Information Sci. Res. Lab., NTT Basic Res. Labs., 3-9-11 Midori-cho, Musashino-shi, Tokyo 180, Japan
A magnetic position-sensing device is one of the promising tools for measuring articulatory movements. The device (Articulograph AG100, Carstens Medizinelektronik GmbH, Gottingen, Germany) is evaluated in terms of measurement accuracy, effects of tilt and lateral displacement of the receiver coil, interference between adjacent coils, and temperature drift. The results show that measurement distortion is 0.93 mm on average in a 120-x80-mm rectangle on the midsagittal plane. If the tilt angle is 20 deg with respect to both the x and y axes, the distortion increases to 1.1 mm on the midsagittal plane and to 2.8 mm for a lateral displacement of 5 mm. The positions of four receiver coils placed on the tongue are monitored simultaneously with ultrasonic pulsed-echo imaging of the tongue contour. The magnetic and ultrasonic data are compared to reveal the accuracy of the magnetic data for measuring tongue movements. Also the relationship between positions on the tongue and the tongue shape was quantitatively investigated. Finally, simultaneous measurements of the tongue, jaw, lips, soft palate, and larynx movements are demonstrated.