Feedback control of limb position: a random walk approach

The fluctuations in a postural task, which is archetypical of 'simple' motor control, are investigated using a correlated random walk approach. The authors compare the fluctuations in a subject's finger position when his eyes are closed with the variations recorded when he has access to a visual display of the position. The Hurst index (of the ratio of range over standard deviation) is analysed, in view of distinguishing a scaling relationship in the two-point correlation as a function of time intervals. The authors' preliminary results indicate more structure in these correlograms than can be accounted for by a random walk description.