Variability in a Dynamic Systems Theory Approach to Second Language Acquisition M. VERSPOOR AND M. VAN DIJK Introduction The role of variability in human development was first pointed out by dynamic systems theorists Thelen and Smith (1994). They argue that development should not be seen as a teleological process—a process that is predetermined and guided by design (p. xv). Instead, they point out that development is an individual, rather erratic discovery process. The learner must discover, try out, and practice each part of the process him or herself, and this is accompanied with a great deal of trial and error, referred to as “variability.” (Note: we will use the term “variability” to refer to variation in performance within one indi- vidual and “variation” to refer to differences among learners). In this entry, we will first briefly discuss their findings so it may become clear why it is interesting to look at the everyday messy detail of development, in our case second language development, and why it is interesting to trace different variables over time. Then we will review several studies in both first and second language acquisition to show that variability can provide new insights in language development. Variability in Motor Skills Thelen and Smith focus on motor development. They argue that for a child to learn to walk, of course, some preconditions first have to be met before development can take place. The child must have a brain, a spinal cord, and peripheral neuromotor and sensory pathways. For walking specifically, the learner has to have bones, joints, muscles, a cardio- vascular system, a respiratory apparatus, skin, and so on, each of which will have its own developmental path, and all of which will interact with one another and with the muscles and neurological pathways needed for walking. If we focus on the process of learning to walk from a bit of a distance, we can see that there are several distinct stages: kicking (first one leg, then both legs), pulling up, moving upright, standing still, finding balance, taking a few wobbly steps, until finally the child can walk. From afar it may seem that each stage follows neatly after the other, but when we look up close we see not only that there are no clear boundaries between each stage but that the transition from each stage is far from smooth and involves lots of variability. Thelen and Smith thus argue that there is not one direct cause for new behavior, but that it emerges from the confluence of different subsystems in muscle development, motor control and intentionality. Within this process, variability in some subsystems will occur because it is necessary to drive the developmental process, allowing the learner to explore and select. According to dynamic systems theory (DST), variability is especially large during periods of rapid development because at that time the learner explores and tries out new strategies or modes of behavior that are not always successful and may therefore alternate with old strategies or modes of behavior (Thelen & Smith, 1994). From a more formal perspective, systems have to become “unstable” before they can change (Hosenfeld, Van der Maas, & Van den Boom, 1997). For instance, high intra-individual variability implies that qualitative developmental changes may be taking place (Lee & Karmiloff-Smith, 2002, in Granott & Parziale, 2002). The cause and effect relationship between variability and 10-0227Variability in a Dynamic.indd 1 10-0227Variability in a Dynamic.indd 1 26/11/2011 10:16 AM 26/11/2011 10:16 AM