Robot-Aided Upper-limb Proprioceptive Training in Three-Dimensional Space

Proprioception, the ability to sense body position and limb movements in space without visual feedback, is one of the key factors in controlling body movements and performing activities of daily living. However, this capability might be affected after neural injuries such as stroke. Robotic platforms can be used to monitor and promote arm movements and, therefore, can assist in developing rehabilitation protocols that aim to improve proprioception through repetitive reaching motions without vision. The objective of this paper is to investigate if a robotic training protocol improves the end-position reaching proprioceptive sense in three-dimensional (3D) space. As an initial step towards clinical application, a robotic platform was employed to train the end-position proprioceptive sense in six healthy participants. During the training phase, volunteers used their dominant hand to reach without vision to two different targets in 3D space. Positions of these targets were carefully chosen to create a hand movement pattern similar to that used when self-feeding, which is an important activity of daily living. At the end of each training trial, participants were provided with visual feedback to help them move their hands to the exact locations confirmed through haptic feedback. Their performance was evaluated before and after the training in an assessment phase during which participants were asked to move from the start position to the same two targets as well as an additional third one without any visual or haptic feedback. The results from this study show significant improvements in overall reaching accuracy and trajectory smoothness, demonstrated by 41% decrease in the average end-position error and 13% reduction in the average index of curvature after the training. This research suggests the potential of designing robotic rehabilitation protocols for improving 3D proprioception.