Adaptation Behavior of Skilled Infant Bouncers: Leg Movements and Mechanisms of Control.

Rhythmic behavior in nonlinear systems can be described as limit cycles or attractors. System perturbations may result in shifts between multiple attractors. We investigated individual cycle-to-cycle leg movement kinematics of three prewalking skilled infant bouncers (10.6 ±0.91 months) during four different spring frequencies (0.9, 1.15, 1.27 and 1.56 Hz). A novel visual analysis phase-plane methodology was introduced to analyze the lower body joint kinematics. It was found that as infants' bounce frequency increased to match the natural frequency of the system, their joint ranges of motion decreased and lower extremity dynamics shifted from forced to simple harmonic motion. All infants produced highly synchronized and coordinated movements, as supported by moderate to high inter- and intralimb correlations. This study extends from previous work (Habib Perez et al., 2015) by focusing on the lower extremity kinematic movements, joint coordination and the occurrence of different movement patterns for individual bounce cycles over four spring conditions.