Perceiving and Moving

People might think that infants are passive creatures at first, unable to do much. But that is far from the truth: Developmentalists have traced the rapid development of every sense and skill.

The Senses

Every sense functions at birth. Newborns have open eyes, sensitive ears, and responsive noses, tongues, and skin. Indeed, very young babies seem to use their senses to attend to everything without much judgment. For instance, in the first months of life, they smile at strangers and suck almost anything in their mouths.

Why are new infants not more discriminating? Because sensation precedes perception. Then perception leads to cognition. Thus, in order to learn, babies begin by responding to every sensation that might be significant.

Sensation occurs when a sensory system detects a stimulus, as when the inner ear reverberates with sound or the retina and pupil of the eye 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.

Genetic selection over more than 100,000 years affects all the senses. Humans cannot hear what mice hear, or see what bats see, or smell what puppies smell; humans do not need those sensory abilities. However, survival requires babies to respond to people, and newborns innately do so with every sense they have (Konner, 2010; Zeifman, 2013).

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. If a particular sensation occurs often, it connects with past experience, making a particular sight worth interpreting (M. E. Diamond, 2007).

Some sensations are beyond a baby’s comprehension at first. A newborn has no idea that the letters on a page might have significance, that Mother’s face should be distinguished from Father’s, or that the smells of roses and garlic have different connotations. Perceptions require experience.

Infants’ brains are especially attuned to their own repeated social experiences; that is where evidence of perception first appears. You already saw this with face recognition.

Thus, perception follows sensation, when sensory stimuli are interpreted in the brain. Then cognition follows perception, when people think about what they have perceived. (Later, cognition no longer depends on sensation: People imagine, fantasize, hypothesize.) The sequence from sensation to perception to cognition requires that an infant’s sense organs function. No wonder the parts of the cortex dedicated to hearing, seeing, and so on develop rapidly: That is the prerequisite for human intellect. Now some specifics.

The sense of hearing develops during the last trimester of pregnancy; fetuses hear sounds. At birth, familiar, rhythmic sounds such as a heartbeat are soothing: That is one reason kangaroo care reduces newborn stress (see Chapter 4). If a newborn is deaf (many states require testing at birth), early remediation—either a cochlear implant or sign language—allows language and cognition to develop normally.

In the early weeks, babies come to expect the familiar rhythms, segmentation, and cadence of the words they hear long before they understand their meaning (Minagawa-Kawai et al., 2011). By 14 months, they not only prefer their native speech, but they like strangers better who speak whatever language they have often heard—even if they understand nothing of the content of the talking (Buttelmann et al., 2013).

By contrast, vision is immature at birth. Although in mid-pregnancy the eyes open and are sensitive to bright light (if the pregnant woman is sunbathing in a bikini, for instance), the fetus has nothing much to see. Consequently, newborns are legally blind; they focus only on things between 4 and 30 inches (10 and 75 centimeters) away (Bornstein et al., 2005).

Almost immediately, experience combines with maturation of the visual cortex to improve the ability to see shapes and then notice details. Vision improves so rapidly that researchers are hard-pressed to describe the day-by-day improvements (Dobson et al., 2009). By 2 months, infants not only stare at faces but also, after perception and then cognition, smile. (Smiling can occur earlier but not because of perception.)

As perception builds, visual scanning improves. Thus, 3-month-olds look closely at the eyes and mouth, smiling more at smiling faces than at angry or expressionless ones. They pay attention to patterns, colors, and motion (Kellman & Arterberry, 2006).

Because binocular vision (coordinating both eyes to see one image) is impossible in the womb (nothing is far enough away to need two eyes), many newborns seem to use their eyes independently, momentarily appearing wall-eyed or crosseyed. Normally, experience leads to rapid focus and binocular vision. Usually between 2 and 4 months, both eyes focus on a single thing (Wang & Candy, 2010).

This ability aids in the development of depth perception, which has been demonstrated in 3-month-olds, although it was once thought to develop much later. Experienced crawlers and walkers are very adept at deciding if a given path is safe to cross upright, thereby illustrating the coordination of the senses and motor skills (Kretch & Adolph, 2013). (This does not mean that toddlers can be trusted not to fall off tables or out of windows.)

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 spoonfuls of the family dinner.

Some herbs and plants contain natural substances that are medicinal. The foods of a particular culture may aid survival: For example, bitter foods provide some defense against malaria, hot spices help preserve food and thus work against food poisoning, and so on (Krebs, 2009). Thus, for 1-year-olds, developing a taste for their family cuisine may save their lives.

Adaptation also occurs for the sense of smell. When breast-feeding mothers used a chamomile balm to ease cracked nipples during the first days of their baby’s lives, those babies preferred that smell almost two years later, compared with babies whose mothers used an odorless ointment (Delaunay-El Allam et al., 2010).

Learning About a Lime As with every other normal infant, Jacqueline’s curiosity leads to taste and then to a slow reaction, from puzzlement to tongue-out disgust. Jacqueline’s responses demonstrate that the sense of taste is acute in infancy and that quick brain perceptions are still to come.

CINDY CHARLES/PHOTOEDIT, INC.

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 get in the tub with the baby. The smells of the adult’s body mix with the smell of soap, making the experience comforting.

The sense of touch is acute in infants. Wrapping, rubbing, massaging, and cradling are each soothing to many new babies. Even when their eyes are closed, some infants stop crying and visibly relax when held by their caregivers. The ability to be comforted by touch is one of the skills tested in the Brazelton Neonatal Behavioral Assessment Scale (NBAS, described in Chapter 4).

Pain and temperature are not among the five senses, but they are often connected to touch. Some babies cry when being changed because sudden coldness on their skin is distressing. Some touches seem intrusive and distressful—such as a poke, a pinch, or a pat—although this varies from one baby to another, and some adults do not realize that their friendly touch may not be perceived as such.

Scientists are not certain about infant pain. Some experiences that are painful to adults (circumcision, setting of a broken bone) are much less so to newborns. For many newborn medical procedures, from a pinprick to minor surgery, a taste of sugar right before the event is an anesthetic. An empirical study conducted with an experimental group and a control group found that newborns typically cry lustily when their heel is pricked (to get a blood sample, routine after birth) but not if they have had a drop of sucrose beforehand (Harrison et al., 2010).

Some people imagine that the fetus feels pain; others say that the sense of pain does not mature until months after birth. Many young infants cry inconsolably for 10 minutes or more; digestive pain is the usual explanation. Often infants fuss before their first tooth erupts: Teething is said to be painful. However, these explanations are unproven; infant crying may not indicate pain (nor does adult crying, necessarily).

Many physiological measures, including stress hormones, erratic heartbeats, and rapid brain waves, are studied to assess pain in preterm infants, who typically undergo many procedures that would be painful to an adult (Holsti et al., 2011). But infant brains are immature: We cannot assume that they do, or do not, feel pain.

Motor Skills

The most dramatic motor skill (any movement ability) is independent walking, which explains why I worried when Bethany did not take a step. All the motor skills, from the newborn’s head-lifting to the toddler’s stair-climbing, develop over the first two years.

The first evidence of motor skills is in the reflexes, explained in Chapter 4. Although the definition of reflexes implies that they are automatic, their strength and duration vary from one baby to another. Most newborn reflexes disappear by 3 months, but some morph into more advanced motor skills.

Caregiving and culture matter. Reflexes become skills if they are practiced and encouraged. As you saw in the chapter’s beginning, the foundation for my fourth child’s walking was set by Mrs. Todd when Sarah was only a few months old. Similarly, some very young babies can swim—if adults have helped them in the water.

Deliberate actions that coordinate 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. Infants first control their heads, lifting them up to look around. Then they control their upper bodies, their arms, and finally their legs and feet (see At About This Time).

Young Expert This infant is an adept crawler. Note the coordination between hands and knees as well as the arm and leg strength needed to support the body in this early version of push-ups. This boy will probably become an expert walker and runner.

CATHARINA VAN DEN DIKKENBERG/ISTOCKPHOTO

Sitting develops gradually; it is a matter of developing the muscles to steady the top half of the body. By 3 months, most babies can sit propped up in someone’s lap. By 6 months, they can usually sit unsupported.

Crawling is another example of the head-down and center-out direction of skill mastery. 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 whatever surface they are lying on.

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” the infant has had, which is affected by culture (Zachry & Kitzmann, 2011).

Between 8 and 10 months after birth, most infants 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 as well as maturation. Some normal babies never do it, especially if the floor is cold, hot, or rough, or if they have always lain on their backs (Pin et al., 2007). It is not true that babies must crawl to develop normally.

All babies find some way to move before they can walk (inching, bear-walking, scooting, creeping, or crawling), but many resist being placed on their stomachs (Adolph & Berger, 2005). Overweight babies master gross motor skills later than thinner ones: Practice and balance is harder when the body is heavy (Slining et al., 2010).

Bossa Nova Baby? This boy in Brazil demonstrates his joy at acquiring the gross motor skill of walking, which quickly becomes dancing whenever music plays.

RICK GOMEZ/MASTERFILE

As soon as they are able, babies walk, falling frequently but getting up undaunted and trying again, because walking is much quicker than crawling, and it has another advantage—free hands (Adolph et al., 2012).

The dynamic system underlying every motor skill has three interacting elements. We illustrate those three here with walking.

1. Muscle strength. Newborns with skinny legs and 3-month-olds buoyed by water make stepping movements, but 6-month-olds on dry land do not; their legs are too chubby for their underdeveloped muscles. As they gain strength, they stand and then walk.
2. Brain maturation. The first leg movements—kicking (alternating legs at birth and then both legs together or one leg repeatedly at about 3 months)—occur without much thought. As the brain matures, deliberate leg action becomes possible.
3. Practice. Unbalanced, wide-legged, short strides become a steady, smooth gait.

This last item, practice, is powerfully affected by caregiving before the first independent step. Some adults spend hours helping infants walk (holding their hands or the back of their shirts) or providing walkers (dangerous if not supervised).

Once toddlers are able to walk by themselves, they practice obsessively, barefoot or not, at home or in stores, on sidewalks or streets, on lawns or in mud. They fall often, but that does not stop them—“they average between 500 and 1,500 walking steps per hour so that by the end of each day, they have taken 9,000 walking steps and traveled the length of 29 football fields” (Adolph et al., 2003, p. 494).

Small body movements are called fine motor skills. The most valued fine motor skills are finger movements, enabling humans to write, draw, type, tie, and so on. Movements of the tongue, jaw, lips, and toes are fine movements, too.

Actually, mouth skills precede finger 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 teach using spoons, or chopsticks, or markers. By contrast, skilled spitting or chewing is not praised; only other children admire blowing bubbles with gum.

Success At 6 months, this baby is finally able to grab her toes. From a developmental perspective, this achievement is as significant as walking, as it requires coordination of feet and fingers. Note her expression of determination and concentration.

VAVA VLADIMIR JOVANOVIC/SHUTTERSTOCK

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 they cannot yet grab and hold on unless an object is placed in their hands, because of limited eye–hand coordination.

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 almost any object that is of the right size. Some can even transfer an object from one hand to the other. Almost all can hold a bottle, shake a rattle, and 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.)

As with gross motor skills, fine motor skills are shaped by culture and opportunity. For example, when given “sticky mittens” (with Velcro) that allow grabbing, infants master hand skills sooner than usual. Their perception advances as well (Libertus et al., 2010; Soska et al., 2010). As with the senses, each motor skill expands the baby’s cognitive awareness.

In the second year, grasping becomes more selective. Toddlers learn when not to pull at a sister’s braids, or Mommy’s earrings, or Daddy’s glasses.

Dynamic Sensory-Motor Systems

Young human infants are, physiologically, an unusual combination of motor immaturity (they cannot walk for many months), sensory acuteness (all senses function at birth), and curiosity (Konner, 2010). What a contrast to kittens, for instance, who are born deaf, with eyes sealed shut, and who stay beside their mother although they can walk.

Human newborns listen and look from day 1, eager to practice every motor skill as soon as possible. An amusing example is rolling over. At about 3 months, infants can roll over from their stomachs to their backs, but not vice versa because their arms are no help when they are not on their stomachs. Once they can roll from stomach to back, many babies do so and then fuss, turtle-like, with limbs flailing. When some kind person flips them back on their stomachs, they immediately roll over again, only to fuss once more.

The most important experiences are perceived with interacting senses and skills, in dynamic systems. Breast milk, for instance, is a mild sedative, so the newborn literally feels happier at Mother’s breast, connecting that pleasure with taste, touch, smell, and sight. But in order for all those joys to occur, the infant must actively suck at the nipple (an inborn motor skill, which becomes more efficient with practice). Because of brain immaturity, cross-modal perception (using several senses to understand the same experience) is particularly common in young infants.

By 6 months babies have learned to coordinate senses and skills, expecting another person’s lip movements to synchronize with speech, for instance (Lewkowicz, 2010). For toddlers, crawling and walking are dynamic systems that allow exploration. Piaget named the first two years of cognition “sensorimotor” for good reason. The next chapter will describe some of the specifics. But first, there is one obvious prerequisite for all the growth already described—staying alive.