Tolerance of time delay to the sense of agency for operating electric prosthetic hands: a preliminary experiment with the appearance and gripping action

Rehabilitation in patients with phantom limb pain using an electric prosthetic hand is a promising way to mitigate their pain. This method is thought to reconstruct the patient’s sensory-motor loop that connects a command from the brain for a particular movement with the perception that the electric prosthetic hand is actually being driven by this command. A sense of agency (SoA), offered by the feeling that the prosthetic hand is being operated by the patient’s own intentions, is important for this rehabilitation. However, the relationship between characteristics of the prosthetic hand, especially the degree of reproducibility of its appearance and of gripping actions, and the associated SoA is not clear. This study therefore investigated the influence of the reproducibility of gripping action of an electric prosthetic hand and its appearance on participants’ (n = 60) SoA. In advance of adopting patient with phantom limb pain, this study focused on the difference of SoA scores of healthy participants. Significant differences were observed in SoA scores due to the changes in reproducibility of the appearance and gripping action. It is suggested that SoA is more strongly perceived when the prosthetic hand does not strictly resemble a human hand.