Introduction
Motor development refers to the development of motor skills, or voluntary control over the body and its parts. Gross motor development refers to the development of skills or behaviors that involve the large muscle masses and large body movements (such as crawling, walking, running, and throwing), whereas fine motor development refers to the development of small muscle movements, usually in reference to the hands (as in grasping, writing, and fastening buttons). Motor skills develop rapidly during the early years of life and follow a predictable sequence of stages.
Motor development proceeds according to three developmental principles: from head to toe (cephalo-caudal development), from the center of the body to the body’s periphery (proximo-distal development), and from large to small muscle control, with actions becoming more refined and directed (mass-to-specific development). Cephalo-caudal development is illustrated by the fact that infants gain control over their heads and shoulders before their legs. Proximo-distal development is shown by young children gaining control over their arms before their hands and fingers, and mass-to-specific development is illustrated by the fact that infants reach for an object with both arms extended before they can reach out with one arm at a time.
The development of both gross and fine motor skills depends on the maturation (development attributable to one’s genetic timetable and not to experience) of the nervous system. Voluntary movements develop as the cortex, which is the outer layer of the brain, matures. Whereas the cortex is barely functioning at birth, the “lower” parts of the brain—such as the brain stem and the midbrain—that control basic, nonthinking functions such as breathing, heartbeat, digestion, and reflexes are mature at birth. This is part of the reason that newborns have only reflexive, involuntary movements during the first few months of life. Voluntary control over the body develops gradually as connections between the muscles and the higher brain centers such as the cortex become established. The parts of the brain concerned with posture and balance also develop gradually over the first year of life; they contribute to infants being able to sit up, stand, and then walk.
The gradual acquisition of fine and gross motor skills has a number of important implications for a child’s social, cognitive, and personality development. The development of fine motor skills allows infants to examine and experiment with objects, explore their environment, and even communicate with others by showing objects or by pointing. Gross motor milestones provide children with a new and progressively complex perspective of the world, more opportunities to explore and learn about the physical and social environment, and increasing degrees of independence—which have implications for children’s developing sense of mastery and competence. These motor milestones in turn affect parents’ interactions with, and treatment of, their increasingly independent children.
Sequences of Development
Gross motor and fine motor skills follow a specific sequence of development. Gross motor (or locomotor) development eventually results in a young child being able to walk and run. To reach this point, a child must first develop control of his or her head, sit up, and then develop enough balance and strength to stand. By approximately two months of age, most infants can lift their heads, and by three to four months of age they are usually able to roll over. At five or six months they can sit up, and by seven to nine months they usually begin crawling. Infants may be able to stand while holding on to an object at six months, pull themselves to standing between eight and ten months, and walk independently at around twelve to fourteen months. By eighteen months of age, toddlers are usually able to run, walk backward, throw a ball, and climb stairs; between twenty-four to thirty-six months, they may be able to ride a tricycle. From two to six years of age, children continue to refine their movements. For example, a two-year-old’s awkward gait and poor balance change by three years of age to a more stable and balanced gait, allowing the child to hop, jump, and run back and forth. By four years of age, children’s walking movements are similar to adults’, allowing them to move easily up and down stairs and even to hop on one foot. By age five, children are well coordinated, have good balance, and are able to move skillfully and gracefully while walking, running, climbing, and throwing.
Fine motor development eventually results in refined eye-hand coordination, which will enable a child to write. To achieve this, children must first be able to reach, grasp, and manipulate objects voluntarily and possess refined finger (especially thumb-to-index-finger) control. At birth, no voluntary control exists. By three months of age, babies begin to make poorly directed swiping movements with their entire arms (fists closed). At around four months, infants use an open-handed, scooping movement with a slightly better aim; by five months, infants can reach and grasp objects with both hands, holding the object in the center of the palm by all fingers. Between nine and ten months, infants can hold objects by the palm and middle fingers in a palmar grasp. The ability to use the thumb and index finger together (pincer grasp) typically develops between nine and fifteen months. Infants who have developed this skill usually enjoy practicing it and will pick up tiny objects such as lint or bugs from the floor. By eighteen months of age, toddlers are able to hold crayons and to open drawers and cupboards; by twenty-four months, the development of full thumb-to-index-finger control makes it easier for them to turn doorknobs, unscrew lids, scribble, and feed themselves. By age three, children may be able to put some puzzle pieces together. They also have better control when using forks and can begin to dress themselves. (The ability to lace shoes, fasten buttons, and pull zippers, however, generally does not appear until age six or seven.) By age four or five, eye-hand coordination and fine motor skills improve. Children may be able at this time to print large letters that look pieced together; they are typically placed anywhere on a piece of paper. Many can print their first names and a few numbers by age five. From age six on, hand movements become more fluid and refined; writing is characterized by more continuous strokes and is less choppy.
Although the sequence of stages of motor development is uniform in normal individuals, there is wide variation among individuals in the ages at which certain skills are acquired. This normal variation is attributable to both biological and environmental factors, including maturation, heredity, neurological maturity, health, activity level, experience, and nutrition.
Role of Biological Maturation
Learning to walk, achieving bowel and bladder control, and even learning to read and write are not physiologically possible until the child’s nervous and motor systems are sufficiently developed. Although normal experience (such as that offered by an average home environment) appears to be necessary for normal motor development, biological maturation places limits on what can be achieved through experience or practice. In fact, efforts by parents or other adults to teach or push young children to learn particular skills before they are maturationally ready may actually be harmful to their development.
Learning to walk, for example, requires central nervous system maturity, postural balance, muscular and skeletal strength, and well-developed sight and hearing. Studies have suggested that practicing the early walking reflex in infants to speed up their learning to walk may actually be harmful, because it may interfere with the development of the “higher” (cortical) areas of the brain that gradually take over the control of mature, independent walking. Early walking movements, which are evident between birth and three months of age, are actually a reflex that is controlled by the “lower” parts of the brain that control involuntary behavior. In addition, other studies have found that using walkers (seats on frames with wheels) too early or too often may damage infants’ hip sockets.
Toilet training is also dependent on nervous system maturation. The neurons (nerve cells) controlling bowel and bladder movements mature at about the same time that children generally achieve voluntary control, around eighteen to twenty-four months of age. Bowel control is achieved before bladder control, and girls typically achieve bowel and bladder control before boys do.
Being able to ride a tricycle (which usually occurs around age three) or a bicycle (which typically occurs by age six or seven) also requires that a certain level of muscle strength, posture, and balance be achieved before these skills are possible. Catching a ball is usually too difficult and complex for four-year-olds because it requires timing, distance perception, quick reactions, and coordinated movements of the arms, hands, eyes, and body. A successful way of playing “catch” with children of this age is to roll the ball on the ground.
Fine motor skills (such as pouring juice from a pitcher, writing with a pencil, assembling a puzzle with many small pieces, cutting food with a knife and fork, or fastening small buttons) develop more slowly than gross motor skills during infancy and early childhood and are therefore more difficult for young children to master. Children lack the motor control necessary to complete these tasks successfully because the central nervous system is not completely developed at this age—the parts of the brain governing fine motor coordination take years to mature fully.
Reading and writing also depend on maturational readiness. Reading requires focused attention, controlled coordination between the eye muscles and the brain, and a certain level of nervous system maturity. Children younger than six years of age usually are not physiologically capable of moving their eye muscles slowly and deliberately across lines of small letters. They also have a difficult time sustaining controlled and systematic focusing and are farsighted. Writing, on the other hand, depends on the eyes, brain, and small muscles of the fingers working together. As nervous system maturation progresses, greater fine motor control is achieved, and children’s hand strokes become more fluid and continuous during the school-age years.
Finally, hand preference (“handedness”) is also biologically based. Hand preference in reaching, grasping, and writing may be found even in infancy. Hand preference appears to be determined partly by heredity but also by the organization of the brain, with structural and functional differences between the left and right sides of the brain evident at birth. Most children develop hand preferences by age three or four, with the majority (85 to 90 percent) showing a right-hand preference. It may, however, take some children several years after this to solidify their hand preference. Forcing children to change their handedness may create a number of problems, including stuttering and other language problems, fine motor skill deficits, and emotional problems.
Evolution of Research
Early interest in motor development focused primarily on outlining the sequence of stages of motor development, identifying approximate ages at which these milestones occur, and speculating about the relative contributions of biology and the environment to motor development. These themes mirror two principal concerns of developmental psychology: the sequence of stages of development and the influence of biology versus experience on development.
Interest in, and observations of, early motor development date back at least to the eighteenth century. The earliest accounts of children’s development, known as “baby biographies,” were detailed descriptions of the developmental sequence of behavior during the early years of life. A more methodical approach to outlining behavioral milestones began around the early 1900s, when normative studies (studies investigating the typical performance of children at different ages) were undertaken. In 1911, for example, Arnold Gesell
founded the Yale Clinic of Child Development and constructed norms for such motor skills as grasping, crawling, swimming, standing, and walking. His norm charts were used throughout most of the twentieth century.
The general conclusion of Gesell and others during the 1930s and 1940s was that motor development is under biological control; however, studies have since shown that severe environmental deprivation can retard motor development and that environmental improvement by age two is necessary for infants to recover fully. Most researchers today believe that both maturation and experience play important roles in the course of motor development.
Although there was interest in motor development during the first half of the twentieth century, this interest declined somewhat from the 1950s until the 1980s. During this lull, however, motor development was still considered an integral part of Jean Piaget’s well-known theory of cognitive development in young children. Whereas motor development was originally viewed as the gradual acquisition of isolated skills, motor skill acquisitions are currently viewed as parts of a complex, interrelated motor system that parallels brain growth and development. It is likely that future research will continue to examine these issues as well as the relationship of motor development to cognition, language acquisition, and social development.
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