Inter-session Transfer Learning in MI Based BCI for Controlling a Lower-Limb Exoskeleton.

Motor imagery (MI) brain-computer interfaces (BCI) have a critical function in the neurological rehabilitation of people with motor impairment. BCI are systems that employ brain activity to control any external device and MI is a commonly used control paradigm based on the imagination of a movement without executing it. The main limitation of these systems is the time necessary for their calibration, before using them for rehabilitation. A shorter calibration scheme was proposed for a lower-limb MI based BCI for controlling an exoskeleton. Each subject participated in 5 experimental sessions. Before each session with the exoskeleton, users were guided to perform MI with visual feedback in a virtual reality scenario. Training with virtual reality involves less physical effort and users can have a previous practise on the MI mental task. In addition, transfer learning was employed, so information from previous training sessions was used for the new one. Results showed that the performance of BCI was superior in comparison with baseline methodologies when transfer learning was used.