Infant Motor Development
Infants’ motor development, their ability to coordinate their movement, begins even before birth — as every expectant mother can attest after being kicked repeatedly during pregnancy. Starting at birth, infants begin to learn how to make use of their bodies through movement, and to coordinate their perceptions (seeing, hearing, touching) with their actions on the world (hitting, mouthing, squeezing). Some aspects of motor coordination are present at birth, whereas others develop gradually throughout infancy and early childhood.
Reflexes
Infants are born with a set of automatic motor behaviors — or reflexes — that are elicited by particular types of stimulation. Reflexes, such as the sucking reflex that helps babies begin to seek nourishment immediately after birth, fill important survival needs for the infant. Obviously this is a valuable instinct. If babies had to take the time to learn to suck, their body weights would drop dangerously in the process. But reflexes are only the start.
Learning to Coordinate Movement
Although babies are born with some instinctual movements, they must learn other types of movement gradually through trial and error. As with many developmental milestones, the age at which children reach particular motor milestones varies enormously from child to child, although children almost always acquire these motor milestones in the same order. Infants’ earliest motor accomplishment is learning to reach for objects first, starting out using two handed reaches but progressing to one-handed grabs. The most noticeable and most exciting motor accomplishments are when infants began to locomote — move themselves around. Most babies start out creeping along the floor on their tummies before they learn to crawl on hands and knees (and some babies skip crawling altogether). Soon, they begin pulling themselves to a standing position (holding on to furniture or people) and will often develop a “cruising” strategy of working their way around a room by sashaying sideways while clinging to furniture, before they eventually learn to walk. Both standing and walking with a parent holding their hands are helpful practice for babies learning to walk — standing builds muscles and balance while walking with support develops their motor coordination before they have to pull all those skills together to walk on their own.
It’s difficult for adults as “expert” reachers and walkers to appreciate how complex such movements actually are. Even something as basic as reaching for your coffee mug on the breakfast table requires complex calculations of the amount of force and speed with which you will move your arm, what shape your hand should assume, and how much muscle strength will be required to bring it to your mouth. Babies start out with no sense of how much strength and speed is required to grasp objects around them, and little ability to control or predict where their hands are going to go once they start to move them. Infants have a lot to master, but practice makes perfect!
Factors Influencing Motor Development
There are a variety of cross-cultural and individual differences in how soon children achieve motor milestones. Some children crawl and walk much earlier than others. These differences across children are influenced by a variety of factors. For example, heavier babies achieve these milestones more gradually because they need to build up their muscles more before they can support their own weight.
Another factor that influences rate of motor development is experience — how much and what type of experience children have to practice their motor coordination also influences the rate of motor development. Infants who spend most of their time on mom’s lap or in crib have fewer opportunities to practice moving themselves from place to place under their own steam than infants who get more “tummy time” on a blanket on the floor. Cultural and attitude differences in parenting styles influence the kinds of opportunities that infants have to explore their environments to build strength and coordination. For example, nurses on most maternity wards teach new mothers to swaddle their infants tightly in blankets, which provides an important sense of warmth, security, and familiarity for new babies. This, of course, limits movement of the arms and legs. Whereas American mothers tend to swaddle their babies only for the first couple weeks or months of life, infants in Peru and China are tightly swaddled throughout the first year. Swaddled babies tend to cry less and sleep more soundly, but the motor development of babies who are swaddled throughout the first year is slower as a result. In contrast, many African and West Indian mothers engage in a variety of stretching, massage, and strength building exercises with infants. This practice, which sometimes looks harmful to American eyes (how often do we see mothers dangling their babies by one arm?), actually accelerates infants’ motor development by strengthening their muscles and agility early on.
Explaining Motor Development
Physical maturation clearly plays an important role in infants’ motor development. As children’s bodies and brains develop, they acquire increasingly more complex motor behaviors. However, the fact that there is so much normal variability across individuals and cultures in the timing of developmental milestones indicates that experience plays an important role in building up motor routines. We don’t want to place babies in situations that overtax their limited strength and coordination (such as placing them in a swing before they have the neck strength to hold themselves upright against the momentum), but it’s important to give babies an opportunity to explore their physical world through trial and error. The challenges of bringing a rattle to their mouths or stretching for a toy just out of reach are the kinds of experiences that will help babies’ motor coordination and strength develop.