11. The method according to claim 10 , wherein the plurality of speech characteristic sensors are configured to sense two or more from the group consisting of a sound produced by the user, an air flow produced by the user, a lip movement produced by the user, a lip gesture produced by the user, a physical contact between the tongue and a palate of the user, a muscle movement produced by the user, and an electrical activity of a brain of the user.
10. An assistive method of providing information useful in improving a user's speech based on real-time tracking at least one of a position, orientation, and movement of a tongue of the user during speech comprising: receiving magnetic sensor signals from magnetic sensors; measuring, based on the magnetic sensor signals, a magnetic flux density at a location of a tracer unit, the tracer unit being located in a non-obstructive manner on the tongue of the user; performing a tongue tracking signal processing algorithm, the algorithm including minimizing a cost function that correlates to the measured magnetic flux density and an estimated magnetic flux density at the location of the tracer unit, the location of the tracer unit being defined within a three-dimensinal, non-discrete space; determining, based on the algorithm, one or more of a position, orientation, and movement of the tracer unit in real time within the three-dimensinal, non-discrete space; receiving speech characteristic signals from speech characteristic sensors; combining the one or more determined position, determined orientation, and determined movement of the tracer unit with the speech characteristic sensor signals; and generating, based on the combining, assistive speech-related feedback data, the assistive speech-related feedback data representing temporally and spatially continuous tracking of the user's tongue movement in real time.