Virtual stick balancing: Sensorimotor uncertainties related to angular displacement and velocity

Sensory uncertainties and imperfections in motor control play important roles in neural control and Bayesian approaches to neural encoding. However, it is diffcult to estimate these uncertainties experimentally. Here we show that magnitude of the uncertainties during the generation of motor control force can be measured for a virtual stick balancing task by varying the feedback delay, tau . It is shown that the shortest stick length that human subjects are able to balance is proportional to tau^2. The proportionality constant can be related to a combined effect of the sensory uncertainties and the error in the realization of the control force, based on a delayed proportional-derivative (PD) feedback model of the balancing task. The neural reaction delay of the human subjects were measured by standard reaction time tests and by visual blank out tests. Experimental observations provide an estimate for the upper boundary of the average sensorimotor uncertainty associated either with angula...