The impact of context manipulations on movement patterns during a transition period

According to principles of dynamic systems theory, behavior is both unstable and more easily shifted into new patterns during transitional periods than during stable periods. We examined this principle by analyzing the stepping response of infants when they were in a transitional period of treadmill stepping. We tested 12 infants with Down syndrome (M age=13.3 months) by supporting them upright on a small treadmill in the traditional protocol and in four manipulations of this context. All the infants were, developmentally, at a point of producing few steps and multiple step types when on the treadmill. We used context manipulations that we predicted would shift infants' behaviors into a dominance of alternating steps over other step types and would increase the number of steps produced overall. Context manipulations included Velcro, nubbly, girdle, and weights. Our results showed that infants produced more total steps and more alternating steps in the altered conditions compared to baseline. The effectiveness of each manipulation varied; the Velcro context tended to have the strongest impact overall. Changes in context also significantly affected the trajectory of foot displacement in swing. Our results illustrate the importance of (a) extrinsic factors on the developmental trajectory we observe in motor behavior over time and (b) understanding behavior during transitional as well as in stable periods. Psyc INFO classification: 2330; 2800