3.2 Perceiving and Moving

People who don’t know infants might think they are passive creatures at first, unable to do much. But that is far from the truth: Developmentalists have traced the immediate and rapid development of every 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 attend to everything without much judgment. For instance, in the first months of life, they smile at strangers and put almost anything in their mouths (Adolph & Berger, 2005).

Why are new infants not more cautious? Because sensation precedes perception, and perception leads to cognition. In order to learn, babies need to 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. Sensation at birth is affected by genetic selection over more than 100 000 years. 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 people to respond to other people, and newborns innately do so (Konner, 2010; Lloyd-Fox et al., 2009).

Perception occurs when the brain notices and 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 comprehension at first. A newborn has no idea that the letters on a page might have significance, that the mother’s face should be distinguished from the 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, and that is how perception occurs. Thus, a newborn named Emily has no concept that Emily is her name. However she is born with crucial sensations, including the brain and auditory capacity to hear sounds in the usual speech range (not the high sounds that only dogs can hear) and an inborn preference for repeated patterns and human speech.

By about 4 months, when her auditory cortex is rapidly creating and pruning dendrites, the repeated word Emily is perceived as well as sensed, especially because that sound emanates from the people Emily has come to love (Saffran et al., 2006). By 6 months, Emily may open her eyes and turn her head when her name is called. It will take many more months before she says “Emmy” and still longer before she knows that Emily is indeed her name.

Thus, perception follows sensation, when senses are noticed by the brain. Then cognition follows perception, when people think about what they have perceived. (Later, cognition no longer requires sensation: People imagine, fantasize, and 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 the senses develop rapidly: That is the prerequisite for human intellect. Now, some specifics.

Touch and PainThe sense of touch is acute in infants, with wrapping, rubbing, and cradling all soothing to many new babies. Some infants relax when held by their familiar caregiver, even when their eyes are closed. The ability to be comforted by touch is one of the important skills tested in the Brazelton Neonatal Behavioral Assessment Scale (NBAS, described in Chapter 2).

Although newborns respond to being securely held, soon they prefer specific, familiar touches. Caressing, swaddling, kissing, massaging, tickling, bouncing, and rocking are various means of soothing infants.

Pain is not one of the five senses, but it is often connected to touch. Some babies cry when being changed because sudden coldness on their skin is distressing. Some touches seem to be intrusive and produce crying.

Since the process of myelination, which speeds the transmission of nerve impulses between neurons, is not complete in infant brains, scientists have debated for years whether newborns experience pain to the same degree as adults. Now, the consensus seems to be that newborns do feel some kind of pain when undergoing procedures such as circumcision or setting a broken bone.

In a recent longitudinal study on infant pain response to heel pricking (routine after birth), Williams and her colleagues concluded that preterm infants do indeed experience pain right after birth and that their pain response increases as they get older (Williams et al., 2009). Many physiological measures, including stress hormones, erratic heartbeats, and rapid brain waves, are now studied to assess pain in preterm infants.

One tool designed to measure pain in both preterm and full-term infants is called the Neonatal Infant Pain Scale, which was developed at the Children’s Hospital of Eastern Ontario (Lawrence et al., 1993). It uses five parameters to assess infant pain: facial expression, cry, breathing patterns, movement of arms and legs, and state of arousal.

Hearing and Seeing

The sense of hearing develops during the last trimester of pregnancy, which means that fetuses hear sounds in the womb. Since infants have experiences with their mothers’ voice prenatally, they develop voice/sound preferences. Some studies have shown that human fetuses seem to recognize and respond more positively to the sound of their own mother’s voice than to that of other women (Kisilevsky et al., 2003). They also often develop a preference for female voices to male voices, but do not seem to have a preference for their father’s voice over other male voices (Brazelton, 1978; DeCasper & Fifer, 1980).

Researchers have also explored the hearing abilities of fetuses starting at 24 weeks after gestation. For example, DeCasper and Fifer (1980) had pregnant mothers read The Cat in the Hat twice a day 6.5 weeks before they were to give birth. After birth, those infants who had heard this story in the womb were more likely to suck on a pacifier faster (an indication that they recognized the story) each time their mothers read this story rather than another story.

Before Leaving the Hospital Many hospitals require that newborns, such as 1-day-old Henry, have their hearing tested via vibrations of the inner ear in response to various tones. The computer interprets the data and signals any need for more tests—as is the case for about 1 baby in 100. Normal newborns hear quite well; Henry’s hearing was fine.

AP PHOTO/THE PLAIN DEALER, DAVID I. ANDERSEN

For newborns, familiar, rhythmic sounds, such as a heartbeat, are soothing—one reason kangaroo care reduces newborn stress (see Chapter 2). Newborn hearing is routinely checked because the sense of hearing is normally quite acute: If a newborn seems deaf, early remediation may allow language to develop normally.

By 4 months of age, infants have developed perceptions of speech, as is evident in the Emily example. Babies expect the rhythms, segmentation, and cadence of the words they hear long before they understand meaning (Minagawa-Kawai et al., 2011).

Vision is the least mature sense at birth. Although the eyes open in mid-pregnancy and are sensitive to bright light (if the pregnant woman is at the beach in a bikini, for instance), the fetus has nothing much to see. Newborns are legally blind; they focus only on things 10 to 75 centimetres away (Bornstein et al., 2005).

Depth Perception This toddler is crawling on the experimental apparatus called a visual cliff. She stops at the edge of what she perceives as a drop-off.

MARK RICHARDS/PHOTOEDIT

Almost immediately, experience combines with maturation of the visual cortex to improve the ability to see shapes and then notice details, with vision improving 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 occur, 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, colours, 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 two eyes independently, momentarily appearing wall-eyed or cross-eyed. Normally, visual experience leads to rapid development of focus and binocular vision; usually between 2 and 4 months, both eyes can focus on a single object (Wang & Candy, 2010). This helps in the development of depth perception, which has been demonstrated in 3-month-olds, although it was once thought to develop much later due to infants’ reactions on an experimental apparatus called the visual cliff (see photo).

Smelling and TastingThrough the amniotic fluids, infants develop their senses of taste and smell while still in the womb. Schaal and colleagues (2000) found that women who consumed anise-flavoured products during pregnancy gave birth to babies who showed a marked preference for the smell of anise during the first few days after birth. Another group of researchers discovered that infants who were exposed to the flavour of carrot juice, either through amniotic fluid or breast milk, enjoyed eating carrot-flavoured cereal more than plain cereal once they started consuming solid food (Mennella et al., 2001).

Learning About a Lime Like her peers, Jacqueline’s curiosity leads to taste and then to a slow reaction, from puzzlement to tongue-out disgust. Her responses demonstrate that the sense of test is acute in infancy and that quick brain reactions are still to come.

CINDY CHARLES/PHOTOEDIT, INC.

Some herbs and plants contain natural substances that are medicinal. The foods of a particular culture may aid survival: Bitter foods provide some defence against malaria, spicy ones preserve food and thus work against food poisoning, and so on (Krebs, 2009). Thus, developing a taste for family food may be life-saving.

Adaptation also occurs for the sense of smell. When breastfeeding 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 odourless ointment (Delaunay El-Allam et al., 2010). Amazingly, 4-day-old infants can discriminate between the smell of their own mother’s breast milk and that of another mother’s milk (Porter & Reiser, 2005).

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.

Motor Skills

The most dramatic motor skill (any movement ability) is independent walking; this is one reason why Mrs. Todd was determined that Sarah would walk by the age of 1 year (see the beginning of this chapter). Walking and all other motor skills, from the newborn’s head-lifting to toddler’s stair-climbing, develop gradually over the first two years. The first evidence is in reflexes, already explained in Chapter 2.

Caregiving and experience matter. Reflexes become skills if they are practised and encouraged. As you saw in the chapter’s beginning, the foundation for Sarah’s walking was laid by Mrs. Todd’s experience and caregiving when Sarah was only a few months old, long before her first step.

Gross Motor SkillsDeliberate actions that coordinate many parts of the body, producing large movements, are called gross motor skills. These emerge directly from reflexes and proceed in a cephalocaudal (head-down) and proximodistal (centre-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.

Sitting develops gradually, 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. Standing, and then walking, takes longer.

Crawling is another example of this head-down and centre-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 or so, they use their arms, and then legs, to inch 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 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 figure out some way to move before they can walk (inching, bear-walking, scooting, creeping, or crawling), but many resist “tummy time” by rolling over and fussing (Adolph & Berger, 2005). Overweight babies master gross motor skills later than thinner ones: Practice is harder when the body is heavy (Slining et al.,2010).

The dynamic systems underlying motor skills have three interacting elements, each illustrated here with an example related to 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.
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.

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 be walking soon.

CATHARINA VAN DEN DIKKENBERG/ISTOCKPHOTO

The first item, muscle strength, may explain why newborns’ innate stepping reflexes disappear. When newborns are held upright, they show well-coordinated walking movements—stepping. However, it is not until two months later that these stepping movements can be purposefully accomplished by the infant. Some researchers believe that stepping disappears because of the effects of gravity on muscle function (Thelen et al., 1982). As infants gain weight, they dramatically increase their leg mass, which alters the dynamics of their moving limbs. Thus, the strength of the leg muscle is not sufficient to lift the leg or to support the infant’s full weight when in an upright position.

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

The last item in the list, 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 can walk themselves, at around 1 year old, they practise 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 1500 walking steps per hour so that by the end of each day, they have taken 9000 walking steps and travelled the length of 29 football fields (Adolph et al., 2003).

Fine Motor SkillsSmall body movements are called fine motor skills. Finger movements are fine motor skills, 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). Every culture encourages finger dexterity, so children practise finger movements. However, mouth skills such as spitting or chewing are not praised.

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, partly because their eye–hand coordination is limited.

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 hold 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. Once grabbing is possible, babies practise it enthusiastically: “From 6 to 9 months, reaching appears as a quite compulsive behaviour for small objects presented within arm’s reach” (Atkinson & Braddick, 2003).

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).

As with gross motor skills, fine motor skills are shaped by culture and opportunity. For example, infants given “sticky mittens” (with Velcro) that allow grabbing master hand skills sooner than usual. Their perception advances as well (Libertus & Needham, 2010; Soska et al., 2010).

In the second year, grabbing becomes more selective. Toddlers learn when not to pull at a sister’s braids, or Mommy’s earrings, or Daddy’s glasses. However, as you will learn, the curiosity of the “little scientist” may overwhelm this inhibition.

Dynamic Sensory-Motor Systems

The entire package of sensations and motor skills furthers three goals:

1. social interaction
2. comfort
3. learning.

Physiologically, young human infants are, an unusual combination of motor immaturity (they cannot walk for many months), sensory acuteness, 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.

Compare a kitten to a human newborn, listening and looking from day one, eager to practise every motor skill as soon as possible. An amusing example is rolling over. At about 3 months, infants can roll over from their stomach to the back, but not vice versa. Many a baby rolls over, fusses until someone puts him or her stomach down again, and then immediately rolls over again, only to fuss once more.

Sensory Exuberance Human animals are unusual in that all the senses function at birth, but motor skills develop slowly. This Ontario boy loves to grab the rings, or even bend over to taste and bite them, even though he cannot yet sit up unsupported.

ZHIYU WENG

The most important experiences are perceived with interacting senses and skills, in dynamic systems (see Chapter 1). 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 for all those joys to occur, the infant must actively suck at the nipple (an inborn motor skill, which becomes more efficient with practice).

Similarly, 6-month-olds coordinate their senses and skills, expecting lip movements to synchronize with speech, for instance (Lewkowicz, 2010), and making responsive noises themselves. For toddlers, crawling and walking are part of dynamic systems; they are used to explore, and thus sensations lead to perception and cognition.

Piaget named the first two years of cognitive development “sensorimotor” for good reason, as you will soon see. But first, there is one obvious prerequisite for all the growth already described—staying alive.