An Augmented Cooperative Setting for Training the Embodiment of an Artificial Lower Limb

Literature highlights how virtual and augmented settings offer engaging solutions to improve one's feeling of an artificial limb embodiment. In this paper, we explored the potential of a setting for Spatial Augmented Reality (SAR, where a display augments a surface without making the user wear any visor) in two conditions of a lower limb ownership training involving subjects without disabilities. In the first condition, the subject must contract the quadriceps of a leg for commanding (through electromyography, EMG) a virtual leg (a 3D model of the Hybrid Knee prosthesis) to kick a virtual wall: each collision corresponds to a vibratory feedback on the thigh (a position defined for upcoming tests with transfemural amputees). The second condition adds a social context to engage the user: the subject is asked to cooperate with another (fictional) player to kick on the same virtual wall. Subjective (through questionnaires) and objective (according to the number of kicks as a performance index, and the proprioceptive drift as an embodiment index) assessments have been performed before a rubber leg illusion test. Overall, we observed how the cooperative task can engage the subject to be more active. However, this condition can reduce the impact of the training on the embodiment itself, probably because the social task generates a distraction. Nevertheless, such findings suggest the possibility to alternate these two tasks in the same session to increase the duration of a prosthetic embodiment training.