A temporal limit for the influence of volition on stability of rhythmic bimanual coordination

The present study tests a limit of the voluntarily maintained bimanual coordination (180 degrees of relative phase). In particular we emphasized a vanishing of the volitional influence as a function of time on task. The manipulation of oscillation frequency and trial duration was expected to increase the overall variability of the system because of a progressive depletion of the positive intentional influence. Eighteen participants, divided in three groups according to the performance duration (30 s, 150 s and 300 s), performed an anti-phase bimanual coordination pattern at three frequencies according to their own critical frequency. They were instructed to maintain a maximal level of intentional effort. The results revealed an increase in the number of cycles out of a local stationary solution (180 degrees), indexing a decrease in coordination stability as a function of time and oscillation frequency. The data revealed a possible implication of trial duration in the HKB model (Haken, Kelso, & Bunz, 1985) and its extended "intentional" version (Schoner & Kelso, 1988).