Use of optical distance sensing to track tongue motion

The authors have designed a device that uses a reflected-light-sensing technique to monitor tongue movement in the frontal oral cavity. The sensing unit is composed of a LED light source and a phototransistor, mounted together onto an artificial palate, and attached to the hard palate. The basic sensing function of this unit is governed by the formula r/(r2+ x(o)2)(3/2) rather than by the inverse square distance law. In this equation, r is the distance between the sensor and the reflector, namely, the tongue surface. The x(o) is the separation between the source and the photosensor. Two potential problems, the beam dispersion effect of the light source and the nonparallel movement of the tongue, were anticipated. They can be theoretically represented or technically prevented. The softness of the tongue and the protuberances of its surface are also favorable aspects of this method, creating special light reflection from the tongue surface. The available output function was from 0 to 40 or 50 mm. This gives the device the capability of detecting both vowel and consonantal articulation. The method can be useful to further speech research and the development of a language teaching aid system.