Stability of rhythmic visuo-motor tracking does not depend on relative velocity.

It is well established that the in-phase pattern of bimanual coordination (i.e. a relative phase of 0 degrees ) is more stable than the antiphase pattern (i.e., a relative phase of 180 degrees ), and that a spontaneous transition from antiphase to in-phase typically occurs as the movement frequency is gradually increased. On the basis of results from relative phase perception experiments, Bingham (Proceedings of the 23rd annual conference of the cognitive science society. Laurence Erlbaum Associates, Mahwah, pp 75-79, 2001; Ecol Psychol 16:45-53, 2004; Advances in psychology 135: time-to-contact. Elsevier, Amsterdam, pp 421-442, 2004) proposed a dynamical model that consists of two phase driven oscillators coupled via the perceived relative phase, the resolution of which is determined by relative velocity. In the present study, we specifically test behavioral predictions from this last assumption during a unimanual visuo-motor tracking task. Different conditions of amplitudes and frequencies were designed to manipulate selectively relative phase and relative velocity. While the known effect of phase and frequency were observed, relative phase variability was not affected by the different conditions of relative velocity. As such, Bingham's model assumption that instability in relative phase coordination is brought about by relative velocity that affects the resolution of the perceived relative phase has been invalidated for the case of rhythmic unimanual visuo-motor tracking. Although this does not rule out the view that relative phase production is constrained by relative phase perception, the mechanism that would be responsible for this phenomenon still has to be established.