Recent studies have shown that motor adaptation is an optimisation process on both kinematic error and effort. This work aims to induce a motor adaption in an experimental setup solely relying on the effort without any explicit kinematic error. In this experiment, the intervention space and adaptation space are decoupled: while the force field only applies to the hand linear velocity, the adaptation is expected to happen in the arm joint null space ( i.e. the swivel angle). The primary hypothesis is that such an effort-based force field can induce a movement pattern change in an indirect manner. Secondarily, assuming that this adaptation may be further promoted through subtle prompts to explore the cost space, a variation of the approach with a progressive goal is also tested. Twenty naive subjects were allocated into two groups with slightly different implementations of the force field: one with a Constant Goal (CG) and another one with a Progressively changing Goal (PG). Subjects were asked to perform reaching tasks while attached to a 3D manipulandum. During the intervention, the device applied a resistive viscous force at the subject’s hand as a function of the subject’s swivel angle to encourage an increase of the latter. Significant increases of the swivel angle of 4.9° and 6.3° were observed for the CG and the PG groups respectively. This result confirms the feasibility of inducing motor adaptation in the redundant joint space by providing a task space intervention without explicit error feedback.
