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The objective of the present experiments was to evaluate the multi-scaled nature of human rhythmic movement with respect to simple dynamical systems and phase transitions. Experiment 1 evaluated the statistical nature of the underlying dynamics of human rhythmic movement in a golden-mean (i.e., quasiperiodic) coupling relationship with another oscillator. It was predicted that human rhythmic movement can be shown to belong to the same universality class as a sine-circle map. Participants synchronized their arm movement to a virtual quasiperiodic oscillator. Results showed that participants’ dynamics were of higher dimension than predicted, but within the range of a second order system coupled to two first order systems, and that scaling regions were wider than those predicted. These results indicate that the hypothesis was not supported under the established conditions, though local scaling was shown to have a positive relation with global dimensionality. The second experiment evaluated whether the fluctuations found in behavior during the acquisition of new cognitive structure extend to re-organizations of rhythmic behavior. A coupling was established between a virtual pendulum driven by an independent driver and the movement of each participant. Participants were tasked with coordinating with the pendulum system such that the peak amplitude of the pendulum stayed within a specified range. As the trial progressed, the coupling strength of the driver was increased in small increments to beyond the point where the combined strength of the participants’ movement and the driver was sufficient to push the pendulum out of the directed region. It was predicted that the multifractal analogue of a thermodynamic quantity would be sensitive to qualitative transitions in behavior, and that participants who underwent such transitions spontaneously, i.e., intrinsically, rather than under direction, i.e., extrinsically, would exhibit critical fluctuations, prior to undergoing qualitative changes in their movement. Results showed that participants switched to anti-phase behavior around the critical point, regardless of condition. The proposed multifractal measure was sensitive to the transition, though it did not show differences between groups. The standard deviation of the relative phase between the participants and the driver showed similar patterning to the multifractal measure, but decayed more slowly after the transition point in the intrinsic group than in the extrinsic group. This study succeeded in establishing a link between a measure with conceptual foundations in thermodynamic phase transitions and human behavior, further demonstrating the utility of multi-fractal analyses and corroborating the notion that human beings are softly-assembled, complex systems.

The present study investigated whether constraining movement affects interpersonal coordination and cognitive performance. Participants worked in pairs to complete a series of cooperative picture-puzzle tasks in which they discussed and found differences between their respective puzzles relying only on verbal communication. Pairs participated in each of three degree-of-constraint conditions: either both participants were free to move their hands (FF), both participants had their hands restrained (RR), or one participant (Person 1) had his or her hands restrained while the other was free to move (FR). During any given trial, neither participant was informed of the degree-of-constraint of his/her partner. Eye tracking data was collected, and movement was measured at the waist, hand, and head in the Anterior-Posterior (AP) direction. Data were analyzed using Cross-Recurrence Quantification Analysis (CRQ) and Joint-Recurrence Quantification Analysis (JRQ). Postural sway coordination, gaze coordination, as well as cognitive performance were predicted to be highest in FF, followed by RR. The lowest degree of coordination and cognitive performance was expected to be found in the FR condition. Results showed that whenever there were significant differences in coordination patterns between conditions, the asymmetric condition generally exhibited lesser degrees of coordination, and that, whenever there was a difference in the overall amount of coordination, the condition in which both participants were free to move exhibited greater coordination. However, it was also the case that the structural patterning of coordination was dependent upon the location of measurement for the conditions in which both individuals were restrained and when both individuals. Additionally, in spite of the fact that the restraint manipulation did not have a significant influence on task performance, correlations between task performance and movement measures showed significant positive relationships between movement, number of utterances, and number of differences found, indicating a relationship between movement and task performance consistent with my hypotheses. Taken in sum, these results show that both coordination and cognitive performance are sensitive to constraints placed the action system.