The illusion box of syndactyly: setup and ad hoc algorithm to induce virtual fingers webbing

Inclusion of the prosthesis in the body schema lets the device felt by the user as an extension of the self and consequently improves its performance and acceptability. Two paradigmatic models that faced the issue of the illusory embodiment, the rubber hand illusion and the mirror box, revealed that such process goes in parallel with changes in the activity of cortical sensorimotor areas devoted to the limb and that a key factor is represented by the visual inflow that overrides the mismatching kinesthesia. In spite of that, vision alone is not able to trigger prosthesis embodiment in amputees everyday-life. In order to disentangle the contributes of visual and proprioceptive feedback in the induction of sensorimotor plasticity we develop the Illusion Box of Syndactyly that, through an ad hoc algorithm, produces an index-middle finger illusory fingers webbing. The algorithm works in realtime and, trough background difference, it segments the hands, recognizes the fingers and produces the virtual syndactyly. We perform preliminary tests on a healthy subject, suggesting that the setup is robust and efficient to induce the illusion.