8.3 Improving Motor Skills

Maturation of the prefrontal cortex allows impulse control, whereas myelination of the corpus callosum and lateralization of the brain permit better physical coordination. No wonder children move with greater speed, agility, and grace as they age. (See Visualizing Development, p. 228.)

Mastery of gross and fine motor skills results not only from maturation but also from extensive, active play. A study in Brazil, Kenya, and the United States tracked how young children spend their time. Cultural variations and differences based on socioeconomic status (SES) emerged. For example, middle-class European American children did the most talking with adults, and working-class Kenyan children did the most chores. But at every income level in all three nations, children spent more time playing than doing anything else—chores, lessons, or conversations (Tudge et al., 2006).

Gross Motor Skills

Gross motor skills improve dramatically. When playing, many 2-year-olds fall down and bump clumsily into each other. By contrast, some 5-year-olds are skilled and graceful, performing coordinated dance steps or sports moves.

Many North American 5-year-olds can ride a tricycle, climb a ladder, and pump a swing, as well as throw, catch, and kick a ball. A few can do these things by age 3, and some 5-year-olds can already skate, ski, dive, and ride a bike—activities that demand balanced coordination and use of both brain hemispheres. Elsewhere, some 5-year-olds swim in oceans or climb cliffs. Brain maturation, motivation, and guided practice undergird all motor skills.

Adults need to make sure children have a safe space, time, appropriate equipment, and playmates. Children learn best from peers who demonstrate whatever the child is ready to try, from catching a ball to climbing a tree. Of course, culture and locale influence particulars: Some small children learn to ski, others to sail.

VISUALIZING DEVELOPMENT

Developing Motor Skills

Every child can do more with each passing year. These examples detail what one child might be expected to accomplish from ages 2 to 6. But each child is unique, and much depends on culture, practice, and maturity.

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Practice with the Big Kids Ava is unable to stand as Carlyann can (left) but she is thrilled to be wearing her tutu in Central Park, New York, with 230 other dancers in a highly organized attempt to break a record for the most ballerinas on pointe at the same moment. Motor skills are developing in exactly the same way on the other side of the world (right) despite superficial opposites (boys, Japan, soccer, pick-up game).

TIMOTHY A. CLARY/AFP/GETTY IMAGES
SEIYA KAWAMOTO/GETTY IMAGES

Recent urbanization concerns many developmentalists. A century ago children with varied skill levels played together in empty lots or fields without adult supervision, but now more than half the world’s children live in cities. Many of these are “megacities … overwhelmed with burgeoning slums and environmental problems” (Ash et al., 2008, p. 739).

Crowded, violent streets not only impede development of gross motor skills but also add to the natural fears of the immature amygdala, responding to the learned fears of adults. Gone are the days when parents told their children to go out and play, to return when hunger, rain, or nightfall brought them home. Now many parents fear strangers and traffic, keeping their 3- to 5-year-olds inside (Taylor et al., 2009).

Observable dangers are not the only problem. Children who breathe heavily polluted air tend to be impaired in brain development. Is this correlation or causation? Such children often live in low-SES households, in crowded neighborhoods, and attend poor schools. Some rarely play outside. Are we certain that dirty air is one cause of learning problems?

Scientists have grappled with this question and answered yes: Environmental substances cause problems in young children at every SES level, but especially those in lower-income families. This conclusion is easiest to demonstrate with asthma, which reduces oxygen to the brain. In the United States, asthma is far more prevalent among children who live in poverty than among those who do not (U.S. Department of Health and Human Services, 2012).

As you already know, the dynamic systems approach to development means that every impairment has many causes, both in the immediate context and in the impact of past genetic and environmental factors. Nonetheless, a recent study conducted in British Columbia, where universal public health care and detailed birth records allow solid research, showed that air pollution from traffic and industry early in life was one cause, not just a correlate, of asthma (Clark et al., 2010).

This study began with all births in 1999 and 2000 in southwest British Columbia (which includes a major city, Vancouver). For three years, 37,401 children were studied, 3,482 of whom were diagnosed with asthma by age 3. Each of those 3,482 was matched on SES, gender, and so on with five other children from the same group.

Exposure to air pollution, (including carbon monoxide, nitric oxide, nitrogen dioxide, particulate matter, ozone, sulfur dioxide, black carbon, wood smoke, car exhausts, and smoke from parents’ cigarettes) was carefully measured.

One finding was that parents could not always protect their children, partly because they did not always know when substances caused poor health. For example, although carbon monoxide emissions are not apparent, when compared to their five matched peers who did not have asthma, those children who were diagnosed with asthma were more likely to live near major highways, where carbon monoxide is more prevalent. Conversely, because wood smoke is easy to see and smell, some parents tried to avoid it, but burning wood did not increase asthma.

Respiratory problems are not the only early-childhood complications caused by pollution. Research on lower animals suggests that hundreds of substances in the air, food, and water affect the brain and thus impede balance, finger dexterity, and motivation. Many substances have not been tested, but some—including lead in the water and air, pesticides in the soil or on clothing, bisphenol A (BPA) in plastic, and secondhand cigarette smoke—are proven harmful.

The administrator of environmental public health for the state of Oregon said, “We simply do not know—as scientists, as regulators, as health professionals—the health impacts of the soup of chemicals to which we expose human beings” (Shibley, quoted in Johnson, 2011). Whether you think Shibley is needlessly alarmist or is simply stating the obvious depends on your own perspective—and maybe on your amygdala.

Lead, however, has been thoroughly researched. The history of lead exposure in the United States illustrates the long path from science to practice, as the following A View from Science illustrates.

A VIEW FROM SCIENCE

Eliminating Lead

Toxic Shrinkage A composite of 157 brains of adults—who, as children, had high lead levels in their blood—shows reduced volume. The red and yellow hot spots are all areas that are smaller than areas in a normal brain. No wonder lead-exposed children have multiple intellectual and behavioral problems.

CECIL, K. M., BRUBAKER, C. J., ADLER, C. M., DIETRICH, K. N., ALTAYE, M, ET AL. (2008). DECREASED BRAIN VOLUME IN ADULTS WITH CHILDHOOD LEAD EXPOSURE. PLOS MED 5(5): E112. DOI:10.1371/JOURNAL.PMED.0050112

Lead was targeted as a poison a century ago (Hamilton, 1914). The symptoms of plumbism, as lead poisoning is called, were obvious—intellectual disability, hyperactivity, and even death if the level reached 70 micrograms per deciliter of blood.

The lead industry defended the heavy metal as an additive, arguing that low levels were harmless, and blamed parents for letting their children eat flaking chips of lead paint (which tastes sweet). Further, since children with high levels of lead in their blood were often from low-SES families, some argued that malnutrition, inadequate schools, family conditions, or a host of other causes were the reason for their reduced IQ (Scarr, 1985).

Consequently, lead remained a major ingredient in paint (it speeds drying) and in gasoline (it raises octane) for most of the twentieth century. The fact that babies in lead-painted cribs, that preschoolers living near traffic, and that children in lead-painted homes near industrial waste were intellectually impaired and hyperactive was claimed to be correlation, not causation.

Finally, chemical analysis of blood and teeth, with careful longitudinal and replicated research, proved that lead was indeed a poison for all children (Needleman et al., 1990; Needleman & Gatsonis, 1990). The United States banned the use of lead in paint (in 1978) and automobile fuel (in 1996). The blood level that caused plumbism was set at 40 micrograms per deciliter, then 20, then 10 (and recently danger is thought to begin at 5 micrograms), with no level proven to be risk-free (MMWR, April 5, 2013).

Regulation has made a difference: The percentage of U.S. 1- to 5-year-olds with more than 5 micrograms of lead per deciliter of blood was 8.6 percent in 1999–2001, 4.1% in 2003–2006, and 2.6 percent in 2007–2010 (see Figure 8.5). Children who are young, low-SES, and/or living in old housing tend to have higher levels (MMWR, April 5, 2013).

Parents are beginning to do their part: They are increasing their children’s calcium intake, wiping window ledges clean, testing drinking water, avoiding lead-based medicines and crockery (available in some other nations), and making sure children never eat chips of lead-based paint.

Dramatic Improvement in a Decade Once researchers established the perils of high lead levels in children’s blood, the percentage of children suffering from plumbism fell by more than 300 percent. Levels are higher in states that once had heavy manufacturing and lower in mountain and Pacific states.

Source: MMWR (April 5, 2013). Blood lead levels in children aged 1–5 Years—United States, 1999–2010. 62, 245–248.

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In some states (e.g., Colorado and Wyoming), average lead levels for young children are close to zero. In other states that once had extensive lead-based manufacturing, young children are still at risk, probably because of lead in the soil and dust. In 2010, Pennsylvania documented 509 children under age 6 with more than 20 micrograms per deciliter in their blood; Ohio had 417; and Michigan had 254 (National Center for Environmental Health, 2012).

Remember from Chapter 1 that scientists sometimes use data collected for other reasons to draw new conclusions. This is the case with lead. About 15 years after the sharp decline in blood lead levels in preschool children, the rate of violent crime committed by teenagers and young adults fell sharply.

As some nations reduced lead in the environment sooner or later than others, year-by-year correlations became apparent: People who had less lead in their blood as infants commit fewer crimes as teenagers.

A scientist comparing these two trends concluded that some teenagers commit impulsive, violent crimes because their brains were poisoned by lead when they were preschoolers. The correlation is found not only in the United States but also in every nation that has reliable data on lead and crime—Canada, Germany, Italy, Australia, New Zealand, France, and Finland (Nevin, 2007). Not everyone is convinced, but there is no doubt that chemicals in the air, food, and water sometimes affect developing brains.

Fine Motor Skills

Fine motor skills are harder to master than gross motor skills. Whistling, winking, and especially writing are difficult actions. Pouring juice into a glass, cutting food with a knife and fork, and achieving anything more artful than a scribble with a pencil all require a level of muscular control, patience, and judgment that is beyond most 2-year-olds.

Many fine motor skills involve two hands and thus both sides of the brain: The fork stabs the meat while the knife cuts it; one hand steadies the paper while the other writes; tying shoes, buttoning shirts, cutting paper, and zipping zippers require both hands.

Same Situation, Far Apart: Finger Skills Children learn whatever motor skills their culture teaches. Some master chopsticks, with fingers to spare; others cut sausage with a knife and fork. Unlike these children in Japan (left) and Germany (right), some never master either, because about one-third of adults worldwide eat directly with their hands.

WILFRIED MAISY/REA/REDUX
NILS HENDRIK MUELLER/GETTY IMAGES

Limited myelination of the corpus callosum may be the underlying reason that shoelaces get knotted, paper gets ripped, and zippers get stuck. Short, stubby fingers add to the problem. As with gross motor skills, practice and maturation are key; using glue, markers, and scraps of cloth are part of the preschool curriculum. Puzzles—with large pieces of splinter-proof wood—are essential supplies.

Traditional academic learning depends on fine motor skills and body control. Writing requires finger control, reading a line of print requires eye control, sitting for hours at a desk requires bladder control, and so on. These are beyond most young children, so even the brightest 3-year-old is not allowed in first grade.

Slow maturation is one reason some 6-year-olds are frustrated if their teachers expect them to write neatly and cut straight. Some educators suggest waiting until a child is “ready” for school; some suggest that preschools should focus on readiness; still others suggest that schools should adjust to the immaturity of the child, instead of trying to make the child adjust. This controversy is explored in the next chapter.

Fine motor skills—like many other biological characteristics, such as bones, brains, and teeth—typically mature about six months earlier in girls than in boys. This may be one reason that girls typically outperform boys on tests of reading and writing.

Artistic Expression

Bliss for Boys But not for moms. Finger painting develops fine motor skills, which is part of the preschool curriculum in early childhood. This boy shows why most stay-home 3-year-olds miss out on this joy.

AMY WHITT/RADIUS IMAGES/GETTY IMAGES

Young children are imaginative, creative, and not yet self-critical. They love to express themselves, especially if their parents applaud their performances, display their artwork, and otherwise communicate approval. The fact that their fine motor skills are immature, and thus their drawings lack precision, is irrelevant. Perhaps the immaturity of the prefrontal cortex is a blessing: It allows creativity without self-criticism.

All forms of artistic expression blossom during early childhood; 2- to 6-year-olds love to dance around the room, build an elaborate tower of blocks, make music by pounding in rhythm, and put bright marks on shiny paper. In every artistic domain, skill takes both practice and maturation.

For example, when drawing a person, 2- to 3-year-olds usually draw a “tadpole”—a circle head, dots for eyes, sometimes a smiling mouth, and then a line or two beneath to indicate the rest of the body. Gradually, tadpoles get bodies, limbs, hair, and so on.

Cultural and cohort differences are apparent. For the most part, Chinese culture incorporates the idea that drawing benefits from instruction, so young children are guided in how best to draw a person, a house, and—most important for the Chinese—a word. Consequently, by age 9, Chinese children draw more advanced pictures than children of other cultures. Adult encouragement, child practice, and developing technical skill correlate with more mature, creative drawings a few years later (Chan & Zhao, 2010; Huntsinger et al., 2011).