Determination of sagittal tongue shape from the positions of points on the tongue surface

This paper describes a method for determining the shape of the midsagittal tongue contour from the positions of points on the tongue surface. The positions of the points and the tongue shape were measured simultaneously by using an alternating magnetic field device and an ultrasonic B-mode scanner for continuous speech utterances. A comparison between the magnetic and the ultrasonic data revealed that the average measurement difference between the two types of data was 1.16 mm. The shape of the tongue contour was then represented by multivariable linear regression of the magnetically determined positions. The results of the regression analysis showed that the tongue contour was estimated, from four positions on the tongue, with an average estimation error of 1.24 mm. This estimation error could be reduced to 0.84 mm when there was no measurement error between the magnetic and the ultrasonic data, and it was further reduced to 0.43 mm when the receiver coils of the magnetic device were positioned optimally on the tongue. It was also shown that the number of data frames for calculating the regression coefficients could be reduced, while maintaining the estimation accuracy, by appropriately selecting data frames. Finally, the tongue shape was estimated successfully for several phonemes from the magnetically determined positions, thus demonstrating the usefulness of this method for observing the articulatory configuration of the tongue.