Lifespan Development. Tara L. Kuther

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 onto 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 practice 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 childrearing 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 (W. G. 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.

      Motor Development as a Dynamic System

      Motor milestones, such as the ability to crawl, might look like isolated achievements, but they actually develop systematically and build on each other with each new skill preparing an infant to tackle the next (Thelen, 1995, 2000). According to dynamic systems theory, as shown in Figure 4.13, motor development reflects an interaction among developmental domains, maturation, and environment (Thelen, 1995, 2000). Simple motor skills are combined in increasingly complex ways, permitting advances in movement, including a wider range and more precise movements that enable babies to more effectively explore and control their environments. Separate abilities are blended together to provide more complex and effective ways of exploring and controlling the environment. For example, the abilities to sit upright, hold the head upright, match motor movements to vision, reach out an arm, and grasp are all combined into coordinated reaching movements to obtain a desired object (Corbetta & Snapp-Childs, 2009; J. P. Spencer et al., 2000). Motor skills become more specialized, coordinated, and precise with practice, permitting infants to reach for an object with one hand without needlessly flailing the other, for example (D’Souza, Cowie, Karmiloff-Smith, & Bremner, 2016).

      Motor skills also reflect the interaction of multiple domains of development. All movement relies on the coordination of our senses and cognitive abilities to plan and predict actions. Sensory abilities such as binocular vision and the ability to direct gaze combine with exploratory hand and foot movements, designed to determine the opportunities a given surface provides for movement. For example, when 14-month-old infants were tested on a “bridge” of varying widths, they explored the bridge first with quick glances (Kretch & Adolph, 2017). When faced with an impossibly narrow width, infants with walking experience tended to engage in more extensive and time-consuming perceptual and motor exploration, such as touching with hands and feet, to determine whether to cross the bridge.

      Description

      Figure 4.13 Dynamic Systems Theory

      The infant’s abilities to reach out an arm, stretch, and grasp combine into coordinated reaching movements to obtain desired objects. Motor development progresses to sitting, crawling, walking, and eventually running, all reflections of infants’ blending and coordinating abilities to achieve self-chosen goals, such as obtaining toys, and all tailored by environmental supports and challenges.

      Source: ©iStockphoto.com/Essentials Collection; ©iStockphoto.com/Essentials Collection; © Can Stock Photo Inc./harishmarnad

      Motor development reflects goal-oriented behavior because it is initiated by the infant or child’s desire to accomplish something, such as picking up a toy or moving to the other side of the room. Infants’ abilities and their immediate environments (e.g., whether they are being held, lying in a crib, or lying freely on the floor) determine whether and how the goal can be achieved (J. P. Spencer et al., 2000). The infant tries out behaviors and persists at those that enable him or her to move closer to the goal, practicing and refining the behavior. For example, infants learn to walk by taking many steps and making many falls, but they persist even though, at the time, crawling is a much faster and more efficient means of transportation (Adolph et al., 2012). Why? Perhaps because upright posture leads to many more interesting sights, objects, and interactions. The upright infant can see more and do more, with two hands free to grasp objects, making walking a very desirable goal (Adolph & Tamis-LeMonda, 2014). New motor skills provide new possibilities for exploration of the environment and new interactions with caregivers that influence opportunities. Differences in caregiver interactions and caregiving environments affect children’s motor skills, the form they take, the ages of onset, and the overall developmental trend (Adolph & Franchak, 2017).

      Social and cultural contexts contribute to our movements. Motor skills do not develop in isolation; rather, they are influenced by the physical and social context in which they occur. For example, a naturalistic study of video records of at-home interactions of mother–infant pairs from six