323 Torre is with the Sensorimotor Neuroscience Laboratory, MacMaster University, Canada, and Motor Eficiency and Deiciency, University Montpellier I, France. Balasubramaniam is with the Sensorimotor Neuroscience Laboratory, MacMaster University, Canada. Delignières is with Motor Eficiency and Deiciency, University Montpellier I, France. Motor Control, 2010, 14, 323-343 © 2010 Human Kinetics, Inc. Oscillating in Synchrony with a Metronome: Serial Dependence, Limit Cycle Dynamics, and Modeling Kjerstin Torre, Ramesh Balasubramaniam, and Didier Delignières We analyzed serial dependencies in periods and asynchronies collected during oscillations performed in synchrony with a metronome. Results showed that asyn- chronies contain 1/f luctuations, and the series of periods contain antipersistent dependence. The analysis of the phase portrait revealed a speciic asymmetry induced by synchronization. We propose a hybrid limit cycle model including a cycle-dependent stiffness parameter provided with fractal properties, and a parametric driving function based on velocity. This model accounts for most experimentally evidenced statistical features, including serial dependence and limit cycle dynamics. We discuss the results and modeling choices within the framework of event-based and emergent timing. Keywords: Oscillation, asynchrony, 1/f noise, limit cycle model, parametric driving. So far, studies of single-limb oscillations have essentially focused on oscil- lators within-cycle dynamics, especially through the analysis of the phase-plane representation of motion. Serial dependence (i.e., cycle-to-cycle dynamics) has been largely disregarded, except in a few studies focusing on self-paced oscillations (Daffertshofer, 1998; Delignières et al., 2004, 2008; Schöner, 1994). Especially, Delignières et al. (2008) revealed the presence of fractal serial dependencies in series of oscillation periods, which could not be accounted for by classical limit cycle models. We focus in the present paper on oscillations performed in synchrony with a metronome. Our irst aim was to combine the analyses of within-cycle and cycle-to-cycle oscillation dynamics, to provide a complete characterization of the impact of synchronization on the limb dynamics. In a second step, we propose to assess the capability of some candidate models to account for the empirical results. ORIGINAL RESEARCH