Effects of robotic pelvic guidance and visual feedback designs on upper body seated coordination and sense of agency in virtual reality

Abstract

Trunk impairment from neurological conditions such as spinal cord injury, cerebral palsy, and stroke limits postural coordination and functional independence. Sense of agency (SoA), the perceived control over one’s movements, influences motor learning and rehabilitation engagement, yet has not been examined in seated postural training. This study investigates how robotic pelvic guidance and visual feedback (VF) designs influence motor coordination and SoA during a seated reaching task in virtual reality (VR), validated here with able-bodied subjects. Thirty-two healthy adults were randomly assigned to four groups (n = 8) in a 2 × 2 between-subjects design: pelvic guidance (guided vs unguided) and VF type (control VF, CVF: a pursuit-tracking moving target, vs error-based VF, EVF: displaying only the hand–target error). In the guided condition, the pelvic Wheelchair Robot for Active Postural Support (pWRAPS) actively guided pelvic orientation during a four-direction hand-tracking game. In the unguided condition, the robot operated in transparent mode. Participants receiving pelvic guidance showed significantly greater improvements in task performance and pelvis–trunk–hand coordination than unguided participants, regardless of VF type. EVF influenced trunk–pelvis coordination independently of guidance, with CVF yielding greater trunk–pelvis improvement. Trunk–pelvis coordination emerged as the strongest predictor of SoA, and SoA increased significantly at post-test, suggesting that perceived agency reflects coordination quality rather than the presence or absence of robotic assistance. Critically, guidance improved coordination without diminishing SoA, indicating compatible biomechanical and psychological rehabilitation goals. These findings support integrating robotic pelvic guidance with VR-based feedback for seated postural rehabilitation.