Performing a Throw in Mixed Reality: A Validation Study

Lately, Virtual or Mixed reality (VR/MR) tools simulating altered gravity conditions have improved both in terms of realism and efficacy, therefore playing a role in reducing the costs and technical difficulties characterizing the reproduction of altered gravity environments. The evaluation of human performance in altered gravity conditions may also take advantage of the use of VR/MR tools. We developed a serious game aiming at providing some elements for the assessment of motor learning processes in altered gravity conditions. The serious game requires the player to throw a virtual ball toward a virtual target while exposed to a MR environment featuring various gravity conditions (Mars, Moon and Earth gravity). The accuracy of the ball's trajectory reproduced in the MR environment is a crucial factor for a successful use of the game. In this paper, the accuracy of the virtual ball's trajectory as reconstructed in the MR environment is validated against the trajectory measured under Earth gravity conditions by a motion capture system used as a gold standard. Results obtained from four subjects performing five non-consecutive throws showed, on average, errors of -0.003 s in the identification of the instant of ball's release, 6.5
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and 0.18 m/s of difference in the inclination and magnitude of the velocity vector of the ball at release, respectively, and -0.11 m of error in the (theoretical) landing distance. As, on average, the error on landing distance falls within the diameter of the virtual target, the trajectory reconstruction can be considered suitable for the serious game's objectives.