Motor+development+theories

= = toc = = = = = = =**Neural Maturationist Theory**= The foundational idea behind this theory is that structures must develop first before functional movements can occur. More specifically, as the nervous system continues to mature functional skills will further develop. This theory leans towards nature being more important than nurture. Learning new skills cannot occur if the neurological structures are not in place to allow for learning and practice. The rate of development is primarily set by genetic factors and not by the environment. This theory states that motor development follows distinct rules such as the central-to-distal and cephalo-caudal sequences of development. Within this model, reflexes are the building blocks for movements. As higher levels the central nervous system develop the lower centers that are involved with reflexes are overridden to allow for voluntary movement. In addition to believing that reflexes influenced development Gesell also believed that development occurred with alternating periods of flexor and extensor muscle dominance. According to Gesell it was important to have these asymmetrical periods in order to develop critical skills such as manipulation.

This theory states that motor development follows distinct rules such as the central-to-distal and cephalo-caudal sequences of development. The cephalo-caudal sequence of development follows the principal that most children develop from head to toe. Muscular control develops first in the neck, then the upper body, and then the legs. From birth to 6 months of age, children develop initial head control and hand-eye coordination. From 6 months to a year, trunk control and skills such as sitting and crawling develop (17).

Building on this theory of asymmetry, Gesell identified one of his five basic principles of development called the //principle of functional asymmetry//. This principle states that behavior must develop asymmetrically in order for the individual to reach a stage of symmetry at a later stage. Gesell used an example of the asymmetric tonic neck reflex (ATNR) behavior. This function initially develops to promote visual fixation. However, the behavior then leads to hand inspection, hand-eye coordination, and eventually to unidexterity which is the ultimate symmetrical behavior of hand reaching (Heriza et al., 1991).

According to Campbell et al. the development of pediatric physical therapy was based on this model. Therefore, increasing levels of neural maturation were indicated by increasing stages of reflex development and motor milestones in children. Thus, the higher the stage of reflex and/or the more motor milestones that were reached, the greater the neural maturation. Research in this area looks at the time of appearance of milestones reached in order to devise standards of childhood development.

//Gesell and Amatruda//
The research done by Gesell was very important, as it lead to developing tests for significant motor milestones and adaptive behaviors. These milestones have had great influence in the recognition and diagnosis of developmental delays in children. Gesell believed that developmental stages were based on the child's need to survive (biological imperative). He also acknowledged that children do have individual differences, and recognized that the environment has an effect on cognitive development. In addition to his research Gesell was an early advocate in allowing children with and physical disabilities to receive special education.

As stated previously, the neural maturationist theory describes nature being more important than nurture for development. Gessell explains this phenomenon using preterm infants as an example. Although these infants have been exposed to an environment earlier than most, they continue thriving and developing throughout the course of life with no added complications stemming from this additional influence. This prematurity does not help nor hinder the child from developing properly, despite the fact that they have had this longer exposure to environmental influences. Gesell and Amatruda mentioned that "Prematurity neither retards nor accelerates." This is one of the strongest pieces of evidence for Gesell's argument that maturation follows the unwavering laws of growth (Dalton, 2005).

This link shows original video footage of Gesell's developmental theory regarding fine motor skills. http://www.youtube.com/watch?v=ByBRqMNTcNQ

//Peiper//
In 1963 Peiper stated a theory that basic motor skills like crawling, standing and walking are not learned by experience, but are the result of cerebral maturation. Functional brain activity begins in the brain stem and spreads to the cerebral hemispheres. His theory is illustrated in a case report of a girl who had to be placed in a full cast from age 6 months to 18 months, preventing her from walking during this time. Upon replacement with a half cast at 18 months, the girl was able to stand upright and ambulate unassisted after only one day. 4

//McGraw//
McGraw’s research occurred mainly between the 1930-1940s when the neuronal- maturationist theory was at its peak. She theorized that endogenous rules did not determine motor development in infants. McGraw studied infant motor tasks including swimming, rolling, prone progression, sitting and erect progression. These behaviors were correlated to central nervous system growth and maturation and can be seen in her //Seven phases of erect locomotion in human infants model.// This model exhibits a progression from reflexive to deliberate patterns of motor behavior (Heriza,1991). Her well-known experiment involved twins: Johnny and Jimmy. Johnny experience transient hypoxia after birth for months while Jimmy was normal. Johnny received intensive motor practicing for the first 2 years of his life while Jimmy was restricted from his environment by being confined to his crib for specific periods of time. The twin boys reached developmental milestones are the same ages. McGraw is not a pure Neuronal-maturationist as she concluded that some neural maturation is required for the environment to modify function.

Neuroplasticity Video
This is a five minute youtube video explaining the basics of neuroplasticity and gives some examples. media type="youtube" key="iAzmyB9PFt4" height="315" width="560"

=Cognitive Theory=

The below offers a nice simple comparison of the two primary cognitive theories Comparison of Cognitive Behavioral vs. Cognitive Piagetian Theory (Table 2-1 p. 38, Campbell 4th edition)
 * **Cognitive: Behavioral** || **Cognitive: Piagetian** ||
 * Stages merely empirical descriptions of behavior || Stages represent alternating periods of equilibrium and disequilibrium ||
 * Development occurs through interaction of the individual with the environment || Development occurs through interaction between cognitive-neural structures and environmental opportunities for action ||
 * Pavlovian responses to environmental stimuli || First actions using reflexes and later from voluntary actions ||

Piaget's Theory of Cognitive Development
The cognitive theory of child development is often attributed to Dr. Jean Piaget. Piaget based many of his findings on observations made of his own children. He noted certain behaviors such as imitation and play as part of child development. He also realized that much of what children learn intellectually is based upon motor movement. Piaget described the individual using the processes of //assimilation// and //accommodation// to adapt to the environment. Assimilation is the incorporation of new information into preexisting schemes by modifying the environment or experiences so they fit in preexisting cognitive ideas with previous existing information. Accommodation is the process of changing cognitive schemes to adapt to include new information from the environment or new experiences. Piaget thought of advancement through his developmental stages as a product of striking an equilibrium between assimilation and accommodation. Through these two mechanisms children can adapt to their environment in increasingly complex ways. It was based upon these observations, and further child studies that Piaget developed his Theory of Cognitive development. It was based upon these observations, and further child studies that Piaget developed his Theory of Cognitive development. In Piaget’s view the cognitive development could be broken into four stages: Sensorimotor, Preoperational, Concrete Operational and Formal Operational.


 * The sensorimotor stage lasts from birth to age two. The child's knowledge of the world is based on physical interaction and repetition. Motor skill development allows the child to begin to develop new intellectual function. During this stage children master the concept of object permanence, the idea that people and things continue to exist even though they out of the child's field of vision. In what Piaget refers to as primary, secondary and tertiary circular reactions, children learn through repetition of motor acts that their intentional movement can elicit specific reactions, e.g. many children discover a strong self-soothing stimulus through thumb sucking. Understanding of the cause and effect relationship of their actions provides children a critical foundation for motor development.
 * The preoperational stage ranges from 2-7 years and was considered an egocentric time period in which children are focused on themselves. The child develops the use of symbols, language, memory, and imagination. However, mental constitutions are unsophisticated, non logical, and non-reversible.
 * The concrete operational period lasts from age 7-12 and was described as the time in which egocentric thought diminishes and children may consider more than a single view point. Operational thinking develops and mental constitutions are reversible, logical, and systematic manipulation of symbols can relate to concrete objects. Although children are unable to complete abstract problems.
 * The formal operational stage beyond age 12 includes abstract thought and reasoning. Mental constitutions are demonstrated through the use of symbols to related to abstract concepts.

Picture from []

More information can be found on Piaget's Theory via the following link: []

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Above is a video of common tests done with children of different ages to assess and demonstrate the different stages of cognitive development according to Piaget’s theory.


 * Vygotsky's Sociocultural Theory**

Lev Vygotsky is a Russian education psychologist who was a contemporary to Piaget. Vygotsky believed that social and cultural interactions mold and shape a child’s thoughts and behaviors. In order for a child to properly develop in a culture, Vygotsky believes that face to face interaction is key to proper cognitive development. One can do this three different ways, imitative learning, and collaborative learning. Once a child has had the appropriate interaction with a more knowledgeable elder in the culture, he or she will have developed habits of thinking and behavior that construct that culture. Vygotsky’s Sociocultural Theory has four ideologies that guide the theory’s implementation: “children construct their knowledge, development cannot be separated from its social context, learning can lead development and language plays a central role in mental development.” Speaking to oneself is very important in constructing their own knowledge, especially as a child thinks through a new or difficult task. Each child is different and may speak out loud, whisper or have mental conversations with one’s self. In addition to children constructing their knowledge, Vygotsky believes that development cannot be separated from its social context, also known as a zone of proximal development (ZPD). This can be predominantly seen in the educational system. For example, when a child does not know how to do a task the first thing they do is to seek help from a more knowledgeable person. In order to ZPD to be successful it must be subjectivity and scaffolding. Subjectivity occurs when children with different understandings of a subject at the beginning of a discussion arrive at a communal understanding while scaffolding is representative of a child’s evolving support system while learning. A child will become more successful at completing a learned task. Lastly, ZPD is a good indicator of a child’s readiness for learning. More information can be found at: []

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The above video is a brief introduction to Vygotsky's sociocultural theory of cognitive development the provides excellent outlines of each concept and explains how Vygotsky's research indicated a more complex relationship between learning and development than Piaget's cognitive theory.

Control and Construction of Hierarchies of Skills
Kurt W. Fischer of the University of Denver created a psychological review of the Cognitive Development Theory in 1980. The article discuses The Skill Theory which predicts that skills develop step by step through a series of 10 hierarchical levels which are divided into three tiers. The tiers are broken down into the following categories: sensory-motor skills (levels 1-4), representational skills (levels 4-7), and abstract skills (levels 7-10). These levels specify skills of gradually increasing complexity. Below is a Table that shows age periods at which levels first develop. The full article can be located using the following link: []


 * **Age Periods at Which Levels First Develop** ||
 * **Cognitive level** || **Age period** ||
 * 1: Single sensory-motor sets || Several months after birth ||
 * 2: Sensory-motor mappings || Middle of first year ||
 * 3: Sensory-motor systems || End of first year and start of second year ||
 * 4: Systems of sensory-motor systems, which are single representational sets || Early preschool years ||
 * 5: Representational mappings || Late preschool years ||
 * 6: Representational systems || Grade school years ||
 * 7: Systems of representational systems, which are single abstract sets || Early high school years ||
 * 8: Abstract mappings || Late high school years ||
 * 9: Abstract systems || Early adulthood ||
 * 10: Systems of abstract systems || Early adulthood ||

Behavioral Theory
The behavioral theory of B.F. Skinner is based on how learning with reinforcements from the environment nurture motor and cognitive development. As an individual goes through the process of learning, he/she comes into contact with reinforcing stimuli within the social and physical environment. The developing individual’s behavior is then shaped by the reinforcing stimuli. The behavioral theory encompasses the idea of operant conditioning. According to Boeree, operant conditioning is when “the behavior is followed by a consequence, and the nature of the consequence modifies the organism's tendency to repeat the behavior in the future.” The link below is an example of operant conditioning. In the example, the pigeon is the “developing individual,” who is learning in its environment. Boeree states, “The operant is the behavior prior to the reinforcement.” In this example the operant is the peck or the turn. The reinforcement is the food that drops once the pigeon does the task. There are stimuli that encourage the operant behavior such as giving the pigeon food; whereas there are stimuli that discourage the operant behavior such as zapping the pigeon. Timing and frequency of the reinforcement stimuli also affect how the individual interacts with the environment. With this theory, it is important to not view the individual as passive, rather the individual is responding and interacting with their environment. = media type="youtube" key="I_ctJqjlrHA" height="109" width="150" =

Both positive and negative reinforcers are used to strengthen human behaviors. Humans tend to respond to verbal operants without having experience with what repercussions may occur if they disobey. Some verbal operants include, taking advice, listening to advice give by others, and obeying rules. A unique aspect to human behavior is that when previous behaviors are rewarded, children are more likely to repeat them because they feel that they are choosing to do these behaviors. On the other hand, children choose to avoid behaviors that resulted in a negative reinforcement, which may make them feel like their free will is being taken away. In the past many parents use negative reinforcement to control unwanted behaviors. However, now negative reinforcement is being used more as a last resort. Teachers and parents of growing and developing children are now using positive reinforcement to encourage appropriate behavior. This shift in behavior modification will put emphasis on accepted behavior and not put the emphasis on unwanted behavior.
 * Positive and Negative Reinforcers**

Bandura’s Social Cognitive Theory
Bandura’s theory of learning differs from other theories in that instead of reinforcement to teach, people can learn through observation and experiences. One of the main concepts of his theory is modeling. His famous study demonstrating the power of learning through observation/ modeling is the “Bobo Doll Behavior Study of Aggression”. In this study, adults were filmed being aggressive towards a Bobo doll. The video was shown to children and they were then left alone in a room with the Bobo doll. It was found that the kids who had seen the video did in fact act aggressively towards the doll, whereas the kids who did not see the video were less likely to have such behaviors. Bandura’s theory is still seen today in the media, marketing, and even in the growth of children. Throughout childhood it is easy to recognize this theory in action. It is common for small children to go through phases of wanting to be like mom or dad, then like a big brother or sister, then maybe someone famous. Through this quest of being similar to someone they look up to, they pick up actions which will mimic those they are observing. For more on Bandura and his Bobo Doll experiment see the following link: []

Picture taken from []

=Dynamical Systems Theory=

Definitions:
Dynamical System: any system that changes over time. High-Dimensional Systems: any system that has many degrees of freedom (that is many components that make up the system)

What is it?
The Dynamical Systems Theory (DST) has emerged as a framework that examines human movement as an interaction of a series of sub-systems such as respiratory, musculoskeletal and circulatory systems. These systems are formed from "self-organization," the idea that many parts come together and act collectively as a unit. The units functioning together allows for increased coordination and decreases the need for higher centers to control movement. Motor system complexity is decreased in this theory by the coordination of many working units/synergies. This decreased complexity allows for "attractor states" which are functionally preferred states of movement that have small variability and are highly stable, leading to consistent movement patterns for specific tasks. An example of an attractor state given in the Shumway-Cook text is an efficient walking pace.

The underlying assumption of the DST approach is that biological organisms are complex, multidimensional cooperative systems. No one subsystem has logical priority for organizing the behavior of the system, and no system operates in isolation but is sensitive to variables such as the weight of the limb, orientation in respect to gravity, arousal, etc. This sensitivity cannot be programmed prior to an action because of these variables. Furthermore, the sensitivity of the system is far to precise and quick to be the result of corrections made from feedback. However, considering that each subsystem contributes to a behavior in a cooperative, interdependent relationship with other subsystems the sensitivity of the musculoskeletal system can be understood as an emergent property of the interaction of subsystems. The interaction of these subsystems can vary in almost infinite variety of ways, yet the movements produced can look relatively stable or similar. While most functional tasks can be achieved through a variety of movement patterns, we tend to use the ones that require the least amount of energy and is the most efficient melding of the many parts involved.

Control Parameters and Variability:
A control parameter is a variable that regulates change in the behavior of the entire system (Shumway-Cook 14). Variability within the control of movement is needed in order to achieve optimal function
 * 1) Control parameters cause 1 behavioral pattern to change to a new behavioral pattern - - from this a new movement will emerge
 * 2) An example of this is the change in behavioral patterns when one switches from walking to running.
 * 3) For this example the control parameter would be velocity
 * 4) When the velocity of walking reaches a “critical point” then the behavioral pattern switches to a new pattern in order for the organism to run
 * 5) Difference between walking and running: Campbell et al. state that young runners have difficulty with generating both horizontal forces (reflected in small increases in stride length over that used in walking) and vertical forces (reflected in little flight and little hip extension in running). Whitall and Getchell state that the ability to produce or regulate force by the ankle extensors was a key control parameter for the emergence of running. Another control parameter might be the ability to organize posture during high-velocity movement.
 * 1) Unlike other theories variability within the dynamic system theory is not viewed as an error within an movement pattern
 * 2) Variability is considered necessary in order for optimal function
 * 3) allows the organism to adjust to changes in the surrounding environment
 * 4) too little or too much variability can result in injury
 * 5) Small amounts of variability within a movement pattern indicates a highly stable behavior
 * 6) Stable behaviors are considered the preferred movement pattern
 * 7) The more stable a movement pattern is, the more difficult it will be to change

6 Propositions Related to Movement and Motor Development

 * 1) Moving and developing organisms are high-dimensional systems, and behavior represents a compression of degrees of freedom.
 * 2) Behavior emerges in a self-organizing fashion as a function of the cooperation of the many subsystems in a task content.
 * 3) Moving and developing organisms occupy preferred but not obligatory regions of their state space.
 * 4) New behavior forms emerge in development as a series of phase shifts.
 * 5) Developmental change can be envisioned as a series of stabilizing and destabilizing attractors.
 * 6) The control parameters change over time.

__Proposition 1 example__: A high-dimensional system is comprised of many degrees of freedom, this could include bones, joints, tendons, neurons, muscles, etc. These high-dimensional systems can then be collectively described as low-dimensional systems by combining all the components into one collective action i.e. walking.

__Proposition 2 example:__ Walking behavior is self-organizing and requires the cooperation of the cardiovascular system (many cardiac cells working as one unit), the respiratory system, the musculoskeletal system and sub-units of the musculoskeletal system which can be thought of as separate muscle groups (flexor and extensor groups).

=Dynamic Systems Theory and Practice:= There are five aspects in which this theory helps the therapist treat a patient through facilitating functional activity and participation. This theory and it's ideas are just beginning to be implemented into practice. These aspects are listed in order of 1-5 by Campbell et al. as:
 * 1) Search for the constraints in subsystems that limit motor behavior such as contractures or weakness leading to treatment goals related to reduction of impairments.
 * 2) Creation of an environment that supports or compensates for weaker less mature components of the systems that contribute to development of the motor control so as to promote activity and participation.
 * 3) Attention to setting up a therapeutic environment that affords opportunities to practice tasks in a meaningful and functional context.
 * 4) Use of activities that promote exploration of a variety of movement patterns that might be appropriate for a task.
 * 5) Search for control parameters, such as speed of movement or force production, that can be manipulated by the intervention to facilitate the attainment of therapeutic goals, especially during sensitive periods of development during which behavior is less stable.
 * 6) Ex: One area of practice in which velocity and momentum come into play is treating children with Cerebral Palsy (CP). An article by Karen Sauve and Doreen Bartlett ([]) explains that using moments of "transition" in motor skills of children with CP is the best time to optimize the use of intensive therapy. Research shows that variability is increased just before moments of transition from one movement pattern to another. Variability is described in the DST as being a "necessary condition for optimal function." (Shumway-Cook, 14). Taking this into consideration, the researches treating children with CP note that it is during these transitional periods that intense phases of treatment is optimal. The challenge is being able to recognize these periods of transition.

According to Cambell et al. Eight subsystems are assumed during the normal development of infant locomotion are:
 * 1) Pattern generation of the coordinative structure leading to reciprocal lower extremity activity
 * 2) Development of reciprocal muscle activity of flexor and extensor muscles
 * 3) Strength of extensor muscles needed for opposing the force of gravity
 * 4) Changes in body size and composition
 * 5) Antigravity control of upright posture of the head and trunk
 * 6) Appropriate decoupling of tight synchronization characteristic of early reciprocal lower extremity movements. An example would be the knee moving out of phase with the hip and ankle
 * 7) Visual flow sensitivity required to maintain posture while moving through the environment
 * 8) Ability to recognize the requirements of the task and be motivated to move toward a goal

The list above makes it clear that development of a particular motor pattern, in this case upright locomotion, __depends on a combination of mechanical, neurological, cognitive, and perceptual factors in addition to environmental contributions specific to both the task and the context of the infant’s action__. Each subsystem develops at its own rate but is constrained or supported by both physical and environmental factors, such as a nutritional diet and experiences providing the opportunity to practice antigravity trunk extension while prone, standing upright, and stepping.

Application to Cerebral Palsy:
[]

This website provides great insight into clinical treatment for children with Cerebral Palsy. The website talks about the importance of incorporating the dynamical systems theory into daily treatment interventions. According to DST, the best time to introduce new motor skills into therapy is when the child is going through a "transitional period." This means, for example, that once the child has mastered independent sitting, this is the point when you can introduce new motor skills such as sitting and reaching or sitting with head rotation. The new skills will then be focused on and practiced in a variety of settings until the sub-systems are primed to the new motor skills. In theory this is the best practice for motor development in children with Cerebral Palsy, however, there is a need for clinical tools that will identify the transition period of the sub-systems. This website focuses on using DST as a framework providing the best way to progress motor learning for children with Cerebral Palsy to gain the most optimal outcomes.

To further expand on the information above it is important to remember that the dyanmical systems approach is based on the principle that, " process rather than hierarchically structured plans and places neural maturation on an equal plane with other structures and processes that interact to promote motor development." With an approach in this manner it can be confusing when you think about it from a formal method such as input/output pathways. Confusing in the manner that the dynamical systems approach is very nonlinear, in order to be successful there has to be interdependent action occurring simultaneously with varying levels of contribution. Initially with the development of a process there are a lot of degrees of freedom, as mentioned in the literature degrees of freedom are very hard to control. In the process of learning a new behavior it is the same, the degrees of freedom vary between the multiple sub-systems causing chaos initially. A behavior (i.e. walking) is defined by Kamm, et al, as the compression of the degrees of freedom as the system as a whole assembles itself into a functional pattern

When thinking about PT intervention, the goal of the intervention is the same as the goal of dynamical systems theory. That goal being to find a more adaptive movement sequence using the least amount of energy possible while maximizing efficiency. Assessing and evaluating patient's strength's, weaknesses, and limitations is broadly the same thing as assessing systems. Then it is combined with environment, emotion, and cognition. After that has been done, the treatment plan is developed with all those factors equally considered to determine how the patient will react to the treatment. Once the anticipated reactions to treatments are established the PT can determine the best way to go about fine tuning those reactions, progressing them into function. In short this theory is very PT based once it is broken down. A simple and concise example of this would be with prescribing a patient with a walker as well as strengthening exercises. The walker could very well alter the ambulation pattern, influencing the overall posture and postural control. Strengthening and endurance training on the newly involved muscles will then in turn influence a new way to control posture. Neither of these factors contain the instructions to ambulate with a more efficient pattern however the small changes created facilitate the system to seek alternate and potentially better ways of moving. Now once you combine that with patient targeted education during treatment based on the other factors evaluated in the overall assessment you have an effective treatment.

=References= > St. Louis: Saunders Elsevier > >
 * 1) Boeree, George C. "B. F. Skinner." //My Webspace Files//. 2006. Web. 18 Feb. 2012. .
 * 2) Campbell, S., Vander Linden, D., & Palisano, R. (2006). Physical Therapy for Children (3rd Ed.). P 35-36, 39. St. Louis: Saunders Elsevier.
 * 3) Cherry, Kendra. (2012). Background and Key Concepts of Piaget's Theory. //About//. 
 * 4) Dalton, Thomas C.. "Arnold Gesell and the Maturation Controversy." //Integrative Physiological and Behavioral Science// Oct. 2005: 182-204. //SpringerLink//. Web. 20 Feb. 2012.
 * 5) Fischer, K. W. (1980). A theory of cognitive development: the control and construction of hierarchies of skills. //Psychological Review//. 87:6, 477-531.
 * 6) Hadders-Algra, M. (2000). The Neuronal Group Selection Theory: a framework to explain variation in normal motor development. //Developmental Medicine & Child Neurology.// 42: 566-572.
 * 7) Heriza, C. (1991). Contemporary Management of Motor Control Problems. Chap. 13. http://www.udel.edu/PT/galloway/motordevelopment.pdf
 * 8) Heriza, C.B. (1991). Implications of a dynamical systems approach to understanding infant kicking behavior. //Physical Therapy, 71,// 222-235.
 * 9) Huitt, W., & Hummel, J. (2003). Piaget's theory of cognitive development. //Educational Psychology Interactive//. Valdosta, GA: Valdosta State University. Retrieved [19Feb2012] from []
 * 10) Kamm, K. Thelen, E. Jensen, J. (1990). A Dynamic Systems Approach to Motor Development. Physical Therapy, 70, 763-775.
 * 11) Presnell, F. (1999, 5). //Jean piaget//. Retrieved from http://www.muskingum.edu/~psych/psycweb/history/piaget.htm
 * 12) Shumway-Cook,A., Woollacott, M. (2012). Motor Control: Translating Research into Clinical Practice (4th ed.) P. 13-15. Philadelphia: Lippincott Williams & Wilkins.
 * 13) Palisano, Robert J., and Margo N. Orlin. //Physical Therapy in Children//. By Suzann K. Campbell. 4th ed. Elsevier Saunders. 41. Print.
 * 14) DeRu, Esther. //Theories of Motor Development //. IPPEG, 2007. Doc.
 * 15) Grace, E. (2011, July 4). //B.f. Skinner's Behavioural Theory//. Retrieved from []
 * 16) Whitall, J., & Getchell, N. (1995). From walking to running: Applying a dynamical systems approach to the development of locomotor skills. //Child development, 66//, 1541-1553.
 * 17) Motor Development - Transition From Reflex Movement To Voluntary Movement, Principles Of Development, Motor Milestones, Assessment Of Gross Motor And Fine Motor Development. //[]//
 * 18) Campbell, S., Vander Linden, D., & Palisano, R. (2012). Physical Therapy for Children (4rd Ed.). P 40-41,