family to another. Depending on such variations, infant neurons connect in particular ways; some dendrites grow and others disappear (Stiles & Jernigan, 2010). In other words, every baby needs to develop language — that is expectant; brains are primed for it. But that language could be Tajik, Tamil, Thai, or Twi. That is experience-dependent; brains are shaped so that each baby will learn their native language. Infant brains are extraordinarily plastic, molded to their culture (Kolb et al., 2017).

growth in infancy

In infancy, growth is so rapid and the consequences of neglect are so severe that gains are closely monitored. Length, weight, and head circumference are measured monthly at first, and every organ is checked to make sure it functions well.

STAGES ONE AND TWO

Stage one, called the stage of reflexes, lasts only a month. It includes senses as well as motor reflexes, the foundations of infant thought. In this stage, infants adapt their sucking reflex to bottles or breasts, pacifiers or fingers, each requiring specific types of tongue pushing. This adaptation signifies that infants have begun to interpret sensations; they are using their minds — some would say "thinking." Soon sensation leads to perception, which ushers in stage two, first acquired adaptations (also called the stage of first habits). During this stage, infant cognition leads babies to suck in some ways for hunger, in other ways for comfort — and not to suck fuzzy blankets.

Where Should Babies Sleep?

For many in Asia, Africa, and Latin America, the custom has been for infants to sleep beside their mothers. In those cultures, nighttime parent-child separation is often considered cruel. By contrast, most U.S. infants traditionally slept in cribs in their own rooms. Psychiatrists feared that babies would be traumatized if their parents had sex, and many nonprofessionals thought children would be spoiled if they depended too much on their mothers at night. A 19-nation study found that Asian and African mothers worry about separation, whereas mothers with European roots worry more about privacy. In the extremes of that study, 82 percent of Vietnamese babies slept with their mothers, as did 6 percent in New Zealand (Mindell et al., 2010) (see Figure 3.2). Sleeping alone may encourage independence for both child and adult—a quality valued in some cultures but discouraged in others. Sleeping patterns are changing in the United States. Since 2000, co-sleeping has been recommended by North Americans who advocate attachment parenting (Sears & Sears, 2001). Many companies sell "co-sleepers" that allow babies to sleep beside their mothers without a soft mattress or blankets. Bed-sharing (not just co-sleeping) is becoming more popular in the United States: The rate doubled from 6.5 percent in 1993 to 13.5 percent in 2010 (Colson et al., 2013). Many experts seek to safeguard infants who sleep with their parents (Ball & Volpe, 2013). Their advice includes never sleeping beside a baby if the parent has been drinking and never using a soft comforter, pillow, or mattress near a sleeping infant. Some worry that co-sleeping will continue for months and years, disrupting the marital relationship and, perhaps, the entire family. One study found that U.S. families usually kept newborns in the parents' bedroom but moved them to a separate room by 6 months. In that study, mothers who were depressed, and who were unhappy with the father's involvement, were more likely to keep the baby in their room (Teti et al., 2015). The authors suggest that depression and marital problems correlate with co-sleeping only if co-sleeping is not the norm. However, even in Japan, bed-sharing and marital strain often occur together. One Japanese mother wrote: I take care of my baby at night, since my husband would never wake up until morning whatever happens. Babies, who cannot turn over yet, are at risk of suffocation and SIDS because they would not be able to remove a blanket by themselves if it covers over their face. In my case, I sleep with my older child and baby. By the way, my husband sleeps in a separate room because of his bad snoring. [Shimizu et al., 2014] Contrary to this woman's rationalization, sudden infant death syndrome (SIDS, discussed later) is twice as likely when babies sleep beside their parents. Researchers pinpoint the reason: Many parents occasionally sleep beside their baby after drinking or taking drugs. Then bed-sharing can be fatal (P. Fleming et al., 2015). As one review explained, "There are clear reasons . . . [for bed-sharing] warmth, comfort, bonding, and cultural tradition, but there are also clear reasons against doing so, such as increased risk of sudden infant death syndrome" (Esposito et al., 2015). As with many aspects of child care, this decision is cultural and complex. Over time, the sleep patterns of each family member affect the sleep of the others, and a good night's rest benefits everyone. So parents need to establish sleep hygiene (calming routines and regular schedules) (Bathory & Tomopoulos, 2017; El-Sheikh & Kelly, 2017). Exactly what that means is . . . opposing perspectives.

FIRST WORDS

Finally, at about a year, the average baby utters a few words, understood by caregivers if not by strangers. In the first months of the second year, spoken vocabulary increases gradually (perhaps one new word a week). Meanings are learned rapidly; babies understand much more than they say. Initially, the first words are merely labels for familiar things (mama and dada are common). Each early word soon becomes a holophrase, a single word that expresses an entire thought. That is accompanied by gestures, facial expressions, and nuances of tone, loudness, and cadence (Saxton, 2010). Imagine meaningful communication in "Dada," "Dada?" and "Dada!" Each is a holophrase.

PUTTING WORDS TOGETHER

Grammar includes all of the methods that languages use to communicate meaning. Word order, prefixes, suffixes, intonation, verb forms, pronouns and negations, prepositions and articles — all of these are aspects of grammar. grammar All of the methods—word order, verb forms, and so on—that languages use to communicate meaning, apart from the words themselves. Grammar is evident in holophrases: One word is spoken differently depending on meaning. Grammar becomes essential when babies combine words (Bremner & Wachs, 2010). That typically happens between 18 and 24 months. Children's proficiency in grammar correlates with sentence length, which is why mean length of utterance (MLU) is used to measure a child's language progress (e.g., Miyata et al., 2013). The child who says "Baby is crying" is more advanced than the child who says "Baby crying" or simply "Baby!"

Language: What Develops in the First Two Years?

Human linguistic ability by age 2 far surpasses that of full-grown adults from every other species. Very young infants listen intensely, responding as best they can. One scholar explains, "infants are acquiring much of their native language before they utter their first word" (Aslin, 2012, p. 191). How do they do it?

stress

If the brain produces an overabundance of cortisol (the stress hormone) early in life (as when an infant is frequently terrified), that derails the connections between parts of the brain, causing atypical responses to stress lifelong. Years later that person may be hypervigilant (always on alert) or emotionally flat (never happy or sad). Adults need to comfort crying babies, not tell them to stop crying. Indeed, because the prefrontal cortex has not yet developed, infants cannot decide to stop crying. If a frustrated adult shakes a crying baby, that may stop the crying because ruptured blood vessels in the brain break neural connections — a phenomenon called shaken baby syndrome, or abusive head trauma (Christian & Block, 2009). Death is the worst consequence; lifelong intellectual impairment is the more likely one.

Surviving and Thriving

In 1950, one young child in seven died, but only about one child in 30 died in 2017 (United Nations, 2017). In earlier centuries, more than half of all children died at birth or in their first year. This progress is good news, not only for families but for developmentalists. It also presents a challenge: We are learning how to improve survival so that infant death in any nation becomes rare.

TOUCH AND PAIN

The sense of touch is acute in infants. Wrapping, rubbing, massaging, and cradling are comforting. Even when their eyes are closed, some infants stop crying and visibly relax when held securely by their caregivers. In the first year, the heartbeat slows and muscles relax when infants are stroked gently and rhythmically (Fairhurst et al., 2014). That explains why, worldwide, parents cuddle their newborns — rocking, carrying, and so on. Some touch (gentle of course) seems experience-expectant, essential for normal growth. Beyond that, how much a baby is touched is experience-dependent, varying by culture. In some nations, daily massage begins soon after birth (Trivedi, 2015). Indeed, in rural India, mothers need to be taught that the newborn's need for warmth is more important than immediate bathing and massage, since both of those common practices may inadvertently harm. Mothers are encouraged to wipe their newborns with a dry cloth and breast-feed immediately — practices that keep the baby warm, use the sense of touch, and reduce early death (Acharya et al., 2015). Have you noticed that some adults are comforted by a reassuring touch and others cringe? Those opposite reactions reflect opposite childhood experiences. Pain and temperature are not among the traditional five senses, but they are often connected to touch. Some babies cry when being changed, distressed at the sudden coldness on their skin. Some touches are painful — a poke, pinch, or pat — although at first babies look carefully at the person touching to discern intention, which tells the baby whether or not pain is involved. Scientists are not certain about infant pain (Fitzgerald, 2015). Some believe that pain receptors are less sensitive at birth — otherwise, how could a baby endure being born? Some experiences that are painful to adults (circumcision, the setting of a broken bone) are much less so to newborns. However, this does not mean that newborns never feel pain (Reavey et al., 2014). Physiological measures including hormones, heartbeat, and brain waves are studied to assess infant pain, but the conclusions are mixed. Infant brains are immature: They have some similar responses to pain and some dissimilar ones when compared to adults (Moultrie et al., 2016). If surgery is required at birth, anesthesia is very sparingly used, since overuse might risk death due to slowed breathing. Fortunately, the other senses reduce pain: A drop of sugar water before a heel stick decreases crying, and listening to Mother's voice, or even to calming music, reduces distress (Filippa et al., 2017). Many hospital NICUs have adopted practices that make the first days of life better for preterm babies, including allowing parents to touch their fragile infants, eliminating bright lights and noisy monitors, reducing distress through careful swaddling and positioning, and so on. The result is improved social and cognitive development later on (Montirosso et al., 2017). A few weeks after birth, infants seem to feel pain. Some cry inconsolably for more than three hours, more than three days a week. Digestive pain (colic) caused by the gut microbiome is the usual explanation (Pärtty & Kalliomäki, 2017). Pediatricians know that colic usually disappears by 3 months, so they are not troubled by it; but many parents are overwhelmed. Therefore, developmentalists take crying seriously; it may impair the relationship between infant and caregiver.

sleep

Throughout life, health and growth correlate with regular and ample sleep (El-Sheikh & Kelly, 2017). As with many health habits, sleep patterns begin in the first year. Newborns sleep about 15 to 17 hours a day. Every week brings a few more waking minutes. For the first two months the norm for total time asleep is 14¼ hours; for the next 3 months, 13¼ hours; for the next 12 months, 12¾ hours. Remember that norms are averages; individuals vary. Parents report that, among every 20 infants in the United States, one sleeps 9 hours or fewer per day and one sleeps 19 hours or more (Sadeh et al., 2009). National averages vary as well. By age 2, the typical New Zealand toddler sleeps 15 percent more than the typical Japanese one (13⅓ hours compared to 11⅔) (Sadeh et al., 2010). Over the first few months, the time spent in each stage of sleep changes. Preterm babies may seem to be frequently dozing, never in deep sleep, but that may be caused partially by the constant bright lights and frequent feedings in the traditional NICU (neonatal intensive care unit). When they come home, they usually adjust to a day-night schedule (Bueno & Menna-Barreto, 2016). About half the sleep of full-term newborns is REM (rapid eye movement) sleep, with flickering eyelids and rapid brain waves. That indicates dreaming, now thought to consolidate memories. REM sleep declines over the early weeks, as does "transitional sleep," the half-awake stage. At 3 or 4 months, quiet sleep (also called slow-wave sleep) increases markedly. Sleep varies not only because of biology (maturation and genes) but also because of culture and caregivers. Infants who are fed formula and cereal sleep longer and more soundly — easier for parents but not better for the baby. The location of sleep depends primarily on the baby's age and culture, with bed-sharing (in the parents' bed) or co-sleeping (in the parents' room) the norm in some cultures but not in others (Esposito et al., 2015). Bed-sharing is more common in breast-fed babies. A study in Sweden of preterm infants (who are fed every two or three hours) found that most slept with their mothers — especially if the mother had trouble getting back to sleep if she got up to feed her infant (Blomqvist et al., 2017). Full-term newborns also have brain patterns and hunger needs that do not allow long stretches of deep sleep. If this lasts for months, the family may be affected: Maternal depression and family dysfunction are more common when infants wake up often (Piteo et al., 2013). This could be a cause or a consequence. Mothers' sleep patterns correlate with those of fathers and children (El-Sheikh & Kelly, 2017). Overall, 25 percent of children under age 3 have sleeping problems, according to parents surveyed in an Internet study of more than 5,000 North Americans (Sadeh et al., 2009). Problems are especially common with the first-born child.

AGE AND CULTURE

When U.S. infants are grouped by ethnicity, generally African American babies are ahead of Hispanic American babies when it comes to motor skills. In turn, Hispanic American babies are ahead of those of European descent. Internationally, the earliest walkers are in sub-Saharan Africa, where many well-nourished and healthy babies walk at 10 months. As found in detailed studies in Senegal and Kenya, babies in many African communities are massaged and stretched from birth onward and are encouraged to walk. They may take their first independent step at 9 months. The latest walkers may be in rural China (15 months), where infants are bundled up against the cold (Adolph & Robinson, 2013). Some cultures discourage walking if danger (poisonous snakes, open fires) abounds, so infants are safer if they cannot wander. By contrast, some cultures encourage running. Their offspring run marathons (Adolph & Franchak, 2017). Remember that difference is not deficit. However, slow development relative to local norms may indicate a problem that needs attention; lags are much easier to remedy during infancy than later on. The age at which walking occurs is a better predictor than simple chronological age of a child's verbal ability, perhaps because walking children elicit more language from caregivers than crawling ones do (Walle & Campos, 2014). The correlation could go in the opposite direction as well: Walkers see their caregivers more, so they talk more (Adolph & Tamis-LeMonda, 2014, p. 191).