1/f (beta) fluctuations in bimanual coordination: an additional challenge for modeling.

We analyzed the correlation structure of discrete relative phase (DRP) series in bimanual in-phase and anti-phase coordination by associating a number of fractal methods and using discrete rather than continuous relative phase measurement. ARFIMA/ARMA modeling provided statistical evidence for the presence of long-range correlation, and the series were unambiguously characterized as 1/f (beta) noise. Diverging accounts of bimanual coordination are defended in the literature. Since the evidence for 1/f (beta) noise provides new insight into the properties of stability in coordination, it should be considered as an empirical criterion for determining which mechanisms are likely to be engaged in bimanual coordination models. We discussed some implications for studying the neural basis of coordination, and we tested the performance of three current models in accounting for 1/f (beta) noise in DRP. None of these models was proven to generate the expected correlation structure.