Competitive Training in Spatial Augmented Reality for Prosthetic Leg Embodiment

Literature highlights how trainings in virtual and augmented settings can contribute to a higher level of embodiment of bionic prosthetic limbs. In this paper, a Spatial Augmented Reality (SAR, where the augmentation of a real environment is based on displays on surfaces instead of being worn by the user) system was used in two conditions characterised by the absence or the presence of a social feature that should improve the user engagement. In the first condition, the subject has to contract the quadriceps of the right leg to command, through EMG sensors, a virtual prosthetic leg to break a virtual wall on a computer screen. In this condition, each foot-wall collision causes a vibratory feedback on the subject's knee, a visual one given by the breaking of the wall, and an auditory one of the sound of falling debris. The second condition, on the other hand, adds a level of sociality whereby the subject must break the virtual wall before a virtual (fictional) competitor. Fourteen unimpaired subjects were administered both conditions in a randomized way, each repeated three times. Questionnaire scores and quantitative data (proprioceptive drift and the number of kicks) have been collected after the training and a subsequent Rubber Leg Illusion session. Overall, it was observed that the competitive condition increased the subject's commitment to completing the task. Although it increases the engagement factor, thus increasing the subject's focus on the task to be performed, the condition in which the social sphere appears negatively impacts the embodiment process itself probably because of the complexity of the task that creates an increase in the subject's distraction and mental workload. However, these results suggest the possibility that an alternation of a neutral and a social task, in the same session, could lead to increased training time and a higher level of limb embodiment.