Use of a virtual environment to investigate planning of unconstrained reach actions after stroke: A feasibility study

Planning of reach actions can be inferred through examination of the scaling of kinematic features and through a deterministic statistical model that delineates a premovement plan and early compensatory adjustments. The influence of stroke-induced hemiparesis on these motor planning features is currently unknown. The purpose of this study is to determine the feasibility of using a 3-dimensional (3-D) virtual environment (VE) to investigate the planning of unconstrained reach actions in individuals post-stroke. Two non-disabled adults and one individual post-stroke reached to 9 targets displayed in 3 directions (straight, right 45deg, left 45deg) and 3 extents (8 cm, 16 cm, 24 cm) for a total of 108 trials with each arm. Reach trajectories were analyzed, kinematics variables extracted, and a statistical model applied to infer motor planning. All participants were able to complete the VR task although changes were required to ease accuracy requirements for the participant with stroke. In the non-disabled participants, movement time averaged < 500 msec and mean endpoint error increased based on target extent. The participant with stroke had similar movement times (485 plusmn 98 msec) when reaching with the right/ipsilesional UE but longer movement times (761 plusmn 202 msec) when reaching with the left/contralateral UE. Endpoint errors increased based on target extent in both arms in the participant with stroke but errors were overall larger when reaching with the left/contralateral UE. All participants scaled peak velocity to target distance although absolute values differed based on the arm used and the presence of stroke-induced hemiparesis. Scaling of peak acceleration was less consistent across participants. Overall, over 80% of movement distance could be explained by peak velocity and target distance in the non-disabled participants when trials were collapsed across direction. When reaching with the right/ipsilesional UE, the participant with stroke demonstrated an increased reliance on the premovement plan and decreased use of early compensatory adjustments. A similar trend was seen with the left/contralesional UE. Our results suggest that it is feasible to use an immersive VE to investigate the planning of 3-D reach actions in non-disabled adults and an individual with stroke-induced hemiparesis. Future work will develop a calibration system to determine system errors, compare performance in the VE with an analogous real-word task, and extend data collection to a larger group of individuals post-stroke.