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Past research has revealed that a person's rhythmic limb movements become spontaneously entrained to an environmental rhythm if a.) visual information about the environmental rhythm is available and b.) its frequency of the environmental rhythm is near that of the person's movements. Further, this research has demonstrated that if the eyes track the environmental stimulus, the spontaneous entrainment to the environmental rhythm is strengthened. Experiments were performed to investigate two hypotheses that could explain this eye-tracking enhancement of spontaneous entrainment. One hypothesis is that eye tracking allows for the pick up of important coordinative information at the turn-around points of a movement trajectory. Another hypothesis is that the limb movements entrain to the moving eyes through a neuromotor synergy linking the eyes and limb. Results of these experiments will help delineate the informational and dynamical constraints that can impact the acquisition of skilled actions.

The current study investigated the movement dynamics of a complementary collision-avoidance task. Participant pairs performed a repetitive targeting task in which they moved computer stimuli back and forth between sets of target locations without colliding into each other. Pairs converged onto a stable relative phase relationship of around 35°, with one participant spontaneously adopting the role of "phase leader" and the other participant adopting the role of "phase follower". In addition, those participants who adopted the role of phase leader tended to exhibit more of a straight-line trajectory between targets, whereas participants who adopted the role of phase follower tended to exhibit a more elliptical trajectory. This role differentiation was essential to task success and reflected the spontaneous relaxation and recruitment of available movement degrees-of-freedom defined across the joint-action system.