NeglectARm3D: a robotic and virtual reality platform for the three-dimensional assessment of unilateral spatial...

Unilateral Spatial Neglect (USN) significantly impacts functional outcomes post-stroke, yet traditional assessment methods, relying predominantly on two-dimensional (2D) paper-and-pencil tasks, fail to capture the disorder's complexity across three-dimensional (3D) space and, in particular, the role of depth. This paper introduces NeglectARm3D, a platform for the objective and repeatable 3D assessment of USN that integrates the precise kinematic and force measurement of a 7-DOF torque-controlled robot (Franka Research 3) with the immersive 3D stimulus presentation of a commercial head-mounted display (Meta Quest 3). A Cartesian variable impedance controller lets the participant reach freely toward randomized 3D targets (Phase 1, subject in charge), enabling the reconstruction of a volumetric exploration map, and delivers smooth haptic guidance toward neglected targets (Phase 2, robot in charge). As a first step toward clinical deployment, we evaluated the technical behavior, safety, and tolerability of the platform in twelve healthy adults performing thirty reaching trajectories (twenty in Phase 1, ten in Phase 2). The system preserved natural movement velocity ( $0.10\pm 0.02$ vs. $0.10\pm 0.01$ m/s), achieved large position error in free reaching ( $32.46\pm 14.71$ mm) versus precise robot-led convergence ( $3.01\pm 0.43$ mm) with reduced interaction force ( $4.96\pm 0.84$ vs. $2.59\pm 0.32$ N), and maintained physiological movement smoothness (SPARC $-1.87\pm 0.29$ vs. $-1.63\pm 0.32$ , benchmark $-1.40$ ). Usability was high (System Usability Scale $85.60\pm 8.10$ ), simulator sickness was low across all subscales, and all participants reported no pain and no perception of danger. These results support the technical feasibility and short-term tolerability of the integrated platform in healthy adults and justify subsequent clinical and psychometric evaluation in stroke survivors with USN.