Interpersonal coordination in a ball-and-beam paradigm: Transfer of skill from solo action to joint action

Interpersonal coordination is paramount to the success of a joint action. While the pattern formation process of interpersonal coordination is relatively well understood, models like HKB lack an ecological dimension that relates the motor pattern to the environment. We investigated this dimension in a two-step study using the ball-and-beam paradigm. Participants rolled a ball back-and-forth between two targets on a beam, by manipulating the beam inclination either individually or dyadically. In an (earlier reported) first step, 16 participants performed two solo action sessions of the task, allowing us to identify pertinent performance characteristics. Here, those participants were paired into 8 dyads to perform a joint action session, allowing us to assess the solo-to-joint transfer of those characteristics. Over blocks, dyads improved their performance by increasing the ball speed and accuracy. While the relative variability of the beam's inclination angle decreased, the range and the timing of the beam motion remained unchanged. Variables (indirectly) related to ball speed, such as the range and timing of the beam motion, were strongly propagated from solo to joint action, while the variables related to ball accuracy, like the beam variability, were only moderately transferred. Most dyads established an anti-phase mode of coordination, with a significant decrease in phase variability over blocks. We also observed significant asymmetries in the coordination. Dyad members with a better solo-action performance were more likely to lead the interaction. We concluded that interpersonal coordination in the ball-and-beam paradigm emerged from the interaction, while being constrained by the goal of the task.