Error prediction determines the coordinate system used for the representation of novel dynamics

Skillful object manipulation requires a representation of the object's dynamics. Despite extensive research, previous studies have not been able to provide a consistent view of this representation in the motor system, with each study providing evidence favoring an extrinsic coordinate system, an intrinsic coordinate system, an object-based representation, or mixtures of these coordinate systems. In a series of experiments, we show that the motor system combines different representations based on their reliability. Specifically, since noise creates an error between planned and executed force production which depends on the arm state, the motor system will rely more on the representation for which the plan is less affected. In addition, we show that the same mechanism predicts the different results made about dynamics representation and thus explains the discrepancies between influential past studies. Overall, we are able to reconcile all of the apparently disparate findings under a single cohesive model of dynamics representation.