Article summary of The development of motor behavior by Adolph & Franchak - 2017 - Chapter

What is motor behavior?

Motor behavior includes every kind of movement from involuntary twitches to goal-directed actions in every part of the body, in every physical and social context, from the beginning of life until the end. Movements depend on generating, controlling, and exploiting physical forces, and on core psychological functions. Perception and cognition are necessary to plan and guide motor behavior. Social and cultural factors spur and constrain motor behaviors.

How can we understand motor behavior in a developmental systems view?

According to a developmental systems view, motor behaviors need to be viewed in the bodily, environmental, and social/cultural context in which they occur. New motor skills bring new parts of the environment into play and provide new opportunities for learning and doing. Differences in the way caregivers structure the environment and interact with their children affect the form of new skills, the ages when they first appear, and the shape of their developmental trajectory.

What is posture?

Posture is the position in which the body is held while standing, sitting, or lying down. It is the most important motor action, because it is the foundation upon which the other motor skills are built. The emergence of most skills need to wait for the development of sufficient postural control. Posture must be sufficiently stable to allow movement of the extremities. Maintaining a stable posture sets up the necessary conditions for looking around, handling objects, going somewhere, or having conversations.

How does development in postural control provide a means for acquiring new knowledge about the world?

As infants learn to control their posture, they start to have many more opportunities to learn. Independent sitting facilitates more sophisticated bimanual object exploration, such as fingering, transferring, and rotating, which facilitates learning about the three-dimensionality of objects. Infants also start to have more attention for changes in object appearance, object size, multimodal information about objects, and other people´s intentions to grasp objects.

How do infants overcome gravity?

Generally speaking, infants go through a top down progression. They gain increasing control from head to toe, from the head, neck, shoulders, waist, to the hips. They eventually learn to tripod sit: sitting by stabilizing their torso with their arms between their outstretched legs. They then learn to sit independently without their hands supporting them, eventually gaining sufficient stability to manage destabilizing forces caused by turning the head, twisting the torso, and moving the arms.

What is dynamic postural control?

Dynamic postural control is the ability to maintain the center of mass within the base of support while the body is subjected to internal or external perturbations that are anticipated or not.

What is body sway?

Sometimes postures appear stationary, but they are not. The body gently sways back and forth within the base of support. A sway in one direction must be met by a muscle-induced compensatory sway in the opposite direction. Infant´s compensatory sways are excessive and they often stagger and fall. Visual information for body sway is extremely powerful, and infants are learning to use visual information for postural control.

What is locomotion?

Locomotion refers to movement or the ability to move from one place to another. Locomotion is not reflexive or hardwired, but improves with practice. Infants find different ways to solve the problem of moving and often come up with different creative solutions. Generating new forms of locomotion can involve cognitive skills such as problem solving, representing goals and spatial locations, and tool use.

What is the newborn stepping reflex?

When newborn are held upright with their feet on a hard surface, they move their legs in an alternating pattern that resembles walking. This is called the newborn stepping reflex. It usually disappears by two months of age and reappears at eight to ten months when infants begin walking with support. The reflex is caused as a newborns response to optic flow. Infants can deliberately modify their leg movements in various configurations that can be kinematically equivalent and produced by the same muscle, though they may look different. In reality, with daily practice in an upright posture, the stepping movements never disappear.

How do infants learn to walk?

On average, infants take their first walking steps at twelve months. Walking onset requires sufficient strength and balance to support the body on one leg as the other leg swings forward. Experience in standing, stepping, and moving upright facilitates gains in strength and balance and accelerates the onset of walking. The first steps are wobbly and uneven, with a wide stance between feet, a small front-to-back distance between steps, long periods when both feet are on the floor, and short periods when one foot is in the air. Children rapidly improve their walking skills as they discover the relevant parameters that control upright balance and propulsion.

How do infants learn to navigate obstacles?

Children generate the requisite perceptual information through exploratory movements, such as looking, touching, and testing various options. Learning does not transfer from earlier to later developing postures. Infants learn to generate and use perceptual information about the current status of their body relevant to the environment. They learn the relevant parameters for each new posture in development and the relevant exploratory behaviors for calibrating those parameters in new situations. Over weeks of experience with each posture, judgements improve so that infants attempt safe increments within their ability and avoid risky obstacles beyond their ability.

What is manual action?

The hands are used in a wide range of actions such as feeding, locomotion, body maintenance, communication, and play. Manual actions begin prenatally, but outside the womb, infants require a stable postural base to support arm movements and perceptual information to guide movements adaptively. Tools extend children´s manual abilities.

What is spontaneous motility?

Manual action appears long before birth. Fetuses can extend their arms, wiggle their fingers, clench their fists, explore their own bodies, such their thumbs, etc. Spontaneous arm and hand movements continue after birth.

How do infants learn to reach and grab?

Goal-directed reaching requires perceptual information about the location of the object vis-à-vis the hand. Initially reaches are jerky and crooked and it takes years before children´s reaches become as smooth and straight as those of an adult. Jerky trajectories may result in part from postural constraints and unanticipated reactive forces. Reaching precedes grabbing, because control of the arms precedes control of the hands. Prospective control of grasping based on visual information for object size, orientation, and substance appears months after infants begin reaching. With increased hand/finger control, infants adapt their grip configuration to object properties, but they do so after contacting the object, not during the reach.

Why is exploring objects a multimodal development?

With increasing skill, object exploration becomes increasingly multi-modal. At first, infants use their hands only to be able to look and mouth an object. As their grip strengthens, they can heft, rub, squeeze, and finger objects, as well as transfer objects from hand to hand and rotate them in front of their eyes. Hands begin to serve a complementary function. They can use one hand to support the object and keep it in view, while using the other to generate information about the object properties.

How can infants extend their abilities by using tools?

Tool use has its roots in early motor actions and relies on motor actions for its execution. Exploring relations between objects and surfaces sets the stage for using objects as effective tools. Tool use requires infants to perceive that a goal is beyond their abilities and to recognize that an object can serve as a means to augment their abilities. Then they need to execute the necessary movements to use the tool.

What is infant facial action?

All the parts of the face begin moving prenatally. After birth, infants continue to produce facial movements as they become integral to everyday functions. Swallowing is used to suckling, eating, and talking. Vocalizations and facial expressions are used for communication. Head and eye movements are used for visual exploration of the environment.

How do infants such, chew, and swallow?

Newborns must coordinate movements of the tongue, jaws, and lips to create suction, draw liquid into the mouth, pull the liquid into the pharynx, and divert the liquid to the esophagus while pulling air into the trachea. Chewing is more complicated. Infants rely on lateral jaw movements to do most of the chewing, whereas older children use rotary jaw movements and use the lips and tongue. Infants use the same chewing movements regardless of the type of food, whereas older children select the appropriate jaw movements and muscle forces based on the food consistency.

How do children learn to speak?

Facial expressions and vocalizations appear long before infants can speak. The movements needed for speech production are one of the most complex movements to learn. The jaws, lips, and tongue must be precisely positioned to shape each sound as air travels through the oral and nasal cavities. Infants rely primarily on jaw movements as they discover functional strategies to produce speech sound. As they gain better control over their lips and learn to incorporate those movements into the jaw movements, they are able to produce a greater variety of speech sounds.

How do infants develop their visual perception?

Looking involves coordination among body, head, and eyes. Newborns who cannot turn their heads tend to watch whatever happens to be in front of them. Even as posture improves, much of what infants see is opportunistic. Looking is more functional and adaptive when the eye, head, and body movements are more controlled. To track a moving object, infants must anticipate its speed and trajectory to keep their eyes moving at the right pace. As targets move too quickly, the eyes lag behind, and infants often make corrective saccades to catch up to the target. With practice, they use less corrective saccades.