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Nicholas Stergiou, Yawen Yu and Anastasia Kyvelidou

Movement variability is considered essential to typical motor development. However, multiple theoretical perspectives and measurement tools have limited interpretation of the importance of movement variability in biological systems. The complementary use of linear and nonlinear measures have recently allowed for the evaluation of not only the magnitude of variability but also the temporal structure of variability. As a result, the theoretical model of optimal movement variability was introduced. The model suggests that the development of healthy and highly adaptable systems relies on the achievement of an optimal state of variability. Alternatively, abnormal development may be characterized by a narrow range of behaviors, some of which may be rigid, inflexible, and highly predictable or, on the contrary, random, unfocused, and unpredictable. In the present review, this theoretical model is described as it relates to motor development in infancy and specifically the development of sitting posture.

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Mathias Hegele and Friedrike Seyfried

In this opinion paper, we aim to delineate the development of the person–object differentiation in visuomotor behavior as established during the first two years of life, which can be conceived as a precursor for the broader distinction between animate and inanimate entities, which in turn form the basis of the more inclusive biological–nonbiological distinction (Poulin-Dubois, Lepage, & Ferland, 1996). We then discuss embodied sensorimotor simulation, which allows us to use the self as a model for perceiving objects in our environment, as a potential mechanism underlying this distinction.

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Amanda J. Arnold and Laura J. Claxton

If adults are carrying an object and start to experience a loss of balance, they frequently maintain hold of that object instead of dropping it. In these loss-of-balance situations, adults tend to maintain hold of the object, instead of freeing both hands to aid in balance recovery. The current study investigated the ontogeny of this behavior by examining if infants also maintain hold of objects when experiencing a fall. Sixteen newly standing infants were video-recorded while standing and holding a toy and standing while not holding a toy. Similar to adults, when infants experienced a loss of balance, they did not drop held objects. However, maintaining hold of objects only partially interfered with the use of upper-limb protective strategies while falling. These results suggest that the tendency to maintain hold of an object while falling is present early in development and with little independent standing experience.

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Julia Dillmann, Christian-Dominik Peterlein and Gudrun Schwarzer

It was the aim of this study to examine the motor and cognitive development of infants with congenital idiopathic clubfoot, compared with typically developing infants. We repeatedly tested the gross motor, fine motor, and cognitive abilities of 12 infants with clubfoot and 12 typically developing infants at the ages of 4, 6, 9, and 12 months with the Bayley-III Scales. All infants with clubfoot were treated with the Ponseti method, which led to a restriction of normal movements of the lower extremities in the first months of life. They showed a great delay in gross motor development but not in fine motor or cognitive development. However, in the clubfoot group, we found some slight deficits in specific cognitive tasks, including problem solving and spatial memory. In addition, our results revealed significant correlations between gross and fine motor performance and cognitive performance in the control group but only between fine motor and cognitive performance in infants with clubfoot, indicating that both, fine and gross motor skills, are related to cognitive processes and can mutually replace each other to a certain degree. Further research is needed to gain a deeper understanding of clubfoot infants’ development and to clarify the need for mobility training.

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Janna M. Gottwald

This article critically reviews kinematic measures of prospective motor control. Prospective motor control, the ability to anticipatorily adjust movements with respect to task demands and action goals, is an important process involved in action planning. In manual object manipulation tasks, prospective motor control has been studied in various ways, mainly using motion tracking. For this matter, it is crucial to pinpoint the early part of the movement that purely reflects prospective (feed-forward) processes, but not feedback influences from the unfolding movement. One way of defining this period is to rely on a fixed time criterion; another is to base it flexibly on the inherent structure of each movement itself. Velocity—as one key characteristic of human movement—offers such a possibility and describes the structure of movements in a meaningful way. Here, I argue for the latter way of investigating prospective motor control by applying the measure of peak velocity of the first movement unit. I further discuss movement units and their significance in motor development of infants and contrast the introduced measure with other measures related to peak velocity and duration.

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Klaus Libertus and Amy Needham

Four parent-guided training procedures aimed at facilitating independent reaching were compared in 36 three-month-old infants recruited for this study and 36 infants taken from previously published reports. Training procedures systematically varied whether parental encouragement to act on external objects was provided, and whether self-produced experiences of moving an object were present. Reaching behavior was assessed before and after training, and face preference was measured after training by recording infants’ eye gaze in a visual-preference task. Results showed that simultaneous experiences of parental encouragement and self-produced object motion encouraged successful reaching and face preference. Neither experience in isolation was effective, indicating that both external encouragement and self-produced action experiences are necessary to facilitate successful reaching. However, experiences with self-produced object motion increased infants’ face preference. This result provides evidence for a developmental link between self-produced motor experiences and the emergence of face preference in three-month-old infants.

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Wen-Hao Hsu, Daniel Miranda, Diana Young, Kelly Cakert, Mona Qureshi and Eugene Goldfield

We conducted a longitudinal kinematic study of spontaneous arm and leg motions in 4 supine infants at 3, 4½, and 6 months of age. The study addressed two questions: (a) whether there was a longitudinal change in the synchronization of joint rotations at the hips, knees, shoulders, and elbows, indicating that the arms and legs were moving more independently of each other; and (b) whether, during this period, the spatial location of the hands relative to the shoulders was different from that of the feet relative to the hips, indicating that the infants were beginning to use their upper limbs differently than their lower limbs. We found that, in general, the arms and legs were moving more independently of each other by 6 months of age. At the same time, the infants were more likely to hold their hands away from the body in preparation for making contact with an object in the midline, but they brought their feet close to the body to maximize propulsive kicks. Thus, a reorganization of the relative timing of joint rotations appears to be related to the emergence of different arm and leg functions.

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Thomas L. McKenzie

result from focusing on school physical activity policies. This remains a theory, however, because school policy studies are in their infancy and those that have been done have rarely included physical activity as a direct outcome measure. Most studies continue to rely on self-reports, often from

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Robert W. Motl and Rachel Bollaert

consequences is in a stage of infancy—the focus on intervention research might even be considered premature. The time is ripe for focal inquiry on sedentary behavior in MS and for initiating a new paradigm shift on health-behavior change in this population. References Aminian , S. , Ezeugwu , V.E. , Motl

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Theresa L. Miyashita and Paul A. Ullucci

Although research investigating concussion injuries is quite widespread, examination into the cumulative effect of subconcussive impacts is still in its infancy. A subconcussion is defined as a “cranial impact that does not result in known or diagnosed concussion on clinical grounds.” 1 Although