Tuesday, October 4, 2011

Beyond Physical Milestones, Part V: Dynamic Systems

            In the 1990s, a new developmental theory emerged. The dynamics systems approach to development seems to take Bernstein’s concept of redundancy (for a review of Bernstein and his findings, check out the first post of this series) and multiplies it by infinity. The new theory states that development is non-linear because the basic components involved (the person, environment, and the task) are in constant flux.  Consequently, each of these components must be considered from every angle in order to understand an individual’s developmental progress. This makes development truly unique to each individual and not necessarily something that unfolds along a set timeline as argued by proponents of maturation theory.  No wonder some people have started to call the dynamics system theory “chaos theory.”
            One key point of the dynamic systems theory is that human development occurs through various timescales, but these timescales cannot be treated as individual events.  Research in this field analyzes the relationships between the timescales of each component of development.  A component of human development might be a signal sent by the central nervous system and its timescale would be only milliseconds. Simultaneously, the action itself (such as crawling) might be another component which would then be analyzed by millisecond. These flashes in time might be analyzed next to the larger component of learning a new skill, a component whose timescale can be years. 
A second key point of dynamic systems theory is that these various components and timescales self-organize. Dynamic systems theorists believe this self-organization is the cooperation between the infinite components and their timescales which manifests itself through a new development milestone.  So, when all of the timescales align perfectly, baby can complete a new skill!

         Now, assuming that you have made it this far in the reading, an example that might clear things up. Or, only provide further support for the name “chaos theory.”  Esther Thelen, an American psychologist who was instrumental in the research that supports dynamic systems theory, proposes that there are eight sub-components in the development of walking.  She hypothesizes that when the sub-components listed below self-organize, walking emerges.  The accompanying figures show the change of the components at their different timescales (13-5) and how these components must align or self-organize with the correct environmental context in order to produce a new development milestone (13-6). 
1.    Pattern generation- The coordination of multiple muscles and joints to form a single motion.
2.    Articular differentiation- Fancy way to say that joints movement becomes unsynchronized.  In newborns, the hip, knee, and ankle joints are synchronized during kicking.  As the baby ages, however, the knee joint will move separate from the hip and ankle, which is necessary for walking.
3.    Postural control- increased ability to stand up right
4.    Visual flow sensitivity- Involves balance, awareness of one’s movements in relation to the surroundings, and vision
5.    Tonus control- The shift of dominance from flexor muscles (those that allow us to bend) to the extension muscles (those that allow us to straighten).  This reciprocal interweaving (for review of this concept see the post on maturation) is typically not complete until an infant is 7-12 months old.
6.    Extensor strength- the muscle strength to support upright movement
7.    Body constraints- Babies are just too chunky to lift their own weight, especially their legs!
8.    Motivation- the desire to move towards a goal

And remember, even if all of these components perfectly self-organize to support walking, the context or the environment still needs to be favorable to this new action.  So, hopefully baby isn’t ready to take his first step on top of an icy hill!

Herzia, C. (1991). Motor development: Contemporary and traditional theories.  In Foundation for Physical Therapy (Series Ed.), Contemporary Management of Motor Control Problems (pp.99-126). Retrieved from http://www.udel.edu/PT/galloway/motordevelopment.pdf
Savelsbergh, G., Davids, K., van der Kamp, J., & Bennett, S. (2003). Development of movement co-ordination in children: applications in the field of ergonomics, health sciences, and sport.  London: Routledge.
Smith, L.B. & Thelen, E. (2003). Development as a dynamic system. TRENDS in Cognitive Science, 7(8), 343-348.

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