1. A method of motor learning comprising the steps of: providing a brain-robot interface and a robotic device, the brain-robot interface comprising a neural signal acquisition device; detecting a user's motor intent using the neural signal acquisition device; using a processing unit: obtaining a first score based on the detected motor intent; and calculating a second score based on the first score and a threshold score value for the motor intent, including adjusting the threshold score value for the motor intent by extracting a value from an obtained learning curve that maps a relative performance index to a relative target threshold value variation to quantify an amount of threshold score value adjustment; and using the robotic device to give robotic assistance to the user for executing a motor task associated with the motor intent based on the second score.