Читать книгу Infants and Children in Context - Tara L. Kuther - Страница 248

Much of motor development is driven by maturation, yet opportunities to practice motor skills are also important. In a classic naturalistic study of institutionalized orphans in Iran who had spent their first 2 years of life lying on their backs in their cribs and were never placed in sitting positions or played with, none of the 1- to 2-year-old infants could walk, and fewer than half of them could sit up; the researchers also found that most of the 3- to 4-year-olds could not walk well alone (Dennis, 1960). Recent research suggests that infants raised in orphanages score lower on measures of gross motor milestones at 4, 6, and 8 months of age and walk later compared with home-reared infants (Chaibal et al., 2016). While maturation is necessary for motor development, it is not sufficient; we must also have opportunities to practice our motor skills.

In fact, practice can enhance motor development (Lobo & Galloway, 2012). For example, when infants from 1 to 7 weeks of age practice stepping reflexes each day, they retain the movements and walk earlier than infants who receive no practice (Vereijken & Thelen, 1997; Zelazo, 1983). Newborns show improvement in stepping after practicing on a treadmill (Siekerman et al., 2015). Practice in sitting has a similar effect (Zelazo, Zelazo, Cohen, & Zelazo, 1993). Even 1-month-old infants given postural training showed more advanced control of their heads and necks than other infants (Lee & Galloway, 2012). Similarly, infants who spend supervised playtime prone on their stomachs each day reach many motor milestones, including rolling over and crawling, earlier than do infants who spend little time on their stomachs (Fetters & Huang, 2007; Kuo, Liao, Chen, Hsieh, & Hwang, 2008). In one study, over a 2-week period, young infants received daily play experience with “sticky mittens”—Velcro-covered mitts that enabled them to independently pick up objects. These infants showed advances in their reaching behavior and greater visual exploration of objects, while a comparison group of young infants who passively watched an adult’s actions on the objects showed no change (Libertus & Needham, 2010). Sticky mittens training in reaching at 3 months of age predicts object exploration at 15 months of age (Libertus, Joh, & Needham, 2016).

Practice contributes to cross-cultural differences in infant motor development. Different cultures provide infants with different experiences and opportunities for development. For example, in many cultures, including several in sub-Saharan Africa and in the West Indies, infants attain motor goals like sitting up and walking much earlier than do North American infants. Among the Kipsigi of Kenya, parents seat babies in holes dug in the ground and use rolled blankets to keep babies upright in the sitting position (Keller, 2003). The Kipsigis help their babies practice walking at 2 to 3 months of age by holding their hands, putting them on the floor, and moving them slowly forward. Notably, Kipsigi mothers do not encourage their infants to crawl; crawling is seen as dangerous as it exposes the child to dirt, insects, and the dangers of fire pits and roaming animals. Crawling is therefore virtually nonexistent in Kipsigi infants (Super & Harkness, 2015). Infants of many sub-Saharan villages, such as the !Kung San, Gusii, and Wolof, are also trained to sit using holes or containers for support and are often held upright and bounced up and down, a social interaction practice that contributes to earlier walking (Lohaus et al., 2011). Caregivers in some of these cultures further encourage walking by setting up two parallel bamboo poles that infants can hold on to with both hands, learning balance and stepping skills (Keller, 2003). Similarly, mothers in Jamaica and other parts of the West Indies use a formal handling routine to exercise their babies’ muscles and help them to grow up strong and healthy (Dziewolska & Cautilli, 2006; Hopkins, 1991; Hopkins & Westra, 1989, 1990).

Infants’ motor development varies with cultural styles of interaction, such as a Western cultural emphasis on individualism and Eastern cultural emphasis on collectivism. In one cross-cultural study comparing infants in Germany and in the Cambodian Nso culture, the Nso infants showed overall more rapid motor development. The Nso practices of close proximity, lots of close body contact, and less object play are related to the socialization goals of fostering relationships; they also provide infants with body stimulation that fosters gross motor skills. German mothers displayed a parenting style with less body contact but more face-to-face contact and object play, socialization practices that emphasize psychological autonomy but less gross motor exploration. However, the German infants learned how to roll from back to stomach earlier than the Nso infants, likely because Nso infants are rarely placed on their backs and instead are carried throughout the day (Lohaus et al., 2011).

Although practice can speed development and caregivers in many cultures provide their infants with opportunities for early practice of motor skills, sometimes survival and success require continued dependence on caregivers and delaying motor milestones. For example, crawling may not be encouraged in potentially dangerous environments, such as those with many insects, rodents, and/or reptiles on the ground. The nomadic Ache of eastern Paraguay discourage their infants from crawling or moving independently. Ache infants walk at 18 to 20 months, compared with the 12-month average of North American infants (Kaplan & Dove, 1987).

Even simple aspects of the child-rearing context, such as choice of clothing, can influence motor development. In the 19th century, 40% of American infants skipped crawling, possibly because the long, flowing gowns they wore impeded movement on hands and knees (Trettien, 1990). One study of 13- and 19-month-old infants compared their gait while wearing a disposable diaper, a thicker cloth diaper, and no diaper (Cole, Lingeman, & Adolph, 2012). When naked, infants demonstrated the most sophisticated walking with fewer missteps and falls. While wearing a diaper, infants walked as poorly as they would have done several weeks earlier had they been walking naked. In sum, motor development is largely maturational, but subtle differences in context and cultural emphasis play a role in its timing.