Electromagnetic articulograph (EMA) based on a nonparametric representation of tthe magnetic field

Electromagnetic articulograph (EMA) systems are useful to study the motor control of speech articulators and also to construct models of the speech production process. In the EMA system, the position of the receiver coil is predicted on the basis of a field function representing a spatial pattern of the magnetic field in relation to the relative position between the transmitter and receiver coils. This paper presents a new method of representing the magnetic field by using a multivariate spline function to overcome the problem of the field pattern having local fluctuations caused by interference between the transmitting signals. A procedure for determining the receiver position is also presented, and the piecewise property of the basis functions enables the spline function to flexibly approximate the field pattern and to attain a high measurement accuracy: the mean error in estimating the receiver position was less than 0.1 mm for a 14 × 14-cm measurement area.