Which of the following statements about reflexes and the development of motor skills is TRUE

Summary

Motor development includes the change in motor behavior over the life span and the sequential, continuous, age-related process of change. It is determined by the merging of our genetic predisposition for movement and our experiences. The soft assembled movements allow exploration and skill refinement. The mover and the environment are both changed in the process. Movement emerges from the dynamic interaction of multiple components and systems to meet intrinsic or extrinsic demands. Motor control is the physiological process whereby motor development occurs, and motor learning allows motor development to occur systematically, resulting in a permanent change in motor behavior due to experience. In the following chapter, motor control and motor learning will be explored.

In 1989 Roberton49 proposed that the dynamic systems theory be applied to life-span motor development research. Thelen and Smith14,16,17 have done so with great effect. The DST, along with its underlying premise, neuronal selection theory, continues to be hailed as the unifying theme for understanding motor development.15 If motor development is viewed as the study of change in motor behavior across a lifetime, age becomes a marker variable and may not be the cause of change. Altering the way in which we think about age may allow therapists and researchers to discover new information about why individuals move the way they do at different times in their lives. Knowledge of motor development across the life span is critical for therapists to ascertain the most appropriate therapeutic strategies for people to function optimally regardless of age, occupation, or disability.

Abstract

Motor development includes the evolution from reflexive to voluntary and goal-directed motor actions. These motor actions are never performed in isolation but always in a varying physical environment, often requiring object and social interaction. For a child to function within this context, they require the ability to demonstrate skillful, efficient, and voluntary postures and movement patterns. Furthermore, these movement patterns or motor skills need to be performed in interaction with the environment and in response to diverse stimuli, an ability that is defined as praxis. In this chapter, definitions are provided for the different components of motor function, motor skills, and praxis. The close interaction between perception, cognition, and (motor) action is discussed. Furthermore, crucial periods of typical development of motor and praxis abilities are highlighted, by means of the metaphorical “mountain of motor development,” that is rooted in the dynamic systems perspective on motor development, as a starting point. The chapter ends with a discussion on the evaluation of motor function and praxis, highlighting benefits, and possible pitfalls.

Antidepressant exposure in pregnancy and child sensorimotor and visuospatial development

Motor development underlies many aspects of education and learning. There has been uncertainty about the impact of exposure of antidepressant medication in pregnancy on child motor outcomes. This paper examined whether exposure to antidepressants in utero increased the risk of poorer motor development in two areas: sensorimotor and visuospatial processing. Data were obtained from 195 women and children across three groups: women with untreated depression in pregnancy, women treated with antidepressants and control women. Data were collected across pregnancy, postpartum and until 4 years for mother and child. Maternal depression was established at baseline with the Structured Clinical Interview for DSM-IV. Antidepressant exposure, including type, dose and timing, was measured through repeated self-report across pregnancy and the postpartum, medical records at delivery and in cord blood samples collected at delivery. Child sensorimotor and visuospatial outcomes were assessed at 4 years of age with four subtests from the NEPSY-II. Our study found for sensorimotor development; visuomotor precision completion time was associated with better performance for antidepressant-exposed children compared to those with mothers with untreated depression. Yet another measure of sensorimotor development, motor manual sequences, was poorer in those exposed to antidepressants. One subtest for visuospatial processing, block construction, was associated with poorer performance in antidepressant-exposed children who had poor neonatal adaptation and those exposed to a higher dose of antidepressant. These findings suggest an inconsistent association between sensorimotor development and antidepressant use in pregnancy. However, the findings for visuospatial processing would support further exploration of antidepressant associated poor neonatal adaption and later motor development.

A THE IMPORTANCE OF BALANCE

Motor development is a delicate balancing act. Newborn infants are slaves to the pull of gravity, but by 2 months babies can lift their heads from the crib mattress, balance their heads between their shoulders, and turn to look at an interesting event. By 6 months, they can balance in a sitting position anchored to the floor with their outstretched legs, lean forward to retrieve a fallen toy, and use their hands to play with objects or clap. By 8 months, infants can balance on hands and knees, crawl across the living room floor, steer around furniture, and clamber over objects in their path. By 10 months they can pull themselves to a wobbly stand and walk sideways hanging onto the coffee table or couch for support. By the end of their first year, infants can balance on two feet; walk independently across the room; crouch down to peer under the table; stretch upward to pull books off the shelves; stop, start, and turn corners; and modify their step length and walking speed.

These homely postural accomplishments are the stuff of motor development. Students’ developmental textbooks are graced with a requisite chart of motor milestones. Parents’ home videos and photo albums highlight the postural milestones of their infants’ first year. In fact, the pioneering researchers of the 1930s and 1940s were so captivated by infants’ dramatic transformation from worm to person and by the seeming regularity with which the metamorphoses occurred that the field of motor development was founded on normative descriptions of the ages and stages that characterize the various postural milestones.

Although modern researchers no longer focus on cataloging infants’ postural milestones, they agree that the most basic motor control problem is maintaining balance (Reed, 1982). Balance is not only important for relatively stationary positions such as sitting and standing, but also it provides the necessary stable base to support movements of the head, torso, or limbs. Everyone who has broken a rib or thrown out his or her back has experienced the centrality of posture for controlling movements—lifting an arm from the bed to grasp a glass of water becomes a painful lesson about the muscles involved in stabilizing the torso, and lifting a leg to put pants on or to climb stairs is nearly impossible. In the laboratory, researchers have shown that participants’ abdominal muscles and back muscles fire prior to a reaching movement with the arms, indicating that postural stabilization is a primary part of the motor plan (Hofsten, 1993). Stabilizing the body and keeping it in balance are prerequisites for adaptive control of movement.

Motor Development

Motor development is an area of pronounced delay in many children with Down syndrome. Atypical development of reflexes, low muscle tone, and hyperflexibility are often observed in infancy. As a result of hypotonia, infants with Down syndrome often show unusual postures and leg positions. The achievement of important motor milestones is also delayed during early development in Down syndrome: the average age for rolling over in Down syndrome is 8 months (typical = 5 months); sitting without support happens on average at 9 months (typical = 7 months); walking with support happens on average at 16 months (typical = 10 months); standing alone happens on average at 18 months (typical = 11 months); and walking alone happens on average at 19 months (typical = 12 months).

Later in early childhood, children with Down syndrome show difficulty with the development of motor planning, in the form of reaching and other essential skills. Children with Down syndrome have been shown to exhibit poorer-quality reaching strategies on an object-retrieval task, where children must reach for a desired object through the one side opening of a clear box. In order to reach efficiently, rather than coordinating eye gaze and reach, many children with Down syndrome use less optimal strategies such as looking through the open side of the box, straightening up, and then reaching for the desired object. This type of motor planning is essential for the development of efficient day-to-day adaptive skills, and thus, targeting these skills in early development may have downstream effects on important skills for later independent functioning.

Child-rearing practices

Since motor development has long been considered a maturational phenomenon distinct from environmental influences (Hopkins and Westra, 1988), Western child-rearing practices have been largely based on this view, guided by studies of motor development carried out decades ago on limited numbers of babies in the Euro-American culture (e.g., McGraw, 1945). Our current understanding of developmental neurology has been greatly enhanced by studies of infants brought up in different child-rearing environments (Adolph et al., 2010). Several aspects of motor development have been shown to differ according to culture, i.e., what the infant experiences. The importance of environmental effects and experience on motor development, particularly in the first 18 months, is evident in comparative studies of development in a range of different cultures (Bril, 1986). These studies show what spontaneous ‘parent-initiated’ and ‘environment-specific’ training and practice can accomplish in infants.

Babies of African descent have been shown to be ahead of Caucasian babies specifically in sitting, standing alone and walking (Hopkins and Westra, 1988; Konner 1977). Similar results have been found for manipulation. Babies in the Yucatan, Mexico have advanced hand skills, including early development of a pincer grip, but are relatively delayed in walking. The infants studied were rarely placed on the floor and, when they were, there was little for them to hold on to (Solomons and Solomons, 1975). Kenyan Kipsigis mothers believed it was important to ‘train’ sitting and they set up the conditions by scooping out a hole in the soil in which the infant was placed (Super, 1976). In some tribes in Papua New Guinea, babies do not go through a crawling stage (Wong, 2009). They are carried until they can walk. When necessary, mothers put infants in the sitting position and the preferred way of getting about was scooting. Other cultures are said to have similar child-rearing methods, avoiding putting infants on the ground in order to protect them. Babies born in England to Jamaican mothers were found to be superior at independent sitting when compared with babies of English mothers. The Jamaican mothers trained sitting from age 3–4 months. Parents’ expectations appear to be important considerations. The Jamaican mothers learned their child-rearing practices from their mother, the English from reading child care books. Both the predicted and the actual age of sitting and walking were significantly earlier in the Jamaicans compared to the English (Hopkins and Westra, 1988).

In an intracultural study, Zelazo and colleagues (1972, 1983) found that neonatal stepping can be trained, and the ability maintained through to independent walking; i.e., trained babies did not go through the period of locomotor inactivity reported for Western-reared babies. It has been shown that neonatal stepping has similar characteristics to mature walking and is a precursor to independent walking and not a reflex (Fig. 1.7). Thelen and Cooke (1987) suggested this transition from infant stepping to walking occurred due to the effect of training on muscular development: that is, the trained babies were stronger because the exercises would increase muscle mass.

What Determines Motor Development?

Although motor development may seem to be the simplest aspect of development, it is also the most complex one. To plan and perform motor movements, children do not only need to acquire control over muscles. They must also learn to perceive and anticipate the sensory consequences of those movements not only for the body part that is moved, but also for the postural stability of the whole body. Motion planning requires the child to be able to perceive the spatial layout of the surrounding and what it offers. In order to manipulate objects, their form and function has to be correctly perceived. To understand and predict the movements of objects in the surrounding, children must distinguish object motion from their own movements, and the movements of other people. Social development is a fundamental aspect of motor development. To be able to communicate with and learn from other people, the child must both be able to understand their gestures and speech and be able to perform those gestures and speech movements. Thus, motor development is not an independent entity. It is, in fact, at the heart of development and reflects all the developmental processes of the child, such as the physical growth of the body, the development of sensory and perceptual processes, the growing ability to reflect on the world and foresee future events, and the changing motives and preferences of the child.

In order to develop new modes of action, infants must solve the specific problems associated with those modes and this can only be accomplished through their own activity. The persistence and effort invested in developing new modes of actions is one of the greatest enigmas of development. Long before infants master reaching, they may spend hours trying to attain an object in front of them and although they fail most of the time, they persist and seem to enjoy it. Another example is walking. At a certain time in development, infants will try to take their first step. To begin with, they will fail repeatedly. Why bother to try this new mode of locomotion when they most certainly already possess a different and more efficient mode? It cannot be that they realize that walking in the end will be superior to crawling. The motivating force has to come from within. It seems that infants find it very pleasurable to explore their action capabilities and to find out about new ways of moving.

Apart from learning new action skills from moving around, children also learn them from observing others perform the actions. A special devoted system in the brain, the mirror neuron system, helps us to perceive and understand other people’s actions. It is a distributed system with one part situated close to Broca’s area, one in the rostral part of the parietal cortex and one part in the temporal cortex (STS). The mirror neuron system enables us to simulate other people’s actions in our own motor system through a direct matching process in which observed actions are mapped onto the observer’s motor representations of those actions. This enables us to understand the motives and goals of the observed actions and to repeat those actions ourselves. It is important to note that the mirror neuron system does not create new motor competences. An infant does not learn to stand alone or walk simply by observing other people do it. The motor representations of the observed actions correspond to what is spontaneously generated during everyday activities and whose outcome is known to the acting individual. Thus, imitation learning has to do with learning new instances of actions including their purposes and goals. Therefore, infants are not expected to predict others’ action goals before they can perform such actions themselves. Infants begin to master important socially based manual competences such as imitation, and communication by means of gesture at around 8–12 months of life. It is, thus, expected that the mirror neuron system begins to function for such actions during this period of life.

When we perform visually guided actions, action plans encode proactive goal-directed eye movements, which are crucial for planning and control. We also spontaneously look at the goal of an observed action when it is performed by others, indicating that action plans guide the oculomotor system also in action observation. Falck-Ytter, Gredebäck, and von Hofsten studied 6- and 12-month-old infants’ tendency to fixate the goal of an observed manual action before the hand arrived there. We found that the 12-month-olds consistently shifted gaze to the goal of the observed action before the hand arrived there, but the 6-month-olds did not, thus supporting the mirror neuron hypothesis.

Gross Motor Skill

Gross motor development refers to movements that require the use of large muscle groups. Ambulating, running, jumping, climbing, and ball play are all considered gross motor skills. In neurodevelopmental theory, the mobility necessary for these locomotor skills is superimposed on stability. Consequently, the ability to perform these skills, and the quality with which they are performed, is dependant on the condition of the child's neuromuscular and neurodevelopmental status. Often, the neuromuscular status assessment is considered one component of the child's gross motor status. Accordingly, gross motor includes both evaluation of developmental milestones and observations about the quality of the child's movement patterns. Balance and stability are measured and observed as the child performs a number of motor tasks. These observations of balance also have application to the vestibular processing of a child, illustrating the link between sensory and motor responses.

Assessment of these gross motor areas often is done within the context of play-based assessment or strictly through observation. Having a child go through a simple obstacle course, for instance, can provide a wealth of information about balance, strength, and postural control. Further, within many clinic settings or natural environments a child has the opportunity to explore his or her environment. In doing so, the child likely ambulates, runs, jumps, or has to climb steps. Situations also can be developed to observe catch and throw abilities. Report of functioning during higher-level bilateral motor tasks such as riding a bike and swimming likely may be obtained from the caregiver. As can be seen, throughout the evaluation, both developmental milestones are assessed and the quality with which they are accomplished is observed and analyzed. Deficits in stability noted during gross motor performance, especially trunk, shoulder, and neck, may or may not be present when a child is seated at a table to participate in handwriting tasks.

3.3.2 Cognitive and Sensorimotor Motor Development

Cognitive and motor development can be investigated in young children using the Bayley Developmental Scales. Tasks are given to babies and toddlers, and their parents are interviewed. Two scores result: one for mental development and one for motor development. This is an individual differences test, and the two factors are rationally defined. The Wechsler scales for preschool children (Wechsler Preschool and Primary Scales of Intelligence [WPPSI]) and for school children (Wechsler Intelligence Scale for Children [WISC]) are the most widely used intelligence tests. Wechsler defined intelligence as the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his or her environment. Intelligence was considered to be an individual differences phenomenon. The performance and verbal intelligence factors were rationally distinguished and, in fact, usually correlate at approximately .70. Many factor analyses were conducted. The “three Kaufman factors” (verbal comprehension, perceptual organization, and freedom from distractability) interpretation of the WISC is popular. The existence of these factors is supported by factor-analytical results. The Stanford–Binet scale is the oldest intelligence test. The intelligence quotient (IQ) is defined as a comparison between what is normal for a certain age and what is observed in a specific child.

Early Movement

In typical motor development, neonates respond reflexively to environmental stimuli. Their movements initially often are random and not necessarily purposeful, except for hand-to-mouth behavior for self-calming. Primitive reflexes become less prominent as postural reactions and more purposeful movements appear. Infants begin to turn their heads, track visually, reach toward toys, and roll over in response to visual, auditory, and tactile stimuli in their environment. These early movement experiences create the foundation for higher-level motor skill performance (Effgen, 2005; see also Table 4.10). Continued development of motor control, balance, and postural control and stability leads to the acquisition of more complex gross motor skills.

TABLE 4.10. Early Movement

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From: Bayley Scales of Infant & Toddler Development, Third Edition (Bayley-III). Copyright © 2006 NCS Pearson, Inc. Reproduced with permission. All rights reserved.