A Five-State P300-based Foot Lifter Orthosis: Proof of Concept

Current lower limb prostheses do not integrate re- cent developments in robotics and in Brain-Computer Interfaces (BCIs). In fact, active lower limb prostheses seldom consider the user's intent, they often determine the correct movement from those of healthy parts of the body or from the residual limb. Recently, an emerging idea for non-invasive BCIs was proposed to allow such low bitrate systems to control a lower limb prosthesis thanks to a Central Pattern Generator (CPG) widely used in robotics. This CPG allows to automatically generate a periodic gait pattern. Furthermore, the CPG pattern frequency and magnitude can be adapted according to the specific gait behavior of the patient and his desired speed. This paper proves the concept of combining a human gait model based on a CPG and a classic but non-natural P300 BCI in order to consider the user's intent. The details of how the entire chain can be practically implemented are given. Finally, preliminary results on four healthy subjects for a four-speed P300-based lower limb orthosis with a non-control state are presented. Globally, results are satisfying and prove the feasibility of such systems.