Movement variability resulting from different noise sources: a simulation study

Limb movements are highly variable due in part to noise occurring at different stages of movement production, from sensing the position of the limb to the issuing of motor commands. Here we used a simulation approach to predict the effects of noise associated with (1) sensing the position of the limb ('position sensing noise') and (2) planning an appropriate movement vector ('trajectory planning noise'), as well as the combined effects of these factors, on arm movement variability across the workspace. Results were compared to those predicted by a previous model of the noise associated with movement execution. We found that the effects of sensing and planning related noise on movement variability were highly dependent upon both the planned movement direction and the initial configuration of the arm and differed in several respects from the effects of execution noise. In addition, sensing and planning noise interacted in a complex manner across movement directions. These results provide important insights into the relative roles of sensing, planning and execution noise in movement variability that could prove useful for understanding and addressing the exaggerated variability that arises from neurological damage, and for interpreting neurophysiological investigations that seek to relate neural variability to behavioral variability.