Proximodistal gradient in the perception of delayed stiffness

Introduction of successful telerehabilitation into the variety of techniques that are available to the therapist will forever change the field of rehabilitation. Accurate perception of the remote environment´s mechanical properties and of stiffness in particular is extremely important for successful telerehabilitation. In the current study we present the framework for exploring perception of delayed stiffness when probing is executed using movement with different joints, and provide experimental results supporting the existence of proximodistal gradient in the perception of delayed stiffness. We found that delayed stiffness was underestimated to a larger extent after probing with wrist than with elbow. We suggest that the observed gradient in perception reveals a proximodistal gradient in control: proximal joints are dominated by force control, whereas distal joints are dominated by position control.