Lifespan Development. Tara L. Kuther

      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 Indian 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 skill such as running, hopping, kicking, and catching (Kit, Akinbami, Isfahani, & Ulrich, 2017).

      Brain and Biological Influences on Development

      Hand Preference and Language Development in Infancy

      Infants who show an early preference for their right hand also show advanced language abilities at 2 months of age. It may be that infants with a dominant hand are better at stacking blocks and picking up other small objects and toys. These activites promote cognitive development, a contributor to language development.

      iStock/ fatcamera

      Are you a righty or a lefty? Peopl—even infants—usually show a preference for the right hand over the left. In most people, handedness is lateralized to the left hemisphere (Annett, 2002). Language is also processed asymmetrically in the brain. For example, infants and adults tend to show activity in their left hemisphere in response to language (Dehaene-Lambertz, 2017), especially in response to their native language compared with nonnative language (Vannasing et al., 2016). Given that hand preference has been observed prenatally (Hepper, 2013), some researchers have begun to examine whether hand preference is an early indicator of hemispheric specialization and thereby language development. What is the relationship between handedness and language development? Does hand preference predict language development in infancy?

      Although hand preferences have been observed in the womb, infants show individual differences. Some infants show consistent hand preferences across motor tasks and others show a more unstable pattern, switching hands often (Cochet, 2012; Kotwica, Ferre, & Michel, 2008). Infants who consistently prefer the right hand demonstrate greater left hemispheric specialization than those without a consistent hand preference (E. L. Nelson, Campbell, & Michel, 2015). One longitudinal study followed infants at monthly intervals from 6 to 14 months and again from 18 to 24 months to examine the relationship of handedness and language development (E. L. Nelson, Campbell, & Michel, 2013). Although the infants did not differ on measures of cognition or general motor skills, infants who showed early preferences for their right hand also showed advanced language abilities at 2 months of age. A consistent right-hand preference during infancy suggested greater lateralization and activity in the left hemisphere, in regions long associated with language. It is important to note, however, that an early hand preference predicted advanced language skill, but children without a stable hand preference showed normative language development.

      Why is having a consistent hand preference associated with advanced language acquisition? Perhaps infants who show a consistent hand preference are better at manipulating objects than those without a stable preference (Kotwica et al., 2008). Infants’ skill in object manipulation is associated with cognition because it permits infants to examine objects in greater detail (Bruner, 1973). Fine motor skills enable infants to play in sophisticated ways, such as stacking blocks, picking up small objects, and filling cups and other containers—and then dumping out the contents. Infants with a dominant hand show greater skill in manipulating objects and using tools to carry out these tasks (Michel, Campbell, Marcinowski, Nelson, & Babik, 2016)—and each of these activities promotes cognitive development, a contributor to language development.

      What Do You Think?

      What might be the long-term implications for a consistent hand preference early in infancy? For language? Cognition? Motor skill?

      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).

      Although this infant spends most of his waking hours tightly swaddled to a cradelboard and carried on his mother’s back, he will walk at about a year of age, similar to babies who are not swaddled.

      Danita Delimont/Alamy Stock Photo

      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, Bennett, Rattanathanthong, & Siritaratiwat, 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). Even 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 (H. 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 & Hsiang-han, 2007; Kuo, Liao, Chen, Hsieh,