Exploring the role of sensor noise in movement variability

Numerical simulations were used to explore the consequences of a spatially non-uniform sense of hand position on arm movements in the horizontal plane. Isotropic or anisotropic position errors were introduced into several starting hand positions and the resulting errors in movement direction were quantified. Two separate simulations were performed. In one simulation planned movement directions were defined relative to the starting position of the hand. Movement errors generated in this simulation resulted from a failure to compensate for differing initial conditions. In a second simulation planned movement directions were defined by the vector joining the sensed starting position with a fixed target position. Movement errors in this simulation resulted from both uncompensated changes in initial conditions as well as errors in movement planning. In both simulations, directional error variability generally increased for starting positions closer to the body. These effects were most pronounced for the anisotropic distribution of starting positions, particularly under conditions where movements were directed toward a fixed spatial location.