Comparing proprioceptive acuity in the arm between joint space and task space

Proprioception - the sense of one's body position and movement, without the aid of vision - plays a critical role in human motor control, allowing us to adeptly move our bodies through a high-dimensional task space. The relationship between joint space and task space with regard to proprioception has not been studied in the general population. This work begins to explore the relationship between proprioceptive acuity - the combination of accuracy and precision - in joint space and task space, focusing on the elbow, shoulder, and hand of the arm in single-joint (joint-space) and integrated multi-joint (task-space) active position-matching tests with a planar, robotic arm support. Our results reveal a strong correlation between joint-space proprioception at the shoulder and elbow and task-space proprioception at the hand. However, when joint-space proprioceptive error is propagated through a model of the arm's planar kinematics, it agrees poorly with the proprioceptive error measured explicitly in task space. Task-space proprioception exhibits greater accuracy than joint-space proprioception, as would be expected given the greater biological relevance of a planar reach compared to an isolated joint movement. Task-space and joint-space proprioception also differ in directional precision, exhibiting the greatest variance along nearly orthogonal axes, approximately aligned with the sagittal and frontal body planes. These findings have implications for the diagnosis of sensorimotor impairment and the development of movement therapies following neurological injury.