Infants and Children in Context. Tara L. KutherЧитать онлайн книгу.
By the end of the first month of life, most infants can lift their head while lying on their stomach.
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Voluntary reaching appears at about 3 months of age and slowly improves in accuracy. At 5 months, infants can successfully reach for moving objects. By 7 months, the arms can reach independently, and infants are able to reach for an object with one arm rather than both (Spencer et al., 2000). By 10 months, infants can reach for moving objects that change direction (Fagard, Spelke, & von Hofsten, 2009). As they gain experience with reaching and acquiring objects, infants develop cognitively because they learn by exploring and playing with objects—and object preferences change with experience. In one study, 4- to 6-month-old infants with less reaching experience spent more time looking at and exploring larger objects, whereas 5- to 6-month-old infants with more reaching experience spent more time looking at and touching smaller objects. The older infants did this despite first looking at and touching the largest object (Libertus et al., 2013). With experience, infants’ attention moves away from the motor skill (like the ability to coordinate their movement to hit a mobile), to the object (the mobile), as well as to the events that occur before and after acquiring the object (how the mobile swings and how grabbing it stops the swinging or how batting at it makes it swing faster). In this way, infants learn about cause and how to solve simple problems.
Biological and Contextual Determinants of Motor Development
Motor development illustrates the complex interactions that take place between maturation and contextual factors.
Biological Influences on Motor Development
Maturation plays a very strong role in motor development. Preterm infants reach motor milestones later than do full-term infants (Gabriel et al., 2009). Cross-cultural research also supports the role of maturation because around the world, infants display roughly the same sequence of motor milestones. Among some Native Americans and other ethnic groups around the world, it is common to follow the tradition of tightly swaddling infants to cradleboards and strapping the board to the mother’s back during nearly all waking hours for the first 6 to 12 months of the child’s life. Although this might lead one to expect that swaddled babies will not learn to walk as early as babies whose movements are unrestricted, studies of Hopi Native American infants have shown that swaddling has little impact on when Hopi infants initiate walking (Dennis & Dennis, 1991; Harriman & Lukosius, 1982). Such research suggests that walking is very much maturationally programmed. Other evidence for the maturational basis of motor development comes from twin studies. Identical twins, who share the same genes, have more similarities in the timing and pace of motor development than do fraternal twins, who share half of their genes (Fogel, 2007; Wilson & Harpring, 1972). Samples of young children in the United States show no ethnic or socioeconomic status differences in gross motor skills such as running, hopping, kicking, and catching (Kit, Akinbami, Isfahani, & Ulrich, 2017).
Advancements in motor skill are influenced by body maturation and especially brain development. The pruning of unused synapses contributes to increases in motor speed and reaction time so that 11-year-old children tend to respond twice as quickly as 5-year-olds (Kail, 2003). Growth of the cerebellum (responsible for balance, coordination, and some aspects of emotion and reasoning) and myelination of its connections to the cortex contribute to advances in gross and fine motor skills and speed (Tiemeier et al., 2010). Brain development improves children’s ability to inhibit actions, which enables children to carry out more sophisticated motor activities that require the use of one hand while controlling the other, such as throwing a ball, or that require both hands to do different things, such as playing a musical instrument (Diamond, 2013). As infants and children gain experience coordinating their motor skills, activity in the areas of the brain responsible for motor skills becomes less diffuse and more focused, consistent with the lifespan principle that domains of development interact (Nishiyori, Bisconti, Meehan, & Ulrich, 2016).
Contextual Influences on Motor Development
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