A magneto-inductive sensor based wireless tongue-computer interface

Abstract

We have developed a noninvasive, unobtrusive magnetic wireless tongue-computer interface, called "Tongue Drive," to provide people with severe disabilities with flexible and effective computer access and environment control. A small permanent magnet secured on the tongue by implantation, piercing, or tissue adhesives, is utilized as a tracer to track the tongue movements. The magnetic field variations inside and around the mouth due to the tongue movements are detected by a pair of three-axial linear magneto-inductive sensor modules mounted bilaterally on a headset near the user's cheeks. After being wirelessly transmitted to a portable computer, the sensor output signals are processed by a differential field cancellation algorithm to eliminate the external magnetic field interference, and translated into user control commands, which could then be used to access a desktop computer, maneuver a powered wheelchair, or control other devices in the user's environment. The system has been successfully tested on six able-bodied subjects for computer access by defining six individual commands to resemble mouse functions. Results show that the Tongue Drive system response time for 87% correctly completed commands is 0.8 s, which yields to an information transfer rate of approximately 130 b/min.

Fig. 1

Block diagram of the eTDS.

Fig. 2

eTDS prototype implemented on a hardhat for human trials. Insets clockwise from top: control unit, three-axis magnetic sensor, and permanent magnetic tracer attached on the subject’s tongue using tissue adhesive.

Fig. 3

(a) Relative 3-D position and orientation of the bilateral three-axis sensor modules and the permanent magnetic tracer attached to the user’s tongue. (b) Original, transformed, and differential outputs of the Z-axis sensors when the subject issues two left mouse commands while walking in the laboratory.

Fig. 4

Mouse pointer path recorded during the maze navigation experiment superimposed on the GUI track.

Fig. 5

(a) The percentage of correctly completed commands (CCC%) versus eTDS response time for five human subjects. (b) eTDS information transfer rate versus response time. (c) Mean values and 95% confidence interval of elapsed time for five subjects participating in the maze navigation experiment.