Sampling or intermittency in hand control system dynamics.

A hand control model is proposed. Investigation of the hand's intermittency synchronization shows it corresponds to an input-synchronized sampler rather than the clock-synchronized sampler more typical of engineering systems. A velocity control mechanism, similar to that in an eye tracking system is shown to be absent in the hand. A quantitative transfer function for predictable inputs serves further to define the hand's input adaptive characteristics. Stability margin adjustments of a linear reduced model enabled us to match the available quantitative data. The most exciting result of this study is the evidence for intermittency: a refractory period shown in the short pulse experiment, peaks in the frequency response experiments, and a saccadic sequence of steps in response to an open loop step input and to a closed loop ramp input.