Phase transitions and critical fluctuations in the visual coordination of rhythmic movements between people.

TLDR

Participants seated together synchronized their lower‑leg oscillations, maintaining either a 0° symmetric or 180° alternate phase relationship. The study examined how the stability of these two phase modes differed. Experiments 2 and 3 had participants adopt a noninitial phase angle when it felt more comfortable, allowing observation of phase transitions. In Experiment 1 the alternate mode became less stable at higher frequencies, and analysis of nonsteady cycles showed a switch to the symmetric mode; the observed transition met the criteria of a physical bifurcation—hysteresis, critical fluctuations, and divergence—mirroring prior limb‑coordination findings.

Abstract

By watching each other's lower oscillating leg, 2 seated Ss kept a common tempo and a particular phase relation of either 0 degrees (symmetric mode) or 180 degrees (alternate mode). This study investigated the differential stability of the 2 phase modes. In Experiment 1, in which Ss were instructed to remain in the initial phase mode, the alternate phase mode was found to be less stable as the frequency of oscillation increased. In addition, analysis of the nonsteady state cycles revealed evidence of a switching to the symmetric phase mode for the initial alternate phase mode trials. In Experiments 2 and 3, Ss were instructed to remain at a noninitial phase angle if it was found to be more comfortable. The transition observed between the 2 phase modes satisfies the criteria of a physical bifurcation--hysteresis, critical fluctuations, and divergence--and is consonant with previous findings on transitions in limb coordination within a person.