4.6 Motor Development
The Significance of Early Motor Skills
Parents are highly excited about new motor skills as they empower babies to master their bodies and interact with the environment in novel ways.
For example, sitting upright provides infants with a new visual perspective.
Reaching allows babies to explore objects by physically interacting with them.
Independent movement significantly expands opportunities for environmental exploration.
Motor achievements profoundly influence social relationships.
Fact: Carolyn and David began to restrict Caitlin's movements and expressed mild impatience when she crawled at 77 months, leading to the first "testing of wills" when she walked (Biringen et al., 1995).
Fact: Newly walking babies are more active in attending to and initiating social interaction (Clearfield, 2011; Karasik et al., 2011).
Parents often increase their verbal responsiveness, expressions of affection, and engagement in playful activities in response to their child's new motor skills.
Fact: When faced with risky situations (e.g., a sloping walkway), parents intervene with emotional warnings and rich verbal and gestural information, aiding the child in noticing critical features, regulating motor actions, and acquiring language (Karasik et al., 2008).
Motor, social, cognitive, and language competencies develop interdependently and mutually support one another.
Types and Sequence of Motor Development
Gross-motor development refers to control over large muscle actions that facilitate movement within the environment.
Examples include crawling, standing, and walking.
Fine-motor development pertains to control over smaller, more precise movements.
Examples include reaching and grasping.
Reaching and Grasping Skills
Significance for Cognitive Development
Reaching and grasping play a crucial role in infant cognitive development, allowing infants to learn about the sights, sounds, and feel of objects through physical interaction (grasping, turning over, releasing).
Connection to Gross-Motor Skills
Advancements in gross-motor skills, such as sitting, standing, and walking, significantly change an infant's view of their surroundings, leading them to focus on and explore nearby objects, thereby promoting manual coordination (Kretch, Franchak, & Adolph, 2014).
Stages of Reaching Development
Prereaching: Newborns exhibit poorly coordinated swipes towards objects, which typically drops out around 77 weeks of age due to poor arm and hand control (von Hofsten, 2004).
Purposeful Reaching: At approximately 33 to 44 months, reaching reappears as deliberate forward arm movements, supported by developing eye, head, and shoulder control, and gradually improves in accuracy (Bhat, Heathcock, & Galloway, 2005).
Vision and Refinement: By 55 to 66 months, infants can reach for objects in darkened rooms, suggesting that vision is becoming less critical for the basic act of reaching, allowing it to focus on more complex adjustments (Clifton et al., 1994; McCarty & Ashmead, 1999).
Independent Arm Use: Around 77 months, infants begin to reach with one arm rather than both, demonstrating increased arm independence (Fagard & Pezé, 1997).
Reaching for Moving Objects: Over the months following 77 months, infants become more efficient at reaching for objects that spin, change direction, or move closer/farther away (Fagard, Spelke, & von Hofsten, 2009; Wentworth, Benson, & Haith, 2000).
Stages of Grasping Development
Ulnar Grasp: The newborn's grasp reflex is replaced by the ulnar grasp, a clumsy motion where fingers close against the palm.
Adjusting Grasp: By 44 to 55 months, infants begin to modify their grasp to match an object's size, shape, and texture. This ability refines, allowing them to adjust their hand more precisely in advance of contact during the second half-year (Rocha et al., 2013; Witherington, 2005).
Two-Hand Coordination: Around 44 to 55 months, concurrent with improved sitting ability, infants use both hands to explore objects, holding an object in one hand while the other scans it, and frequently transferring objects between hands (Rochat & Goubet, 1995).
Pincer Grasp: By the end of the first year, babies develop a well-coordinated pincer grasp, using the thumb and index finger opposably. This significantly expands their ability to manipulate small objects, such as picking up raisins, turning knobs, and opening/closing small boxes.
Advanced Cognitive Links to Reaching and Grasping
Anticipatory Actions: Between 88 and 1111 months, as reaching and grasping become well-practiced, infants' attention shifts to events occurring before and after attaining an object. For example, 1010-month-olds adjust their reach to anticipate their next action, such as reaching for a ball faster if they intend to throw it versus push it down a tube (Claxton, Keen, & McCarty, 2003; Kayed & Van der Meer, 2009).
Problem-Solving: Around the same time, infants begin to solve simple problems involving reaching, such as searching for and finding hidden toys.
Social Learning: The capacity to reach for and manipulate objects enhances infants' attention to how adults interact with those same objects. By observing others, babies broaden their understanding of behaviors and the range of actions applicable to various objects (Hauf, Aschersleben, & Prinz, 2007).
Individual Differences in Motor Progress
There are considerable individual variations in the rate at which infants and toddlers achieve motor skills.
A child who develops one skill later (e.g., reaching) will not necessarily be delayed in other skills (e.g., crawling or walking).
Developmental concern arises primarily if many motor skills are significantly delayed.
Challenging the Maturational View
Historically, motor skills were considered discrete, innate abilities emerging in a fixed sequence governed by a built-in maturational timetable. This view has been largely discredited.
Motor skills are profoundly interrelated; each skill is built upon previous motor attainments and contributes to the emergence of new ones.
Children acquire motor skills in highly individual ways, often deviating from standardized sequences.
Example: Grace, who spent much of her early life in a hammock and lacked tummy time, pulled to a stand and walked before she ever crawled.
Fact: Babies exhibit skills such as rolling, sitting, crawling, and walking in diverse orders, rather than adhering strictly to the sequence implied by typical motor norms (Adolph & Robinson, 2013).
Factors Influencing Motor Progress (Dynamic Systems Theory)
The current understanding of motor development aligns with the dynamic systems theory of motor development. This theory posits that motor skills are not genetically preprogrammed but emerge from the complex, continuous interaction of several factors. It emphasizes that mastery of motor skills involves acquiring increasingly complex systems of action where separate abilities blend to produce more effective ways of exploring and controlling the environment. For example, control of the head and upper chest combine into sitting with support, and kicking, rocking on all fours, and reaching combine to become crawling. Crawling, standing, and stepping are then united into walking (Adolph & Robinson, 2015; Thelen & Smith, 1998).
Key factors influencing motor progress in the first two years of life, as per dynamic systems theory, include:
Central Nervous System Development: The maturation of the brain and nervous system provides the foundational capacity for complex movements.
Body's Movement Capacities: The physical characteristics of the child's body, such as muscle strength, balance, and proportions, influence what movements are possible.
Child's Goals: The intrinsic motivation and desire of the child to achieve a goal (e.g., to reach a toy or move across a room) drive the organization and refinement of motor actions.
Environmental Supports: The opportunities and encouragement provided by the environment are crucial.
Physical Environment: Access to firm surfaces for movement, space for exploration, and objects for interaction (e.g., Grace's limited tummy time hampered crawling). Infants with stairs at home learn to crawl up stairs earlier and master the back-descent strategy more readily (Berger, Theuring, & Adolph, 2007). Reduced gravity, like on the moon, would lead to a preference for jumping over walking or running.
Social Environment: Parental and caregiver responses, encouragement, and interventions significantly shape motor learning and exploration (e.g., Carolyn and David's interactions with Caitlin).
Learning and Practice: Repeated attempts and refinements of movements are essential for mastering new motor skills.
When a skill is first acquired, infants must refine it; for example, Caitlin iterated through various "belly-crawling" methods before propelling herself forward.
As babies attempt a new skill, previously mastered skills may temporarily become less secure (e.g., a novice walker's sitting balance may be less stable) (Chen et al., 2007).
Motor mastery involves intense practice. Toddlers learning to walk practice six or more hours a day, traveling distances equivalent to 29292929 football fields. They fall, on average, 17171717 times per hour but rarely cry, quickly returning to motion (Adolph et al., 2012).
Repeated movements promote new synaptic connections in the brain that govern motor patterns.
Challenging Genetic Determinism: Dynamic systems theory demonstrates that motor development cannot be solely genetically determined because it is motivated by exploration, the desire to master new tasks, and varies with context. Heredity can only map it out at a general level. Motor behaviors are "softly assembled" from multiple components, allowing for different paths to the same motor skill, rather than being hardwired (Adolph & Robinson, 2015; Spencer, Perone, & Buss, 2011).
Dynamic Motor Systems in Action
Studies tracking infants' acquisition of motor capacities show that the order of skill development is not always fixed.
Fact: In one investigation, infants as early as 88 weeks of age reached for toys with their feet, a month before reaching with their hands. This pattern occurred because hip joints constrain leg movements less freely than shoulder joints constrain arm movements, making foot reaching easier to control and requiring less practice (Galloway & Thelen, 2004).
These findings confirm that the order of motor skill development depends on the anatomy of the body part, the surrounding environment, and the baby's efforts.
Babies often use advances in one motor skill to support advances in others.
Example: Learning to walk frees the hands for carrying, and new walkers actively fetch distant objects and transport them (Karasik, Tamis-LeMonda, & Adolph, 2011).
Fact: New walkers surprisingly fall less often when carrying objects than when their hands are empty, suggesting they integrate object carrying into their "walking system" to improve balance (Karasik et al., 2012).
Cultural Variations in Motor Development
Cross-cultural research highlights how early movement opportunities and stimulating environments significantly contribute to motor development, while restricted environments can delay it.
Iranian Orphanages (Dennis, 1960):
Infants who spent days lying on their backs in cribs, deprived of toys, generally did not move on their own until after 22 years of age.
Due to constant back-lying experience, they often scooted in a sitting position rather than crawling on hands and knees.
Scooting babies are less likely to pull to a stand as they approach furniture with their feet. By 33 to 44 years of age, only 1515 percent of these orphans could walk alone.
Rural Northeastern China (Mei, 1994):
Mothers place infants on their backs in bags of sand (similar to kitty litter) for most of the day into their second year to ensure safety and ease toileting.
Sandbag-reared babies show significant delays in sitting and walking compared to diapered infants in the same region.
Zinacanteco Indians (Southern Mexico) and Gusii (Kenya) (Greenfield, 1992):
Parents actively discourage infants' gross-motor progress, viewing babies who walk too early as dangerous to themselves (e.g., near cooking fires, weaving looms) and disruptive to others.
Kipsigis (Kenya) and West Indians (Jamaica) (Adolph, Karasik, & Tamis-LeMonda, 2010; Hopkins & Westra, 1988; Super, 1981):
In contrast to Western norms, babies in these cultures hold heads up, sit alone, and walk considerably earlier than North American infants.
Parents emphasize early motor maturity through formal exercises to stimulate skills, such as seating babies in ground holes with rolled blankets for upright posture, frequent standing in laps, bouncing them on their feet, and exercising the stepping reflex.
Infants in these cultures often skip crawling, a motor skill considered crucial in Western nations, due to being supported in upright postures and rarely placed on the floor.
Western Practices and "Tummy Time" (Scrutton, 2005):
The current Western practice of having babies sleep on their backs to protect against SIDS decreases exposure to "tummy time."
This reduced "tummy time" delays gross-motor milestones such as rolling, sitting, and crawling.
Regularly exposing infants to the tummy-lying position during waking hours helps prevent these delays.
Average Ages for Motor Skill Achievement
When held upright, holds head erect and steady:
Average: 6 weeks
Range: 3 weeks – 4 months
When prone, lifts self by arms:
Average: 2 months
Range: 3 weeks – 4 months
Rolls from side to back:
Average: 2 months
Range: 3 weeks – 5 months
Grasps cube:
Average: 3 months, 3 weeks
Range: 2 – 7 months
Rolls from back to side:
Average: 4 months
Range: 2 – 7 months
Sits alone:
Average: 7 months
Range: 5 – 9 months
Crawls:
Average: 7 months
Range: 5 – 11 months
Pulls to stand:
Average: 8 months
Range: 5 – 121 months
Plays pat-a-cake:
Average: 9 months, 3 weeks
Range: 7 – 15 months
Stands alone:
Average: 11 months
Range: 9– 16 months
Walks alone:
Average: 11 months, 3 weeks
Range: 9 – 17 months
Builds tower of two cubes:
Average: 11 months, 3 weeks
Range: 10 – 19 months
Scribbles vigorously:
Average: 14 months
Range: 10– 21 months
Walks up stairs with help:
Average: 16 months
Range: 12– 23
months
Jumps in place:
Average: 23 months, 2weeks
Range: 17 – 30
months
Walks on tiptoe:
Average: 25
months
Range: 16
– 30
months