FREQUENCY-INDUCED PHASE-TRANSITIONS IN BIMANUAL TAPPING

The stability of bimanual performance of the frequency ratios 3:8 and 5:8 was examined from the perspective of the sine circle map and the a ssociated Farey mode-locking hierarchy. By gradually increasing moveme nt frequency, abrupt transitions from the initial frequency ratios to other frequency ratios were induced. In general, transitions occurred to frequency ratios that were near the initial frequency ratio but low er in the Farey ordering and, hence, of higher stability in the sine c ircle map. A fair percentage of these transitions were to unimodularly related ratios. The transition routes from 3:8 and 5:8 remained large ly unaffected by extensive practice of the lower-order ratios 2:5 and 3:5. Collectively, these results suggest that(i) bimanual tapping occu rs in a domain in which frequency-locked states either overlap or are located sufficiently close to each other to make stochastic switching possible (coupling parameter K > 1 or close to I); (ii) the overall st ability of these frequency-locked states decreases as movement frequen cy increases (due to a decrease in K); and, consequently, (iii) the pr obability of transitions to nearby frequency ratios increases as movem ent frequency increases, due to the differential stability of the freq uency locks.