PHASE-TRANSITIONS IN RHYTHMIC TRACKING MOVEMENTS - A CASE OF UNILATERAL COUPLING

Previous research has demonstrated that both within and between person s two limbs coordinated in an anti-phase mode (relative phase of 180 d egrees) spontaneously switch to an in-phase mode (relative phase of 0 degrees) when movement frequency is increased. These phase transitions satisfy the criteria of physical bifurcations. The present experiment s generalize this finding to movements of a single limb (lower arm) co ordinated with the motion of an externally driven visual signal. The r esults support the idea that phase transitions in coordinated rhythmic movements are due to the presence of informational resolution limitat ions of the system, and are therefore to be understood as 'threshold n on-linearities'. Once in a particular behavioural mode a threshold is reached due to changes in a system parameter, a phase transition occur s if, and only if, there is another behavioural mode available under w hich the global task goals can be satisfied at lower informational cos ts. If the spatial conditions of the task are manipulated in such a wa y that the relation between the information specifying the behaviour a nd the information generated by the behaviour is identical for both be havioural modes (in-phase, anti-phase), no phase transitions occur,